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047972327 | summary | High-level nuclear waste, such a fission products, or nuclear waste with a long half-life, such as actinides, is currently immobilized in borosilicate glasses which offer adequate safety guarantees to man and the environment. The Atomic Energy Commission (AEC) has developed an industrial process for the vitrification of fission products (FP). This process (called AVM) consists in calcining the solution of FP and sending the resulting calcinate, at the same time as a glass frit, into a melting furnace. A glass is obtained in a few hours, at a temperature of the order of 1100.degree. C., and is run into metal containers. The glass frit is composed mainly of silica and boric oxide together with the other oxides (sodium, aluminum etc.) necessary so that the total formulation of calcinate+frit gives a glass which can be produced by the known glassmaking techniques and which satisfies the storage safety conditions (conditions pertaining to leaching, mechanical strength, etc.). In the melting furnace, the calcinate is digested and becomes incorporated into the vitreous structure. The chosen temperature must be sufficiently high to hasten the digestion, but must not have an adverse effect on the life of the furnace. To limit this disadvantage, the Applicant Company developed a process in which the constituents of the glass are mixed in an aqueous medium to form a gelled solution, instead of preparing the glass from solid consitutents in the form of oxides. Furthermore, it is known that a glass can be obtained from a gelled solution (or by the so-called "gel method") at temperatures below those required with oxides ("oxide method"). The aim is essentially to manufacture, by the gel method, glasses having the same formulation as those currently prepared by the oxide method, as will be shown in the examples, but any borosilicate formulation acceptable for conditioning waste can be prepared. In the remainder of the text, the following terms will be employed with the meanings defined below: vitrification adjuvant: This comprises all the constituents of the final glass other than the constituents originating from the nuclear waste and except for B and Si. This adjuvant therefore contains no active nuclear components. In the AVM process, it is included in a glass frit; in the process forming the subject of the invention, it is an aqueous solution. final glass: This is the glass in which the nuclear waste is immobilized. sol: This is a solution of orthosilicic acid; the latter, being unstable, changes by polymerizing. Commericial sols, such as Ludox.phi. (du Pont de Nemours), are stabilized solutions containing partially hydrated particles of silica; these colloidal particles are polymers whose polymerization has been stopped but can be unblocked, for example by acidification. gelled solution, or gel: This is a homogeneous solution of variable viscosity, ranging from a solution which flows to a solidified mass, depending on how far the polymerization has advanced. A method, called the sol-gel method, is known for preparing gels in an aqueous medium; it consists in using a sol in water and destabilizing it by modifying the pH, thus causing this solution to gel. The following publication refer to this method: J. ZARZYCKI--J. of Materials Science 17 (1982) p 3371-3379 PA0 R. JABRA--Revue de Chimie Minerale, t. 16, 1979, p 245-266 PA0 J. PHALIPPOU--Verres et Refractaires, Vol. 35, no. 6, Nov. Dec. 1981. PA0 Publication: N. UETAKE--Nuclear Technology, Vol. 67, Nov. 1984 The preparation of an SiO.sub.2 --B.sub.2 O.sub.3 glass by the sol-gel method is described in the literature: addition of a solution of Ludox, adjusted to pH 2, to an aqueous solution of hydrated ammonium tetraborate, also adjusted to pH 2; mixing by stirring for 1 hour (aqueous ammonia being added, if necessary, to bring the pH of the medium to 3.5, which is very favorable for gelling); if the resulting solution shows no precipitation or flocculation, it is considered to be a satisfactory gel; drying for 8 hours at 100.degree. C. and then for 15 h at 175.degree. C. under a vacuum of 0.1 mm Hg; and hot pressing (450 bar--500.degree. to 900.degree.--15 min to 5 hours) in order to densify and vitrify the product (an alternative method is melting). Only binary or ternary glasses have so far been prepared by this method because the presence of a multiplicity of cations makes it difficult to control gelling and even to achieve it. Thus, to produce a glass having the same composition as the glass frit used in the present vitrification process, the following would be necessary: B.sub.2 O.sub.3, SiO.sub.2, Al.sub.2 O.sub.3, Na.sub.2 O, ZnO, CaO, Li.sub.2 O, ZrO.sub.2. PA1 a silica-based gel precursor, PA1 a concentrated aqueous solution of a boron compound, and PA1 a concentrated aqueous solution of the vitrification adjuvant, Now, it is known that: boron makes gelling very difficult (in the HITACHI process described below, boron is actually added after the gel has formed), particularly because of the high insolubility of a large number of boron compounds, and favors recrystallization in mixed gels; aluminum favors precipitation to the detriment of gellling, which opposes the desired result; and sodium, calcium and zirconium lead to the formation of crystals which subsequently constitute fragile points capable of causing local destruction. Due to the multiplicity of components, those skilled in the art are questioning the method of introducing them and the order in which they are introduced. The complexity of the components in the vitrification process, namely: those of the virtrification adjuvant (Al.sub.2 O.sub.3, Na.sub.2 O, ZnO, CaO, Li.sub.2 O, ZrO.sub.2) plus B.sub.2 O.sub.3 and SiO.sub.2, and at the same time those of the solution of FP to be vitrified (around twenty different cations), led industrialists to develop two processes based on gels: (1) Westinghouse and the US Department of Energy developed a process for the vitrification of active solutions involving the preparation of gels, but in an alcoholic medium (alcogels)--U.S. Pat. No. 4,430,257 and U.S. Pat. No. 4,422,965. Their process can be summarized in the following way: mixing and hydrolysis of the inactive constituents of the gel in an alcohol/water medium, the constituents being introduced in the form X(OR).sub.n, for example Si(OR).sub.4, B(OR).sub.3 etc., R being an organic radical or a proton; removal of the water/alcohol azeotrope to give a dry gel; addition of the solution of nuclear waste (the final compound containing a maximum of 30-40% of waste), adjusted to pH 4 to 6; drying; and melting. The gel prepared from comopunds X(OR).sub.n in an alcoholic medium can be obtained more easily because solubility problems are avoided and, furthermore, the peptizing effect of water at high temperature is eliminated by using alcohol. The major disadvantage of this type of process is that the alcoholic medium is prone to fire, explosion etc., so the alcohol has to be removed before introduction of the nuclear waste; this necessitates an additional operation which is rather impractical to carry out. (2) The HITACHI process, in which the gel is obtained from the solution of FP in a solution of sodium silicate, the boron (in the form of B.sub.2 O.sub.3) not being added until after gelling; this necessitates calcining the gel at 600.degree. C., or above, for the time required for the boron to diffuse into the silicate matrix to form the borosilicate structure (for example 3 h); the homogeneity of the product remains a problem. The Applicant Company has developed a process for the immobilization of nuclear waste which does not have the disadvantages of the Westinghous and Hitachi processes and in which a borosilicate matrix is prepared in an aqueous medium, the nuclear waste is subsequently added to the said matrix at any stage during its treatment, and this mixture is then heat-treated to give a borosilicate glass. This process therefore has the advantages of working in an aqueous medium and adding the boron at the precise moment when the gelled matrix is formed, the boron thus participating in the structure of the gelled matrix, which is why the latter is called a borosilicate matrix. In the process forming the subject of the invention, the borosilicate matrix is prepared by mixing the following: in proportions corresponding to the composition of the final glass minus the waste, with stirring at a high rate of shear, at a temperature of between 20 and 80.degree. C. (preferably at 65.degree.-70.degree. C.) and at an acid pH, preferably a pH of between 2.5 and 3.5, so as to form a gelled solution, the said inactive matrix is heattreated and the nuclear waste is added at any stage during the said treatment in order to form, by melting, the final borosilicate glass containing the said waste. In the account of the process, the term "gel precursor" will be used to denote a substance containing particles of silica which may be partially hydrolyzed; it is either in the form of a powder, which can produce a sol when dissolved in acid solution, or directly in the form of a sol. Examples of gel precursors which are sold commerically and are advantageously used in the process are a sol such as Ludox.RTM. (du Pont de Nemours) or alternatively Aerosil.RTM. (Degussa), which is formed by the hydrolysis of silicon tetrachloride in the gas phase. In an acid medium, Aerosil produces a sol and then a firm gelled mass. Ludox is used as it is, in solution. Aerosil, on the other hand, can be used either directly in the form of a powder introduced into the mixture (depending on the technology employed, especially with regard to stirring), or in solution. Furthermore, the gel precursor can consist of a mixture of gel precursors; for example, the silica will be introduced as Ludox and Aerosil in one and the same operation. The gel precursor is placed in an acid aqueous medium, in accordance with the process forming the subject of the invention, so that it is converted to a gelled solution by polymerization starting from the Si--OH bonds. The boron required to form the borosilicate structure is introduced as an aqueous solution of a sufficiently soluble boron compound. This can be for example ammonium tetraborate (ATB), which has a satisfactory solubility between 50.degree. and 80.degree. C. (about 300 g/l, i.e., 15.1% of B.sub.2 O.sub.3). Preferably, the solution is produced and used at 65.degree.-70.degree. C. Boric acid can equally well be employed; its solubility is 130 g/l at 65.degree., i.e. 6.5% of B.sub.2 O.sub.3. The solutions used (boron compound and vitrification adjuvant) are prepared as concentrated solutions so that a gel is produced quickly and the quantity of water to be evaporated off is minimized, as will be explained in the description and the examples. It is difficult to give an exact concentration limit for each of the compounds, but the concentration of the solutions can reasonably be given as at least 75% of the saturation concentration. The compounds, containing the desired elements, which are used to prepare the solution of the adjuvant should be soluble in water at the temperature of the process, be mutually compatible and not add other ions unnecessarily, and their ions which do not participate in the structure of the final glass should be easy to eliminate by heating. An example would be solutions of nitrates in cases where nitric acid solutions of FP are being treated. Solid compounds are preferably dissolved in the minimum amount of water so as to minimize the volumes treated and the amounts of water to be evaporated off. The proportions in which these solutions (except for the solutions of waste) are prepared and mixed depend on the desired formulation of the final glass. It can be considered that the constitutent components of the glass can not volatilized in practice and that the resulting composition of the final glass virtually corresponds to that of the mixture produced. An acceptable glass formulation is indicated in the examples. The qualitative and quantitative composition of the vitrification adjuvant is adapted according to the composition of the final glass and that of the solution of waste to be treated. The mixture is prepared at between 20.degree. and 80.degree. C. The concentrated solution of the boron compound is kept at between 50.degree. and 80.degree. C. in order to prevent precipitation. The other solutions are produced at ambient temperature. It is then possible either to mix the solutions at the temperature at which they are produced or arrive, or to heat all the solutions to a higher temperature. The latter case has the following advantage. After mixing has taken place and the gelled solution has started to form, polymerization (gelling) develops over a so-called ageing period. This is favored by raising the temperature. It is therefore very advantageous to produce the mixture at between 50.degree. C. and 80.degree. C. In the process forming the subject of the invention, the ageing of the gelled solution takes place during drying, preferably at 100.degree.-105.degree. C. The solutions of the constituents of the glass have different pH values: the gel precursor in solution is alkaline (Ludox) or acid (Aerosil in nitric acid solution), the solution of vitrification adjuvant is acid and the solution of boron compound is acid (boric acid) or alkaline (ATB). In the process described here, the pH of the mixture must be below 7 and preferably between 2.5 and 3.5. The pH can be adjusted if necessary. For the solutions employed, the components are as follows: ______________________________________ % of oxide constituents of the glass Temperature ______________________________________ A Gel precursor a% of SiO.sub.2 25.degree. to 80.degree. C. B Boron solution b% of B.sub.2 O.sub.3 50.degree. to 80.degree. C. C Vitrification d% of oxides 50.degree. to 80.degree. C. adjuvant ______________________________________ In the process forming the subject of the invention, the components are mixed by being introduced simultaneously and being stirred at "a high rate of shear". These components can be introduced separately or, if they do not react with one another, they can be introduced together. The expresiion "a high rate of shear" is used to qualify stirring which is effected by a device rotating at a minimum of 500 rmp, preferably 2000 rpm, and for which the thickness of the stirred layer (distance between the stirrer blade and the wall of the mixing zone) does not exceed 10% of the diameter of the blade. This stirrer can be a turbine, for example for industrial-scale application. Laboratory tests with a mixer or a mechanical stirrer in a narrow beaker demonstrated an adequate mixing capacity. In the present state of knowledge, there is every reason to think that the stirring must be the more intense and hence the shorter, the greater the risks of precipitation. What is actually required is to create a homogeneous mixture, by stirring, in a time which is very short compared with the precipitation time, and to ensure that the gel forms as quickly as possible so as to solidify the various ions and, by preventing any diffusion of these ions, prevent a possible reaction between the said ions. In the process forming the subject of the invention, an important advantage not formerly obtained by the other gelling techniques is that large quantities of gel can be prepared without difficulty. With a turbine, 40 kg/h of gel was reached very easily, and this does not represent the limit. Mixing produces a solution called a gelled solution, its viscosity and texture changing with time and ranging from those of a fluid solution to those of a gel. When mixing is effected at a high rate of shear, the phenomenon of thixotropy occurs, the viscosity drops and a homogeneous dispersion of particles is produced. When not stirred, the viscosity of this mixture increases and the ions trapped in the structure can no longer react; the structure "freezes". The inactive borosilicate matrix thus obtained in the form of a gelled solution is then heat-treated, the nuclear waste being added at any stage during the said treatment. Different possibilities for inclusion of the nuclear waste will now be examined. The process can be applied to various types of solid and/or liquid nuclear waste. It is particularly suitable for the vitrification of solutions of FP by themselves or with other active effluents, for example the soda solution for washing the tributyl phosphate used to extract uranium and plutonium, it even being possible for this soda solution to be treated on its own by this process. The solutions of FP are nitric acid solutions originating from reprocessing of the fuel; they contain a large number of elements in various chemical forms and a certain amount of insoluble material. An example of their composition is given below. The soda effluent is based on sodium carbonate and contains tributyl phosphate (TBP) degradation products entrained by the washing process (Example 2). The high level of sodium in this effluent has to be taken into account when determining the composition of the borosilicate matrix. 1st case: The nuclear waste in solution is added to an inactive borosilicate matrix whose volume has been reduced. The gelled solution obtained by mixing the constituents under the conditions described is dried at between 100.degree. and 200.degree. C., preferably at 100.degree.-105.degree. C. During this operation, the water evaporates off and the volume is reduced. For the remainder of the process, it is possible either to carry out thorough drying to give a friable solid product, or simply to make do with a volume reduction--more quickly achieved--of 25 to 75% of the initial volume so as to give a paste. The resulting matrix of reduced volume is dispersed and mixed by stirring with the solution of nuclear waste to be treated. It can be advantageous to mix the components at a temperature of between 60.degree. and 100.degree. C. so as to reduce the volume of water at the same time as effecting mixing. In another embodiment, the dried matrix is introduced into the calciner, the solution of waste is introduced simultaneously into this calciner and mixing takes place in the calciner, which rotates about its longitudinal axis. The produce obtained is sent directly to the melting furnace. Whichever embodiment is used, the process has the same characteristics: preparation of the matrix--drying--addition of the waste--heat treatment ranging from a drying temperature to a melting temperature (drying-calcination-melting). The mixture obtained is dried if necessary (at between 100.degree. and 200.degree. C., preferably at 100.degree.-105.degree. C.), for example in an oven; drying in vacuo is a further possibility. After drying, calcination is carried out at between 300.degree. and 500.degree. C. (preferably at 350.degree. to 400.degree. C.), during which the water finishes evaporating off and the nitrates partially decompose. Calcination can be carried out either in a conventional calciner (of the type used in the AVM process) or in a melting furnace, for example of the ceramic melter type. The decomposition of the nitrates is always terminated during melting. On entering the furnace, the product rapidly passes from its calcination temperature to its melting point. This is the so-called introduction zone. Then, in the so-called refining zone, it is at a temperature slightly above the melting point and then at the pouring temperature. The value is advantageously between 1035.degree. C. and 1100.degree. C., at which the viscosity of the glass, between 200 poises and 80 poises, enables the glass to be poured under good conditions. The melting point of the mixture depends on the composition of the said mixture. In fact, sodium improves the fusibility of glasses, but has the disadvantage of lowering their resistance to leaching. Also for the purpose of immobilizing nuclear waste, the AEC has produced a glass formulation which satisfies the nuclear safety conditions and can be treated by the known glassmaking techniques in accordance with the so-called oxide method. When a mixture having the AEC formulation is prepared in an aqueous medium by the so-called gel method, the refining times are found to be shorter than those required in the so-called oxide method. The throughputs of the furnace can therefore be increased. Furthermore, the process forming the subject of the invention makes it possible to vitrify various types of waste, in particular sodium-rich waste, since the composition of the borosilicate matrix is adjusted to the type of waste treated. Thus, for sodium-rich waste, a low-sodium (or even sodium-free) borosilicate matrix is prepared, as will be shown in the examples. In this way, the formulation produced by the AEC, which is highly satisfactory, can easily be obtained with diverse types of waste; other formulations which would be acceptable could equally well be prepared. The drying-calcination-melting steps described correspond to heat treatments in defined temperature zones. Sinilar heat treatments in other devices are obviously suitable, as is in general any technique for producing glass from the gel. 2nd case: The nuclear waste in solution is added to a calcined borosilicate matrix. The borosilicate matrix in the form of a gelled solution is dried (at between 100.degree. and 200.degree. C., preferably at 100.degree.-105.degree. C.) and then calcined at between 300.degree. and 500.degree. C., preferably at a temperature below 400.degree. C., in devices similar to those described for the 1st case. With a calcination temperature below or equal to 400.degree. C., the gel obtained is friable, which facilitates its dispersion in the solution of waste; furthermore, this gel has a maximum specific surface area in this zone; above 400.degree. C., sintering in fact begins and closes the pores. The calcined matrix obtained is dispersed and mixed with the solution of waste to be treated. As previously, the operation is advantageously carried out above 60.degree. C., preferably at 100.degree.-105.degree. C., so as to dry while mixing. This operation of mixing the calcined matrix with the solution of waste can be carried out in a reactor or alternatively in the calciner itself. In the latter case, the calciner is fed with the solution of FP and the calcined matrix introduced separately in the desired proportions. Consequently, the operation takes place at nearly 200.degree. C. at the entrance of the calciner. the temperature rising to about 400.degree. C. In a reactor, the substances are mixed by means of a stirrer; in a calciner, mixing is effected by the rotation of the calciner itself about its longitudinal axis. The mixture obtained (calcined matrix+waste) is subjected to a heat treatment (drying, calcination, melting) under the conditions already described for forming a glass. 3rd case: The waste is in solid form. Consideration has been given to the case where the nuclear waste in solution was aded to the calcined borosilicate matrix. It is just as feasible to introduce the waste in solid form, for example as a calcinate. This process has the advantage that it can be implemented immediately in present-day production lines, making it possible to adapt the vitrification adjuvant to the waste treated (as will be shown in Example 3). It is also possible to add the waste in solid form, for example as a calcinate, to the dried matrix. |
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claims | 1. A radiation detector comprising:a main body;a radiation probe detachably attached to the main body; anda collimator for collimating radiation, the collimator being provided in the distal end portion of the radiation detection probe,the radiation detection probe having: a detection unit including a radiation detection element; a first terminal electrically connected to the radiation detection element; and a cap-shaped shield member mounted to the detection unit so as to cover the radiation detection element, the shield member being made of a material which blocks the radiation, the shield member having a front wall facing the radiation detection element, and a cylindrical side wall extending from the edge of the front wall, the collimator being a through-hole provided in the front wall,the main body having a connector to which the proximal end of the radiation detection probe is detachably mounted, the connector including a second terminal which is detachably connected to the first terminal when the radiation detection probe is mounted to the connector,the radiation detection probe further having:a cap-shaped probe cover which covers the shield member and the detection unit, the probe cover being detachably mounted to the connector; anda seal ring sandwiched between the probe cover and the connector to seal the main body and the radiation detection probe when the probe cover is mounted to the connector. 2. A radiation detector according to claim 1, whereinthe detection unit has an input face which faces the collimator and transmits the radiation, andthe radiation detection element is arranged so as to receive the radiation which has passed through the input face. 3. A radiation detector according to claim 1, whereinthe shield member is disposed in the probe cover to allow a hollow portion of the shield member and a hollow portion of the probe cover to communicate with each other, andthe detection unit is fitted into these hollow portions which communicate with each other. 4. A radiation detector according to claim 3, wherein the shield member is detachably provided in the probe cover. 5. A radiation detector according to claim 3, wherein the shield member is fixed in the probe cover. 6. A radiation detector according to claim 1, whereinthe probe cover has a cap-shaped first component detachably mounted to the connector, a cap-shaped second component detachably attached to the first component to accommodate and fix the shield member, and a seal ring sandwiched between the outer surface of the first component and the inner surface of the second component to seal the probe cover when the second component is attached to the first component, andthe second component is attached at positions variable along the axis of the probe cover. 7. A radiation detector according to claim 1, whereinthe probe cover has an input plate facing the front wall of the shield member to close an end of the collimator, and a cylindrical side wall extending from the edge of the input plate to surround the side surfaces of the shield member and the detection unit, andthe input plate is made of a material which transmits the radiation and blocks an electromagnetic wave having an energy of 1 keV or less. 8. A radiation detector according to claim 1, whereinthe detection unit has a casing for accommodating the radiation detection element,an opening is provided on the distal end of the casing so as to extend from an end face of the casing toward the radiation detection element, andthe opening has substantially the same cross-section as that of the collimator and communicates with the collimator. 9. A radiation detector comprising:a main body;a radiation detection probe detachably attached to the main body; anda collimator for collimating radiation, the collimator being provided in the distal end portion of the radiation detection probe,the radiation detection probe having a detection unit including a radiation detection element, and a first terminal electrically connected to the radiation detection element,the main body having a connector to which the proximal end of the radiation detection probe is detachably mounted, the connector including a second terminal which is detachably connected to the first terminal when the radiation detection probe is mounted to the connector,the radiation detection probe further having:a cap-shaped probe cover which covers the detection unit, the probe cover being detachably mounted to the connector; anda seal ring sandwiched between the probe cover and the connector to seal the main body and the radiation detection probe when the probe cover is mounted to the connector,the probe cover being made of a material which blocks the radiation,the collimator being an opening provided on the distal end of the probe cover to extend toward the radiation detection element,the radiation detector further comprising an input plate for closing an end of the collimator, the input plate being provided on the distal end surface of the probe cover, and the input plate being made of a material which transmits the radiation and blocks an electromagnetic wave having an energy of 1 keV or less. 10. A radiation detector according to claim 9, whereinthe detection unit has an input face which faces the collimator and transmits the radiation, andthe radiation detection element is arranged so as to receive the radiation which has passed through the input face. 11. A radiation detector comprising:a main body;a radiation detection probe detachably attached to the main body; anda collimator for collimating radiation, the collimator being provided in the distal end portion of the radiation detection probe,the radiation detection probe having a detection unit including a radiation detection element, and a first terminal electrically connected to the radiation detection element,the main body having a connector to which the proximal end of the radiation detection probe is detachably mounted, the connector including a second terminal which is detachably connected to the first terminal when the radiation detection probe is mounted to the connector,the connector further including a support bar protruding from the distal end of the main body and being thinner than the radiation detection probe, andthe support bar having a proximal end connected to the distal end of the main body and a distal end connected to the radiation detection probe. 12. A radiation detector according to claim 11, whereinthe detection unit has an input face which transmits the radiation,the radiation detection element is arranged so as to receive the radiation which has passed through the input face, andthe collimator is an opening which faces the input face. 13. The radiation detector according to claim 11, whereinthe connector further includes a slide member slidably attached to the support bar, andthe collimator moves along with the slide member, and the distance between the collimator and the radiation detection element varies went the slide member slides relative to the support bar. 14. A radiation detector comprising:a main body;a radiation detection probe detachably attached to the main body; anda collimator for collimating radiation, the collimator being provided in the distal end portion of the radiation detection probe,the radiation detection probe having a detection unit including a radiation detection element, and a first terminal electrically connected to the radiation detection element,the main body having a connector to which the proximal end of the radiation detection probe is detachably mounted, the connector including a second terminal which is detachably connected to the first terminal when the radiation detection probe is mounted to the connector,one of the first and second terminals including a plurality of pins having different fitting lengths and different polarities, and the other including a plurality of sockets into which the plurality of pins are fitted, the plurality of sockets having fitting lengths and polarities corresponding to the plurality of pins. 15. A radiation detector according to claim 14, whereinthe detection unit has an input face which transmits the radiation,the radiation detection element is arranged so as to receive the radiation which has passed through the input face, andthe collimator is an opening which faces the input face. 16. A radiation detector comprisinga main body, anda radiation detection probe detachably attached to the main body,the radiation detection probe having a radiation detection element, a first terminal electrically connected to the radiation detection element, a cylindrical element cover surrounding the radiation detection element, and a cylindrical casing for accommodating the element cover,the main body having a connector to which the proximal end of the radiation detection probe is detachably mounted, the connector including a second terminal which is detachably connected to the first terminal when the radiation detection probe is mounted to the connector,the element cover being made of a material which blocks radiation, andthe radiation detection element being disposed behind the distal end of the element cover. 17. A radiation detector according to claim 16, further comprising a fastener detachably mounted to the main body to fasten the radiation detection probe to the connector. 18. A radiation detector according to claim 17, further comprising a seal ring sandwiched between the fastener and the connector to seal the main body when the fastener is mounted to the connector. 19. A radiation detector according to claim 16, whereinan input plate facing the radiation detection element is provided on the distal end surface of the casing, andthe input plate is made of a material which transmits the radiation and blocks an electromagnetic wave having an energy of 1 keV or less. |
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claims | 1. An electro magnetic oscillator tube with enhanced isotopes, the system comprising:at least one layer, wherein each layer of said at least one layer comprises an axial sequence of a first magnet, a conduction block, and a second magnet of opposite polarity;an elongate axially disposed emitter of isotopic particles;said conduction block having an RF port;said conduction block having an opposite electrical polarity relative to said emitter of isotopic particles forming between said emitter of isotopic particles and said conduction block;a coating of material, chosen from the group consisting of a carbon coating and a metallic coating, on an inner periphery of said conduction block representing an outermost radius of an outermost space;thermal conduction paths within radii of said conduction block between said resonant cavities;a potential defining a radial electrical vector E;said conduction block disposed in a plane about said emitter of isotopic particles and having an interior radial periphery relative to said emitter of isotopic particles defining an interaction space;an outer periphery of said interaction space defining a polar array of resonant cavities in said conduction block separated from each other by surfaces in communication with said interaction space;each of said resonant cavities having an LC value, wherein each resonant cavity generates a resonant frequency responsive to a particular annular motion and energy of isotopic particles of a cloud of isotopic particles also passing said surfaces and a plurality of entrances of said resonant cavities;said first magnet comprises an upper magnet outside and above said resonant cavity and said second magnet comprises a lower magnet of opposite polarity outside and below said resonant cavity, wherein said upper magnet and said lower magnet are in magnetic communication with said interaction space;a plurality of electrically biased grids disposed concentrically about said emitter of isotopic particles within said interaction space to influence emission characteristic of isotopic particles, within an energy spectrum of said isotopic particles to an integrity of said cloud of isotopic particles in said interaction space, shape thereof, and density of effective LC values at said resonant cavities;a connection between selected groups of said resonant cavities at locations of like electrical polarity, wherein said connection comprises conductive strapping elements within said conduction block; andeach grid in said plurality of electrically biased grids employs a polar slit. 2. The system as recited in claim 1, further comprising:a plurality of dielectric materials disposed concentrically about said emitter of isotopic particles within said interaction space to influence an emission characteristic of the isotopic particles. 3. The system as recited in claim 1, further comprising:a plurality of layers, wherein each layer of said plurality of layers is axially disposed upon each other;each layer of said plurality of layers comprises said sequence of said first magnet, said conduction block, and said second magnet of opposite polarity separated from an abutting layer by a dielectric material; andsaid emitter of isotopic particles is common to each layer of said plurality of layers. 4. The system as recited in claim 3, further comprising:within said interaction space, a plurality of dielectric layers disposed about said emitter of isotopic particles have a electrostatic grid defining a segment;each of said dielectric layers in a plane are substantially transverse to that of an axis of said emitter of isotopic particles in which a plurality of variables are radial at each of said dielectric layers and axial height of each of said electrostatic grids;each of said dielectric layers in a plane are substantially transverse to that of an axis of said emitter of isotopic particles in which an extent of transverse by each of said electrostatic grids defines a radial region through which emitted isotopics escape from said emitter of isotopic particles into said interaction space;an extent of each of said dielectric layers exists outside each of said electrostatic grids between said emitter of isotopic particles and a portion of the conduction block in a plane of each of said dielectric layers; anda radius of each of said dielectric layers within said interaction space are of a lesser dimension than that of an inner radius of said conduction block. 5. The system as recited in claim 1, in which at least one of said resonant cavities includes a dielectric material. 6. The system as recited in claim 5, in which properties of said dielectric material is tunable by adjusting an LC value of each resonant cavity. 7. The system as recited in claim 1, further comprising a power port including a rectifier for providing power conversion of said resonant energy, collected from said resonant cavities, to an electrical output of the system. 8. The system as recited in claim 1, in which said conduction block surfaces comprise:fin-like structures which define said resonant cavities of said conduction block, in which a polarity of each successive fin alternates between positive and negative during rotation of said cloud of isotopic particles. 9. The system as recited in claim 8, in which said fin-like structures are printable upon a flexible substrate which may be bent into a circular geometry having an internal radius corresponding to a desired radius of said interaction space of said conduction block. 10. The system as recited in claim 1, in which said conduction block surfaces comprise:stub-like structures which define said resonant cavities of said conduction block, in which a polarity of each successive stub alternates between positive and negative during rotation of said cloud of isotopic particles. 11. The system as recited in claim 1, in which said coating of carbon comprises a diamond coating. 12. The system as recited in claim 1, further comprising:an external heat sink in communication with thermal outputs of said radial conduction paths. 13. The system as recited in claim 1 in which said plurality of electrically biased grids are supported by at least one of said dielectric surfaces. 14. The system as recited in claim 13, further comprising:a dielectric layer separating said upper magnet and said lower magnet, each dielectric layer disposed radially outwardly of said interaction space. 15. The system as recited in claim 1, in which said plurality of electrically biased grids support at least one dielectric surface. 16. The system as recited in claim 15, in which said plurality of electrically biased grids expand axially upward and downward from at least one radial dielectric base. 17. The system as recited to claim 1, in which each grid in said plurality of electrically biased grids expand axially upwardly and downwardly from a plurality of rigid dielectric bases respectively abutting at least one of said upper magnets and said lower magnets. 18. The system as recited in claim 17, further comprising:a dielectric material disposed concentrically about said emitter of isotopic particles within said interaction space to further an emission characteristic of emitted isotopic particles. 19. The system as recited in claim 18, in which said emitter comprises a beta isotope. 20. The system as recited in claim 18, in which said emitter of isotopic particles comprises an alpha isotope. 21. The system as recited in claim 18, comprising:a non-ionizing fluid provided within said interaction space. 22. The system as recited in claim 21, comprising:said non-ionizing fluid provided radially inwardly of said plurality of electrically biased grids. 23. The system as recited in claim 21, comprising:said non-ionizing fluid provided radially outwardly of said plurality of electrically biased grids. 24. An electro magnetic oscillator tube with enhanced isotopes, the system comprising:at least one layer, wherein each layer of said at least one layer comprises an axial sequence of a first magnet, a conduction block, and a second magnet of opposite polarity;an elongate axially disposed emitter of isotopic particles;said conduction block having an RF port;said conduction block having an opposite electrical polarity relative to said emitter of isotopic particles forming between said emitter of isotopic particles and said conduction block;a coating of material, chosen from the group consisting of a carbon coating and a metallic coating, on an inner periphery of said conduction block representing an outermost radius of an outermost space;thermal conduction paths within radii of said conduction block between said resonant cavities;a potential defining a radial electrical vector E;said conduction block disposed in a plane about said emitter of isotopic particles and having an interior radial periphery relative to said emitter of isotopic particles defining an interaction space;an outer periphery of said interaction space defining a polar array of resonant cavities in said conduction block separated from each other by surfaces in communication with said interaction space;each of said resonant cavities having an LC value, wherein each resonant cavity generates a resonant frequency responsive to a particular annular motion and energy of isotopic particles of a cloud of isotopic particles also passing said surfaces and a plurality of entrances of said resonant cavities;said first magnet comprises an upper magnet outside and above said resonant cavity and said second magnet comprises a lower magnet of opposite polarity outside and below said resonant cavity, wherein said upper magnet and said lower magnet are in magnetic communication with said interaction space;a plurality of electrically biased grids disposed concentrically about said emitter of isotopic particles within said interaction space to influence emission characteristic of isotopic particles, within an energy spectrum of said isotopic particles to an integrity of said cloud of isotopic particles in said interaction space, shape thereof, and density of effective LC values at said resonant cavities;a connection between selected groups of said resonant cavities at locations of like electrical polarity, wherein said connection comprises conductive strapping elements within said conduction block; andeach grid in said plurality of electrically biased grids employs a horizontal slit. |
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claims | 1. A display control apparatus for controlling display of a radiograph to be displayed on a head mounted display, comprising:a generation unit adapted to generate an X-ray moving image by detecting X-rays that irradiate a subject;a setting unit adapted to, when displaying the X-ray moving image superimposed on a main image to be displayed on a display unit of the head mounted display, set a display ratio of the main image and the X-ray moving image in accordance with a display condition;an image composition unit adapted to generate a composite image by superimposing the X-ray moving image on the main image on the basis of the ratio set by said setting unit;a display processing unit adapted to display the composite image on the display unit of the head mounted display; anda viewpoint detection unit adapted to detect information about a viewpoint of a user who is wearing the head mounted display,wherein when said viewpoint detection unit detects that the viewpoint of the user exists in a display area of the X-ray moving image, said setting unit switches the ratio to display the X-ray moving image with a priority over the main image, andsaid image composition unit generates the composite image by superimposing the X-ray moving image on the main image on the basis of the ratio switched by said setting unit. 2. A radiographic image display control apparatus comprising:a generation unit adapted to generate an X-ray moving image by detecting X-rays that irradiate a subject;a setting unit adapted to, when displaying the X-ray moving image superimposed on a main image to be displayed on a head mounted display, set a display ratio of the main image and the X-ray moving image in accordance with a display condition;an image composition unit adapted to generate a composite image by superimposing the X-ray moving image on the main image on the basis of the ratio set by said setting unit;a display processing unit adapted to display the composite image on a display unit of the head mounted display; anda tilt detection unit adapted to detect a tilt of the head mounted display,wherein when said tilt detection unit detects that the tilt of the head mounted display is not less than a reference value, said setting unit switches the ratio to display the X-ray moving image with a priority over the main image, andsaid image composition unit generates the composite image by superimposing the X-ray moving image on the main image on the basis of the ratio switched by said setting unit. 3. A radiographic image display control apparatus comprising:a generation unit adapted to generate an X-ray moving image by detecting X-rays that irradiate a subject;a setting unit adapted to, when displaying the X-ray moving image superimposed on a main image to be displayed on a head mounted display, set a display ratio of the main image and the X-ray moving image in accordance with a display condition;an image composition unit adapted to generate a composite image by superimposing the X-ray moving image on the main image on the basis of the ratio set by said setting unit;an image display unit adapted to display the composite image on a display unit of the head mounted display;a read unit adapted to read measurement data of an auxiliary device; andan analysis unit adapted to analyze whether the measurement data falls within a normal range with respect to a reference value,wherein when said analysis unit analyzes that the measurement data falls outside the normal range with respect to the reference value, said setting unit switches the ratio to display the X-ray moving image with a priority over the main image, andsaid image composition unit generates the composite image by superimposing the X-ray moving image on the main image on the basis of the ratio switched by said setting unit. |
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abstract | The invention relates to a system for synthesizing radiopharmaceuticals employing one or more single-use integrated kits of materials, valves and vessels fitted to one or more stationary apparatus in the manner that the kit can be safely ejected and disposed of without manual operations. Fluidic connections on the kits are made with flexible tubing that can be inserted into the various components by hand. This, along with the use of flexible configuration rotary valves, makes it possible to configure them to carry out a variety of processes. |
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description | 1. Field of the Invention The present disclosure relates to feed-through elements in general, but in particular to improved feed-through elements which are capable to be used in harsh environments with high operation or emergency temperatures above 260 degrees Celsius (° C.). In particular, the feed-through elements of the present disclosure can withstand operational and/or emergency pressures above 42000 pounds per square inch (psi). Therefore they can be used in a variety of applications, especially in downhole drilling equipment as well as in the safe containment of toxic matter and in spacecrafts. 2. Description of Related Art Feed-through elements in general are well known in the art and are incorporated in a lot of devices. In general terms, such feed-through elements usually comprise an electrical conductor which is fixed within a feed-through opening by an electrically insulating material. The parameters which characterize the performance of such feed-through devices are mainly the electrical resistance of the insulating material, the capabilities to withstand heat and pressure which tends to let the insulating material and/or the conductor burst out of the feed-through access opening. Although such feed-through elements represent a very suitable technology to guide e.g. electrical current through the housing of devices, said parameters often limit the possible application areas in which devices which contain such feed-through elements can be used. In U.S. Pat. No. 5,203,723 feed-through elements are described which are built from a metal pin which is surrounded by a polymer material as electrically insulating material. The geometry of the polymer material which surrounds the electrical conductor is adapted to withstand higher pressures by means of recesses and protrusions such as shoulders. The described feed-through elements are used for making connections within a sonde of a downhole oil well measuring or logging tool and can be used at operational temperatures above 260° C. and pressures of at maximum 28000 psi. The volume resistance of the used polymers is about 8.0×1014 Ωcm and therefore considerably excellent. However, the long term stability of such polymers is decreased with the time of the exposure to higher operational temperatures, the exposition to electromagnetic radiation such as UV or gamma radiation and also the mechanical degradation due to physical abrasion. Feed-through elements which contain an inorganic material such as glass as electrically insulating material are also known. U.S. Pat. No. 8,397,638 describes e.g. a feed-through device of an airbag igniter, in which the access hole of a metal support body is sealed by a glass material which also holds a pin as electrical conductor. Such feed-through elements are designed to withstand the pressure of the explosive when the igniter is fired, whereas pressures about 1000 bar which correspond to 14500 psi might be observed. The electrical properties of the insulation material are not described, but it can be assumed that the electrical volume resistance of the glass material does not play a major role because the igniter is only fired once with a short electrical pulse and then the device is destructed. Feed-through elements as described are not sufficient for applications in harsh environments, e.g. downhole drilling devices, which facilitate the exploration and/or exploitation of natural oil and/or gas resources in increasing depths and therefore are exposed to higher operational temperatures for a longer period of time. Against this background, it is an object of the present disclosure to provide a feed-through element which is suitable for use at temperatures above 260° C. and secures high electrical insulation properties of the conductor against its surrounding. The object is achieved by the feed-through element according to the present disclosure. A feed-through element according to the present disclosure comprises a support body with at least one access opening, in which at least one functional element is arranged in an electrically insulating fixing material. The electrically insulating fixing material electrically insulates the functional element from the support body and thereby physically and electrically separates the functional element from the support body. Also, in other words, the electrically insulating material seals the access opening of the support body. According to the present disclosure the electrically insulating fixing material contains a glass or a glass ceramic with a volume resistivity of greater than 1.0·1010 Ω·cm at the temperature of 350° C. The term ‘contains’ predominantly include the embodiments in which the electrically insulating fixing material is made only from the glass or glass ceramic, but also a multi layered body which might comprise a sandwich of different glass and/or glass ceramic materials within the described composition range or also comprising other compositions or other materials, such as polymers. The glass or a glass ceramic according to the present disclosure comprises in mole % on oxide basis 25%-55% SiO2, 0.1%-15% B2O3, 0%-15% Al2O3, 20%-50% MO whereby MO is selected from the group consisting of, individually or in combination, MgO and/or CaO and/or SrO and/or BaO, and 0% to less than 2% M2O, wherein M2O is selected from the group consisting of, individually or in combination, Li2O and/or Na2O and/or K2O. At this point some comments have to be made relating to the nature and composition of the glass material. The electrically insulating fixing material might according to the description be a glass. A glass is known to be an amorphous material in which crystallites are not desired. In contrast, a glass ceramics is a material in which crystallized zones are embedded within a glass matrix. The crystallized zones might amount to 99% or more of the overall material. Glass ceramics are often produced from a glass material which is then subjected to a heat treatment in which at least partial crystallization is induced. Because the crystallized zones of the glass ceramics usually have a different CTE (coefficient of thermal expansion) than the amorphous glass matrix, the concentration of the crystallized zones as well as their specific CTE can be used to adapt the overall CTE of the glass ceramics material. In the present disclosure, an amorphous glass material is as suitable as the glass ceramics material. Both have as electrically insulating fixing material being present in the access opening the composition described above. The electrically insulating glass or glass ceramics material with the described composition provides a superior volume resistivity for this group of materials. Because the volume resistivity is a function of the temperature at which the value of the volume resistivity is measured, the volume resistivity at the temperature of 350° C. is specified above. The volume resistivity decreases with increasing temperatures. This limits the maximum operational temperature of the described feed-through elements, because the electrically insulating fixing material loses its insulating properties at a certain temperature. By providing such a high minimum value for the volume resistivity at the temperature of 350° C., the feed-through elements according to this disclosure are most advantageously suitable for applications at high temperatures which were barred before. Approximately the value of the volume resistivity at 250° C. is ten times the value at 350° C. The electrical resistance to be measured between the functional element and the support body also depends, besides on the volume resistance of the electrically insulating fixing material and the temperature to which the feed-through element is exposed, on the geometry of the feed-through device, e.g. from the minimal distance between the functional element surface embedded in the insulating material and the inner wall of the access opening which is in contact with the insulating material. Because of the high value of the insulating material's volume resistivity it is possible to design a feed-through element with a comparably compact size. Such preferred embodiment is represented by a feed-through element, wherein the electrically insulating fixing material electrically insulates the functional element from the support body with an electrical insulation resistivity of at least 500 MΩ at the operational temperature of 260° C. The functional element can fulfill various functions within a feed-through element according to the present description. The most common case is when the functional element is an electrical conductor. In this case the functional element might be a full or hollow pin or tube. Such pin might be made from metal or other suitable conductors. However, the functional element can in the contents of the present description also fulfill other functions, e.g. it can represent a waveguide for e.g. microwaves or sound waves to be guided through the feed-through. In these cases the functional element might mostly be a tube, preferably made from metal or ceramics. The functional element might also be used to guide a cooling fluid such as cooling-water or cooling-gases through the feed-through element. Another possible embodiment of the functional element is simply a holding element, which carries further functional elements, e.g. thermo elements or fibers as light guides. With other words, in this embodiment the functional element might serve as adapter for functional elements which could not be directly fixed in the electrically insulating glass or glass ceramics material. In these cases the functional element might most suitably be a hollow element or a tube. It is not only the geometrical design such as the thickness of the electrically insulating glass or glass ceramics fixing material and the access opening which define the maximum pressure to which the feed-through element according to invention could be exposed, but also the bonding strength of the glass or glass ceramics material within the access opening. If such material is used to seal an access opening, there are chemical and physical bonding phenomena on the contact area of the glass or glass ceramics material and the inner wall of the access opening or the outer surface of the functional element. These bonding phenomena might be chemical reactions or physical interactions between the material of the inner wall of the access opening and therefore the material of the support body and/or the functional element on the one side, and the components of the glass or glass ceramics fixing material on the other side. If the composition of glass or glass ceramics fixing material is chosen in the best way, those bonding phenomena significantly contribute to the strength of the connection between the fixing material and the elements to be fixed. In the context of the present description, the benefit of the described composition can be demonstrated by the maximum pressure exceeding 42000 psi at the operation temperature of 260° C. which the feed-through element according to the description can withstand. This maximum pressure indicates an operational pressure to which the feed-through element can be exposed for a longer period of time. The maximum pressure is also dependent on the operational temperature, at room temperature maximum pressures exceeding 65000 psi can be constructed with the described feed-through element. The short time peak pressures can significantly exceed those maximum pressures. If a described feed-through element suffers from pressure overload, typically the fixing material together with the functional element or the functional element alone bursts out of the access opening. Then surrounding matter can pass the access opening and might destroy equipment nearby. Therefore highest possible values for the maximum pressure are desired. The described electrical insulating glass or glass ceramics fixing material is capable of hermetically sealing at least one access opening. The term hermetical sealing is known to specify the quality of the sealing, in this case the hermetic means that the sealing is essentially completely tight against leakage of all possible media. Normally, hermeticity is measured by helium leak testing. The procedure is known in the industry. Helium leaking rates below 1.0×10−8 cc/sec (cubic centimeters per sec) at room temperature or 1.69×10−10 mbar I/s at room temperature indicate that the sealing of the access opening is hermetic. The described composition range of the electrically insulating fixing material provides the possibility to essentially match the CTE of the electrically insulating fixing material to the CTE of the support body. This means that the values of the CTEs of the electrically insulating fixing material and the support body are essentially the same or at least are similar. In this case, a so called matched seal is present. The forces which hold the electrically insulating fixing material within the access opening are predominantly the chemical and/or physical forces caused by the described interaction of the glass or glass ceramics components and the material of the support body at the interface of the glass or glass ceramics material at the inner access opening wall. As alternative, the composition of the electrically insulating glass or glass ceramics fixing material can be within the described range and/or the material of the support body can be chosen so that a so called compression seal is the result. In this case the CTE of the support body's material is larger than the CTE of the electrically insulating glass or glass ceramics fixing material. When during the manufacturing of the feed-through device the support body together with glass or glass ceramics fixing material (and the functional element) being inserted into the at least one access opening is heated, the glass or glass ceramics fixing material melts and connects with the inner wall of the referring access opening. When this assembly is cooled, the support body virtually shrinks onto the glass or glass ceramics slug within the access opening and provides a physical pressure force onto the glass or glass ceramics slug which contributes to the forces holding the electrically insulating glass or glass ceramics fixing material within at least one access opening. Thereby the support body exerts an additional holding pressure towards the electrically insulating fixing material. This additional holding pressure is at least present at room temperature, and preferably contributes to the secure sealing of at least one access opening up to the temperature at which the feed-through element was manufactured. Of course, the above mentioned chemical or physical molecular forces mentioned in the context of the matched sealing might still be also present. Essentially, the support body can be manufactured from all suitable materials and/or material combinations. However, advantageous materials for the support body are ceramics, preferably Al2O3 ceramics and/or stabilized ZrO2 ceramics and/or Mica. Alternatively, the support body advantageously can be manufactured from metals and/or alloys. Preferred materials from this group are stainless steel SAE 304 SS and/or stainless steel SAE 316 SS and/or Inconel. The functional element is preferably essentially made from a metal material and/or alloy selected from the group consisting of Beryllium Copper and/or Nickel-Iron Alloy and/or Kovar and/or Inconel. Ceramics and metal based materials are known to the one skilled in the art and are therefore not described in further detail. Both, support body and functional element, can of course also comprise other materials than the described ones, e.g. in other regions than nearby the access openings, and/or might contain a sandwich structure from different materials. The performance of the described feed-through element can be tuned if certain material combinations are used for the support body and the functional element. Specifically preferred is the combination of a functional element made from Beryllium Copper combined with a support body made from stainless steel SAE 304 SS or stainless steel SAE 316 SS. As well preferred is the combination of a functional element made from Nickel-Iron Alloy combined with support body made from stainless steel SAE 304 SS or Inconel. Another preferred combination is represented by a functional element made from Kovar combined with support body essentially made from Inconel. Also specifically preferred is the combination of a functional element made from Inconel combined with support body made from Inconel. The preferred combinations are summarized in the following table. support bodyfunctional elementmaterialmaterialSAE 304 SSBeryllium CopperSAE 316 SSBeryllium CopperSAE 304 SSNickel-Iron AlloyInconelNickel-Iron AlloyInconelKovarInconelInconel Within the described composition range of the electrically insulating glass or glass ceramics fixing material there are of course preferred ranges for the contents of its components. Those preferred ranges can provide preferred properties to the glass or glass ceramics fixing material, especially but not necessarily with the aforesaid materials for support body and/or functional element. Preferably, the electrically insulating fixing material contains a glass or glass ceramics comprising in mole % on oxide basis 35%-50% SiO2, 5%-15% B2O3, 0%-5% Al2O3, 30%-50% MO and 0% to less than 1% M2O. Most preferred is the embodiment, in which the electrically insulating fixing material contains a glass or glass ceramics comprises in mole % on oxide basis 35%-50% SiO2, 5%-15% B2O3, 0%-<2% Al2O3, 30%-50% MO and 0% to less than 1% M2O. The meaning of the abbreviations MO and M2O is already described in detail and also has to be applied for the aforesaid preferred composition ranges. Especially preferred is an embodiment in which the glass or glass ceramics within the described composition ranges is essentially free of M2O and/or PbO and/or fluorines. Essentially free means that there is no intentional content of the named components. However, unavoidable impurities might be present which might be caused by erosion of the glass melting equipment during its operation and/or artificial and/or natural contamination of the raw materials used in glass production process. Usually such impurities do not exceed the amount of 2 ppm (parts per million). If M2O is eliminated from the glass composition, the volume resistivity of the electrically insulating glass or glass ceramics fixing material can reach the highest values. However, the sealing of the access openings might be more difficult due to the more demanding glass melting properties. PbO and fluorines are undesired components because of their negative impact on the environment. Additional components might be preferred to improve the glass melting and processing properties of the electrically insulating glass or glass ceramics fixing material. Such preferred additional components are ZrO2 and/or Y2O3 and/or La2O3, which might be present either in the initial or preferred embodiments of the glass or glass ceramics composition, each from 0% up to 10% in mole % on oxide basis, either individually or in every possible combination. It is also preferred that the electrically insulating glass or glass ceramics fixing material comprises up to 30% of the overall volume of fillers. Such fillers are usually inorganic fillers. Most advantageously ZrO2 and/or Al2O3 and/or MgO are chosen, either individually or in every possible combination. Besides choosing the composition of the electrically insulating glass or glass ceramics fixing material within the disclosed composition ranges, it is also possible to improve the pressure resistance of the feed-through element by mechanical measures which can be applied during the manufacturing of the support body. Therefore at least one access opening can be adapted to provide even more resistance against pressure loads. Such measures advantageously are represented by means for preventing a movement of the electrically insulating fixing material in relation to the support body, which are applied to the inner access opening wall. Such means for preventing a movement can be structures which interlock with the electrically insulating glass or glass ceramics fixing material within the access opening. All geometrical structures which provide such interlocking functionality are suitable, e.g. recesses and/or protruding areas of the inner access opening wall. A protruding area might be a shoulder within the access opening, which locally reduces the diameter of the access opening. Such shoulder is most often located near the surface of the support body which is opposite to the side where the pressure load is expected. In most cases at least one access opening has at least a region with a cylindrical profile. Advantageous embodiments of access openings with such measures for preventing a movement of the electrically insulating fixing material in relation to the support body comprise an access opening, which has at least a region with a truncated profile. The truncated profile reduces the diameter of the access opening, the wider diameter is most often located near the surface of the support body which faces the expected pressure load and the narrowed diameter is most often located near the surface of the support body which is opposite to the expected pressure load. Another measure to enhance the maximum pressure loads and to prevent the extrusion of the functional element out of the electrically insulating fixing material is to provide the circumferential wall of the at least one functional element with means for preventing a movement of the functional element in relation to the electrically insulating fixing material and the support body. Again, those means for preventing a movement can be local variations of the diameter of the functional element, e.g. shoulders, recesses, truncated areas etc. Those structures are located in the region of the functional element which is fixed within the electrically insulating fixing material, therefore those means for preventing a movement provide an interlock with the electrically insulating fixing material. The feed-through element according to the present disclosure can be most advantageously used in downhole drilling and/or downhole exploration devices, especially for the exploration and/or exploitation of oil and/or natural gas resources. This application area of course comprises land based as well as underwater applications. Those applications can benefit especially from the pressure resistance and the electrical isolation capabilities the feed-through element provides. Another advantageous application area of the feed-through element according to the present disclosure is the containment of an energy generation or an energy storage device such as power plants and/or gas pressure tanks and/or electrochemical cells and/or molten salt tanks etc. Here, especially the electrical isolation properties at high temperatures are relevant for a safe and reliable containment. The feed-through element according to the present disclosure provides features, which also allow the application for the safe containment of all kind of matter, especially matter which is toxic and or at least harmful for the environment and/or health. For example, a feed-through element according to the present disclosure can be used to connect emergency equipment and/or sensors and/or actuators within the containment with operational devices and/or personnel outside the containment. Such containments are typically present in chemical and/or physical reactors or storage devices, e.g. used for at least intermediate storage of nuclear waste. Also applications in space benefit from the temperature and pressure resistance of the feed-through element according to the present disclosure. Space missions, such as satellites in planetary orbits or interplanetary missions, as well space rover vehicles are subject to extreme environments, especially in view of high and low temperatures and temperature changes. The reliability of feed-through elements used in those devices is often relevant for the success of the mission. The feed-through element according to the present disclosure is especially suitable to provide a feed-through of a housing which encapsulates a sensor and/or actuator. FIG. 1a and FIG. 1b represent the principle of a feed-through element 1 according to the present disclosure. The support body 2 has in this example the outer contour of a cylinder. Of course all structures are possible, e.g. disc shaped elements, are also comprised from the invention. There is an access opening in the support body 2, which is sealed by the electrically insulating fixing material 3. The access opening defines a passageway through the support body 2 and naturally has an inner access opening wall, which interfaces with the electrically insulating fixing material 3. The functional element 4 is arranged within and is held by the electrically insulating fixing material 3 within the access opening. In this embodiment, the functional element 4 is a pin which serves as conductor for electric current. In this example, the support body 2, the access opening and the functional element 4 are arranged in a coaxial configuration. In this example, the access opening also has a cylindrical profile. The access opening might be a bore within the support body, which is an appropriate way to produce an access opening in a generally cylindrical support body 2 made from a full material. It is also possible to produce such a support body 2 from a cast material, where the access opening might already be created during the casting process. The embodiment represented by FIG. 2 generally corresponds to the embodiment according to FIG. 1a and FIG. 1b, but the access opening has a truncated profile. This truncated profile narrows the diameter of the access opening at the bottom side of the feed-through element 1. In this principle drawing of the example, the truncated profile spans over the entire length of the access opening. Of course it is also possible that the truncated profile is only present in a first region of the access opening, whereas a second or further region might have different profiles, e.g. cylindrical profiles. By locally reducing the diameter of the access opening, the pressure which is required to expel the electrically insulating fixing material 3 out of the access opening is increased because the truncated profile interlocks with the fixing material 3 and virtually acts like a wedge when the pressure is applied on the top side of the feed-through element 1, where the diameter of the access opening is comparably wider. Thereby the maximum pressure the feed-through element 1 can withstand can be increased by the design of the access opening's profile. Such truncated profiles can again be produced e.g. by drilling and polishing of a full material, e.g. by using a taper reamer, or by casting using an appropriate forming tool. The advantageous general principle of locally narrowing the diameter of the access opening is also applied within the embodiment according to FIG. 3. Here the access opening has a first region 21 with a cylindrical profile and a second region 22 with a cylindrical profile, whereas the diameter of the cylindrical profile in the second region 22 is smaller than the diameter of the cylindrical profile in the first region 21. Thereby a shoulder in the access opening wall is created, which again serves as means for preventing a relative movement of the electrically insulating fixing material 3 in relation to the support body 2. As also shown in FIG. 3, the functional element 4 has means for preventing a movement 41 of functional element 4 in relation to the electrically insulating fixing material 3 and in relation to the support body 2. In this example, these means are represented by the protruding area 41 of the functional element, which in this embodiment creates a shoulder on the functional element's surface. Although the top view of the embodiment according to FIG. 3 is not shown, it is easily foreseeable for the one skilled in the art that the functional element's protruding area 41 must not have a disc structure. It is also possible that the upper and lower surface of the protruding area 41 has edges, e.g. the in the form of a square, a cross, a star etc., whereby also an interlocking functionality against torsion of the functional element 4 can be provided. When designing a feed-through element 1 with means for preventing a movement of the electrically insulating fixing material 3 and/or the functional element 4 in relation to the support body one of course should have in mind that due to the local reduction of the diameter of the access opening the overall electrical resistance of the feed-through element's electrically insulating fixing material 3 against electrical short cuts, especially between the functional element 4 and the support body 2 might be reduced. Therefore it could be beneficial to use recesses instead of protrusions as means for preventing a movement. The glass or glass ceramics materials used as electrically insulating fixing material 3 described in the present disclosures provide an excellent volume resistivity. However, the overall insulating performance and the flash over voltage of the feed-through element 1 can be further improved by the introduction of further protective elements 31, 32, especially further insulators. Therefore the embodiment according to FIG. 4 also includes protective elements 31, 32 on or at least near the surface of the electrically insulating glass or glass ceramics fixing material 3. The protective elements 31, 32 can be essentially made of other glasses, e.g. solder glass, and/or organic compounds or polymers, e.g. silicone adhesives or high temperature epoxy systems. The feed-through element 1 without protective elements 31, 32 has a typical flash over voltage of 1.0 kV. For the feed-through element 1 with insulators 31, 32 flash-over voltages of 2.0 kV and more can be achieved. As can be also seen from FIG. 4, the protective elements 31, 32 prevent any contact of the glass or glass ceramics surfaces of the electrically insulating fixing material with other media. The glass or glass ceramics fixing materials according to the present disclosure are chemically stable against air and most gaseous media. However, in harsh environments, more aggressive media might come into contact with the surface of the electrically insulating glass or glass ceramics fixing material 3. The corrosion capabilities of these media often also increase with increasing temperatures. Therefore the embodiment according to FIG. 4 also includes protective elements 31, 32 on or at least near the surface of the electrically insulating glass or glass ceramics fixing material 3. These protective elements 31, 32 prevent any contact of the glass or glass ceramic surfaces with other media. As example, the protective elements 31, 32 might be made from the same materials as for the insulators described above. All other suitable materials could be used as well. Of course it is also possible that the protective elements 31, 32 are only present at one side of the electrically insulating glass or glass ceramics fixing material 3. The embodiment comprising at least one protective element 31, 32 are most beneficially used in the downhole exploration and/or exploitation applications. As can be also seen from FIG. 4, in this example the surface of the electrically insulating glass or glass ceramics fixing material 3 is not in line with the top and/or bottom surface of the support body 2. This embodiment might be beneficial for the application of the protective elements 31, 32. However, it is also foreseen and comprised by the invention that these recessed surface levels could also be present in the embodiments without protective elements 31, 32 and that the embodiment with protective elements 31, 32 might also have surfaces of the electrically insulating glass or glass ceramics fixing material 3 being in line with the top and/or bottom surface of the support body 2. FIG. 5a shows the profile of a feed-through element 1 according to present disclosure with a plurality of access opening within a support body 2. This so called planar element has dimensions which are wider than high. As can be seen from FIG. 5b, which shows the top view of the feed-through element 1, the access openings can be arranged in a matrix. The matrix itself is variable, which means that the location of the access openings can be chosen according to the desired application. This embodiment can e.g. be used to provide multiple electrical and/or electronic components with electric current, e.g. to power them and/or to lead signals generated by these components through the support body 2. The support body might or might not seal the housing of a referring device. The support body 2 might be manufactured by a metal and/or alloy, or a ceramics material. In FIG. 6a, the perspective view of a so-called large feed-through element 1 is shown. Such feed-through elements 1 are typically used as feed-through of a containment of a power plant or the feed-through of a containment of a gas container. The support body is in this example a disc shaped element, preferably made from stainless steel. The support body has bores 25, which can be used to fix the feed-through element 1 at other components, e.g. housings and containments. The support body 2 therefore in this example represents a flange. In this embodiment there are three access openings sealed with electrically insulating fixing material 3, in which the functional elements 4 are fixed. The functional element 4 in this example is a conductor for electric current, which is specifically adapted to high power and high voltage. The functional element 4 also has a region 45 at its end, which can be used to provide connector capabilities, especially to connect power lines and/or plugs. FIG. 6b shows the profile of the feed-through element 1 according to FIG. 6a along the cut line A. The bores 25 run through the support body 2. However, all other measures of fixing the feed-through element 1 to another element/or device are also possible. As can be also seen, the functional element 4 comprises two major elements. One is the tube 44, which is in contact with the electrically insulating fixing material 3 and which is held by the electrically insulating fixing material 3 within the access opening. The second element 43 of the functional element 4 is the conductor for electric current 43. The conductor 43 and the tube 44 are usually fixed together e.g. by a brazed or soldered connection. The tube 44 and the conductor 43 consist in this example of different materials, e.g. metals. This construction is beneficial if the conductor 43 due to its material composition cannot build a hermetic connection with the electrically insulating fixing material 3. Then the tube 44 consisting of a metal being capable to be hermetically sealed in the electrically insulating fixing material 3 is used. For example, for the conductor 43 copper might be used especially because of its good capabilities as conductor for electric current. But copper can hardly be fixed within a glass or glass ceramics based electrically insulating fixing material 3. Then a tube 44 consisting essentially e.g. of stainless steel might be sealed within the electrically insulating fixing material 3 and the conductor 43 is soldered with the tube 44. In the example according to FIG. 6b, there also is the protective element 33 which covers the access opening on one side of the feed-through element 1. This protective element can be the same as the protective elements 31, 32 as described used in FIG. 4. Of course other kinds of protective elements 33 could also be used. In this example, the protective element 33 is used to mechanically protect the electrically insulating fixing material 3 within the access opening and to improve the flash-over voltage. The protective element 33 is in this example not in contact with the surface of the electrically insulating fixing material 3. Consequently there is a cavity 35 between the surface of the electrically insulating fixing material 3 and the bottom side of the protective element 33. This cavity might or might not be filled with specified media, e.g. protective fluids or gases. According to FIG. 4, the functional element 4 is furthermore protected by a cap 46 which could help to prevent mechanical damage to the functional element 4, especially the conductor 43 and tube 44 protruding above the level of the support body. Of course the cavity 35 and/or cap 46 could be absent in other embodiment of a feed-through element 1 according to the present disclosure. FIG. 7 shows the principle of the beneficial use of the disclosed feed-through element in downhole exploration and/or exploitation installation. In this example a drilling device is used to reach the reservoir of e.g. oil or natural gas. It is known and state of the art that the drilling device can be steered in various directions. Without such steering capabilities it would be impossible to reach the relevant reservoirs. In order to facilitate such steering capabilities, a drilling device comprises components which have to be contacted via feed-through elements 10 according to the present disclosure. In FIG. 8 the containment 20 of an energy generating device is shown. The generator has to be safely encapsulated within the containment, also in emergency and failure state situations. A feed-through element 1 according to the present disclosure is advantageously used in order to provide contact with the generator and/or devices within the containment. Such devices are e.g. devices to monitor the operation conditions of the generator and/or to steer the generator or other devices. As can be seen from the explanations above, the feed-through element according to the present invention provides its improved performance due to the composition of the electrically insulating glass or glass ceramics material. A large number of examples for glass or glass ceramics materials have been melted and applied to a described feed-through element. The compositions of six preferred glass materials and the value of their respective volume resistivity are summarized in Table 1. TABLE 1Fixing material compositions and volume resistivityComposition[mole %]Ex. 1Ex. 2Ex. 3Ex. 4Ex. 5Ex. 6SiO242.542.538.744.545.047.0B2O313.013.08.98.912.06.4Al2O31.51.51.61.60.01.6BaO33.033.00.034.633.017.3CaO0.00.036.70.00.016.5MgO7.010.06.77.37.08.1Y2O33.00.03.43.13.03.1ZrO20.00.04.00.00.00.0Volume1.5 × 10111.4 × 10113.9 × 10116.0 × 10101.8 × 10113.8 × 1010resistivity at350° C. [Ωcm] All fixing material compositions are listed in mole % on oxide basis. All fixing materials Ex. 1 to Ex. 6 were amorphous glass materials. The advantages of the examples Ex. 1 to Ex. 6 according to the invention are obvious when they are compared with the properties of known glass materials, when these are used for feed-through element according to the present disclosure. Such comparative examples are summarized in Table 2 and named as CE 1 to CE 3. TABLE 2Comparative fixing material compositions and volume resistivityComposition [mole %]CE 1CE 2CE 3SiO263.4 58.0 67.1 B2O3—1.81.5Al2O30.31.13.1PbO29.4 ——BaO0.12.0—Fe2O3—0.8—Li2O—21.8 22.8 Na2O0.23.00.4K2O6.56.92.3F—4.6—Sb2O30.2 0.01—P2O5———ZnO———CaO———Volume resistivity4.0 × 1093.2 × 1076.0 × 105at 350° C. [Ωcm] As can be seen from the comparative examples, the best volume resistivity of those materials is by an order of magnitude lower than the lowest volume resistivity of the fixing materials according to the invention. The temperature dependence of the volume resistivity of the example fixing materials Ex. 1 to Ex. 6 on a logarithmic scale is shown in the graph according to FIG. 9. Also shown is the corresponding graph for the comparative examples named in the graph. As can be seen from the graph according to FIG. 9, the best comparative example is CE 1. However, as it has to be stressed that a logarithmic scale is used, even CE 1 cannot even come close to the volume resistivity behavior of the electrically insulating fixing material according to the invention. With fixing materials with a volume resistivity below 1.0×1010 Ωcm at the operational temperature of 350° C. it was not possible to manufacture a feed-through element with an overall electrical resistivity of at least 500 MΩ at the operational temperature of 260° C. Those properties are only provided by the fixing material disclosed herein. The glass systems according to the Ex. 1 to Ex. 6 showed excellent mechanical stability when used in a feed-through element. Operational maximum pressure values of more than 42000 psi (at 260° C.) and values of more than 65000 psi (at room temperature) were achieved. It even became obvious that higher maximum pressures are possible, but the mentioned values represent the upper limit of the available measurement equipment. Therefore the electrically insulating fixing materials according to the present disclosure provide by their volume resistivity and their pressure resistance two significant advantages to feed-through elements which are thereby enabled for the application in harsh environments. |
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abstract | A high performance field reversed configuration (FRC) system includes a central confinement vessel, two diametrically opposed reversed-field-theta-pinch formation sections coupled to the vessel, and two divertor chambers coupled to the formation sections. A magnetic system includes quasi-dc coils axially positioned along the FRC system components, quasi-dc mirror coils between the confinement chamber and the formation sections, and mirror plugs between the formation sections and the divertors. The formation sections include modular pulsed power formation systems enabling static and dynamic formation and acceleration of the FRCs. The FRC system further includes neutral atom beam injectors, pellet injectors, gettering systems, axial plasma guns and flux surface biasing electrodes. The beam injectors are preferably angled toward the midplane of the chamber. In operation, FRC plasma parameters including plasma thermal energy, total particle numbers, radius and trapped magnetic flux, are sustainable at or about a constant value without decay during neutral beam injection. |
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claims | 1. A nuclear power generation system including:a steam generator including a vertically elongated steam generating vessel fluidly coupled to a reactor vessel having an internal cavity;a reactor core comprising nuclear fuel disposed within the internal cavity and operable to heat a primary coolant;a primary coolant flow loop formed between the reactor vessel and the steam generating vessel, the primary coolant flow loop being configured and operable to circulate primary coolant through the reactor vessel and steam generating vessel via thermally induced gravity flow; anda secondary coolant flow loop formed between the steam generating vessel and a low pressure turbine, the secondary coolant flow loop being configured and operable to circulate secondary coolant through the steam generating vessel in which the primary coolant heats and converts the secondary coolant from liquid to steam, the steam flowing through the secondary coolant flow loop to the low pressure steam turbine;wherein a temperature differential between the primary coolant leaving the steam generating vessel and secondary coolant entering the steam generating vessel is at least 175 degrees F. sufficient to induce natural thermally driven gravity circulation of the primary coolant through the primary coolant flow loop;wherein the pressure of steam entering the low pressure turbine is less than 400 psia; andwherein the secondary coolant flow loop does not include a high pressure turbine. 2. The nuclear power generation system of claim 1, wherein the temperature of steam entering the low pressure turbine has a temperature of at least 575 degrees F. and is superheated steam. 3. The nuclear power generation system of claim 1, further comprising a single feedwater heater disposed in the secondary coolant flow loop between an outlet from the low pressure turbine and the steam generating vessel, the feedwater heater configured to heat the secondary coolant using secondary coolant extracted from the low pressure turbine;wherein the secondary coolant flow loop does not include any additional feedwater heaters between the low pressure turbine outlet and the steam generating vessel. 4. The nuclear power generation system of claim 3, further comprising:a condenser disposed in the secondary coolant flow loop between an outlet from the low pressure turbine and the steam generating vessel; anda single feedwater heater disposed in the secondary coolant flow loop between the condenser and the steam generating vessel, wherein the secondary coolant flow loop does include any additional feedwater heaters between the condenser and the steam generating vessel. 5. The nuclear power generation system of claim 4, wherein the steam generating vessel and reactor vessel are disposed inside a containment vessel, and the turbine, condenser, and feedwater heater are disposed outside the containment vessel. 6. The nuclear power generation system of claim 4, wherein secondary coolant is heated in the feedwater heater using secondary coolant extracted from the low pressure feedwater heater at two different extraction points having different secondary coolant temperatures and pressures. 7. The nuclear power generation system of claim 1, wherein the primary coolant flows through the reactor pressure vessel to cool the reactor core and through the steam generating vessel to transfer heat to a secondary coolant flowing through the steam generating vessel. 8. The nuclear power generation system of claim 1, wherein the steam generating vessel includes a vertically stacked preheat section, main steam generating section, and a superheater section. 9. A nuclear power generation system including:a steam generator including a vertically elongated steam generating vessel fluidly coupled to a reactor vessel having an internal cavity;a reactor core comprising nuclear fuel disposed within the internal cavity and operable to heat a primary coolant;a primary coolant flow loop formed between the reactor vessel and the steam generating vessel, the primary coolant flow loop being configured and operable to circulate primary coolant through the reactor vessel and steam generating vessel via thermally induced gravity flow;a secondary coolant flow loop formed between the steam generating vessel and a single steam turbine, the secondary coolant flow loop being configured and operable to circulate secondary coolant through the steam generating vessel in which the primary coolant heats and converts the secondary coolant from liquid to steam, the steam flowing through the secondary coolant flow loop to an inlet on the single steam turbine;a condenser disposed in the secondary coolant flow loop between an outlet from the single turbine and the steam generating vessel, the condenser configured to cool and condense steam exiting the single turbine thereby converting the secondary coolant from steam to liquid; anda single feedwater heater disposed in the secondary coolant flow loop between the condenser and the steam generating vessel, the feedwater heater configured to receive and heat the liquid secondary coolant from the condenser,wherein the secondary coolant flows directly from the feedwater heater into the steam generating vessel without any intervening feedwater heaters between the condenser and the steam generating vessel;wherein a temperature differential between the primary coolant leaving the steam generating vessel and secondary coolant entering the steam generating vessel is sufficient to induce natural thermally driven gravity circulation of the primary coolant through the primary coolant flow loop; andwherein the single steam turbine is a low pressure turbine characterized by steam entering the turbine at a pressure less than 400 psia. 10. The nuclear power generation system of claim 9, wherein the secondary coolant flow loop does not include any additional turbines. 11. The nuclear power generation system of claim 9, wherein the steam is superheated. 12. The nuclear power generation system of claim 9, wherein the temperature of steam entering the steam turbine has a temperature of at least 575 degrees F. and is superheated steam. 13. The nuclear power generation system of claim 9, wherein a temperature differential between primary coolant leaving the steam generating vessel and secondary coolant entering the steam generating vessel is at least 175 degrees F. 14. The nuclear power generation system of claim 13, wherein the temperature differential is between and including 175-215 degrees F. 15. The nuclear power generation system of claim 9, wherein the secondary coolant is heated in the feedwater heater using secondary coolant extracted from the turbine at two different extraction points, at least one of the extraction points being at sub-atmospheric pressure. 16. The nuclear power generation system of claim 15, wherein each of the extraction points is at sub-atmospheric pressure. 17. The nuclear power generation system of claim 9, wherein the feedwater heater is a shell and tube heat exchanger, colder secondary coolant from the condenser flowing on the tube side and hotter secondary coolant at least partially in steam form extracted from turbine flowing on the shell side for heating the tube side secondary coolant. 18. The nuclear power generation system of claim 17, wherein the secondary coolant extracted from the turbine is at sub-atmospheric pressure. 19. The nuclear power generation system of claim 9, wherein the steam generating vessel includes vertically stacked heat exchangers comprising a preheat section, a steam generator section, and a superheater section, the secondary coolant being converted from liquid to superheated steam flowing upwards through the steam generating vessel. 20. A method for inducing thermally driven gravity flow of primary coolant through a nuclear reactor, the method comprising:providing a vertically elongated steam generating vessel fluidly coupled to a reactor vessel housing a nuclear fuel core which heats a primary coolant;circulating the primary coolant through a primary coolant flow loop formed between the steam generating vessel and reactor vessel, the primary coolant entering the steam generating vessel from the reactor vessel at a first temperature and exiting the steam generating vessel at a second temperature lower than the first temperature;heating a secondary coolant in the steam generating vessel using the primary coolant which converts the secondary coolant from a liquid entering the steam generating vessel to steam exiting the steam generating vessel, the secondary coolant entering the steam generating vessel at a third temperature and exiting the steam generating vessel at a fourth temperature higher than the third temperature;circulating the secondary coolant through a secondary coolant flow loop having an external portion outside to the steam generating vessel;expanding the steam in a single steam turbine for producing electric power;condensing the steam in a surface condenser to convert the secondary coolant from steam back into liquid form;heating the liquid secondary coolant received from condenser in a single feedwater heater to the third temperature using fluid extracted from the turbine; andflowing the heated liquid secondary coolant from the feedwater heater directly to the steam generating vessel without any intervening feedwater heaters between the condenser and the steam generating vessel;wherein the temperature differential between the second temperature of the primary coolant and the third temperature of the secondary coolant is at least 175 degrees F. selected to induce natural thermally driven gravity circulation of the primary coolant through the primary coolant flow loop; andwherein the single steam turbine is a low pressure turbine characterized by steam entering the turbine at a pressure less than 400 psia. |
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summary | ||
047909765 | summary | The invention relates to a device for flushing out a lance-housing tube and for aligning in a reactor pressure vessel of a boiling-water reactor a dry power distribution detector (PDD) lance, which partly protrudes with a pressure-tight lance feedthrough or passthrough from an end flange on the lance-housing tube of the reactor pressure vessel. Neutron flux density in a reactor core is an important characteristic for monitoring and controlling nuclear power generating stations. It is measured with detectors, respective groups of four detectors with a surrounding supporting tube forming a so-called PDD lance. During assembly, these lances are vertically inserted by a gripper of a lifting device into a partially unloaded core while the reactor pressure vessel is opened and flooded, and are held in a mounting at an upper end of the lance by upwardly spring-loaded locking pins. Accordingly, the lower end of the lance with a pressure-tight feedthrough or passthrough and a lance protection tube partly protrudes from an end flange on the lance-housing tube of the reactor pressure vessel. A housing assembled therewith prevents the reactor water from running out during the installation. Instrumentation lances of different construction have become known heretofore. The lance installed most frequently to date is a so-called web wet PDD lance. It remains operative for only a few years and must then be disassembled completely and scrapped. Attempts have therefore been made to replace the wet PDD lances by a relatively new type of lance, the so-called dry PDD lance, which advantageously has an extremely long operating life. Dry PDD lances therefore need not be replaced. In the course of the operation of a reactor, radioactive deposits are formed in the reactor pressure vessel which are disposed in part in the lance-housing tubes, and therefore also on the lance feedthrough or passthrough. If long-lived dry lances are installed which are not to be replaced, the deposits increase continuously so that a consequence is the formation of a locally extremely high radiation level in the periodically accessible region below the reactor pressure vessel. Cleaning the lance-housing tubes, however, has been found not to be economically feasible heretofore because the reactor must be shut down considerably longer than for a change of fuel assemblies and must be partially discharged. Because the lances increase in diameter from top to bottom, they can be pulled out of the core with an upward inclination only if the reactor pressure vessel is opened and flooded. The adjacent fuel assembly cases must moreover be removed first in order to avoid damage. Only then it is possible to lift a lance so that the end flange is flushed out or rinsed by reactor water which runs out under controlled conditions and must then be collected underneath the reactor pressure vessel. The heretofore conventionally used wet lances have a circular cross section so that angular orientation is unnecessary during assembly. Installation under water thereby presents no problems. The new dry PDD lances which are preferred for reasons of cost and environment protection are, however, thicker because of their liquid-tight construction and have a pronounced profile. Their cross section has, for example, the shape of a clover leaf, so that the space available in the core grid is better utilized. A dry PDD lance must therefore be aligned accurately relative to the reactor core in order to avoid damage. Because of the great length and the elasticity of the lances they cannot be inserted under water from above into the reactor pressure vessel. The danger would exist that the profiled lances would become twisted or tilted during the alignment and cause damage to the fuel assembly cases or casings when released. Because the conical sealing seat of the lance is loaded by the lance weight of approximately 250 N (Newton) as well as by a pressure of approximately 50 m water column, a rotation of the lance in the sealing seat would damage the sealing surfaces, especially if residual dirt is occluded. This would require costly repairs. If, on the other hand, the lance were lifted for rotation in order to preserve the sealing surfaces, the installation personnel would be endangered by escaping contaminated reactor water. A flushing operation by conventional means is therefore not feasible economically. It would delay and impede work on the upper side of the pressure vessel when that work may have tight deadlines. It is therefore an object of the invention to provide such a device which, for the first time, ensures a flushing to the lance-housing tubes when the reactor pressure vessel is closed and pressureless and, in addition, aligns the dry PDD lances relative to the reactor core. With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for flushing out a lance-housing tube in a reactor pressure vessel of a boiling-water reactor and for aligning therein a dry PDD lance which partly protrudes with a pressure-tight lance passthrough from an end flange on the lance-housing tube of the reactor pressure vessel, includes a tubular housing surrounding from below a part of the lance protruding from the reactor pressure vessel and sealed by a lance protection tube, the tubular housing being fastenable to the end flange; and a piston arranged in the tubular housing underneath the sealed lance, the piston being vertically displaceable and rotatable. By this device, the lance feedthrough or passthrough and the lance protection tube assembled therewith at the end flange are first enclosed in a pressure-tight manner. Then, the piston is moved and lifted, respectively, by hand in the housing until it tangibly engages the lower end of the lance protection tube. Thereafter, if a dry PDD lance is used, the piston is rotated until it snaps in at the lower end of the lance protection tube. There, the piston, together with the lance, is pushed vertically upwardly. The lance is thereby lifted a short distance from its seat in the end flange so that reactor water runs out and the lance housing tube as well as the sealing seat of the lance is flushed out or rinsed. After the flushing operation is completed, the lance with the device according to the invention is deposited again in the sealing seat. If necessary, the dry lance is aligned beforehand exactly to the reactor core by rotating the piston. With the device according to the invention, the advantage is attained that lances inserted into a reactor pressure vessel are freed of impurities and are subsequently arranged reliably again in a pressure-tight manner in the end flange after shutdown, even when the reactor pressure vessel is closed. Working above the reactor is not impeded. The importance of the device according to the invention increases by the fact that dry PDD lances are used increasingly. Whereas with each change of a short-lived lance, a flushing or rinsing operation is performed simultaneously, the long-lived dry PDD lances must be flushed out at given intervals, which can advantageously be performed with the device according to the invention. In accordance with another feature of the invention, the piston is formed with an entrainer pin cooperatively engaging in a slot formed in the lance protection tube. In accordance with a further feature of the invention, the lance protection tube is formed at an upper end in the interior thereof with a spherical member engageable in a marker slot formed in the lance passthrough. Movements of the piston are thereby transmitted exactly to the lance via the lance protection tube which originally served only for sealing during the assembly. For lifting and lowering the unit formed of the piston, the protective tube and the lance, the device, according to an added feature of the invention is equipped with a cap screw which supports the piston and is cooperatively secured with a thread formed on an outer surface of the tubular housing. This cap screw is provided with handles. An advantage is thereby achieved that the lance will always be lifted sensitively without tools and with little effort even though it is loaded with a water column of about 50 m and its own weight of about 250 N (Newton ). In accordance with an added feature of the invention, the piston is formed with a flow passage for reactor water, and including a valve disposed in said passage. The flow of discharging reactor water flushing out the lance is thereby controlled. If only clean water flows off, the lance is again deposited in the sealing seat. In order that the dry PDD lance should remain or be aligned exactly, and in accordance with a concomitant feature of the invention, a telescoping folding lever, for example, is arranged on the piston of the device. With this relatively long pointer lever, the dry lance is slightly turned, if necessary, before being deposited or seated, thereby assuring an exact alignment or orientation with the geometry of the reactor core and the fuel assembly casings, respectively. The aligned lance is then deposited in the end flange by downwardly screwing the cap screw which supports the piston of the device. Thereafter, the device is drained and detached from the end flange after a test for tightness i.e. for leaks. With the invention, an advantage is achieved, in particular, that dry PDD lances, which remain operative in the reactor for the entire operating period, can be retrofitted even in previously contaminated installations. Not economical shutdown times are thereby shortened and the production of highly radioactive scrap is drastically reduced. 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 device for installing dry PDD lances and for flushing out lance-housing tubes in boiling-water reactors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. |
056169272 | abstract | Proposed is an improved frame-supported pellicle, which is an integral body consisting of a rigid frame, a transparent plastic resin film adhesively bonded to one end surface of the frame in a slack-free fashion and a layer of a pressure-sensitive adhesive on the other end surface of the frame. The improvement consists in the use of a specific pressure-sensitive adhesive capable of being imparted with a greatly decreased bonding strength when it is heated at a temperature higher than a critical temperature or irradiated with UV light in a dose exceeding a critical dose so as to facilitate demounting of the frame-supported pellicle from a photomask on which the pellicle is mounted when it is to be replaced with a new pellicle without leaving any fragments of the adhesive adherent to the photomask surface. |
summary | ||
claims | 1. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens;an aperture plate positioned on the optical axis of the primary beam to block the orbit of secondary electrons emitted from the sample, the aperture plate having an opening through which the primary beam passes and being mounted at the crossover point or a position between the crossover point and the objective lens; anda charged-particle detector positioned to detect backscattered electrons emitted from the sample and passed through the opening of the aperture plate, the charged-particle detector being mounted at a position closer to the beam source than the crossover point. 2. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens;a first charged-particle detector positioned on the optical axis of the primary beam to block the orbit of secondary electrons emitted from the sample for detecting the secondary electrons, the first charged-particle detector having an opening through which the primary beam passes and being mounted at the crossover point or at a position between the crossover point and the objective lens; anda second charged-particle detector positioned on the optical axis of the primary beam to detect backscattered electrons emitted from the sample and passed through the opening of the first charged-particle detector, the second charged-particle detector being mounted at a position closer to the beam source than the crossover point. 3. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens; anda charged-particle detector positioned on the optical axis of the primary beam to detect secondary electrons emitted from the sample, the charged-particle detector having an opening through which backscattered electrons from the sample pass as well as the primary beam passes and being mounted at the crossover point or at a position between the crossover point and the objective lens. 4. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a magnetic objective lens. 5. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a cathode lens, and wherein a potential difference is produced between an outer wall of an electron optical column and a sample holder. 6. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-cathode lens, and wherein a potential difference is produced between an outer wall of the objective lens and a sample holder. 7. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-decelerating electrostatic objective lens, and wherein a potential is produced between an outer wall of the objective lens and the inside of the objective lens. 8. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-cathode lens, and wherein the objective lens is at ground potential and a high voltage is applied to a sample holder. 9. A beam apparatus as set forth in any one of claims 1 to 3, wherein a beam-shaping aperture is mounted between said beam source and said condenser lens. |
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description | This divisional patent application claims the benefit of priority under 35 U.S.C. § 119(e) from U.S. patent application Ser. No. 14/715,646, filed May 19, 2015, entitled A NUCLEAR FUEL ASSEMBLY SUPPORT FEATURE, which claims priority to U.S. Provisional Patent Application Ser. No. 62/096,017, filed Dec. 23, 2014, entitled A NUCLEAR FUEL ASSEMBLY SUPPORT FEATURE. This invention relates in general to nuclear fuel assemblies and more particularly to a support feature for laterally supporting a Nuclear Fuel Assembly. The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel 10 having a closure head 12 enclosing a nuclear core 14. A liquid reactor coolant, such as water is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. The core 14 comprises a large number of fuel assemblies. FIG. 2 shows an elevational view, represented in vertically shortened form, of a fuel assembly being generally designated by reference character 22. The fuel assembly 22 is the type used in a pressurized water reactor and has a structural skeleton which, at its lower end includes a bottom nozzle 58. The bottom nozzle 58 supports the fuel assembly 22 on a lower core support plate 60 in the core region of the nuclear reactor (the lower core support plate 60 is represented by reference character 36 in FIG. 2). In addition to the bottom nozzle 58, the structural skeleton of the fuel assembly 22 also includes a top nozzle 62 at its upper end and a number of guide tubes or thimbles 54, which extend longitudinally between the bottom and top nozzles 58 and 62 and at opposite ends are rigidly attached thereto. The fuel assembly 22 further includes a plurality of transverse grids 64 axially spaced along and mounted to the guide thimbles 54 (also referred to as guide tubes) and an organized array of elongated fuel rods 66 transversely spaced and supported by the grids 64. Although it cannot be seen in FIG. 3 the grids 64 are conventionally formed from orthogonal straps that are interleafed in an egg-crate pattern with the adjacent interface of four straps defining approximately square support cells through which the fuel rods 66 are supported in transversely spaced relationship with each other. In many conventional designs springs and dimples are stamped into the opposing walls of the straps that form the support cells. The springs and dimples extend radially into the support cells and capture the fuel rods therebetween exerting pressure on the fuel rod cladding to hold the rods in position. Also, the assembly 22 has an instrumentation tube 68 located in the center thereof that extends between and is mounted to the bottom and top nozzles 58 and 62. With such an arrangement of parts, fuel assembly 22 forms an integral unit capable of being conveniently handled without damaging the assembly of parts. As mentioned above, the fuel rods 66 in the array thereof in the assembly 22 are held in spaced relationship with one another by the grids 64 spaced along the fuel assembly length. Each fuel rod 66 includes a plurality of nuclear fuel pellets 70 and is closed at its opposite ends by upper and lower end plugs 72 and 74. The pellets 70 are maintained in a stack by a plenum spring 76 disposed between the upper end plug 72 and the top of the pellet stack. The fuel pellets 70, composed of fissile material, are responsible for creating the reactive power of the reactor. The cladding which surrounds the pellets functions as a barrier to prevent the fission by-products from entering the coolant and further contaminating the reactor system. To control the fission process, a number of control rods 78 are reciprocally moveable in the guide thimbles 54 located at predetermined positions in the fuel assembly 22. Specifically, a rod cluster control mechanism 80 positioned above the top nozzle 62 supports the control rods 78. The control mechanism has an internally threaded cylindrical hub member 82 with a plurality of radially extending flukes or arms 52. Each arm 52 is interconnected to the control rods 78 such that the control rod mechanism 80 is operable to move the control rods vertically in the guide thimbles 54 to thereby control the fission process in the fuel assembly 22, under the motive power of control rod drive shafts 50 (shown in phantom) which are coupled to the control rod hubs 80, all in a well-known manner. The pressurized water reactor fuel assemblies 22 are thus long elongated structures that are supported within a core 14 of a nuclear reactor at their lower ends by a bottom nozzle 58 that has holes that sit on pins that extend from the upper surface of a bottom core plate 60 and are supported at their upper ends by alignment pins that fit in holes in the surface of the underside of an upper core support plate. Some space exists between fuel assemblies for the passage of coolant. There have been instances of upper core plate alignment pins being bent during reactor internals reassembly after the reactor core has been accessed for maintenance. These pins have to be removed before the upper core plate can be reseated over the fuel assemblies. Reseating of the upper core plate after the alignment pins have been removed can result in the fuel assembly for that location being misaligned. The plant then typically has to impose a power penalty for that misalignment, which can be significant. The top nozzle pop out spring 48 provides some alignment to that core location during operation because the fuel assembly is supported by the adjacent assemblies. Also, Fuel assembly to fuel assembly gaps allow for impact between fuel assemblies, resulting in increased impact loads on spacer grids during Seismic/LOCA events. However, some gap between fuel assemblies during outages is desirable to facilitate fuel handling. A need exists to reduce or eliminate the gap only during reactor operation while enabling some clearance between fuel assemblies during outages in which the assemblies need to be moved. This invention achieves the foregoing objectives by providing a nuclear fuel assembly having an elongated dimension and comprising a plurality of interconnected components. At least some of the interconnected components comprise: a top nozzle; a bottom nozzle; a plurality of guide thimbles extending between the top nozzle and the bottom nozzle; and a plurality of grids arranged in a tandem spaced relationship that extends between the top nozzle and the bottom nozzle along the elongated dimension, with each of the grids having a plurality of cells some of which support fuel rods and others through which the guide thimbles respectively pass and attach to the grid. At least some of the interconnected components have a peripheral surface area that extends in a plane a distance along the elongated dimension. At least some of the interconnected components have a bimetallic spring that moves between a first and second position relative to the plane as the fuel assembly transitions in a reactor core from a shutdown temperature to an operating temperature, with one of the first and second positions placing the bimetallic spring in contact with an adjoining component of the reactor core. In one embodiment, the bimetallic spring does not extend substantially out of the plane at temperatures substantially below the nuclear reactor operating temperature and protrudes outwardly from the nuclear fuel assembly at operating temperatures of the nuclear reactor to an extent to contact the adjoining component of the core of the nuclear reactor. In another embodiment, the bimetallic spring is placed on a border grid strap at a mid-grid location and in another embodiment, the bimetallic spring is supported on an upper or lower border grid strap or both the upper and lower border grid strap. In still another embodiment, the bimetallic spring is supported on the top nozzle. The bimetallic spring may be a circular disc shape, optionally with relief holes or it may have an elongated rectangular shape. The rectangular shape may be oriented horizontally or vertically. The attached figures in FIGS. 3-14 show varying configurations of the bimetallic concept to attain different benefits. One embodiment of this invention is a fuel assembly 22 with a mid-grid with a bimetal protrusion spring 26 arrangement formed in an outer grid strap 24 shown in FIGS. 3-6. Any arrangement of these springs 26 could be present on each outer strap 24 (such as one in each corner as shown in the FIG. 9). A rectangular shaped spring/protrusion 28 will likely be oriented vertically to minimize concerns for fuel handling should the spring not return fully to the flat original shape or return beyond the outer strap envelope. However, the rectangular shaped spring may also be mounted horizontally and fall within this concept. The spring may also be of a circular shape 30 such as a “pop-out” disc or other configuration that result in the desired deflection and load capability as shown in FIGS. 7 and 8. The bimetal area may be a lamination attached mechanically or a coating on the base strap material. This grid spring 26 will provide the benefit of reducing or eliminating the fuel assembly gaps during operation to reduce seismic/LOCA (Loss Of Coolant Accident) impact loads, and to provide energy absorption during such accident conditions to prevent grid damage. Another embodiment disclosed herein is a bimetallic protrusion spring attached to a fuel assembly top or bottom nozzle 62 and 58, or Inconel top or bottom grid. This feature would provide alignment benefits for conditions such as damaged upper core plate fuel assembly alignment pins that have been removed. The top nozzle 62 or other host component would support itself upon all adjacent nozzles 62 (or other like-adjacent components) with this feature, ensuring alignment with the intent of reducing or eliminating penalties for removed pins. This second feature may be on all the fuel assemblies or just the ones with damaged alignment. However, preferably it is on the fuel assemblies with damaged pins and the adjacent fuel assemblies have recesses 32 in which the springs can seat. Sample calculations for many of the arrangements are also available showing significant load capability can be attained depending on the feature geometry. Thus, this invention employs bimetallic features to provide either fuel assembly alignment benefits or improved fuel assembly response during seismic/LOCA accident conditions. More specifically, one such feature is the top nozzle alignment spring shown in FIGS. 10-14. This bimetallic spring attached to a fuel assembly top nozzle would provide alignment benefits for conditions such as upper core plate fuel assembly alignment pins that have been damaged and removed. The top nozzle would support itself upon all adjacent nozzles with this feature, ensuring alignment with the intent of reducing or eliminating cut pin penalties that such plants must impose. This spring may be of varying shapes such as a rectangular beam 28 or circular disc 30 as shown in the figures. It may be attached with varying methods such as brazing, riveting, or welding. The spring may be fabricated from various materials or alloys, but will most likely be an INVAR™/Stainless combination to attain the desired deflection and load capability while facilitating attachment to the nozzle or other host component. INVAR™ is generally known as FeNi36 or 64FeNi. Another concept feature is a typical outer grid strap 24 containing a bimetal material spring feature 26 as shown in FIGS. 3-11. The outer strap bimetal features would extend outside the nominal grid envelope at operating temperature due to the high expansion side of the material to reduce or eliminate the gap between fuel assemblies, allowing for support between adjacent assemblies. This support between adjacent fuel assemblies during operation would result in lower fuel assembly loads during Seismic/LOCA events. The features may be of long rectangular beam designs similar to grid springs, “pop out” disc shaped designs shown in FIGS. 7 and 8, or some other unique design shape needed to attain the desired deflection and load capability. The bimetallic spring features may only be needed at one or two mid-grid locations near the axial center of the fuel assembly. This would reduce any neutronic penalty due to the material used. The bimetal combination could consist of many materials, but for the purposes of doing sample calculations to determine the feasibility of the concepts, a bimetal laminate of INVAR™ as the low expansion material and a stainless steel variant as the high expansion material was considered. The bimetal feature may also be obtained by coating the base strap material with a low-to negative coefficient of thermal expansion material. The basic feature could also be joined to the grid similar to the top nozzle feature described above. Significant load capability can be designed into the features for Seismic/LOCA load absorption. This feature can also be used in reverse, i.e., wherein the spring retracts at operating temperature and is in an expanded state below operating temperature to facilitate alignment of the fuel assemblies when the upper core plate is being installed. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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claims | 1. A process for testing an information handling system thermal subsystem during manufacture of the information handling system, the process comprising:assembling hardware components into an information handling system, the components operable to process information at least in part under the control of firmware, the components including a thermal subsystem;embedding a thermal diagnostics module in firmware of the information handling system;powering up the information handling system;performing one or more manufacturing activities on the information handling system;monitoring one or more thermal parameters with the thermal diagnostics module during the manufacturing activity;storing at least some of the thermal parameters;reading the stored thermal parameters after completion of the manufacturing activity; andcomparing the monitored thermal parameters with expected thermal parameters to determine either correct operation or failure of the thermal subsystem. 2. The process of claim 1 further comprising:disabling the thermal diagnostics module after a determination of correct operation of the thermal subsystem. 3. The process of claim 1 wherein embedding a thermal diagnostics module further comprises embedding the module in a BIOS of the information handling system. 4. The process of claim 1 wherein monitoring further comprises monitoring the maximum temperature zone reached within the information handling system during the manufacturing activity. 5. The process of claim 1 wherein the manufacturing activity comprises running diagnostics on hardware loaded in the information handling system. 6. The process of claim 1 wherein the manufacturing activity comprises copying an image to a hard disk drive of the information handling system. 7. The process of claim 1 wherein the manufacturing activity comprises running diagnostics on applications loaded in the information handling system. |
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claims | 1. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to an internal core structure of the nuclear power reactor; anda plurality of elongated, extruded fuel elements supported by the frame, each of said plurality of fuel elements comprising:a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, anda cladding surrounding the fuel kernel;wherein each of the fuel elements has a multi-lobed profile that forms spiral ribs,wherein the plurality of fuel elements provide all of the fissile material of the fuel assembly,wherein each of the plurality of fuel elements is disposed in a different grid position of a grid pattern defined by the frame such that a subset of the plurality of fuel elements are disposed along an outer perimeter of the grid pattern,wherein the cladding at a tip of at least one spiral rib of at least one outer side of the cladding on at least some of the fuel elements disposed along an outer perimeter of the grid pattern is thinner than the cladding at other tips of the same fuel element. 2. The fuel assembly of claim 1, wherein:the frame comprises a shroud such that all of the plurality of fuel elements are disposed inside the shroud, andthe laterally shortened outer sides of the cladding contact the shroud. 3. The fuel assembly of claim 1, wherein, in a cross section of the fuel assembly that is perpendicular to an axial direction of the fuel elements, an area of each of the fuel kernels of the at least some of the fuel elements disposed along an outer perimeter of the grid pattern is smaller than an area of at least one of the fuel kernels of in a remainder of the plurality of fuel elements. 4. The fuel assembly of claim 1, wherein the fuel material comprises ceramic fuel material disposed in the matrix of metal non-fuel material. 5. The fuel assembly of claim 1, wherein the cladding is at least 0.4 mm thick throughout each of the plurality of fuel elements. 6. The fuel assembly of claim 1, wherein:the fuel assembly is thermodynamically designed and physically shaped for operation in a conventional land-based nuclear power reactor of a conventional nuclear power plant having a reactor design that was in actual use before 2013; andthe frame is shaped and configured to fit into the land-based nuclear power reactor in place of a conventional uranium oxide fuel assembly for said reactor. 7. The fuel assembly of claim 1, wherein the spiral ribs of adjacent ones of the plurality of fuel elements periodically contact each other over the axial length of the fuel elements, such contact helping to maintain the spacing of the fuel elements relative to each other. 8. The assembly of claim 1, wherein a portion of the fuel assembly that supports the subset of the elongated fuel elements is inseparable from a portion of the fuel assembly that supports the rest of the plurality of fuel elements. 9. The fuel assembly of claim 1, wherein:the grid pattern defines a 17×17 pattern of grid positions; andguide tubes occupy grid positions at row, column positions: 3,6; 3,9; 3,12; 4,4; 4;14; 6,3; 6,15; 9,3; 9,15; 12,3; 12,15; 14,4; 14,14; 15,6; 15,9; and 15,12. 10. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to an internal core structure of the nuclear power reactor; anda plurality of elongated, extruded fuel elements supported by the frame, each of said plurality of fuel elements comprising:a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, anda cladding surrounding the fuel kernel;wherein each of the fuel elements has a multi-lobed profile that forms spiral ribs,wherein the plurality of fuel elements provide all of the fissile material of the fuel assembly,wherein each of the plurality of fuel elements is disposed in a different grid position of a grid pattern defined by the frame such that a subset of the plurality of fuel elements are disposed along an outer perimeter of the grid pattern,wherein the cladding at a tip of at least one spiral rib of at least one outer side of the cladding on at least some of the fuel elements disposed along an outer perimeter of the grid pattern is thinner than the cladding at other tips of the same fuel element,wherein at least some of the plurality of fuel elements are separated from adjacent fuel elements by a common centerline-to-centerline distance, andwherein a circumscribed diameter of the at least some of the plurality of fuel elements equals the centerline-to-centerline distance. |
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description | This application claims priority from U.S. Provisional Pat. App. 61/394,971, filed Oct. 20, 2010, which is hereby incorporated by reference. The invention relates to a method of investigating a sample using Scanning Electron Microscopy (SEM), comprising the following steps: Irradiating a surface (S) of the sample using a probing electron beam in a plurality (N) of measurement sessions, each measurement session having an associated beam parameter (P) value that is chosen from a range of such values and that differs between measurement sessions; Detecting stimulated radiation emitted by the sample during each measurement session, associating a measurand (M) therewith and noting the value of this measurand for each measurement session, thus allowing compilation of a data set (D) of data pairs (Pi, Mi), where 1≦i≦N. A method as set forth in the opening paragraph is known from U.S. Pat. No. 5,412,210, and makes use of the insight that changing the primary beam energy in SEM leads to deeper penetration inside the sample being investigated. In principle, such an approach can be used to generate three-dimensional (3D) tomograms of regions of interest in the sample. Up to now, attempts to exploit this approach have involved acquiring two or more images with increasing primary beam energy, adjusting contrast between the images, and then subtracting lower-energy images from higher-energy images to reveal submerged layers in the sample. A drawback of such known approaches is that said inter-image contrast adjustment (which is a key step) can only be performed using knowledge about the composition and geometry of the sample. Consequently, prior applications of this technique have tended to limit themselves to wafer defect inspection and other semiconductor applications, in which there is generally good a priori knowledge of the sample's (default) composition and geometry. Since the required compositional and geometrical information is typically not available for biological samples, the known technique has not yet been successfully applied to investigations in the life sciences. A method of investigating a sample using Scanning Electron Microscopy (SEM), comprising the following steps: Irradiating a surface (S) of the sample using a probing electron beam in a plurality (N) of measurement sessions, each measurement session having an associated beam parameter (P) value that is chosen from a range of such values and that differs between measurement sessions; Detecting stimulated radiation emitted by the sample during each measurement session, associating a measurand (M) therewith and noting the value of this measurand for each measurement session, thus allowing compilation of a data set (D) of data pairs (Pi, Mi), where 1≦i≦N,wherein: A statistical Blind Source Separation (BSS) technique is employed to automatically process the data set (D) and spatially resolve it into a result set (R) of imaging pairs (Qk, Lk), in which an imaging quantity (Q) having value Qk is associated with a discrete depth level Lk referenced to the surface S. A suitable example of such a BSS technique is Principal Component Analysis (PCA), e.g. employing a Karhunen-Loeve transform operation. This technique allows high-resolution 3D volume reconstruction from a sequence of backscattered images acquired by a SEM. The method differs from known techniques in that it can be used on complex samples with unknown structure. With this method, one can compute compensation factors between high- and low-energy images using second-order (or higher-order) multivariate statistics, which allows for the effective separation of different depth layers in a sample without using a priori knowledge of sample structure. The method has a wide range of applications in life-science and material science imaging. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The accompanying drawings are intended to aid in understanding the present invention and, unless otherwise indicated, are not drawn to scale. In the Figures, where pertinent, corresponding parts are indicated using corresponding reference symbols. For purposes of clarity, not every component may be labeled in every drawing. It is an object of the present invention to address the issue set forth above. More specifically, it is an object of the present invention to provide a SEM imaging method that lends itself to application with samples comprising unknown composition/geometry. In particular, it is an object of the present invention that such a method should allow automatic de-convolution of measured SEM data, and automatic generation of depth-resolved imagery. These and other objects are obtained in a SEM-based method as set forth in the opening paragraph, characterized in that a statistical Blind Source Separation technique is employed to automatically process the data set (D) and spatially resolve it into a result set (R) of imaging pairs (Qk, Lk), in which an imaging quantity (Q) having value Qk is associated with a discrete depth level Lk referenced to the surface S. In research leading to the invention, the inventors realized that, for complex samples with unknown structures (such as those encountered in biological applications, for example), it is generally not possible to perform the prior-art signal value adjustment through user input. This is due inter alia to the fact that characteristics at a scanned location (such as the density and thickness of stain for biological samples) are not known a priori to the SEM user. Given that the SEM image is formed as a localized interaction between the employed (scanned) electron beam and irradiated sample areas having such unknown characteristics, having no more information at hand than the employed beam properties will prevent determination of signal adjustment factors. Moreover, the content of deeper layers (levels) will be unknown, thus preventing the user from reliably using multiple trials at different adjustment parameters in order to reveal some information about subsurface regions. To deal with this problem, the inventors set themselves the goal of developing an automatic approach for determining scaling factors from measured data. In analyses that ultimately culminated in the development of the present inventive approach, the inventors arrived at the following insights: Signals associated with backscattered (BS) electrons generally yield sufficient information from all generation depths within their detectable range. The mathematical Point Spread Function (PSF) of BS electrons in several types of samples, including stained bio-samples and polymers, is generally (highly) linear. The PSF of detectable BS electrons in such samples was also shown to be (highly) laterally confined throughout a depth of several tens of nanometers (more than 50 nm). This fact proves to be highly useful for 3D volume imaging, since it means that one will have a relatively low loss of lateral resolution if one uses BS signals to probe inside a sample. In complex samples, encountered across a range of applications, signals coming from layers (levels) located at different depths in a sample tend to be highly independent in a statistical sense, given that different layers are likely to contain different structures and a wide range of local density and topology variations. These realizations ultimately allowed the inventors to develop a generalized, automated method of tomographic (volume) imaging of a general class of samples using SEM. More particularly, exploiting the insights set forth above, the inventors found that they could use second-order and higher-order statistics from a range of Blind Source Separation (BSS) techniques to disentangle (de-convolute/spatially resolve) signals coming from different layer (level) depths within a general sample. In particular, the technique of Principal Component Analysis (PCA) was found to be quite successful in this context. In a particular embodiment of the method according to the present invention, PCA is applied to a set of N spatially aligned (and, if necessary, scaled) images acquired with varying primary beam energy and BS electron detection, or alternatively using energy band filtering. After mean-centering each image and applying PCA, one obtains a set of N de-correlated images that are related to the input ones by linear transformations (each input image can be expressed as a linear combination of these de-correlated images). The linear mappings can be obtained using various suitable methods, such as a Karhunen-Loeve Transform, for example. The inventors noticed that new information in BS images acquired with increasing primary landing energy is mostly due to signals coming from new depth layers reached by the incident electrons; the effect of PCA de-correlation thus results in the effective separation of the different depth layers. Using PCA, one obtains several de-correlated images, including a strong component associated with the matrix material of the sample (e.g. epoxy in the case of stained life-science samples). The inventors observed that sets of images with lower Eigenvalues in a Karhunen-Loeve transform correspond to deeper layers. In the image associated with these deeper components, top layers are canceled using information from all available lower energy images. Based on these observations, one can develop an algorithm that uses N input images, as follows: Step 1. Acquire N BS images at increasing landing energies. Step 2. Laterally align and/or scale the image sequence thus obtained. Step 3. To compute (distil) the image associated with a discrete layer (level) of ordinal k counted from the sample surface (k=1 . . . N): Apply PCA decomposition to the first k images in the sequence. Boost independent components having low weight (which emanate from deeper layers); this can, for example, be done by multiplying such components by a weighting factor that is equal or proportional to the reciprocal of their PCA (e.g. Karhunen-Loeve) Eigenvalue. Reconstruct a depth image with re-weighted independent components and a background (matrix) component. Step 4. Post-process the obtained sequence using 2D and 3D de-noising and restoration methods. If desired, so-called “layer de-blurring” (viz. lateral/xy de-convolution) can also be performed at this stage. Using such an approach, the relative thickness of the computed slices (layers/levels) can be adjusted by suitable choice of the beam energy increments applied during acquisition of the BS image sequence. This can result in very high depth resolution in many applications, especially when the associated PSF has good linearity. The discussion above makes multiple references to PCA, but it should be realized that this is not the only BSS technique that can be applied in the context of the present invention. For example, one could alternatively employ Independent Component Analysis (ICA), which decomposes a set of input images in a way similar to PCA, but minimizes an entropy-based mutual information criterion instead of a correlation criterion. Alternatively, one could consider employing techniques such as Singular Value Decomposition (SVD) or Positive Matrix Factorization (PMF). More information with regard to BSS techniques can, for example, be gleaned from: {1} P. Comon and C. Jutten, Handbook of Blind Source Separation: Independent Component Analysis and Applications, Academic Press, 2010. {2} A. Hyvärinen and E. Oja, Independent Component Analysis: Algorithms and Applications, Neural Networks, 13(4-5):411-430, 2000. {3} I. T. Jolliffe, Principal Component Analysis, Series: Springer Series in Statistics XXIX, 2nd ed., Springer, N.Y., 2002. In the dissertation above: (i) The stimulated radiation comprises backscattered (BS) electrons. However, in principle, one could also exploit other types of stimulated radiation, such as secondary electrons or X-ray radiation, for example. An advantage of BS electrons over X-rays, for example, is that X-rays are generally not produced at relatively low incident beam energies, whereas BS electrons are. (ii) The beam parameter (P) is beam energy (landing energy). However, in principle, one could alternatively select beam convergence angle (incidence angle) or beam focal depth (penetration depth) as the beam parameter to be varied. (iii) The measurand (M) is detector current (associated with BS electrons). However, one could also select intensity as a measurand (e.g. when detecting X-rays as stimulated radiation). (iv) The imaging quantity (Q) is intensity. However, one could also choose other imaging quantities, such as current, energy spread or angular distribution, for example. Often, Q and M will be chosen to be the same quantity; however, one can also choose a different quantity for Q than for M. In an embodiment of the method according to the present invention, successive values of the measurement parameter (P) associated with successive measurement sessions differ from one another by a substantially constant increment (ΔP), and successive discrete depth levels in the obtained result set (R) are correspondingly separated from one another by a substantially constant distance increment (ΔL). In experiments, the inventors observed that, for example, in commonly used, high-Z-stained biological samples, increments in landing energy of 100 eV typically resulted in distance increments of the order of about 4-5 nm (i.e. of the order of a bilayer) between successive subsurface levels (Lk) in the result set R. However, it should be noted that P does not have to change by a constant increment between successive measurement sessions, and that successive levels Lk also do not have to be spaced at equal distance increments. One should take care not to confuse the present invention with known tomographic techniques based on Transmission Electron Microscopy (TEM), whereby depth information is gleaned from a sample by employing a range of different sample tilt angles. Inter alia, one can identify the following differences between the two: TEM apparatus is generally much more expensive than SEM apparatus. The TEM approach uses much higher input beam energies (typically of the order of 200-300 keV), which can cause sample damage. In contrast, the method according to the present invention works satisfactorily with much lower input beam energies (e.g. of the order of 1-5 keV). TEM tomography can only be used on very thin samples (generally <1 μm in thickness). Because the present invention does not rely on transmission of electrons through the sample, it does not suffer from this restriction on sample thickness. A SEM-based technique such as that used in the present invention has a much greater lateral reach than a TEM-based technique, because of the (lateral) scanning nature of the former. By its very nature, TEM tomography does not generate the type of convoluted depth data associated with the present invention, and, accordingly, does not require statistical processing techniques to perform depth resolution upon such convoluted data. The methodology set forth above can be described as entailing “computational slicing” into a sample. It is advantageous in that it provides very good z-resolution, but is limited as regards the extent of its z-penetration into the sample (z being a coordinate perpendicular to an x/y surface of the sample). If desired, such computational slicing can be combined with “physical slicing”, so as to provide a hybrid approach that augments the obtainable z-penetration. Such physical slicing involves the physical removal of (at least one layer of) material from the sample, and may be performed using mechanical techniques (e.g. using a microtome/diamond knife) and/or radiative/ablative techniques (e.g. using a laser beam or broad ion beam, or milling the sample by scanning a focused ion beam over it). In a particular embodiment of such a hybrid approach, the above-mentioned computational slicing and physical slicing are employed alternately, whereby: An exposed surface S of a sample is investigated using the computational slicing technique according to the current invention; A physical slicing technique is then used to “skim” off material from the surface S, thus creating a newly exposed surface S′ at a depth D below S; This newly exposed surface S′ is then investigated using the computational slicing approach according to the current invention; If desired, several iterations of this hybrid approach are performed, involving alternate application of computational slicing and physical slicing, and thus providing greater and greater z-penetration into the sample. FIG. 1 shows a flowchart of an embodiment of a SEM-based 3D volume imaging method according to the present invention. The various steps in this flowchart can be further elucidated as follows: 101: Acquisition parameters are decided upon. Here, one makes selections as regards N (number of measurement sessions), P (beam parameter to be varied between measurement sessions), ΔP (size of increment in P between measurement sessions), the stimulated radiation to be detected, and M (which measurand of the stimulated radiation is to be measured). For example, one may choose N=7, P=landing energy, ΔP=100 eV, stimulated radiation=BS electrons, M=BS electron current. 103: On the basis of the parameters selected in step 101, a set of BS images is acquired. These images represent convoluted data as regards depth information in the sample under investigation. 105: The N acquired BS images form a raw data set. 107: The elements of the data set are laterally aligned and/or scaled with one another to form an aligned data set. 109: The aligned data set acts as input set for a statistical de-convolution operation in accordance with the invention. 111: An iterative series of data processing steps is performed in which, for each integral value of k in the range [2, . . . , N], PCA decomposition is applied to the subset of data pairs (Pi, Mi), i=1, . . . , k. 113: Independent components of this decomposition having least correlation to the decomposed subset are identified. 115: The least-correlated components thus identified are associated with level Lk beneath the surface S. In this manner, one generates a result set R=((Q1, L1), . . . , (QN, LN)) comprising a spectrum of discrete levels Lk progressing from the surface (S) into the sample. FIGS. 2A and 2B show results of SEM-based 3D slicing into progressively deeper layers of a stained biological sample (in this particular case, a brain cell of a mouse). In both cases, the sample was irradiated at progressively higher energies—in the range 700 eV to 1900 eV, in 200 eV increments—and BS electrons emanating from the irradiated sample were detected. The results are illustrated as follows: FIG. 2A shows the BS image sequence of a mitochondrion in the sample, without any attempt at de-convolution of detected data. FIG. 2B shows a corresponding image sequence after application of a method according to the present invention, representing de-convolved, depth-resolved images of the same mitochondrion, and revealing 3D structures not (clearly) visible in FIG. 2A. The linearity assumptions in image formation elucidated above can be represented in the model:Q=AI (1)in which: I=(I1, I2, . . . , IN)T is the set of images acquired by varying beam parameters; Q=(Q1, Q2, . . . , QN)T is a set of source images that are statistically de-correlated and that represent information coming from different depth layers (levels); A=(a1, a2, . . . , aN)T is a square matrix transforming the original images into so-called principal components. PCA decomposition obtains the factorization in equation (1) by finding a set of orthogonal components, starting with a search for the one with the highest variance. The first step consists in minimizing the criterion: a 1 = arg max a = 1 E { ( a T I ) 2 } ( 2 ) The next step is to subtract the found component from the original images, and to find the next layer with highest variance. At iteration 1<k≦N, we find the kth row of the matrix A by solving: a k = arg max a = 1 E { ( a T ( I - ∑ i = 1 k - 1 w i w i T I ) ) 2 } ( 3 ) It can be shown (see, for example, literature references {1} and {3} referred to above) that successive layer separation can be achieved by using so-called Eigenvector Decomposition (EVD) of the covariance matrix ΣI of the acquired images:ΣI=E{ITI}=EDET (4)in which: E is the orthogonal matrix of eigenvectors of ΣI; D=diag(d1, . . . , dN) is the diagonal matrix of Eigenvalues.The principal components can then be obtained asQ=ETI (5)The Eigenvalues are directly related to the variance of the different components:di=(var(Qi))2 (6) In cases in which noise plays a significant role, the components with lower weights (Eigenvalues) may be dominated by noise. In such a situation, the inventive method can be limited to the K (K<N) most significant components. The choice to reduce the dimensionality of the image data can be based on the cumulative energy and its ratio to the total energy: r = ∑ i = 1 K d i ∑ i = 1 N d i ( 7 ) One can choose a limit for the number of employed layers K based on a suitable threshold value t. A common approach in PCA dimensionality reduction is to select the lowest K for which one obtains r≧t. A typical value for t is 0.9 (selecting components that represent 90% of the total energy). Noise effects can be minimized by recombining several depth layers with a suitable weighting scheme. Additionally, re-weighting and recombination of layers can be useful to obtain an image contrast similar to the original images. In the previously described PCA decomposition, the strongest component (in terms of variance) is commonly associated with the background (matrix) material. Adding this component to depth layers enhances the visual appearance and information content of the obtained image. One can achieve the effect of boosting deeper-lying layers, reducing noise, and rendering proper contrast by re-scaling the independent components by their variances and reconstructing the highest-energy image using the rescaled components, as follows: Q = ED - 1 2 E T I ( 8 ) The skilled artisan will appreciate that other choices for the linear weighting of depth layers can also be used. As an alternative to the PCA decomposition set forth above, one can also employ a BSS approach based on ICA. In ICA, one assumes a linear model similar to (1). The main difference with PCA is that one minimizes a higher-order statistical independence criterion (higher than the second-order statistics in PCA), such as so-called Mutual Information (MI): MI ( Q 1 , … , Q N ) = ∑ i = 1 N H ( Q i ) - H ( Q ) ( 9 ) With marginal entropies computed as: H ( Q ) = - ∑ k = 1 S P ( Q i = q k ) log ( P ( Q i = q k ) ) ( 10 ) and the joint entropy: H ( Q ) = - ∑ k = 1 S P ( Q i = q k , … , Q N = q k ) log ( P ( Q i = q k , … , Q N = q k ) ) ( 11 ) in which: P(Q) is the probability distribution of the imaging quantity Q; qk is a possible value for said imaging quantity; and S is the total number of scanned sites on the sample (e.g. in the case of rectangular images, this is the product of height and width). Other criteria—such as the so-called Infomax and Negentropy—can also be optimized in ICA decomposition. Iterative methods—such as FastICA—can be employed to efficiently perform the associated depth layer separation task. Adding more constraints to the factorization task can lead to more accurate reconstruction. If one adds the condition that sources (layers) render non-negative signals and that the mixing matrix is also non-negative, one moves closer to the real physical processes underlying image formation. A layer separation method based on such assumptions may use the so-called Non-Negative Matrix Decomposition (NMD) technique with iterative algorithms. For more information, see literature references {1} and {2} cited above. In yet another alternative—using NMD—one solves the non-negativity-constrained minimization problem: min Q ≥ 0 , L ≥ 0 J ( A , L ) = min Q ≥ 0 , L ≥ 0 Q - AL 2 ( 12 ) in which J(A,L) is a particular criterion pertaining to two matrices A and L. One common approach to solving this problem is to use the so-called Alternating Least Squares (ALS) algorithm, where one first minimizes the criterion J(A,L) in (12) with respect to one of the sought matrices, then minimizes for the second matrix, and then repeats these two steps until convergence is obtained. If we minimize first with respect to A, we compute the derivative of the criterion and then set it to zero: ∂ J ( A , L ) ∂ A = - ( A T Q - A T AL ) = 0 ( 13 ) resulting in the updated rule:L=(ATA)−1ATQ (14)Computing the derivative with respect to L and setting to zero leads to a second updated rule:A=QLT(LLT)−1 (15) In every iteration, the matrices are computed according to rules (14) and (15), and the pertinent non-negativity constraint (symbolized by [.]+; see below) is imposed—for example by truncating any negative values to zero or by using an active set method as explained in reference {2}—leading to:L=[(ATA)−1ATQ]+ (16)A=[QLT(LLT)−1]+ (17) If the imaging noise deviates significantly from Gaussian, other divergence measures D(Q∥AL), such as the Kullback-Leibler divergence or other I-divergence measures, can be used instead of a least squares criterion. FIG. 3 illustrates an embodiment of the current invention whereby computational slicing (e.g. as set forth in Embodiments 1, 3 and/or 4 above) is combined with physical slicing, so as to allow SEM-based 3D volume imaging (with excellent z-resolution) at progressively deeper regions of a sample (thus yielding greater overall z-penetration). FIG. 3A (left) depicts a computational slicing step, whereby a sample is scanned with varying landing energies (E1, E2, E3) and a depth layer separation algorithm is applied, as set forth above. This allows (virtual) imaging of discrete depth levels (L1, L2, L3). In FIG. 3B (center), subsequent use is made of a physical slicing step, whereby a mechanical cutting device (e.g. a diamond knife) or a non-mechanical approach (e.g. involving a focused/broad beam of ions, or a focused electromagnetic beam) is used to physically “skim off” a certain depth of material from the sample, thus producing a newly exposed surface. In FIG. 3C (right), one executes a subsequent computational slicing operation on said newly exposed surface. This allows (virtual) imaging of new discrete depth levels (L4, L5, L6). This combined/hybrid approach is further elucidated in the flowchart of FIG. 4. The computational slicing procedure in this flowchart is similar to that depicted in FIG. 1 (for example), but is here followed by a physical slicing procedure (refer to the “physical layer removal” step at the bottom of the flowchart in FIG. 4), with a subsequent (iterative) return to the top of the flowchart. Such alternate application of computational slicing and physical slicing techniques can be repeated for as many iterations as are necessary to achieve a given cumulative z-penetration into a particular sample. |
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055457975 | claims | 1. A method of atomic scale fixation and immobilization of plutonium to provide a durable, disposable waste product, said method including the steps of: providing plutonium in the form of one of the group consisting of PuO.sub.2 and Pu(NO.sub.3).sub.4 ; providing ZrO.sub.2 and SiO.sub.2 ; mixing said PuO.sub.2 or Pu(NO.sub.3).sub.4, ZrO.sub.2 and SiO.sub.2 together to form a mixture; cold pressing said mixture to form a pressed product; and heating said pressed product under pressure to form said durable, disposable waste product in the form of (Zr,Pu)SiO.sub.4. 2. A method according to claim 1, wherein said step of providing plutonium comprises converting plutonium metal to Pu(NO.sub.3).sub.4 in dry form. 3. A method according to claim 1, wherein said step of providing plutonium comprises converting plutonium metal to PuO.sub.2 by oxidation thereof. 4. A method according to claim 1, wherein said mixing step includes adding a neutron poison in the form of Gd.sub.2 O.sub.3 powder. 5. A method according to claim 1, wherein said mixing step includes adding one of the group consisting of a .UPSILON.-emitter, and powdered ZrSiO.sub.4 doped with a .UPSILON.-emitter. 6. A method according to claim 3, wherein said heating step comprises sintering said pressed product at 1150.degree.-1350.degree. C. for 1 to 2 hours at 15-30 MPa. 7. A method according to claim 2, wherein said heating step comprises sintering said pressed product at about 1800.degree. C. 8. A method according to claim 2, which includes the step, prior to said cold pressing step, of calcining said mixture at about 650.degree. C. 9. A method according to claim 1, wherein said mixing step comprises intimately mixing said constituents in a screw blender. 10. A method according to claim 1, wherein said step of cold pressing said mixture comprises pressing said mixture in a bellows. 11. A method according to claim 10, wherein said heating step comprises heating said pressed product under pressure in said bellows. |
047132124 | claims | 1. A process for the fully automated supervision and control of loading and unloading operations of groups of combustible nuclear elements into a core of a reactor, a reactor pool and a spent fuel pit by means of a reactor pool loading machine having a telescopic mast, upon the end of which is provided a gripping head with pinchers, for supplying the reactor and the reactor pool having a buffer rack, a fixed deposit station a transfer basket and a plurality of mobile deposit stations, and a deactivation pool handling machine having a telescopic mast, upon the extremity of which is provided a gripping head with pinchers for supplying the spent fuel storage pit containing storage racks and a transfer apparatus assuring the connection between the reactor pool and the spent fuel pit, comprising the steps of: (a) recording a position of each group in the core of the reactor, the storage rack and the buffer rack, (b) recording a position of the reactor pool loading machine, the deactivation pool handling machine, the transfer apparatus and the mobile deposit stations, (c) verifying the identification of each group at the moment of gripping and/or at the moment of release of each group in the core of the reactor, in the buffer rack, in the transfer basket, in the storage rack, in the fixed deposit stations, and in the mobile deposit stations, (d) supplying command and control signals for the manipulation of the reactor pool loading machine, the deactivation pool handling machine, the transfer apparatus and the mobile deposit stations; (e) comparing the command signals and control signals of each manipulation ordered to the reactor pool loading machine, to the deactivation pool handling machine, to the transfer apparatus, and to each mobile deposit station with recorded signals of a pre-established loading sequence and the position of each group, for producing a signal in one of: (f) carrying out one of (1) the manipulation of the reactor pool loading machine, the deactivation pool handling machine, the transfer apparatus and the mobile deposit station in response to said signal in said first state, and (2) a blocking of subsequent ordered manipulation by the reactor pool loading machine, by the deactivation pool handling machine, by the transfer apparatus or by any of the mobile deposit stations, (g) updating the position of the group moved by the ordered manipulation; and (h) establishing a table of final positions of each group in the core of the reactor, in the storage racks, and in the buffer rack for establishing a plan of disposition of the groups. (a) a reactor pool loading machine having a telescopic mast upon the end of which is provided a gripping head with pinchers for supplying the reactor and the reactor pool having a buffer storage rack, a fixed deposit station and a mobile deposit station, (b) a deactivation pool handling machine having a telescopic mast, upon the end of which is provided a gripping head with pinchers for supplying the spent fuel storage pit containing storage racks and a transfer apparatus interconnecting the reactor pool and the spent fuel pit, (c) at least one memory unit for storing current coordinates and identification marks of each group and coordinates of permanent and temporary obstacles in the core, the reactor pool and the spent fuel pit, (d) a central calculating unit for determining the absolute position, orientation and speed of displacement of the gripping head mounted at the end of the reactor pool loading machine and the gripping head mounted at the end of the deactivation pool handling machine wherein the degree of opening of the pinchers mounted on the gripping head and the load taken by the reactor pool loading machine and the deactivation pool handling machine are converted to signals, (e) a treatment unit for receiving said signals wherein current coordinates of the groups, coordinates of the manipulations of the groups and coordinates of permanent obtacles in the core, the reactor pool and the spent fuel pit are stored in the at least one memory unit and transmitted to the central calculating unit, and (f) a programmable unit for transmitting a pre-established loading sequence to the central calculating unit wherein signals from the treatment unit are transmitted to the central calculating unit for comparison with the pre-established loading sequence and the current coordinates of the groups, and according to the result of this comparison, either recorded in the at least one memory unit indicating coincidence or provides a reactive signal indicating a lack of coincidence. 2. A process according to claim 1 further including the step of storing the command and the control signals of each manipulation carried out by the reactor pool loading machine, the deactivation pool handling machine, the transfer apparatus, and by each mobile deposit station for obtaining a trace of the manipulations carried out. 3. A process according to claim 1 including causing the actuation of motors powering the reactor pool loading machine, the deactivation pool handling machine, and the transfer apparatus according to the pre-established loading sequence. 4. An apparatus for fully automated supervision and control of loading and unloading operations of groups of combustible nuclear elements into a core of a reactor, a reactor pool and a spent fuel pit comprising: 5. A supervision and control apparatus according to claim 4 wherein the pre-established loading sequence furnished by the programmable unit and the signals from the treatment unit are recorded in at least one additional memory unit after transmission to the central calculating unit. 6. A supervision and control apparatus according to claim 4 wherein the reactive signal emitted by the central calculating unit comprises an alarm signal that blocks further manipulation of the reactor pool loading machine upon approaching an obstacle. 7. A supervision and control apparatus according to claim 4 wherein the central calculating unit enables the energizing of motor means for the reactor pool loading machine, the deactivation pool handling machine, the transfer apparatus, and the mobile deposit station, when there is coincidence between the pre-established loading sequence furnished by the programmable unit and the signals received by the treatment unit. 8. A supervision and control appparatus according to claim 4 including a conversational system for introducing the pre-established loading sequence into the programmable unit and for modifying the pre-established loading sequence. |
abstract | Embodiments of the present invention provide a multi-leaf collimator with a plurality of leaves and at least one motor for each leaf. The motor for each leaf has a lateral width which is equal to or narrower than the corresponding leaf, and in this way the motors can be arranged within the lateral extent of the leaf. A cut-out section in the leaf allows the motor to lie at least partially within the depth of the leaf, and in this way the drive mechanism and the multi-leaf collimator as a whole are made extremely compact. This in turn allows the leaves to be deeper than would otherwise be the case, increasing their efficacy in blocking radiation. |
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047599049 | abstract | A calandria assembly is received within the pressure vessel of a nuclear reactor system, at an elevation corresponding to the level of the outlet nozzles of the vessel, and receives pressurized coolant traveling in an axial flow direction within the vessel and turns same to a radial direction for exit through the outlet nozzles. Hollow tubes mounted in parallel relationship at opposite ends to first and second plates of the calandria in conjunction with a cylindrical skirt of cylindrical configuration joining the first and second plates of the calandria, present a redundant structure introducing the potential of thermal stresses, which are limited by selection of the pattern of flow holes in the lower plate and the provision of flexible annular weld joints of J-shaped configuration between the lower ends of the calandria tubes and the lower, second calandria plate. |
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abstract | An IORT device (10) for radiotherapy treatment of cancer patients, comprising a source of particles, an accelerating device (11), which sends a beam of particles (12) on a target (14) through an applicator (15), a scattering filter (16), which allows the distance between the source of particles and the target (14) to be kept within a range compatible with the use of IORT devices (10) in standard operating rooms, and an optical system for collimating the beam of particles (12), which is placed between the scattering filter (16) and the applicator (15); specifically, the optical collimating system of the beam of particles comprises a primary screen (17), configured to shield the radiation produced by the scattering filter (16), a secondary screen (18), configured to shield the photons produced on the primary screen (17), and a collimating apparatus (19), which provides for housing the monitor chambers (20). |
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050892169 | abstract | A unique and optimum nuclear steam supply system operating configuration for integration of a chemical decontamination system is disclosed. The chemical decontamination system is connected to, and returns to, the residual heat removal system downstream of a residual heat removal heat exchanger, thereby utilizing the residual heat removal system to control the temperature of process fluids entering the decontamination system. A reactor coolant pump or pumps generates heat for the chemical processes as needed and a nitrogen blanket within the primary system pressurizer is utilized for system pressure control. |
claims | 1. A radiation shielding apparatus comprising:a plurality of positionable radiation-shielding stacks of tiles, wherein the stacks are arranged in a contiguous peripheral configuration; anda tile positioning mechanism configured to extend and retract the tiles in each stack along a vertical axis between a retracted position wherein all the tiles are aligned horizontally and a vertically extended position, wherein in both the retracted position and 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 and adjacent side-margins thereof, wherein the tiles in each stack have opposed faces with a rail extending in a vertical direction attached to one of the opposed faces and a slide element extending in a vertical direction attached to another of the opposed faces to allow each tile to slide along a length of each adjacent tile within a stack. 2. The apparatus of claim 1, wherein the tiles, as well as their corresponding opposing side-margins, are non-flat. 3. The apparatus of claim 2, wherein the non-flat corresponding opposing side-margins have a zig-zag or V-shaped profile. 4. The apparatus of claim 2, wherein the non-flat corresponding opposing side-margins have a wavy or S-shaped profile. 5. The apparatus of claim 1, wherein the stacks of tiles form a structure having two or more faces, each face including at least one tile stack; and corner tile stacks connecting two adjacent faces thereof. 6. The apparatus of claim 1, wherein corner tile stacks cover an area of at least about a 90° angle between two adjacent faces. 7. The apparatus of claim 1, wherein the rails and slide elements on vertically adjacent pairs of tiles are peripherally spaced apart so that they do not overlap when the tiles are retracted in a stack to reduce thickness. 8. The apparatus of claim 7, wherein the rails and slide elements within a stack are nested in recesses formed the opposed faces of the tiles, thereby providing a compact structure of tiles in a stack. 9. The apparatus of claim 8, wherein the recesses accommodate therein a rail of said tile and a respective slide element of a sequentially adjacent tile. 10. The apparatus of claim 9, wherein the recesses of vertically adjacent tiles within each stack are aligned such that the recesses in vertically adjacent tiles nest when the stack is retracted, thereby providing for a compact structure of tiles in a stack. 11. The apparatus of claim 1, wherein each tile comprises a first side margin with a concave or V-shaped profile and an opposite second side margin with a convex or upside down V-shaped profile, and the tiles of subsequent and adjacent tile stacks are arranged such that the concave or V-shaped profile of the tiles within one stack overlap the convex or upside down V-shaped profile of the tiles within the subsequent and adjacent tile stack. 12. The apparatus of claim 1, wherein the tiles are manufactured from a composite material comprising at least one carbon fiber layer, a binding material and at least one radiation attenuating material. 13. The apparatus of claim 12, wherein the binding material comprises a thermoset resin, a polyester, a vinyl ester, a polyamide, or a combination thereof. 14. The apparatus of claim 13, wherein the thermoset resin comprises an epoxy resin. 15. The apparatus of claim 12, wherein the radiation attenuating material comprises a metal selected from the group consisting of: tungsten; lead; bismuth; antimony; barium; and tantalum, or a combination thereof. 16. The apparatus of claim 12, wherein the composite material further comprises a material selected from the group consisting of: aramid; aluminum; ultra-high-molecular-weight polyethylene; and glass fibers, and a combination thereof. 17. The apparatus of claim 12, wherein the composite material comprises a plurality of carbon fiber layers; and a mixture of a binding material and particles of radiation attenuating material. 18. The apparatus of claim 12, wherein the radiation attenuating material includes a foil or a film-like structure. 19. The apparatus of claim 12, wherein the radiation attenuating material includes a powder mixed within said binding material, and wherein said mixture is applied onto at least one of said fibers. 20. The apparatus of claim 1, wherein the tiles are manufactured from a thermoplastic material mixed with a radiation attenuating material. |
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abstract | A method is provided for assembling a collimator module including a plurality of first collimator plates arrayed in a first direction, each first collimator plate having a plurality of slots formed on a plate surface, and a plurality of second collimator plates arrayed in a second direction orthogonal to the first direction, wherein each second collimator plate penetrates respective slots along the first direction so as to form a lattice-shape. The method includes positioning the plurality of first collimator plates by moving a first collimator plate in one direction along the second direction, so that a side wall of a first cutout formed on an edge of a radiation incident side or a radiation output side of the first collimator plate contacts a member extending in the first direction. |
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abstract | An entrainment-reducing assembly may include a container configured to hold a liquid. A venting arrangement may extend into an upper portion of the container and be configured to direct condensable and non-condensable gases into the container. A suction structure may extend into a lower portion of the container and be configured to carry out an extraction of excess liquid from the container caused by condensed gases. A deflector may be disposed between the suction structure and the venting arrangement within the container. As a result, an entrainment of uncondensed gases during the extraction of the liquid by the suction structure may be reduced or prevented, thereby protecting the pump from cavitation and failure. |
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description | This claims priority to U.S. Provisional Patent Application No. 62/049,781, filed on Sep. 12, 2014, which is hereby incorporated herein by reference in its entirety. The present application is related generally to x-ray fluorescence (XRF) analyzers. In x-ray fluorescence (XRF) analysis, x-rays are emitted from an x-ray source to a sample. The sample can receive x-rays from the source then fluoresce x-rays that have an energy spectrum specific to chemical elements in the sample. An x-ray detector can receive these x-rays emitted from the sample. The detector, along with associated electronics, can analyze these x-rays to determine chemical composition of the sample. It can be difficult in the analysis to determine elements in low concentrations. It can also be difficult to distinguish between elements that emit similar energy spectra. Filtration of x-rays emitted from the source can improve analysis in these situations. Filtration of x-rays can provide a narrow energy band specific to a target element, allowing easier detection of that element. A user of an XRF analyzer typically would use the analyzer for detection of multiple, different elements. Thus, the user might desire different filters for different applications. It is sometimes desirable to do an XRF analysis of a small sample. X-rays from the source that impinge on material surrounding the sample can result in undesirable noise because these surrounding materials can also fluoresce x-rays to the detector. It would be beneficial in these situations to narrow the x-ray beam to a smaller size. An XRF analysis typically includes energizing the x-ray source to allow the x-ray source to emit x-rays. Energizing the x-ray source can include application of a high voltage across an x-ray tube and heating a filament. Energizing the x-ray source for each use takes time. It can be beneficial to a user to minimize the time required for each analysis. After each analysis, the x-ray source is typically de-energized. Until this energy drops below a certain threshold, x-rays can continue to emit from the x-ray source. This can be a safety concern for a user who might not be aware of such continued emission. It would be beneficial to improve XRF analysis safety. Portable XRF analyzers are often used in harsh environments where delicate windows on the x-ray source or the x-ray detector can be damaged by sharp objects or corrosive materials. It would be beneficial to protect the x-ray source and the x-ray detector from damage. Vibration of the x-ray source or the x-ray detector in an XRF analyzer can adversely affect analysis results. It can be beneficial to avoid or minimize vibration of the x-ray source and the x-ray detector caused by moving components. It has been recognized that it would be advantageous to provide multiple, different filters for x-rays emitted from the x-ray source; to provide a means of narrowing the x-ray beam; to minimize the time required for each analysis; to improve XRF analysis safety; to avoid or minimize vibration of the x-ray source and the x-ray detector; and to protect the x-ray source and the x-ray detector from damage. The present invention is directed to various embodiments of x-ray fluorescence (XRF) analyzers that satisfy these needs. Each embodiment can satisfy one, some, or all of these needs. The XRF analyzer can comprise an x-ray source having an x-ray emission end, and an x-ray detector having an x-ray receiving end, both carried by a housing. The x-ray source can be positioned and oriented to emit x-rays from the x-ray emission end towards a focal point. The x-ray detector can be positioned and oriented to face the focal point, and can be configured to receive, through the x-ray receiving end, fluoresced x-rays emitted from a sample disposed at the focal point. In one embodiment, the XRF analyzer can further comprise a rotatable filter structure disposed between the x-ray emission end and the focal point and disposed between the x-ray receiving end and the focal point. The filter structure can be rotatable to separately position x-ray source modification region(s) between the x-ray emission end and the focal point and x-ray detector modification region(s) between the x-ray receiving end and the focal point. In another embodiment, the XRF analyzer can further comprise a rotatable source filter wheel disposed between the x-ray emission end and the focal point and a rotatable detector filter wheel disposed between the x-ray receiving end and the focal point. The source filter wheel can include multiple x-ray source modification regions. The detector filter wheel can include multiple x-ray detector modification regions. The source filter wheel and the detector filter wheel can each have a gear at an outer perimeter. The XRF analyzer can further comprise a gear wheel which can mesh with the gear on the source filter wheel and the gear on the detector filter wheel. The gear wheel can be configured to cause the source filter wheel and the detector filter wheel to rotate together. As illustrated in FIGS. 1, 2, 3, and 7, x-ray fluorescence (XRF) analyzers 10 and 70 can comprise an x-ray source 12 having an x-ray emission end 12x, and an x-ray detector 11 having an x-ray receiving end 11x, both carried by a housing 13. The x-ray source 12 can be positioned and oriented to emit x-rays 22 from the x-ray emission end 12x towards a focal point F. The x-ray detector 11 can be positioned and oriented to face the focal point F, and can be configured to receive, through the x-ray receiving end 11x, fluoresced x-rays 21 emitted from a sample 14 disposed at the focal point F. As shown in FIGS. 1-3, a rotatable filter structure 15 can be disposed between the x-ray emission end 12x and the focal point F and disposed between the x-ray receiving end 11x and the focal point F. The filter structure 15 can be rotatable to separately position at least two different x-ray source modification regions 15s between the x-ray emission end 12x and the focal point F and at least two different x-ray detector modification regions 15d between the x-ray receiving end 11x and the focal point F. The filter structure 15 can have a material and thickness configured to substantially block x-rays from being emitted through the filter structure 15 except through certain source modification regions 15s and detector modification regions 15d designed for x-ray 21 transmission therethrough. The source modification regions 15s and the x-ray detector modification regions 15d can provide many benefits, as will be described in the following several paragraphs. The source modification regions 15s can include multiple, different, solid x-ray filters. For example, one filter can be made of a different material than other filter(s). X-rays 22 emitted from the x-ray source 12 can pass through the filter, thus filtering the x-rays 22 and providing a relatively narrow energy band specific to a target element, allowing easier detection of that element. X-ray source modification regions 15s can include a first, solid x-ray filter configured to filter x-rays for one x-ray energy band and a second, solid x-ray filter configured to filter x-rays for a different x-ray energy band. Another example of different filters is that one filter can have a different thickness than other filter(s). There can be multiple filters, all made of the same material, but having different thicknesses. Having a thicker overall filter can allow for more accurate analysis of a narrow energy band but increases time of analysis. In some situations, the more accurate analysis outweighs the problem of increased time. Filters can be made of any solid material that can be formed into a thin film or window. Filters are typically a metal or metal alloy, such as for example silver, gold, rhodium, iron, copper, aluminum, tin, etc. It is sometimes desirable to do an XRF analysis of a small sample. X-rays from the source that impinge on material surrounding the sample can result in undesirable noise because these surrounding materials can also fluoresce x-rays to the detector. The source modification regions 15s can include multiple, different, sized collimators 15c. For example, the collimators 15c can include a first collimator having a first diameter and a second collimator having a second diameter. The first diameter can be substantially different from the second diameter in order to provide a different x-ray collimation at the first collimator relative to the second collimator. Multiple, different sized collimators 15c can allow collimation of the x-ray beam 22 to different diameters for different applications. The different collimators 15c can be tubes of different lengths. The collimators 15c can be open holes (i.e. no solid material) or can be x-ray windows. A collimator 15c and filter can be combined to both collimate and filter the x-rays 22. The source modification regions 15s can include a solid blocking structure having a material (e.g. high atomic number) and thickness configured to substantially block x-rays from being emitted through the blocking structure. Between separate analyses, the XRF analyzer can be programmed to rotate the filter structure to place the blocking structure in front of the x-ray emission end 12x. This can allow the x-ray source 12 to continue to emit x-rays 22 between analyses instead of fully de-energizing the x-ray source. The x-ray source 12 would then be ready (or ready very quickly if there was only partial de-energizing) for the next analysis. By avoiding the need to fully energize and fully de-energize the x-ray source 12 between each analysis, required time for completion of each analysis can be reduced. The blocking structure can also improve user safety. If the x-ray source 12 is de-energized following an individual analysis, x-rays can continue to emit from the x-ray source until energy of the x-ray source 12 drops below a certain threshold. This can be a safety concern for a user who might not be aware of such continued emission. By blocking x-rays 22 with a blocking structure at the end of each analysis, XRF analyzer user safety can be improved. Portable XRF analyzers are often used in harsh environments where delicate windows on the x-ray source can be damaged by sharp objects or corrosive materials. The source modification regions 15s can include a protective structure. The protective structure can comprise a solid, protective material configured to protect the x-ray source 12 from damage by solid objects. For example, the protective structure can be a sheet of metal. The blocking structure and the protective structure can be the same source modification regions 15s, to both block x-rays and to protect the x-ray source 12 from damage. Alternatively, the protective structure can be a solid x-ray window having a material and thickness to allow x-rays to substantially pass therethrough, but made of a material to substantially protect the x-ray source, such as protection against corrosive chemicals for example. The detector modification regions 15d can include a solid, protective structure configured to protect the x-ray detector 11 from damage by solid objects. The detector modification regions 15d can also include an aperture configured to allow x-rays to pass therethrough. The aperture can be various shapes, including a round hole or an elongated slot. The aperture can be an opening with no solid material. Alternatively, the aperture can be a solid x-ray window having a material and thickness to allow x-rays to substantially pass therethrough. The solid window aperture can be made of a material to substantially protect the x-ray detector 11 against corrosive chemicals. This solid window aperture can be useful if the XRF analyzer is used in harsh, chemical environments. Thus, during an XRF analysis, the filter structure 15 can be rotated to place an aperture between the x-ray receiving end 11x and the focal point F, then after an analysis or between different analyses, the filter structure 15 can be rotated to place a protective structure between the x-ray receiving end 11x and the focal point F. At least one of the modification regions can be used as either a detector modification region 15d or a source modification region 15s. A shaft 16 can be attached to the filter structure 15. The shaft 16 can be attached to a base end 15b of the filter structure 15. A motor 17 with a gear 17g can mesh with a gear 16g on the shaft 16 to cause the shaft 16 to rotate, and thus also causing the filter structure 15 to rotate to separately position the source modification regions 15s between the x-ray emission end 12x and the focal point F and the detector modification regions 15d between the x-ray receiving end 11x and the focal point F. As just described, the filter structure 15 can provide many benefits to XRF analysis. An additional benefit by use of this filter structure 15 can be avoidance of vibration which can adversely affect XRF analysis. Vibration of the x-ray source 12 or the x-ray detector 11 can adversely affect analysis results. A single filter structure 15 for both the x-ray source 12 and the x-ray detector 11 can be placed in a central location of the XRF analyzer 10 and need not be directly attached to either the x-ray source 12 or the x-ray detector 11. It is possible to not attach the filter structure 15 directly on the x-ray source 12 or the x-ray detector 11. This can minimize or avoid adversely affecting XRF analysis by vibration as the filter structure turns. The filter structure 15 and/or the motor 17 can be mounted on the housing 13 with vibration isolation devices or pads, thus further minimizing the effect this vibration can have on XRF analysis. As shown in FIG. 3, the filter structure 15 can be shaped and located to position the source modification regions 15s such that a plane 15sp of the source modification regions 15s is substantially parallel to a face 12p of the x-ray emission end 12x. The filter structure 15 can also be shaped and located to position the detector modification regions 15d such that a plane 15dp of the detector modification regions 15d is substantially parallel to a face 11p of the x-ray receiving end 11x. These parallel-relationships can be maintained as the filter structure 15 rotates. For example, a three-dimensional cone-shaped filter structure 15 could be shaped and positioned for this alignment. This parallel alignment as described above can allow adequate filtration, collimation, protection, or blocking of x-rays. The filter structure 15 can have various shapes. The filter structure 15 can be solid except for channels for x-rays to pass in some of the modification regions. Alternatively, the filter structure 15 can have a shape like a cup with a concave portion or hollow and thus can also be called a filter cup. A choice of whether to use a solid filter structure or a hollow filter cup can depend on factors such as weight requirements; effectiveness at blocking, filtering, collimating, and protecting; and manufacturability. As shown in FIG. 4, the filter structure 15 can taper down in diameter from an open end 15o to a base end 15b. The filter structure 15 can be cone-shaped or frustum-shaped. As shown in FIG. 5a, a cross section of the filter structure 15 at any point from the open end 15o to the base end 15b can have a circular shape. As shown in FIG. 5b, a cross section of the filter structure 15 at any point between the open end 15o and the base end 15vb can have a polygon shape. All sides of the polygon shape can be substantially equal in size. If the cross section is a polygon shape, then source modification regions 15s and x-ray detector modification regions 15d can be disposed at faces of the polygon shape. A choice of filter structure 15 shape can be made based on the shape's effect on blocking, filtering, collimating, and protecting; manufacturability; or the cost of the filter structure 15. As shown in FIG. 6, the filter structure 15 can include an inner cup 65 disposed at least partially inside of an outer cup 66. The inner cup 65 and the outer cup 66 can each have at least two of the source modification regions 15s and at least one of the detector modification regions 15d. The inner cup and/or the outer cup can have at least two of the detector modification regions 15d. Use of both the inner cup 65 and the outer cup 66 can allow multiple filters that each can combine with any one of multiple collimators. For example, the source modification regions 15s on one of the inner cup 65 or the outer cup 66 can include multiple, different filters, and the source modification regions 15s on the other of the inner cup 65 or the outer cup 66 can include multiple, different collimators. As another example, the source modification regions 15s on one of the inner cup 65 or the outer cup 66 can have filters of the same material, which can be aligned for a thicker overall filter. Both the inner cup 65 and the outer cup 66 can include a detector modification region 15d that is an aperture to allow x-rays to pass. At least one of the inner cup 65 or the outer cup 66 can include a detector modification region 15d that is a solid, protective structure to protect the detector 11 from damage. The inner cup 65 and the outer cup 66 can be rotatable to separately position the source modification regions 15s between the x-ray emission end 12x and the focal point F and the detector modification region(s) 15d between the x-ray receiving end 11x and the focal point F. The inner cup 65 and the outer cup 66 can each have a base end 65b and 66b opposite of an open end 65o and 66o. The open ends 65o and 66o of both the inner cup 65 and the outer cup 66 can be disposed between the x-ray emission end 12x and the focal point F and between the x-ray receiving end 11x and the focal point F. A convex portion of the inner cup 65 can nest within a concave portion of the outer cup 66. The inner cup 65 and the outer cup 66 can be supported and rotated by dual, concentric, tubes 61 and 62. An inner tube 61 can connect to the inner cup 65. The inner tube 61 can be configured to rotate with the inner cup 65 and can cause the inner cup 65 to rotate. An outer tube 62 can connect to the outer cup 66. The outer tube 62 can be configured to rotate with the outer cup 66 and can cause the outer cup 66 to rotate. A motor 17 can have two gears 17g1 and 17g2 that can mesh with gears 61g and 62g on the inner tube 61 and the outer tube 62, respectively. The motor 17 can be configured to cause the inner tube 65 and the outer tube 66 to rotate independently, thus allowing certain source modification regions 15s (e.g. filter) on the inner cup 65 to align with certain source modification regions 15s (e.g. collimator) on the outer cup 66. As shown in FIGS. 7-9, a rotatable source filter wheel 12w can be carried by the housing 13 and can be disposed between the x-ray emission end 12x and the focal point F. The source filter wheel 12w can include multiple, different x-ray source modification regions 15s including at least one of: 1. a first, solid x-ray filter configured to filter x-rays for one x-ray energy band and a second, solid x-ray filter configured to filter x-rays for a different x-ray energy band; 2. a first, solid x-ray filter having a different thickness than a second, solid x-ray filter; 3. a first collimator 15c1 having a first diameter and a second collimator 15c2 having a second diameter wherein the first diameter is substantially different from the second diameter in order to provide a different x-ray collimation at the first collimator 15c1 relative to the second collimator 15c2; 4. a solid blocking structure having a material and thickness configured to substantially block x-rays 22 from being emitted through the blocking structure; 5. a protective structure comprising a solid, protective material configured to protect the x-ray source 12 from damage by solid objects; or 6. combinations thereof.The filter(s), the collimator(s), the solid blocking structure, and the protective structure can have characteristics and benefits as described above in reference to the filter structure 15. Also shown in FIG. 7-9, a rotatable detector filter wheel 11w can be carried by the housing 13 and can be disposed between the x-ray receiving end 11x and the focal point F. The detector filter wheel 11w can include multiple, different x-ray detector modification regions 15d including: 1. a protective structure comprising a solid, protective material configured to protect the x-ray detector 11 from damage by solid objects; and 2. an aperture configured to allow x-rays to pass therethrough. The source filter wheel 12w and the detector filter wheel 11w can each have a gear 12g and 11g at an outer perimeter. A gear wheel 76g can mesh with the gear 12g on the source filter wheel 12w and with the gear 11g on the detector filter wheel 11w. Thus, the gear wheel 76g can be configured to cause the source filter wheel 12w and the detector filter wheel 11w to rotate together. “Together”, as used in this context, means both filter wheels 11w and 12w rotate at the same time, caused by the rotation of the gear wheel 76g; however, “together” does not necessarily mean that both filter wheels 11w and 12w rotate in the same direction or for the same angular displacement. The term “mesh” as used in this context, means that the filter wheels 11w and 12w and the gear wheel 76g directly contact each other or that the gear wheel 76g directly contacts one or more intermediate gears and one of the intermediate gears directly contacts the filter wheels 11w and 12w. In either case, this meshing of the gear wheel 76g with the filter wheels 11w and 12w can result in rotation of the filter wheels 11w and 12w as the gear wheel 76g rotates. The gear wheel 76g can be attached to a shaft 16 which can be attached to a motor 17 (see FIG. 1). The motor 17 can cause the gear wheel 76g, and thus also the filter wheels 11w and 12w, to rotate. As described below, an electronic processor 18 can control the motor 17. The various embodiments of XRF analyzers described above can further comprise an electronic processor 18 (see FIG. 1). The electronic processor 18 can be configured to receive a program input by a user and to select and position the source modification regions 15s and the detector modification regions 15d based on the program. The electronic processor 18 can be configured to analyze x-rays 21 received by the x-ray detector 11 (defining an analysis) and to select and position the source modification regions 15s based on the analysis. A method of using the various embodiments of XRF analyzers described above can comprise the following steps, and can be performed in the following order: 1. inputting a guess of a material of a sample 14 to be analyzed into the XRF analyzer; 2. allowing the XRF analyzer to automatically select one of the source modification regions 15s based on the guess; 3. analyzing the sample 14 (defining an analysis); and 4. changing the selected source modification region 15s based on initial results of the analysis. Some or all of the above description, and the following claims, may also be applicable to laser-induced breakdown spectroscopy (LIBS), x-ray diffraction (XRD) analyzers, and Raman spectroscopy tools. The term “XRF analyzer” used herein can be replaced by some or all of the following: LIBS spectrometer, XRD analyzer, Raman spectroscopy equipment, and XRF analyzer. |
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summary | ||
063226936 | claims | 1. A system for processing drilling waste comprising: a) a first mixing tank system comprising at least one mixing tank having an agitation system situated therein; b) a first separation system coupled to an output of the first mixing tank system, the first separation system comprising at least one separation device; c) a first slurry tank system coupled to an output of the first separation system, the first slurry tank system comprising at least one slurry tank having a shearing system situated within said slurry tank; d) a second separation system coupled to an output of the first slurry tank system, the second separation system comprising at least one separation device; e) a second mixing tank system coupled to an output of the second separation system, said second mixing tank system having at least one mixing tank with an agitation system situated therein; f) a manifold coupled to an output of the second mixing tank system and an input of the first mixing an system, wherein the manifold recirculates drilling waste product from the second mixing tank system to the first mixing tank system; g) a holding tank system coupled to an output of the second mixing tank system; and h) an injection pump coupled to an output of the holding tank system for injecting waste product from the holding tank system into a wellbore. a) a first mixing tank system comprising at least one mixing tank having an agitation system situated therein; b) a first separation system condensing at least one separation device, said first separation system being connected to said first mixing tank system; c) at least one slurry tank system comprising at least two slurry tanks having a shearing system situated within each of said slurry tanks, said slurry tank system being connected to said first separation system; d) a second separation system comprising at least two separation devices, said separation system being connected to said slurry tank system; e) a second mixing tank system comprising at least two mixing tanks having a second agitation system situated within each of said mixing tanks, said second mixing tank system being connected to said second separation system; f) a manifold coupled to an output of the second mixing tank system and an input of the first mixing tank system, wherein the manifold recirculates drilling waste product from the second mixing a system to the first mixing tank system; g) a holding tank system coupled to an output of the second mixing tank system; and h) an injection pump coupled to an output of the holding tank systems for injecting waste product from the holding tank system into a wellbore. 2. The waste processing system of claim 1 further comprising a plurality of conduits for connecting said mixing tank, said first separation system, said slurry tank system and said second separation system. 3. The waste processing system of claim 1 further comprising a pump system for pumping waste through said waste processing system, said pump system being capable of pumping a carrier liquid through said waste processing system, said pump system comprising a plurality of injection and centrifugal pumps. 4. The waste processing system of claim 1, wherein said agitation system of said first mixing tank system comprises a gear box, at least one motor, and a plurality of blades. 5. The waste processing system of claim 1, further comprising a second slurry tank system connected to an input of said second separation system, said second slurry tank system comprising at least one slurry tank having a shearing system situated therein. 6. The waste processing system of claim 1, wherein each of said first and second separation systems comprise at least one screen. 7. The waste processing system of claim 6, wherein said first and second separation systems each comprise a plurality of screens having varying screen mesh sizes. 8. The waste processing system of claim 1, wherein said second mixing tank system comprises at least one mixing tank having a sampling system for testing processed waste. 9. The waste processing system of claim 1, wherein said shearing system of said first slurry tank system comprises a gear box, at least one motor, a plurality of blades, a shearing mixer and gun lines. 10. The waste processing system of claim 1, wherein said first mixing tank system comprises a mixing pump and said first slurry tank system comprises a shearing pump. 11. A system for processing drilling waste comprising: 12. The waste processing system of claim 11 further comprising a plurality of conduits for respectively connecting said first mixing tank system, said first separation system, said slurry tank system, said second separation system, and said second mixing tank system. 13. The waste processing system of claim 11 further comprising a pump system for pumping waste through said waste processing system. 14. The waste processing system of claim 13, wherein said pump system comprises at least one pump having impellers for shearing the waste. 15. The waste processing system of claim 13, wherein said pump system comprises a plurality of injection and centrifugal pumps. 16. The waste processing system of claim 13, wherein said pump system is capable of pumping a carrier liquid through said waste processing system. 17. The waste processing system of claim 11, wherein said shearing system of said slurry tank system comprises a gear box, a least one motor, a plurality of blades, shearing mixer and gun lines. 18. The waste processing system of claim 11, wherein each of said first and second agitation system of said first and second mixing tank system comprises a gear box, at least one motor, and a plurality of blades. 19. The waste processing system of claim 11, wherein each of said first and second mixing tank system comprises at least one mixing tank having a jet line. 20. The waste processing system of claim 11, wherein said second mixing tank system comprises at least one mixing tank having a sampling system for testing the waste. 21. The waste processing system of claim 11, wherein each of said first and second separation devices comprising at least one screen. 22. The waste processing system of claim 11, wherein said separation system comprises a plurality of screens having varying screen mesh sizes. |
claims | 1. A method for generating a focused beam of charged particles, the method comprising:a) generating a beam of charged particles;b) emitting a laser pulse;c) generating a focusing magnetic field structure in a target by means of an interaction of said laser pulse with said target; andd) causing at least partial penetration of the beam of charged particles into said focusing magnetic field structure,wherein in step b), a laser contrast of the laser pulse is increased. 2. The method according to claim 1, wherein a power of the laser pulse is substantially between 1 terawatt and about 100 terawatts. 3. The method according to claim 1, wherein a duration of the laser pulse is substantially between about 10 femtoseconds and about 10 picoseconds. 4. The method according to claim 1, whereinin step c) the laser pulse is focused on the target at the level of a focal spot, andin step d) the beam of charged particles passes at least partially through said focal spot. 5. The method according to claim 1, wherein the target is made at least in part of a metal. 6. The method according to claim 5, wherein the target is made at least in part of a metal selected from a group comprising gold, copper and aluminum. 7. The method according to claim 6, wherein the thickness of the target lies substantially between 500 nanometers and about 100 micrometers. 8. The method according to claim 1, whereinthe target extends substantially along a plane of extension between a front face and a rear face, said faces being opposite to one another in a thickness direction perpendicular to the plane of extension and separated by a thickness measured in said thickness direction, andin step d) said beam passes through the target substantially in said thickness direction. 9. The method according to claim 1, wherein step a) of generating a particle beam comprises:emitting a generating laser purse; andgenerating a non-focused beam of particles by means of an interaction of said generating laser pulse with a generating target. 10. A device for generating a focused beam of charged particles, the device comprising:means for generating a beam of charged particles;a laser source for emitting a laser pulse;a target for generating a focusing magnetic field structure by means of an interaction of said laser pulse with said target, said beam of charged particles penetrating at least partially into said magnetic field structure; anda device for increasing a laser contrast of the laser pulse. 11. The device according to claim 10, wherein the means for generating a beam of charged particles comprising:a laser source for emitting a generating laser pulse; anda generating target for generating a beam of charged particles upon an interaction of said generating laser pulse with said generating target. |
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description | The present application claims priority from Japanese Patent application serial no. 2012-017612, filed on Jan. 31, 2012, the content of which is hereby incorporated by reference into this application. 1. Technical Field The present invention relates to a method of repairing a shroud support and a repair apparatus thereof and more particularly to a method of repairing a shroud support and a repair apparatus thereof which are preferably applicable to repair of a weld of the shroud support in a reactor pressure vessel during a in-service period of a nuclear power generation plant. 2. Background Art A shroud support disposed in a reactor pressure vessel of a nuclear power generation plant includes a shroud support cylinder, a shroud support plate and a plurality of shroud support legs. The welds of the shroud support include many welds such as a weld (H9) between an inner surface of the reactor pressure vessel and a shroud support plate, a weld (H8) between a shroud support cylinder and the shroud support plate, a weld (H10) between the shroud support cylinder and a shroud support leg, a weld (H11) between the inner surface of the reactor pressure vessel and the shroud support leg, and a weld (H7) between the shroud support cylinder and a lower portion of a core shroud 6. In the respective welds, cracks may be considered to generate and a plurality of cracks may be considered to generate at optional positions through the length of each weld line. In this case, when cracks are generated at a plurality of positions, every time, an apparatus having a structure dependent upon the position is prepared, thus a problem arises from the viewpoint of cost reduction. Further, when cracks are generated at a plurality of positions, if the apparatus is moved and installed at each position and repair operation is executed, a problem arises similarly from the viewpoint of operation term reduction and operability improvement. At least, the welds (H8 and H9) of the shroud support have a weld line at 360° in the circumference and when cracks are generated in the entire perimeter, the consideration of a repair method capable of repairing continuously for the entire perimeter of each weld line is preferable from the viewpoint of the process, cost, and radiation exposure reduction. As a maintenance method and apparatus of the shroud support disposed in the reactor pressure vessel of the nuclear power generation plant which are conventionally proposed, there are an operation apparatus and an operation method (see Japanese Patent No. 4585079) of repairing from a lower side of the shroud support plate by a pantograph mechanism from an inside of the core shroud and an intra-reactor repair apparatus having a structure which it is clamped in a plate thickness direction of the shroud support leg and receives reaction force and an intra-reactor repair method (see Japanese Patent No. 4634742). On the other hand, as a method for changing an access route, an inspection repair maintenance apparatus (see Japanese Patent Laid-Open No. 2001-296386) of the shroud support for passing through the jet pump and repairing a lower portion of the shroud support, a repair system (see Japanese Patent No. 4262450) of a reactor narrow portion for approaching from a side of an annulus portion and repairing an upper portion of the shroud support plate, and an operation apparatus and an operation method (see Japanese Patent No. 4528711) using an underwater traveling vehicle are proposed. [Patent Literature 1] Japanese Patent No. 4585079 [Patent Literature 2] Japanese Patent No. 4634742 [Patent Literature 3] Japanese Patent Laid-Open No. 2001-296386 [Patent Literature 4] Japanese Patent No. 4262450 [Patent Literature 5] Japanese Patent No. 4528711 However, in a maintenance correction method of, for example, the shroud support in the reactor pressure vessel described in the above Japanese Patent No. 4585079, the operation apparatus having the pantograph mechanism and operation equipment mounted to the pantograph mechanism is seated on one control rod drive mechanism (CRD) housing and the operation equipment is brought close to the weld of the shroud support from the one control rod drive mechanism housing being a starting point by the pantograph mechanism. In this case, an operable range is extremely limited, so that when cracks are generated at a plurality of positions, the apparatus must be moved and installed repeatedly according to the position of the objective cracks. Further, the shroud support leg is a hindrance to an area positioned on a rear side of the shroud support leg, so that repair by another means must be considered, and a plurality of apparatuses are required, so that it is a factor of an increase in cost. Further, the intra-reactor repair apparatus described in Japanese Patent No. 4634742 similarly uses the shroud support leg at one position as a support starting point, so that the area capable of similarly executing the repair operation is limited. The same may be said with the inspection repair maintenance apparatus of the shroud support of Japanese Patent Laid-Open No. 2001-296386 which is another prior art. Further, the repair system of the reactor narrow portion described in Japanese Patent No. 4262450 inserts a repair apparatus of the repair system on the shroud support plate by using a guide pipe disposed in the annulus portion in a state that the inside of the reactor pressure vessel is held an aerial environment and, and then travels itself to the repair place, so that it can approach the entire perimeter of the shroud support plate. However, if one apparatus is equipped with necessary functions such as welding, grinding, and PT, enlargement of the apparatus is caused in order to prepare each head, process a large amount of cable hoses, and ensure a thrust due to self travel for pulling around. As a consequence, miniaturization for application to a dimensional restriction of a narrow place is difficult. Further, when the welding, grinding, and PT functions are made independent, every time, the entire apparatus must be put in and out and the operation efficiency is lowered. Further, the operation apparatus and operation method using the underwater traveling vehicle disclosed in Japanese Patent No. 4528711 improve in mobility, however, a problem arises that they cannot be applied to the repair operation in the aerial environment such as a repair welding and a PT inspection. An object of the present invention is to provide a method of repairing a shroud support and a shroud support repair apparatus which can shorten the time required for the repair operation and also performing a highly-reliable repair operation. A feature of a method of repairing a shroud support of the present invention for attaining the above object comprises steps of setting a plurality of rails along a weld of the shroud support in a reactor pressure vessel over either an entire perimeter on an inner circumference of the reactor pressure vessel or a repair range; attaching movably a repair device to the rail, and performing repair operation of the weld of the shroud support by the repair device. Further, a first feature of a shroud support repair apparatus of the present invention for attaining the above object comprises a plurality of rails installed over an entire perimeter on circumference or a repair range of a weld of a shroud support in a reactor pressure vessel; a plurality of support arms for supporting the rails; a plurality of rail guide members for guiding the rail set thereon; a plurality of support apparatuses for fixing each of the rail guide members and each of the support arms; and a repair device movably set on the rail. A second feature of a shroud support repair apparatus of the present invention for attaining the above object comprises a plurality of rails set on circumference of a lower surface of a weld of a shroud support in a reactor pressure vessel, a plurality of rail support apparatus for supporting the rails, a plurality of second support apparatus for supporting the rail support apparatus, and a repair device movably set on the rail. A third feature of the present invention for attaining the above object is a shroud support repair apparatus installed in an annulus portion where a plurality of jet pumps are installed on an upper surface of a shroud support plate for partitioning vertically an annulus space formed between a reactor pressure vessel and each of a shroud support cylinder configuring a shroud support, and a core shroud disposed on the shroud support cylinder, the shroud support repair apparatus comprising a plurality of first rails set to each of a plurality of rise pipes communicated with each of the jet pumps; each of a plurality of second rails inserted between the first rails being adjacent to each other and set to an end portion of each of the first rails being adjacent to the second rail; a third rail being longer than the second rail, inserted between the other first rails being adjacent to each other and set to a end portion of each of the other first rails being adjacent to the third rail; a travel apparatus moving on the first rails, the second rails and the third rail; and a repair device disposed below the travel apparatus and attached to the travel apparatus. According to the present invention, the time required for the repair operation for each weld of the shroud support can be shortened and a highly-reliable repair operation can be performed. Hereinafter, embodiments of a shroud support repair apparatus of the present invention will be explained based on drawn embodiments. Further, in each embodiment, same numerals are used for the same constituent parts. [Embodiment 1] FIG. 1 is a partial perspective view showing an arm development repair apparatus according to embodiment 1, which is a preferred embodiment of a shroud support repair apparatus of the present invention, installed in a lower portion of a reactor pressure vessel. FIG. 2 is a longitudinal sectional view showing a reactor pressure vessel to which a shroud support repair apparatus of the present invention is applied. FIG. 3 is an explanatory drawing showing welds of a shroud support in an enlarged portion A shown in FIG. 2. As shown in FIG. 2, in a boiling water nuclear power plant, a shroud support cylinder 3 configuring a shroud support 2 and a core shroud 6 supported by the shroud support cylinder 3 are installed in a reactor pressure vessel 1. An upper grid plate 7 and a core support plate 8 are disposed in the core shroud 6 and fixed to the core shroud 6. A plurality of control rod drive mechanism housing (hereinafter, referred to as a CRD housing) 9 and a plurality of incore monitor housings (hereinafter, referred to as an ICM housing) 10 stand together a reactor bottom of the reactor pressure vessel 1. Further, an annulus space between the reactor pressure vessel 1 and the core shroud 6 is referred to as an annulus portion 40. An annular shroud support plate 4 is horizontally disposed in the annulus portion 40. An outer surface of the shroud support plate 4 is attached to an inner surface of the reactor pressure vessel 1 and an outer surface of the shroud support plate 4 is attached to an outer surface of the shroud support cylinder 3. The annulus portion 40 is vertically divided by the shroud support plate 4. A plurality of jet pumps 41 is arranged in the circumferential direction in the annulus portion 40 and attached to an upper surface of the shroud support plate 4. The shroud support cylinder 3 is supported from the bottom portion of the reactor pressure vessel 1 by a plurality of shroud support legs 5 arranged at established intervals in a circumferential direction of the shroud support cylinder 3. As aforementioned, welds of the shroud support 2 include many welds such as a weld H9 between an inner surface of the reactor pressure vessel 1 and the shroud support plate 4, a weld H8 between the shroud support cylinder 3 and the shroud support plate 4, a weld H10 between the shroud support cylinder 3 and the shroud support leg 5, a weld H11 between the inner surface of the reactor pressure vessel 1 and the shroud support leg 5, and a weld H7 between the shroud support cylinder 3 and the lower portion of the core shroud 6 (see FIG. 3). Hereinafter, as an example, an arm development repair apparatus 70 of the present embodiment for repairing the weld H9 between the inner surface of the reactor pressure vessel 1 and the shroud support plate 4 will be explained by referring to FIG. 1. The arm development repair apparatus 70 of the present embodiment shown in FIG. 1 is an example of a rail assembly system and is roughly configured by a plurality of rails 11 set along a circumference of a lower surface of the weld of the shroud support plate 4, a plurality of support arms 16a and 16b for supporting the rails 11 from the lower surface at two places, a plurality of support apparatuses 14 to which the support arms 16a and 16b are fixed, a plurality of rail guide members 15 for guiding the rail 11 toward the inner surface of the reactor pressure vessel 1, a plurality of rail push-out apparatuses 17 for pushing out the rails 11 toward the inner surface of the reactor pressure vessel 1 and a repair device 12 set movably on the rail 11. In the present embodiment, the support apparatus (first support apparatus) 14 is seated on the CRD housings 9 via a support base 13 and the support arms 16a and 16b are individually mounted on both sides of the support apparatus 14 and support the rail 11 at two places. The rail guide member 15 is connected to the support apparatus 14, fallen down in a horizontal direction at a fulcrum of the upper end portion of the support apparatus 14 and is an apparatus for playing a role of a guide when it is fallen down in the horizontal direction and the rail 11 is pushed out in a radius direction of the reactor pressure vessel by the rail push-out apparatus 17 fitted into the upper end portion of the support apparatus 14. Further, after the rail 11 was pushed out in the radius direction, both ends of the bent rail 11 are spread upward along the curvature of tops of the support arms 16a and 16b and are fixed by upper ends of the support arms 16a and 16b. These rails 11 are disposed in the respective intervals of the shroud support legs 5 in the similar constitution. Each of the rails 11 are connected each other, thus the rails 11 can be laid at 360° in the overall perimeter. These connected rails 11 are disposed between the shroud support legs 5 and the reactor pressure vessel 1 at directly below the shroud support plate 4. The shroud support legs 5 arranged in a circumferential direction of the shroud support cylinder 3 is surrounded by the connected rails 11 disposed directly below the shroud support plate 4. The repair device 12 is inserted at directly below the shroud support plate 4 through an opening portion 71, which is formed between the shroud support legs 5, from the vicinity of the repair place and set on the rail 11. The repair device 11 moves along the coupled rails 11 within the laying range of the rails 11, so that cracked places of the weld over a wide range can be repaired efficiently. A setting procedure of the arm development repair apparatus 70 of the present embodiment will be explained by referring to FIGS. 4 to 12. With respect to the setting of the arm development repair apparatus 70 of the present embodiment, firstly, the support base 13 is set. The support base 13 is set at the upper ends of the CRD housings 9 in two places, so that the support base 13 hanging by a wire 72 hanged from a ceiling crane (not shown) passes through a narrow place such as an opening portion (not shown) formed in the core support plate 8 in a lengthwise posture, and then as shown in FIG. 4, changes to a horizontal posture, and is seated on the tops of the CRD housings 9. Thereafter, as shown in FIG. 5, the support apparatus 14 is hanged down on the support base 13. At this time, the rail guide member 15 is connected to the support apparatus 14 with pins 18a and 18b and is set on the support base 13 in the state that it is positioned in the axial direction of the support apparatus 14. Each CRD housing 9 on which each of the support apparatus 14 is set is a part of all the CRD housings 9 installed to a bottom head of the reactor pressure vessel 1, and is disposed in a outermost region of CRD housing array. In addition, as shown in FIG. 6, the pin 18a is positioned at a lower end portion of the support apparatus 14 and is connected to a beam 19, and on the other hand, the rail guide member 15 is connected to the beam 19 by the pin 18b. A wire 72 connected to the upper end of the rail guide member 15 is loosened after seated, thus the beam 19 falls down in the radius direction, and so as to follow it, the rail guide member 15 falls down similarly by rotating in a axial direction of the reactor pressure vessel 1 and is horizontally positioned. As a consequence, the rail guide member 15 is set perpendicularly, that is, horizontally in a groove formed in an upper end portion of the support apparatus 14. At this time, the rail guide member 15 is inserted in the opening portion 71 and an end of the rail guide member 15 reaches directly below the shroud support plate 4. Next, as shown in FIG. 7, the support arm 16a is hanged down on one side of the support apparatus 14. As shown in FIG. 8, the support arm 16a falls down at a fulcrum of a pin 20 by loosening the wire 72 after the support arm 16a is seated on the support apparatus 14 and reaches the vicinity of the inner surface of the reactor pressure vessel 1 through the opening portion 71. Similarly, the support arm 16b is installed on the opposite side of the support apparatus 14. At this time, the support arms 16a and 16b are disposed in the state that the angle is opened toward the leading edge side of the support arms at a center of the support apparatus 14. Next, as shown in FIG. 9, the bent rail 11 is hanged down. The reason is that the opening portions of the upper grid plate 7 and the core support plate 8 are narrow and the long rail 11 cannot pass through in the present state, so that the rail 11 is hanged down in the bent state. After the rail 11 is set on the rail guide member 15 and moved directly below the shroud support plate 4, the bent portions of the rail 11 are spread. In the bent state, the rail 11 is seated on the top of the rail guide member 15. The rail guide member 15 is provided with a concave groove at the center in the guide direction. When the rail 11 is seated, the convex portion existing on a lower portion of each bent portion of the rail 11 is fitted into the groove of the rail guide member 15. The rail 11 spread and disposed directly below the shroud support plate 4 is set on each upper end of the rail guide member 15 and the support arms 16a and 16b and supported by these. Thereafter, as shown in FIG. 10, the repair device 12 is set on the rail 11. Further, in the arrangement of the rails 11, when the repair device 12 is not set in the proper position and only the rails are assembled, the operation of setting the repair device 12 is removed and the next process is performed. Next, the rail push-out apparatus 17 is hanged down and is set on the support apparatus 14, as shown in FIG. 11, after the repair device 12 is movably set on the rails 11. The rail push-out apparatus 17 pushes out the rail 11 toward the inner surface of the reactor pressure vessel 1 along the rail guide member 15 through the opening portion 71, as shown in FIG. 12. A pulley 21 for guiding a cable to be connected to the repair device 12 is mounted to the side of the rail push-out apparatus 17. However, the installation of the pulley 21 is excluded when the repair device 12 is not set and only the rail 11 is set. FIGS. 13 and 14 show the rail push-out apparatus 17. As shown in the drawings, the rail push-out apparatus 17 is provided with an apparatus body 73, a bolt 22 rotatably attached to an upper end portion of the apparatus body 73, a ball screw 23 rotatably attached to the apparatus body 73 and connected to the bolt 22, a table 24 for vertically moving by the rotation operation of the ball screw 23, and a conveyer type chain 25 connected to a lower surface of the table 24. The table 24 is movably mounted to the apparatus body 73. Further, the conveyer type chain 25 has a structure that inner links and outer links are assembled alternately and a roller is installed in the position of the connection pin of each link. The bolt 22 is rotated by inserting a socket ball 26 from above, thus the ball screw 23 is rotated, and the table 24 descends. At that time, the conveyer type chain 25 attached to the lower surface of the table 24 is pushed down. The chain 25 in which a plurality of links is connected to each other is bent in the horizontal direction along the rail guide member 15 positioned in an orthogonal direction to the rail push-out apparatus 17, moves along groove formed in the rail guide member 15, pushes out the convex portion of the rail 11 fitted into the groove, and moves the rail 11 to the leading edge of the rail guide member 15 through the opening portion 71 (see FIGS. 13 and 14). The rail 11 positioned on the leading edge of the rail guide member 15 is disposed directly below the shroud support plate 4. Since the support arms 16a and 16b are set in a state that the top thereof has a curvature shape, the bent rail 11 is pushed out along the upward curvature line of the support arms 16a and 16b, are spread gradually, and become one successive rail 11 at the leading edge of the rail push-out guide 15. When coupling the rails 11 on the circumference between the shroud support legs 5 and the inner surface of the reactor pressure vessel 1, similarly to this procedure, all the rails 11 moved directly below the shroud support plate 4 through each of the opening portions 71 formed between all the shroud support legs 5 are assembled each other at the adjoining position. According to the present embodiment, for the weld H9 between the inner surface of the reactor pressure vessel 1 and the shroud support plate 4, the time required for the repair operation can be shortened and a highly reliable repair operation can be performed. Further, in the present embodiment, an example that an object of the weld H9 between the inner surface of the reactor pressure vessel 1 and the shroud support plate 4 is repaired is explained, however, the similar method can be applied to the repair of the weld H8 between the shroud support cylinder 3 and the shroud support plate 4, by setting in an inward direction of repair device 12 and shortening push-out distance of the rail 11 in the radius direction by the rail push-out apparatus 17. Further, the similar method to the method applied to the weld H8 can be applied to the weld H10 between the shroud support cylinder 3 and each of the shroud support legs 5 by lowering the support apparatus 14 and the support arms 16a and 16b in an axial direction of the reactor pressure vessel 1. The weld H9 between the inner surface of the reactor pressure vessel 1 and the shroud support plate 4, the weld H8 between the shroud support cylinder 3 and the shroud support plate 4, and an outside half of thickness of the weld H10 between the shroud support cylinder 3 and the shroud support legs 5 are positioned outside the shroud support legs 5, so that a curvature surface of a bottom head of the reactor pressure vessel 1 is positioned directly below the shroud support plate 4, and a structure for supporting the rail 11 does not exist. Further, since a lower region existing directly below the shroud support plate 4 and formed between the reactor pressure vessel 1 and the shroud support legs 5 is positioned outside the positions of the upper grid plate 7 and the core support plate 8, the lower region cannot be accessed from the upper portion of the reactor pressure vessel 1 through the annulus portion 40. Accordingly, the remote setting of the rail 11 and a support mechanism indicated in the present embodiment are necessary. However, the weld H11 between the inner surface of the reactor pressure vessel 1 and the shroud support leg 5, the weld H7 between the shroud support cylinder 3 and the lower portion of the core shroud 6, and an inside half of thickness of the weld H10 between the shroud support cylinder 3 and the shroud support legs 5 are positioned inside the shroud support legs 5 and the shroud support cylinder 3, and can be accessed through the opening portions individually formed the upper grid plate 7 and core support plate 8 from the upper portion of the reactor pressure vessel 1, and there exist the CRD housings 9 at any position on the circumference below the welds, so that the complicated mechanism used in the present embodiment is unnecessary, and the rails 11 can be set by being seated the rails 11 at the upper ends of the CRD housings 9 and coupling the respective rails 11. Further, when raising the height level, the intervals between the CRD housings 9 and the rails 11 can be increased. [Embodiment 2] A pile-up repair apparatus according to embodiment 2, which is another preferred embodiment of a shroud support repair apparatus of the present invention, will be explained by referring FIG. 15. The pile-up repair apparatus 74 of the present embodiment shown in FIG. 15 is installed in the reactor pressure vessel 1 shown in FIG. 1, similarly to the arm development correction apparatus 70 of embodiment 1. The pile-up repair apparatus 74 is applied to the boiling water nuclear power plant. The pile-up repair apparatus 74 of the present embodiment shown in FIG. 15 is an example of the rail assembly system and is provided with a plurality of rails 27 set along the circumference of the lower surface of the weld of the shroud support plate 4, a plurality of rail support apparatuses 28 for supporting the rails 27, and a plurality of second support apparatuses. Each second support apparatus includes an upper portion support apparatuses 29 and a lower portion support apparatuses 30. The upper portion support apparatus 29 is supported by the lower portion support apparatus 30 and the rail support apparatus 28 is supported by an upper end of the upper portion support apparatus 29. The shroud support legs 5 are arranged at 12 places at established intervals in a circumferential direction of the shroud support cylinder 3 and installed on an inner surface of the bottom head of the reactor pressure vessel 1. The upper portion support apparatus 29 and the lower portion support apparatus 30 are installed in line with each other between the outside of the shroud support legs 5 and the inside of the reactor pressure vessel 1. Each load of the upper portion support apparatus 29 and the lower portion support apparatus 30 is applied to the shroud support legs 5. Falling prevention of the upper portion support apparatus 29 and the lower portion support apparatus 30 is realized by a lower support arm 32 mounted to the lower portion support apparatus 30 and made contact with the inner surface of the bottom head of the reactor pressure vessel 1. Thus an independent structure of the upper portion support apparatus 29 and the lower portion support apparatus 30 is established. The rail support apparatus 28 is supported by the upper end of the upper portion support apparatus 29 and an upper support arm 31 mounted to the upper portion support apparatus 29. These rails 27 are similarly set through each opening portion 71 at 11 places of the other shroud support legs 5, thus the rails 27 can be laid at 360° in the overall perimeter between the reactor pressure vessel 1 and the shroud support legs 5. The shroud support legs 5 arranged in a circumferential direction of the shroud support cylinder 3 is surrounded by the laid rails 27 disposed directly below the shroud support plate 4. As a consequence, the similar effects to the arm development correction apparatus of embodiment 1 can be obtained. A setting procedure of the pile-up repair apparatus 74 of the present embodiment will be explained by referring to FIGS. 16 to 31. The setting of the pile-up repair apparatus 74 is to firstly set the lower portion support apparatus 30 on the inner surface of the bottom head of the reactor pressure head 1 using an operation apparatus 33 while making contact with the outer surface of the shroud support legs 5, and successively pile up the upper portion support apparatus 29 on an upper end of the lower portion support apparatus 31 thereon. Firstly, as shown in FIG. 16, the operation apparatus 33 passes through a narrow place such as the opening portion formed in the core support plate 8 in the state of downward holding the lower portion support apparatus 30 and is hanged down to the reactor bottom. Next, the operation apparatus 33 is bent upward between the shroud support legs 5 (see FIG. 17), and the lower portion support apparatus 30 is transported outside the shroud support legs 5 through the opening portion 71 by the operation apparatus 33 (see FIG. 18). After the transportation of the lower portion support apparatus 30, the operation apparatus 33 is bent sideways, directs a leading edge portion 76 of an arm 75 of the operation apparatus 33 toward the rear side of the shroud support legs 5 (see FIG. 19). Further, the operation apparatus 33 expands the leading edge portion 76 of an arm 75 (see FIG. 20), and descends, and sets the lower portion support apparatus 30 on the bottom head (see FIG. 21). Thereafter, as shown in FIG. 22, the operation apparatus 33 pushes the lower support arm 32 down toward the inner surface of the reactor pressure vessel 1 and makes the lower portion support apparatus 30 independent. At this time, a leading edge of the lower support arm 32 is making contact with the inner surface of the reactor pressure vessel 1 and this lower portion support apparatus 30 is disposed directly below the shroud support plate 4. A structure of the lower support arm 32 is shown in FIGS. 23 and 24. As shown in the drawing, a bolt 34 is rotatably mounted to the side of an apparatus body 77, a gear 35 is attached to the bolt 34, and gears 35B and 35C are rotatably mounted to the apparatus body 77. The gear 35B engages with the gears 35A and 35C. A lower end portion of the lower support arm 32 is connected to a rotating shaft attached to the gear 35C. If the bolt 34 is rotated, the lower support arm 32 can be rotated via the gears 35A, 35B and 35C. A socket wrench 36 in which a torque motor is embedded is set on the bolt 34 by an operation pole (not shown) or the operation apparatus 33 and the rotation of the bolt 34 is performed by rotating the socket wrench 36. As shown in FIG. 25, the upper portion support apparatus 29 is set on the upper end of the lower portion support apparatus 30. The setting of the upper portion support apparatus 29 is performed by using the operation apparatus 33 similarly to the lower portion support apparatus 30 and the procedure is the same. Thereafter, as shown in FIG. 26, the upper support arm 31 is rotated by using the similar structure shown to FIGS. 23 and 24 and mounted in the upper portion support apparatus 29, falls down toward the inner surface of the reactor pressure vessel 1. The rail support apparatus 28 is set on an upper end of the upper support arm 31 by the operation apparatus 33 (see FIG. 27). Next, the installation of the rail 27 will be explained. As shown in FIG. 28, each rail 27 is transferred outside the shroud support legs 5 through the opening portion 71 by the operation apparatus 33 and is set on an upper surface of the rail support apparatus 28. Continuously, each medium rail 37 is transferred outside the shroud support legs 5 through the opening portion 71 and inserted between the rails 27 being adjacent to each other in a circumferential direction of the reactor pressure vessel 1 by the operation apparatus 33. Both end portion of the medium rail 37 are coupled to two rails 27 being adjacent to the inserted medium rail 37. Finally, a repair device 38 is set on the medium rail 37 by the operation apparatus 33. As shown in FIGS. 29 and 30, the repair device 38 is hanged down to the reactor bottom by the operation apparatus 33, and the operation apparatus 33 is bent upward through the opening portion 71. Thus, the repair device 38 is transferred toward the medium rail 37 through the opening portion 71. Thereafter, as shown in FIG. 31, the repair device 38 is set in the medium rail 37. The present embodiment can obtain the effects generated in embodiment 1. [Embodiment 3] A rail-type repair apparatus according to embodiment 3, which is further another preferred embodiment of a shroud support repair apparatus of the present invention, will be explained. The rail-type repair apparatus 78 (see FIG. 34) of the present embodiment is disposed directly above the shroud support plate 4 in the annular portion 40. The rail-type repair apparatus 78 is applied to the boiling water nuclear power plant. FIG. 32 is a plan view showing the annulus portion 40 formed above the shroud support plate 4 disposed in the reactor pressure vessel 1 and disposed. A plurality of jet pumps 41 are disposed in the annular portion 40. As shown in FIG. 32, the annulus portion 40 is formed between the reactor pressure vessel 1 and each of the core shroud 6 and shroud support cylinder 3, and positions directly above the shroud support plate 4. The plurality of jet pumps 41 are installed on the shroud support plate 4. The jet pump 41, as shown in FIG. 33, is provided with a nozzle 42A, a bell mouth 42B, a throat 42C and a diffuser 42D. The nozzle 42A is disposed directly above the bell mouth 42B and an upper end of the throat 42C is attached to the bell mouth 42B. The throat 42C and the diffuser 42D are connected with a slip joint. In the slip joint, a lower end portion of the throat 42C is inserted into an upper end portion of the diffuser 42D. A lower end of the diffuser 13 is joined with the shroud support plate 4. One riser pipe 43 disposed in the annular portion 40 is communicated with each nozzle 42A of two jet pumps 41. A lower end portion of the riser pipe 43 is connected to 90° elbow connected to a pipe 43A extending in the horizontal direction and penetrating the reactor pressure vessel 1. Further, instrumentation pipes 45 for each diffuser 42D of the two jet pumps 41 are connected to each side of the two diffusers 42D. Further, an instrumentation pipe 45 is connected to the side of each of the diffusers 42. The jet pumps 41 structured like this are arranged almost symmetrically right and left for the 0° and 180° axes on a cross section of the reactor pressure vessel 1 and the gap is very narrow. However, an access hole 44 is formed in the shroud support plate 4 at the 0° and 180° positions, respectively and the space is comparatively opened at directly above each access hole 44. The rail-type repair apparatus 78 disposed in the annulus portion will be explained by referring to FIG. 34. As shown in the drawing, the rail-type repair apparatus 78 is provided with a plurality of support rails 46 attached to the riser pipe 43 (specifically speaking the pipe 43A), a plurality of connection rails 47 for coupling to the support rails 46 being adjacent to this connection rail 47, a plurality of long rails 48 positioned directly above the access hole, a travel apparatus 49 for moving on these rails 46, 47, and 48, and a repair device 50 mounted on the lower surface of the travel apparatus 49. The support rail 46 has two pawls 51 for opening and closing. The support rail 46 is held on the riser pipe 43, and more specifically, the pipe 43A by closed pawls 51. Further, the connection rail 47 is inserted between the support rails 46 set to the pipes 43A from above and both end portions of the inserted connection rail 47 are coupled to the support rails 46 being adjacent to the inserted connection rail 47. A distance in directly above the access hole 44 and between the support rails 46 being adjacent to each other is longer than a distance between the support rails 46 being adjacent to each other except for the position existing directly above the access hole 44, so that a long rail 48 is used in the position existing directly above the access hole 44. The travel apparatus 49 moves on these rails with a front wheel 52 and a rear wheel 53, so that the front wheel 52 and the rear wheel 53 are configured by a plurality of wheels to respond to the gaps of the coupling portions of the rails. Further, the repair device 50 is mounted on the lower surface of the travel apparatus 49. A setting procedure of the rail-type repair apparatus 78 of the present embodiment will be explained by referring to FIGS. 35 to 44. With respect to the setting of the rail-type repair apparatus 78, firstly, as shown in FIG. 35, the support rail 46 is hanged down through a gap between the jet pumps 41 in the state that both sides are held by a clamp jig 55 and is set on one riser pipe 43, that is, one pipe 43A. At this time, pawls 51 of the support rail 46 are opened, as shown in FIG. 36 and after the support rail 46 set on the one riser pipe 43, the pawls 51 are closed. The rotating shaft of each of the pawls 51 has a winding spring 54 and winding springs 54 always permit the spring force to act the pawls 51 in the closing direction, though the clamp jig 54 clamps each side of the pawls 51, so that the operation closing each of the pawls 51 is stopped. Thereafter, when the support rail 46 is set on the riser pipe 43, the clamp jig 55 is removed from the support rail 46, thus as shown in FIG. 37, the pawl 51 is closed to be fixed to the riser pipe 43. By the similar procedure, as shown in FIG. 38, the support rail 46 is set on the other riser pipe 43. Next, the setting of the connection rails 47 will be explained. Both end portions of the connection rail 47 are convex, and both end portions of the support rail 46 is concave. As shown in FIG. 39, the connection rail 47 is hanged down from above to position of the support rail 46 set on the riser pipe 43. The hanged down connection rail 47 is inserted between the support rails 46 being adjacent to each other in a circumferential direction of the reactor pressure vessel 1. The convex surface of both end portion of the inserted connection rail 47 is fitted to the concave surface of each of the support rails 46 being adjacent to the inserted connection rail 47. Thus, Both end portion of the inserted connection rail 47 are coupled to two rails support rails 46 being adjacent to the inserted connection rail 47. The long rail 48 is long, so that as shown in FIG. 40, it is firstly hanged down lengthwise, is thereafter pulled up sideways, and then is set on the adjoined support rail 46 at directly above the access hole 44, as with the connection rail 47. FIG. 41 shows the rail set state of the support rails 46, the connection rails 47, and the long rail 48. In this state, the travel apparatus 49 and the repair device 50 are set. The repair device 50 is set in the state that it is fixed to the travel apparatus 49. The travel apparatus 49 is hanged down and set by using a place in which comparatively sufficient space exists, positioning directly above the access hole 44 at 0° or 180° of the reactor pressure vessel 1, as shown in FIG. 42. FIG. 43 shows the constitution of the travel apparatus 49. As shown in the drawing, the travel apparatus 49 has the front wheel 52 and the rear wheel 53 configured by a plurality of wheels and moves by laying and attaching movably the front wheel 52 and the rear wheel 53 to the rail. The movement includes a forward movement and a backward movement in two directions, and the forward movement is performed by the front wheel 52, and the backward movement is performed by the rear wheel 53. One wheel included in the front wheel 52 is driven by a travel motor 56 and the other wheels included in the front wheel 52 are connected to the one wheel with a chain 57 and drive similarly. Furthermore, one wheel included in the rear wheel 53 is driven by a travel motor 56A and the other wheels included in the rear wheel 53 are connected to the one wheel with a chain 57A and drive similarly. The wheels can be connected by a belt or a gear. The lower surface of the travel apparatus 49 has a rail 58 and the repair device 50 has a wheel 59 and a travel motor 60, so that it can move on the rail 58 of the travel apparatus 49. The grinding function will be indicated as an example for the repair device 50. A grindstone 61 is attached to a leading edge of the repair device 50 and operated by a grindstone rotation motor 62 mounted to the repair device 50. Further, the concerned portion is vertically driven to push in the grindstone 61 and is operated by a vertical drive motor 63 and the ball screw connected to it. The travel apparatus 49 has a cable reel 66 for winding and fixing beforehand the cable hose length equivalent to the travel distance, and a guide pulley 65 and an adsorption pad 64 which are provided on the long rail 48 (see FIG. 44). The reason is that when the travel apparatus 49 moves within the range, for example, from the 0° direction to 90° of the reactor pressure vessel 1, the cable hose 79 inserted from the 0° position is received once by the guide pulley 65 and is guided in the 90° direction, and the cable hose 79 wound round the cable reel 66 provided in the travel apparatus 49 is extended, thus the cable hose length becoming deficient during movement is covered. Further, when repairing the forward portion of 90° or more, the travel apparatus 49 is inserted from the 180° position and moves counterclockwise, thus the troubleshooting is enabled by the minimum movement distance. Even by use of such a constitution of the present embodiment, the present embodiment can obtain the effects generated in embodiments 1 and 2. The rail setting procedure is explained above, however, when executing a weld repair among the repair operations, an aerial environment in the reactor pressure vessel 1 is desirable. Regarding the rail setting apparatus from the lower side of the shroud support plate 4 shown in FIGS. 1 and 15, the repair device setting in the aerial environment is shown in FIG. 45 using embodiment 2 as an example. As shown in the drawing, when filling the reactor pressure vessel 1 with water, the settings of the rail 27 and the medium rail 37 are finished, and thereafter, a first shielding body 67 is installed on the flange portion of the reactor pressure vessel 1, and a second shielding body 68 is installed on the upper portion of the core shroud 6, and a guide pipe 69 passing through the first shielding body 67 and the second shielding body 68 is set. Thereafter, the removal of the water in the reactor pressure vessel 1 is performed using a drain pipe. After completion of the water removal, the aerial environment is formed in the reactor pressure vessel 1 and the repair device (for example, welding device) 38 is set on the medium rail 37 by the operation apparatus 33 transferred in the guide pipe 69 and the repair operation is performed. Further, also in embodiment 1, as shown in FIGS. 10 and 11, beforehand, the setting excluding the rails 11 at one place where the repair device 12 is set in the underwater environment and the setting of the one place of the concerned rails 11 are executed up to the level equivalent to FIG. 9, and after the underwater environment is changed to the aerial environment, the guide pipe 69 is permitted to pass through the one place of the concerned rails 11, and the repair device 12 is passed through the guide pipe 69 and installed on the rails 11, and the rail push-out apparatus 17 that is similarly passed through the guide pipe 69 is installed on the support apparatus 14, and then the socket ball 26 with motor is hanged down by remote control, and the rails 11 are pushed out, and the repair device 12 is installed, thus the repair operation is executed. Further, in each embodiment aforementioned, the welding apparatus is explained as an example of a repair device, however, it is needless to say that the repair operation can be executed using various processing apparatuses or an inspection apparatus in place of the welding apparatus. Further, in each embodiment, the rails installed in the reactor pressure vessel are laid at 360° in the overall perimeter of the reactor pressure vessel, however, there is no need to lay rails in the overall perimeter of the reactor pressure vessel. If the weld is inspected beforehand by an ultrasonic inspection apparatus and the place where cracks exist is confirmed, rails may be laid over the repair range of the place of the weld where cracks exist. [Reference Signs List] 1: reactor pressure vessel, 2: shroud support, 3: shroud support cylinder, 4: shroud support plate, 5: shroud support leg, 6: core shroud, 7: upper grid plat, 8: core support plate, 9: control rod drive mechanism housing, 10: incore monitor housing, 11, 27, 58; rail, 12, 38, 50: repair device, 13: support base, 14: support apparatus, 15: rail guide member, 16a, 16b: support arm, 17: rail push-out apparatus, 18a, 18b, 20: pin, 19: beam, 21: pulley, 22, 34: bolt, 23: ball screw, 24: table, 25, 57, 57A: chain, 26: socket ball, 28: rail support apparatus, 29: upper portion support apparatus, 30: lower portion support apparatus, 31: upper support arm, 32: lower support arm, 40: annulus portion, 41: jet pump, 42A: nozzle, 42C: throat, 42D: diffuser, 43: riser pipe, 44: access hole, 45: instrumentation pipe, 46: support rail, 47: connection rail, 48: long rail, 49: travel apparatus, 51: pawl, 52: front wheel, 53: rear wheel, 54: winding spring, 55: clamp jig, 56, 56A, 60: travel motor, 59: wheel, 61: grindstone, 62: grindstone rotation motor, 63: vertical drive motor, 64: adsorption pad, 65: guide pulley, 66: cable reel, 67: first shielding body, 68: second shielding body, 69: guide pipe, 70: arm development repair apparatus, 71: opening portion, 74: pile-up repair apparatus, 78: rail-type repair apparatus. |
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040615340 | description | DESCRIPTION OF PREFERRED EMBODIMENTS Referring firstly to FIG. 1, this drawing seeks to illustrate the invention as it may be applied by way of example to a sodium-cooled nuclear reactor of the kind described and illustrated in the Paper by A. G. Frame et al read before the London Conference on Fast Breeder Reactors, May, 1966 and reported at pages 291 - 315 of the Proceedings of that Conference published in 1967 by Pergammon Press. This reactor is provided with a double-walled vessel for containing the bulk sodium in which the reactor core, primary heat exchangers and a pump are submerged, the interspace being employed as a leak jacket for collecting and detecting any leaks from the inner vessel. The vessel is disposed in a concrete vault. Thus there are separate walls to ensure that no catastrophic draining away of the sodium shall occur. The present invention provides the moans to simplify and make more economic the containing of the sodium without relaxing the high degree of integrity of the existing design as typified in the said Paper. Instead of employing a double-walled vessel, the concrete vault is formed to the desired shape of the sodium-containing vessel given the necessary amount of pre-stressing (ducted cables 9 in FIG. 1) to enable it to serve as a task. Its wall, a portion of which is illustrated in the drawing and designated 1, is provided with a membrane lining 2 which can be of an inexpensive material such as mild steel. Pipes 3 for a cooling or refrigerating fluid 4 are embedded in the wall 1 so as to be in contact with the lining 2 over as much of the inner surface thereof as is necessary. Further pipes 5 are provided on the outer side of the lining 2 and contact as much of its outer surface as is necessary, the contact positions being chosen to be in staggered relationship to those of the inner pipes 3, whereby as little as possible of the lining 2 is left uncontacted by either pipes 3 or 5. Cooling or refrigerating fluid 6 flows through the pipes 5, and may be the same fluid as 4, where this is compatible with sodium, or is a fluid which is compatible with sodium where the fluid 4 is not. Thus the fluid 4 may be water, a freon or an areton, whereas the fluid 6 must not be any of these substances, which are strongly reactive with sodium. The fluid 6 (and additionally the fluid 4 if desired) may be the sodium/potassium eutectic (which is fluid at room temperatures), or may be a pressurized gas e.g. helium, argon, carbon dioxide, or may be a proprietory coolant known as DOWTHERM (Registered Trade Mark) Grade E, which is understood to be a treated orthodichlorobenzene with a freezing point of -7.degree. F, a boiling point of 352.degree. F, and a thermal conductivity at 500.degree. F of 0.120 B.T.U. hr.sup.-1 sq.ft..sup.-1 .degree. F.sup.-1. All of these coolants are compatible with sodium over the operating temperature range applicable to the type of reactor envisaged. The effect of cooling employing the fluids 4 and 6 in the pipes 3 and 5 respectively, is twofold. Firstly, with a mean temperature of about 400.degree. C of a sodium pool P contained in the lined vault, the cooling is designed to keep the temperature of the lined surface of the concrete wall 1 well within the limit prescribed for concrete, and furthermore keeps the temperature gradient across the concrete wall from lined surface to outer surface (not shown) to about 50.degree. C, which is a figure chosen as an optimum against the necessity of providing extra prestressing to guard against the effects of differential expansion. It may be necessary to augment the cooling effect produced by the pipes 5 and fluid 6 by the provision of thermal insulation over the pipes 5 (as shown in the drawing in dot-and-dash lines and designated 7) in order to bring about a reduction of temperature from the mean of about 400.degree. C of the bulk sodium P down to about 50.degree. C at the lined surface of the concrete. The second effect of the cooling is that it brings about freezing of the molten sodium pool P at the volume thereof which is adjacent, in contact with and supported by the lining 2 of the wall 1 (pure sodium freezes at 98.degree. C). In the drawing, the frozen volume is indicated diagrammatically by the shaded area 8, and the boundary of the volume is indicated by the broken line 9'. It is accomplished, by control of the cooling, that the boundary 9' is clear of the pipe 5 and, where provided, the thermal insulation 7, so as to produce an unbroken surface of the frozen sodium volume 8. It is this surface which in effect now forms the wall of the sodium-containing vessel, with all th advantages which accrue, including compatibility (identical material), self-sealing property, and ability to act as cold trap for impurities (either reinforcing or replacing existing cold trapping facilities). It is desirable to provide instrumentation to indicate any variation of parameters adjacent the concrete wall 1. Such instrumentation may include thermocouples, and thickness gauges to monitor the thickness of the frozen sodium layer. There may be feed-back from such instrumentation to control the amount of cooling produced by one or both fluids. Further advantages accrue from the ability more readily to shape a coolant-containing vessel to as complicated a shape as desired, since it is easier and less expensive to shape a concrete structure and relatively thin mild steel lining than it is to shape a metal vessel constructed to exacting pressure vessel standards, and from the general principle of its being more economic to employ existing containment structure with the addition of a lining and cooling means instead of having to provide a separate vessel built to exacting pressure vessel standards. Referring now to FIGS. 2 and 3, those drawings illustrate a large (600 MW(E)) power generating fast breeder nuclear reactor cooled by liquid sodium, and having the present invention incorporated in the design thereof. As the invention resides in the sodium-containing part of the reactor, features unconnected therewith will only be briefly mentioned. The core 10 (including radial and axial breeder regions) of the reactor is generally cylindrical and is supported on a diagrid 11 carried by a massive centre pillar 12 and a concentric ring of secondary pillars 13 mounted on the floor of a concrete vault 14, there being roller bearings 15 on the pillars 13 but not the massive centre pillar 12 to allow the diagrid 11 to adapt position transversely as a result of thermal expansion and contraction of itself and of connected equipment. A core catcher 55 is provided below the diagrid 11 in case of melt-down. The core 10 is surrounded peripherally by a radial neutron shield 16, and above by an upper neutron shield which is included in a lid 17 which completes an enclosure 18 for the core and radial shield 16. Primary sodium which has passed over fuel rods in fuel sub-assemblies constituting the core and breeder regions leaves the enclosure 18 via ducts 19 and is taken to intermediate heat exchangers (of which there are four) designated generally 20, where it flows over tubes 21 and transfers heat to secondary coolant (also sodium) flowing in the tubes 21, the secondary sodium being employed externally of the reactor to raise steam to drive a turboalternator (not shown) to generate power. Each heat exchanger 20 has a circulating pump 22 for the primary sodium associated with it. Return ducts 23 take the feed of primary sodium from pumps 22 back to the lower end of core enclosure 18 for flow upwardly through the core and breeder regions. A fuel store 24 situated at one side of the core 10 has its own shielding 25 and provides accommodation for both new and irradiated fuel and radial breeder sub-assemblies prior to charging the new sub-assemblies into or after withdrawing the irradiated sub-assemblies from, the core or breeder regions. A refuelling machine 26 serves for supplying new fuel to and withdrawing irradiated fuel from, the fuel store 24 by lowering or lifting, respectively. The machine 26 also serves, in conjunction with rotation of an outer rotatable shield 27 in a roof 28 integral with the vault 14, to transfer fuel sub-assemblies from fuel store 24 to core 10 and vice-versa. The outer rotatable shield 27 has its axis eccentric to the axis of the core 10, but coincident with the joining line of the major and minor axes of the container (described in more detail hereafter) for the sodium pool in which the enclosed core 10 is submerged. The outer shield 27 has within its boundary an inner shield 29 rotatable therein, the axis of the inner shield being coaxial with the core 10 axis. The inner shield 29 is joined by a pillar 30 to the core enclosure lid 17 and in addition to being rotatable is also raisable relative to outer shield 27 by jacks 31 (of which there are conveniently 15 spaced around the periphery), such raising also serving to raise the core lid 17 and thus withdraw from penetration into the core various monitoring devices (not shown) such as outlet channel thermocouples and sampling pipes for failed fuel element detection. This raising permits the outer shield 27 to be itself rotated for refuelling purposes. The inner shield 29 carries control and shut-down rod tubes 32 and control rod operating mechanisms 33, the latter being mounted on the external surface of the shield 29 for access purposes. Control and shut-down rods (not shown) are detached from their operating mechanisms and left in the core during refuelling operations involving rotation of outer shield 27. Dip seals 34, 35 employing mercury are provided for the shields 27, 29 respectively. The sodium-containing features of the reactor, the subject of the present invention, will now be described in detail. The concrete vault 14, consisting of a base 36, wall 37 and the roof 28, has a generally rectangular-with-rounded-ends section (FIG. 3), and forms a support means 38 with substantially vertical sides and a flat bottom. The wall 37 and base 36 have a metal lining 39 on a layer 40 of a known concrete which is specially adapted to withstand a higher temperature than ordinary concrete. Along the joining plane bottom the layer 40 and the ordinary concrete, a multiplicity of pipes 41 which generally follow the contours of the sides and base, are laid. At the upper end of the support means 38, the pipes 41 extend outwardly and into the nearest of a number of series-connected chambers (two only of which are shown in FIGS. 2 and 3, designated 42) which extend all around the structure, within the wall 37. At the lower end of the support means 38, the pipes 41 extend in the base 36 to nearly the core axis, then bend and extend downwardly to join a header 43 which header connects to the lower end of a series of surge tank chambers 44 diposed beneath the chambers 42 (FIG. 3). A duct 45 connects the lower end of the chambers 42 to the upper end of the chambers 44. Each of the chambers 42 is divided into upper and lower regions 46, 47 respectively, by a heat exchanger 48 extending across the chamber. Forced draught air, employing a conventional air circulator, is supplied to the regions 47 of all the chambers 42 and flows downwardly into the surge tank chambers 44, over the surge tanks 49 therein, along the header 43, and along the pipes 41, cooling the concrete of the base 36 and wall 37 in its passage, before returning to the upper regions 46 of chambers 42 for discharge. On the inside of the metal lining 39 of the wall 37 and spaced therefrom there is disposed a continuous thermal insulation structure 50. Between the structure 50 and the lining 39 and at spaced intervals around the wall 37 (FIG. 3) are a multiplicity of pipe runs 51 spaced from the lining 39, each of which extends downwardly to the base 36, bens to follow the base 36 still spaced from the lining 39, extends radially nearly to the core axis (shown in FIG. 2 but not in FIG. 3 for clarity), then reverse to form a return run 52 generally parallel to run 51 but, along the wall 37, lying on the inside of structure 50. Along the base 36, the pipe run 52 is associated with built-up thermal insulation generally indicated by the reference numeral 53. The pipe runs 51, 52 at the top of the wall 37 extend outwardly through the and into the respective chamber 42 being connected to the inlet and outlet of the heat exchanger 48 therein so as to provide closed loop circuits. The pipe run 51 is therefore the `cool` leg and the pipe run 52 is the `hot` leg. The closed loops are each filled with sodium/potassium alloy (NaK). The forced draft air fed to regions 47 of the chambers 42, in addition to providing the concrete and surge tank cooling circuits, also flows through the heat exchangers 48 to cool the NaK in the closed loop circuits. The purpose of the closed loop circuits of NaK is to cause sodium in the vault 14 (up to level L, FIG. 3) to solidify in the interspace between the lining 39 and the structure 50 (in the case of the wall 37) and between the lining 39 and the insulation 53 (in the case of the base 36). This solidified sodium 60 provides the container for the sodium pool in vault 14, the vault 14 providing the supporting means 38 for the solidified sodium container. The surge tanks 49 are connected by ducts 54 which enter the vault 14 at the top, extending through thermal insulation 57 provided on the lower surface of roof 28. Thermal insulation 57 is also provided on the lower surface of shields 27, 29. Normal level of sodium is indicated by L in FIG. 2 and the space 58 above the sodium is occupied by a blanket gas, preferably argon. Should the sodium pool reach an excessive temperature and not only expand but also melt some or all of the solid sodium layer 60 so that the sodium level rises from the normal level L to fill the vault 14, the ducts 54 and surge tanks 49 (which are cooled by the air flow from regions 47 of chambers 42) from an additional volume for overflow. The main heat exchangers have manually operable valves (not shown) in ducts 56 (FIG. 3) for establishing communication and convection flow between the pool sodium and the enclosed primary circuit sodium, mainly to be able to employ the pool sodium as a heat sink should a sodium pump or pumps fail. In any event, a small amount of leakage between the primary circuit and the pool will take place at the core lid 17 due to differential thermal expansion. The provision of the novel, sodium-containing solid sodium layer 60 is consider to provide the reactor with an important safety feature which has particular revelance to large plants, for the reasons implicit in the advantages hereinbefore set forth. The invention is seen as being widely applicable to nuclear reactors necessitating the containing of a freezable liquid coolant. Other examples of liquid coolants to which the invention appears to be applicable are other liquid metals in addition to sodium, polyphenyls, and fused salts. An example of the last-named is a mixture of lithium fluoride and beryllium difluoride, published as having been employed for the secondary coolant in the Molten Salt Reactor Experiment (MSRE), Oak Ridge National Laboratory, U.S.A. |
description | This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/563,737 filed Nov. 25, 2011 and titled “X-ray Apparatus with Multiple Adjustments.” This application also claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/563,739 filed Nov. 25, 2011 and titled “Range Finder.” Both of the foregoing applications are hereby incorporated by reference in their entireties. Non-limiting and non-exhaustive embodiments of the disclosure are described herein, including various embodiments of the disclosure with reference to the figures, in which: FIG. 1 is a perspective view of one embodiment of an x-ray apparatus. FIG. 2 is a cross-sectional view of the x-ray apparatus depicted in FIG. 1. FIG. 3 is a perspective view of one embodiment of a collimator for use in connection with an x-ray apparatus. FIG. 4 is another perspective view of the collimator depicted in FIG. 3, shown from the side opposite to the side depicted in FIG. 3. FIG. 5 is an exploded view of the collimator depicted in FIGS. 3 and 4. FIG. 6 is a cross-sectional view depicting certain internal components, including an x-ray source and a visible light generator, according to one embodiment of an x-ray apparatus. FIG. 7 is a close-up, cross-sectional view of a base including a LASER according to one embodiment of an x-ray apparatus. FIG. 8 is a perspective view depicting a reticle of one embodiment of an x-ray apparatus. FIG. 9 depicts certain distance characteristics relating to one embodiment of an x-ray apparatus comprising a reticle having non-equidistant dash lines. The present disclosure provides apparatus, systems, and methods relating to the delivery of radiation, such as x-ray radiation, for medical diagnosis and/or treatment. In x-ray procedures, it may be beneficial for complete and accurate imaging to know where the x-ray beam is being aimed. However, in order to avoid artifacts in the x-ray image, it may be desirable to position an aim light such that it is not arranged in the x-ray beam. Instead, it may be desirable to position an aim light or ranging beam near the x-ray beam. It may also be desirable to not just see a spot or center location of the x-ray beam, but the entire size and shape of the x-ray pattern. Thus, in some embodiments, visible light may be provided that is at least partially coincident and coaxial with an x-ray beam so as to form a light beam of at least substantially the same area as the x-ray beam at any given distance along the respective x-ray and light beams. The x-ray beam and light beam can both be directed through a collimator, as discussed below, which may shape and size the beams identically and simultaneously. Some embodiments may comprise a collimator comprising a shutter mechanism for collimating x-rays having one or more horizontal shutters and one or more vertical shutters. The movement of the shutters may be accomplished by rotating disks having angled slots that may be coupled with engagement pins or other protruding members on the shutters. The rotation of the disks may be converted to linear motion of the shutters. One disk may be associated with the horizontal shutters and another may be associated with the vertical shutters, thereby allowing for independent movement of each set of shutters. Together, each of the shutters may make up a collimation aperture. The collimator may be mounted in front of an x-ray generating device to control the shape and/or size of the x-ray beam. The shutters may be aligned to be perpendicular to the centerline of the generated x-ray beam. This allows the center of the x-ray to always be known. In some embodiments, as further discussed below, a visible light source may also be provided that may overlap with the x-ray beam. In this manner a user may be able to fully visualize at least a portion of or, in some embodiments, the full extent of, the x-ray beam being delivered by the device. In some embodiments, an x-ray apparatus may be provided comprising a first rotatable disk comprising a first plurality of angled slots and a first shutter comprising a first plurality of protruding members. At least one of the first plurality of protruding members may be positioned within a first angled slot of the first plurality of angled slots, and at least one of the first plurality of protruding members may be positioned within a second angled slot of the first plurality of angled slots. This configuration may provide stability to prevent the shutter from pivoting with respect to a single protruding member and/or to prevent binding of the shutters relative to the collimator. The first shutter may at least partially define an x-ray collimation aperture. The apparatus may also be configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the x-ray collimation aperture. Some embodiments may further comprise a second rotatable disk comprising a second plurality of angled slots, along with a second shutter comprising a second plurality of protruding members. Similar to the first rotatable disk, at least one of the second plurality of protruding members may be positioned within a first angled slot of the second plurality of angled slots, and at least one of the second plurality of protruding members may be positioned within a second angled slot of the second plurality of angled slots. Again, this configuration may be useful to provide a more stable movement of the shutters along a desired path. The first shutter and the second shutter may at least partially define the x-ray collimation aperture, and the apparatus may be further configured such that rotation of the second rotatable disk results in movement of the second shutter to alter the size of the x-ray collimation aperture. In some embodiments, the second shutter may be configured to move in a direction at least substantially perpendicular to the first shutter. In other embodiments, the second shutter may be configured to move in a direction at least substantially opposite from the first shutter. In some embodiments, as discussed in greater detail below with reference to the accompanying drawings, four shutters may be provided. In some such embodiments, two shutters may be operably coupled with the first rotatable disk and two shutters may be operably coupled with the second rotatable disk. In some such embodiments, the two shutters operably coupled with the first rotatable disk may be configured to move in directions at least substantially opposite from one another such that these two shutters close towards one another. Similarly, the other two shutters operably coupled with the second rotatable disk may be configured to move in directions at least substantially opposite from one another such that these two shutters close towards one another. However, the two shutters operably coupled with the second rotatable disk may be configured such that they both move in directions at least substantially perpendicular to the directions in which the two shutters operably coupled with the first rotatable disk move. Some embodiments may further be configured such that the collimation aperture cannot be fully closed. For example, one or more of the shutters may be configured such that movement in a direction to decrease the size of the collimation aperture is prevented before the collimation aperture is entirely closed by the shutters. As described below, this may be useful for certain embodiments that provide a visual indication of an x-ray target such that the visual indication never completely disappears. In some embodiments, the apparatus may be configured such that the first rotatable disk can be rotated independently of the second rotatable disk. In addition, in some embodiments, the apparatus may be configured such that rotation of the first rotatable disk through a first angle results in movement of the first shutter of a first distance, such that rotation of the second rotatable disk through the first angle results in movement of the second shutter of a second distance, and such that the first distance differs from the second distance. This feature may be useful for embodiments having a rectangular, non-square field-of-view, such as embodiments designed to match up with a 10 inch×12 inch detector, for example. With regard to such embodiments, it may be useful to configure the apparatus such that the horizontal shutters move farther than the vertical shutters for the same amount of rotation of the rotatable disks in order to maintain a constant horizontal to vertical “aspect ratio” throughout at least a portion of the whole range of motion. Some embodiments, however, may be configured such that the smallest size of the collimation aperture is a square. Some embodiments, however, may be configured such that the aspect ratio changes slightly throughout the rotation. For example, in some embodiments, the largest size of the collimation aperture may be a rectangle with a given aspect ratio, such as 10×12, and the smallest size of the collimation aperture may a square. Thus, the two rotatable disks may be configured such that equal rotation angles result in different shutter movement speed (due to different slot angling between the front and rear rotatable disks) to allow for constant adjustment of the aspect ratio between the two terminal positions. Alternatively, the apparatus may be configured such that the vertical shutters stop moving before the horizontal shutters stop moving so as to allow the aperture to be changed from its smallest possible rectangular, non-squared shape to a corresponding minimally-sized square. In some embodiments, the x-ray apparatus may be configured such that the first angled slot extends towards a center of the first rotatable disk at a first angle, such that the second angled slot extends towards the center of the first rotatable disk at a second angle, and such that the first angle is greater than the second angle. In some such embodiments, the first angled slot may have a first radius of curvature, the second angled slot may have a second radius of curvature, and the first radius of curvature may be greater than the second radius of curvature. In some embodiments, a second shutter comprising a second plurality of protruding members may be provided. At least one of the second plurality of protruding members may be positioned within a third angled slot of the first plurality of angled slots, and at least one of the second plurality of protruding members may be positioned within a fourth angled slot of the first plurality of angled slots. The third angled slot may be configured to extend towards the center of the first rotatable disk at a third angle, wherein the third angle is at least substantially identical to the first angle. The fourth angled slot may extend towards the center of the first rotatable disk at a fourth angle, wherein the fourth angle is at least substantially identical to the second angle. In some embodiments, one or more of the rotatable disks may further comprise a plurality of protrusions positioned along at least a portion of a perimeter of the rotatable disk(s). Such protrusions may be configured to protrude beyond the perimeter of the rotatable disk(s) adjacent to the protrusions. These protrusions may be configured to allow a user to rotate the rotatable disk(s) in order to alter a size of the collimation aperture. The protrusions of one rotatable disk may be configured to have at least one of a different shape and a different size relative to the protrusions of another rotatable disk. In this manner, a user may be able to see and/or feel the difference between the two sets of protrusions to provide information about which shutter or shutters will be opened or closed by rotating the disk associated with the protrusions. In one particular embodiment of an x-ray apparatus, the apparatus may comprise an x-ray generator configured to generate x-ray electromagnetic radiation. The x-ray apparatus may further comprise a visible light generator configured to generate visible electromagnetic radiation. In some embodiments, the visible light generator may comprise a light-emitting diode. The visible light generator may be configured to deliver the visible electromagnetic radiation such that the visible electromagnetic radiation at least partially overlaps the x-ray electromagnetic radiation. In this manner, a user may be able to visualize the path of the x-ray radiation and determine a treatment or diagnosis area defined by the x-ray radiation delivered by the device. The collimation aperture may be configured to deliver overlapping radiation comprising x-ray electromagnetic radiation from the x-ray generator and visible electromagnetic radiation from the visible light generator, and may be configured to deliver the visible electromagnetic radiation in a visible target shape, and to deliver the x-ray electromagnetic radiation in an x-ray target shape. The size of the visible target shape may vary according to the size of the collimation aperture, and the size of the x-ray target shape may also vary according to the size of the collimation aperture. The x-ray apparatus may also comprise a first rotatable disk and a first shutter operably coupled with the first rotatable disk such that rotation of the first rotatable disk results in movement of the first shutter to alter the size of the collimation aperture. The x-ray apparatus may further comprise a mirror that is positioned and configured to reflect light from the visible light generator through the collimation aperture. The mirror may be transparent to x-ray electromagnetic radiation, and may be positioned in between the x-ray generator and the collimation aperture. In such embodiments, the mirror may be further configured such that x-ray electromagnetic radiation from the x-ray generator passes through the mirror before being delivered through the collimation aperture. The mirror may also comprise a silver coating, such as a silver oxide coating. In some embodiments, the x-ray generator may be positioned away from a center of the mirror by a first distance and the visible light generator may be positioned away from the center of the mirror by a second distance. The first distance may be at least substantially identical to the second distance. In yet another example of an embodiment of an x-ray apparatus, the apparatus may comprise an x-ray generator configured to generate x-ray electromagnetic radiation and a visible light generator configured to generate visible electromagnetic radiation. The visible light generator may be configured to deliver the visible electromagnetic radiation such that the visible electromagnetic radiation at least partially overlaps the x-ray electromagnetic radiation. The apparatus may further comprise a first rotatable disk comprising a first plurality of angled slots and a second rotatable disk comprising a second plurality of angled slots. The apparatus may also comprise a first shutter comprising a first plurality of protruding members. At least one of the first plurality of protruding members may be positioned within a first angled slot of the first plurality of angled slots, and at least one of the first plurality of protruding members may be positioned within a second angled slot of the first plurality of angled slots. Similarly, the apparatus may comprise a second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a first angled slot of the second plurality of angled slots, and wherein at least one of the second plurality of protruding members is positioned within a second angled slot of the second plurality of angled slots. As mentioned elsewhere herein, some embodiments may comprise four shutters, two of which oppose one another in a first direction and two of which oppose one another in a second direction at least substantially perpendicular to the first direction. The first and second shutters may at least partially define a collimation aperture, and the apparatus may be configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the collimation aperture, and such that rotation of the second rotatable disk results in movement of the second shutter to alter a size of the collimation aperture. The apparatus may be configured to deliver overlapping radiation comprising x-ray electromagnetic radiation from the x-ray generator and visible electromagnetic radiation from the visible light generator. The collimation aperture may be configured to deliver the visible electromagnetic radiation in a visible target shape and to deliver the x-ray electromagnetic radiation in an x-ray target shape, wherein the size of the visible target shape varies according to the size of the collimation aperture, and wherein size of the x-ray target shape also varies according to the size of the collimation aperture. In this manner, a user may be able to visualize and alter, if necessary, the bounds of the x-ray beam being delivered by the apparatus. In still another example of an embodiment of an x-ray apparatus, the apparatus may comprise an x-ray generator configured to generate x-ray electromagnetic radiation, a visible light generator configured to generate visible electromagnetic radiation, and a projection member comprising a material at least partially transparent to visible light. The projection member may comprise an image positioned within the path of the visible electromagnetic radiation so as to project a secondary image comprising a shadow defined by the image. In some embodiments, the projection member may comprise a reticle. The apparatus may also comprise a ranging beam configured to deliver a visible light beam at an angle relative to the visible electromagnetic radiation such that the visible light beam intersects at least a portion of the secondary image at a predetermined distance from the ranging beam. In some embodiments, the ranging beam may comprise a LASER configured to deliver a LASER beam at an angle relative to the visible electromagnetic radiation such that the LASER beam intersects at least a portion of the secondary image at a predetermined distance from the LASER. The x-ray apparatus may comprise a handheld x-ray apparatus. For example, the apparatus may comprise a handle configured to allow a user to hold and operate the x-ray apparatus with one hand. With respect to such embodiments, the ranging beam may be positioned on the handle. The handle may comprise a base configured to allow the x-ray apparatus to be placed upon a flat surface with only the base in contact with the flat surface, and the LASER may be positioned on the base. In embodiments in which the projection member comprises a reticle, the reticle may comprise a plurality of non-equidistant dash lines. The non-equidistant dash lines may be spaced apart by a greatest amount at a lower portion of the reticle and wherein the spacing between the non-equidistant dash lines grows progressively smaller from the lower portion of the reticle to an upper portion of the reticle. The apparatus may be configured such that at least some of the non-equidistant dash lines represent equidistant distances away from the x-ray generator and/or another fixed portion of the apparatus. To provide a more specific example, in some embodiments, the reticle may comprise a first dash line, a second dash line positioned adjacent to the first dash line, and a third dash line positioned adjacent to the second dash line. The first dash line may be spaced apart from the second dash line by a first length, the third dash line may be spaced apart from the second dash line by a second length less than the first length. In such embodiments, the apparatus may be configured such that an object intersecting the LASER beam at the first dash line is separated from the x-ray generator or another fixed point on the apparatus by a first distance, an object intersecting the LASER beam at the second dash line is separated from another fixed point on the apparatus by a second distance, and an object intersecting the LASER beam at the third dash line is separated from another fixed point on the apparatus by a third distance. The difference between the first distance and the second distance may be at least substantially identical to the distance between the second distance and the third distance. In some such embodiments, the reticle may therefore be configured such that the spacing with respect to adjacent dash lines is non-equidistant, but the corresponding distances between the locations at which the ranging beam intersects such adjacent dash lines are equidistant. Some embodiments may further comprise a collimation aperture configured to deliver overlapping radiation comprising x-ray electromagnetic radiation from the x-ray generator and visible electromagnetic radiation from the visible light generator. The size of the secondary image may vary according to the size of the collimation aperture. In another specific example of an embodiment of an x-ray apparatus, the apparatus may comprise an x-ray generator configured to generate x-ray electromagnetic radiation, a visible light generator configured to generate visible electromagnetic radiation, and a reticle comprising a material at least partially transparent to visible light. The reticle may comprise a plurality of non-equidistant dash lines positioned within the path of the visible electromagnetic radiation so as to project an image comprising a shadow defined by the dash lines. Such a plurality of dash lines may comprise a first dash line, a second dash line positioned adjacent to the first dash line, wherein the first dash line is spaced apart from the second dash line by a first length, and a third dash line positioned adjacent to the second dash line, wherein the third dash line is spaced apart from the second dash line by a second length. The first length may be greater than the second length such that the dash lines are non-equidistant. The apparatus may further comprise a ranging beam configured to deliver a visible light beam at an angle relative to the visible electromagnetic radiation such that the visible light beam intersects at least a portion of the image at a predetermined distance from the ranging beam. The apparatus may be configured such that an object intersecting the ranging beam at the first dash line is separated from another fixed point on the apparatus by a first distance, such that an object intersecting the ranging beam at the second dash line is separated from another fixed point on the apparatus by a second distance, and such that an object intersecting the ranging beam at the third dash line is separated from another fixed point on the apparatus by a third distance. The difference between the first distance and the second distance may be at least substantially identical to the distance between the second distance and the third distance. Another embodiment may comprise an x-ray generator configured to generate x-ray electromagnetic radiation, and a visible light generator, such as an LED, that is configured to generate visible electromagnetic radiation. The apparatus may further comprise a projection member comprising a material at least partially transparent to visible light, wherein the projection member comprises an image positioned within the path of the visible electromagnetic radiation so as to project a secondary image comprising a shadow defined by the image. The apparatus may also comprise a ranging beam configured to deliver a visible light beam at an angle relative to the visible electromagnetic radiation such that the visible light beam intersects at least a portion of the image at a predetermined distance from the ranging beam. Some embodiments may also comprise a collimator. Such a collimator may comprise one or more rotatable disks. The collimator may further comprise a first shutter at least partially defining a collimation aperture, wherein the first shutter is operably coupled with a first rotatable disk such that rotation of the first rotatable disk moves the first shutter to alter a size of the collimation aperture. Similarly, a second shutter at least partially defining the collimation aperture may be operably coupled with a second rotatable disk such that rotation of the second rotatable disk moves the second shutter to alter a size of the collimation aperture. The apparatus may be configured such that the collimation aperture at least partially defines a size of the secondary image and such that the collimation aperture at least partially defines a size of an x-ray target shape delivered by the x-ray generator. As described earlier, rotation of the first rotatable disk through a first angle may result in movement of the first shutter of a first distance, and rotation of the second rotatable disk through the first angle may result in movement of the second shutter of a second distance, wherein the first distance differs from the second distance. As also described above, the first rotatable disk may comprise a first plurality of angled slots and a second plurality of angled slots. The first shutter may comprise a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots. At least one of the first plurality of protruding members may be positioned within a second angled slot of the first plurality of angled slots. The first angled slot may extend towards a center of the first rotatable disk at a first angle, and the second angled slot may extend towards the center of the first rotatable disk at a second angle, wherein the first angle is greater than the second angle. Like other embodiments previously described, the first rotatable disk may comprise a plurality of protrusions positioned along at least a portion of a perimeter of the first rotatable disk, and the second rotatable disk may comprise a plurality of protrusions positioned along at least a portion of a perimeter of the second rotatable disk. The first plurality of protrusions may protrude beyond the perimeter adjacent to the protrusions, and may be configured to allow a user to rotate the first rotatable disk in order to alter a size of the collimation aperture. Similarly, the second plurality of protrusions may be configured to allow a user to rotate the second rotatable disk in order to alter a size of the collimation aperture. In some embodiments, the first plurality of protrusions may be configured to have a distinct tactile feel relative to the second plurality of protrusions such that a user can distinguish the first plurality of protrusions from the second plurality of protrusions by way of tactile feel alone. In the following description, numerous specific details are provided for a thorough understanding of the various embodiments disclosed herein. The systems and methods disclosed herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In addition, in some cases, well-known structures, materials, or operations may not be shown or described in detail in order to avoid obscuring aspects of the disclosure. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more alternative embodiments. The present disclosure describes various examples of apparatus, systems, and methods relating to the delivery of radiation, such as x-ray radiation, for medical diagnosis and/or treatment. Details of certain embodiments will now be described in greater detail with reference to the accompanying drawings. FIG. 1 depicts an x-ray apparatus at 100. As shown in this figure, x-ray apparatus 100 comprises a handle 110, a collimator 120, cage 170, and inclinometer 175. Cage 170 may comprise an at least partially conical shape. In some embodiments, the shape of cage 170 may at least substantially coincide with the shape of the x-ray beam delivered from x-ray apparatus 100. Knowledge of the angle of inclination of an x-ray apparatus can be extremely important for certain types of x-rays. For example, in podiatry, it is often necessary to take an x-ray with the x-ray source located at a specific, known angle relative to the patient's foot. Additionally, for certain x-rays, it may be desirable for the user of an x-ray apparatus to know the angle at which an x-ray is taken in order that subsequent x-rays of the same patient may be taken at the same angle. Thus, embodiments of x-ray apparatus may comprise an inclinometer 175 to provide a user with information about the angle at which x-ray radiation is being delivered. Inclinometer 175 may be used to measure such an angle of inclination of x-ray apparatus 100 at the time of exposure with respect to the ground (perpendicular to the direction of the force of gravity). Inclinometer 175 may immediately provide an indication to a user of the angle of inclination for the orientation of the imaged object. Inclinometer 175 may comprise four angle pointers which pivot on a central axle and may be weighted to maintain its orientation to the natural horizon during movement of the x-ray apparatus 100. In some embodiments, the four angle pointers may allow the angle of inclination to be read from any position, including for example from the top, bottom, or side of the device. This feature may be provided in some embodiments by having one or more of the pointers extend away from the body/frame of x-ray apparatus, and by providing a transparent window that allows for viewing the pointers not only from the face of inclinometer 175 but also from above or below inclinometer 175. In some embodiments, one or more sensors may be provided adjacent to particular locations on inclinometer 175. Such sensors may sense the location of one or more of the pointers and may transfer this information to a CPU and/or memory of the device. This information may then, in some embodiments, be transferred to one or more displays, such as a digital display, to provide information to the user about the angle of inclination. This data may also be stored by x-ray apparatus 100 and electronically linked with a particular x-ray image so that a physician or other such person may be able to view an inclination angle while viewing a particular x-ray image. Inclinometer 175 may be permanently affixed to the x-ray apparatus 100 or, alternatively, may comprise a portable, stand-alone device that can be attached to x-ray apparatus 100. X-ray apparatus 100 and/or inclinometer 175 may therefore comprise a clip or other temporary mounting means that allows inclinometer 175 to be removably attached to a particular location on x-ray apparatus 100. Once imaging is completed, or once the angle is noted, inclinometer 175 may be removed from x-ray apparatus 100 and retained by the user for a later use. As mentioned above, x-ray apparatus 100 may further comprise a memory module which is configured to record and store the angle of inclination at the time of imaging. This module and/or another such module may also be configured to link the angle with the image. X-ray apparatus 100 may also include an output module for passing the angle of inclination to another device to upload the information for later use. Inclinometer 175 may have one or more angle pointers that pivots on a central axle and are weighted to maintain their respective orientations to the natural horizon. The angle pointers on the depicted embodiment extend from the central axle at 0, 90, 180, and 270 degrees. When x-ray apparatus 100 is tilted or angled, the angle pointers remain at their original orientations with respect to the horizon, but their positions relative to the markers/display on inclinometer 175 change to display the angle at which the x-ray apparatus 100 is located relative to the horizon. Inclinometer 175 may also comprise a clear cover having one or more angle indicators with degree markings which may be used to accurately read the angle of inclination. The degree markings may surround the outer edge of the cover and be on at least one of the side and face of the cover. The cover may be divided into four equal quadrants. The degree markings may indicate degrees from zero to 45 degrees and then back to zero degrees, such markings may be in five degree increments. The degree markings may be of different lengths to indicate different increments. The user may be able to visually read the angle by looking through the cover and noting which degree marking the angle pointer is closest to. Since inclinometer 175 has four different quadrants and four pointers the angle can be read from the top, bottom, or either side of the display. This feature may be useful for a handheld x-ray apparatus, such as x-ray apparatus 100. As a user moves the apparatus, the user may use the device to easily note the angle of inclination. Handle 110 comprises a handle base 112 comprising a battery 114. Handle 110 may be configured to allow the x-ray apparatus 100 to be stably positioned upon a flat surface with only the base 112 (battery 114 and/or the bottom surface of the remaining portion of base 112 in the absence of battery 114) in contact with the flat surface. A trigger 116 may also be provided. Trigger 116 may be used to initiate generation of x-ray or other radiation from the device. Trigger 116 may also, or alternatively, be used to actuate and/or alter a feature of some other mechanism, such as a ranging beam 113—which is shown positioned on handle base 112 in FIG. 2—and/or a visible light generator 190. In some embodiments, trigger 116 may comprise multiple parts that may be actuated independently. Alternatively, or additionally, trigger 116 or one or more subparts to trigger 116 may be configured such that a first pull or a partial pull results in actuation of a first mechanism and a second pull or a further pull results in actuation of a second mechanism. FIG. 2 is a cross-sectional view of x-ray apparatus 100. As shown in this figure, x-ray apparatus 100 further comprises an x-ray delivery shield 180 configured to deliver x-ray radiation from an x-ray source 182. As those of ordinary skill in the art will appreciate, x-ray source 182 may comprise an electron-beam vacuum tube that generates x-rays when an electron beam impinges on a metal anode. Other examples of x-ray sources include radioactive isotopes, synchrotrons, or other radiation-generating machines, secondary x-ray sources, such as those generated by x-rays, charged particles, gamma-rays, or other higher-energy radiation impinging on a material that then fluoresces secondary x-rays, and spark-gaps or other electrical discharge sources that generate x-rays. X-ray apparatus 100 may be configured to deliver x-ray radiation in the form of a cone directed towards an object to be examined or towards an x-ray-sensitive sensor, such as a photographic plate or a digital sensing means, for example. X-ray source 182 may be configured to emit x-ray radiation from one point on x-ray source 182. In order to facilitate delivery of x-ray radiation in the form of a cone, x-ray delivery shield may have an at least substantially conical, or frusto-conical, shape. The radiation cone may generally have crosswise dimensions which are greater than the dimensions of the object to be examined or the sensing means. A mirror 185 may be positioned within x-ray delivery shield 180. Mirror 185 may be positioned and configured to reflect light from a visible light generator 190. In some embodiments, visible light generator may comprise an LED. Mirror 185 may also be configured so as to be transparent, or at least substantially transparent, to x-ray radiation, such that mirror 185 may be positioned such that x-ray source 182 may deliver x-ray radiation that passes through mirror 185 before being delivered outside of x-ray apparatus 100. In some embodiments, mirror 185 may also comprise a silver coating, such as a silver oxide coating. In some embodiments, the x-ray source/generator 182 may be positioned away from a center of mirror 185 by a first distance and the visible light generator 190 may be positioned away from the center of the mirror by a second distance that is at least substantially identical to the first distance. In some embodiments, mirror 185 may also be angled and/or otherwise configured such that visible light being delivered from x-ray apparatus 100 is delivered in an at least substantially conical shape that may be at least substantially identical to the shape of the x-ray beam being delivered from x-ray apparatus 100. X-ray delivery shield 180 may also contribute to forming a desirable shape, such as a conical shape, for the visible light being delivered from the device by way of visible light generator 190. FIGS. 3-5 depict an embodiment of a collimator 120. As described in greater detail below, collimator 120 may be positioned between x-ray source 182 and the object to be examined and/or treated with the x-ray radiation. This may allow for a portion of the x-ray beam to be blocked off whereby radiation is only, or at least primarily, applied to the object to be examined inside an examination region or in a region corresponding to a radiation sensor. Collimator 120 may be adjustable to allow for different examinations. The ideal dimensions of an x-ray signal are often dependent on the particular application involved. For example, in certain types of diagnostic radiology, an x-ray beam having a relatively large pattern may be used to produce images of relatively large portions of a patient's body. At other times, a smaller and more focused x-ray beam may be used to produce detailed images of relatively small portions of a patient's body, such as regions of the head, for instance. The adjustment of collimator 120 may also protect the safety of a patient and/or healthcare provider from unnecessary radiation exposure. It may therefore be desirable for the collimator 120 to be capable of a high degree of positional accuracy to ensure an accurate x-ray dosage to the patient through a well-defined aperture, and to prevent accidental exposure of others. The rotatable disks may be made of any material that allows the parts to function as described herein, such as polyethylene or another polymer, for example. It should also be noted that other embodiments are contemplated that are not limited to collimating x-rays. Other embodiments could also be used for collimating other types of radiation. As described in greater detail below, the shutters used with collimator 120 may be at least substantially planar. In some embodiments, one or more horizontal shutters may be provided and one or more vertical shutters may also be provided. The horizontal shutter(s) may be mounted in a common plane, and the vertical shutter(s) are mounted in a common plane parallel to that of the horizontal shutters, but slightly offset to allow the shutters to open and close without mechanical interference. The shutters can be made of any x-ray opaque material. In some embodiments, the rotatable disks may also be made of and/or coated with an x-ray opaque material, but other embodiments are contemplated in which the rotatable disks are not made up of such a material. This is because the device may be configured with an x-ray delivery shield, as discussed below, that may deliver the x-ray radiation in such a manner that the shutters alone, if made up of an x-ray opaque material, are sufficient to fully or at least sufficiently contain the x-ray beam. This may provide for cost savings and/or weight reduction in such embodiments since x-ray opaque materials tend to be more costly and heavier than x-ray transparent materials. FIG. 3 is a perspective view of collimator 120. FIG. 4 is another perspective view of the collimator depicted in FIG. 3, shown from the side opposite to the side depicted in FIG. 3. FIG. 5 is an exploded view of the collimator depicted in FIGS. 3 and 4. As shown in these figures, collimator 120 comprises a rear rotatable disk 122, a front rotatable disk 132, a center plate 140, and a front disk cover 150. Each of these components comprises a central opening. Namely, rear rotatable disk 122 comprises central opening 128, front rotatable disk 132 comprises central opening 138, center plate 140 comprises central opening 148, and front disk cover 150 comprises central opening 158. Openings 128, 138, 148, and 158 allow for the passage of x-rays. Although these openings are shown in the drawings as being circular, other embodiments are contemplated in which one or more such openings are of a different shape, including but not limited to a rectangle, oval, etc. The inner edge of one or more of the rotatable disks (i.e. edge surrounding the central openings) may be coated in or otherwise made of an x-ray opaque material. Front and front rotatable disks 122 and 132, respectively, are each operatively coupled with two separate shutters that are configured to move when the rotatable disks are rotated. More particularly, rear rotatable disk 122 is operatively coupled with shutters 153 and 155. Similarly, front rotatable disk 132 is operatively coupled with shutters 157 and 159. When rear rotatable disk 122 is rotated in a first direction, shutters 153 and 155 are approximated. Otherwise stated, when rear rotatable disk 122 is rotated in a first direction, shutters 153 and 155 are approximated so as to move in directions at least substantially opposite from one another such that these two shutters close towards one another. When rear rotatable disk 122 is rotated in a second direction opposite from the first direction, shutters 153 and 155 move in directions at least substantially opposite from one another such that these two shutters open away from one another. Similarly, when front rotatable disk 132 is rotated in a first direction, the other two shutters, namely, shutters 157 and 159, move in directions at least substantially opposite from one another such that these two shutters close towards one another. In addition, when front rotatable disk 132 is rotated in a second direction opposite from the first direction, shutters 157 and 159 move in directions at least substantially opposite from one another such that these two shutters open away from one another. However, shutters 157 and 159 may be configured to move in directions at least substantially perpendicular to the directions in which shutters 153 and 155 move. In some embodiments, shutters 153 and 155 may therefore be configured to move in at least substantially horizontal directions, and shutters 157 and 159 may be configured to move in at least substantially vertical directions when x-ray apparatus 100 is in an upright position. Some embodiments may further be configured such that the collimation aperture defined by shutters 153, 155, 157, and 159 cannot be fully closed. For example, one or more of the shutters may be configured such that movement in a direction to decrease the size of the collimation aperture is prevented before the collimation aperture is entirely closed by the shutters. This may be useful for certain embodiments that provide a visual indication of an x-ray target to prevent the visual indication from completely disappearing. In this manner, a user may be provided with a visual indication of the treatment/diagnosis area at all times during operation, or at least during all times in which an x-ray beam is being delivered. In some embodiments, the x-ray apparatus 100 may be configured such that the rear rotatable disk 122 can be rotated independently of the front rotatable disk 132. In addition, in some embodiments, the x-ray apparatus 100 may be configured such that rotation of the rear rotatable disk 122 through a first angle results in movement of the shutters 153 and/or 155 of a first distance, such that rotation of the front rotatable disk 132 through the first angle results in movement of shutters 157 and/or 159 of a second distance, wherein the first distance differs from the second distance. This feature may be useful for embodiments having a rectangular, non-square field-of-view, such as embodiments designed to match up with a 10 inch×12 inch detector, for example. With regard to such embodiments, it may be useful to configure x-ray apparatus 100 such that the horizontal shutters (shutters 153 and 155, for example) move farther than the vertical shutters (shutters 157 and 159, for example) for the same amount of rotation of the rotatable disks in order to maintain a constant horizontal to vertical “aspect ratio” throughout at least a portion of the whole range of motion. Some embodiments, however, may be configured such that the aspect ratio changes slightly throughout the rotation. For example, in some embodiments, the largest size of the collimation aperture may be a rectangle with a given aspect ratio, such as 10×12, and the smallest size of the collimation aperture may a square. Thus, the two rotatable disks may be configured such that equal rotation angles result in different shutter movement speed (due to different slot angling between the front and rear rotatable disks) to allow for constant adjustment of the aspect ratio between the two terminal positions. In other embodiments, the x-ray apparatus 100 may be configured such that the vertical shutters stop moving before the horizontal shutters stop moving so as to allow the aperture to be changed from its smallest possible rectangular, non-squared shape to a corresponding minimally-sized square. In such embodiments, the aspect ratio, and the shutter movement speed per given rotation, may be constant throughout the rotation movement until the movement is stopped on one of the rotatable disks. FIGS. 3-5 also depict a series of angled slots. More particularly, rear rotatable disk 122 comprises angled slots 123-126 and front rotatable disk 132 comprises angled slots 133-136. Each of the shutters comprises a plurality of protruding members. Namely, shutter 153 comprises two opposing protruding members, identified at 154 and 154′ in the drawings and, similarly, shutter 155 comprises two opposing protruding members identified at 156 and 156′. Likewise, shutter 157 comprises two opposing protruding members 158 and shutter 159 comprises two opposing protruding members 160. In embodiments configured to provide for a constant aspect ratio, the angled slots 123-126 of rear rotatable disk 122 may comprise angles that differ from the angles of angled slots 133-136 of front rotatable disk 132. By providing, for example, for steeper angled slots on a rotatable disk that is operably coupled with vertical shutters, such vertical shutters may be configured to move a greater distance with an equivalent amount of rotation relative to the horizontal shutters in order to provide for a collimation aperture with at least a substantially constant aspect ratio. Other embodiments may be configured such that the front and front rotatable disks are coupled with one another such that rotation of one disk results in rotation of the other disk. Such embodiments may further be configured, if desired, to maintain a constant aspect ratio. For example, a rotation of a first disk may result in a greater amount of rotation of a second disk. Similarly, a rotation of the second disk may result in a lesser amount of rotation of the first disk in order to maintain a constant aspect ratio. The term “slot” is intended to be broadly interpreted to include any type of channel, hole, track, or sliding mechanism that allows the protruding members to slide or otherwise move within the slot and to transfer a rotational motion to an appropriate translation or other movement of one or more corresponding shutters. The angled slots may be of an appropriate length to allow the shutters to move from a fully open position to a closed, or a nearly closed position. The protruding members may, in some embodiments, be made of the same material as the shutters, and may be integrally formed with the shutters in some embodiments. Alternatively, the protruding members may be attached to a shutter, for example, by an adhesive, and be made up of any material which allows them to slide within an angled slot. Although the protruding members in the depicted embodiment are circular, it should be noted that the protruding members could be any shape or size that allows them to slide within an angled slot. In some embodiments, at least one of a first plurality of protruding members of a single shutter may be positioned within a first angled slot of the first plurality of angled slots, and at least one of the first plurality of protruding members of the same shutter may be positioned within a second angled slot of the first plurality of angled slots. This configuration may provide stability to prevent the shutter from pivoting with respect to a single protruding member and/or to prevent binding of the shutters. For example, in the depicted embodiment, two separate protruding members 154 and 154′ of a single shutter 153 may be positioned within two different angled slots of rear rotatable disk 122, namely, angled slots 124 and 125. Similarly, two separate protruding members 156 and 156′ of another single shutter 155 may be positioned within two different angled slots of rear rotatable disk 122, namely, angled slots 123 and 126. With respect to the shutters operatively coupled with the front rotatable disk 132, the configuration may operate in a similar manner. For example, two separate protruding members 158 of shutter 157 may be positioned within two different angled slots, namely, angled slots 133 and 135. Similarly, two separate protruding members 160 of another shutter 159 may be positioned within two different angled slots, namely, angled slots 134 and 136. In some embodiments, x-ray apparatus 100 may be configured such that one or more of the angled slots extends towards the center of its respective rotatable disk at a different angle than one or more other such angled slots. For example, in some embodiments, a first angled slot may extend towards a center of the rear rotatable disk 122 at a first angle and a second angled slot may extend towards the center of the rear rotatable disk 122 at a second angle that differs from the first angle. In some such embodiments, the first angled slot may have a first radius of curvature, the second angled slot may have a second radius of curvature, and the first radius of curvature may be greater than the second radius of curvature. For example, with reference again to the collimator 120 depicted in FIGS. 3-5, opposing slots 125 and 126 of rear rotatable disk 122 extend towards center opening 128 at a steeper angle/rate than opposing slots 123 and 124. Similarly, opposing slots 133 and 134 of front rotatable disk 132 extend towards center opening 138 at a steeper angle/rate than opposing slots 135 and 136. This configuration may be desirable in order to maintain a substantially parallel movement of one or more shutters during rotation of the disk that is operatively coupled therewith. In some embodiments, one or more of the slots of a particular rotatable disk may also have a different width than one or more of the remaining slots of the rotatable disk. For example, as best seen in FIG. 3, opposing slots 125 and 126 in rear rotatable disk 122 are narrower than opposing slots 123 and 124. Similarly, as best seen in FIG. 5, opposing slots 133 and 134 in front rotatable disk 132 are narrower than opposing slots 135 and 136. One or more of the protruding members may similarly have a greater width than one or more of the remaining protruding members of a particular shutter and/or of those operatively coupled with a particular rotatable disk. For example, with reference again to FIG. 3, one of the two protruding members 154′ may be wider than the other protruding member 154 on the same shutter 153. Likewise, one of the two protruding members 156′ on shutter 155 may be larger than the other protruding member 156. As such, collimator 120 may be configured such that the larger of the two protruding members on shutter 155 (protruding member 156′) will not fit within slot 126 and the larger of the two protruding members on shutter 153 (protruding member 154′) will not fit within slot 125. This configuration may be substantially repeated on the front rotatable disk 132. This configuration may be useful in facilitating assembly of collimator 120, including restricting or preventing misassembly of collimator 120. As further depicted in FIGS. 3-5, front rotatable disk may comprise one or more assembly slots 127 and 162. Assembly slots 127 are positioned around the periphery of rotatable disk 122 and extend in a curved path at least substantially corresponding to the curvature of rotatable disk 122. One or more of the peripheral assembly slots 127 may be configured to have a larger size than the remaining peripheral assembly slots 127. In this manner, proper assembly of collimator 120 may be facilitated and misassembly prevented or at least reduced. For example, one or more protruding assembly pieces 166 may be positioned to extend from another portion of the device, such as from the front disk cover 150 in the depicted embodiment. Protruding assembly pieces 166 may be configured to extend through one or more other pieces in the assembly making up collimator 120. For example, protruding assembly pieces 166 may extend through peripheral assembly slots 137 in front rotatable disk 132, through peripheral assembly slots 147 in center plate 140, and then through peripheral assembly slots 127 in rear rotatable disk 122. In embodiments in which one or more of the peripheral assembly slots 127 is larger than the remaining slots, a corresponding number of protruding assembly pieces 166 may be larger than the remaining protruding assembly pieces. In this manner, incorrect assembly can be prevented or at least reduced. To further reduce the possibility of incorrect assembly, another assembly slot 162 may be formed on rear rotatable disk 122. Similarly, another assembly slot 164 may be formed on front rotatable disk 132. Assembly slot 162 may be configured to receive a pin 163, or another equivalent protruding member, formed on center plate 140. A similar pin 168 or equivalent protruding member may be formed on front disk cover 150 and may be configured to be received within a similar assembly slot 164 formed within front rotatable disk 132. By positioning assembly slot 162 at a different location and/or with different dimensions relative to assembly slot 164, misassembly of x-ray apparatus 100 may be prevented or at least inhibited. One or more fastening members 152 may also be used to secure the various components of collimator 120 together. In addition, one or more spring members 121 may be formed upon one or more of the components making up collimator 120. For example, in the depicted embodiment, rear rotatable disk 122 comprises four spring members 121 that extend towards the exterior of collimator 120. Similarly, front rotatable disk 132 comprises four spring members 119 that extend towards front disk cover 150. Spring members 119 and 121 may help prevent collimator 120 and/or one or more of its internal components from being broken or rattling during use. These components may also allow for gaps in the parts stack to improve tolerance requirements. In addition, spring members 121 may allow for wear over time without allowing various components of the mechanism to become loose or damaged. In some embodiments, one or more of the rotatable disks may further comprise a plurality of protrusions positioned along at least a portion of a perimeter of the rotatable disk(s). Such protrusions may be configured to protrude beyond the perimeter of the rotatable disk(s) adjacent to the protrusions. These protrusions may be configured to allow a user to rotate the rotatable disk(s) in order to alter a size of the collimation aperture. For example, in the depicted embodiment, a plurality of protrusions 129 are positioned along the perimeter of rear rotatable disk 122 and a plurality of protrusions 139 and positioned along the perimeter of front rotatable disk 132. Protrusions 129 and/or 139 may comprise tabs, knobs, handles, or teeth, for example, that extend from an outer edge of a rotatable disk. As shown in the accompanying drawings, the rotatable disks may be shaped like a sprocket and may have many protrusions extending from the outer edge of the disks. The protrusions may allow the disks to be rotated by hand in either a clockwise or counter-clockwise direction. The protrusions may be used to simplify manual adjustment of the circular disk and to provide a visual indicator of the shutter positions. The protrusions and/or another component of the collimator that does not rotate with the protrusions may have markings and/or indentations to indicate the location of the shutters in a particular configuration. In some embodiments, the protrusions may be engaged with a motor or other mechanical actuation means to provide for automated movement of the disks, and therefore shutters. The protrusions of one rotatable disk may be configured to have at least one of a different shape and a different size relative to the protrusions of another rotatable disk. In this manner, a user may be able to see and/or feel the difference between the two sets of protrusions to provide information about which shutter or shutters will be opened or closed by rotating the disk associated with the protrusions. For example, in the depicted embodiment, protrusions 129 are smaller than protrusions 139. In addition, the device is configured such that protrusions 129 can be positioned within recesses defined by protrusions 139 in a particular configuration. X-ray apparatus 100 may, in some embodiments, be configured such that each configuration in which protrusions 129 are interleaved between protrusions 139 is a stable configuration. In other words, the device may be configured such that rotation of one of the rotatable disks with respect to the other continues in a smooth manner until protrusions 129 are positioned in between protrusions 139, at which point the two disks have a tendency to stay in such a configuration and additional force is required to continue such a rotation action. In some embodiments, each stable configuration in which protrusions 129 are positioned in between protrusions 139 may correspond with a particular, desired size of the collimation aperture, such as a size corresponding to a common treatment, diagnosis, and/or sensor size at a particular distance. In some embodiments, markings may also be provided on the protrusions and/or on another part of the device that does not rotate with the rotatable disks in order to provide information to a user about the size/status of the collimation aperture. FIG. 6 is a cross-sectional view depicting certain internal components of an embodiment of an x-ray apparatus, including x-ray source 182, which is depicted as a point source, mirror 185, visible light generator 190, and x-ray delivery shield 180. FIG. 6 also depicts certain components of collimator 120. As this figure indicates, light from visible light generator 190 is directed towards mirror 185, which is positioned at an appropriate angle to direct such light towards an exit defined at least partially by x-ray delivery shield 180. X-ray radiation from x-ray source 182 is also delivered through x-ray delivery shield 180, and may be delivered through mirror 185, which may be transparent to x-ray radiation. As further indicated in this figure, one or more of the shutters used with collimator 120 may have angled edges in order to provide more well-defined borders to a visible light target shape delivered by visible light generator 190 through collimator 120, and/or to similarly provide more well-defined borders to an x-ray target shape delivered by x-ray source 182 through collimator 120. For example, as shown in FIG. 6, instead of being at right angles relative to the front and back surfaces of shutters 157 and 159, edge 167 of shutter 157 is angled and edge 169 of shutter 159 is angled to at least substantially match the angle of the conical shape of visible light delivered by visible light generator 190 and/or to at least substantially match the angle of the conical shape of x-ray radiation delivered by x-ray source 182. It should be further understood that, although the edges of shutters 153 and 157 of rear rotatable disk 122 are not visible in FIG. 6, such edges may be similarly angled such that all four sides (four embodiments having a collimation aperture defining a rectangular-shaped target shape) of the target shape have relatively well-defined borders. FIG. 7 is a close-up, cross-sectional view of a handle base 112 including a ranging beam 113 according to one embodiment of x-ray apparatus 100. Ranging beam 113 may comprise a LASER. As shown in the figure, LASER 113 is positioned at a distance D1 from a bottom surface of handle base 112 and is angled upward from the bottom surface of handle base 112. The angle at which LASER 113 is angled upward is A1. As those of ordinary skill in the art will appreciate, the values of D1 and A1 may be adjusted so as to configure the ranging beam 113 to intersect the projection of reticle or another projection member image at a desired distance. Ranging beam 113 may be configured to deliver a visible light beam, such as a LASER in certain embodiments, at an angle relative to the visible electromagnetic radiation delivered by visible light generator 190 such that the visible light beam from ranging beam 113 intersects at least a portion of a projected image projected by visible light generator 190 at a predetermined distance from the devices, such as from ranging beam 113, for example. In this manner, a user may be able to visualize one or more distances at which a treatment, diagnosis, or other similar use of the device may be applied. The ranging beam 113 and related concepts presented herein may be used on an x-ray apparatus, as described in great detail herein, but may also be useful on other devices such as rifles and other firearms, photography, lab equipment, and other applications where it is useful to determine and provide a visualization of a distance from an object. In addition, although ranging beam 113 is shown as being located near the bottom of handle 110 in the handheld x-ray apparatus 100 depicted in the drawings, in other embodiments the ranging beam 113 may be located elsewhere on the device. For example, in a non-handheld x-ray apparatus, the ranging beam may be located above or below the clear window of the projection member at an appropriate distance to intersect the crosshair reticle or other projected image. The ranging beam may be at a fixed location and angle or, in other embodiments, the location and/or angle of the ranging beam may be adjustable. Further, the apparatus may be configured such that the ranging beam adjustments may be done by hand or the device may include an adjustment module which is configured to adjust the laser to a specific angle automatically after receiving user input for a desired angle and/or distance. For example, in some embodiments, the x-ray apparatus may comprise a user input that allows a user to input a particular angle and/or focus distance. The ranging beam may then be configured to automatically adjust to the distance and/or angle input in order to place the ranging beam at the center of the reticle or projected image from the projection member at the distance input. Similarly, the x-ray apparatus may be configured such that the ranging beam is manually adjustable and the angle is automatically translated into a distance measurement at which the ranging beam will intersect a particular portion of the projected image, such as at the center of a cross-hair reticle. The distance may then be provided to the user on a display. X-ray apparatus 100 may also be configured with a projection member that may be configured to work in conjunction with visible light generator 190 in order to project an image that may be used with ranging beam 113 to determine a desired treatment/diagnosis distance. For example, FIG. 8 is a perspective view depicting one embodiment of a projection member 200. Projection member 200 comprises a reticle. However, it should be understood that a wide variety of alternative projection members may be used, as will be apparent to one of ordinary skill in the art after having received the benefit of this disclosure. A light field may be transmitted through reticle 200, which may comprise a clear window, to thereby project an image of the reticle on a wall or object. As described elsewhere herein, a LASER or another ranging beam may be placed outside of the light field and directed at an angle towards the light field. The ranging beam may be positioned and angled to intersect a specific location along the projected reticle. The angle of the ranging beam can be adjusted to insure that the intersection of the projected reticle and laser is at the specific distance. The clear window may be made of any material that is transparent to both visual light and x-rays, such as glass or polycarbonate for example, to allow the light field and x-ray field to travel through without being distorted. The clear window may have a reticle, such as a cross-hair reticle, or another projection member printed, etched, or otherwise disposed on the clear window. The cross-hair reticle may be any desirable pattern or grid. The intersection of two primary cross-hairs may delineate the center of the clear window, and may also delineate the center of the x-ray field when the x-ray apparatus is in use. Projection member 200 may comprise a material at least partially transparent to visible light. The projection member 200 may also comprise an image positioned within the path of visible electromagnetic radiation, such as light from visible light generator 190 so as to project an image comprising a shadow defined by the image. For example, in embodiments in which projection member 200 comprises a reticle, such as the embodiment depicted in FIG. 8, the image may comprise a plurality of dash lines that may be projected in an image with the dash lines defining shadows from light generated from visible light generator 190. The ranging beam and the projected cross-hair reticle or other projected image from a projection member may create a parallax effect. This parallax effect can be used to define a specific distance from the x-ray device where the ranging beam and the projected cross-hair reticle intersect. The target intersection of the ranging beam and projected cross-hair reticle may therefore be configured to take place at a specific desired distance. The location and/or angle of the ranging beam can be adjusted so the intersection occurs at the center of the cross-hair reticle, or at a different marking on the projected cross-hair reticle. Once the target intersection is known and the device is in use, the intersection of the ranging beam and cross-hair reticle can be adjusted by moving the x-ray device closer or further away from the starting location. For example, in some embodiments, a LASER may be positioned at a specific angle to intersect the cross-hair reticle at 28 inches from the x-ray source. The distance of 28 inches may be chosen for certain applications because this may be the distance necessary to produce a 10 inch by 12 inch x-ray size, a common size used in the detector industry. In this embodiment, the specific angle of the LASER may be about 19.5 degrees from the natural horizon. The center of the cross-hair reticle may be projected 28 inches in front of the x-ray radiation source. In some embodiments, the cross-hair reticle and laser may be fixed in location such that the angle and location can only be adjusted before the device is in use. A user can move the x-ray device closer or further away from the starting location until the LASER intersects the projected cross-hair reticle at the center marking, thereby ensuring that the x-ray radiation source is 28 inches from the intersection. In embodiments in which the projection member comprises a reticle, the reticle may comprise a plurality of non-equidistant dash lines. For example, with reference again to the embodiment depicted in FIG. 8, reticle 200 comprises a plurality of non-equidistant dash lines positioned along a vertical cross bar 210. Vertical cross bar 210, along with a corresponding horizontal cross bar 230, may together define cross hairs defining a target. The target area defined by vertical cross bar 210 and horizontal cross bar 230 may be further delineated by a target marker 220. In the depicted embodiment, target marker 220 comprises a circle. By providing a target marker 220, a user may be able to position x-ray apparatus 100 such that a LASER or another light projected from ranging beam 113 hits a particular location on a patient's body or on a sensor with the LASER positioned within the bounds of target marker 220 in order to precisely determine a desired treatment/diagnosis area. The non-equidistant dash lines may be spaced apart by a greatest amount at a lower portion of the reticle 200. The spacing between the non-equidistant dash lines may also grow progressively smaller from the lower portion of the reticle 200 to an upper portion of the reticle 200. For example, in the embodiment depicted in FIG. 8, dash line 212, which is the lower-most dash line in reticle 200, is positioned adjacent to dash line 214 by a first distance. Dash line 216 is positioned adjacent to dash line 214 by a second distance less than the first distance. Dash line 216 is positioned adjacent to horizontal cross marker 230 (which may, in some embodiments, also serve functionally as a dash line) by a third distance less than the second distance. Similarly, dash line 218, which is above horizontal cross bar 230, is positioned adjacent to horizontal cross bar 230 by a fourth distance less than the third distance. Dash line 222 is positioned adjacent to dash line 218 by a fifth distance less than the fourth distance. And, finally, dash line 224 is positioned adjacent to dash line 222 by a sixth distance less than the fifth distance. In some embodiments, the positioning of the non-equidistant dash lines may be specifically configured such that at least some of the non-equidistant dash lines represent equidistant distances away from the x-ray generator and/or another fixed point on the apparatus. In other words, the placement of the non-equidistant dash lines may be precisely determined to allow a user to precisely determine various distances away from the apparatus. A more specific example is shown in FIG. 9, which may be referenced in conjunction with FIG. 8 in order to obtain a full understanding of the operation of one embodiment. As shown in FIG. 9, a series of equidistant distance markers are depicted that correspond with the non-equidistant dash lines of reticle 200, as depicted in FIG. 8. More particularly, distance marker 330 corresponds with horizontal cross bar 230. Thus, at distance D2, light from ranging beam 113 intersects the projection of the image on reticle 200 at cross bar 230. Similarly, distance marker 312 from FIG. 9 corresponds with dash line 212 from FIG. 8, distance marker 314 corresponds with dash line 214, distance marker 316 corresponds with dash line 216, distance marker 318 corresponds with dash line 218, distance marker 322 corresponds with dash line 222, and distance marker 324 corresponds with dash line 224. Each of the adjacent distance markers depicted in FIG. 9 therefore corresponds with adjacent dash lines from reticle 200. Each of these distance markers is separated from an adjacent distance marker by the same distance, namely, D3. In this manner, a user can not only confirm one distance that may correspond with the center of the projected image from the reticle, but can confirm a series of distances and can move a target patient, sensor, or another target item closer to, or away from, the device by precise multiples of a particular distance. When used in combination with certain embodiments of the collimator discussed above, a user can both determine a precise desired location from the device and visualize the full extend to the area that is to receive x-ray radiation for diagnosis, treatment, or other such uses. FIG. 9 also depicts an angle A2 between a beam perpendicular to collimator 120 (delivered from x-ray source 182 and/or visible light generator 190) and an angled beam delivered from ranging beam 113. As mentioned above, this angle may be adjusted as desired for a particular application. The foregoing specification has been described with reference to various embodiments. However, one of ordinary skill in the art will appreciate that various modifications and changes can be made without departing from the scope of the present disclosure. For example, although the embodiment depicted in the accompanying drawings comprises dash lines along a vertical cross bar, other embodiments may additionally, or alternatively, comprise dash lines along the horizontal cross bar. In addition, various operational steps, as well as components for carrying out operational steps, may be implemented in alternate ways depending upon the particular application or in consideration of any number of cost functions associated with the operation of the system. Accordingly, any one or more of the steps may be deleted, modified, or combined with other steps. Further, this disclosure is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope thereof. Likewise, benefits, other advantages, and solutions to problems have been described above with regard to various embodiments. However, benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced, are not to be construed as a critical, a required, or an essential feature or element. It will also be readily understood that the order of the steps or actions of the methods described in connection with the embodiments disclosed may be changed, as would be apparent to those skilled in the art. Thus, any order in the drawings or Detailed Description is for illustrative purposes only and is not meant to imply a required order, unless specified to require such an order. Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims. |
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055240330 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to gadolinium for use as a burnable poison for nuclear fuel, comprising: a plurality of isotopes of gadolinium, wherein a content of at least one even mass numbered isotope of said plurality of isotopes is smaller than a content of said at least one even mass numbered isotope in natural gadolinium, and a fuel assembly comprising a plurality of fuel rods comprising the gadolinium. As seen in Table 2, when natural gadolinium is used, Gd-156, Gd-157 and Gd-158 contribute to about the same degree to the loss of reactivity after burnout of the gadolinium. In the case of Gd-156, that produced from Gd-158, neutron absorption and that which is found naturally are present in a ratio of about 15:20. In the case of Gd-158, that produced from Gd-157 by neutron absorption and that which is found naturally are present in a ratio of about 16:25. Therefore, by making the content of Gd-156 and Gd-158 low, the loss of reactivity due to these isotopes can be greatly reduced. Lowering the Gd-156 moreover enables the reactivity loss due to Gd-157 to be reduced. The change with time of the atom density of Gd-157 after the naturally present Gd-157 has all been converted into Gd-158 is expressed by the following equation. EQU dN7/dt=-N7.sigma.7 .phi.+N6.sigma.6 .phi. where N6 and N7 are the atom densities of Gd-156 and Gd-157, respectively .sigma.6 and .sigma.7 are their respective cross-sections, and .phi. is the neutron flux. Since .sigma.6 is very much smaller than .sigma.7, with the lapse of sufficient time dN7/dt=0. At this point, N6 .sigma.6 .phi.=N7.sigma.7 .phi., and an equilibrium condition is produced in which the neutron absorption factors of Gd-156 and Gd-157 are equal and the atom density of Gd-157 is proportional to the atom density of Gd-156. As shown in FIG. 4, the atom density of Gd-156 after the Gd-155 has been fully converted to Gd-156 is practically constant and is determined by the quantities of Gd-155 and Gd-156 that were present initially. The loss in reactivity due to Gd-157 can therefore also be reduced by lowering the Gd-156 content. Also, by maintaining the contents of Gd-155 and Gd-157, which function in essential part as burnable poisons, reactivity control can be achieved for the necessary initial period, so isotopes other than these can be removed and the gadolinia concentration can therefore be lowered by a corresponding amount. As a result, the thermal conductivity of the fuel is raised so the benefits of higher burnup and/or reduction in local power peaking can be obtained and gadolinia concentration can be raised, thereby making it possible to raise the availability factor by long-term operation. Furthermore, since the Gd-155 and Gd-157 are present in the same ratio as in natural gadolinium, the peak value of the infinite multiplication factor will not get too large. It is therefore possible to solve the problems of adverse effect on shutdown margin and increase in channel peaking. In a fuel assembly according to the present invention, Gd-157-enriched gadolinium, having Gd-157 content higher than natural abundance, is employed as a burnable poison, and fuel rods are allocated into a plurality of groups of mutually different burnable poison concentrations. The atom density variation of Gd-157 and Gd-155 shown in FIG. 4 can therefore be obtained by simulation. This makes it possible to reduce the peak value of the infinite multiplication factor, so the problems of adverse effect on the shutdown margin and increased channel peaking can be overcome. In one embodiment of the present invention, gadolinium containing no Gd-156 at all (shown in Table 4) is employed as a burnable poison in a fuel assembly as shown in FIG. 1. The gadolinium is included in the fuel in the form of gadolinia at a gadolinia concentration of 3.2%. The total mass content of Gd-155 and Gd-157 is the same as when natural gadolinium is used with a gadolinia concentration 4.0%. The neutron absorption factor at 25 GWd/st in this embodiment is 0.60%, providing a reactivity gain of 0.21% when compared with the gain of 0.81% which is obtained when natural gadolinium is used, as shown in Table 2. Consequently, compared with a prior art example using natural gadolinium, burnup can be prolonged by about 1% for the same uranium concentration. Alternatively, the uranium concentration to achieve the same burnup as in the prior art example can be lowered by about 0.03%. FIG. 3 shows the burnup variation (13) of the infinite multiplication factor in this embodiment. It can be seen from the Figure that a burnup variation is displayed which is very similar to that of the infinite multiplication factor (11) in the prior art example in which natural gadolinium is employed. Since the peak of the infinite multiplication factor does not get too large, there is no risk of adverse effects on shutdown margin and channel peaking. FIG. 7 is a schematic diagram showing an example of a laser device for manufacturing the gadolinium shown in Table 4. First of all, gadolinium metal is melted and evaporated by a metal vapor generating device (15) in the interior of a separation cell (14) maintained at high vacuum. The neutral vapor current (16) that is thus generated is fed into an optical reaction unit (17) where only the Gd-156 is ionized by irradiating the vapor with laser light (19) introduced from a laser system (18). Preferably, rather than carrying out the ionization directly from the ground state, a selective excitation laser beam (20) is used to temporarily selectively excite the Gd-156 to a specific excited condition. The excited Gd-156 is then ionized by irradiating with a further ionizing laser beam (21). Laser devices (22) and (23) are constituted by a pumping laser, variable-wavelength laser, frequency modulating device and pulse laser amplifier. The ionized Gd-156 vapor current (24) which is obtained in this way is adsorbed onto an ion recovery electrode plate (25). Vapor current (26) consisting of the other gadolinium isotopes which have not been ionized is recovered onto a neutral atom recovery plate (27). Gadolinium of lower Gd-156 content than the natural abundance can therefore be obtained by recovering the gadolinium from neutral recovery plate (27). TABLE 4 ______________________________________ Isotope Content (%) Neutron absorption factor (%) ______________________________________ Gd-154 3 0.04 Gd-155 19 0.05 Gd-156 0 0.11 Gd-157 20 0.12 Gd-158 31 0.21 Tb-159 0 0.05 Gd-160 27 0.02 Total 100 0.60 ______________________________________ As a further embodiment, gadolinium containing no Gd-156 or Gd-158 at all, as shown in Table 5, is employed as a burnable poison in a fuel assembly as depicted in FIG. 1. The gadolinia concentration is 2.2%, and the total mass content of Gd-155 and Gd-157 is the same as when natural gadolinium is used with gadolinia concentration of 4.0%. The neutron absorption factor at a burn up of 25 GWd/st in this embodiment is further reduced from that in the first embodiment at 0.45%. In other words, a reactivity gain of 0.36% is obtained compared with the gain of 0.81% which is obtained when natural gadolinium is used, as shown in Table 1. Consequently, compared with a prior art example using natural gadolinium, burnup can be prolonged by about 2 for the same uranium concentration. Alternatively, the uranium concentration to achieve the same burnup as in the prior art example can be lowered by about 0.04%. In this embodiment also, since the peak of the infinite multiplication factor does not get too large, there is no risk of adverse effects on shutdown margin and channel peaking. TABLE 5 ______________________________________ Isotope Content (%) Neutron absorption factor (%) ______________________________________ Gd-154 4 0.04 Gd-155 27 0.05 Gd-156 0 0.11 Gd-157 29 0.12 Gd-158 0 0.09 Tb-159 0 0.02 Gd-160 40 0.02 Total 100 0.45 ______________________________________ Comparing the above described embodiments, it can be seen that the reduction in reactivity loss produced by removing the Gd-158 is 0.15%. In order to reduce reactivity loss, it is therefore of initial importance to remove the Gd-156 and it is next important to remove the Gd-158. The other isotopes of even mass number present in gadolinium are Gd-152, Gd-154 and Gd-160. Since the content of Gd-152 and Gd-154 is in any case small, little reactivity loss improvement results from their removal. Next, Gd-154 has a neutron absorption factor due to Gd-154 itself of 0.04%. However, it acts as a source of Gd-155, which has a neutron absorption factor of 0.05%. Consequently by removing the Gd-154 a reactivity gain of 0.09% is obtained. Removing Gd-154 can therefore come third in order of reference. In contrast, Gd-160 has a large natural abundance of 22%, but, as shown in Table 1, its cross-section is small, so its removal gives little benefit in terms of lowering reactivity loss. However, since there is a large Gd-160 content, removing it is beneficial in raising thermal conductivity, and so is effective in achieving high burnup and/or prolonging reactor operation. FIG. 8 shows a transverse cross-sectional view of a fuel assembly constituting another embodiment of the present invention. This embodiment is an example in which the Gd-157 content is made higher than the natural abundance. In fact, gadolinium consisting solely of Gd-157 is employed as burnable poison. The gadolinia concentration is 1.2% in the case of eight fuel rods G1 and 1.5% in the case of five fuel rods G2. Specifically, the burnup variation of Gd-157 shown in FIG. 4 is simulated by the gadolinia of G1 and the burnup variation of Gd-155, which has a slower burnup rate, is simulated by the gadolinia of G2. Furthermore, since the gadolinia content is substantially greater in G2, the number of gadolinia-containing fuel rods can be reduced by 1 to 13 rods. The uranium concentration in this embodiment is 0.1% lower than 4.0%, i. e., 3.9%. FIG. 3 shows the burnup variation (28) of the infinite multiplication factor of this embodiment. In this embodiment, the infinite multiplication factor (11) of conventional fuel using natural gadolinium is closely simulated. In particular, the peak value of the infinite multiplication factor can be made smaller. The reactivity loss due to the gadolinia can thereby be reduced and the same burnup as in the conventional example can be achieved with a lower uranium concentration, without adverse effect on the shutdown margin or channel peaking. It is desirable to set the ratio of gadolinia concentration of the rods G1 to the rods G2 at about 1.2 to 1.3 as in this embodiment. In this way, the burnup variation in atom number density of Gd-155 and Gd-157 shown in FIG. 4 can be roughly simulated. Although, in this embodiment, two levels of gadolinia concentration were employed, three or more levels of gadolinia concentration could be used. In a fuel assembly according to an additional embodiment of the present invention, the transverse cross-sectional plane is the same as in the prior art example of FIG. 1, but the gadolinia in gadolinia-containing fuel rods (10) is different in the vertical axial direction. Specifically, gadolinium consisting solely of Gd-157 is employed in the bottom while in the top portion natural gadolinium is employed. The gadolinium concentrations are 1.2% in the bottom and 4.0% in the top portion. The neutron importance on reactor shutdown is a maximum at a location 1/4 to 1/3 of the total length below the top of the core. The infinite multiplication factor at the bottom of the core has scarcely any effect on the effective multiplication factor of the core at shutdown. With this embodiment, gadolinium of high Gd-157 content is only used in the bottom of the fuel assembly, so the possibility of excessive peaking of the infinite multiplication factor is confined to the bottom of the fuel assembly. Reactivity loss in the bottom of the fuel assembly can therefore be decreased with no risk of adverse effect on the shutdown margin. In general in a boiling water nuclear reactor, power peaking in the axial direction is liable to occur in the bottom of the core. Consequently, in this embodiment, if the uranium concentrations are the same in the top and bottom portions of the fuel assembly, the infinite multiplication factor is largest in the bottom, where the reactivity loss produced by the gadolinia is smallest. As a result, there is a possibility of increased axial power peaking in the bottom of the core. In such a case, means may be adopted such as making the uranium concentration at the bottom of the fuel assembly lower than at the top, using more gadolinia-containing fuel rods in the bottom than in the top, or making the gadolinia concentration at the bottom of the fuel assembly richer than in this embodiment. Early Japanese Patent Publication Sho. 54-13899 discloses a technique of making the gadolinia concentration used in the bottom of the fuel assembly richer than at the top, in order to reduce axial power peaking occurring at the bottom of the core in a boiling water reactor. In a fuel assembly making use of this technique shown in FIGS. 9(A) and (B), in all the fuel rods, natural uranium is employed in portions at the top and bottom ends while enriched uranium is employed in the middle portion. The gadolinia-containing fuel rods (10) are of two kinds: in fuel rods G3, the gadolinia concentration is 4.0% at both top and bottom; in fuel rods G4, it is 4.0% at the top and 5.0% at the bottom. In this example, since the gadolinia concentration is higher at the bottom of fuel rods G4, the thermal conductivity here is lower, so the degree of uranium enrichment of the entire middle portion of fuel rods G4 is lower than the degree of uranium enrichment of the middle portion of fuel rods G3. As a result, local power peaking in the cross-sectional plane of the fuel assembly is adversely affected. In a further embodiment of the present invention, the gadolinium which does not contain Gd-156, as indicated in Table 4, is used in the bottom of fuel rods G4, and natural gadolinium is used for the top. The gadolinia concentration is 4.0% at both the top and the bottom. With such a gadolinia distribution, the same reactivity control as in the prior art example can be achieved. In this embodiment, the uranium concentration of fuel rods G3 and fuel rods G4 is the same. As a result, lower power peaking in the cross-sectional plane of the fuel assembly is improved in comparison with the prior art example. Of course, gadolinium which does not contain Gd-156 could be used in both the top and bottom of G3 and G4, but this is more expensive to manufacture than natural gadolinium, so in order to keep costs down, it may be used, as in this embodiment, only in the bottom portion of the fuel assembly. Obviously, instead of using gadolinium which does not contain Gd-156, the same effect can be obtained by using gadolinium in which the Gd-157 content is raised above its natural abundance. The initially loaded fuel loaded in the first cycle of reactor operation has a gadolinia concentration higher than that of the replacement fuel loaded in the second and subsequent cycles. Gadolinia of concentration 7 to 8% is used in this initially loaded fuel. This is because the operating period of the first cycle for the start-up test is longer than the operating period of the second and subsequent cycles. If the initially loaded fuel is made of high enrichment in order to raise fuel economy, the number of rods to be replaced on first replacement is reduced so the excess reactivity of the second cycle must be borne by gadolinia present in the initially loaded fuel. Consequently, with higher enrichment of the initially loaded fuel, if one seeks to raise the gadolinia concentration, and if in the initially loaded fuel the gadolinia concentration in the bottom portion is richer than in the top portion, the gadolinia concentration will in fact be restricted by the gadolinia concentration present in the bottom portion of the fuel assembly. In such cases too, it is appropriate to use more in the bottom than in the top of the fuel assembly of either (a) gadolinium whose Gd-156 content is lowered below the natural abundance or (b) gadolinium whose Gd-157 content is raised above the natural abundance as in this embodiment. A fuel assembly according to an additional embodiment of this invention is the same as the prior art example of FIG. 1 in the transverse cross-sectional plane but the gadolinia concentration in gadolinia-containing fuel rods (10) is different between top and bottom in the axial direction. Specifically, for the top portion, gadolinium containing no Gd-156 and no Gd-158 at all, as shown in Table 5 and used in an earlier embodiment, is employed, while natural gadolinium is employed for the bottom portion. The gadolinium concentration is 2.2% in the top portion and 4.0% in the bottom portion. The infinite multiplication factor of the fuel assembly according to this embodiment is greater, at 0.49%, in the top than in the bottom, so the occurrence of axial power peaking in the bottom of the core in the boiling water reactor is diminished and the thermal margin is therefore raised. Obviously, instead of using gadolinium which does not contain Gd-156 and Gd-158, the same effect can be obtained by using gadolinium in which the Gd-157 content is raised above its natural abundance. As shown in FIG. 1, in a fuel assembly employed in a boiling water reactor, normally gadolinia is used in the fuel rods other than those at the outer periphery. In contrast, Early Japanese Patent Publication Sho. 58-216989 discloses an invention in which the shutdown margin is improved and higher fuel burnup achieved by using gadolinia for the fuel rods in the outer periphery. However, owing to the more rapid elimination of gadolinium resulting from the large neutron flux in the fuel rods at the outer periphery, the gadolinia concentration has to be raised, by reducing the number of gadolinium containing fuel rods. However, this led to the problem that it was difficult to raise the gadolinia concentration sufficiently, owing to the drop in thermal conductivity which this caused. FIG. 10 is a transverse cross-sectional view of a fuel assembly according another embodiment of this invention. In this embodiment, apart from two fuel rods G5 in the central region, gadolinia is used in eight outer peripheral fuel rods G6. The central fuel rods G5 contain natural gadolinium in a gadolinia concentration of 4.0%; the peripheral fuel rods G6 contain gadolinium which does not contain Gd-156, Gd-158 or Gd-160, in a gadolinia concentration of 2.0%. By using such a gadolinia concentration, an infinite multiplication factor equivalent to infinite multiplication factor (11) of the prior art example shown in FIG. 1 can be achieved. In this embodiment, if natural gadolinium is employed for the outer peripheral fuel rods G6, a gadolinium concentration of 6.0% must be used. This presents an obstacle to obtaining higher burnup since it results in lowered thermal conductivity or lower thermal output of the fuel rods due to lower uranium concentration. In this embodiment the same effect can be obtained by using for the peripheral fuel rods G6, gadolinium in which the Gd-157 content is raised. Also for central fuel rods G5, gadolinium which does not contain Gd-156, Gd-158 or Gd-160, or gadolinium in which the content of Gd-157 is raised, can be employed. Moreover this embodiment can clearly also be applied to many of the above described embodiments. The embodiments obtained by such combinations are preferred in that their respective benefits can be achieved concurrently. In the above embodiments the cases were described in which gadolinium from which specific gadolinium isotopes of even mass number had been completely removed, or gadolinium consisting solely of Gd-157 was employed. However, if Gd-156 removal is performed using a separation device as shown in FIG. 7, complete ionization is in fact impossible to achieve. The gadolinium recovered from neutral atom absorption plate (27) therefore still contains some Gd-156 which was not ionized. Also in the case of ionizing Gd-157, a proportion of neutral atoms which have not been ionized adheres to ion recovery electrode plate (25) so the gadolinium element recovered from ion recovery electrode plate 25 still contains some isotopes other than Gd-157. Clearly, however, the present invention can still be applied and corresponding benefits achieved even using gadolinium element of this type as actually obtained in practice. Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the present invention can be practiced in a manner other than as specifically described herein. |
046735445 | claims | 1. In a nuclear reactor installation having a fuel assembly with spacers holding a multiplicity of nuclear fuel rods disposed parallel to one another in a geometric array, a pushing device for simultaneously sliding from the spacers a plurality of fuel rods disposed in a pattern, said pushing device comprising: a plurality of axially movable push rods equal in number to the plurality of fuel rods to be simultaneously removed from the spacers, said push rods being disposed parallel to each other in the pattern in which said plurality of fuel rods is arranged; first mounting means including a pressure plate secured to said push rods at one end thereof for supporting said push rods and further including a guide plate disposed at an opposite end of said push rods in a disengaged state of the pushing device for guiding said push rods during operating of said pushing device, said guide plate having a plurality of bores at least equal in number to said push rods and with substantially the same cross sectional area and shape as said push rods, said bores being disposed in the same pattern as said push rods, said push rods traversing said bores; second mounting means, including a base plate on a side of said pressure plate opposite said guide plate and guide rods secured to said base plate and said guide plate, for slidably securing said pressure plate for motion in a direction parallel to said push rods; third mounting means connected to said base plate and said guide plate for supporting same in an operating position juxtaposed to the fuel assembly; drive means operatively connected to said base plate and said pressure plate for moving said pressure plate relative to said base plate, thereby sliding said plurality of fuel rods from said spacers by means of said plurality of push rods; and locking means connected to said push rods for preventing motion of at least any one push rod upon the exceeding of a threshold pressure by the force transmitted by said one push rod. 2. The pushing device defined in claim 1, wherein said first mounting means includes a mounting plate slidably attached to said guide rods between said pressure plate and said guide plate, said mounting plate having a plurality of bores at least equal in number to said push rods and with substantially the same cross sectional area and shape as said push rods, the bores in said mounting plate being disposed in substantially the same pattern as said push rods, said push rods traversing the bores of said mounting plate. 3. The pushing device defined in claim 2 wherein said drive means includes at least one threaded spindle traversing said base plate and connected to said pressure plate, a threaded nut engaging said spindle and supported on said base plate, and a rotary power source operatively connected to said nut. 4. The pushing device defined in claim 3 wherein said locking means includes a switch operatively connected to said drive means for disengaging said drive means upon the exceeding of said threshold pressure by the force transmitted by said one push rod, said first mounting means including spring means engaging said pressure plate and said push rods in part for transmitting compressive force from said pressure plate to said push rods and in part for determining said threshold pressure. 5. The pushing device defined in claim 4 wherein said third mounting means includes transport means for alternately shifting said push rods, said first mounting means and said second mounting means into and out of said operating position. 6. The pushing device defined in claim 4 wherein said third mounting means includes a tubular mounting fastened to said base plate at a substantially central location thereon. 7. The pushing device defined in claim 3 wherein each push rod is rigidly connected to said pressure plate by means of a shear pin, said shear pin forming a component of said first mounting means and of said locking means. 8. The pushing device defined in claim 7 wherein said third mounting means includes transport means for alternately shifting said push rods, said first mounting means and said second mounting means into and out of said operating position. 9. The pushing device defined in claim 7 wherein said third mounting means includes a tubular mounting fastened to said base plate at a substantially central location thereon. 10. The pushing device defined in claim 2 wherein said drive means includes a spindle rotatably mounted to said base plate and said guide plate and extending substantially parallel to said push rods, said pressure plate being provided with a threaded bore traversed by said spindle, said spindle having an external thread operatively engaging said threaded bore. 11. The pushing device defined in claim 10 wherein said locking means includes a switch operatively connected to said drive means for disengaging said drive means upon the exceeding of said threshold pressure by the force transmitted by said one push rod, said first mounting means including spring means engaging said pressure plate and said push rods in part for transmitting compressive force from said pressure plate to said push rods and in part for determining said threshold pressure. 12. The pushing device defined in claim 11 wherein said third mounting means includes transport means for alternately shifting said push rods, said first mounting means and said second mounting means into and out of said operating position. 13. The pushing device defined in claim 11 wherein said third mounting means includes a tubular mounting fastened to said base plate at a substantially central location thereon. 14. The pushing device defined in claim 10 wherein each push rod is rigidly connected to said pressure plate by means of a shear pin, said shear pin forming a component of said first mounting means and of said locking means. 15. The pushing device defined in claim 1 wherein said drive means includes at least one threaded spindle traversing said base plate and connected to said pressure plate, a threaded nut engaging said spindle and supported on said base plate, and a rotary power source operatively connected to said nut. 16. The pushing device defined in claim 1 wherein said locking means includes a switch operatively connected to said drive means for disengaging said drive means upon the exceeding of said threshold pressure by the force transmitted by said one push rod, said first mounting means including spring means engaging said pressure plate and said push rods in part for transmitting compressive force from said pressure plate to said push rods and in part for determining said threshold pressure. 17. The pushing device defined in claim 1 wherein said third mounting means includes transport means for alternately shifting said push rods, said first mounting means and said second mounting means into and out of said operating position. 18. The pushing device defined in claim 1 wherein each push rod is rigidly connected to said pressure plate by means of a shear pin, said shear pin forming a component of said first mounting means and of said locking means. 19. The pushing device defined in claim 1 wherein said drive means includes a spindle rotatably mounted to said base plate and said guide plate and extending substantially parallel to said push rods, said pressure plate being provided with a threaded bore traversed by said spindle, said spindle having an external thread operatively engaging said threaded bore. |
description | This application is a continuation-in-part of U.S. patent application Ser. No. 09/502,093, filed Feb. 10, 2000, now U.S. Pat. No. 6,459,761 entitled SPECTRALLY SHAPED X-RAY INSPECTION SYSTEM and of U.S. patent application Ser. No. 09/919,352, filed Jul. 30, 2001, now abandoned entitled A SYSTEM AND METHOD FOR INSPECTING AN OBJECT USING SPATIALLY AND SPECTRALLY DISTINGUISHED BEAMS, the disclosures of both of which are incorporated herein, in their entirety, by reference. The present invention relates to systems and methods for inspecting objects and, more particularly, the invention relates to systems and methods for inspecting objects with radiation beams tailored to provide optimized cross-sectional profiles. X-ray inspection systems, such as those used to characterize the contents of concealing enclosures such as baggage or cargo containers, typically employ an irradiating beam of specified cross-section that is swept relative to an object while portions of the beam that are either transmitted through the object or scattered by it are detected. Cross-sectional shapes of beams typically employed include fan beams, otherwise referred to as ‘fan-shaped’ beams, and pencil beams, where the characteristic dimension of the beam governs the spatial resolution of the system. The irradiating beam is characterized by an energy distribution of x-rays that is governed by the nature of the x-ray source and is invariant across the entire cross-section of the beam. For a specified set of beam characteristics, the total photon flux through an object scales with the area of the beam. Thus, higher resolution, achieved by virtue of a tighter beam, is achieved at the expense of photon flux. Therefore, the thickness of the object through which radiation can be detected with a useful signal-to-noise ratio is also limited unless other parameters are changed. In the prior art, this trade-off is part of the design of the system that is performed prior to its operation in the field. In accordance with preferred embodiments of the present invention, there is provided a graduated collimator for providing a beam of increasing average energy as a function of distance measured from a central axis. The collimator has a plurality of concentric areas, each of the areas defined in a plane substantially perpendicular to the central axis, such that any specified area is characterized by an opacity to the beam exceeding that of any area interior to the specified area. In accordance with other embodiments of the invention, at least one of the plurality of concentric areas may be the surface of an x-ray attenuating material, and the plurality of concentric areas may include a central area of substantially no attenuation. A subset of the concentric areas may be surfaces of frames of radially increasing opacity. In accordance with another aspect of the invention, a system is provided for inspecting an object. The system has a source for generating a penetrating radiation beam for irradiating the object, and the beam has an instantaneous power spectrum of intensity as a function of energy at any given instant of time. The system also has a shaper for modulating the generated beam, thereby creating a shaped beam, the shaper comprising at least a first section and a second section, the first section attenuating the intensity of a portion of the generated beam by a first attenuation factor and the second section attenuating the intensity of another portion of the generated beam by a second attenuation factor. Finally, the system has at least one detector for detecting the shaped beam after the shaped beam interacts with the object. The first attenuation factor may be 1. The detector or detectors may detect photons of energies exceeding a first fiducial energy as well as photons of energies exceeding a second fiducial energy, and may operate in an energy-dispersive mode or a current mode. The shaper may spatially separate the shaped beam into a first beam and a second beam, the first beam including the portion of the generated beam attenuated in the first section of the shaper and the second beam including the portion of the generated beam attenuated in the second section of the shaper. One or more detectors may then detect the first beam after the first beam interacts with the object, while another detector detects the second beam after the second beam interacts with the object. One or more detectors may also detect photons of energies in the first beam exceeding a first fiducial energy while another detector detects photons of energies in the second beam exceeding a second fiducial energy. The shaper may be configured in such a manner as to reduce ambient radiation dose. A first section of the shaper may include an element having an atomic number greater than 23. In accordance with other embodiments of the invention, an inspection system is provided for inspecting an object, wherein the system has a source, a shaper, and two detectors. The source generates a penetrating radiation beam for irradiating the object, the beam having, at each instant of time, an instantaneous energy spectrum. The shaper modulates the generated beam, thereby creating a shaped beam, and has at least a first section and a second section, the first section attenuating the intensity of a portion of the generated beam by a first attenuation factor and the second section attenuating the intensity of another portion of the generated beam by a second attenuation factor. The first detector detects the shaped beam attenuated by the first attenuation factor after the shaped beam interacts with the object while the second detector detects the shaped beam attenuated by the second attenuation factor after the shaped beam interacts with the object. The first attenuation factor may be 1, and the first detector may detect photons of energies exceeding a first fiducial energy while the second detector detects photons of energies exceeding a second fiducial energy. The first and second detectors may be arranged in tandem. In accordance with yet further embodiments of the invention, an inspection system for inspecting an object may be provided having a bed moveable along a first direction having a horizontal component, and a source coupled to move with the bed for generating a penetrating radiation beam for irradiating the object, the beam having, at each instant of time, an instantaneous power spectrum of intensity as a function of energy. The system has a motorized drive for moving the bed in the first direction such that the beam is caused to traverse the object as the bed is moved. The system also has a shaper for modulating the generated beam, thereby creating a shaped beam, the shaper comprising at least a first section and a second section, the first section attenuating the intensity of a portion of the generated beam by a first attenuation factor and the second section attenuating the intensity of another portion of the generated beam by a second attenuation factor. Finally, the inspection system has a detector for detecting the shaped beam after the shaped beam interacts with the object, the detector coupled such that the detector moves in coordination with the bed. a. An inspection system may be provided wherein the source of penetrating radiation is coupled to a self-propelled vehicle capable of on-road travel, where the vehicle has one drive train for propelling the vehicle for on-road travel and another drive train, distinct from the first drive train, for propelling the vehicle in a first direction during inspection of the object. This system has a shaper for modulating the generated beam, thereby creating a shaped beam, the shaper comprising at least a first section and a second section, the first section attenuating the intensity of a portion of the generated beam by a first attenuation factor and the second section attenuating the intensity of another portion of the generated beam by a second attenuation factor. The system has a detector for detecting the shaped beam after the shaped beam interacts with the object, the detector coupled such that the detector moves in coordination with the bed. Finally, an inspection system may be provided for inspecting an object, in accordance with the invention, that has a movable bed capable of traversing the object and a source coupled to the movable bed for generating a penetrating radiation beam for irradiating the object, where the beam has, at each instant of time, an instantaneous power spectrum of intensity as a function of energy. The inspection system has a shaper for modulating the generated beam, thereby creating a shaped beam, the shaper comprising at least a first section and a second section, the first section attenuating the intensity of a portion of the generated beam by a first attenuation factor and the second section attenuating the intensity of another portion of the generated beam by a second attenuation factor. Finally, the inspection system has a detector for detecting the shaped beam after the shaped beam interacts with the object, the detector coupled such that the detector moves in coordination with the bed. At least one scatter detector may be coupled so as to move in coordination with the bed. As discussed in U.S. patent application Ser. No. 09/502,093, the design of an x-ray inspection system to examine heterogeneous cargo requires joint consideration of conflicting requirements for penetration, radiation dosage, and sensitivity. For example, the high-energy x-ray components of a radiation beam from a 3 MeV x-ray accelerator penetrate approximately 3 times farther through iron than do the high-energy x-ray components of a radiation beam from a 450 keV x-ray accelerator. However, radiation dosage, that is, the integrated radiated energy, increases as the electron energy from an x-ray accelerator is raised. For example, the radiation dose from a 3 MeV x-ray accelerator operating at 100 microamps is about 5 times greater than the radiation dose from a 450 keV x-ray accelerator operating at 10 mA. In addition, the high-energy x-ray components of a radiation beam are not as “sensitive” for distinguishing among materials as the low-energy x-ray components of a radiation beam, in the sense in which sensitivity is the detected change in transmitted countrate per unit thickness of a specified material. One measure of the ability of an x-ray inspection system to detect “contraband” is the minimum thickness of material that can be detected. In determining that minimum thickness, consider a mono-energetic beam of photons penetrating an object having thickness T. The object has a linear absorption co-efficient λ(E,Z), which is a function of the material and the energy of the photons that penetrate the object. If NO(E) is the number of x-ray photons incident on the object, then N(E), the number of x-ray photons emerging from the object, is given by:N(E)=NO(E)e−λT (Eqn. 1)To determine the minimum thickness, ΔT, that can be detected, differentiate Eqn. 1: Δ N Δ T = - N O λⅇ - λ T ( Eqn . 2 ) The relative change in count rate per thickness is: Δ N N Δ T = - λ ( Eqn . 3 ) The minimal detectable signal may be taken to be 3 times the standard deviation of the signal (or 6 times the standard deviation, with Eqns. 4 and 5 changed mutatis mutandis):ΔN=3√{square root over (N)} (Eqn. 4)Substituting Eqn. 4 into Eqn. 3 yields the minimum thickness that can be detected for a given number of detected counts: Δ T = 3 λ N ( Eqn . 5 ) Thus, the minimum detectable thickness, for a given pixel, varies inversely with the square root of the counts in the detector and inversely with the linear attenuation coefficient λ. The linear attenuation coefficient for iron is 8.8 cm−1 at 60 keV, the energy of the strong, characteristic x-ray beams from a tungsten anode. As the energy of the photon increases, λ(Fe) drops rapidly, for example, at 200 keV, λ(Fe) is 1.1 cm−1 and at 1 MeV, λ(Fe) is 0.47 cm−1. Thus, for the same counts in the detector, a 60 keV photon beam can detect 1/20th the thickness that can be detected by a 1 MeV photon, all other parameters being equal. It follows that a lightly-loaded container is typically better inspected by the low-energy x-ray components of a radiation beam because λ is greater at lower energies. But, a heavily-loaded container must be better inspected by the high-energy x-ray components of a radiation beam. However, the high-energy x-ray components, in turn, increase the ambient radiation dose—the dose of scattered radiation in the surrounding environment. In accordance with an embodiment of the invention, the energy distribution of an x-ray beam is filtered to simultaneously optimize the penetration of the x-ray beam through a high-density object, as well as the sensitivity of the x-ray beam to a low-density object, while minimizing the ambient radiation dose. The term ‘x-ray’ is used herein to encompass penetrating radiation generally and, for example, gamma rays are within the scope of the invention. FIG. 1 is a schematic cross-sectional view of a flying spot x-ray inspection system, i.e., a system in which a scanning pencil beam 20 generated by x-ray radiation source 30 is employed to scan an inspected enclosure such as truck 32. Portions of beam 20 that traverse the inspected enclosure are detected by transmission detector 34, whereas scattered x-rays 36 are detected by one or more scatter detectors 38. Various means are known in the art for mechanically or electronically sweeping a beam of penetrating radiation, including, for example, the rotating chopper wheel 10 depicted in FIG. 1. Electronic scanning is described in detail, for example, in U.S. Pat. No. 6,421,420 which is incorporated herein by reference. In embodiments employing a mechanical rotating chopper wheel, as chopper wheel 10 rotates in the direction of arrow 12, penetrating radiation 14 emitted from the target of X-ray tube 16 passes successively through a plurality (in this case, four) of channels 18. Wheel 10 is fabricated from a material, typically lead, that blocks transmission of x-rays except through channels 18. X-rays 14 emerge from the currently illuminated channel as a pencil beam 20 that is swept across an object undergoing inspection as wheel 10 rotates. The dimensions of the beam 20 typically govern the resolution of a system such as the one depicted. Aperture stop 44 is a collimating aperture disposed, typically at the distal end of each channel 18 of chopper wheel 10 at the point where beam 20 emerges from the wheel. Aperture 44 may have various shapes, and may be circular or rectangular, and may be more specifically tailored as described in the following section. Shaped Beam As alluded to above, the resolution of a flying-spot system is usually limited by the cross-sectional dimensions of x-ray beam 20 at that point in the inspected object where resolution is to be measured. “Tight” beam collimation is a function of both x-ray source target size—the “focal spot” size—and the size of the collimating aperture(s). This is now discussed with reference to FIG. 2. Since the resolution of a flying-spot system, and thus the ability to resolve small articles and obtain sharp images, depends strongly on collimation of the beam into a well-defined pencil beam, it is advantageous to limit the size of region illuminated by the beam to dimensions no bigger than those of a detection pixel, subject to constraints driven by sampling time and scanning speeds. Collimation of the beam is achieved by means of an aperture defined at the position where a beam exits a channel of the chopper wheel. The description of the invention proceeds with reference to the cross-sectional view of the aperture shown in FIG. 2, with the understanding that the actual system may have cylindrical symmetry about central axis 46, but that it typically does not. A characteristic dimension, referred to herein as the “size”, of the focal spot at target 40 is designated as F, while the size of aperture stop 44 is designated S. Target 40 and aperture stop 44 are separated by source-to-aperture distance L1. Object plane 46 refers to a characteristic position within an object being interrogated at which position resolution is to be optimized. F′ represents the size of a pinhole image of the focal spot (i.e., the image through an infinitesimal aperture, S→0) at the designated “object distance”, L2 referred to the plane of target 40, while S′ represents a point projection of the aperture (i.e., from a point source, F→0). At the object plane distance, L2,F′=F(L2−L1)/L1; and S′=S L2/L1 (Eqns. 6) The full beam spread at the object distance is the convolute of F′ and S′, which has a maximum width equal to the sum of F′ and S′, and a full-width at half-maximum (FWHM) equal to the larger of F′ and S′. The size of F is typically governed by the choice of x-ray tube (though it might be variable, within the scope of the invention), while L1 and L2 are typically dictated by other system considerations such as the thickness of chopper wheel material required to extinguish the beam, etc., and S is then typically dimensioned to make F′ and S′ equal, i.e.,S=F(L2−L1)/L2 (Eqn. 7) The flux of x-rays per unit time in the scanning beam is substantially proportional to the product F×S2, or, using Eqn. 7, to F3. Ideally, both F′ and S′ are equal to the pixel size at the object distance; however, this may lead, in view of the small pixel size desired, to an x-ray flux that is too small and thus to a loss of penetration, i.e., to an undesirable limit on how much attenuation may be probed by the interrogating beam. A further limitation is the fact that only a few choices of focal spot F are available if the choice is limited to commercially available x-ray tubes. Consequently, it is common practice to select and available F and to design S in accordance with Eqn. 7 but subject to the condition of providing adequate flux for the desired application. Thus, optimal resolution is not obtained in cases where the beam attenuation is low, i.e., in paths through the inspected object that are radiographically “thin.” Conversely, for “thick” parts of the object (i.e., more highly attenuating of incident penetrating radiation), higher photon flux is required for penetration, even at the expense of resolution. A further characteristic of x-ray sources typically employed in inspection systems is that they are multispectral. Sources that include x-ray tubes emit a continuum of x-ray energies, with a large number of photons per unit energy at the lower energies of the emitted spectrum, with the spectral power density falling off to zero at the operating voltage of the x-ray tube. By virtue of this characteristic of the power density spectrum of an x-ray source, the great numbers of lower energy photons dominate the transmission signal (i.e., the flux of photons incident upon detector 34 (shown in FIG. 1) in regions of relatively low x-ray opacity. In accordance with preferred embodiments of the present invention, collimating apertures of graduated attenuation, such as now described with reference to FIG. 3A, are provided that the collimating apertures gradually become more opaque to x-rays with increasing distance from the central axis of the beam. It is to be understood that, as used herein and in any appended claims, the term “graduated” encompasses within its scope both stepped and continuous variation in attenuation with distance from the central axis. “Graduated” is thus used both in the sense of discrete steps and in the sense in which “grade” is applied to a road. Moreover, it is to be understood that the manner in which attenuation varies with distance from a fiducial axis may have a specified symmetry, either cylindrical or with respect to inversion through the axis, etc., however the variation need not have any symmetry at all within the scope of the invention as taught herein and as claimed in any appended claims. The fiducial axis characterizing the propagation direction of the beam will be referred to herein, without limitation, as a ‘central axis.’ Thus, the apertures, for example, may be asymmetrically disposed with respect to a central axis. Axis 50 designates a central axis of a beam of penetrating radiation. A particular beam spectrum is assumed in the present description, purely for purposes of illustration and without limitation. In particular, a 140 keV x-ray tube is assumed, having a photon distribution as a function of photon energy as depicted by the line designated 70 in FIG. 4. The raw power spectrum of beam intensity of such a beam is as plotted as curve 72, and this is the spectral content of the beam transmitted through the central clear aperture 54 of graduated aperture 52 shown in front view in FIG. 3A. Solely as an illustrative example of typical aperture sizes, and shaping of the power spectrum of the x-ray beam energies in accordance with the invention, the aperture regions of FIG. 3A are now discussed with further reference to FIG. 4. FIG. 3B shows a side cross section of a graduated aperture such as that shown in FIG. 3A. In the embodiment of the invention depicted in FIG. 3A, central aperture 54 is fully open and is characterized by an area designated as A. The distribution with x-ray energy of the number of photons in the beam incident from a typical x-ray tube is designated in FIG. 4 by curve 70. This corresponds to the raw spectrum designated by curve 72, accounting for the energy per photon increasing towards the right. Curve 72 thus represents the spectrum of x-ray power transmitted through central aperture 54. Outside of aperture 54, a frame 56 is disposed having outside length dimensions equal to √3 times that of the length dimension of central aperture 54, such that the incremental area of frame 56 is twice that of the central aperture, i.e., 2A. Frame 56 is made of copper of a thickness corresponding to 1 HVL (half-value-layer) of attenuation for 120 keV x-ray photons and central aperture 54 is simply a hole in frame 56. At lower energies, the attenuation is larger, such that the transmission of photons of higher energy is relatively enhanced. The spectrum transmitted through the additional area of frame 56 is depicted by curve 74. Outside frame 56, a third area 58 is characterized by an attenuating material, such as iron, of thickness corresponding to 2 HVL of attenuation for 120 keV x-ray photons. The third area has outside length dimensions of √7 times that of the length dimension of central aperture 54, such that the incremental area of frame 58 is four times that of the central aperture, i.e., 4A. Similarly, an outer frame 60, characterized by an attenuating material, such as iron, of thickness corresponding to 3 HVL of attenuation for 120 keV x-ray photons. The third area has outside length dimensions of √15 times that of the length dimension of central aperture 54, such that the incremental area of frame 60 is eight times that of the central aperture, i.e., 8A. Outside area 60, surround 62 is fully attenuating to the incident x-rays, i.e., it may be considered an opaque surround. Referring to FIG. 4, assuming the raw spectrum designated by curve 72 for the x-ray energy traversing the inner aperture 54, spectra of the relative intensity transmitted through each of the successive framing areas 56, 58, and 60 are depicted as curves 74, 76, and 78, respectively. The composite spectrum, including transmission through each of the regions, is shown as curve 82. As is apparent from the curves of FIG. 4, the spectral peak of the transmitted energy thus increases as a frame is displaced further from the fiducial (‘central’) axis of the graduated collimator. It is to be understood that the particular ratios of sides, or, for that matter, the rectangular shape of the apertures, as depicted in FIG. 3A are presented solely by way of illustration and other aspect ratios and aperture shapes are within the scope of the present invention. Indeed, the central aperture 54 need not be clear and may itself be subject to attenuation, and the graduation of attenuation outward from a central axis may be continuous rather than stepped as shown. Spectral Tailoring The techniques of spectral tailoring now described may also be referred to as “Shaped Energy™”. FIG. 5 is a schematic top view of an exemplary embodiment of an inspection system in accordance with the invention. The system, referenced as system 100, includes generator 110 and collimator 120. Generator 110 generates penetrating radiation and may include, for example, an x-ray tube or a linear accelerator (“LINAC”). The generated x-ray beam typically includes x-ray energies from below approximately 200 keV to above approximately 9 MeV. Collimator 120 forms the generated radiation into a beam 20 of specified cross-section, as appropriate to differing inspection scenarios. In addition, system 100 includes shaper 130, which shapes the spectrum of beam 20 via section 130a(1), section 130a(2) and section 130b, through which pass distinct spatial segments of beam 20. The term “shaping” as used herein refers to spectral filtering that may be applied differentially with respect to different segments of the beam. Typically, both sections of section 130a, as well as section 130b, attenuate the intensity of the portion of beam 20 that passes through the respective section with specified spectral selectivity. For example, in system 100, section 130b is shown as an opening between section 130a(1) and section 130a(2). Thus, section 130b attenuates the portion of beam 20 that passes through section 130b by a factor of 1. For purposes of discussion herein, an attenuation factor of 1 is the same as no attenuation. Section 130a(1) and section 130a(2) also attenuate the portion of the beam that passes through each respective section. Typically, section 130a(1) and section 130a(2) are composed of the same material of the same thickness. For example, section 130a(1) and section 130a(2) may be composed of a “heavy” element, for example, an element having an atomic number greater than 23, such as iron, chromium, or lead. However, depending upon the particular application of use for beam 20, section 130a(1) and section 130a(2) may be composed of: (1) the same material, but of different thicknesses; (2) different material, but of the same thickness; or (3) different material of different thicknesses. In addition, depending upon the particular application of use for beam 20, the configuration of section 130b may be modified. For example, section 130b may be circular in shape. Or, section 130b may be triangular in shape. System 100 further includes detector 150, which detects shaped beam 20 after shaped beam 20 has passed through object 140. In FIG. 5, object 140 is moving in a direction away from the bottom of the page and toward the top of the page. Detector 150 may be a single detector that efficiently detects both the low-energy x-ray components of shaped beam 20 and the high-energy x-ray components of shaped beam 20. In this embodiment, if the count rate of detector 150 is low enough for pulse counting, then the low-energy and high-energy x-ray components of beam 20 can be distinguished by their pulse heights, a method known in the art. However, if the count rate in detector 150 is too high for pulse counting, the gain in sensitivity for lightly-loaded objects will be less than the gain in sensitivity when more than one detector is used (discussed below). In regard to sensitivity to thickness change in a heavily-loaded object, the sensitivity is the same for one detector as for more than one detector. When object 140 is a “high-density” object, for example, λT>1 at low energies, then the x-ray components that penetrate to detector 150 are substantially the high-energy x-ray components. In turn, when object 140 is a “low-density” object, for example, object 140 is lightly-loaded, then the x-ray components that penetrate to detector 150 are substantially all of the x-ray components of shaped beam 20. FIGS. 6A–6C show the exemplary energy spectra of a radiation beam that is substantially unattenuated (FIG. 6A), substantially attenuated (FIG. 6B), and shaped in accordance with an exemplary embodiment of the invention (FIG. 6C). In particular, FIG. 6A is an exemplary energy spectrum of a substantially unattenuated 300 keV x-ray beam. As shown, the maximum intensity of the integrated intensity of the energy spectrum is between approximately 60 keV and approximately 75 keV. In contrast, FIG. 6B is an exemplary energy spectrum of a 300 keV x-ray beam that has passed through 2 cm of copper. As shown, the “bulk” of the integrated intensity is between approximately 150 keV and approximately 250 keV. In other words, the 2 cm thick copper has attenuated the intensity of the 300 keV x-ray beam by an attenuation factor, specifically, the 2 cm thick copper has reduced the low-energy x-ray components of the 300 keV x-ray beam by more than a factor of 10,000, and has reduced the high-energy x-ray components of the 300 keV x-ray beam by approximately a factor of 10. While the reductions differ for the different x-ray energies of the beam, for purposes of discussion herein, these reductions are referred to simply as an energy-dependent attenuation factor. In other words, the use herein of the phrase “attenuation factor” may mean that a particular material reduces different x-ray energies by different factors. Additionally, as used herein and in any appended claims, “modulate” means “to modify a characteristic of,” whether such modulation is a function of space, energy, or time. FIG. 6C is an exemplary energy spectrum of a radiation beam shaped in accordance with an exemplary embodiment of the invention, in particular, with reference to the exemplary embodiment shown in FIG. 5. Specifically, FIG. 6C shows the spectrum of a 300 keV x-ray beam, generated by generator 110, that has passed through shaper 130, in which section 130a(1) and section 130a(2) of shaper 130 are composed of copper that is 2 cm in thickness, and section 130b of shaper 130 allows an areal fraction of approximately 2% of the 300 keV x-ray beam to pass through section 130b without attenuation. As shown, the “bulk” of the intensity of the energy spectrum is between approximately 60 keV and approximately 75 keV and between approximately 150 keV and approximately 250 keV. In other words, the ‘shaped’ spectrum is the sum of approximately 2% of the energy spectrum shown in FIG. 6A and approximately 100% of the energy spectrum shown in FIG. 6B. Accordingly, the ‘shaped’ spectrum contains sufficient low-energy x-ray components to inspect a low-density object 140, for example, object 140 has an absorption equivalent to 1 cm of iron, and sufficient high-energy x-ray components to inspect a high-density object 140, for example, object 140 has an absorption equivalent to 10 cm of iron, while substantially reducing the ambient radiation dose. FIG. 7 is a schematic top view of another exemplary embodiment of an inspection system in accordance with the invention. As in the exemplary embodiment shown in FIG. 5, the system, referenced as system 300, includes a generator 310 and a collimator 320. In this exemplary embodiment, however, the shaper 330, modulates beam 930 by both attenuating the intensity of at least a portion of the beam, beam 930, and separating beam 930 into a first beam 932 and a second beam 934. In particular, section 330a(1), section 330a(2), and section 330b attenuate the intensity of the portion of beam 930 that passes through the respective sections. Thus, the first beam 932, which passes through section 330b, is attenuated in accordance with a first attenuation factor (which, for this exemplary embodiment, equals 1), and the second beam 934, which passes through section 330a(2), is attenuated in accordance with a second attenuation factor. Depending upon the particular application of use for beam 930, beam 930 may pass through section 330a(1) and section 330b, rather than section 330a(2) and section 330b. Or, in the alternative, beam 930 may pass through all three sections of shaper 330. In addition, as discussed above, the configuration of section 330b may be modified. Moreover, as discussed above, section 330a(1) and section 330a(2) may be composed of: (1) the same material of the same thickness; (2) the same material, but of different thicknesses; (3) different material, but of the same thickness; or (4) different material of different thicknesses. Of course, description of the system in terms of three attenuating sections is for the purpose of example only and any number of attenuating sections may be employed within the scope of the invention. System 300 further includes two or more detectors, shown as detector 350 and detector 360. Detector 350 detects the first beam 932 of shaped beam 930 after the first beam has passed through object 340. As with object 140 in FIG. 5, object 340 is moving in a direction away from the bottom of the page and toward the top of the page. Detector 360 detects the second beam 934 of shaped beam 930 after the second beam has passed through object 340. In one exemplary embodiment, the first beam 932 of beam 930 may include, for example, the low-energy x-ray components of beam 930. In this embodiment, detector 350 might be designed to be primarily sensitive to the low-energy x-ray components of beam 930. Similarly, the second beam may include, for example, the high-energy x-ray components of beam 930. In this embodiment, detector 360 might be designed to be primarily sensitive to the high-energy x-ray components of beam 930. FIG. 8 is a schematic top view of still another exemplary embodiment of an inspection system in accordance with the invention. As in the exemplary embodiment shown in FIG. 5, the system, referenced as system 400, includes a generator 410, a collimator 420, and two detectors 450 and 460. In this exemplary embodiment, however, detector 450 and detector 460 are in tandem. In addition, the shaper, shaper 430, modulates the beam, beam 940, by attenuating the intensity of beam 940, but not by separating beam 940 into a first beam and a second beam. Rather, as with shaper 130 of FIG. 5, shaper 430 attenuates the intensity of an areal portion of beam 940 in accordance with a first attenuation factor, and attenuates the intensity of the remaining portion of beam 940 in accordance with a second attenuation factor. Moreover, in this exemplary embodiment, section 430b of shaper 430 is composed of some material of some thickness. Thus, unlike section 130b and section 330b, section 430b attenuates the portion of beam 940 in accordance with an attenuation factor that is not equal to 1. Section 430b may be composed of the same material, but of a different thickness, than section 430a(1) or section 430a(2). Or, section 430b may be composed of a different material, but of the same thickness, as section 430a(1) or section 430a(2). Or, section 430b may be composed of a different material of different thickness than section 430a(1) or section 430(a)(2). In turn, as discussed above, section 430a(1) and section 430a(2) may be composed of: (1) the same material of the same thickness; (2) the same material, but of different thicknesses; (3) different material, but of the same thickness; or (4) different material of different thicknesses. Moreover, as discussed above, the configuration of section 430b may be modified. As discussed, detector 450 and detector 460 are in tandem. Typically, detector 450 is optically isolated from detector 460, to stop scintillation from detector 460 being detected in detector 450. This may be achieved, for example, by painting the back side of detector 450 (the side facing detector 460) with black paint. In one exemplary embodiment, detector 450 might be designed to be primarily sensitive to the low x-ray energy components of beam 940 and detector 460 might be designed to be primarily sensitive to the high-energy components of beam 940. For example, detector 450 may be a 0.6 mm thick detector of CsI scintillator and detector 460 may be a 1 cm thick detector of CsI scintillator. In this embodiment, detector 450 has photo-diode 452 to detect the photons generated in its scintillator, and detector 460 has photo-diode 462 to detect the photons generated in its scintillator. The signal current from photo-diode 452 measures the low-energy x-ray components of shaped beam 940, and the signal current from photo-diode 462 measures the high-energy x-ray components of shaped beam 940. In another exemplary embodiment with detector 350 and detector 360 arranged in tandem, detector 350 might be designed to be efficient for detecting the low-energy x-ray components of beam 930 and inefficient for stopping the high-energy x-ray components of beam 930. In turn, detector 360 might be designed to be highly efficient for stopping all energy components of beam 930 but, because detector 350 absorbs the low-energy x-ray components of beam 930, detector 360 need only detect the high-energy x-ray components of beam 930. Mobile Inspection System with Spatially and Spectrally Tailored Beams In other embodiments of the present invention, a cargo container inspection device uses flying-spot x-ray imaging (either in transmission, backscatter, or both) as practiced from a mobile inspection vehicle employing spatially and spectrally tailored beams as described above. Referring now to FIG. 9A, a perspective view is shown of a cargo container inspection system, designated generally by numeral 820, in accordance with a preferred embodiment of the invention. Further description of the rudiments of a mobile inspection system are provided in U.S. Pat. No. 5,764,683 (Swift et al.), issued Jun. 9, 1998, which is incorporated herein by reference. In FIG. 9A, cargo container inspection system 820 is shown deployed for inspection of passenger cars 822 and 823. FIG. 9B shows a preferred embodiment of the invention. With reference to FIGS. 9A and 9B, a truck 824, typically 35′ long×8′ wide×10′6″ high, houses and supports the x-ray inspection equipment, ancillary support and analysis systems, and a hydraulic slow-speed drive mechanism to provide the scan motion. Truck 824 serves as both the platform on which the mobile system is transported to its intended operating site, and a bi-directional translation stage, otherwise referred to herein as a “bed,” to produce the relative motion required during a scan. Chopper 826 is used, in accordance with flying spot generation discussed above, in reference to FIGS. 1–8, to scan beam 828 of penetrating radiation recursively in a vertical direction. Radiation scattered by the contents of the cargo container, shown here as passenger car 823, is detected by x-ray backscatter detectors 830. Boom 832 allows beam stop 834 to intercept beam 828 as it emerges from the distal side of the scanned cargo container. Beam stop 834 is also referred to as a “beam catcher.” In addition or alternatively to beam stop 834, an x-ray transmission detector, designated by numeral 34 in FIG. 1, may be mounted in opposition to beam 828. It is to be understood that the positions of the source 840 and the transmission detector 34 may be reversed, and that source 840 may be carried on the side of the cargo container that is distal to truck 824. It is, furthermore, to be understood that the term ‘source’ as used herein and in any appended claims, and as designated by numeral 840 in the drawings, refers to the entirety of the apparatus used to generate beam 828, and may have internal components that include, without limitation, apertures, choppers, collimators, etc. Referring now to FIG. 10, a top schematic view of the layout of the system shown in FIG. 9B, is depicted as configured for transport. FIG. 11 is the corresponding side elevation, additionally showing the detectors in one of two available deployed positions. The modular components comprising the cargo container inspection system are: the penetrating radiation source assembly 840; x-ray high voltage generating subsystem including high voltage power supply 842 and high voltage tanks 844; backscatter detector modules 830, comprised of an upper bank 846 of detectors and a lower bank 848 of detectors; detector electronics module 850; and operator's console 852. The dashed position of upper backscatter detector banks 846 indicate the position for inspection of cargo containers. The x-ray source 840, high-voltage power supply 842, and positive and negative high-voltage tanks 844, are all in accordance with ordinary practice in the art of x-ray generation. In a preferred embodiment of the invention, a 450 kV x-ray tube is employed. FIG. 12A shows a cargo container inspection system 820, in accordance with a preferred embodiment of the invention, as deployed for inspection of a full-sized tractor-trailer 860 while FIG. 12B shows the same cargo container inspection system 820 deployed for inspection of a passenger van 862. The angle of elevation 864 of the 43° scanning beam can be changed depending upon the application. For optimum versatility, the range of limiting angles extends from at least 55° below horizontal to 55° above horizontal. This corresponds to an angular adjustment of the source axis from −33.5° to +33.5°. Operationally, one side of a large truck 860 (up to 14′ height), as depicted in FIG. 12A, can be completely covered in three passes; however, in many cases, satisfactory coverage can be achieved in two passes, such as through the use, for example, of an x-ray source having a 90-degree opening angle. The system operators must choose between doing a third pass or tolerating a small amount of corner cutoff 866, in which case, higher inspection throughput can be achieved. Since the scanning system is bi-directional, alternate passes can be in the forward and reverse directions. Operationally, as well, one-side of passenger cars and small trucks may be scanned in a single pass of the system. Depending upon the situation, it may be necessary to scan the opposite side as well. The upper set 846 of backscatter detectors can be deployed over the top of smaller vehicles as shown in FIG. 12B, substantially improving the scatter collection efficiency and producing higher quality images. Backscatter detector modules 846 and 848, two are typically 6′ long and 1′ wide, and each typically comprises four segments. In a preferred embodiment of the invention, the cargo container inspection system has two scan-speed modes: nominally 3 inches/sec and 6 inches/sec. The faster speed results in higher throughput, the slower mode—higher image quality. In accordance with one embodiment of the invention, image data in either mode is acquired into a 1024×4096×12 bit image memory and displayed onto a 1024×1024 high-resolution display via a continuously-adjustable 12-bit-to-8-bit look-up table. Additional displays can be provided to allow simultaneous viewing of more than one image, or, alternatively, images may be superposed or combined, as known to persons skilled in the art. Backscatter detectors are mounted to allow efficient collection of scattered radiation from close to the road surface, all the way to the roof of the inspected container. A motorized mechanism enables the upper set of detectors to be deployed over a small vehicle, as shown in FIG. 12B, though other means of deployment are readily apparent to persons skilled in the mechanical arts and are within the scope of the invention. The operator's console 852 (shown in FIG. 11), provides for the console operator to control the x-ray system and display images. Various display monitors may be provided. One preferred embodiment has an upper display for transmission images, and a lower display for the corresponding backscatter image. Similarly, various display functions may be provided: Zoom, pan and scroll—Joystick controls allow the operator to display any part of the image at 2× and 4× magnifications. Continuous density expand—This contrast-enhancing feature allows the operator to display any contiguous subset of the 12-bits (4096 digital intensity levels) of image data over the full black-to-white range of gray levels on the display monitors. The implementation is through a set of 10 pre-set push buttons, along with a trackball for fine-tuning. Edge enhancement—A mathematical algorithm sharpens the image and extends the effective dynamic range of the display for faster and easier image analysis. Reverse video—Operators may select between positive (black-on-white) or negative (white-on-black) image display, depending on personal preference. Image archiving—Operators may “mark and annotate” the images from the console keyboard, and store them on optical disk for future recall. Truck 824 containing cargo container inspection system 820 is fitted with a custom-built box (or truck body) 868 (shown in FIGS. 12A and 12B) specified to accommodate the imaging equipment, and to provide support structures, environmental control, and electrical power distribution. Truck 824 is provided with both front- and rear-wheel drive: Standard rear-wheel drive from the truck's engine is used for normal over-the-road travel. An alternative drive mode is powered by a low-RPM hydraulic motor to obtain the very low speeds employed for the scan. The two drives are connected via a switchable gearbox to preclude the possibility of having both active at the same time. The hydraulic motor controls, including speed selection, drive direction, and motion start/stop, are located in the cab of the truck under the control of the driver. As an additional safety feature, actuation of the truck's brake will automatically cause disengagement of the hydraulic clutch. A similar arrangement using a hydraulically-powered front or rear wheel drive is known in the art for other special applications requiring very slow vehicle motion. Deployable beam stop 834 is employed to assure compliance with FDA radiation safety requirements. However, the output radiation of the system is so low that the health and safety requirements for low radiation levels is met only a few feet away from the source even if no beam stop is used. Beam stop 834 uses a dense shielding material such as lead that is deployed from the end of a boom 832 that extends about 14′ from the side of truck 824 at the location of the x-ray beam 828. Generation of x-rays is prevented by interlock circuits unless boom 832 and beam stop 834 are properly deployed. To stow the beam stop for road travel, the beam stop is retracted into the hollow boom 832. Boom 832 is then rotated parallel to the truck axis and lowered into a cradle in truck box 868. The scan motion is exceedingly slow—typically, ⅓ to ⅙ of a mile per hour. An audible alarm is actuated whenever the scan drive mechanism is engaged for motion in either direction. Since this motion also coincides with x-ray generation, the audible warning also provides an “X-RAYS ON” warning. The x-ray high voltage power supply 842 is interlocked so that it cannot be energized unless both chopper wheel 826 is up to speed and truck 824 is in motion. This additional safety precaution ensures that the scanning beam will not be stationary over any one region of space for a long time, thus ensuring low delivered dose. Operation will be described as it applies to the inspection of one or more passenger cars; scanning of large vehicles will be similar, except that the upper detectors do not need to be swung outboard in this case. It will also be assumed that the system will first be set up, and that vehicles to be scanned will then be brought to it. An alternative whereby the system is deployed beside parked vehicles or containers calls for a minor variation of procedures. Upon arrival at the intended inspection site, the operators will first assure that the site is suitable: i.e., that there is a sufficient space available for system operation and that operating space can reasonably be secured for safe operations. They will then position the truck at the starting position for the first scan, assuring that there is sufficient room to move the truck ahead for the required scan distance, usually about 65 feet. (Scans will normally alternate, forward and back; it is also possible to scan sequentially in the forward direction only, to scan a continuous line of parked vehicles for example, provided that the necessary space is free.) Once positioned, the on-board generator is started to provide power for system operation, lighting, and a cooling unit. Operator's console 852 is powered up at this time. The operators then manually deploy the backscatter detectors and the beam stop using a motorized mechanism provided for that purpose. Only the upper set of detectors 846 deploy, as shown in FIG. 12B. The beam stop is deployed by rotating the boom into a position orthogonal to the truck, and then lowering the beam stop out of the boom to its preset limit. This action closes an interlock circuit that is required before x-ray generation is possible. An x-ray tube warm-up sequence, if necessary, is then initiated from operator console 852. Following warmup, the physical configuration of the system setup is completed by rotating the x-ray beam angle to the direction (elevation) required for the intended scan operations. This is done by a manually-actuated electric motor, and with the aid of an indicator gauge to assist in setting the desired scan elevation. Scanning operations can then commence. Scan operations are simple and straightforward. One or more vehicles are directed to positions along the scan path (up to 65 feet of total vehicle length may be imaged in a single scan) and the drivers and passengers exit the vehicles. Using menu-driven software, the system's computer is readied for image acquisition. This places the computer and data acquisition electronics into a status wherein c-rays will be initiated and image acquisition started upon receipt of a “scan” command initiated by the system's slow-speed drive controls. The computer also transmits a “ready” status signal to the scan drive control located next to the driver of truck 824. The driver sets the desired scan speed and direction at the scan drive control. After the “ready” status is received from the computer, the driver starts the scan by pushing a “start” button and releasing the truck brakes. “Start” initiates motion via the slow-speed drive. The driver has continuous control over the truck. He is responsible for steering, and may stop the truck at any time by actuating the brake. Otherwise, the scan will stop automatically after a full data set has been acquired by the computer (and the “ready” status is removed). As soon as the truck is in motion, a “scan” signal is sent to the computer. The computer then triggers the x-ray generator to ramp up to its pre-set operating conditions, and upon confirmation that they have been reached (about 5 seconds later) it starts data acquisition. Data acquisition continues until either the “scan” command is interrupted or the image memory is full. To break the system down for transportation, electronic systems are shut down and the beam stop and detector mechanisms are retracted and secured for travel. The hydraulic drive is disengaged and its power shut off. The generator is switched off. In a further embodiment, preferred in various applications, the intensity of the transmitted x-ray beam may be measured by a single, elongated transmission detector located on the opposite side of the inspected object from the x-ray source and carefully aligned with the plane of the x-ray beam. The detector is designed to accept and respond to x-rays striking anywhere along the length of its linear entrance slit. The detector is oriented so that the flying-spot beam sweeps repetitively from end-to-end along the slit while truck 824 moves past the inspected object. The detected signal is amplified, integrated, sampled and digitized into an image memory over many sequential, short time intervals during each sweep of the pencil beam. Each such digitized sample forms one pixel of the final image, and the series of samples acquired during one sweep of the beam constitutes one line of image data—typically 1024 samples per line. A complete image frame is constructed by acquiring successive lines as the object is moved through the scan plane. In the flying beam mode, the positional image information is acquired by correlating the instantaneous detector output with the position of the flying-spot beam at that instant of time. In a corresponding “fanbeam” system an entire line is illuminated at once and individual pixels along the line are acquired either by a large number of discrete detectors arranged along the line, or one or more detectors with positional sensitivity. The transmission detector may comprise scintillators optically coupled to photomultiplier tubes. This method is more efficient and exhibits less electronic noise than a method using a photodiode array. The resulting improvement in signal/noise allows equivalent images to be made at lower doses and with lower beam energies. It is to be understood that, within the scope of the invention, the source of penetrating radiation may lie on the opposite side of the inspected object as the mobile platform 824. Relocatable Inspection System with Spatially and Spectrally Tailored Beams In other embodiments of the present invention, a cargo container inspection device uses flying-spot x-ray imaging (in transmission, backscatter, or both) with spatially and spectrally tailored beams as described above, and backscatter imaging technologies, where inspection is practiced from two segments disposed astride an inspected item such as a cargo container or a truck. Referring now to FIG. 13, a perspective view is shown of a cargo container inspection system, designated generally by numeral 500, in which an enclosure 32, shown here as the trailer of a truck, is inspected while at rest. One or more sources 502 provide one or more beams of penetrating radiation that are incident at points on the surface of enclosure 32 that vary as source 502 moves with respect to the enclosure. In the embodiment shown in FIG. 13, an x-ray inspection module 504 is driven along a set of parallel tracks 506 and thus traverses cargo enclosure 32. Inspection module 504 includes a lower module 508 containing a source of x-ray irradiation, typically a LINAC with spectral shaping of a beam as described above, and an upper module 510 in which an operator's console is located for control of the inspection system during the course of inspection. Modules 508 and 510 are preferably cargo containers themselves for ease of transportation to and from and particular inspection site. In accordance with embodiments of the present invention, independent x-ray generators are used to provide sources of penetrating radiation for transmission and scatter images. One or more x-ray generators may be used for each modality. Referring to FIG. 14, a top view of a cargo container 32 being examined by two backscatter x-rays systems 512 and 514, one on either side of container 32, and a spectrally shaped transmission system 516. It is to be understood that the horizontal disposition of each of systems 512, 514 and 516, is a matter of descriptive convenience and that, within the scope of the present invention, any of the systems may be at another angle, such as vertical, with respect to the ground. Describing, first, backscatter x-rays systems 512 and 514, x-ray beam 520 is emitted by an x-ray source 522 of one of various sorts known to persons skilled in the art. Beam 520 may also be comprised of other forms of penetrating radiation and may be monoenergetic or multienergetic, or, additionally, of varying spectral characteristics. Backscatter x-ray beam 520 is typically generated by a DC voltage applied to the anode of an x-ray tube 522 so that beam 520 is typically continuous. However, a beam 520 of other temporal characteristics is within the scope of the invention. Beam 520 has a prescribed cross sectional profile, typically that of a flying spot or pencil beam. Beam 520 will be referred to in the present description, without limitation, as an x-ray beam, and also, without limitation, as a pencil beam. In a preferred embodiment of the invention, a scanned pencil beam, whose position and cross section is well known at every point in time, is used. The cross section of the pencil beam defines the spatial resolution of the images. Typical pencil beam sizes are a few mm in diameter at a distance of a meter from the beam defining collimation; that is, an angular spread in the beam of <5 milliradians. Backscatter beam 520 is typically characterized by x-ray energies in the range below 450 keV, and even below 220 keV, so that detected backscatter has a component significantly dependent on the composition of the scattering material Penetrating radiation scattered by an object 527 within enclosure 32 is detected by one or more x-ray detectors 526 and 528 (shown also in FIG. 13). X-ray detectors 528 may be disposed more distantly from x-ray beam 520 than other detectors 526 detect x-rays singly scattered only from more distant objects 527 whereas any scattering incident on outer detector 528 from a near-field object 530 must be due to multiple scattering of the x-ray radiation within the near-field object and is thereby sharply attenuated. Consequently, inner detectors 526 are preferentially more sensitive to near-field objects 530, while outer detectors 528 are preferentially more sensitive to far-field objects 527. Since beam 520 is typically a pencil beam, i.e., a beam having a narrow angular extent, typically on the order of 1°, the source of detected scattering may be localized both with respect to depth and with respect to lateral position. In order to obtain greater spatial resolution of the source of scattered radiation, collimators 532 may be employed, as known to persons skilled in the x-ray art, for narrowing the field of view of segments of detector 528. Backscatter system 514, with source 515 and detectors 529 is disposed on the same side of enclosure 32 as transmission source 536. Transmission system 516 is now described. X-ray beam 534 is produced by source 536 which is typically a high energy source of penetrating radiation such as a LINAC for example. In certain embodiments of the invention, beam 534 may be a fan beam, subtending typically 30°. The spectrum of beam 534 is shaped in accordance with the teachings above referring to FIGS. 5 and 6A–6C. The transmission x-ray source from a linear accelerator is inherently pulsed, with typical pulse rates in the range between 100 and 400 pulses per second. The portion of transmission beam 534 which traverses enclosure 32 and objects 530 and 538 contained within the enclosure is detected by transmission detector 540 which may be coupled to the inspection modules 508 and 510 by means of gantry 550 (shown in FIG. 13). Sources 536, 515, and 520 produce respective beams that are spatially staggered so that a given object within the enclosure passes successively through the beams as the inspection module 504 passes along tracks 506 with respect to stationary enclosure 32. In accordance with other embodiments of the present invention, the backscatter signals and transmission signals may also be rendered completely independent of one another by temporal gating of the different detectors. The electrical output signals produced by detectors 526, 528, and 540 are processed by processor 542 to derive characteristics such as the geometry, position, density, mass, and effective atomic number of the contents from the scatter signals and transmission signals using algorithms known to persons skilled in the art of x-ray inspection. In particular, images of the contents of enclosure 32 may be produced by an image generator. As used in this description and in the appended claims, the term “image” refers to an ordered representation of detector signals corresponding to spatial positions. For example, the image may be an array of values within an electronic memory, or, alternatively, a visual image may be formed on a display device 544 such as a video screen or printer. The use of algorithms, as known in the art of x-ray inspection, for identifying suspect regions within the enclosure, and identification of the presence of a specified condition by means of an alarm or otherwise, is within the scope of the present invention. In many applications, it is desirable that enclosure 32 be inspected in a single pass of the inspection module 504 past the enclosure 32 in direction 501. Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention. These and other obvious modifications are intended to be covered by the appended claims. |
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description | By means of FIGS. 1-6 an illustrative embodiment of the present invention will be described. This embodiment forms the xe2x80x9cMINItracexe2x80x9d Integrated Radiation Shield: A primary object of the invention is to create a radiation shield for a PET isotope production system, which presents a single unit having a limited size making it suited to be operated at an adequate floor size available for instance at a regular hospital utilising radioactive tracers in the form of short-lived isotopes. Another object of the invention is to still achieve a design of the,radiation shield, which also presents an aesthetic timeless design. Therefore the radiation shield and its integrated subsystems are housed in a carefully shaped shell, which is still offering the full desirable radiation protection shield. An overall picture of the apparatus according to the present invention is disclosed in FIG. 1 and consists of four moulded sections, two fixed section 1 and 2 and two additional movable sections 3 and 4 forming doors. The installation of a PET isotope production system normally includes rigging work of a relatively heavy cyclotron device. Being able to, in a simple way, move, i.e. open, the additional radiation shield sections 3 and 4 constituting the doors provides an effective method to quickly access and service the PET isotope production system. The match casting technology makes the fitting between the sections almost perfect, i.e. no slots, and close fitting to floor surface due to tight casting tolerances. The no time consuming alignment of shield sections is valuable when installing the PET isotope production system. To achieve a simple opening of the radiation shield the sections 3 and 4, according to FIGS. 3 and 4, are forming doors on heavy-duty hinges taking up the load of the weight of the sections 3 and 4. Such a door section in a preferred embodiment has a weight of the order 7-8 tons, and thus the entire radiation shield has a mass corresponding to 10 m3 of special concrete. Correspondingly each section 1 and 2 has a weight of 10-11 tons. A portion of each of the hinges 5 is fixedly moulded into the sections forming the concrete constituting the radiation shield, thereby eliminating all risks for having to perform adjustments over time (i.e. the hinges in fact forming an integral part of the shield) Furthermore these doors 3, 4 are suspended on roller bearings in the hinges 5 forming a virtually xe2x80x9czero friction systemxe2x80x9d making door motion possible with a very low driving force which also is beneficial for eventual pinch hazards. Additionally the hinges 5 are adjustable in all directions facilitating all the options for the necessary final fine adjustment, to obtain a non-leakage radioactive and an almost airtight closure of the casing design enclosing the cyclotron device. The casing according to the invention does not need any floor penetrations for installation of this xe2x80x9cMINItracexe2x80x9d Integrated Radiation Shield. The user will be able to use an existing floor surface and there will be no time consuming preplanning and surface breaking needed for cable ducts, radiation shield rails and driving systems. Preferably before installation of the xe2x80x9cMINItracexe2x80x9d Integrated Radiation Shield the floor surface may be treated with a self levelling low viscosity resin making the floor surface perfectly flat and levelled and ready to use after one night of hardening. On top of the section 2 there are situated a number of intake openings for the externally separated circuits, for instance for the wiring. Each radiation shield section as well as the cyclotron device are equipped with lifting fittings for hydraulic jack rollers making lifting and movement of these heavy components quick and easy during the installation phase. The xe2x80x9cMINItracexe2x80x9d radiation shield consists of a dense concrete body especially designed to balance attenuation properties and the volume/weight ratio of the shield. The heavy ballast is chosen to be mainly iron ore for good gamma radiation attenuation with additional Boron and Hydrogen components to strengthen the neutron radiation attenuation capacity. In a preferred embodiment the radiation shield is having a hydrogen radiation protection mass of the order 25 kg/M3 and 5-10 kg/M3 of pure Boron and maximising the density by means of a magnetite (black ore Fe3O4) content for obtaining a final density of the order 3.5. Furthermore, the targets are surrounded by a shielding of sandwich type containing PE plastics and lead (Pb). Finally the xe2x80x9cMINItracexe2x80x9d radiation shield will form a virtually air-tight container which prevents accidental leakage of radioactivity from the xe2x80x9cMINItracexe2x80x9d interior system to the outside of the casing to create a low radiation environment in a room where the system is operating. Connections are easily provided for creating an under-pressure inside the shield (if regulations call for this). Also note that no air circulation from the surrounding air outside the shield is necessary for cooling purposes of the interior systems of the radiation shields, which assists in keeping the external environment of the casing at very low radiation hazard. Inside the radiation shield there is a space 7 housing a cyclotron with its internal subsystems like ion source, radio frequency electrode system and beam extraction elements and the visible subsystems such as vacuum case and pumps, targets with cooling water, and target window cooling. For easy maintenance of the cyclotron its magnet coils and poles are positioned such that the plane of the ion beam is vertical. Due to this design and the movable sections 3 and 4 the vacuum chamber of the cyclotron can even be divided in this vertical plane for simple access of its interior containing the closely spaced electromagnetic poles forming the acceleration gap for the ion beam and the other internal subsystems. This cyclotron is particularly designed for acceleration of a negative hydrogen ion beam then particularly used for production of short lived radioactive diagnostic tracers for medical applications. Also integrated in the radiation shield there is provided a Waste Gas Delay Line 8 positioned within the concrete portion 1, which is indicated in FIG. 2. It consists of a xe2x80x9clongxe2x80x9d plastic tube embedded in the concrete in such a way that the concrete will provide full radiation shielding for potential radioactivity loaded into the Waste Gas Delay Line 8. At the left side of the concrete casing portion 1 there is created a further compartment 9 (indicated in FIGS. 1 and 5). The compartment 9 offers target media handling 10 for the gas targets (e.g., isotopes 11C, and 15O) consisting of valves and pressure gauges and water dispensing systems 11 for the water targets (e.g., isotopes 13N, and 18F), the processing systems 12 for tracers 15O and processing systems 14 for tracers 11C. The compartment 9 further contains a lead radiation shield 13 embracing the 15O processing system 12 and a similar lead radiation shield 15 for the 11C processing system 14. The lead shields 13, 15 are furnished with doors supported by hinges for easy access of the gas processing systems. At the right shield side of the xe2x80x9cMINItracexe2x80x9d casing there is also, still a compartment 16 (indicated in FIGS. 1 and 6) containing the secondary cooling system 17, mains power distribution 18, vacuum system controller 19 and the ion gas source controller 20. Further at the top of the radiation shield created by the four portions 1-4 there are arranged shield surface driving motors for motions for doors as well as warning signs, e.g. indicating xe2x80x9cMagnet field activexe2x80x9d, xe2x80x9cBeam onxe2x80x9d. Thus, the disclosed apparatus according to the present invention forms an integrated closed radiation-proof system for PET isotope production, which can easily be housed in connection to a main hospital for an easy access of short-lived radioactive tracers for medical diagnostic purposes. The advantages of the present disclosed system primary lies in the design of the compact self-supporting radiation-proof casing which then easily can be applied as a localised facility. |
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abstract | Embodiments provide a multi-cone X-ray imaging Bragg crystal spectrometer for spectroscopy of small x-ray sources with a well-defined spectral resolution. The spectrometer includes a glass substrate machined to a multi-cone form; and a thin crystal slab attached to the glass substrate, whereby the multi-cone X-ray imaging Bragg crystal spectrometer provides rotational symmetry of a ray pattern, providing for accurate imaging, for each wavelength in the spectral range of interest. One or more embodiments include a streak camera and/or a gated strip detector. |
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042973040 | summary | BACKGROUND OF THE INVENTION The present invention relates to a method for solidifying high and medium radioactivity and/or actinide containing aqueous waste concentrates or fine-grained solid wastes suspended in water for final noncontaminating storage in which the waste concentrates or the suspensions are subjected, together with absorbing and/or hydraulically binding inorganic materials, to a ceramic firing process so as to produce a solid sintered body. It has been known for a long time to solidify radioactive aqueous solutions by first reducing the volume of such wastes, thereby concentrating the radioactive substances, and then treating the concentrates either by (1) subjecting them together with glass formers to a heat treatment until the radioactive substances become distributed throughout the resulting glass melt and then having the melt solidify into a solid body, or (2) by mixing the concentrated wastes with silicate-containing clays or with ion exchangers, respectively, and firing the resulting mix ceramically so as to form a solid body. Some of the drawbacks of producing glass blocks having radioactive waste substances incorporated therein include the need to use relatively complicated and expensive apparatus which must be operated by trained personnel. Moreover, in the course of prolonged storage, decomposition of the glass structure may occur due to the continued emission of radiation and heat energy by the incorporated highly radioactive substances with the result that the resistance of the glass structure to leaching deteriorates with time and its ability to effectively retain radioactive materials is diminished, especially as compared to the relatively good leaching properties of nondecomposed glass waste blocks. When clay-radionuclide mixtures are fired according to the prior art, the quality of the solidified products containing high concentrations of radioactive substances has not been sufficient for final storage purposes. An additional problem encountered with prior art solidification by glass and fired clay processes is that during the high temperature stages, significant quantities of radioactive substances evaporate from the not yet solidified waste. These escaping impurities must be trapped and removed by complicated waste gas purification techniques involving solids filters, gas washing columns and condensate separators. German Pat. No. 1,127,508 to Alberti proposes mixing aqueous atomic waste with fireproof cement and then increasing the density of the resulting hardened block by ceramic firing to produce a sintered body which is resistant to leaching. In order to increase the mechanical stability of the hardened block, the patent suggests adding fireproof additives such as fire clay or brick chips to the fireproof cement. For example, a cylindrical molded body was produced from molten alumina cement and radioactive liquid. The molded body, after hardening, was uniformly heated for a period of 5 hours to a temperature of 500.degree. C. to evaporate excess water. The molded body was then rapidly brought to a firing temperature of, for example, 1100.degree. C. and kept at this temperature for about 2 to 4 hours after which the molded body was cooled slowly. No information is given in the patent about the radioactivity of the radioactive liquid being treated. There is also no disclosure in the patent as to the quantities of liquid being treated in the 3-liter vessels used by Alberti or as to the water-cement values, or the like. Results of leaching experiments likewise were not disclosed. The Alberti process may be useful for the solidification of low radioactivity aqueous wastes, but it is very expensive and unnecessarily complicated. Further, it cannot be used for the solidification of high or medium radioactivity and/or actinide containing aqueous wastes. Medium activity waste solutions have been solidified in cement, concrete or bitumen at temperatures of more than about 150.degree. C. Solidification of medium activity waste solutions with cement, concrete or bitumen leads to end products which have low thermal stability and relatively low radiation resistance over extended periods of time. As a result, special safety measures become necessary when depositing these products for intermediate or final storage. When seeking to store actinide concentrates, the intensive development of radiolysis gases and heat in the product, as a result of the radioactive decomposition of the actinides, renders bitumen, cement or concrete solidification processes completely unsuitable. Suspended combustion ashes or ion exchangers have previously been solidified in cement and put into barrels which act as sheaths. The thus sheathed, solidified products have then been put directly into storage. The properties of such blocks, however, particularly with respect to mechanical stability and leaching resistance, are not particularly good, so that this type of solidification is used only for weakly active wastes. SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide a method for solidifying high and medium radioactivity aqueous wastes as well as actinide containing aqueous wastes and/or suspended powdery solid wastes, in which the solidification products do not exhibit the drawbacks of the prior art fixing processes and which meet all requirements for final storability. It is a further object of the invention to provide a process for preparing radioactive wastes for storage in which the wastes are securely stored and not easily leached. It is yet another object of the invention to provide a process which is simple and uncomplicated but effective in preventing radioactive contamination. An additional object of the invention is to provide a process for producing a solidified product which is not troubled by emissions of radiolysis gases. To achieve the foregoing objects and in accordance with its purposes, the present invention provides a method for solidifying high and medium radioactivity and/or actinide containing aqueous waste concentrates or fine-grained solid wastes suspended in water for final noncontaminating storage in which the waste concentrates or the suspensions are subjected together with absorbing and/or hydraulically binding inorganic material, to a ceramic firing process so as to produce a solid sintered body, comprising (a) setting the waste concentrates or suspensions by evaporation to form an evaporate (B) having a water content in the range between 40 and 80 percent by weight and a solid content whose metal ion and/or metal oxide component lies between 10 and 30 percent by weight of the evaporate (B) being formed, and setting the pH of the evaporate (B) to between 5 and 10; (b) kneading the evaporate (B) obtained from step (a) with a clay-like substance containing a small quantity of cement or such a clay-like substance or mixture of clay-like substance with a small quantity of cement containing an additive for suppressing the volatility of alkalis, esp. cesium or alkali earths, esp. strontium and/or an additive for suppressing the volatility of any decomposing anions which may be present in the evaporate from the group including sulfate, phosphate, molybdate and uranate ions, at a weight ratio range of evaporate (B) to clay-like substance of 1:1 to 2:1; (c) producing molded bodies from the kneaded mass obtained from step (b); (d) heat treating the molded bodies, including drying at temperatures between room temperature and about 150.degree. C., calcining at temperatures up to about 800.degree. C. and subsequently firing at temperatures between about 800.degree. C. and 1400.degree. C. to practically undissolvable mineral phases; and (e) enclosing the molded bodies of fired mineral phases on all sides in a dense, continuous ceramic or metallic matrix. DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a liquid which may, for example, be either a suspension or solution of radioactive waste materials is prepared for noncontaminating final storage. The waste materials treated according to the present invention are the by-products of manufacturing, processing and reprocessing of nuclear fuels as well as the wastes of nuclear plants and the like. The wastes treated according to the present invention may be categorized and defined as follows: (1) High activity waste solutions--these comprise nitric acid solutions containing predominantly heavy metal nitrates, which are produced during the separation of fission products from spent nuclear fuels. (2) Medium activity waste solutions--these are predominantly nitric acid solutions, generally containing a large amount of sodium nitrate, which are obtained during reprocessing of nuclear fuels and during decontamination processes in nuclear plants. (3) Actinide concentrates--these are solutions or powders or combustion residues, which are obtained mainly as waste products during the processing and manufacture of nuclear fuels. (4) Ashes and residues from the combustion of organic radioactive wastes--these ashes and residues are fine-grained solid wastes and are suspended in water. In the process of the present invention, the waste concentrates or suspensions being treated are set by evaporation to a water content in the range between 40 and 80 percent by weight and a solid content whose metal ion and/or metal oxide component lies between 10 and 30 percent by weight of the evaporate (B) being formed. In addition, the pH of the evaporate (B) is set to between 5 and 10. The pH of the evaporate is set such that it is between about 5 and 10. The setting may, for example, be made by the addition of highly alkaline solutions or by denitration of nitrate containing wastes, by known means such as by adding formic acid or formaldehyde. The setting of the pH of the evaporate can be effected either by treating the waste concentrates or suspensions before the evaporation or by treating the evaporate. Concentration to produce evaporate (B) by evaporation, which may take place before and/or after adjustment of the pH, can be effected until a barely flowable concentrate is obtained. The concentrated radioactive evaporate having the desired pH is then transferred into a mixer or kneader where it is stirred and homogenized with the addition of a dry mixture of additives, which mainly include clay-like materials to form a stiff dough. The mixture of the additives comprises a main component and preferably an ancillary component. Main components include kaolin, clay, alumina and/or quartz meal, with cement being an ancillary component. The mixing ratio of substances contained in the radioactive concentrate and the additive mixture should preferably be selected such that shape-retaining bodies can be produced from the doughy mass which has a water content of about 50 percent by weight. Additionally, the ratio of substances selected should be such that the resulting molded bodies, after drying and sintering, have a chemical composition which corresponds to that of natural, stable minerals or rocks. The mixture of the additives may contain 7 to 20 percent by weight cement with reference to the clay-like material plus the cement. By adding cement, there is obtained a molded body which, after complete hardening, maintains its shape even when treated with water. This advantage is utilized in such a manner that water soluble salts which have come to the surface of the molded body during the subsequent drying (hardening) process can be removed by rinsing with water. The wash water can then be returned to the radioactive solution at the start of the process. A further advantage resulting from the addition of cement is the added mechanical and structural stability which it imparts to the molded bodies during subsequent process steps. The kneaded doughy product is then converted into molded bodies by either pressing the dough into molds or by extruding them, for example, by means of an extrusion press. When shaped by molding, the dough is kept in the mold only until it can easily be removed after shrinking. In an advantageous embodiment of the method of the present invention, the kneading of the evaporate is effected with a mixture of about 10 parts by weight clay-like substance and about 1 to 2 parts by weight of a cement which contains about 20 to 30 weight percent SiO.sub.2 and about 40 to 70 weight percent CaO. The clay-like substance advantageously contains SiO.sub.2 in the range from 45 to 70 percent by weight and Al.sub.2 O.sub.3 in the range from 15 to 40 percent by weight and has a loss due to heating in the range from 5 to 15 percent by weight. The clay-like substance may be one or more species selected from the group of pottery clays, stoneware clays, porcelain clay mixtures and kaolins. In an alternate embodiment of the present invention, instead of or together with adding cement to the clay-like substance, the clay-like substance is provided with one or more additives to suppress or limit the volatility of certain components. The additive for suppressing the alkali, esp. cesium, and alkali earth, esp. strontium volatility can comprise 1 to 3 parts per weight TiO.sub.2 powder compared to 20 parts per weight of clay-like material, or 1 to 5 weight percent TiO.sub.2, with respect to the kneaded mass. The additive for suppressing sulfate, molybdate and uranate volatility comprises about 1 to 5 percent by weight BaO while the additive for suppressing phosphate volatility comprises about 2 to 10 percent by weight MgO or BeO or ground, natural beryllium, each weight percentage being with reference to the kneaded mass. A given evaporate does not necessarily contain each ion from the group sulfate, phosphate, molybdate and uranate ions, and thus an additive need be provided only for the ions present in the evaporate. After making the molded bodies from the kneaded mass, but before heat treatment, the molded bodies are allowed to harden and may be surface decontaminated with water. The molded bodies are advantageously dried and hardened in a stream of air at room temperature which requires a period of time for cement containing products of up to 30 days until they are completely hardened. The completely hardened molded bodies can then be washed with water to remove water soluble salts from their surfaces. Thereafter, the molded bodies are subjected to the heat treatment which includes further drying the molded bodies in a drying furnace at higher temperatures so that any nitrates contained therein are thermally decomposed. The heating sequence for this heat treatment is largely dependent on the chemical composition of the molded bodies and their dimensions. Several hours are generally required at temperatures ranging from room temperature to about 150.degree. C. to expel chemically unbound water. At the calcining temperatures ranging from about 150.degree. C. to about 800.degree. C., chemically bound water is expelled and the thermal decomposition of metal nitrates into metal oxides and nitrous gases takes place. The thermal decomposition temperatures of nitrates which are present in higher concentrations must be given particular consideration and it is, therefore, necessary to control the heating rate taking the characteristic decomposition temperatures of each of the nitrates into account. This may necessitate slowing up the heating in a particular temperature range or maintaining it at a given temperature for a period of time until the exhaust air stream contains no significant moisture and no nitrous gases. Thus, the heating is in effect carried out in stages with the heating being stopped or slowed at the decomposition temperatures of the nitrate compounds present as well as at the temperatures at which the water may be removed. Control and regulation of the heating program is effected simply by continuous quantitative measurement of the amount of condensate collected from the furnace exhaust gases in a condensate separator and by a continuous quantitative measurement of the concentration of nitrous gases in the furnace exhaust gas. The furnace exhaust gases preferably can be purified in a washing column with dilute nitric acid so as to absorb nitrous gases. These washing solutions, as well as the condensates from the condenser connected upstream of the washing column, are evaporated in an evaporator. The resulting distillates are treated further as weakly active waste solutions and are not part of the process of the present invention. The concentrates from this evaporator can be introduced as waste materials at the start of the process. After reaching the final temperature of about 800.degree. C. in the drying furnace, the molded bodies are sintered in a sintering furnace to produce the desired end product. Instead of a separate drying furnace and a separate sintering furnace, drying and sintering can take place in the same furnace. The sintering process is performed at temperatures between about 800.degree. C. and about 1400.degree. C. preferably between 1100.degree. C. and 1400.degree. C., to form bodies having practically undissolvable mineral phases and results in significant shrinkage of the molded bodies. Therefore, in order to prevent the formation of cracks and cavities in the end product, care must be taken, depending on the size of the molded bodies, that the sintering process be performed at a sufficiently slow rate. The optimum sintering temperature and time must be adapted to the respective product composition. The monolithic sintered bodies are then inserted into metal containers. Because of the heat given off as a result of radioactive decay, the air space between the sintered body and the metal vessel can be filled by encasing the sintered bodies in a dense continuous matrix having a higher heat conductivity than the bodies themselves, such as cement or low melting point metals or alloys such as lead, bronzes and the like. The metal container itself will then be the final storage container for the radioactive wastes that are solidified in the ceramic. In one embodiment of the present invention, the sintered bodies are comminuted and the comminuted, sintered bodies are enclosed in the continuous matrix. In this instance, the bodies are preferably comminuted to particles or chips between about 1 mm. and 10 mm. in size. The continuous matrix completely encloses the molded body or chips and preferably can be made of either cement rock, produced from at least one kind of cement from the group comprising portland cement, iron portland cement, shaft furnace cement, trass cement, oil shale cement and alumina cement in weight ratios of clay-like material to cement ranging from about 10:1 to 4:1. To further improve heat conductance, the continuous matrix may comprise a copper-zinc alloy, a copper-tin alloy, lead or a lead alloy having a lead content of more than about 50 percent by weight. In cases where the continuous matrix is not made of a metal or an alloy, respectively, ceramic firing, possibly with simultaneous use of pressure, terminates the densification of the matrix waste mixture. Compared to the prior art processes for solidifying high activity waste solutions, such as, for example solidification in a glass matrix, etc., the process according to the present invention has a number of distinct advantages. For example, in the process of the present invention, primary solidification takes place at room temperature, so that during the subsequent drying and sintering processes activity can escape only through the surface of the solidified products so that the solidified products themselves act as filters during these high temperature treatments. Further, whereas the known methods require complicated apparatus and procedural devices with remote control in hot cells or alpha-tight cells, the process according to the present invention uses very simple devices which are adapted very easily to the operating conditions for handling radioactive substances. The process according to the present invention has the further advantage that the troublesome corrosion problems normally encountered during the melting of glass are avoided. The products produced according to the process of the present invention are stable up to temperatures of more than 1000.degree. C. and, due to their particular chemical nature, do not develop radiolysis gases. Thus, it is also possible to solidify high concentrations of actinides in the ceramic matrix since adverse effects on the properties of the end product, which are relevant for final storage, which might otherwise result from the development of radiolysis gases as a result of alpha radiation or high storage temperatures are eliminated. Yet another advantage of the process according to the present invention is its easy adaptability to changes in the chemical and physical consistency and composition of the radioactive wastes. |
052951650 | claims | 1. A self-locking plug for plugging a hole defined by a surrounding structure, comprising: (a) a plug body sized to be disposed in the hole for plugging the hole; (b) a locking mechanism pivotally connected to said plug body for locking said plug body to the structure, said locking mechanism including a catch having a hook portion integrally formed therewith for engaging the structure to lock said plug body to the structure; (c) a cam slidably connected to said plug body and capable of engaging said locking mechanism for pivoting said catch; (d) a piston connected to said cam for driving said cam into engagement with said locking mechanism; (e) a ram connected to said plug body for ramming said plug body into the hole to seat said plug body in the hole, whereby said plug body is seated in the hole as said ram rams said plug body into the hole, whereby said cam engages said locking mechanism as said piston drives said cam, whereby said catch pivots as said cam engages said locking mechanism and whereby said plug body is locked to the structure as said catch pivots; (f) first biasing means interposed between said catch and said plug body for biasing said catch toward the structure; (g) second biasing means interposed between said cam and said plug body for biasing said cam into engagement with said catch; and (h) third biasing means interposed between said ram and said plug body for biasing said plug body into the hole. (a) a plug body matingly disposed in the hole, said plug body having a longitudinal bore terminating in a transverse slot; (b) a locking mechanism connected to said plug body, said locking mechanism including: (c) an elongate cam slidably extending through the bore and having an end portion of predetermined contour for matingly engaging the cam surface of each catch; (d) a piston connected to said cam for driving said cam into engagement with the cam surface of each catch; (e) a ram connected to said plug body for ramming said plug body into the hole to seat said plug body in the hole to substantially reduce fluid flow through the hole whereby said plug body seats in the hole as said ram rams said plug body into the hole, whereby the contoured end portion of said cam matingly engages the contoured cam surface of each catch as said piston drives said cam, whereby each catch pivots in the slot about its respective pin as the end portion of said cam engages the cam surface of each catch, whereby said plug body is locked to the structure as each catch pivots about its respective pin to position the hook portion adjacent the bottom surface of the flange; (f) a first coiled spring interposed between said catches for outwardly biasing said catches toward the flange, said first coiled spring having ends thereof connected to respective ones of said catches; (g) a second coiled spring surrounding said cam and interposed between the end portion of said cam and said plug body for biasing said cam into engagement with said catch; and (h) a third coiled spring surrounding said plug body and interposed between said ram and said plug body for biasing said plug body into the hole. 2. In a nuclear reactor pressure vessel having a core barrel disposed therein, the core barrel having a flange therearound having a bottom surface thereon and a counter-bored access hole therethrough capable of allowing fluid flow through the hole, a self-locking plug for plugging the hole to substantially reduce fluid flow through the hole, the plug comprising: |
description | The application is a Divisional application of, and claims the benefit of, U.S. patent application Ser. No. 15/294,532, filed Oct. 14, 2016, which is a Divisional application of, and claims the benefit of, U.S. patent application Ser. No. 12/612,533, filed Nov. 4, 2009, which issued as U.S. Pat. No. 9,472,309 on Oct. 18, 2016, which are all hereby incorporated by reference in their entirety. The present disclosure relates to tiles for fusion power reactor environments. In particular, it relates to machine-replaceable plasma-facing tiles for fusion power reactor environments. The present disclosure relates to an apparatus, system, and method for machine-replaceable plasma-facing tiles for fusion power reactor environments. In one or more embodiments, the method for installing a machine-replaceable plasma-facing tile for fusion power reactor environments involves providing a tile, where the tile is fish scale shaped and has a tile support tube attached to the back portion of the tile. The method further involves inserting the tile support tube into a manifold channel of a first wall of a fusion power reactor such that the tile is in an install/remove orientation. Also, the method involves rotating the tile until the tile is in a locked orientation in the manifold channel of the first wall of the fusion power reactor. In some embodiments, the tile is rotated in a clockwise direction. In alternative embodiments, the tile is rotated in a counter-clockwise direction. In one or more embodiments, the plasma-facing portion of the tile is manufactured from tungsten (W). In at least one embodiment, the back portion of the tile is manufactured from international thermonuclear experimental reactor-grade (ITER-grade) stainless steel. In some embodiments, the surface of the back portion of the tile is coated with an electrically insulating material. In at least one embodiment, the tile support tube includes at least one coolant channel. In one or more embodiments, each coolant channel is manufactured from international thermonuclear experimental reactor-grade (ITER-grade) stainless steel. In one or more embodiments, a method for removing a machine-replaceable plasma-facing tile for fusion power reactor environments involves providing a tile that is installed in a locked orientation in a manifold channel of a first wall of a fusion power reactor. The tile is fish scale shaped, and has a tile support tube attached to the back portion of the tile. The method also involves rotating the tile until the tile is in an install/remove orientation. In some embodiments, the tile is rotated in a clockwise direction. In alternative embodiments, the tile is rotated in a counter-clockwise direction. The method further involves providing a tile removal tool, where the tile removal tool comprises an elongated handle and two tines. One end of each tine is connected to a first end of the handle. Also, a second end of the handle is located opposite the first end of the handle. Further, the method involves rotating the second end of the handle of the removal tool such that the two tines are in an open state. Additionally, the method involves inserting the two tines of the removal tool between the outer edges of the tile and the first wall of the fusion power reactor. Also, the method involves rotating the second end of the handle of the removal tool such that the tines are in a closed state and grasp the tile support tube. The method further involves lifting the tile away from the first wall of the fusion power reactor with the removal tool such that the tile is completely removed from the manifold channel of the first wall of the fusion power reactor. In one or more embodiments, a machine-replaceable plasma-facing tile apparatus for fusion power reactor environments comprises a tile that is fish scale shaped, and a tile support tube that is attached to a back portion of the tile. In some embodiments, the tile support tube includes at least one coolant channel and at least one guard vacuum region. In at least one embodiment, at least one coolant channel is in a vertical orientation. In one or more embodiments, at least one coolant channel is in a horizontal orientation. The methods and apparatus disclosed herein provide an operative system for tiles for fusion power reactor environments. Specifically, this system allows for machine-replaceable plasma-facing tiles for fusion power reactor environments. The system of the present disclosure teaches an easily machine-replaceable high heat and radiation flux tolerant tile for lining the inner wall of a fusion reactor that produces power-plant levels of heat and radiation flux. The tile of the present system protects the underlying structures of the reactor from damage by plasma impact as well as from tritium and alpha particle infiltration from a fusing deuterium (2H)—tritium (3H) nuclear reaction in a magnetically confined plasma. Projections from current experiments indicate that the plasma in a fusion power reactor will be sufficiently energetic such that in a well controlled reactor, it will be capable of destroying the innermost layer of the plasma chamber in a matter of weeks to months. Currently, there is no known economically acceptable way to replace the interior of the reactor every few months. There are three ways to mitigate this problem. The first way is to better control the plasma such there are fewer plasma impacts on the first interior wall of the reactor. The second way is to manufacture the first interior wall of the reactor from materials that are able to tolerate many plasma impacts. And, the third way is to manufacture the first interior wall such that it is easy and cheap to replace, and such that it protects the other wall layers that lie behind it. In addition, projections from current experiments and the state of the art in technologies for control and materials also indicate that all three approaches will be required for a viable fusion reactor. The system of the present disclosure addresses the third approach. Another problem realized from current experiments is that, in reactor conditions, most known materials become somewhat permeable to tritium (3H), which is the radioactive component of the fuel of the reactor. This permeability allows the materials that line the reactor chamber to absorb some tritium. As such, the materials become slightly radioactive themselves. This causes some tritium to pass through the materials, thereby causing some of the radioactive tritium fuel to leak away. The system of the present disclosure also addresses the tritium permeability problem. Currently, there are several proposed solutions to address these above-discussed problems. The first proposed solution is to build plasma control systems that are able to reduce plasma impacts from several per minute to several per month. The second proposed solution is to find a material that is able to tolerate multiple plasma impacts per minute in the high heat and radiation flux environment of a fusion power reactor without suffering significant erosion, embrittlement, and absorption of tritium. The third proposed solution is to replace the multi-ton first wall/breeding blanket structures lining the interior of the fusion power reactor every few months. However, it should be noted that none of the above-mentioned proposed solutions have yet been developed beyond the concept stage, let alone demonstrated. Also, there are several notable disadvantages to these three proposed solutions. The first disadvantage is that control systems have not been built that are able to reduce plasma impacts from several per minute to one per month, and may never be possible. The second disadvantage is that models and experiments indicate that there is no known material that will survive more than ten fusion power reactor level plasma impacts near the same spot without suffering significant material erosion. And, the third disadvantage is that replacing the multi-ton first wall/breeding blanket structures lining the interior of the fusion power reactors will be so difficult and expensive that it will be impractical to replace these structures at any rate exceeding once every three years. Several constraints must be solved simultaneously for the first interior wall of a fusion power reactor. These constraints are as follows. The first constraint is that the energy flux through the first wall, which is in the form of neutrons, gammas, and alpha particles, will exceed 1 mega Watt per square meter (MW/m2). The second constraint is that, for efficient thermodynamics of the power reactor and for the effective use of the reactor for the production of hydrogen, the first wall (and breeding blanket) coolant outlet temperature should be at least 700° Celsius (C), and preferably will be 950° C. The third constraint is that neutrons from the reaction are energetic enough to break any molecular bond and knock metal atoms out of their original positions in the metal lattice. The fourth constraint is that the first wall must not release vapors into the vacuum surrounding the plasma. The fifth constraint is that the first wall must be manufactured from materials that have a minimal propensity for neutron activation. The sixth constraint is related to the fact that some alpha particles from the reaction will enter the first wall and become trapped. There, the alpha particles will pick up electrons, thereby becoming neutral helium atoms. Eventually enough atoms will accumulate to form bubbles in the material of the wall. As such, the first wall must tolerate or neutralize these bubbles. The seventh constraint is related to the fact that tritium from the fuel will enter the first wall material, thereby making the material both brittle and slightly radioactive. Thus, the first wall must have a way to mitigate the brittleness and remove the tritium. The eighth constraint is that the first wall must be able to tolerate plasma impacts or be easily replaceable after damage from impacts, but before accumulated damage breaches the first wall. The ninth constraint is that the first wall must be very thin such that it does not interfere with the transit of neutrons from the reaction through the first wall and into the breeding blanket located behind the first wall. The tenth constraint is that the first wall must be repairable or replaceable by machine. Despite the intent to build fusion reactors from materials that are not prone to neutron activation, an activation will occur. This means that the reactor will become radioactive itself to a level such that it will not be approachable by human maintainers until after being off for approximately one month. And, the eleventh constraint is that the elements of the first wall must be recyclable after only a short cooling period, even if the recycling only consists of the elements being made into new tiles for fusion reactors. The system of the present disclosure addresses the above constraints in a variety of ways. These various ways are discussed in detail below. In the following description, numerous details are set forth in order to provide a more thorough description of the system. It will be apparent, however, to one skilled in the art, that the disclosed system may be practiced without these specific details. In the other instances, well known features have not been described in detail so as not to unnecessarily obscure the system. FIG. 1 is an illustration of the interior of a fusion power reactor 100, in accordance with at least one embodiment of the present disclosure. In this figure, it can be seen that the fusion power reactor 100 is of a torus shape. It should be noted that the system of the present disclosure can be used with various different types and shapes of fusion power reactors. The first wall of the fusion power reactor 100 is lined with small tile apparatus units 110. Each small tile apparatus unit 110 is individually replaceable. Tile installation and removal is performed by a remote robotic maintenance system that enters the plasma chamber through an access port. An example of a remote robotic maintenance system is the Mascot remote maintenance device that used for the Joint European Torus fusion energy experiment. It should be noted that various other types of remote robotic maintenance systems may be used for the system of the present disclosure. The remote robotic maintenance system will need only simple tools, such as those shown in FIG. 6 to install and remove the tile apparatus units 110. The tiles apparatus units 110 that line the first wall of the fusion power reactor 100 overlap each other in a fish scale pattern. FIG. 2 shows the overlapping fish scale arrangement of the tile apparatus units 110 that are installed on the interior wall a fusion power reactor, in accordance with at least one embodiment of the present disclosure. FIG. 3 is a depiction of a single machine-replaceable plasma-facing tile apparatus 110 for fusion power reactor environments, in accordance with at least one embodiment of the present disclosure. Each machine-replaceable plasma-facing tile apparatus 110 comprises a tile 300 that is fish scale shaped, and a tile support tube 310. The tile support tube 310 is attached to the back portion of the tile 300. In one or more embodiments, the tile support tube 310 includes at least one coolant channel (not shown in figure) and/or at least one guard vacuum region (not shown in figure). FIGS. 4A and 4B illustrate the steps for installing a machine-replaceable plasma-facing tile apparatus 110 for fusion power reactor environments, in accordance with at least one embodiment of the present disclosure. For FIGS. 4A and 4B, the spot on the tile 300 of the tile apparatus 110 indicates the axis on which the tile apparatus 110 rotates. And, the circle on the tile 300 indicates the location of the tile support tube 310 (not shown in figure), which is attached to the back portion of the tile 300 of the tile apparatus 110. For the first step, which is shown in FIG. 4A, the tile apparatus 110 has its tile support tube 310 (not shown in figure) inserted into a manifold channel of a first wall of a fusion power reactor such that the tile apparatus 110 is in an install/remove orientation. For the second step, which is shown in FIG. 4B, the tile apparatus 110 is rotated until it is in a locked orientation in the manifold channel of the first wall of the fusion power reactor. In one or more embodiments, for the second step, the tile apparatus 110 is rotated in a clockwise direction. In alternative embodiments, for the second step, the tile apparatus 110 is rotated in a counter-clockwise direction. FIGS. 5A through 5H depict the steps for removing a machine-replaceable plasma-facing tile apparatus 110 for fusion power reactor environments, in accordance with at least one embodiment of the present disclosure. For FIGS. 5A through 5H, the spot on the tile 300 of the tile apparatus 110 indicates the axis on which the tile apparatus 110 rotates. And, the circle on the tile 300 indicates the location of the tile support tube 310 (not shown in figure), which is attached to the back portion of the tile 300 of the tile apparatus 110. For the first step, which is shown in FIG. 5A, a tile apparatus 110 is installed in a locked orientation in a manifold channel of a first wall of a fusion power reactor. For the second step, which is shown in FIGS. 5B through 5E, the tile apparatus 110 is rotated until the tile apparatus 110 is in the install/remove orientation. In one or more embodiments, for the second step, the tile apparatus 110 is rotated in a counter-clockwise direction. In alternative embodiments, for the second step, the tile apparatus 110 is rotated in a clockwise direction. A tile removal tool 500 is used for the third step of the installation procedure. FIG. 6 shows an illustration of a tile removal tool 500, in accordance with at least one embodiment of the present disclosure. The tile removal tool 500 comprises an elongated handle 600 and two tines 610. One end of each tine 610 is connected to a first end 620 of the handle 600. A second end 630 of the handle is located opposite the first end 620 of the handle 600. For the third step, the second end 630 of the handle 600 of the tile removal tool 500 is rotated such that the two tines 610 are in an open state. In one or more embodiments, the second end 630 of the handle 600 of the tile removal tool 500 is rotated in a clockwise direction in order to orient the two tines 610 in an open state. In alternative embodiments, the second end 630 of the handle 600 of the tile removal tool 500 is rotated in a counter-clockwise direction in order to orient the two tines 610 in an open state. FIG. 7A shows a top view of the tile removal tool 500 in an open state, in accordance with at least one embodiment of the present disclosure. For the fourth step, which is shown in FIG. 5F, the two tines 610 of the tile removal tool 500 are inserted between the outer edges of the tile 300 and the first wall of the fusion power reactor. For the fifth step, which is shown in FIG. 5G, the second end 630 of the handle 600 of the tile removal tool 500 is rotated such that the two tines 610 are in a closed state and grasp the tile support tube 310 (not shown in figure). In one or more embodiments, the second end 630 of the handle 600 of the tile removal tool 500 is rotated in a counter-clockwise direction in order to orient the two tines 610 in a closed state. In alternative embodiments, the second end 630 of the handle 600 of the tile removal tool 500 is rotated in a clockwise direction in order to orient the two tines 610 in a closed state. FIG. 7B shows a top view of the tile removal tool 500 in a closed state, in accordance with at least one embodiment of the present disclosure. For the sixth step, which is shown in FIG. 5H the tile apparatus 110 has been lifted away from the first wall of the fusion power reactor with the removal tool such that the tile apparatus 110 is completely removed from the manifold channel of the first wall of the fusion power reactor. For the system of the present disclosure, it should be noted that the tiles 300 are not intended to seat tightly against each other. Their purpose is to be a sacrificial first wall that is easily replaceable, and protects the structures that lie behind it. The tiles 300 will overlap, and should touch, but only if the outermost surface of the back sides of the tiles 300 are electrically insulating. Because if the tiles touch and can conduct electric currents from one tile 300 to another, there is too great of a chance of the tiles 300 being welded to each other by plasma disruptions, which would make replacement of damaged tile apparatus units 110 difficult. The reason the tiles 300 should touch is so that they can provide some mechanical support to each other to help them resist the electromagnetic forces that are generated during plasma disruptions. However, the tiles 300 must not lock or seal to each other as electromagnetic forces could damage an interlocking system in ways that could prevent it from being unlocked. Because the tiles 300 are not sealed against each other, the tiles apparatus units 110 need to have a portion of their interior channels employed by a vacuum pumping system, which is located behind the tiles 300. This will serve several purposes. First it will prevent the build-up of gases behind the tiles 300. Second, it will prevent any gas that is leaking from the tile attachment system from getting into the plasma. And, third it will allow the size of the main vacuum pumping ports to be reduced. In one or more embodiments, the tile apparatus units 110 are made entirely of refractory materials. This feature will prevent the tile apparatus units 110 from releasing vapors into the vacuum. The refractory materials to be used for the tile apparatus units 110 have low neutron activation cross sections and are able to resist plasma impacts. These features will facilitate the recycling of the tile apparatus units 110. Examples of materials to be used for the tile apparatus units 110 include, but are not limited to, tungsten (W) for the plasma-facing portions of the tiles 300, and international thermonuclear experimental reactor-grade (ITER-grade), low activation, stainless steel for the back portions of the tiles 300, the tile coolant channels, and the tile support tubes 310. In some embodiments, the outermost surface of the back portion of each tile 300 is coated with an electrically insulating material, such as silicon carbide (SiC) or tungsten carbide (WC). In one or more embodiments, the tiles 300 are hollow and thin-walled, and have a cooling fluid, such as helium (He), that possibly contains a tracer consisting of another noble gas (e.g. argon (Ar)), flowing through them. The thin walls of the tiles 300 allow for neutrons to pass largely unimpeded through the tiles 300 into the breeding blanket. Because of their charge, tritons (tritium nuclei) do not pass through metals as easily as neutrons. Tritons escaping from the plasma will mostly be stopped on or in the tile 300 walls, where they will be neutralized. Once neutralized, the tritium atoms have some ability to migrate through metals. The thin walls of the tiles 300 will allow tritium entering into the tiles to easily migrate through the walls into the helium coolant, which will carry them away for chemical capture. The fusion reactions will also produce alpha particles, most of which will stop in the tile 300 walls like the tritons. As with the tritium, the thin tile 300 walls will allow helium forming from the alpha particles to easily diffuse to the coolant channel for removal with only minimal damage to the walls themselves, because the distance the helium must migrate will be very short. The coolant will enter and leave the tiles 300 through tubes that project radially outward from the tiles 300 (i.e. the coolant channels in the tile support tubes 310) through the breeding blankets to connections to the helium supply and the return manifolds, which could be located inside or beyond the breeding blankets. Because the tile apparatus units 110 are rotated during the installation and removal process, a very simple method for attaching the tile apparatus units 110 and making the coolant connections is possible. The attachment and connection methods must be simple, so as to minimize the possibility that electromagnetic forces occurring during a disruption will distort the tile 300 and tile support tube 310 so greatly that the tile apparatus unit 110 cannot be easily removed. There are several ways the attachment can be accomplished. But the simplest, which is the preferred embodiment, is to have the tile support tubes 310 manufactured to have one or more sets of offset semi-circular shoulders and to have similar semi-circular shoulders located on the inside of the manifold channels into which the tile support tubes 310 are inserted. By rotating the tile apparatus units 110 multiple times during installation, or by rotating the tile apparatus units 110 multiple times back and forth through by half circles, the offset shoulders on each tile support tube 310 can be made to clear the offset shoulders in each manifold channel until the tile support tube 310 is fully inserted. FIGS. 8A through 8D show an example of a way to manufacture the offset shoulders on a tile support tube 310 that attaches to a manifold channel 820 in the breeding blanket. In the event that the coolant manifold is located beyond the breeding blanket, rather than being in it, the tile support tubes 310 will be manufactured to be much longer in length, and they will each have at least two sets of shoulders. The set of shoulders located closest to the plasma will be only for mechanical support. And, a second set of shoulders will be located farther from the plasma, where they can engage the coolant passages in a manifold beyond the blanket. FIGS. 8A through 8D also show an example way that inlet and outlet coolant connections can be made between the coolant channels 800 of a tile support tube 310 and the coolant channels 810 in a manifold channel 820. These figures show the routing of coolant channels 800 in a tile support tube 310 such that they come to the inboard faces of the shoulders on the tile support tube 310, and mate to corresponding coolant channels 810 located on the outboard faces of the shoulders in the manifold channel 820. The simplest way to make these connections is to start by manufacturing the tile support tubes 310 and the walls of the manifold channels 820 of the same material, such as ITER-grade stainless steel. That will minimize problems from differential thermal expansion of various parts, and will allow for the use of simple metallic, such as copper (Cu), seals between the faying steel surfaces. In addition, FIGS. 8A through 8D show a simple way to make the seal between the shoulders 830a, 830b of the tile support tube 310 and the shoulders 840a, 840b of the manifold channel 820, which is to simply have a spring 850 attached to the end of the tile support tube 310, which pushes the shoulders up against each other (e.g., for a first set of shoulders, shoulder 830a is pushed up against shoulder 840a; and for a second set of shoulders, shoulder 830b is pushed up against shoulder 840b). In one or more embodiments, the spring 850 is a captive spring such that it can be easily replaced if thermal cycling or radiation damages it. It should be noted that because of the intense radiation environment, the seals cannot be made from elastomeric materials, and are metal. Because the seals are simple, there is a possibility of an occurrence of unacceptable leakage of radiation. Possible leakage is prevented from being a problem by the use of a standard vacuum system technology, such as a guard vacuum. A guard vacuum is simply a separate volume that is located between two volumes having different pressures. The guard vacuum usually has a pressure that is between the pressures of the two volumes being separated. A guard vacuum reduces leakage through vacuum seals by reducing the pressure difference across each seal. Simply adding two seals might appear to accomplish the same thing. However, if two seals are implemented, the space between them traps gas, which leaks out very slowly, and is called a “virtual leak”. The creation of a guard vacuum eliminates the risk of creating a virtual leak between the two seals. FIGS. 9A and 9B show in detail views from above and below of the coolant connection system. FIG. 9A depicts a top view of a tile support tube 310 of a machine-replaceable plasma-facing tile apparatus and FIG. 9B shows a bottom view of a tile support tube 310 of a machine-replaceable plasma-facing tile apparatus, in accordance with at least one embodiment of the present disclosure. In FIG. 9A, it can be seen that the tile support tube 310 contains a tube support body 900, two vertical coolant channels 910, four horizontal coolant channels 920, two guard vacuum regions 930, two first vacuum seals 940, two second vacuum seals 950, two tube shoulders 970, and two coolant passages 960 in the tube shoulders 970. From FIG. 9B, it can be seen that the tile support tube contains a tube support body 900, two guard vacuum regions 930, two first vacuum seals 940, two second vacuum seals 950, two tube shoulders 970, and two coolant passages 960 in the tube shoulders 970. Variations on the attachment system can be developed in the event that the disclosed simple approach does not hold the tile support tubes 310 firmly enough, or if the coolant seals require more normal force to work properly. For example, tile support tubes 310 could be made of copper (Cu), while the manifold channels 820 that they are set into are formed from ITER-Grade stainless steel. Copper is acceptable in the fusion environment, as long as copper alloys containing high-neutron activation elements, such as nickel (Ni), are avoided. If copper is used for the tile support tube 310, and a lower set of mechanical stops is put in the manifold channel 820 in addition to the spring 850, then when the system heats during operation, the copper will expand more than the stainless steel. That will cause the distance between the stop and the coolant connection shoulders on the tile support tube 310 to grow more than the distance between the stop and the coolant connection shoulders in the manifold channel 820. The effect of that will be that, as the device heats, the force will grow with which the faying surfaces and the seal for the coolant connections are pushed together. FIG. 10 is a cross-sectional view of the single replaceable plasma-facing tile apparatus 110 for fusion-power reactor environments of FIG. 3 illustrating the tile 300 that is hollow 1000 and thin-walled 1010, in accordance with at least one embodiment of the present disclosure. Although certain illustrative embodiments and methods have been disclosed herein, it can be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods can be made without departing from the true spirit and scope of the art disclosed. Many other examples of the art disclosed exist, each differing from others in matters of detail only. Accordingly, it is intended that the art disclosed shall be limited only to the extent required by the appended claims and the rules and principles of applicable law. |
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abstract | A working apparatus has: a working equipment for doing works on a structure; an operation mechanism adapted to actively move the working equipment relative to the structure; and an adhering/traveling module coupled to the operation mechanism and adapted to adhere to the structure so as to have the weight of the working apparatus borne by the structure and travel/move on the structure for positioning. With this arrangement, the working apparatus can perform accurate positioning operations in a narrow environment and complex scanning operations by means of various pieces of the working equipment such as inspection sensors, and can secure a large working area within a short period of time and reduce the overall working hours. |
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047568534 | summary | BACKGROUND OF THE INVENTION The present invention relates to a process for the conversion into a usable condition of actinide ions contained in the solid residue of a sulfate reprocessing process for organic, actinide-containing radioactive solid waste, which actinide ions together with cationic impurities are present in the solid residue in the form of water soluble sulfato complexes. Among sulfate reprocessing processes for organic solid wastes are included such decomposition processes, as those by which the wastes are oxidatively decomposed in a sulfate- or bisulfate-melt at high temperatures, for example, at 800.degree. C., as well as those by which the wastes are treated with comparatively highly concentrated sulfuric acid, for example, with 90%, or with concentrates H.sub.2 SO.sub.4 (so-called wet incineration process). Wet incineration processes are processes for the treatment of combustible, solid waste materials with sulfuric acid at raised temperature, by which simultaneously and/or afterwards the waste material exposed by the reaction is brought into contact with nitric acid or nitrogen dioxide. By this means, carbon-containing material is oxidized to non-combustible gas products and to a non-combustible residue having low volume. In the field of nuclear technology, especially in the field of the th reprocessing of exposed nuclear fuel- and/or fertile materials, such combustible solid wastes, which can be comprised, for example, of spent ion-exchange resin, paper, rubber gloves, synthetic parts of different materials, etc., contain radioactive materials, especially actinides, as, for example, uranium and plutonium. With regard to doing as little damage to the environment as possible by radioactive material, it is necessary that radioactive wastes of whatever type undergo as extensive a volume reduction as possible before solidification in a long term stable matrix and consequent final storage. Here it is desirable not only for an improved waste treatment but also for the reuse of certain valuable materials, such as, for example, actinides, to remove the actinides present in the waste, especially uranium and plutonium, before the solidification of the wastes. One of the process methods useful for this is wet combustion, as described in a process variation example in German Published Patent Application No. 23 47 631, corresponding generally to U.S. Pat. No. 3,957,676. Here, the actinide compounds contained in the solid waste are converted by the hot sulfuric acid into sulfato complexes, which, because of their low solubility in the relatively concentrated sulfuric acid, precipitate and form a solid reaction residue with other constituents of the waste. For subsequent treatment of solid residues containing actinide ions and sulfate ions of sulfate reprocessing processes for organic solid wastes, it is known for example to leach and wash this solid residue with diluted sulfuric acid, to treat the combined leaching and washing solutions with an organic extraction agent solution to transfer the actinides from the aqueous phase into the organic phase, to treat the organic phase charged with actinides with nitric acid for the re-extraction of actinides into the aqueous phase, thereafter to precipitate the actinides from the aqueous solution with, for example, oxalic acid, and to calcinate the precipitated oxalates or to dissolve them in HNO.sub.3. See, Radioactive Waste Management, Volume 2, Int. Atomic Energy Agency, Vienna, 1984, No. IAEA-CN-43/44. pages 335 to 346. In still another method for the subsequent treatment of the residue containing actinides with or without sulfate ions which residue was absorbed with water to form an aqueous solution, a process for the selective separation of plutonium and uranium can also be used, by which sulfuric acid is added to the aqueous solution containing Pu.sup.4+ and UO.sub.2.sup.2+ in amounts such that the uranium forms anionic sulfato complexes, then a cationic surfactant is added to the solution to form a uranium containing precipitate, the resulting precipitate then is separated from its mother liquor in a known way; after separation of the uranium-containing precipitate, the pH value of remaining mother liquor is changed so that henceforth the Pu.sup.4+ forms anionic sulfato complexes, then a cationic surfactant is added to form a plutonium containing precipitate, the resulting precipitate then is separated from its mother liquor in a known way, and the plutonium is recovered from the precipitate by means of calcination. See German Published Patent Application No. 32 24 803. For all known processes, the final product is actinide dioxide. Depending on the separation method used, the actinide dioxide could contain residual amounts of sulfate ions or, if it was calcined at high temperatures, could be insoluble. But both of these disadvantages reduce the reuseability of the product of the process. Moreover, with the use of this process the plutonium loss can reach, for example, up to 4 or 5 weight %, respectively. Furthermore, the known processes are relatively expensive regarding the handling and number of process steps. SUMMARY OF THE INVENTION An object of the present invention is to produce a simple process for the conversion of actinide ions contained in the solid residue of a sulfate reprocessing process for organic, actinide-containing radioactive solid waste in an extractive reprocessing process of exposed nuclear fuel- and/or fertile materials, the aqueous phases of which are nitric acidic, as, for example, in the Purex process, by which a high recovery of actinides is guaranteed without the danger of co-converting quantities of sulfate ion in the extractive reprocessing process, with the smallest possible expenditure of energy, time and apparatus. Additional objects and advantages of the present invention will be set forth in part in the description which follows and in part will be obvious from the description or can be learned by practice of the invention. The objects and advantages are achieved by means of the processes, instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing objects and in accordance with its purpose, the present invention provides a process for the conversion into a usable condition of actinide ions contained in the solid residue of a sulfate reprocessing process for organic, actinide-containing radioactive solid waste, which are present in the form of water soluble sulfato complexes, comprising (a) dissolving the solid residue with water or 1 to 2 molar nitric acid so that the residue or the largest amount of the residue goes into solution, (b) separating the resulting solution from the insoluble constituents of the residue in case of any insoluble residue, and heating the solution or the separated solution to a temperature in the range of 40.degree. C. to below the boiling point of the solution to form a hot solution, (c) adding to the hot solution an aqueous barium nitrate solution having an amount of barium ions which corresponds to a small excess of barium ions over the amount required stoichiometrically for complete precipitation of the sulfate ions, holding the resulting reaction solution at a selected temperature in the same range as in step (b) for a period in the range of 0.5 to 2 hours to precipitate barium sulfate, (d) subsequently cooling the reaction solution to room temperature and then separating the reaction solution from the barium sulfate precipitate to form a sulfate free actinidenitrate solution, and (e) feeding the sulfate free actinide-nitrate solution obtained after the separation to an extractive reprocessing process of exposed nuclear fuel- and/or fertile materials, the aqueous phases of which are nitric acidic. Largest amount of the residue means about 80 weight-% of the residue or more; this quantity depends on the amount of the insoluble materials in the sulfate reprocessing process. When the solid residue contains several actinides, the sulfate free actinide-nitrate solution is fed into the aqueous phase before the uranium-plutonium- separation. When the solid residue contains Pu, the sulfate free actinide-nitrate solution is fed into the aqueous phase before the first Pu-purification cycle. When the solid residue contains U, the sulfate free actinide-nitrate solution is fed into the aqueous phase before the first U-purification cycle. See the Reactor Handbook, 2nd Edition, Volume II, Fuel Reprocessing, Chapter 4, for a description of the uranium-plutonium separation, the first Pu purification cycle and the first U-purification cycle of the extractive reprocessing process, which chapter is hereby incorporated by reference. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, but are not restrictive of the invention. DETAILED DESCRIPTION OF THE INVENTION According to the origin and nature of the organic solid waste, it is possible for one or several actinides, as, for example, uranium, plutonium, neptunium, americium, etc., to be present in the solid residue sulfato complexes resulting during the sulfate reprocessing process. In the present invention, the solid residue is dissolved with water or with 1 to 2 molar nitric acid so that as much as possible of the residue goes into solution, about 80 weight-% of the residue or more; this quantity depends on the amount of the insoluble materials in the sulfate reprocessing process. The dissolving of the residue by water or nitric acid and the leaching of the sulfato complexes which occurs during dissolving preferably is accomplished by employing about 1 liter water, or 1 liter of 1 to 2 molar nitric acid, respectively, per 100 to 250 g of residue. The solution resulting from the dissolving in case of any insoluble residue then is separated from the insoluble constituents of the residue. This separation of the resultant solution from possibly undissolved remaining constituents of the residue can be achieved, for example, by filtration and short re-washing of the residue with little water. Thereafter, the solution or the separated solution, generally in the form of a filtrate is then heated to a temperature in the range of 40.degree. C. to below the boiling point of the solution to form a hot solution, and preferably is heated up to 60.degree. to about 80.degree. C. To the hot solution is then added, preferably with stirring, an aqueous barium nitrate solution having an amount of barium ions which corresponds to a small excess of barium ions over the amount required stoichiometrically for a complete precipitation of the sulfate ions to form a reaction solution. Preferably, the barium nitrate solution has a concentration of barium nitrate in the range of 50 to 80 g/l. Care must be taken that the barium ions required for the sulfate precipitate are added only in a small excess, preferably in the range between 5 and 10 weight %. The resulting reaction solution is held at a selected temperature for a period of 0.5 to 2 hours to effect a well filtrating sulfate precipitate. Generally, the selected temperature is the same as the temperature of the hot solution in which is added the barium nitrate solution. Preferably, the barium nitrate solution is heated to this temperature before it is added to the hot solution. During the sulfate precipitation, the actinide sulfato complexes are decomposed and the sulfate ions formed are bound by the barium ions. The reaction solution is then cooled to room temperature and the precipitate is separated out of the reaction solution, for example, by filtration. The precipitate can then be washed with relatively little pure water. The resultant precipitate free solution is free of sulfate ions and contains the entire amount of the actinides or of the actinides and cationic impurities of the waste as nitrate solution. The rate of recovery of the actinides previously contained in the residue is 99 weight % or above. A particular advantage of the process according to the present invention can be seen in that it practically requires only one process step, and the resulting actinide nitrate solution without conducting further intermediate steps can be supplied to a suitable position of a reprocessing installation, where the fine purification of the actinide salts occurs in each case. It is inconsequential for the process according to the present invention whether the resulting barium sulfate precipitate contains occlusions of any ions and how large the particles to be removed are; it is only necessary that they can be quickly and well filtrated. Because the barium sulfate precipitate is a neutral salt that is difficult to dissolve, and possibly contains incorporated radioactive impurities, it can be incorporated without further pre-treatment into a stable final storage matrix. An exemplary experiment is described below to illustrate the invention. 10 kg of a simulated organic solid waste material (chlorine content about 30 weight %), consisting of 50 weight % polyvinylchloride, 25 weight % neoprene, 15 weight % polyethylene and 10 weight % chemical pulp which contained 120 g cerium dioxide for the simulation of the chemical behavior of plutonium dioxide, were mixed with 12 liters of concentrated sulfuric acid and treated according to the so-called wet combustion. A 50 g sample was removed from the filtrated residue of this process method and dissolved in 250 ml of water. The remaining insoluble residue amounted to only a small weight % (about 10%) and was separated by filtration. 10 ml of the filtrate was heated to about 60.degree. C. and mixed with 60 ml of a 0.42 molar aqueous solution of barium nitrate in small portions likewise heated to about 60.degree. C. A precipitate of barium sulfate thereby precipitated, which could easily be filtrated after maintaining the suspension about 1 hour at 60.degree. C. A filtrate is obtained after the separation of the BaSO.sub.4 which contained cerium ions in an amount that resulted in a yield of 99 weight %, based on the entire amount of added cerium. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims. |
description | This is a continuation of U.S. patent application Ser. No. 12/376,542 filed Feb. 5, 2009 and now U.S. Pat. No. 8,071,941, which is a 371 application of PCT/CH2007/000371 filed Jul. 27, 2007, which two applications are incorporated herein by reference, and which claims priority from Swiss patent application no. 1380/06 filed Aug. 29, 2006, which claim of priority is repeated here. The invention relates to a mass spectrometer arrangement. Mass spectrometric measuring methods are currently applied in manifold type and manner in the field of process engineering, technology and product development, medicine and in scientific research. Typical application areas are herein leakage testing of structural parts in various industrial fields, quantitative determination of the composition and purity of process gases (partial pressure determination of gas fractions), complex analyses of reactions on surfaces, investigation and process monitoring in chemical and biochemical procedures and processes, analyses in the area of vacuum engineering, for example of plasma processes, such as, for example, in the semiconductor industry, etc. For this purpose a multiplicity of different methods for the physical mass separation of particles has been developed and, correspondingly, measuring instruments for practical use have been realized. All of these measuring instruments have in common that they require vacuum for their operation. The neutral particles to be analyzed are inducted into the vacuum of the system and ionized in a reaction zone. This component is conventionally referred to as ion source. The ionized particles are subsequently conducted out of this zone with the aid of an ion optics and supplied to a system for mass separation. There are various concepts for the mass separation. For example, in one case the ions are deflected via a magnetic field, wherein, depending on their mass, the particles are subject to large deflection radii which can be detected. Such a system is known by the name sector field mass spectrometer. In a further, very widely used system the mass filter is comprised of an electrostatic system of four rods into which the ions are shot. On the rod system is impressed a high-frequency alternating electrical field, whereby the ions execute oscillations of different amplitude and trajectory, which can be detected and separated. Among experts this system is known as a quadrupole mass spectrometer. This mass spectrometer has various advantages such as, in particular, high sensitivity, wide measuring range, high measurement repetition rate, small dimensions, arbitrary mounting orientation, direct compatibility in important applications in vacuum engineering and good operability. The ion sources of these known mass spectrometers conventionally employ a thermionic cathode which includes a heated filament, thus an incandescent cathode, for the generation of electrons which ionize the neutral particles under bombardment. While on this conceptual basis, the quality, for example of the quadruple spectrometer, is already quite good, the thermionic cathodes utilized, however, have various disadvantages which then also have an overall negative effect on the mass spectrometer. One problem is that from an incandescent cathode, material of the filaments is also always vaporized and thereby undesirable particles are superimposed on the particles to be measured, which increases the so-called signal noise and consequently negatively effects the measuring accuracy or falsifies the measurement signal. A further problem consists in that on or in the proximity of the hot filament chemical reactions take place with the particles to be measured and thereby the measurement is falsified and the resolution decreased. The emission of light, thus of photons which can interact, is herein of disadvantage. The hot arrangement leads additionally to increased temperature fluctuations which result in increased drift behavior and poor reproducibility of the measurement results. A filament, moreover, is vibration-sensitive, which can lead to undesirable signal fluctuations (microphony) or even to breakage under severe shock. The present invention addresses the problem of eliminating or reducing the disadvantages of the prior art. The problem in particular is involved by providing a mass spectrometer arrangement which permits generating an undisturbed spectrum of the gas to be measured at a better signal/noise ratio, which permits higher resolution and sensitivity and to achieve this in particular for quadrupole mass spectrometer arrangements. The mass spectrometer arrangement, additionally, is to be economically producible. The problem is resolved with the mass spectrometer arrangement of the invention. According to the invention the mass spectrometer arrangement comprises a cathode configuration for the emission of electrons, a reaction zone, which is connected with an entrance opening for the supply of neutral particles, wherein this opening is operatively connected with the cathode configuration, for the ionization of neutral particles, an ion extraction system, which is disposed such that it communicates with the effective region of the reaction zone, means for guiding ions to a detection system within the mass spectrometer arrangement and means for evacuating the mass spectrometer arrangement. The cathode configuration herein includes a field emission cathode with an emitter surface, wherein at a short distance from this emitter surface is disposed an extraction grid for the extraction of electrons, which grid substantially covers the emitter surface. The emitter surface herein encompasses at least partially a hollow volume, such that a tubular structure is formed. The formation according to the invention of the field emission cathode configuration within the mass spectrometer arrangement permits the cold operation without photon emission in the ion source avoiding the problems listed above, which leads to the corresponding substantial improvement of the properties of the mass spectrometer. Such a cathode and ion source is, moreover, simpler to construct and fewer measures need also to be expended in the remaining parts and in the electronic evaluation circuitry for error compensation. This leads to greater economy of production of the entire measuring system and offers better capabilities for analyzing the results, such as the generated spectra. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure and are entirely based on Swiss priority application no. 1380/06 filed Aug. 29, 2006, and International application PCT/CH2007/000371 filed Jul. 27, 2007, and U.S. patent application Ser. No. 12/376,542 filed Feb. 5, 2009, the PCT and U.S. applications being incorporated here by reference. A mass spectrometer arrangement according to the invention comprises substantially an ion source 6, 4, 5, an ion optics 4, 1, 10, 11 for the extraction and guidance of the ions 22, as well as an analyzer system 12, as is depicted in longitudinal section in FIG. 1 in the preferred example of a quadrupole mass spectrometer with a rod system 12 as the analyzer. The ion source includes a cathode configuration 6 which includes an emitter surface 7 as field emitter, which is formed as a two-dimensional field emission cathode and at a short distance in front of this surface 7 an extraction grid 9 is disposed which is impressed with a voltage source 24 at a voltage VG with respect to the emitter surface 7 for the formation and extraction of electrons 21, as is also shown in detail in FIG. 3. The extraction voltage VG on the extraction grid 9 is set to a positive value in the range between 70 V to 2000 V for the extraction of electrons 21. For the overall dimensioning herein a voltage in the range of 70 V to 200 V is especially advantageous. The extraction grid 9 can be produced from a metal sheet with apertures, an etched structure with apertures or preferably a wire mesh with as large a transmission factor for the electrons as possible. The extraction grid 9 should as much as possible be disposed at a uniform distance over the emitter surface 7. For this purpose, insulating etched support elements can be provided, preferably insulating spacer elements 8, which are correspondingly distributed on the surface in order to be able to maintain stably the desired specified distances. The distance between the extraction grid 9 and the emitter surface 7 should be set to a value in the range of 1.0 μm and 2.0 mm, advantageously to a value in the range of 5.0 μm and 200 μm, which simplifies the structuring. The selected value is advantageously to be substantially uniformly employed over the entire emitter surface. The emitter surface 7 is formed as an arcuate surface and encompasses at least partially a hollow volume 13 such that a tubular structure is formed. It can also be divided into sector elements, thus have discontinuities. In this case only the emitter surface 7 as a layer can itself be divided and not the support or the support can also be divided. However, preferred is a substantially nondivided surface which is self-closing and thereby the hollow volume 13, at least on the wall of the tubular structure, is also closed. The tubular structure is advantageously formed substantially cylindrically. This simplifies the structuring and permits better signal optimization. The dimension of the emitter surface 7 should be in the range from 0.5 cm2 to 80 cm2, the range from 1.0 cm2 to 50 cm2 being preferred. The diameter of the formed hollow volume 13 is in the range between 0.5 cm and 8.0 cm, preferably in the range from 0.5 cm to 6.0 cm. The length of the hollow volume 13 in the axial direction is in the range between 2.0 cm and 8.0 cm. The emitter surface 7 is comprised of an emitter material or is produced as a coating from this material, this material containing at least one of the materials of carbon, metal or a metal mixture, a semiconductor, a carbide or mixtures of these materials. Preferred are herein metals, in particular molybdenum and/or tantalum. Especially preferred are corrosion-resistant steels. Mixtures of these metals can also be employed. If the emitter surface 7 is deposited as a thin layer onto the wall 2 of a support, vacuum processes are preferred, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD). An especially advantageous implementation of the emitter surface 7 comprises that this surface is comprised of the material of the wall 2 of the support itself and covers at least a portion of the surface of the housing wall 2 thus formed, preferably however assumes, if possible, the entire surface of wall 2 which encompasses the hollow volume 13. The housing wall 2 comprises in this case one of the above listed metals itself or a metal alloy, preferably a corrosion-resistant steel. The wall 2 could also be covered with a type of sleeve of the emitting material. If the housing wall 2 and the emitter surface 7 are comprised of the same material, the arrangement can be realized more simply and better. The housing wall can in this case also be formed directly as a vacuum housing, whereby a further simplification is attained. It is then also of advantage if the housing wall 2, and therewith the emitter surface 7, is electrically at ground potential, as is shown in FIG. 3. Consequently, the electron emitter or the emitter surface 7 is implemented as a type of tube wall emitter. The surfaces of said coating or the surface of the solid material of the housing wall 2 must be roughened such that a suitable emitter surface 7 is formed, which subsequently has field emission properties, such that it is capable of emitting sufficient electrons 21 at the low grid extraction voltage VG. The roughening can be carried out mechanically, preferably by etching, such as plasma etching or preferably through chemical etching. Hereby in extremely simple manner a multiplicity of irregularly distributed prominences is generated, which are sharp-edged and/or tip-like with dimensions in the nanometer range, whereby field emission of electrons is possible even at low field strengths. Such prominences have heights compared to the mean base surface within a range of 10 nm to 1000 nm, preferably within 10 nm to 100 nm. Known field emitters, such as Spint Mikrotips, are structured, for example, as an array-form uniformly distributed tip arrangement. This takes place through multiple, complex erosion and application of material. For this purpose complex and expensive multi-stage structuring processes are necessary. Such processes can also not take place on any surface, such as for example on inner surfaces of small tubular parts. In contrast, in the present invention the present surface is roughened simply. The roughening herein takes place exclusively using a single structuring step, such that the desired sharp-edged or tip-like elements are formed, which permit the desired field emission. In the mechanical working of the surface this is generated, for example, through a grinding process. In the preferred etching this is generated through the inherently present grain structure of the basic material. The emitting tips are thereby distributed stochastically. The electrons 21 generated in such manner with the cathode configuration 6 and accelerated impinge within a reaction zone 3 onto the neutral particles 20 which are here ionized. The reaction zone 3 is thus connected with an entrance opening 14 for the supply of neutral particles 20. In an embodiment of the invention, such as depicted in FIG. 1, the hollow volume 13 of the cathode configuration 6 is adjoined by an electron extraction lens 5, which extracts the electrons 21 in the axial direction of the mass spectrometer arrangement from this hollow volume 13 and guides them into a reaction zone 3 where through electron collision the neutral particles 21 are ionized. Opposite the electron extraction lens 5 is disposed at a spacing in the axial direction the ion extraction lens 4. These two lenses 4, 5 encompass the reaction volume 3. In the arrangement depicted here, the two extraction lenses can be at the same electric potential, they thus form together with a wall encompassing the reaction zone 3 a type of housing in whose wall openings 14 are provided for the transit of neutral particles 20 to be measured. The ion extraction lens 4 includes a lens opening at which a field penetration factor through the succeeding electro-optical elements is brought about whereby the ions are extracted from the ionization region of the reaction zone 3 in the axial direction. The neutral particles 20 in this formation are admitted into this reaction volume 3 radially with respect to the axis, laterally of the reaction volume 3 through the entrance opening 14. The extracted ions 22 are guided through the ion optics 4, 1 onto a focusing means 10, 11 and subsequently into the analyzer 12. In the preferred quadrupole mass spectrometer the ion optics includes, for example, an extraction lens 4 and a further lens 1, here shown as base plate at ground potential and the succeeding focusing means includes a focusing lens 10 and an injection aperture plate 11, as well as the detection system as a four-fold rod system. In FIG. 1 is shown an arrangement with the reaction volume 3 separated from the hollow volume 13 of the cathode configuration 6 and lateral supply of the neutral particles 20. The entire arrangement is, in addition, developed such that for operation it can be evacuated, be that by flanging it to pumped vacuum systems and/or by providing it with its own pumps. A further preferred embodiment of the invention is depicted in FIG. 2 and in detail in FIG. 3. The Figures also show schematically the preferred implementation on a quadrupole mass spectrometer arrangement. The emitter surface 7 of the field emitter is disposed on the tube wall such that the reaction zone 3 is located within the hollow volume 13 and that here the ionization takes place. The ionization volume consequently is located within the electron source or the cathode configuration 6. In addition to the omission of a focusing device 5, a substantially simplified structuring results since no separate ionization volume is required. Nevertheless, the necessary potential relations are substantially maintained, since the extraction grid 9 with respect to the emitter surface 7 or the wall 2 is at a positive potential VG and this surface or wall is advantageously at ground potential M. The emitter surface 7 forms thus together with the grid 9 the electron source. The voltage VG at the extraction grid 9 has a value in the range of 70 V to 2000 V, depending on which material for the emitter surface 7 and which distance of the extraction grid 9 from the emitter surface 7 has been selected. Values in the range of 70 V to 200 V are especially suitable since in the present implementation of the cathode configuration sufficient electrons 21 can always still be generated whereby a further simplification of the system becomes possible. The ion extraction lens 4 is disposed at the end side with respect to the hollow volume 13 or to the reaction zone 3 and in the simplest case is comprised of an aperture plate. By applying with a voltage source 25 a negative voltage VI with respect to the emitter surface 7 or the wall 2, the ions are extracted in the axial direction out of the hollow volume 13 and moved in the direction of the detection system 12 and thus to the mass filter system. At higher values of the extraction voltage VG a slightly positive voltage VI is also possible if it is markedly lower than VG. The neutral particles 20 to be analyzed are admitted through an entrance opening 14 into the hollow volume 13 of the tubular cathode configuration. This entrance opening is located at the end side with respect to the tubular hollow volume 13, opposite to the ion extraction lens 4. The tubular cathode configuration 6 with the ion extraction lens 4 is advantageously axially oriented, thus in line with respect to the longitudinal axis of the quadrupole mass spectrometer arrangement. The motion direction 23 of the extracted ions 22 leads here along the longitudinal axis in the direction of the analyzer 12. FIG. 3 depicts by way of example in detail a preferred arrangement with a plate-like ion extraction lens 4, which, for the extraction of the ions, includes in its center an aperture as lens opening and which is not connected with the wall 2 under a vacuum seal. The remaining portion of the mass spectrometer arrangement is here evacuated through the electron or ion source, which also simplifies the structuring in terms of vacuum engineering. A further preferred arrangement according to the invention is shown in FIG. 4 in section along the longitudinal axis. The cathode configuration 6 is here disposed orthogonally to the longitudinal axis of the mass spectrometer, thus laterally of the ion source which also, as is also shown in FIG. 1, is realized as a type of closed chamber 5, wherein the lateral chamber wall includes an opening toward the cathode configuration 6 and thus forms the electron extraction lens 5. The electron extraction lens 5 itself, as stated, is here formed as a type of chamber and thereby encompasses the reaction zone 3 for the ionization of the neutral particles 20. In addition, in the wall of this chamber one or several openings 14 are provided for the introduction of the neutral particles 20 to be analyzed. In the axial direction this chamber 3 terminates again with an ion extraction lens 4 for the extraction of the formed ions into the analyzer of the mass spectrometer. FIG. 5 depicts a further preferred embodiment, in which the tubular cathode configuration 6 is disposed coaxially to the longitudinal axis of the mass spectrometer arrangement and the electron extraction lens 5 formed like a chamber, such as has been described previously in conjunction with FIG. 4. The cathode configuration 6 encompasses herein the chamber with the reaction zone 3, at least partially, whereby it becomes possible to place optionally on the periphery of the wall of the chamber, thus of the extraction lens 5, an opening or preferably two or even several extraction openings for the electrons 21. The neutral particles 20 are also, as depicted in the arrangement according to FIG. 4, inducted through at least one opening 14 in the chamber wall. Through the arrangement according to FIGS. 4 and 5 with the radial shooting of the electrons 21 into the reaction zone 3, compared to the axial disposition, a better separation of the ions to be measured compared to other undesirable particles is possible, which could also reach the analyzer and subsequently would degrade the measuring quality. |
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claims | 1. A neutron shield comprising a two-part reactive cold-setting epoxy resin produced by combining a main component of an aliphatic glycidyl ether epoxy resin, and a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct. 2. The neutron shield according to claim 1 , further comprising boron carbide. claim 1 3. The neutron shield according to claim 1 , further comprising aluminum hydroxide containing 0.1% by weight or less of soda. claim 1 4. The neutron shield according to claim 1 , further comprising aluminum hydroxide containing 0.07% by weight or less of soda. claim 1 5. A neutron shield comprising a two-part reactive cold-setting epoxy resin produced by combining a main component of an aliphatic glycidyl ether epoxy resin; a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct; a refractory comprising at least one of aluminum hydroxide and magnesium hydroxide; and a neutron absorbing material. 6. The neutron shield according to claim 5 , wherein the aluminum hydroxide contains 0.1% by weight or less of soda. claim 5 7. The neutron shield according to claim 5 , wherein the aluminum hydroxide contains 0.07% by weight or less of soda. claim 5 8. A cask comprising: a neutron shield comprising a two-part reactive cold-setting epoxy resin produced by combining a main component of an aliphatic glycidyl ether epoxy resin, and a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct, wherein the neutron shield is disposed on the outer circumference of the cask; a shell main body which can shield gamma-rays; a basket formed of a plurality of square pipes having neutron absorbing capability, where the basket has a cross section which has angles, and the basket is for housing spent fuel assemblies in each square pipe; and a cavity for inserting the basket, where the inner shape of the cavity is in accordance with the outer shape of the basket. 9. A cask comprising: a neutron shield comprising a two-part reactive cold-setting epoxy resin produced by combining a main component of an aliphatic glycidyl ether epoxy resin, and a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct, a refractory comprising at least one of aluminum hydroxide and magnesium hydroxide, and a neutron absorbing material, where the neutron shield is disposed on the outer circumference of the cask; a shell main body which can shield gamma-rays; a basket formed of a plurality of square pipes having neutron absorbing capability, where the basket has a cross section which has angles, and the basket is for housing spent fuel assemblies in each square pipe; and a cavity for inserting the basket, where the inner shape of the cavity is in accordance with the outer shape of the basket. 10. A method of making a neutron shield, the method comprising curing a mixture of an aliphatic glycidyl ether epoxy resin, and a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct; and producing the neutron shield of claim 1 . claim 1 11. A method of making a neutron shield, the method comprising curing a mixture of an aliphatic glycidyl ether epoxy resin, a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct; a refractory comprising at least one of aluminum hydroxide and magnesium hydroxide; and a neutron absorbing material, and producing the neutron shield of claim 5 . claim 5 12. A method of making a cask, the method comprising forming a neutron shield by curing a mixture of an aliphatic glycidyl ether epoxy resin; and a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct, and using the neutron shield to produce the cask of claim 8 . claim 8 13. A method of making a cask, the method comprising forming a neutron shield by curing a mixture of an aliphatic glycidyl ether epoxy resin; a hardener comprising at least one of an alicyclic polyamine, a polyamide polyamine, an aliphatic polyamine and an epoxy adduct; a refractory comprising at least one of aluminum hydroxide and magnesium hydroxide; and a neutron absorbing material, and using the neutron shield to produce the cask of claim 9 . claim 9 |
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summary | ||
048851230 | summary | BACKGROUND OF THE INVENTION The present invention relates to an apparatus for handling constituent elements of a reactor core, and particularly to a technique of handling fuel assemblies, control rod assemblies, and control rods of the core by utilizing a common apparatus. FIG. 6 shows a conventional example of the reactor structure of a fast breeder reactor. The structure shown in FIG. 3 which was reported in "SUPERPHENIX NEWS" issued on March, 1987 is similar to the structure of a fast breeder reactor shown in FIG. 6. As shown in FIG. 6, the fast breeder reactor has a reactor vessel 1 and a roof deck 2 which covers the upper portion of the reactor vessel 1. The roof deck 2 comprises a large rotating plug 3 and a small rotating plug 4 which can rotate independently of each other. The vessel which is covered in this manner contains a core 5, a primary coolant sodium 6 which removes the heat generated by the nuclear reaction of the core 5, a circulating pump 7 for forcibly circulating the primary coolant so as to pass it through the core 5, and an intermediate heat exchanger 8 for performing heat exchange between the primary coolant whose temperature is increased by being passed through the core and a low temperature secondary coolant which is supplied from the outside of the vessel. The large rotating plug 3 is disposed so that it can rotate relative to the roof deck 2, and the small rotating plug 4 is disposed so that it can rotate relative to the large rotating plug 3. A core upper mechanism 9 and a fuel exchanger 10 are provided in the small rotating plug 4. In addition, as shown in FIG. 7, the core 5 comprises as core constituent elements core fuel assemblies 11, blanket fuel assemblies 12, control rod assemblies 13, moving neutron shields 14, and fixed neutron shields 15. The side of the core 5 is provided with a transit pot for receiving the core constituent elements for a while before they are taken off to the outside of the reactor, so that the core constituent elements are carried out of the furnace from the transit pot in a fuel bucket by means of a fuel handling machine (not shown). An example of such a fuel handling machine is discussed in NUCLEAR TECHNOLOGY, Vol 68 (Feb. 1985) pp. 160-170. Of the core constituent elements, the core fuel assemblies 11, the blanket fuel assemblies 12, the control rod assemblies 13, and the moving neutron shields 14 are required to be exchanged with new elements outside of the furnace or reactor, while the fixed neutron shields 15 need not be taken out of the furnace during the lifetime of a plant and are remained disposed in the furnace, as suggested by the name. Of the fuel assemblies which are brought into and removed from the furnace, the core fuel assemblies 11, the blanket fuel assemblies 12, and the moving neutron shields 14 all have the structure shown in FIG. 8 which comprise a handling head 16 at the upper end thereof for engaging with the claws of a gripper of the fuel exchanger, thereby allowing the assembly to be handled by the fuel exchanger. As shown in FIG. 9, each of the control rod assemblies 13 comprises a guide tube 17 and a control rod 18, in which a handling head 19 of the control rod 18 is gripped by the claws of a gripper of a control rod drive mechanism when the output of the core is to be controlled, so that each control rod can be moved longitudinally. In addition, when the control rod assemblies 13 are brought into or removed from the furnace or reactor, each of the assemblies 13 can be handled by gripping the upper end of the guide tube 17 by means of the claws of the gripper of the fuel exchanger. FIG. 10 shows a fuel exchanger. As shown in the drawing, the fuel exchanger 10 has a fuel exchanger body 20 which is supported by chains 24 operated by a winch 23 so that the body can be moved upward and downward, and a guide sleeve 21. The fuel exchanger body 20 is provided for the purpose of gripping each of the core constituent elements, and the guide sleeve 21 is provided on the body 20 for the purpose of preventing swinging of the gripper during an earthquake. The fuel exchanger body 20 is driven upward and downward through the chains 24 and comprises claws for gripping the core constituent elements, a claw-operating shaft 26 for closing and opening the claws 25, and a claw driving apparatus 27 for driving upward and downward the claw-operating shaft 26 with an external cylinder which prevents the transverse vibration of the claw-operating shaft 26. As shown in FIG. 11, the claw-operating shaft 26 is pulled by the claw-driving apparatus 27 in order to grip the core constituent elements, and the fuel exchanger body 20 is moved downward to a position right above a given core constituent element in a state wherein the lower ends of the claws 25 are closed so that the claws 25 can be inserted into the handling head 16 of that core constituent element. As shown in FIG. 12, the claw-operating shaft 26 is moved downward by the claw-driving apparatus 27 so that the lower ends of the claws 25 are opened and engaged with the handling head 16 of the core constituent element. In this state, the fuel exchanger body 20 is moved upward by an elevating drive mechanism 23 so that the core constituent element can be taken out of the core. When a new fuel is charged into the core, the above-described operation may be performed in the reverse order. An analogue of this fuel exchanger is described in Japanese Patent Laid-Open No. 137293/1981. FIG. 13 shows a control rod drive mechanism 28 which can be roughly divided into a drive mechanism part 29 and an upper guide tube part 30. The upper guide tube part 30 is supported on the upper surface of the small rotating plug 4 and is provided in the furnace including the primary coolant sodium 6 and argon atmosphere, the lower end being connected to a control rod 18 through the gripper 31. The drive mechanism 29 is accommodated in in a core upper mechanism 32 placed above the small rotating plug 4 and adjacent to the uppermost portion of the upper guide tube part 30. The gripper 31 is closed and opened by operating an operational shaft 10 in a similar manner to that in the fuel exchanger. Although, as described above, an apparatus for handling the core constituent elements comprises the fuel exchanger and the control rod drive mechanism, the diameter of the small rotating plug is large and the diameter of the large rotating plug is hence large too, because the fuel exchanger as well as the core upper mechanism containing the control rod drive mechanism are provided on the small rotating plug in the above-described reactor. In addition, the diameters of the small and large rotating plugs are determined to be large in value so that the fuel exchanger can gain access to all the core constituent elements to be handled upon rotation of the two rotating plugs. Therefore, there has been a limit in reductions in the diameter of the large rotating plug in the prior art when attempts have been made to reduce the size of the structure of the fast breeder reactor and to reduce the construction cost thereof. SUMMARY OF THE INVENTION It is an object of the present invention to provide a reactor in which the diameter of a rotating plug can be reduced and which thus allows the size of a reactor vessel to be reduced. In order to achieve the above object, the present invention can provide an apparatus for handling core constituent elements of a reactor that comprises a core having as core constituent elements control rod assemblies each containing a control rod and fuel assemblies each containing nuclear fuel, a small rotating plug rotatably provided on the core, and a control rod drive mechanism provided on the small rotating plug, the control rod drive mechanism being characterized by a plurality of grippers each having a hook projecting inwards so that it can engage with a handling head of the control rod and a hook projecting outwards so that it can engage with a handling head of each of the core constituent elements at a distance in the longitudinal direction; an operational head for opening and closing the grippers; a third elevating drive mechanism for vertically driving the operational head; a second elevating frame for supporting the third elevating drive mechanism and the grippers; a second elevating drive mechanism for vertically driving the second elevating frame; a first elevating frame for supporting the second elevating drive mechanism and the second elevating frame; a first elevating drive mechanism for vertically driving the first elevating frame; and a frame which supports the first elevating drive mechanism and is provided on the small rotating plug. |
description | This application is a continuation-in-part (CIP) application based upon the International Application PCT/JP2010/007420, the International Filing Date of which is Dec. 22, 2010, the entire content of which is incorporated herein by reference, and is based upon and claims the benefits of priority from the prior Japanese Patent Application No. 2009-290391, filed in the Japanese Patent Office on Dec. 22, 2009, the entire content of which is incorporated herein by reference. The present embodiments relate to a nuclear reactor vibration monitoring device and monitoring method for monitoring vibrations of internal equipment from the outside of nuclear reactor pressure vessel by using ultrasonic waves. Concerning a reactor vibration monitoring device that monitors vibrations of equipment in a nuclear reactor while the nuclear reactor is in operation, there has been known a technique of using ultrasonic waves to monitor vibrations of the internal equipment from the outside of reactor pressure vessel (for example, see Japanese Patent Application Laid-Open Publication Nos. 2009-068987 and 11-125688, the entire contents of which are incorporated here by reference). Such a reactor vibration monitoring device will be described with reference to FIG. 16. FIG. 16 is a block diagram showing a schematic configuration of a conventional nuclear reactor vibration monitoring device 107. As shown in FIG. 16, the reactor vibration monitoring device 107 includes an ultrasonic transducer 103 which is installed on the outside surface of a reactor pressure vessel 100, transmits ultrasonic pulses to a reflector 102 attached to internal equipment 101 in the reactor pressure vessel 100, and receives reflected pulses. The reflected pulses received by the ultrasonic transducer 103 are converted into a received signal through an ultrasonic receiver 104. The signal from the ultrasonic receiver 104 is received and processed by a signal processing unit 105. Vibration information processed by the signal processing unit 105 is displayed on a display unit 106. In such a reactor vibration monitoring device 107, the reflector 102 is attached to the internal equipment 101 so that ultrasonic pulses transmitted from the ultrasonic transducer 103 are reflected by the reflector 102 and returned to the ultrasonic transducer 103. Consequently, even if the internal equipment 101 has a tilt and/or curvature, ultrasonic pulses can be transmitted and received with high sensitivity and reliability by a single ultrasonic transducer 103. Vibrations can be monitored based on changes in the time of signal received by the ultrasonic transducer 103. In order for the reactor vibration monitoring device 107 to accurately monitor vibrations of the internal equipment 101 having a tilt and/or curvature, the reflector 102 needs to be attached to the internal equipment 101 so that ultrasonic waves are reflected with high efficiency. There has thus been a problem of attaching the reflector 102 in water by remote control. The present invention has been achieved to solve the foregoing problem, and it is thus an object thereof to provide a reactor vibration monitoring device and monitoring method capable of accurately detecting vibrations of internal equipment having a tilt and/or curvature without attaching a reflector to the internal equipment in a reactor pressure vessel. In order to achieve the object written above, according to an aspect of the present invention, there is provided a reactor vibration monitoring device comprising: ultrasonic wave transmission means that is installed on an outside surface of a reactor pressure vessel and transmits ultrasonic pulses to an interior of the reactor pressure vessel; ultrasonic wave receiving means that is installed on the outside surface of the reactor pressure vessel and receives reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object in the reactor pressure vessel; preprocessing means for performing processing to exclude reflected ultrasonic pulses reflected in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; and calculation means for determining vibrations of the inspection object from the reflected pulse signal processed by the preprocessing means based on observation time of the inspection object. In order to achieve the object written above, according to another aspect of the present invention, there is also provided a reactor vibration monitoring method comprising: an ultrasonic wave transmission step in which ultrasonic wave transmission means is installed on an outside surface of a reactor pressure vessel and transmits ultrasonic pulses to an interior of the reactor pressure vessel; an ultrasonic wave receiving step in which ultrasonic wave receiving means is installed on the outside surface of the reactor pressure vessel and receives reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object in the reactor pressure vessel; a preprocessing step of performing processing to exclude reflected ultrasonic pulses occurring in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; and a calculation step of determining vibrations of the inspection object from the reflected pulse signal processed in the preprocessing step based on observation time of the inspection object. Hereinafter, embodiments of the reactor vibration monitoring device according to the present invention will be described with reference to the drawings. Here, identical or similar parts will be designated by the same reference symbols, and redundant description will be omitted. FIG. 1 is a block diagram showing a schematic configuration of a reactor vibration monitoring device 14 according to a first embodiment of the present invention. Initially, the basic configuration of the reactor vibration monitoring device 14 will be described with reference to FIG. 1. As shown in the diagram, the reactor vibration monitoring device 14 includes an ultrasonic wave transmission and receiving means 3 including: an ultrasonic wave transmission means 3a which is installed on an outside surface of a reactor pressure vessel 1 and transmits ultrasonic pulses to the interior of the reactor pressure vessel 1; and an ultrasonic wave receiving means 3b for receiving reflected pulses reflected by an inspection object 2 in the reactor pressure vessel 1. That is, the ultrasonic wave transmission means 3a transmits ultrasonic pulses to the interior of the reactor pressure vessel 1, and ultrasonic pulses reflected by the inspection object 2 are received by the ultrasonic wave receiving means 3b. The ultrasonic wave receiving means 3b receives reflected ultrasonic pulses and transmits a received signal to a preprocessing means 4. The preprocessing means 4 performs an analog-to-digital conversion on the received signal of the ultrasonic wave receiving means 3b, and performs differential processing between the waveform of the received signal including a reflection ultrasonic pulse signal and a waveform stored in advance. The received signal that is differential-processed by the preprocessing means 4 is transmitted to a calculation means 5. The calculation means 5 determines vibrations of the inspection object 2 based on changes in the observation time of the reflected ultrasonic pulses from the inspection object 2. An interrupting means 6 for interrupting ultrasonic pulses transmitted to the usually-immersed inspection object 2 for an arbitrary time is arranged between an inside surface of the reactor pressure vessel 1 and the inspection object 2. For example, the interrupting means 6 is composed of an air compressor 6a which supplies compressed air and a bubble jetting means 6b which jets out the compressed air. The reactor vibration monitoring device 14 is applicable to various types of nuclear reactors such as a boiling water reactor and a pressurized water reactor. When in operation, the outside surface of the reactor pressure vessel 1 is in a high temperature and high radiation environment. For example, the temperature of the outside surface reaches approximately 300 degrees Centigrade in the case of a boiling water reactor, and approximately 325 degrees Centigrade in the case of a pressurized water reactor. A clad weld layer 8 which interferes with propagation of ultrasonic waves lies on the inside surface of the reactor pressure vessel 1. The inspection object 2 is internal equipment that is installed in water in the nuclear reactor. In the case of a boiling water reactor, the inspection object may include the shroud and the jet pumps. Such internal equipment has a complicated shape. A portion to be irradiated with the ultrasonic waves for vibration measurement is often shaped to have a curvature and/or tilt. While in the example of FIG. 1, the inspection object 2 is shown in a sectional elevational view, the inspection object 2 is shaped to have tilted vertical surfaces and a curved horizontal cross-section. The ultrasonic wave transmission means 3a is an ultrasonic transducer using a piezoelectric effect, and may be made of a piezoelectric element of lead zirconate titanate (PZT), lithium niobate (LN), lithium tantalite (LT), or the like. The frequency of ultrasonic waves to be transmitted and received by the ultrasonic wave transmission and receiving means 3 is set to, for example, between several hundreds of kilohertz and several tens of megahertz so that the ultrasonic waves propagate through steel material and water. The ultrasonic wave transmission and receiving means 3 is fixed to the outside surface of the reactor pressure vessel 1 using contact medium of soft metal such as Au, Ag, Cu, Al, and Ni. The ultrasonic wave receiving means 3b may be made of an electrodynamic transducer using a magnetostrictive effect. While the ultrasonic wave transmission and receiving means 3 composed of the ultrasonic wave transmission means 3a and the ultrasonic wave receiving means 3b has been described, an ultrasonic wave transmission and receiving means that serves both as a transmission means and a receiving means may be used. The preprocessing means 4 includes: a not-shown analog-to-digital converter to electrically amplify an input signal and then to convert the same into digital data; a storage circuit that stores the digital data; and a calculation circuit that performs a differential calculation between the input signal converted into the digital data and the stored digital data and makes an output. The analog-to-digital converter operates at time intervals of Δt (sec), and converts an input signal of predetermined time width, including reflected ultrasonic pulses, into digital data with a sampling frequency of f (Hz). Based on the sampling theorem, f (Hz) is set at or above twice the frequency of ultrasonic waves to be transmitted and received. Similarly, the digital data stored in the storage circuit is data of a sampling frequency that is set at or above twice the frequency of ultrasonic waves to be transmitted and received. Next, the calculation means 5 is a signal processing circuit that determines vibrations and amplitude of the inspection object 2 from reflected ultrasonic pulses reflected by the inspection object 2. When the inspection object 2 vibrates, the propagation time of the reflected ultrasonic pulses from the inspection object 2 changes. Here, an input signal of predetermined time width including reflected ultrasonic pulses is obtained at time intervals of Δt (sec). The propagation times of the reflected ultrasonic pulses extracted from input signals obtained in succession can be arranged in a time series to acquire data on changes in the propagation time of the reflected ultrasonic pulses. Then, the acquired data can be analyzed in frequency to determine the vibration frequency of the inspection object 2. The magnitude of the vibration amplitude can be determined by determining a time change width of the propagation time in the acquired data, multiplying the time change width by the velocity of sound, and dividing the resultant by 2. The time change width of the propagation time may be more accurately determined from interpolated data of the acquired data or from the function approximation of the acquired data. Since the propagation time is turnaround time to and from the inspection object 2, the vibration amplitude of the inspection object 2 needs to be determined by a division by 2. Based on the sampling theorem, 1/Δt (Hz) must be set to be higher than or equal to twice the vibration frequency of the inspection object 2. The interrupting means 6 is a means for interrupting or scattering ultrasonic waves that propagate through the reactor water between the reactor pressure vessel 1 and the inspection object 2, so that reflected ultrasonic pulses from the inspection object 2 do no reach the ultrasonic wave receiving means 3b. In the above-described configuration example, the air compressor 6a sends compressed air to the bubble jetting means 6b. The bubble jetting means 6b or a nozzle jets out bubbles into the propagation path of ultrasonic waves with an adjusted flow rate and bubble size, thereby interrupting the ultrasonic waves. Here, the bubble size is set to be sufficiently greater than the wavelength of ultrasonic waves to be transmitted and received. For another example of the interrupting means 6, a steel plate or the like that reflects or scatters ultrasonic waves may be inserted into the propagation path as an interrupting means. In such a case, care needs to be taken to prevent the inserted steel plate or the like from dropping. Alternatively, the water level may be lowered to put the propagation path into the air for interruption of ultrasonic waves. In the present embodiment of such a configuration, ultrasonic pulses transmitted from the ultrasonic wave transmission means 3a are passed through the wall of the reactor pressure vessel 1 and the clad weld layer 8 and made to enter the reactor water perpendicularly. Here, the ultrasonic pulses are reflected and attenuated by the boundary between the wall of the reactor pressure vessel 1 and the clad weld layer 8 and the boundary between the clad weld layer 8 and the reactor water. The ultrasonic pulses are further attenuated in the clad weld layer 8. Entering the reactor water, the ultrasonic pulses then travel straight and are reflected by the inspection object 2. Since the inspection object 2 has a tilt and/or a curvature, the reflected ultrasonic pulses propagate with additional spreading and angles. For example, if the inspection object 2 has a curvature as shown in FIG. 3, the reflected ultrasonic pulses horizontally spread out due to the effect of the curvature of the inspection object 2. If the inspection object 2 is tilted as shown in FIG. 4, the reflected ultrasonic pulses vertically propagate with additional angle due to the effect of the tilt of the inspection object 2. Moreover, as shown in FIG. 5, some of the ultrasonic pulses repeat reflections in the wall of the reactor pressure vessel 1 before reaching the ultrasonic wave receiving means 3b. Like the transmitted ultrasonic pulses, the reflected ultrasonic pulses are also reflected and attenuated by the boundary between the wall of the reactor pressure vessel 1 and the clad weld layer 8 and the boundary between the clad weld layer 8 and the reactor water. The reflected ultrasonic pulses are further attenuated in the clad weld layer 8. As seen above, the reflected ultrasonic pulses from the inspection object 2 are reflected and attenuated by the boundary between the wall of the reactor pressure vessel 1 and the clad weld layer 8 and the boundary between the clad weld layer 8 and the reactor water, and further attenuated in the clad weld layer 8. In addition, the reflected ultrasonic pulses are significantly attenuated due to the spreading caused by the tilt and curvature of the inspection object 2. Ultrasonic pulses observed also include ones that are reflected in the wall of the reactor pressure vessel 1 before reaching the ultrasonic wave receiving means 3b. Consequently, the received signal of the ultrasonic wave receiving means 3b includes reflected ultrasonic pulses from the inspection object 2, which makes it difficult to distinguish from noise such as ultrasonic pulses reflected in the wall of the reactor pressure vessel 1. Here, the processing to be performed by the preprocessor 4 will be described with reference to FIG. 6. FIG. 6 is an explanatory diagram showing examples of output of the preprocessing means 4. FIG. 6(a) is a graph of an unprocessed waveform that is input from the ultrasonic wave receiving means 3b to the preprocessing means 4. FIG. 6(b) is a graph of a waveform stored in advance in the preprocessing means 4. FIG. 6(c) is a graph of the result of differential processing of FIGS. 6(a) and 6(b). The amplitudes are in an arbitrary unit. The preprocessing means 4 performs a differential calculation between the waveform of reflected ultrasonic pulses converted into digital data, shown in FIG. 6(a), and the waveform intended for differential processing shown in FIG. 6(b). The waveform shown in FIG. 6(b) is one in a state where no reflected ultrasonic pulse from the inspection object 2 is received by the ultrasonic wave receiving means 3b. In other words, the waveform shown in FIG. 6(b) results from reflected ultrasonic waves and the like in the wall of the reactor pressure vessel 1, and thus corresponds to the noise in the waveform of FIG. 6(a) other than reflected ultrasonic pulses. As for the waveform of FIG. 6(b), for example, data for a case where ultrasonic pulses and reflected ultrasonic pulses propagating through the reactor water between the reactor pressure vessel 1 and the inspection object 2 are interrupted or scattered or equivalent digital data is prepared in advance (for example, data acquired in past operations or determined by simulation), and stored in the preprocessing means 4. The differential processing of FIGS. 6(a) and 6(b) thus removes noise from FIG. 6(a) to produce a waveform as shown in FIG. 6(c). The resulting waveform has a high S/N ratio (signal-noise ratio) with respect to reflected ultrasonic pulses from the inspection object 2. When it is difficult to prepare a waveform to be used for differential processing in advance or when acquiring a more accurate waveform from actual equipment, the interrupting means 6 can be used to acquire a waveform corresponding to FIG. 6(b). The method will be described below. First, a method of acquiring the waveform of FIG. 6(b) by using the foregoing interrupting means 6 including the air compressor 6a and the bubble jetting means 6b will be described below. The air compressor 6a of the interrupting means 6 shown in FIG. 1 is operated for an arbitrary time, so that the bubble jetting means 6b sends bubbles into the propagation path and fills the propagation path with bubbles. As a result, ultrasonic pulses and reflected ultrasonic waves are scattered by the bubbles in the propagation path and are substantially interrupted. In such a state, ultrasonic waves or ultrasonic pulses transmitted from the ultrasonic wave transmission means 3a will not be reflected by the inspection object 2 to reach the ultrasonic wave receiving means 3b. The output of the ultrasonic wave receiving means 3b thus has a waveform like FIG. 6(b). Pieces of digital data shown in FIG. 6(b) can thus be acquired as many as needed. If the interrupting means is configured as a steel plate or the like inserted between the ultrasonic wave transmission and receiving means 3 and the inspection object 2 as mentioned above, the inserted steel plate or the like reflects and attenuates ultrasonic waves. Even in such a case, ultrasonic waves can be interrupted and data can be acquired as in the case of using the air compressor 6a and the bubble jetting means 6b. When an interrupting means 6 such as described above is difficult to apply, a partial replica 7 shown in FIG. 2 may be used instead. The partial replica 7 is provided with an ultrasonic wave transmission and receiving means 31 which is composed of an ultrasonic wave transmission means 31a and an ultrasonic wave receiving means 31b for replica. A sample of the actual wall may be used as the partial replica 7. As shown in FIG. 2, the ultrasonic wave transmission and receiving means 31 is arranged on the partial replica 7 that is installed near the ultrasonic wave transmission and receiving means 3 attached to the reactor pressure vessel 1, in the same relative positional relationship as that of the ultrasonic wave transmission and the receiving means 3 of FIG. 1. More specifically, the partial replica 7 is a partial replica that simulates a part of the wall of the reactor pressure vessel 1. The partial replica 7 has the same material and thickness as those of the wall of the reactor pressure vessel 1 shown in FIG. 1, and has the clad weld layer 8. The partial replica 7 has dimensions or size such that the ultrasonic wave transmission means 31a and the ultrasonic wave receiving means 31b of the ultrasonic wave transmission and receiving means 31 can be installed. The partial replica 7 is desirably installed near the ultrasonic wave transmission and receiving means 3 so as to be in the same temperature environment as that of the wall of the reactor pressure vessel 1 where the ultrasonic wave transmission means 3a and the ultrasonic wave receiving means 3b are installed. It will be understood that the installation position need not necessarily be near the ultrasonic wave transmission and receiving means 3, because similar temperature environment may be created by using a heater or the like. Consequently, the received signal acquired by using the ultrasonic wave transmission and receiving means 31 installed on the partial replica 7 results mainly from reflected ultrasonic waves in the wall of the partial replica 7, and a waveform equivalent to FIG. 6(b) can be obtained. In the present embodiment of such a configuration, reflected ultrasonic pulses in the wall of the partial replica 7 shown in FIG. 7 are stored into the preprocessing means 4 as digital data, whereby propagation time thereof can be determined. As a result, noise occurring from ultrasonic waves reflected in the wall of the reactor pressure vessel 1 can be excluded by waveform differential processing. This facilitates identifying reflected ultrasonic pulses from the inspection object 2. Another method for avoiding noise occurring from ultrasonic waves reflected in the wall of the reactor pressure vessel 1 will be described below. FIG. 5 shows in full lines the path of ultrasonic waves that are reflected once in the wall of the reactor pressure vessel 1 and reach the ultrasonic wave receiving means 3b, and in broken lines the path of ultrasonic waves that are reflected three times and reach the ultrasonic wave receiving means 3b (the clad weld layer 8 is omitted from the diagram). The lengths of such ultrasonic wave paths can be determined from the thickness of the wall of the reactor pressure vessel 1, the installation positions of the ultrasonic wave transmission means 3a and the ultrasonic wave receiving means 3b, and the numbers of reflections of ultrasonic waves. If temperature is known, the velocity of sound is known and the observation time at the ultrasonic wave receiving means 3b can be determined. Even when temperature is unknown, the observation time of ultrasonic waves reflected three times or more in the wall can be determined based on a first peak in the received waveform of the ultrasonic wave receiving means 3b if the first peak can be identified, because the first peak represents ultrasonic waves that are reflected once in the wall of the reactor pressure vessel 1 and reach the ultrasonic wave receiving means 3b. Using such a method, the observation time of reflected ultrasonic pulses in the wall can be determined to exclude the reflected ultrasonic pulses in the wall of the reactor pressure vessel 1. Peaks of the reflected ultrasonic waves in the wall can thus be prevented from being misjudged to be reflected ultrasonic pulses from the inspection object 2. In addition, the exclusion of reflected ultrasonic pulses in the wall of the reactor pressure vessel 1 is performed by processes such as reducing signals of the corresponding observation time or excluding reflected ultrasonic pulses from the corresponding observation time when identifying reflected ultrasonic pulses from the inspection object 2. The processing of excluding reflected ultrasonic pulses in the wall of the reactor pressure vessel 1 can be used with the foregoing waveform differential processing. As a result, the calculation means 5 can easily extract reflected ultrasonic pulses from the inspection object 2 as shown in FIG. 6(c). In addition, various types of techniques may be applied to the extraction of reflected ultrasonic pulses, including retrieval of maximum and minimum values, a threshold determination on amplitude intensity, and retrieval of maximum values in correlative calculation with transmitted ultrasonic pulses. Then, the vibration frequency and vibration amplitude of the inspection object 2 can be determined from the data on changes in the propagation time of the reflected ultrasonic pulses extracted. Furthermore, the identification of reflected ultrasonic pulses from the inspection object 2 may be performed based on a waveform barycenter, for example. According to the present embodiment, even when detecting vibrations of internal equipment having a tilt and/or curvature in the reactor pressure vessel 1, reflected ultrasonic pulses from the internal equipment can be obtained at a high S/N ratio by differential processing of measurement data including the reflected ultrasonic pulses from the internal equipment and storage data stored in advance including no reflected ultrasonic pulse from the internal equipment. This allows accurate vibration detection. The ultrasonic-wave interrupting means can be used to interrupt ultrasonic pulses and reflected ultrasonic waves for an arbitrary time, whereby data intended for differential processing, including no reflected ultrasonic pulse from the internal equipment, can be quickly acquired. Then, differential processing with measurement data including reflected ultrasonic pulses from the internal equipment can determine reflected ultrasonic pulses from the internal equipment at a high S/N ratio, which allows accurate vibration detection. If reflected ultrasonic pulses in a wall are measured by using the partial replica 7 that is installed near the ultrasonic wave transmission and receiving means 3 attached to the reactor pressure vessel 1, it is possible to acquire measurement data on propagation time almost same as or quite similar to that of reflected ultrasonic pulses in the wall of the reactor pressure vessel 1. Then, the foregoing differential processing can be performed to increase the S/N ratio of reflected ultrasonic pulses from the inspection object 2 for accurate vibration detection. In addition, reflected ultrasonic pulses in a wall are identified by calculation using the positional relationship of the ultrasonic wave transmission and receiving means 3 and the wall thickness and temperature of the reactor pressure vessel 1. Since a peak that is observed in minimum time results from ultrasonic waves reflected once by the inside surface of the reactor pressure vessel 1, the velocity of sound can be determined based on the observation time of the peak. Using the velocity of sound, the observation times of ultrasonic pulses reflected a plurality of times in the wall can also be experimentally identified. Then, reflected ultrasonic pulses in the wall can be excluded from the measurement data including reflected ultrasonic pulses from the internal equipment, even if noises having higher amplitudes can be circumvented for accurate vibration detection. FIG. 8 is a block diagram showing a schematic configuration of a reactor vibration monitoring device according to a second embodiment of the present invention. Parts identical or similar to those of FIG. 1 will be designated by the same reference symbols, and redundant description will be omitted. As shown in the diagram, the reactor vibration monitoring device 15 includes: an ultrasonic wave transmission and receiving means 3 which is installed on the outside surface of a reactor pressure vessel 1, transmits ultrasonic pulses to the interior of the reactor pressure vessel 1, and receives reflected pulses reflected by an inspection object 2; a preprocessing means 9 which processes a reflected pulse signal received by an ultrasonic wave receiving means 3b based on the wall thickness of the reactor pressure vessel 1 and the attached positions of an ultrasonic wave transmission means 3a and the ultrasonic wave receiving means 3b which constitute the ultrasonic wave transmission and receiving means 3; and a calculation means 5 which determines vibrations of the inspection object 2 from the reflected pulse signal processed by the preprocessing means 9 based on observation time of the inspection object 2. Like the preprocessing means 4 of FIG. 1, the preprocessing means 9 includes a not-shown analog-to-digital converter that performs conversion into digital data, as well as a mask circuit that extracts digital data from the converted digital data according to designated start position and end position, a calculation circuit that performs four arithmetic operations on the digital data, and a filtering circuit that performs frequency filtering on the digital data. The analog-to-digital converter has a sampling frequency off (Hz). Based on the sampling theorem, the maximum possible value of the filtering frequency of the filtering circuit is limited to f/2 (Hz). The preprocessing means 9 according to the present embodiment converts reflected frequency pulses into digital data, squares the value of the digital data, and then performs frequency filtering processing of passing a low frequency range including the frequency of transmitted ultrasonic waves. Such processing produces noise-reduced high-S/N (signal-to-noise ratio) reflected ultrasonic pulses as shown in FIG. 9. If the dimensions and arrangement of the inspection object 2 are known from a drawing or by actual measurement, the propagation time of reflected ultrasonic pulses in a wall can be calculated from the positional relationship of the inspection object 2 based on the positional relationship of the ultrasonic wave transmission means 3a and the ultrasonic wave receiving means 3b and the temperature of the reactor pressure vessel 1. As a different process, the preprocessing means 9 may determine the velocity of sound from the output waveform of the ultrasonic wave receiving means 3b without known temperature since reflected ultrasonic pulse observed in minimum time is the ultrasonic wave reflected once by the inside surface of the reactor pressure vessel 1. Consequently, the observation time of reflected ultrasonic pulses from the inspection object 2 can be determined by using the velocity of sound and the distance between the ultrasonic wave transmission and receiving means 3 and the inspection object 2. As a result, the preprocessing means 9 can determine the propagation time of the reflected ultrasonic pulses from the inspection object 2, and extracts a certain time domain caused by variation of temperature and distance. FIG. 10 shows the processing result. Noise-based peaks can be prevented from being misjudged to be reflected ultrasonic pulses from the inspection object 2, and the reflected ultrasonic pulses from the inspection object 2 can be detected with higher reliability. As described above, the calculation means 5 can easily extract reflected ultrasonic pulses as shown in FIGS. 9 and 10, and can determine the vibration frequency and vibration amplitude of the inspection object 2 from the data on changes in the propagation time of the reflected ultrasonic pulses extracted. According to the present embodiment, the propagation time of reflected ultrasonic pulses is determined from the dimensions and arrangements of the inspection object, and a certain time domain caused by variation of temperature and distance is extracted. This makes it possible to detect reflected ultrasonic pulses from the internal equipment without fail, allowing accurate vibration detection. Even when detecting vibrations of the internal equipment 2 having a tilt and/or a curvature in the reactor pressure vessel 1 in the presence of errors in dimensions and arrangements, heat deterioration and/or measurement errors in temperature, the observation time of reflected ultrasonic pulses from the inspection object 2 is extracted from the received waveform including a reflected pulse signal. This can remove reflected ultrasonic pulses occurring in the wall of the reactor pressure vessel 1 to increase the S/N ratio of reflected ultrasonic pulses from the internal equipment 2, and vibrations of the inspection object 2 can be accurately detected. Moreover, even when detecting vibrations of the internal equipment having a tilt and/or a curvature in the reactor pressure vessel 1, reflected ultrasonic pulses from the internal equipment 2 can be obtained with a high S/N ratio by squaring the amplitude of measurement data including the reflected ultrasonic pulses from the internal equipment and then performing frequency filtering processing of passing a low frequency range including the frequency of the transmitted ultrasonic waves. This allows accurate vibration detection. FIG. 11 is a block diagram showing a schematic configuration of a reactor vibration monitoring device 16 according to a third embodiment of the present invention. Parts identical or similar to those of FIG. 1 will be designated by the same reference symbols, and redundant description will be omitted. As shown in the diagram, the reactor vibration monitoring device 16 includes: a pulse train generating means 10 which is installed on the outside surface of a reactor pressure vessel 1 and transmits an ultrasonic pulse train to an inspection object 2 in the reactor pressure vessel 1; and an ultrasonic wave receiving means 3b which receives reflected ultrasonic pulses reflected by the inspection object 2. The reactor vibration monitoring device 16 also includes: a preprocessing means 11 which calculates a correlation between a received waveform including a reflected pulse signal of a pulse train received by the ultrasonic wave receiving means 3b and the waveform of the transmitted ultrasonic pulse train; a calculation means 5 which extracts a reflected pulse signal and determines vibrations of the inspection object 2 from temporal changes in observation time; and a position adjusting means 12 which adjusts positional relationship of the ultrasonic wave receiving means 3b. Like the ultrasonic wave transmission means 3a shown in FIG. 1, the pulse train generating means 10 mentioned above is an ultrasonic wave transmission element using a piezoelectric transducer or electromagnetic acoustic transducer. The pulse train generating means 10 receives input of an arbitrary number of consecutive electrical pulses and generates ultrasonic waves of pulse train form shown in FIG. 12. In the example of FIG. 12, the pulse train includes ten pulses, whereas the number of pulses of ultrasonic waves and the frequency of the ultrasonic waves may be arbitrarily set. Aside from a not-shown analog-to-digital converter and a not-shown storage circuit as in FIG. 1, the preprocessing means 11 includes a calculation circuit that performs a correlation calculation between converted digital data of an input signal and stored digital data and makes an output. The position adjusting means 12 is a moving mechanism for changing the position of the ultrasonic wave receiving means 3b. The position adjusting means 12 moves over the outside surface of the reactor pressure vessel 1 by such means as wheels and a reaction force of a blower, and fixes the ultrasonic wave receiving means 3b by a magnetic force, suction force, etc. It should be appreciated that such a position adjusting means 12 may also be applied to the reactor vibration monitoring device 14 shown in FIG. 1 and the reactor vibration monitoring device 15 shown in FIG. 8. In the present embodiment of such a configuration, as in the first embodiment, ultrasonic waves of pulse train form transmitted from the pulse train generating means 10 are reflected and attenuated by the boundary between the wall of the reactor pressure vessel 1 and the clad weld layer 8 and the boundary between the clad weld layer 8 and the reactor water, and further attenuated in the clad weld layer 8. The ultrasonic waves also spread out due to a tilt and/or a curvature of the inspection object 2, and the ultrasonic wave receiving means 3b receives reflected ultrasonic pulses of pulse train form shown in FIG. 13. The positional relationship between the pulse train generating means 10 and the ultrasonic wave receiving means 3b may be affected by errors in the dimensions and arrangements of the reactor pressure vessel 1 and the inspection object 2, heat deterioration, measurement errors in temperature, etc. Then, the relative position of the ultrasonic wave receiving means 3b can be adjusted by using the position adjusting means 12 so as to circumvent the effect of errors, heat deterioration, etc. Consequently, the position adjusting means 12 can be operated to change the position of the ultrasonic wave receiving means 3b so that the reflected ultrasonic pulses of pulse train form shown in FIG. 13 have an improved S/N ratio. Next, the preprocessing means 11 performs analog-to-digital conversion on the ultrasonic pulses shown in FIG. 13, and performs a calculation to calculate a correlation value with respect to the waveform of the ultrasonic pulse train shown in FIG. 12, transmitted from the pulse train generating means 10. Such a calculation corresponds to processing of extracting the same waveform as that of the ultrasonic pulse train shown in FIG. 12 from the waveform of FIG. 13. As the waveform of FIG. 13 is scanned from left to right for the ultrasonic pulse train, the correlation value has the peaks where the pattern is the same as or similar to that of the ultrasonic pulse train. FIG. 14 shows an example of the result of the correlation calculation. The correlation value increases gradually near the observation time of the ultrasonic pulse train, shows a maximum value, and then decreases gradually. The time when the correlation value shows the maximum value is the observation time of the ultrasonic pulse train. The correlation value can thus be determined to identify the observation time of the ultrasonic pulse train from the inspection object 2. Consequently, as shown in FIG. 14, the calculation means 5 can calculate a correlation value between the ultrasonic pulse train and the reflected pulse signal to easily identify reflected ultrasonic pulses from the inspection object 2, and determine the vibration frequency and vibration amplitude of the inspection object 2 from the data on changes in the propagation time of the reflected ultrasonic pulses extracted. According to the present embodiment, even when detecting vibrations of the internal equipment 2 having a tilt and/or a curvature in the reactor pressure vessel 1 in the presence of errors in dimensions and arrangements, heat deterioration, and/or measurement errors in temperature, the position adjusting means 12 can be operated to change the position of the ultrasonic wave receiving means 3b so as to increase the S/N ratio of reflected ultrasonic pulses from the internal equipment 2. Vibrations can be detected without attaching a reflector to the internal equipment 2. In addition, a correlation value between an ultrasonic pulse train generated by the pulse train generating means 10 and a reflected pulse signal received by the ultrasonic wave receiving means 3b can be calculated to identify reflected ultrasonic pulses from the internal equipment 2 for accurate vibration detection. Now, a reactor vibration monitoring method will be described with reference to FIGS. 8 and 15. Initially, in an ultrasonic wave transmission step S1, the ultrasonic wave transmission means 3a is installed on the outside surface of the reactor pressure vessel 1 and transmits ultrasonic pulses to the interior of the reactor pressure vessel 1. Next, in an ultrasonic wave receiving step S2, the ultrasonic wave receiving means 3b is installed on the outside surface of the reactor pressure vessel 1 and receives reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by the inspection object 2. Then, in a preprocessing step S3, reflected ultrasonic pulses occurring in the wall of the reactor pressure vessel 1 are identified and removed from the reflected pulse signal received by the ultrasonic wave receiving means 3b, or a reflected pulse signal reflected by the inspection object 2 is selectively extracted. Moreover, in a calculation step S4, vibrations of the inspection object 2 are determined from the reflected pulse signal processed in the preprocessing step S3 based on observation time of the inspection object 2. According to the present embodiment, even when detecting vibrations of the internal equipment 2 having a tilt and/or a curvature in the reactor pressure vessel 1 in the presence of errors in dimensions and arrangements, heat deterioration, and/or measurement errors in temperature, reflected ultrasonic pulses occurring in the wall of the reactor pressure vessel 1 can be removed from the received waveform including the reflected pulse signal or the reflected pulse signal reflected by internal equipment 2 can be selectively extracted to increase the S/N ratio of the reflected ultrasonic pulses from the internal equipment 2. Vibrations of the internal equipment 2 can be detected without attaching a reflector to the internal equipment 2. While embodiments of the present invention have been described above, the present invention is by no means limited to the foregoing embodiments. The configurations of the embodiments may be combined to make various modifications without departing from the gist of the present invention. |
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description | The present application claims the benefit, under 35 U.S.C. 119(e), of the provisional patent application filed on Dec. 14, 2008 and assigned application No. 61/122,401. The direct conversion of radioisotope beta (electron) emissions into usable electrical power via beta emissions directly impinging on a semiconductor was first proposed in the 1950's. These devices are known as Direct Conversion Semiconductor Devices, Beta Cells, Betavoltaic Devices, Betavoltaic Batteries, Isotope Batteries etc. These direct conversion devices promise to deliver consistent long-term battery power for years and even decades. For this reason, many attempts have been made to commercialize such a device. However, in the hopes of achieving reasonable power levels, the radioisotope of choice often emitted unsafe amounts of high energy radiation that would either destroy the semiconductor within the betavoltaic battery or the surrounding electronic devices powered by the battery. The radiated energy may also be harmful to operators in the vicinity of the battery. As a result of these disadvantages and in an effort to gain approval from nuclear regulatory agencies for these types of batteries, the choice for radioisotopes has been limited to low energy beta (electron) emitting radioisotopes such as Nickel-63, Promethium-147 or Tritium. Due to the fact, that Promethium-147 is regulated more stringently and requires considerable shielding and Nickel-63 has a low beta flux, Tritium has emerged as a leading candidate for such a battery device. Tritium betavoltaic batteries, sometimes referred to as Tritium betavoltaic devices or Tritium direct conversion devices, have been promoted during the last thirty years. Tritium is a relatively benign radioisotope with low beta energy emission that can easily be shielded with as little as a thin sheet of paper. Tritium has a long track record in commercial use in illumination devices such as EXIT signs in commercial aircraft, stores, school buildings and theatres. It is also widely used in gun sights and watch dials, making it an ideal power source for the direct conversion devices. Unfortunately, Tritium's beta emissions are so low energy that it is has been difficult to efficiently convert it into usable electrical power for even the most low power applications, such as powering SRAM memory to prevent the loss of stored data. Several attempts have been made to produce useful current from a Tritium betavoltaic battery. For example, polycrystalline or amorphous semiconductor based betavoltaic batteries are less expensive to manufacture and have been studied as possible Tritium batteries due to the fact that large surface areas may be produced in a thin-film-like fashion with embedded Tritium within the semiconductor or on the surface of the semiconductor. However, this approach is extremely inefficient (much less than 1%) with respect to the beta energy emissions entering the semiconductor. The main reason for this low semiconductor conversion efficiency is the high dark current or leakage current of the semiconductor that acts as a negative current. This high dark current competes with the battery current produced by the electron hole pairs (EHPs) created via the Tritium beta particles impinging on the semiconductor. In short, the polycrystalline and amorphous semiconductors have a high number of defects resulting in recombination centers for the EHPs created by the Tritium beta particles in the semiconductor and therefore resulting a very poor efficiency. Other recent attempts have involved single crystalline semiconductor devices with a Tritium source such as a Tritiated polymer, aerogel or Tritiated metal hydride placed in direct contact with the semiconductor. Single crystalline semiconductors have longer carrier lifetimes and fewer defects resulting in a lower dark current. To date, the highest reported efficiencies for Tritium betavoltaic battery were published in a reference text entitled: “Polymers, Phosphors and Voltaics for Radioisotope Microbatteries” edited by K. Bower et al. The direct conversion single crystal semiconductors were exposed to a Tritium Metal Hydride source atop the semiconductor. The following homojunction semiconductor cells were utilized with the following results: Silicon Cells: Short Circuit Current=18.1 nA/cm^2 Open Circuit Voltage=0.162 Fill Factor=0.513 Tritiated Titanium Source=0.23 microwatts/cm^2 Efficiency=1.3% Aluminum Gallium Arsenide (AlGaAs) Cells: Short Circuit Current=58 nA/cm^2 Open Circuit Voltage=0.62 Fill Factor=0.751, Power=27 nW/cm^2 Tritiated Titanium Source=0.48 microwatts/cm^2, Efficiency=5.6% Silicon cells are a preferred choice due to their low cost. However, their low efficiency makes them a poor choice for even the most low power applications, such as SRAM memory devices. The performance of the AlGaAs homojunction cell is attractive with one of the highest reported efficiencies and would be suitable for powering an SRAM memory device through the stacking of Tritiated metal hydride layers and AlGaAs homojunction cells. However, AlGaAs homojunctions cells are difficult to reproduce consistently with uniform dark currents across a semiconductor device due to the oxidation of the aluminum. AlGaAs is also an expensive option to scale up. In addition, the materials production technology is not well developed. The main disadvantage with the above listed approaches for betavoltaic devices is the construction of the semiconductor with the same design structure as a solar cell structure. Hence the betavoltaic device suffers in efficiency, especially when a weak beta emitter such as Tritium is utilized. Moreover, the need for a high efficiency single crystalline semiconductor with a uniform low dark current across a whole production wafer is key to allowing the Tritium betavoltaic battery to be affordably commercialized. Safety concerns over containment of the Tritium based battery have emerged as another obstacle to commercialization of the Tritium battery. In commercially available products such as Tritium illumination products (e.g. EXIT signs, gun sights and watch dials) the Tritium is in gaseous form and contained within a glass vial. Many accidents involving Tritium release due to the breakage of the Tritium vials in EXIT signs have caused public concerns and resulted in costly clean ups. In the case of a Tritium battery with a solid Tritium metal hydride, the risk to exposure is much less than in gaseous form. However, the Tritium metal hydride still involves a miniscule amount of Tritium release when open to the environment at room temperature. Although several Tritium based batteries have been proposed including direct conversion devices built within an integrated circuit, a method of effectively hermetically packaging the battery containing the Tritium metal hydride has yet to be proposed. A major obstacle to hermetically sealing this type of battery is the risk associated with using a sealing process that involves high temperatures, i.e., above 200-300° C., where Tritium is released from the metal hydride causing failure of the battery after sealing or worse, causing Tritium exposure at the manufacturing facility and to the operator of the equipment for sealing the battery. In addition to the above listed obstacles, the texturing of a direct conversion semiconductor device to increase the surface area exposed to radiation emission has been proposed several times in the past. For example, on page 282 of the book titled “Polymers, Phosphors and Voltaics for Radioisotope Microbatteries” edited by K. Bower et al., the use of porous Silicon and Tritium inserted into porous silicon holes was proposed as a means of increasing the surface area of the semiconductor device by 20 to 50 times, in contrast to the original planar semiconductor surface area. The following published patent applications and patents each propose a method of increasing the surface area of the semiconductor by textured growth of the semiconductor or a post-growth texturing method: US Patent Application Publication 2004/0154656 US Patent Application Publication 2007/0080605 U.S. Pat. No. 7,250,323 U.S. Pat. No. 6,949,865 Central to this approach is the hope that an increase in surface area exposed to radioisotope emissions will increase the power per unit volume of the direct conversion semiconductor device. The overall goal of this approach is to not only reduce the size of the direct conversion device but also to potentially reduce the cost associated with producing the equivalent surface area in a planar semiconductor device. The problem with such an approach arises when a relatively low energy radioisotope such as Tritium is used. In this case, the incident power is quite small per unit area exposed and the dark current of the semiconductor device is a significant factor in the overall efficiency of the device. For this reason, it is preferred to use single crystal semiconductors where device defects are minimized and the dark current is sufficiently low to produce electrical power. Unfortunately, alterations to the semiconductor surface, as proposed above, risk increasing lattice defects, resulting in a high number of recombination centers for electron hole pairs (EHP's). This creates a direct conversion semiconductor device with a low open circuit voltage and short circuit current resulting in a low overall efficiency. In accordance with common practice, the various described features are not drawn to scale, but are drawn to emphasize specific features relevant to the invention. Like reference characters denote like elements throughout the figures and text. Before describing in detail the particular methods and apparatuses related to tritium direct conversion semiconductor devices, it should be observed that the present invention resides primarily in a novel and non-obvious combination of elements and process steps. So as not to obscure the disclosure with details that will be readily apparent to those skilled in the art, certain conventional elements and steps have been presented with lesser detail, while the drawings and the specification describe in greater detail other elements and steps pertinent to understanding the invention. The following embodiments are not intended to define limits as to the structure or method of the invention, but only to provide exemplary constructions. The embodiments are permissive rather than mandatory and illustrative rather than exhaustive. The present invention relates to a Tritium Direct Conversion Semiconductor Device comprised of a single crystal semiconductor and a device structure with both a low dark current and high efficiency for Tritium conversion. It should be understood that the high efficiency and long term life (e.g. over 10 years) of the various device structure embodiments are suitable for use with other candidate radioisotopes for betavoltaic operations (e.g., Promethium-147 and Nickel-63). One embodiment of the present invention proposes a novel use of Indium Gallium Phosphide homojunction semiconductor 8 in conjunction with a Tritiated metal hydride source 10, as illustrated in FIG. 1, for supplying power to a load 12. The Tritiated metal hydride source (e.g, Scandium Tritide (Tritiated Scandium), Titanium Tritide etc.) is directly in contact with the semiconductor to generate electrical power at an efficiency of 7.5% or higher with respect to the beta electrons impinging on the Indium Gallium Phosphide homojunction. InGaP is one of the larger band gap materials and has never been used in a Tritium based Direct Conversion Battery. One embodiment uses a compositions of the Indium Gallium Phosphide homojunction comprising In0.49 Ga0.51 P (subsequently referred to as InGaP). The band gap of this semiconductor is 1.9 eV and the materials production technology is well developed by the solar cell industry. The technology also lends itself to high quality growth with few lattice defects and low dark current characteristics. In addition, InGaP may be mass produced with a high yield due to its manufacturing process maturity over other type III-V semiconductors, such as AlGaAs, thus lowering the cost of Tritium betavoltaic batteries based on InGaP. InGaP device structures are grown by metal-organic-vapor-deposition (MOCVD) as is known by those skilled in the art. The description of this embodiment presents novel and non obvious features that allow efficient conversion of tritium beta flux to electrical power. FIGS. 2 and 3 illustrate the physical structure and electron band diagram, respectively. Each layer has the same lattice constant as GaAs substrate so that the number of dislocations generated by growth of the individual layers is minimized. The beta particles represented by arrowheads in FIG. 2 are released by the Tritiated Scandium material of FIG. 1. FIG. 2 illustrates the individual layers of the homojunction semiconductor 8, comprising, from the bottom: a GaAs substrate a p+InGaP layer (a back surface field or reflector or antiwindow) a pInGaP layer (base) an intrinsic InGaP layer (for preventing diffusion between the p-doped and n-doped layers) an nInGaP layer (emitter) an nInAlP layer (window layer that allows electrons to pass but blocks holes with a closely matched lattice structure to one or both layers it is contact with) a GaAs cap layer (may be highly doped)In another embodiment the GaAs substrate is replaced by a Germanium substrate. There are several features of this structure that allow efficient betavoltaic energy conversion: (a) High quality, large band gap semiconductor junction resulting in a highly efficient device; (b) Back-surface field created by highly doped the p+InGaP layer (can also be created by p-type InAlP or InAlGaP); (c) A lattice-matched n-type InAlP window layer to reflect holes in the emitter leading to a low dark current; (d) A GaAs Cap layer of about a few hundred angstroms or less; (e) and a 1000 to 3000 Å layer of intrinsic InGaP to act as a buffer to dopant zinc diffusion into the n-type emitter region. The features (a), (b) and (c) may be important for solar cell operation but their utilization in Tritium betavoltaic application is considered novel in the present embodiment. The novel features (d) and (e) may be important for betavoltaic conversion, but are not necessarily used for photovoltaic conversion. Both of these features allow the achievement of low dark currents preferred for betavoltaic operation. The novel lattice-matched InAlP window layer prevents the formation of dislocations at the InAlP-InGaP interface, which would increase the dark current. The GaAs Cap layer keeps the InAlP layer from oxidizing, the absence of which would introduce defects for EHP recombination at the InAlP-InGaP region. This cap layer, therefore augments hole reflection at that interface. The GaAs Cap layer does not absorb a significant percentage of the beta flux, and therefore can be tolerated. In solar cell operation the GaAs cap layer is typically removed except under the metal gridline contacts. This is required since a cap layer across regions between the metal gridline contacts would significantly reduce the efficiency of the solar cell by absorbing too many of the high energy photons. For this reason, the GaAs Cap layer is normally etched away completely in a solar cell, except for the regions under the gridline metal contacts. Since in solar cell operation the remaining GaAs Cap layer under the metal gridline contacts is a conduit for the electrons to the grid metal lines, the GaAs Cap layer is normally doped to a level of 10^19 ND/cm^3 in order to create good conduction for milliamps or higher current levels required in photovoltaic operations. This high doping may unfortunately create defects in the n-type InAlP layer for betavoltaic operations. In other words, the dark current and voltage can be reduced due to the high doping of this layer. This is not important for photovoltaic operations since the dark current is so low compared to the milliamps current levels generated in a solar cell photovoltaic operation, but it is extremely important for the betavoltaic operation where the current levels are in the range of nanoamps. For this reason, the novel application of a reduced dopant layer may be introduced. The betavoltaic GaAs cap layer doping may be reduced to a level of 10^18 ND/cm^3 reducing the number defects that are caused by diffusion of the GaAs Cap layer dopant into the n-type InAlP layer. The novel intrinsic InGaP layer is not used in photovoltaic operation but may be important for betavoltaic operation due to the fact that it can achieve low dark currents. All layers of the InGaP device structure are grown at high temperatures (e.g. 500° C.-700° C.). In particular, the intrinsic layer, the n-InGaP emitter layer, the n-InAlP layer and the n-GaAs Cap layer are all grown at high temperatures. During the time required for growth of these layers, the p-type dopant zinc in the p-InGaP layer will diffuse toward the n-type films. If the intrinsic layer is too thin and allows zinc to diffuse into the emitter layer and the InAlP region, the dark current will increase and the betavoltaic device performance is degraded. Thus, since low dark currents are critical for Tritium betavoltaic energy conversion, the intrinsic layer must be thick enough to be an effective buffer to zinc diffusion. An intrinsic layer of approximately 1000-3000 Angstroms or more is sufficient to produce a low dark current betavoltaic device. Although the present invention utilizes an intrinsic layer of InGaP that is 1000-3000 Å, it is also possible in one embodiment of the invention to remove the intrinsic layer or to use a substantially smaller thickness of about e.g., 50-100 Å. In another embodiment of the invention the GaAs cap layer may be also be removed from the structure. Note that without the intrinsic layer, the uniformity of the low dark current across a wafer is decreased significantly to yields of 30-40% or less per wafer. This is due to a higher number of resulting defects per wafer processing run. However, with the intrinsic layer in place, the low dark current yield is approximately 80-100% of the wafer. This results in a significant cost reduction in the processing of betavoltaic devices. Furthermore, the intrinsic layer lowers the dark current and produces a higher open circuit voltage for the InGaP betavoltaic device of about 0.1 volts as opposed to an InGaP betavoltaic device without the intrinsic layer. This has helped increase the efficiency of the InGaP betavoltaic device. It should be noted that the Tritium InGaP betavoltaic structure presents novel and non-obvious features that provide a low dark current and a high voltage and collection efficiency. The following data was obtained with solid Tritiated metal hydride sources (e.g. Titanium Tritide, Scandium Tritide etc.) and have the highest reported efficiency of 7.5% with respect to the incident beta radiation impinging on the InGaP homojunction. In particular, for a Tritiated Scandium source with a 250 to 500 nanometer thick Scandium film and an InGaP homojunction as shown in FIG. 2 the following results were achieved: InGaP: Short Circuit Current=45.2 nA/cm^2 Open Circuit Voltage=0.77 Fill Factor=0.79, Power=27.5 nW/cm^2 Tritiated Scandium Source=0.369 microwatts/cm^2, Efficiency=7.5% In general the present invention demonstrates that the intrinsic layer in Tritium betavoltaic devices serves three important purposes: (a) it acts as a buffer to diffusion of dopant atoms from the base region into the emitter region; (b) it allows efficient collection of electron-hole pairs produced as a result of beta particle absorption; and (c) as a consequence, the base region can be heavily doped so that the built-in voltage can be maximized. The high dopant density in the base region (with reference to FIG. 2, the pInGaP layer) is novel to the betavoltaic structure. This is due to the fact that it is not necessary to have a finite diffusion length in the base region for efficient carrier collection; hence a relatively high dopant density can be used in the base region to maximize the built-in potential. Minimizing diffusion of dopant atoms from the base to the emitter and window layers is desirable for achieving a low dark current. With EHP's mainly being produced in the high field region, a large collection efficiency can be achieved. Tritium beta particle penetration in semiconductors is less than about one micron. Thus, it is clear that the emitter and window layers need to be very thin, preferably on the order of a few hundred Å so that most of beta particle absorption occurs in the high field region in the depletion layer (with respect to FIG. 2, the intrinsic InGaP layer or in another embodiment a material region between a p-doped and an n-doped region). Homojunctions are typically formed by abruptly reducing one dopant (e.g., for n-type material) and immediately introducing the other dopant (e.g., for p-type material). The intrinsic regions formed in devices discussed herein are created by reducing one dopant input to zero followed by film growth with neither donors nor acceptors introduced to form the intrinsic layer, and then initiating introduction of the other dopant. Unless noted otherwise, all of the device structures considered herein have an intrinsic layer between the emitter (e.g., the nInGaP layer) and base region (the pInGaP layer). The thickness of the intrinsic layer is selected so that most of the beta particle absorption occurs in the intrinsic layer. Thus, the intrinsic layers for Tritium betavoltaic devices is typically several thousand Angstroms thick. The basic approach to solar cell fabrication does not typically include the intentional formation of a relatively wide intrinsic layer. However, since the Tritium betas are absorbed in a few thousand Angstroms, there is great flexibility regarding an increased doping density in the base. In addition to the InGaP PIN structure already presented, the present invention can be applied to other PIN (p-doped layer—intrinsic layer—n-doped layer) homojunctions. Table 1 lists several exemplary PIN betavoltaic structures. Only structures for p-type base regions are listed in Table 1, but it should be noted that the base region may be switched to an n-type base and corresponding p-type emitter, a p-type lattice-matched window layer, and a p-type cap layer. TABLE 1Examples of PIN Structures with Lattice Matched Window Layers for Tritium BetavoltaicsEg ofBaseIntrinsicEmitterWindowCapBase/EmitterRegionLayerRegionLayerLayer1.9 eVp-InGaPi-InGaPn-InGaPn-InAlPn-GaAs2.3 eVp-InAlPi-InAlPn-InAlPn-ZnSen-GaAs1.45p-GaAsi-GaAsn-GaAsn-InGaPn-GaAs2.25p-GaPi-GaPn-GaPn-AlPn-GaP2.25p-GaPi-GaPn-GaPn-ZnSn-GaAs1.12p-Sii-Sin-Sin-GaP—1.12p-Sii-Sin-Sin-ZnSn-GaP As shown in Table 1, the lattice-matched window layer is critical for high efficiency Tritium betavoltaic devices. Since it is desirable to achieve as large a voltage as possible under the Tritium beta flux the dark current must be as low as possible. As noted for the specific case of InGaP PIN devices, the lattice matched window layer prevents the formation of dislocations in the window layer, which could cause formation of recombination centers at the interface of the window layer and emitter, and increase the dark current. The cap layer referred to in Table 1 has two main functions. For the cases involving Al-containing window layers, the cap layer of GaAs prevents oxidation that would cause degradation of the current voltage characteristics. The cap layer is also characterized by reasonably low sheet resistance that allows effective current collection from the emitter. Since the current levels produced by the Tritium betavoltaic batteries are relatively low, the sheet resistance of the GaAs cap layer can be greater than 100 ohms/□. Thus the cap layer thickness only needs to be 50 to 100 Å. In the cases of the non Al-containing window layers, the primary function of the cap layer is for providing an adequate value of sheet conductance. The cap layer is important for ensuring that the window layers containing aluminum are of high quality. If a window layer containing aluminum is oxidized, this may cause creation of interface states at the emitter-window interface, which will affect the dark current of the betavoltaic device and its charge collection efficiency. Another important effect of the cap layer is to provide for a higher yield in cell growth due to the oxidation protection provided by the cap layer. Higher yield translates into lower production costs. The cap layer is critical for betavoltaic devices. In the case of solar cells, a thin cap layer absorbs solar photons, and therefore is not utilized in such devices. Solar cells are designed with a relatively thick emitter to provide good sheet conductance and thus do not require a cap layer for sheet conductance. The emitter in the typical III-V solar cell contributes to the collection efficiency. Since Tritium betas are absorbed in such a short distance, the PIN device is designed with a very thin emitter such that Tritium betas are primarily absorbed in the intrinsic region. In another embodiment of the present invention a new device structure is presented for efficient direct conversion of Tritium. The betavoltaic device comprises an innovative three layer device structure comprising a Metal/Inter-Layer/Semiconductor (MILS). The inter-layer can be an insulator or a semiconductor with a band gap larger than the band gap of the base semiconductor material. A lattice-matched wide band gap semiconductor is the preferred choice for an Inter-Layer. However, very good results have been achieved with Inter-Layers that are insulators. By insulator, we refer to a material that has a very large band gap and cannot be doped. The total thickness of the metal and Inter-Layer is typically a few hundred Angstroms. Thus, only a small percentage of the incident Tritium beta flux is absorbed in the metal and Inter-Layer. The semiconductor layer is the primary absorber of the betas and is the region where the electron-hole pairs are produced. MILS structures have three desirable features: (a) Large values of short circuit current; (b) Low dark current due to the effect of the inter-layer; (c) Reduced fabrication cost compared to homojunctions due to a simplified device structure. Table 2 lists some examples of efficient MILS devices under Tritium beta flux. TABLE 2Examples of MILS structuresSemiconductor MetalInter-LayerAbsorberAl for p-InGaP, Au for n-InGaPInAlP (Lattice Matched)InGaPAl for p-GaAs, Au for n-GaAsAlGaAs (Lattice Matched)GaAsAl for p-GaAs, Au for n-GaAsInGaP (Lattice Matched)GaAsAl for p-Si, Au for n-SiSiO2SiliconAl for p-Si, Au for n-SiZnS (Lattice Matched)SiliconAl for p-Si, Au for n-SiGaP (Lattice Matched)Silicon The choice of metal depends on the whether the semiconductor absorber is n-type or p-type and on the absorber material electron affinity. Usually the metal films will be Al for p-type semiconductors and Au or Pt for n-type material. In one embodiment, the general physical structure of an MILS device based on InGaP is illustrated in FIG. 4 with the corresponding electron band structure given in FIG. 5. The metal responsible for formation of the built-in voltage is Aluminum. The work functions for Aluminum and p-type InGaP are approximately 4.1 eV and 5.8 eV, resulting in a barrier of approximately 1.7 eV, which is similar to that expected for an InGaP homojunction. Therefore, it is possible to achieve the same dark current with the InGaP MILS device. An exemplary film of Gold is shown on top of the Aluminum. This film protects the Aluminum from oxidation, and does not affect the junction characteristics. The Inter-Layer for this structure is a thin film of lattice-matched n-type InAlP. This layer reflects holes but allows electrons to pass. The absorber semiconductor region includes a layer of intrinsic InGaP (no dopants) to act as a buffer to zinc diffusion from the p-type InGaP region. FIG. 5 describes the electron band diagram and indication of electron and hole transport upon absorption of betas. In another embodiment a Silicon MILS device provides an increase in efficiency over prior art Silicon based homojunction cells due to the MILS construction providing a decrease in dark current and increasing short circuit current. The Tritium based Silicon MILS device efficiency can be approximately 2-3%. FIGS. 6 and 8 illustrate the physical structure and corresponding electron band diagram for an Al/SiO2/p-Si. betavoltaic device. SiO2 is an insulator that cannot be made conductive. As noted in Table 2, ZnS and GaP are examples of large band gap semiconductor Inter-Layers. These materials are particularly interesting because they lattice-match silicon. In general, there can be interface states at an Inter-Layer and silicon boundary. The density of these states are relatively low for a SiO2/Si interface, and could be low for the lattice matched interfaces. As noted, Gold and Platinum can be used for MILS cells fabricated with n-type Silicon. In yet another embodiment, FIG. 7 illustrates an approach to using bidirectional sources with thin Silicon wafers. The wafers can typically be 4 mils (−100 microns) thick and have minority carrier diffusion lengths greater than about 100 microns. The Silicon wafers are polished on both sides, doped with Boron to give a resistivity on the order of 0.1 ohm-cm, and have a back-surface-field established on the back surface (BSF). The BSF would be formed by doping with a high concentration of Boron. Beta particles enter the top and bottom surfaces. The large minority carrier diffusion length allows excited carriers throughout the wafer to be collected so that the current produced is about two times that of a device coupled to a unidirectional source. In a stacking arrangement, the system efficiency approximates two-times that of a stack based on unidirectional sources, thereby achieving a high efficiency Tritium betavoltaic with a Silicon semiconductor. In both PIN and MILS betavoltaic device structures the Tritium source is a Tritium metal hydride (sometimes referred to as a Metal Tritide), that is in contact with the top surface of the betavoltaic structure as shown in FIG. 1. The Tritium metal hydride may be formed by methods known in the art. Some examples of Tritium metal hydrides include Scandium Tritide, Titanium Tritide, etc. These Tritium metal hydrides may be formed on an independent foil or substrate that is then physically laid on top of the semiconductor containing the betavoltaic device. Alternatively, the Tritium metal hydride may be formed as a thin film (e.g. about 100 nm-500 nm) on top of the semiconductor containing the betavoltaic device using methods known in the art. For example a Scandium or Titanium film is deposited as a thin film (e.g. sputtered, evaporated, etc.) onto the semiconductor or substrate and then tritiated using methods known in the art. In another embodiment of the present invention the contact lines on the top surface of the betavoltaic homojunction can be very thin and on the perimeter of the semiconductor. This contact ring is used to collect the charge current from the semiconductor while providing a minimal shadowing effect to the radioactive source's beta flux that impinges on the surface of the semiconductor. The contact ring for the betavoltaic semiconductor may be formed in the same manner as solar cell industry uses to make contact gridlines on the solar cell semiconductor. However, the betavoltaic cell contact ring is substantially different from a solar cell where a series of gridlines are uniformly covering the surface of the semiconductor and can cover approximately 5-10% of the semiconductor surface. This uniform coverage creates a shadowing effect resulting in a proportional loss of power from the solar cell. In contrast the betavoltaic cell's contact ring may be reduced to a small perimeter (e.g. outlining a 1 cm×1 cm cell or 3 cm×3 cm cell etc.) or it may be just a set of contact points or lines. This is due to the low current collection from the betavoltaic device that is in the nanoamp to microamp per square centimeter range as opposed to solar cells where the range is more in the milliamp per square centimeter range, thus requiring less series resistance by the inclusion of more contact line coverage. As an example, the contacts in a betavoltaic semiconductor can result in a shadow coverage that is much less than about 1%, thereby providing a higher efficiency betavoltaic battery. Specific shadow coverage and thicknesses of contact ring, lines or dots required by a betavoltaic semiconductor is dictated by a consideration of diffusion length of the carriers to the contact points/lines and the series resistance that may be tolerated by the incident beta flux density and betavoltaic semiconductor's efficiency. In all embodiments of the present invention the edges of the betavoltaic structure are shielded from beta particles. This constitutes another novel aspect of the present invention. As is known in the art, if the energy of a beta particle is large enough, the particle can cause the displacement of an atom in a crystalline semiconductor. Atomic vacancies can act as a recombination center for EHP's in semiconductors and can cause degradation of betavoltaic efficiencies. Fortunately, the threshold for atomic displacement in semiconductors is typically greater than 250 keV. Therefore, tritium beta particles as well as beta particles from Promethium-147 and Nickel 63 do not cause degradation of semiconductor diode properties as a result of beta absorption within the bulk of the material. However, low energy betas can create dangling bonds along the junction periphery, which can cause shunting currents or carrier recombination at the junction edges. If the edges are not properly shielded or protected from the beta flux, the betavoltaic device performance/efficiency will degrade. As illustrated in FIGS. 9-11, the junction edges may be protected by the keeping the Tritium source within the perimeter contact metal gridlines at a distance that the beta particle cannot reach the edges of the semiconductor. Furthermore, the metal perimeter contact gridlines act as a physical barrier to the beta flux, thus preventing the beta particles from hitting the edge of the device. It should be understood that protection of the edges may be accomplished through a variety of means such as all forms of physical barriers (e.g. deposited metal barriers, polymers, insulators etc.) or simply physical distance acting as a barrier to beta particles impinging on the betavoltaic semiconductor's edges. In all embodiments of the present invention, the voltage and current may be scaled up via the stacking of betavoltaic semiconductors and Tritium sources (betavoltaic cells) as illustrated in the approaches to connecting betavoltaic cells in series and parallel configurations in FIGS. 9-11. Arranging multiple (N) layers of n-on-p (n/p) cells in series is illustrated in FIG. 9. If it is assumed that all cells have identical properties, namely, the same values for short circuit current (Isc), open circuit voltage (Voc) and maximum power (Pmax), and assuming the contacts betweens devices are ideal, the characteristics for the series stack are: (Isc)stack=Isc, (Voc)stack=N×Voc, and (Pmax)stack=N×Pmax The electrical connection between cells can be establish by a soft metal such as indium or by a deposited peripheral strip of gold or another appropriate metal. Although n/p cells are shown in FIG. 9, the same approach can be used for p/n cells. It should be noted that the n/p and p/n configurations can be utilized for PIN, NIP structures, as well as homojunctions, heterojunctions and MILS devices. In the case of an MILS cell, the second letter for the device designation in FIGS. 8, 9 and 10, can be identified as the base region of the cell. For example, an Al/SiO2/p-Si MILS cell can be considered an n/p device in the Figures. FIGS. 10A and 10B illustrate a novel approach for combining n/p and p/n cells in series with bidirectional beta sources, i.e. sources that emit beta particles in two directions as shown. This approach allows for the efficient use of a Tritium layer in a bidirectional capacity. Contacts can be formed as discussed above for the series stack. If the cells have identical properties, except for polarity, the two cell unit provides: (Isc)unit=Isc, (Voc)unit=2×Voc and (Pmax)unit=2×Pmax FIGS. 11A and 11B illustrate a configuration for combining two n/p (or p/n) cells in parallel and coupled to a bidirectional source. In this case, characteristics of the two cell unit are: (Isc)unit=2×Isc, (Voc)unit=Voc and (Pmax)unit=2×Pmax Joining methodologies of electronic component stacking (e.g., multi-chip stacking) such as, solder connections, wire bonding, and other conductive adhesive materials and techniques, can be utilized to join combinations of the configurations listed in FIGS. 9-11. This allows for a broad variety of design interconnectability, thus achieving betavoltaic batteries with a variety of current and voltage specifications. An embodiment of the present invention involves a method of hermetically sealing a direct conversion semiconductor battery with a Tritium metal hydride source at low temperatures. During construction of the battery and sealing, there is no leakage of Tritium from the metal hydride due to high temperature sealing methods, such as glass frit seals or solder seals, and it poses no risk of Tritium exposure to the operator sealing the battery. Additionally, the hermetic battery design and the sealing method allow for high throughput manufacturing and low contamination of Tritium within the manufacturing facility. Hermetic packaging and sealing techniques for integrated circuits are widely used in the semiconductor industry to prevent dirt, moisture, particulates and ionic impurities from entering the integrated circuit package and causing corrosion of the circuit elements and interconnects. In an embodiment of the present invention a combination of these techniques and packaging designs prevents Tritium from exiting the battery package. That is, the role of hermetic packaging and sealing for integrated circuits is reversed in the case of the Tritium battery, from contamination entering the IC package to preventing radioactive contamination from exiting the Tritium battery package. In this embodiment of the present invention, the battery package is comprised of a ceramic or metal package housing containing electrode pins or leads from an internal area of the package to an external area of the package. These leads serve as conduits of electrical power for the battery and are connected to a load on a circuit board or other device. The leads are hermetically attached and sealed via glass frits or commonly used techniques for hermetic sealing of leads. Although the lead sealing methods involve high temperature processes above 300° C., the leads are sealed on the battery housing prior to containment of the Tritium metal hydride. Note, the package may take any form currently in use for IC packages, i.e. PIN device leads, leadless package, surface mounts, etc. The direct conversion semiconductor is placed or bonded within the ceramic or metal package and is connected to internal areas of the leads via wire bonds or other commonly used techniques. The Tritiated metal hydride source, comprising either Scandium or Titanium or another suitable metal, is placed in contact with the direct conversion semiconductor. A combination of direct conversion semiconductors and Tritium metal hydride source layers in series or parallel may be connected within the package. Additionally, the Tritium metal hydride source layers may be deposited directly onto the direct conversion semiconductor. Also, the direct conversion semiconductors may be formed as epilayers that are approximately 5-50 microns in thickness. In one embodiment, the present invention uses a Kovar lid or Kovar step lid that closes the Tritium battery package. If a ceramic package is used a side brazed Kovar seal ring must be attached using techniques commonly known in the art. Note, the Kovar seal ring is attached prior to inserting the Tritiated metal hydride. The final step in the sealing the package is the sealing of the Kovar step lid to the metal package or the ceramic side brazed package with a Kovar seal ring. See FIGS. 12A (bottom view) and 12B (side view). FIG. 12A illustrates a lid step and a lid edge. The Kovar lid is sealed with a resistance or laser welder that uses localized heating well below 200° C. to hermetically weld the lid to the package. The preferred method for welding is a parallel seam welder, which is inexpensive compared to laser welding and offers a high throughput. Note, the most common method in the IC industry for hermetic sealing is the solder weld using a belt furnace. This method involves temperatures of approximately 360° C., well above the threshold for Tritium containment. Testing of the Tritium battery package seal is achieved by enclosing the parallel seam-sealer and the unsealed Tritium battery package within a helium glove box environment. Helium is flowed across the unsealed package and the Kovar lid is then placed on the package. The sealing is performed under a helium atmosphere enclosing a helium environment within the Tritium battery package. The Tritium battery package is then placed in an ultra-sensitive helium detector with detection levels up to 10^-11 cc/second under a 1 atmosphere differential. A leak rate of 10^-8 cc/second under a 1 atmosphere differential is considered hermetic for the Tritium battery package and easily achieved using the above method. Another approach to testing of the hermetic seal may be achieved with a helium bombing system where the Tritium battery package is enclosed in high-pressure helium environment. Depending on the size of the leaks within the Tritium battery package the helium gas will enter the package. The package is then removed from the high-pressure environment and inserted in the ultra-sensitive helium detector unit to detect leakage rates. In another embodiment, the containment of Tritium and radiation emanating from the Tritium metal hydride is contained within individualized tritiated direct conversion semiconductor dyes or epilayer dyes. These direct conversion dyes and Tritium metal hydrides can be supplied with appropriate encapsulation that serves to contain radiation. Encapsulation in the form of discrete, conformal coatings that can be applied through numerous techniques, such as dipping/immersion process, chemical/physical vapor deposition techniques, (e.g. potting, sputtering, evaporation, etc.). These coatings are applied as thin films and can be metallic or vitreous in nature, providing some modest structural support and robustness to the direct conversion dyes, while still providing an important, necessary, and effective barrier to the emission of beta particles arising from tritium decay and containment of the Tritium radioisotope. Encapsulation is conducted to safeguard against any radiation leakage, but would be accomplished in a conformal manner so as to leave contact leads exposed as necessary for integration into device housings and maintain geometric requirements for the dyes. These dies thusly encapsulated are then facile candidates for regulatory general and/or exempt licensure; in this manner, the encapsulated materials could easily be transported or handled without any risk of radiation exposure and without any need for specialized radiation materials training. For example, the encapsulated Tritium betavoltaic dyes could be shipped to an OEM integrator for inclusion in an integrated circuit package without a hermetic seal. One aspect of the present invention involves increasing the surface area per unit volume in a direct conversion device without increasing the dark current, via a texturing method. Instead of texturing a surface of the betavoltaic semiconductor, an epitaxial liftoff (ELO) process is employed to remove an intact epilayer containing the betavoltaic semiconductor device. The ELO process used may be any of the techniques known to those skilled in the art. This epilayer can be made substantially free of surface defects that may harm the betavoltaic device and thus increase dark current of the device. The epilayer is approximately 0.1 microns to 5.0 microns thick and is usually coupled to a backing layer that may comprise a metallic layer (e.g. gold, copper, aluminum, titanium, scandium, platinum, silver, tungsten, and other alloys) or a polymer material (e.g. polyimide, Kapton, etc.). The composite epilayer, comprising the epilayer and backing layer, is approximately 5-50 microns thick and is flexible. Furthermore, the composite epilayer and Tritium metal hydride comprises a thin betavoltaic device that may be stacked in series or parallel. The resulting power density for a single composite epilayer and Tritium metal hydride can be as thin as 10 microns thick and an approximate power range of 0.1 to 0.2 microwatts. Furthermore, via stacking of these individual layers the power density can reach as high as 100-200 microwatts/cm^3, thereby achieving an increase in surface area per unit volume resulting in a significant increase in power per unit volume. In one embodiment the Tritium metal hydride film may be deposited directly onto the composite epilayer semiconductor surface to reduce the thickness of an individual composite epilayer and Tritium metal hydride. In another embodiment, the Tritium metal hydride may be formed on a separate thin substrate or thin foil (e.g. less than 100 microns thick) and is physically attached to the composite epilayer containing the betavoltaic device. In one embodiment, the composite epilayer is comprised of a III-V semiconductor with a betavoltaic semiconductor device structure. The betavoltaic structure may have any of the constructions or combinations described herein. For example, the composite epilayer may have a PIN or NIP structure with or without a highly doped base, a Cap layer to protect the device from oxidation and/or an MILS structure. The composite epilayer with a betavoltaic device in its structure may be selectively etched/released from the III-V substrate via an intermediary sacrificial layer (e.g. AlGaAs) as is known in the art. The sacrificial layer can have a thickness ranging from about 1 nm to about 200 nm. Once the sacrificial layer has been removed via etching, the epilayer and backing layer together are released. In doing this, the betavoltaic device thickness is reduced from standard semiconductor wafer thickness to less than 50 micron thickness. Furthermore, a cost reduction occurs due to the fact that the substrate may be reused to grow another epilayer, thereby reducing the cost of the base substrate material of the semiconductor device. It should be understood that any III-V direct conversion device may be formed into an epilayer through this liftoff process by utilizing a selective etch process to release the epilayer. The various embodiments of the present invention allow construction of a single flexible epilayer Tritium betavoltaic battery. For example a thin epilayer Tritium betavoltaic battery may be constructed with either the Tritium metal hydride film connected to the epilayer or directly deposited on the epilayer. This battery may be connected to a lithium ion thin film battery available from companies such as Front Edge Technologies of Baldwin Park, Calif. These two batteries may be connected together as a joint film that may be pasted within an integrated circuit package to run the device periodically via power bursts from the lithium thin film battery. The Tritium epilayer battery can trickle charge the lithium ion film battery. Periodically the film battery can discharge power bursts at milliwatt power levels and then be recharged via the trickle charging by the Tritium Epilayer Battery. The Tritium epilayer battery, due to its thinness and flexibility, may be inserted into the conformal coating of an integrated circuit and power the integrated circuit stealthily. It can also be combined with a lithium ion thin film battery into the conformal coating of an integrated circuit as a source of power for the integrated circuit. The Tritium epilayer battery can also be placed within an integrated circuit's package. Another approach of the present invention involves texturing the Tritium metal hydride substrate to increase the surface area of the deposited Tritium. Using this method, the substrate is textured to produce surface roughness and then a suitable metal (e.g. palladium, titanium, scandium) for Tritium capture is deposited on the surface. Texturing the Tritium metal hydride substrate rather than the semiconductor in the betavoltaic device may avoid creating defects on the semiconductor's surface that result in a high dark current and poor efficiency. The textured Tritium metal hydride source is then placed in direct contact with the smooth semiconductor device's surface resulting in a higher density of Tritium beta flux entering the semiconductor device. Note the Tritium may be deposited on the textured substrate via any means known in the art. Some examples include aerogels and polymers that may be deposited directly onto the textured substrate surface. In one embodiment, a silicon substrate's surface is textured using a potassium hydroxide (KOH) etchant as is known in the art for texturing silicon solar cells to prevent reflection of sunlight. In this embodiment, square based pyramids with approximately 10 micron tall peaks, as measured from the base, are formed on the surface. The resulting surface area is 1.8 times the original planar surface. As mentioned elsewhere herein, a suitable metal is then deposited on the surface with a thickness of approximately 0.1 to 1 micron and then treated with Tritium. The metal to be tritiated is then deposited using methods known in the art. This results in a Tritium metal hydride with increased surface area on a stainless steel surface. In another embodiment, a metal substrate (e.g. stainless steel or Titanium) surface is mechanically roughened. Conversely, periodic triangular rows are grated through the surface via a laser or other suitable method that can increase the surface area. Note, if triangular rows are formed where the triangles are equilateral in nature, the surface can reach twice the surface area of the original planar surface. A Tritiated metal hydride is then formed on the substrate. Some of the most secure processors and field programmable gate arrays (FPGA's) are using SRAM memory to store encryption keys. However current battery technologies depend on chemistries that are unreliable over long periods of time (i.e. several years) especially under wide temperature ranges, such as −55° C. to +125° C. The Tritium betavoltaic batteries of the present invention are able to power the SRAM memory for periods of 15-20 years or more through these extreme temperatures. Note, the voltage of Tritium betavoltaic batteries based on III-V compounds will fluctuate less in higher temperatures than silicon-based MILS devices. However, silicon-based MILS devices require higher power levels than Tritium InGaP Homojunctions to compensate for higher temperatures. The Tritium based betavoltaic batteries of this invention allow soldier-to-base wireless communications and computer-to-base communication to be encrypted using FPGA's with encryption keys stored in SRAM as well as defense and telecom applications that experience a wide range of temperatures. Note, the Tritium betavoltaic batteries are hermetically sealed batteries packaged in surface mount packages that may be soldered to circuit board with the FPGA's Another application of Tritium based betavoltaic batteries of the present invention is for supplying power to anti-tamper volume protection for electronics and other devices that require protection from intruders. These type of batteries provide the critical longevity of more than 10 years for anti-tamper protection. Note, the temperature resilience of these batteries is critical to the longevity and reliability. In one embodiment a volume protection membrane from W. L. Gore is used on a circuit card to protect encryption keys stored in SRAM from a reverse engineering attack. The Tritium betavoltaic batteries of this present invention may be hermetically sealed in a surface mount package and soldered on the circuit board to provide power to both the volume protection device, the anti-tamper trigger in the processor and the encryption keys held in SRAM. If an attack occurs on the volume protection device (i.e., W. L. Gore volume protection membrane), the Tritium betavoltaic battery power allows the volume protection device to detect the attack and the anti-tamper trigger will erase all critical information residing in the electronics, including the encryption keys. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. |
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051134233 | summary | BACKGROUND OF THE INVENTION This invention relates in general to devices which emit radiation, and in particular to a device which improves the coherence of radiation from a partially coherent source, particularly an x-ray source. It is currently difficult and expensive to generate coherent x-rays using laser techniques. Accordingly, when coherent x-rays are required for interference experiments and the like, it is typical to employ a source of partially coherent x-rays followed by slits which filter out non-coherent portions of the beam. But this technique for improving coherence has a disadvantage: the slits permit only a fraction of the total beam energy to pass to the exit port. This inefficiency results in longer experiment times, and increased expense, and when the signal to noise ratio is too low, it may inhibit the experiment altogether. In the process of increasing the transverse coherence of a radiation beam pulse by the method of this invention, the emittance of the beam is being reduced along at least one transverse direction. "Transverse direction" is defined here as one which is perpendicular to the direction of propagation of the beam. That reduction can be useful even if the beam is not to be used for interference experiments, for example, when it is desired to compress the length of the original beam pulse, i.e. to have substantially all of the radiation impinge on a surface during a time, .delta.t, shorter than the original time duration of the pulse. That can be accomplished by dynamical optical means and the smallest achievable .delta.t depends on the transverse emittance of the beam pulse. A reduction of the transverse emittance along at least one direction will, therefore, allow one to achieve smaller .delta.t values. OBJECT OF THE INVENTION Thus, it is an object of this invention to provide an apparatus and method for improving the coherence of a beam of radiation in a manner such that efficient use is made of the total beam energy of a partially coherent source. An added benefit, is that the length of the resultant radiation beam pulse can be compressed more readily by dynamical means, than the original beam pulse could be. The method can be applied not only to electromagnetic radiation beams, but also to beams of other types of particles. SUMMARY OF THE INVENTION A partially coherent beam-shaped pulse of particles (referred to in the following as x-rays) is sectioned longitudinally into numerous beam-shaped pulses of smaller cross section. The diameter of these smaller beams more closely approaches the transverse coherence length desired in a particular experiment. The various beams are guided along separate paths which have different lengths in order to delay each pulse by a different period of time. The delayed pulses are then directed toward a rotating mirror which deflects them all along the same path, one after another. In this manner, a relatively wide and short beam-shaped pulse with poor transverse coherence is converted into a long, narrow pulse with good transverse coherence. |
claims | 1. A neutron conversion foil for being used in a neutron detector, said neutron conversion foil being configured to be arranged in a scintillator volume and comprising a substrate having a first side and a second side,whereby said substrate is covered at least on one of said first side and said second side with a neutron conversion layer made of a neutron reactive material and being capable of capturing neutrons to thereafter emit light and/or charged particles to be detected by a light sensing device, andwhereby said neutron conversion layer and substrate are transparent to light originating from conversion of the neutrons, and are configured to be arranged such that the light originating from the conversion of the neutrons can pass through and away from the substrates and neutron conversion layers of one or several of said neutron conversion foils and thereafter be collected and detected by the light sensing device. 2. The neutron conversion foil as claimed in claim 1, wherein said substrate is covered on said first side and said second side with a neutron conversion layer made of a neutron reactive material and being capable of capturing neutrons to thereafter emit light and/or charged particles. 3. The neutron conversion foil as claimed in claim 1, wherein said neutron conversion layer contains Li-6 or B-10. 4. The neutron conversion foil as claimed in claim 3, wherein said neutron conversion layer comprises a coating applied to the substrate, wherein the coating comprises LiF and a suitable binder in a weight ratio between 1:1 and 15:1, and that appropriate measures such as LiF nanosizing or refractive index matching are performed to ensure high transparency. 5. The neutron conversion foil as claimed in claim 3, wherein said neutron conversion layer has a layer thickness of between 1 μm and 40 μm, especially between 3 μm and 20 μm. 6. The neutron conversion foil as claimed in claim 1, wherein said substrate is a transparent PET foil. 7. The neutron conversion foil as claimed in claim 6, wherein said transparent PET foil has a thickness of between 2 μm and 19 μm. 8. The neutron conversion foil as claimed in claim 1, wherein each of said neutron conversion layers is overcoated with a wavelength shifting layer being capable of shifting short wavelength light impinging upon it and reemitting light with a wavelength to which said neutron conversion foil is transparent. 9. The neutron conversion foil as claimed in claim 8, wherein said wavelength shifting layer contains Tetra Phenyl Butadiene (TPB), an organic wavelength shifter, or an organo silicate compound. 10. The neutron conversion foil as claimed in claim 9, wherein said wavelength-shifting layer has a layer thickness of between 0.05 μm and 1 μm, especially between 0.05 μm and 0.2 μm. 11. The neutron conversion foil as claimed in claim 1, wherein that said substrate is a mesh. 12. A neutron detecting device comprising:a scintillation volume filled with a scintillating material such as a noble gas;at least one light sensing device in optical contact with the scintillating volume;one or more neutron conversion foils, the neutron conversion foils each comprising a substrate having a first side and a second side, whereby said substrate is covered at least on one of said first side or said second side with a neutron conversion layer made of a neutron reactive material and being capable of capturing neutrons to thereafter emit light and/or charged particles to be detected by the at least one light sensing device, and whereby said neutron conversion layer and substrate are transparent to light originating from conversion of the neutrons, and are configured to be arranged such that the light originating from the conversion of the neutrons can pass through and away from the substrate and neutron conversion layers of one or several of said neutron conversion foils and thereafter be collected and detected by the at least one light sensing device,wherein said one or more neutron conversion foils are positioned in said scintillation volume and in optical contact with said scintillating material, and are configured to be arranged such that charged conversion products arising from neutron capture in said one or more neutron conversion foils escape into said scintillation volume and produce light, to which said one or more neutron conversion foils is transparent, and wherein the produced light is detected by the light sensing device. 13. The neutron detecting device as claimed in claim 12, wherein at least one light-sensing device is provided in optical contact with said scintillation volume. 14. The neutron detecting device as claimed in claim 13, wherein said at least one light sensing device is a solid state light sensor, especially one of a silicon photomultiplier (SiPM) or pixelated Geiger mode avalanche photodiode. 15. The neutron detecting device as claimed in claim 13, wherein said scintillation volume is composed primarily of a noble gas such as helium, argon or xenon or a mixture of noble gases, such as helium doped with xenon, and/or wherein said scintillation volume contains predominantly PVT or a liquid scintillator, thereby allowing the simultaneous measurement of gammas and neutrons. 16. The neutron detecting device as claimed in claim 15, wherein said scintillation volume is predominantly filled with helium, thereby allowing the simultaneous measurement and distinction of fast neutrons, thermal neutrons, and/or photons and electrons produced by the interaction of photons with a detector wall, and/or with xenon, thereby allowing gamma spectrometry to be performed while also measuring neutrons. 17. The neutron detecting device as claimed in claim 14, wherein said at least one solid state light sensor is arranged within said scintillation volume. 18. The neutron detecting device as claimed in claim 15, wherein an in-situ gas purification device such as a getter is immersed in the gas of said scintillation volume, thereby assuring a stable gas composition. 19. The neutron detecting device as claimed in claim 13, wherein said scintillation volume is surrounded by a highly reflective material in the area of which a plurality of light sensing devices can be interspersed. 20. The neutron detecting device as claimed in claim 12, wherein plural neutron conversion foils are arranged in parallel in said scintillation volume. 21. The neutron detecting device as claimed in claim 12, wherein said neutron detecting device is part of a detector system, and wherein a plurality of detector subunits are connected with a control center for evaluating detector data via a wireless network. 22. The neutron detecting device as claimed in claim 21, wherein said neutron detecting device is part of at least one of said detector subunits. 23. The neutron detecting device as claimed in claim 22, wherein said neutron detecting device is connected within said detector subunit to a single board computer, which itself is connected to a network unit and comprises detector software and a data aggregation software/network protocol. 24. The neutron detecting device as claimed in claim 23, wherein a GPS unit for determining the actual position of said detector subunit is connected to said single board computer. 25. A method for operating the neutron detecting device according to claim 12, wherein signals arising from a neutron conversion in said one or more neutron conversion foils are discerned from signals arising from said scintillation volume by pulse shape discrimination, whereby the signals involving light emitted by said one or more neutron conversion foils have a different time structure than the signals from said scintillation volume. 26. The method as claimed in claim 25, wherein light signals arising directly or indirectly from said neutron conversion in said one or more neutron conversion foils are discerned from signals from said scintillation volume alone by pulse shape discrimination, whereby the signals from neutron conversion have a different time structure than the signals from said scintillation volume. 27. A method for operating the neutron detecting device according to claim 12, wherein the presence, the intensity and/or the type of gamma radiation interacting with the scintillating volume is determined by analyzing the distribution of the energy spectrum of the interaction events accumulated during a predetermined period of time of operation, especially in a range from 1 to 100 seconds. 28. A method for operating the neutron detecting device according to claim 12, wherein two overlapping spectral distributions resulting from the simultaneous interaction of gamma radiation and neutron radiation with the scintillating volume and/or the converter foil and being accumulated during a predetermined period of time of operation, especially in a range from 1 to 100 seconds, are analyzed employing statistical methods, whereby a net neutron count rate can be determined by subtracting the spectral response obtained by the gamma radiation from the total spectrum. 29. The neutron conversion foil as claimed in claim 1, wherein the neutron conversion foil comprises a flexible foil. 30. The neutron conversion foil as claimed in claim 1, wherein the neutron conversion foil comprises a foil which is sufficiently thin, such that deposition of energy by gamma radiation is reduced. |
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053435079 | abstract | A shutdown cooling system for a nuclear reactor operates during lapse of normal power and emergency power and has an independent power source fo removing residual heat while cooling the seals of the main reactor coolant pump. A high pressure pump delivers cooling water to the reactor cooling pump seals, a low pressure pump circulates core coolant, and a cooling mechanism discharges the decay heat. Electrical power for the pumps and associated valves and controls is provided by a dedicated power source apart from the regular residual heat removal apparatus of the reactor, and apart from the emergency generators provided for regular power failure backup. |
045253234 | claims | 1. In a system comprising means for extracting useful energy in a controlled manner from a target imploded by energy from at least one ion beam, said target having a centrally located quantity of fusion fuel which gives off useful energy in a controlled manner when imploded by ion beam energy, the improvement consisting of: a pusher consisting of TaCOH positioned substantially contiguously about said fuel, said pusher inhibiting energy transport into said fuel and preventing preheat of said fuel, said pusher while containing relatively little mass and because of a small density difference between said fuel and said pusher functioning to decrease fluid instabilities caused by pusher-fuel mixing during final stages of implosion of the fuel; and a tamper surrounding and substantially contiguous about said pusher, said tamper consisting of Pb, said pusher of TaCOH includes about 1 atomic percent of tantalum, said tamper and said tantalum of said pusher having a combined total density times radial thickness (.rho.r) of less than 1 gm/cm.sup.2. 2. The improvement defined in claim 1, wherein said quantity of fuel consists of a shell of frozen DT. 3. The improvement defined in claim 1, wherein said fuel has a density of about 0.21 gm/cm.sup.3, a mas of about 1.00 mg, an inner radius of about 0.19004 cm and an outer radius of about 0.2000 cm; wherein said pusher has a density of about 1.26 gm/cm.sup.3, a mass of about 16.8 mg, an inner radius of about 0.20000 cm, and an outer radius of about 0.22360 cm; and wherein said tamper has a density of about 11.3 gm/cm.sup.3, mass of about 72.1 mg, inner radius of about 0.22360 cm, and an outer radius of 0.23333 cm. |
046844929 | abstract | A repair fixture for water-cooled nuclear reactors including an openable reactor pressure vessel having a wall, and conduits passing through the pressure vessel wall for flooding the pressure vessel, includes a sealing box disposed in the opened, flooded pressure vessel, a device connected to the sealing box for pressing the sealing box liquid-tightly against the pressure vessel wall enclosing at least some of the conduits, and a device connected to the sealing box for evacuating the conduits enclosed by the sealing box. |
041742540 | summary | BACKGROUND OF THE INVENTION This invention relates to compression hubs for fusion reactor systems and in particular to a structure to facilitate cooling of the hub. Superconducting magnets are used to attain intense magnetic fields in magnetic confinement systems for fusion reactors. The magnets are located in a polygonal relationship and intense forces are generated tending to draw these magnets together. Accordingly, a hub must be supplied to buck these horizontal forces. The superconductor of the magnet which is surrounding the hub must be cooled below a critical temperature in order to obtain desired magnetic field. These critical temperatures are very close to absolute zero. For instance, the critical temperature of niobium-titanium is 9.4.degree. kelvin while niobium-tin is 18.0.degree. kelvin. These conductors are normally operated at 4.2.degree. to 4.9.degree. kelvin so as to avoid losing the superconductivity property with slight heating, and to maintain it in intense magnetic fields. In order to obtain this low temperature, the conductors are cooled by liquid helium which boils at 4.2.degree. kelvin at atmospheric pressure. Since the temperature level is not only extremely low, but the transition from superconductivity is also very sharp, it is important that the surrounding structural material also be maintained at the extremely low temperature. This includes the hub since any heat transferred from the hub to the magnet would destroy the effectiveness of the equipment. Prior to starting operation of the reactor, the hub is obviously at room temperature. It must be cooled about 300.degree. kelvin in order to reach the operating temperature. The practice of depending on the cooling of the magnets to remove heat conducted from the hub would require a start-up time of many weeks before operating conditions could be reached. Passing liquid helium through the hub would provide means for cooling the hub independently of the magnet cooling system. Since the coolant itself is only about 4.2.degree. kelvin, and the temperature level is very critical, it is clear that the last portion of the cooling is most critical. Very little temperature gradient exists for the purpose of cooling the hub. It follows that in order to obtain reasonable cooling time, the coolant flow path must be arranged in such a manner that no portion of the hub is a significant distance (say 25 centimeters) away from the coolant itself. The drilling of vertical openings through the hub on such spacings is unacceptable since it weakens the hub to too great an extent. The openings through the hub would increase the structural elasticity of the hub. This in turn permits the superconducting magnets to move or flex during operation. As a result of this movement, the friction will heat the conductor above the critical temperature. Consequently, such loss of stiffness in the hub cannot be tolerated. SUMMARY OF THE INVENTION It is an object of the invention to resist the forces of magnets of a fusion reactor with an apparatus which can be relatively quickly cooled to facilitate start-up time and which is sufficiently rigid to avoid deleterious flexing and heating of the superconducting magnets. The invention permits the support of the magnetic loads and the attainment of a relatively short cool down time for the structure. A plurality of polygonal metallic pancakes or layers are arranged in a stacked relationship. The pancakes are sealed, usually by welding around the perimeter to confide the coolant and are spaced from one another throughout the adjacent surfaces. Flow chambers are thereby formed between the adjacent pancakes through which coolant passes. The pancakes are relatively thin and no portion of the metal is more remote from the coolant than one-half the thickness of the pancakes. A limited number of vertical openings through each of the pancakes connects the flow chambers. The major flow openings are horizontal in a direction parallel to that of the major loads carried by the structure. Accordingly, the required stiffness of the structure under compressive horizontal loads is maintained. Locating openings in adjacent pancakes remote from one another enforces the desired horizontal flow through the flow chambers. Spacing means may be located between adjacent pancakes to ensure a desired opening and to space the pancakes prior to seal welding the perimeter. The spacing means may also be located so as to baffle the flow through the openings. Alternately, grooves may be placed in adjacent pancakes for the purpose of encouraging flow in particular flow paths. |
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041525850 | claims | 1. An assembly for the transport and storage of radioactive nuclear fuel elements comprising: a transport flask having means for disposing the transport flask in a vertical orientation for loading fuel elements into the flask and in a horizontal orientation for transporting the fuel elements; holding means for fuel elements disposed within the flask; a liquid in the flask which submerges any fuel elements in the holding means when the transport container is in the vertical or the horizontal orientation; a plurality of reservoirs for containing liquid and gas and located around the fuel element holding means; inlet means on each of the reservoirs to admit liquid to the interior of the reservoir to compensate for any increase in volume of the liquid in the flask arising from temperature variations with the flask, the admission of liquid causing the gas in the reservoirs to be pressurized; said inlet means comprising an opening in the reservoir providing communication between the interior of the reservoir and the interior of the flask, said opening being located at the end of the reservoir which is lowermost when the flask is in the vertical orientation and being located below the level of liquid in the reservoir when the flask is in the horizontal orientation; trapping means on each reservoir to prevent egress of the pressurized gas from the reservoirs when the flask is in the vertical or the horizontal orientation; said trapping means comprising a tube providing further communication between the interior of the reservoir and the interior of the flask, said tube extending from said lowermost end of the reservoir to a position which is above the level of liquid in the reservoir when the flask is in the vertical orientation but below the level of liquid in the reservoir when the flask is in the horizontal orientation and said tube being shaped to prevent egress of pressurized gas when the flask is in the horizontal orientation; said inlet means and trapping means providing self-regulating ullage means in which liquid is maintained in each of the reservoirs in the vertical and horizontal orientations of the flask. 2. An assembly for the transport and storage of radioactive fuel elements as claimed in claim 1 in which the fuel element holding means comprises a removable basket assembly having compartments in which fuel elements are received, said plurality of reservoirs being located around the basket assembly. |
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048624900 | summary | BACKGROUND OF THE INVENTION This invention relates to x-ray machines, and more particularly, to vacuum windows for x-ray machines. DESCRIPTION OF THE PRIOR ART X-rays can be generated by the bombardment of a metal target by a beam of electrons. By necessity, the target and electron beam are contained within an evacuated chamber for the proper generation and acceleration of the electron beam. X-rays comprise electromagnetic radiation of extremely short wavelength. "Hard" x-rays are generally defined as x-rays with wavelengths shorter than a few Angstroms, while "soft" x-rays have wavelengths of tens of Angstroms or more. For example, carbon K-alpha x-rays have wavelengths of approximately 44 Angstroms, and, thus, are soft x-rays. There is a class of analytical machines which utilize x-rays to determine the composition and structure of substances. These machines direct a beam of x-rays towards a sample of the substance, and then detect the resultant scattering, reflection, and absorption of the beam with a number of x-ray detectors surrounding the sample. Since different samples have different x-ray scattering, reflecting, and absorbing characteristics, the chemical nature and structure of the sample can be determined by an analysis of the data gathered by the x-ray detectors. Hard x-rays can be used to analyze the composition and structure of matter having relatively high atomic mass. The hard x-rays are formed within the evacuated chamber and are then beamed out of the chamber through a "vacuum window" and into the sample to be tested. The vacuum window must, therefore, be capable of withstanding continuous x-ray bombardment and a pressure differential of approximately one atmosphere. These prior art, hard x-ray vacuum windows are typically made from a thin, metal foil approximately 50 micrometers thick and having an atomic number (Z) less than 14. Light elements such as hydrogen or oxygen cannot be detected with hard x-rays because they tend to ionize and otherwise react with the x-rays. Therefore, lower energy, soft x-rays would have to be used to detect light elements. Unfortunately, soft x-rays are not sufficiently energetic to adequately penetrate prior art vacuum windows. For example, a prior art vacuum window which can pass a significant percentage of incident hard x-rays may only pass a fraction of a percent of incident soft x-rays. One theoretical solution to this problem is to place the sample within the evacuated chamber where the soft x-rays are generated. Unfortunately, this immediately eliminates the possibility of analyzing gaseous samples, since the presence of the gas would destroy the vacuum within the chamber. This solution would, therefore, be limited to the analysis of non-volatile, solid samples which could be safely placed within an evacuated chamber. Even so, this arrangement would be expensive and cumbersome, since it would require an enlarged vacuum chamber, special high-vacuum detectors, portholes, larger vacuum systems, etc. As noted above, most prior art hard x-ray windows are made from thin, metal foil. Another type of hard x-ray window is described by Smith, et al. in "Prospects for X-Ray Fabrication of Si IC Devices", Journal of Vacuum Science Technology, Vol. 12, No. 6, November/December, 1975. In their paper, Smith, et al, describe a unitary vacuum window structure made from a silicon wafer which includes an annular perimeter, a number of parallel ribs, and a thin silicon membrane supported by the perimeter and reinforced by the ribs. While the vacuum window of Smith, et al would appear to be satisfactory for use in hard x-ray applications, it would not be possible to make the membrane portion of the window structure thin enough to pass a significant proportion of soft x-rays and still hold one atmosphere of pressure. This is due, in part, to the physical limitations of silicon for this purpose, and is also due to a weakening of the silicon membrane caused by the etching process, which tends to produce pits, grooves, and pinholes. It is also known from the prior art to make electron permeable vacuum windows from thin membranes of SiC, BN, B.sub.4 C, Si.sub.3 N.sub.4 and Al.sub.4 C.sub.3, see U.S. Pat. Nos. 4,468,282 and 4,494,036. SUMMARY OF THE PRESENT INVENTION An object of this invention is to produce a practical x-ray vacuum window which is relatively transparent to soft x-rays. Another object of this invention is to provide a method for producing a soft x-ray vacuum window. Briefly, the invention includes a support substrate provided with an aperture, and a membrane formed over the support substrate. The membrane includes a window portion aligned with the aperture having a number of thin pane sections which are relatively transparent to soft x-rays. The thin pane sections are supported and reinforced by a number of relatively thick rib sections attached to a perimeter portion of the membrane. The substrate should be made from a material having a low atomic number but high tensile strength. Three materials which are suitable for the formation of the membrane of the present invention are boron nitride, boron carbide and silicon carbide. The method in accordance with the present invention for making a soft x-ray vacuum window includes the steps of: growing a thick, boron nitride membrane on both sides of a silicon wafer; patterning the boron nitride on one side of the silicon wafer to form a window aperture pattern; patterning the boron nitride on the other side of the silicon wafer to form a number of pane openings; depositing a thin layer of boron nitride over the pane openings; and etching a window aperture into the back of the silicon wafer through the window aperture pattern. Since the pane sections are formed by deposition rather than by etching, they are virtually defect-free and have great structural integrity. An advantage of the present invention is that vacuum windows for x-ray machines can be produced which permit the transmission of soft x-rays. Another advantage of this invention is that light elements such as hydrogen and oxygen can be detected without placing them inside of a vacuum environment. These and other objects and advantages of the present invention will be apparent to those skilled in the art after reading the following descriptions and studying the various figures of the drawing. |
052727432 | abstract | A key member, a method for insertion and/or removal of the fuel rods in a nuclear fuel assembly using the key member and a method of disassembling the nuclear fuel assembly using the same key member are disclosed. The key member has first projections and second projections formed on the opposite faces of an elongated key body. In the insertion or removal of the fuel rods or in the disassembling the nuclear fuel assembly, the key member is inserted into the grid and rotated to bring the first projections and the second projections into engagement with the straps of the grids and the springs on the straps to thereby deflect the springs in a direction away from the dimples opposing the springs. In this situation, the insertion and removal of the fuel rods can be carried out. Further, in disassembling the nuclear fuel assembly, space required for inserting the key member into the grids may be ensured by subjecting prescribed portions of control rod-guide pipes and instrumentation pipes to cutting work and bulging the cut ends to move the cut end away from that of the opposing cut ends of the cut piece. The space may be formed by removing the control rod-guide pipes and instrumentation pipes after having formed slits in the pipes. |
abstract | A laser crystallization apparatus which capable of correcting both shift in imaging position caused by thermal lens effect of the imaging optical system and shift due to flatness of the substrate comprises an crystallization optical system which irradiates laser light to a thin film disposed on the substrate to melt and crystallize an irradiated region of the thin film, the apparatus includes a measurement light source which is disposed outside a light path of the laser light, and which emits measurement light being illuminated the irradiated region of the thin film, and a substrate height correction system which illuminates the thin film with the measurement light through an imaging optical system in the crystallization optical system, and which detects the reflected measurement light from the thin film. |
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abstract | A system for non-uniformity pattern identification. A storage device stores multiple theoretical patterns and measurements. Each measurement corresponds to a region on a wafer. The processing unit acquires the theoretical patterns and the measurements on at least two wafers, calculates pattern scores for the respective theoretical patterns of each wafer according to the measurements, and groups at least two of the theoretical patterns into at least one factor according to the pattern scores to identify one or more non-uniformity patterns for the wafers. Each pattern score represents the extent of similarity between one of the theoretical patterns and the measurements in one of the wafers. |
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claims | 1. An apparatus comprising:a plurality of control rod drive mechanisms (CRDMs) each configured to raise or lower a control rod assembly; anda distribution plate configured to be mounted in a nuclear reactor pressure vessel including a reactor core submerged in primary coolant, the distribution plate including a plurality of connection sites at which the CRDMS are mounted, the distribution plate being submerged in the primary coolant and including electrical power distribution lines comprising mineral insulated cables (Ml cables) disposed on or in the distribution plate for distributing electrical power to the CRDMs mounted on the distribution plate,wherein the nuclear reactor pressure vessel includes an upper portion and a lower portion;a mid-flange is disposed between the upper portion and the lower portion of the nuclear reactor pressure vessel; andthe distribution plate is disposed in the lower portion of the pressure vessel above the reactor core and the CRDMs are disposed in the lower portion of the pressure vessel. 2. The apparatus of claim 1, wherein each CRDM includes a plurality of electrical power connectors mating with corresponding electrical power connectors of the connection sites of the distribution plate. 3. The apparatus of claim 2 wherein:the distribution plate further includes hydraulic power distribution lines disposed on or in the distribution plate for distributing hydraulic power to the CRDMs mounted on the distribution plate; andeach CRDM further includes a hydraulic power connector mating with a corresponding hydraulic power connector of the connection site of the distribution plate. 4. The mounting system apparatus of claim 2 wherein the distribution plate also has hydraulic lines embedded in or attached to the distribution plate. 5. The apparatus of claim 1 wherein each connection site of the distribution plate has an opening sized to accommodate a lead screw operated by the CRDM, wherein the opening is keyed to limit installation of the CRDM to a correct orientation. 6. The apparatus of claim 1, wherein the electrical power distribution lines comprise mineral insulated cables (MI cables) disposed inside the distribution plate. 7. The apparatus of claim 1, wherein:the plurality of connection sites of the distribution plate are arranged in rows; andthe MI cables disposed on or in the distribution plate include an MI cable disposed around the outside perimeter of the plurality of connection sites and a plurality of MI cables running straight between rows of connection sites of the plurality of connection sites. 8. The apparatus of claim 1, wherein the distribution plate supports the plurality of CRDMs. 9. An apparatus comprising:a plurality of control rod drive mechanisms (CRDMs) each configured to raise or lower a control rod assembly; anda distribution plate configured to be mounted in a nuclear reactor pressure vessel including a reactor core submerged in primary coolant, the distribution plate including a plurality of connection sites at which the CRDMS are mounted, the distribution plate being submerged in the primary coolant and including electrical power distribution lines disposed on or in the distribution plate for distributing electrical power to the CRDMs mounted on the distribution plate and hydraulic power distribution lines disposed on or in the distribution plate for distributing hydraulic power to the CRDMs mounted on the distribution plate;wherein each CRDM includes a plurality of electrical power connectors mating with corresponding electrical power connectors of the connection sites of the distribution plate and a hydraulic power connector mating with a corresponding hydraulic power connector of the connection site of the distribution plate;wherein the hydraulic power lines convey primary coolant water and the mating of the hydraulic power connector of the CRDM with the corresponding hydraulic power connector of the connection site of the distribution plate forms a leaky hydraulic connection; andwherein the nuclear reactor pressure vessel includes an upper portion and a lower portion;a mid-flange is disposed between the upper portion and the lower portion of the nuclear reactor pressure vessel; andthe distribution plate is disposed in the lower portion of the pressure vessel above the reactor core and the CRDMs are disposed in the lower portion of the pressure vessel. 10. The apparatus of claim 9, further comprising:a nuclear reactor core; anda nuclear reactor pressure vessel containing the nuclear reactor core;the distribution plate being mounted above the nuclear reactor core inside the nuclear reactor pressure vessel, the CRDMs being internal CRDMs disposed inside the nuclear reactor pressure vessel. 11. An apparatus comprising:a nuclear reactor core;a nuclear reactor pressure vessel containing the nuclear reactor core, the nuclear reactor core being submerged in primary coolant;a plurality of internal control rod drive mechanisms (internal CRDMs) disposed inside the nuclear reactor pressure vessel, each CRDM configured to raise or lower a control rod assembly; anda distribution plate mounted within the primary coolant above the nuclear reactor core inside the nuclear reactor pressure vessel and including a plurality of connection sites at which the internal CRDMS are mounted, the distribution plate including electrical power distribution lines disposed on or in the distribution plate and connected to distribute electrical power to the internal CRDMs disposed inside the nuclear reactor pressure vessel,wherein the nuclear reactor pressure vessel includes an upper portion and a lower portion;a mid-flange is disposed between the upper portion and the lower portion of the nuclear reactor pressure vessel; andthe distribution plate is disposed in the lower portion of the pressure vessel above the reactor core and the CRDMs are disposed in the lower portion of the pressure vessel. 12. The apparatus of claim 11, wherein the electrical power distribution lines comprise mineral insulated cables (MI cables) disposed on or in the distribution plate. 13. The apparatus of claim 12, wherein:the plurality of connection sites of the distribution plate are arranged in rows; andthe MI cables disposed on or in the distribution plate include:an outer MI cable arranged outside of the plurality of connection sites and;a plurality of straight MI cables having ends connected with the outer MI cable and running straight between rows of connection sites of the plurality of connection sites. 14. The apparatus of claim 11, wherein the distribution plate is positioned below the plurality of CRDMs and supports the plurality of CRDMs. |
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047028807 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for improving resistance of control rod guide tube split pins in nuclear reactors to stress corrosion cracking which comprises heating said split pin to a critical elevated temperature level, cooling at least the surface portions of the said split pin subject to stress corrosion cracking and then permitting said split pin to come to ambient temperature. 2. Description of the Prior Art Split pins made of iron or alloys thereof are used in nuclear reactors to help position the control rod guide tube bottom flange in relation to the upper core plate and to provide lateral support and to maintain alignment of the guide tube with respect to the fuel assembly guide tube thimbles therein. Machining of these split pins during the manufacturing process results in split pins having high tensile residual stresses on the machined surfaces. When the split pins are assembled on the control rod guide tube bottom flange, and during the operation of the reactor, portions of the split pin develop further tensile stresses at various locations on said split pins. In a nuclear reactor these split pins are generally in a hostile environment, for example, in a pressurized water reactor wherein the water contains dissolved oxygen and chemicals that often remain even after the water has been demineralized. Under these circumstances those portions of the split pin that are under high tensile stresses are subject to stress corrosion cracking, particularly when such split pins are made of stainless steel or high nickel alloys. When this happens, the split pins so affected have to be removed and replaced with new split pins at great cost in time and money. SUMMARY OF THE INVENTION We have found that we can greatly improve resistance of control rod guide tube split pins used in nuclear reactors to stress corrosion cracking using a process which comprises heating said split pin to an elevated temperature level, cooling at least the surfaces of said split pin subject to stress corrosion cracking to a temperature below said elevated temperature level and then permitting said split pin to come to ambient temperature, said elevated temperature level being below the characteristic temperature resulting in metallurgical change in the material of said split pin but at least an elevated temperature level such that the difference between said elevated temperature level and the temperature to which said surface is initially cooled is sufficient to result in plastic flow of said initially cooled surface to a depth equivalent to at least one grain size. |
059862769 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT X-rays represent the energy produced by the rapid deceleration of high speed electrons. Electron streams which have been accelerated by strong electric fields surrounding wires and hardware are intensified by sharp points. Sufficiently high fields cause air to break down or ionize, thus causing coronas. High speed electrons, when slowed by collision with the nuclei of some materials, produce X-rays. High atomic weight nuclei more effectively slow the high speed electrons, and thus produce both more X-rays and higher energy X-rays. Light atomic weight nuclei are less effective in slowing the high speed electrons, requiring multiple collisions, each of which collisions only releases a portion of the total kinetic energy, resulting in lower energy photons, such as light. The percentage of electrons which are able to so interact so as to produce photons is dependent upon the target material. The energy spectrum (if visible light, this would correspond to its color) of the resulting photons is also dependent upon the target material. Both the quantity of high energy photons and their energy (destructive power) are related to the square of the atomic number of the atoms in the target material into which the electrons are impacting. When the target material is composed of more than one element, the effective atomic number (Z) of the composite is determined by summing up the molar percentage of each element present, multiplied by the atomic number of that element: ##EQU1## The target does not have to contain metals; it is preferable that it contain only the lighter elements such as hydrogen, carbon, nitrogen, and oxygen. Substituting carbon (Z=6) for steel (Z=26) as the impact target would reduce the X-rays generated by almost a factor of 19. Replacing it by polyisobutylene (Z.sub.effective =2.67) would reduce the generation by a factor of approximately 95 to 1. The effects would be even greater if the original target were copper (Z=29) or Zinc (Z=30). X-ray "shielding", however, depends roughly on the mass of the shield encountered. Thus lead, being quite dense, requires only a thin layer to effectively shield an X-ray source, as compared with a lower density material such as iron. Thus, the "safe" target sheathing material must be low-Z, while any shielding material must be high-Z. Care must be taken that the shielding material does not accidentally become a target, lest it become a producer of X-rays stronger than would exist if no changes had been implemented. The hydrocarbon target material intercepts the majority of the energetic electrons because of the very short mean path length of an electron in a solid. Referring to FIG. 1, a block diagram showing the flow of monitoring information in a power station, to assure that ionizing radiation does not become hazardous, the sensing instrumentation preferably includes an energy field detector wide band receiver 11, spectrum analyzer 11A and an audiometer 12 for detecting arcing sounds using directed microphones aimed at critical points on a tower. These instruments are continuously monitored by a transponder 14, which stores the data in memory for recall when interrogated by a transceiver 15; the data is transmitted to, and accumulated and displayed at, a distribution substation 16. The communications link between the tower monitors and the substation may be RF or fiber optic. Ideally, the monitoring instrumentation would be installed in every distribution tower in an area where there is human or animal life within 100 feet of the distribution lines. The preferred mounting position of monitor-transponder 10 relative to a distribution lines tower is shown in FIG. 1A and FIG. 1B. Monitor transponder 10 at the tower (FIG. 1B) detects time/amplitude noise spectra and/or discharges due to ionization in the vicinity of the tower, these resulting in electrical arcing when the electrical tension between ions of different charge potential becomes sufficiently high to cause corona in a humid atmosphere. Corona discharges which precede and indicate potential X-rays, are detectable by this method and apparatus. The direction and origin of corona in the area of the tower is detectable by aiming a corona detector (an optical instrument) at the source of the corona. Monitor-transponder 10 is positioned at the center of the tower, between the high voltage conductors and ground, and at the center of any potential X-ray fields which may develop between the high voltage lines and ground, which fields are harmful to biological life. The hazards to biologic life associated with the X-rays produced due to tower electrical equipment faults, such as arcing or dirty insulators, are reduced by shortening the exposure time, as by prompt notification of the problem to repair personnel. Generally downward directed radiation patterns are of most interest. Corona is the phenomenon of air breaking down when the electric stress at the surface of a conductor exceeds a certain elevated potential value. At higher values, the stress results in a luminous discharge with an arcing sound detectable by a directional microphone and amplifier. Common corona sources are the wires themselves, faulty insulators, and mounting hardware with sharp points. As is known in the art, strong electric fields may develop between electrically conducting metal elements, such as between a switch or terminal board and any met al at or near ground potential, such as an electrical tower. The potential difference directs the field between the two closest exposed metal elements, so that high tension electrostatic flux fields develop between the two elements, so that high tension electrostatic flux fields develop between the two elements. The direction of such field is between the two exposed elements or points. The electric field charged particles cause X-ray photons to be created when the particles are accelerated between two high and two low potential metallic elements when the field becomes sufficiently strong. The towers are therefore appropriate places to locate the detectors. The EMI detectors take advantage of the generally isotropic radiation patterns from very small antennae, the individual ionization points. Corona will produce a detectable signal anywhere nearby, as demonstrated by automobile radios near arcing towers. The corona detection capability of the observation instrument 10 warns of an electrical stress build-up at some component at the tower that could produce X-rays if allowed to become too intense. Notification is thus given as an early warning to the substation to send a crew to correct the problem by the conventional methods of cleaning and/or replacing dirty or defective components. The X-rays are not in the form of a single beam, but arise from many corona points either at sharp discontinuities, such as wire ends and point-shaped hardware, or along the body of the conductor when the dielectric strength of the air drops below the field strength. A typical design rule is to pick the conductor diameter, or effective diameter when multiple conductors are used, to produce 15 kV/inch. Dry air has a break down voltage of 20 KV/inch, and very damp air has significantly less. High tension power lines may produce coronas in foggy weather as may be viewed on a dark night. Referring to FIG. 1, the tower-mounted sensing and observation instruments 10 are typically mounted on a platform, which is preferably rotatable for manipulation and aiming of the corona detector for optical observation of the area between the high voltage conductors and the ground about the tower. The directional microphone may also be aimed, in a manner similar to the use of the corona-detector, to detect pre-corona conditions identified by arcing sounds in the audio range. A radio frequency receiver and a spectrum analyzer, locates a source of pre-corona electrical field disturbance and identifies, by the nature of amplitude and noise burst spectra, whether a potential disturbance field is developing. Automatic means may be utilized for spraying low Z material on electrical distribution components where a disturbance field is developing, and operation thereof may be initiated by command via a communications link with a substation. Repair personnel may be required in some instances to analyze and solve the problem. In either case, the possibility of development of a dangerous X-ray field is being prevented. Audio, visual and radio frequency, as well as remote digital instrument control of observation instruments in the tower, and low Z material spray nozzles, can be controlled from a substation via a communications link to prevent formation of X-ray fields. FIGS. 2 and 2A illustrate the use of low atomic number (Z) coating 20 on an electrical conductor 22 to prevent the generation of high energy photons by the impact of highly accelerated electrons 21 into the conductor. The low Z material 20 produces fewer and lower energy electrons when inserted. The formulation of a polymer or combination of several isomer molecules, comprising low atomic number (Z) atoms in a plastic product to form a sheath or outer covering on a conductor or cable, substantially eliminates the generation of X-rays in the area about the conductor. A polymer having an amorphous putty-like consistency is another material to be applied, according to the invention, to points where arcing might occur, thus to reduce corona generation about an electrical conductor and provide a soft target for any X-Radiation that might develop from the remaining corona. Application may be by any appropriate means or method such as spraying, dipping, extruding, chemical grafting and wrapping, as examples. The low Z material application in accordance with the invention is typically of significantly less thickness, weight, thermal resistance, and windage factors than would be needed to provide a full wire-insulator for high tension wires. The low Z target materials are applied about the outside of any of the elevated potential members, including the wires and connector hardware. The electrons accelerated by the high voltage potentials have a high probability of interacting with the low Z material, rather than penetrating to the contained high Z material. The process of the high speed electron being slowed by interaction with the low Z material produces much less X-ray energy and lower energy X-rays than would be produced by the interaction of the same electrons with high Z material. More rigid molded elastomeric forms for other applications are shown in FIGS. 3, 3A and 4. The presence of the low Z discharge target provides an inefficient X-ray target rendering the high speed electrons harmless. FIG. 3 shows the use of a low Z shield on an insulator 31 such as is used in power stations. The supporting insulator device 32, through which the high voltage conductor 33 passes, has low Z shield disks 30, 30A on either side of the conductor to provide a safe target for high speed electrons generated by corona. The insulator device 32 is mounted on the distribution tower structure by means well known in the art. FIG. 3A shows the conductor 33 retained in the insulator by well known means, and the low Z shield disks 30, 30A placed on either side of the conductor to dissipate high velocity electrons that could produce X-rays. The disks also reduce the electric field strength to reduce corona generation. FIG. 4 illustrates the use of low atomic number (Z) polymer putty to reduce corona at points in high tension transmission system wiring, where residual corona and arcing has occurred, to provide an X-ray inhibitor for the residual problem. A conductor 41 for high voltage power, coupled by means of a crimp connector 42 having a tendency to develop an ionizing field at point A, can be electrostatically shielded when the connector 42 is covered with low Z putty coating or low-Z snap covers 43 to reduce the acceleration of electrons necessary to produce X-rays, while also acting as a soft target to further prevent X-ray generation. The electrostatic field shaping means in accordance with the invention, is the surrounding of sharp points of higher Z material with low Z conductive material. Examples are the wire end A in FIG. 4 surrounded with the conductive putty 43, and the conductive low Z disks 30 and 30A surrounding the mounting hardware 32 in FIGS. 3 and 3A. In both cases, the use of large smooth conductive surfaces reduces the electric field that would otherwise arise proximate to a charged pointed object. This is opposite to the effect of using a sharpened pointed conductor to "draw lightning" by maximizing the field strength at the end of a lightning rod. The source of free electrons is the discharge plasma from the ionization of air molecules placed in sufficiently strong electrostatic fields. These electrons gain speed as they accelerate through the same electrostatic fields. Sufficiently strong fields allow a percentage of these electrons to reach the required velocities, finally impinging on the conductor. This percentage is a function of the electric field strength and configuration, the dielectric breakdown strength of the surrounding gas which is a function of humidity and pressure, and the gas pressure. All of these factors affect the mean-free-path length before the average electron of the electron field loses much of its energy by impinging on a gas molecule, losing heat and producing low energy photons. Ionizing energy levels are considered by various sources as between 5-10 eV to 100 eV. FIG. 5 shows a high voltage switch protected by high Z sheet or cast material to absorb ionizing radiation in specific directions, such as toward the ground, for the protection of persons on the ground in a power plant environment. For example, the contact bar 51 on a high power switch 50 in a power station environment can be fitted with a high Z shield 52, which may be a solid high Z material or powered high Z material in a polymeric base, and the fixed contact 53 surrounded by a high Z ring 54, such that any X-rays formed as the switch opens or closes will not reach personnel. The source of the X-rays at the switch is this same accelerated electron from the ionization of air by a sufficiently strong electrostatic field. The highly energetic electrons ionizing the air (blue spark) may also generate soft X-rays if they gain enough energy and impinge on a high Z target, such as switch contacts. These arcs are commonly generated, with technicians in close proximity, when the switches are manually operated. The high Z material forms a "shield" that attenuates/absorbs a significant portion of the X-rays generated in the directions that the personnel are located. The low Z material is used for targets that the high speed electrons are expected to impinge upon, namely the high voltage conductors and attached conductive hardware. As stated earlier high Z material is used as a "shield", such as a lead apron used to protect human body parts not being X-rayed, between the X-ray producing arc at the high Z switch contacts, and the technician operating the switch from below. As indicated in FIG. 5, high Z shielding is provided at locations of high-power switch contacts for switching inductive loads into and out of high current lines. X-rays are developed when the inductive load is interrupted--i.e., when switched out by opening of a switch, a very high voltage arc can automatically produce X-rays. As a further safety measure, a set of low-Z contacts in parallel with the high-power switch contacts, are utilized to short out the inductive voltage rise upon opening of the switch. Some benefit is derived by the low Z contacts connecting before the switch contacts, and "breaking" after the switch contacts, thus to eliminate formation of X-rays. Low Z material is applied where high speed electron generation is expected--i.e., on the arcing points of the switch. The low Z material serves as an impact target for high speed electrons to reduce conversion efficiency between kinetic energy and X-rays. Low Z coatings can be sprayed on existing high Z shields to reduce the initial formation of X-rays on existing power switches in a power distribution system. FIG. 6 illustrates an electrical switch 60 having low Z contacts pair 61, 61A for providing the initial contacting and final breaking points for the circuit. Such contacts prevent arcing at the normal electrical contacts 62, 62A, which would be more prone to X-ray generation, particularly when inductive loads are switched out, with their inductive voltage rise and corona at the switch gap. The second set of contacts, 61, 61A is to provide an initial striking contact and a final breaking contact with a material that generates less X-rays when arcing than does the conventional contact. The shaping of the field is done by elements 52 and 54 (FIG. 5). Similar techniques are the use of spheres in switching stations and Van de Graf generators to minimize ionization; the same effect is used for the opposite purpose in lightning rods and etched microwire cold emitters for solid state tubes. The composition of materials depends on specific applications, and includes the amorphous putty-like polymer material composed of low Z material, possibly filled with carbon or other low Z materials. Other forms, such as plate or cast forms having low Z X-ray inhibitor therein, are useful for electrical componets. An advantageous low Z polymer material is polyarylene ether benzimidazole, known as PAEBI, which is quite erosion resistant and resistant to atomic oxygen. It can be extruded into fibers or threads, and woven for certain applications. A list of such polymers is set forth hereinafter in Table I, and a listing of the Periodic System, Group III or IV atoms possible for use with these polymers, is set forth in Table II. TABLE I __________________________________________________________________________ EXAMPLE OF POLYMERS USABLE AS SAFE TARGET MATERIALS __________________________________________________________________________ Vinyl Acetate Polyvinyl acetate 1 #STR1## 4 #STR2## Isobutylene Polyisobutylene 2 #STR3## 5 #STR4## Methyl methacrylate Polymethyl methacrylate 3 #STR5## 6 #STR6## __________________________________________________________________________ TABLE II __________________________________________________________________________ LOW ATOMIC NUMBER ELEMENTS OF THE PERIODIC SYSTEM n Atomic Shells 1 2 3 4 5 6 7 Number Subshells K L M N O P Q Period Z Elements s s p s p d s p d f s p d f p d f s f s __________________________________________________________________________ I 1 H 1 2 He 2 II 3 Li 2 1 4 Be 2 2 5 B 2 2 1 8 C 2 2 2 7 N 2 2 3 8 O 2 2 4 9 F 2 2 5 10 Ne 2 2 6 III 11 Na 2 2 6 1 12 Mg 2 2 8 2 13 Al 2 2 8 2 1 14 Si 2 2 6 2 2 15 P 2 2 6 2 3 16 S 2 2 8 2 4 17 Cl 2 2 6 2 5 18 Ar 2 2 6 2 8 IV 19 K 2 2 6 2 6 1 20 Ca 2 2 6 2 6 2 21 Sc 2 2 6 2 6 1 2 22 Ti 2 2 6 2 8 2 2 23 V 2 2 6 2 6 3 2 24 Cr 2 2 8 2 8 5 1 25 Mn 2 2 6 2 8 5 2 26 Fe 2 2 8 2 8 8 2 27 Co 2 2 8 2 8 7 2 28 Ni 2 2 8 2 8 8 2 29 Cu 2 2 6 2 6 10 1 30 Zn 2 2 6 2 6 10 2 31 Ga 2 2 8 2 8 10 2 1 32 Ge 2 2 6 2 8 10 2 2 33 As 2 2 6 2 6 10 2 3 34 Se 2 2 6 2 6 10 2 4 35 Br 2 2 8 2 8 10 2 5 36 Kr 2 2 6 2 8 10 2 6 __________________________________________________________________________ Thus there has been shown and described a novel apparatus and method for eliminating X-ray hazards from electrical power distribution fields which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification together with the accompanying drawings and claims. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow. |
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044951396 | abstract | A container has a massive metallic vessel whose interior is adapted to receive radioactive waste and whose mouth is formed with inner and outer spaced generally planar and annular vessel shoulders and formed therebetween with a nonplanar intermediate annular vessel surface. A massive metallic cover formed with a plug fits in the mouth and has respective inner and outer plug shoulders closely juxtaposed with the vessel shoulders and a nonplanar intermediate annular plug surface complementary to the intermediate vessel surface. An inner ring seal engages snugly between the inner shoulders. A pair of generally concentric and spaced outer ring seals engage snugly between the outer shoulders and forming an annular outer chamber therebetween. An intermediate ring seal engages snugly between the intermediate surfaces and forms therebetween and with the inner ring seal an annular inner chamber and therebetween and with the outer ring seals an intermediate chamber. The cover is formed with respective inner, intermediate, and outer passages each having one end opening into the respective chamber and another end. Valves are provided on the cover at the other ends of the passages for sampling gases therein and in the respective chambers. |
abstract | A method and medium are provided for enabling reliable indication of the amount of time a battery will provide sufficient charge to power a computing device. In one embodiment, the time interval that lapses from the charge draining from the battery between two thresholds is determined, and the thresholds are adjusted based on the time interval. Other embodiments provide for classifying a battery as no longer capable of maintaining sufficient charge by comparing the maximum amount of charge the battery could store to the current maximum amount of charge the battery can currently store. Another embodiment determines how long a battery will provide sufficient charge to power a computing device based on profiles of user activity and associated battery drain rates. The current amount of charge stored in the battery is divided by the profile drain rate to determine how long the battery will provide sufficient charge to power the computing device. |
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abstract | A tritium production element for use in a conventional power reactor, and methods of use and making, are provided, wherein the element experiences reduced tritium permeation during irradiation by incorporating a silicon carbide barrier that encapsulates one or more burnable absorber pellets. The tritium production element includes a tubular cladding that encloses a plurality of burnable absorber pellets, such that individual pellets or groups of pellets are disposed within a silicon carbide barrier layer. |
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description | The invention relates to a beam filter for insertion between a radiation source and a detection area. Moreover, it relates to an X-ray device comprising such a beam filter. The U.S. Pat. No. 6,157,703 describes an X-ray filter realized as a copper or beryllium plate with a matrix of apertures. The apertures can selectively be shifted between positions of alignment or misalignment with respect to the holes of a collimator. In the case of a misalignment, the metal of the plate in front of the collimator holes attenuates an X-ray beam and removes particularly low-energy photons, thus “hardening” the spectrum of the beam. Based on this situation it was an object of the present invention to provide filtering means that can particularly be used in devices with spectrally resolved detection. This objective is achieved by a beam filter according to claim 1 and an X-ray device according to claim 10. Preferred embodiments are disclosed in the dependent claims. The beam filter according to the present invention is designed for insertion between a radiation source and a detection area, wherein the radiation source may particularly be an X-ray source. Moreover, the radiation source shall have some spatial extension such that it cannot be approximated by a point source. It typically comprises a comparatively small radiation emitting area, for example the anode surface of an X-ray tube. The “detection area” may just be a virtual geometrical object, though it will typically correspond to the sensitive area of some detector device. The beam filter comprises at least one (first) absorbing body that masks in its working position (i.e. when being disposed between the radiation source and the detection area) different fractions of the radiation emitting area of the radiation source at different points on the detection area. This means that there are at least two points on the detection area from which the (spatially extended!) radiation source is seen partially masked by the absorbing body and for which the fraction of the masked source area is different. The described beam filter has the advantage that different points on the detection area will be reached by different intensities of the radiation that is emitted by the radiation source because these points lie in half-shades of different degrees. The intensity distribution in the detection area can therefore precisely be adapted to the requirements of a particular application. If a patient shall for example be X-rayed, more intensity can be supplied to central regions of the patient's body than to peripheral regions. In general, the absorbing body of the beam filter may have some transmittance for the radiation emitted by the radiation source such that its masking is not total. In a preferred embodiment of the invention, the absorbing body comprises however a material that is highly absorbing over the whole spectrum of the radiation emitted by the radiation source. Said material may particularly comprise materials with a high (mean) atomic number Z like molybdenum (Mo) or tungsten (W), which have a high absorption coefficient for X-rays. Other suited materials are gold (Au), lead (Pb), platinum (Pt), tantalum (Ta) and rhenium (Re). The absorbing body may consist completely or only partially of one of the mentioned materials, and it may of course also comprise a mixture (alloy) of several or all of these materials. The use of highly absorbing materials implies that masked points of the radiation source will not shine through but actually remain dark. The intensity of radiation reaching a point on the detection area will then (approximately) only be determined by the geometry of the absorbing body, which can very precisely be adjusted. A further advantage is that the intensity reduction at some point of the detector area will not imply a modification of the spectrum of the radiation, because the complete spectrum is blended out for the masked zones of the radiation source while the complete spectrum passes unaffectedly for the unmasked zones. This intensity adjustment without spectral modification is particularly useful in spectral CT applications that require a known, definite spectrum of the source radiation for a unique interpretation of the measurements. In a preferred embodiment of the invention, the beam filter comprises a plurality of absorbing bodies that mask in their working position different fractions of the radiation source area at different points of the detection area. Moreover, these absorbing bodies are preferably shaped as absorbing sheets and arranged in a stack, wherein intermediate spaces separate neighboring sheets. Such a stack of absorbing sheets behaves similar to a jalousie with a plurality of lamellae that mask or conceal a light source. The absorbing sheets are preferably flat, though they may in general also assume other three-dimensional shapes. The aforementioned intermediate spaces between neighboring absorbing sheets of the stack are preferably filled with a spacer material like a polymer, particularly a solid polymer, a foamed polymer, or a polymer glue. The spacer material provides stability and definite dimensions for the whole stack and allows to handle it as a compact block. The spacer material should have an attenuation coefficient for the radiation of the radiation source that is significantly lower than the attenuation coefficient of the material of the absorbing sheets. The attenuation coefficient of the spacer may for example be smaller than about 5%, preferably smaller than about 1% of the attenuation coefficient of the absorbing sheets for (the whole spectrum of) the radiation emitted by the radiation source. In another preferred embodiment of the beam filter with absorbing sheets, the sheets lie in planes that intersect in at least one common point. If the radiation source is arranged such that it comprises said intersection point, the emitted radiation will propagate substantially in the direction of the planes. The radiation will therefore impinge onto the absorbing sheets parallel to the sheet plane, which guarantees a high absorption efficiency. It should be noted that if the planes are exactly planar and intersect in two common points, they will inevitably intersect in a complete line. In a further development of the aforementioned embodiment, at least one absorbing sheet has a varying width, wherein said width is measured in radial direction with respect to a given point. Said point is preferably a common intersection point of the planes in which the absorbing sheets lie, because this guarantees that a ray starting at the point will impinge onto the complete width of the corresponding absorbing sheet in its plane. In the aforementioned case, the varying width of the absorbing sheet preferably assumes a minimal value in a central region of the absorbing sheet. As will be explained with reference to the Figures, this will result in an intensity peak in a central region of the radiation passing through the beam filter, which is favorable for example in CT applications. The absorbing sheets optionally have a varying thickness, wherein the thickness may vary between different points on the same absorbing sheet as well as between points on different absorbing sheets. The thickness of the absorbing sheets is a further parameter that can be tuned to establish a desired intensity profile across the detection area. In a further development of the invention, the beam filter comprises a second absorbing body that is movable relative to the first mentioned absorbing body and that is arranged in line with the latter as seen in a direction from the radiation source to the detection area. The first and second absorbing bodies therefore have to be passed consecutively by light rays emitted by the radiation source. As the absorbing bodies can be moved with respect to each other, it is possible to selectively change the overlap between zones of the radiation source that are masked by the first and the second absorbing body, respectively, which in turn changes the overall masking degree. Thus the intensity distribution across the detection area can be changed comparatively simple by moving the second absorbing body with respect to the first absorbing body. The invention further relates to an X-ray device, particularly in the form of a Computed Tomography (CT) scanner, that comprises a radiation source and a beam filter of the kind described above. As was already explained, the beam filter can establish practically any desired intensity profile in an associated detection area with minimal or even no changes to the spectrum of the radiation source. This is especially useful for spectral CT scanners as they require that the radiation passing through an X-rayed object has a known, definite spectrum. Like reference numbers or numbers differing by integer multiples of 100 refer in the Figures to identical or similar components. Beam filters according to the present invention will in the following be described with respect to an application in X-ray devices, particularly in spectral CT scanners, though the invention is not restricted thereto and can favorably be applied in connection with other kinds of electromagnetic radiation, too. Spectral CT is a very promising technology which allows the discrimination of different elements in the body. In general, spectral CT is based on the fact that chemical elements show a distinct difference in the energy-dependence of the attenuation coefficient. In order to measure this energy dependence, some sort of energy discrimination is required on the detector side. Furthermore, the primary spectrum of radiation entering an object to be imaged has to cover a broad range of energies. One important part of spectral CT is the measurement of the photo-absorption contribution to the attenuation coefficient, which relies on the detection of rather low-energy photons. For dose reduction purposes in contemporary CT scanners, so-called “bow-tie” filters can be used to adjust the photon flux along the fan direction to the shape of a patient, i.e. the larger thickness of the patient in the center requires a higher intensity there, while less intensity suffices for the decreasing thickness at the periphery of the body. Such a filter may be realized by a varying thickness of a light metal like Aluminum. The disadvantage of this approach for spectral CT is however that the filter will change the spectral shape of the primary radiation along the fan direction. Particularly the low-energy photons, which are of high importance for the measurement of the photo-absorption, are attenuated. As a consequence, this will reduce the possibility of spectral deconvolution in the edge regime of the fan, where the bow-tie filter exhibits its maximum thickness. Due to these reasons there is a need for an alternative beam filter that allows to control the intensity profile of an X-ray beam, particularly a fan shaped beam, with minimal or ideally no modification of the radiation spectrum. To achieve the aforementioned objective, it is proposed here to use one or more absorbing bodies that mask or conceal the radiation source to different degrees as seen from different points of the detection area. FIG. 1 illustrates the principal setup, which comprises a beam filter 10 located between a spatially extended X-ray source 1 (e.g. the anode area of an X-ray tube) and a detector area 2 (e.g. the scintillator material or direct conversion material of a digital X-ray detector). The beam filter 10 comprises a stack 100 of absorbing sheets 111 that are separated by intermediate spaces 112. X-rays X emitted by the radiation source 1 will have to pass through the beam filter 10 before they can reach the detector area 2. Some of these rays will pass freely through the intermediate spaces 112 while others impinge on the absorbing sheets 111, where they are substantially completely absorbed. The attenuation of the X-ray beam is therefore realized by a “partial total absorption” of the radiation (“partial” with respect to the whole set of rays of the beam, “total” with respect to single absorbed rays), wherein the attenuated radiation basically preserves its initial spectral configuration. FIG. 1 illustrates this filtering principle by showing enlarged sketches of the images IA and IB with which the area of the radiation source 1 is seen from a central point A and a peripheral point B on the detection area 2, respectively. Due to the particular shape of the absorbing sheets 111, the zones MA in which the radiation source 1 is masked in the central image IA have a smaller total area than the zones MB in which the radiation source 1 is masked in the peripheral image IB. Consequently, the central point A will be illuminated with a higher beam intensity than the peripheral point B, as illustrated above the detection area in the profile of the intensity Φ along a line x through points A and B (it should be noted that the intensity profile will be balanced again if an object with a central thickness maximum, e.g. a patient, is placed between the beam filter 10 and the detection area 2). As the total radiation at the points A and B is composed in an all-or-nothing manner only of radiation that freely passed the beam filter 10 (and not or at least to only a minimal degree of radiation that passed an absorbing sheet), the spectral composition of the total radiation arriving at points A and B remains approximately the same. FIG. 2 illustrates the principal geometry of a first embodiment of a beam filter 10 according to the present invention. This beam filter 10 consists of a stack 100 of absorbing sheets 111 of substantially the same shape, wherein said shape corresponds to a quadrilateral in which two opposite sides are bent with different bending radius (wherein the bending radius of the convex side is larger than that of the concave side). Each of the flat absorbing sheets 111 lies in a plain P, wherein all these planes P intersect in a common line L and therefore also in a common “focal point” F (lying also on the symmetry line of the absorbing sheets 111). When the beam filter 10 is applied for example in an X-ray device like that of FIG. 1, the radiation source 1 is located such that it comprises the aforementioned focal point F. Radiation emitted by the source 1 will then propagate approximately radially from the focal point F (not exactly for all rays, as the radiation source 1 is not a mathematical point but has some finite extension). An important aspect of the beam filter 10 is that the width of its absorbing sheets 111 as measures along radii r originating at the focal spot F is variable. As can best be seen in the top view of the stack 100 of absorbing sheets 111 shown in FIG. 3, this width assumes a maximal value dB at the periphery of the absorbing sheets 111 and declines continuously towards the centre of the absorbing sheets 111, where it assumes its minimal value dA. FIGS. 4 and 5 show sections along the lines IV-IV and V-V, respectively, of FIG. 3. It can be seen that the beam filter 10 comprises a stack 100 of (in the example five) absorbing sheets 111 separated by (four) intermediate spacers 112 that are transparent for X-radiation and that may consist for example of a polymethacrylimide hard foam material (commercially available under the name Rohacell® from Degussa, Germany). The absorbing sheets 111 typically consist of a highly absorbing material, for example molybdenum or tungsten. Moreover, the absorbing sheets are focused towards the X-radiation source 1 due to their arrangement in planes P (FIG. 2). As the Figures illustrate particularly for X-rays that propagate parallel to the central symmetry axis of the setup, a larger fraction of the radiation emitted by the radiation source 1 is absorbed in the peripheral part of the beam filter 10 where the absorbing sheets 111 have a high width dB than in the central part where the absorbing sheets 111 have a short width dA. The described design of the beam filter 10 can be modified in various ways, for example by: changing the thickness (measured perpendicular to the sheet plane) of the highly absorbing sheets 111 relative to the thickness of the spacer sheets 112, tilting the whole stack 100, a suitable deformation of the absorbing sheets 111. FIGS. 6 and 7 illustrate a second design of a beam filter 20 with adjustable absorbing properties, said beam filter 20 consisting of two stacks 100, 200 of absorbing sheets 111 and 211, respectively, wherein each of these stacks has a design like the beam filter 10 described above. The two stacks 100, 200 of absorbing sheets 111, 211 are placed one behind the other in the direction of the X-ray propagation. X-rays will therefore have to pass both stacks 100, 200 before they can reach a detector. The area of the X-radiation source 1 that is masked by the absorbing sheets 111, 211 can be changed if the stacks 100, 200 are shifted with respect to each other. FIG. 6 shows in this respect an arrangement in which the absorbing sheets of the two stacks 100, 200 are aligned, while FIG. 7 shows an arrangement in which the second stack 200 is shifted somewhat with respect to the first stack 100, resulting in a reduced intensity of the beam at the output side. In the described embodiments of a primary beam filter with a multi-layer structure, the spectral shape of the radiation is hardly changed as attenuation is realized by partial total absorption. The beam filters are favorably applicable in medical CT, particularly spectral CT. Finally it is pointed out that in the present application the term “comprising” does not exclude other elements or steps, that “a” or “an” does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope. |
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abstract | This invention provides a multi-charged-particle beam exposure apparatus capable of easily correcting at a high precision the electron-optic characteristics of each column which constitutes an electron-optic system. The exposure apparatus has magnetic lens arrays (ML1, ML2, ML3, and ML4) which commonly adjust the electron-optic characteristics of a plurality of columns which constitute the electron-optic system, and dynamic focus lenses or deflector arrays which individually correct the electron-optic characteristics of the columns. |
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summary | ||
051184664 | claims | 1. A nuclear reactor coolant pump for pumping reactor coolant fluid in a reactor coolant system, said pump comprising: (a) a casing having an end defining a central inlet nozzle for receiving a reactor coolant fluid, a peripheral outlet nozzle for discharging the reactor coolant fluid, and an annular passage interconnecting said inlet nozzle and said outlet nozzle through which the reactor coolant fluid can flow in a main stream from said inlet nozzle to said outlet nozzle; (b) a central rotor extending axially through said casing and having opposite ends, one of said ends being disposed adjacent said annular passage defined by said casing end; (c) first and second bearings rotatably mounting said rotor adjacent said opposite ends thereof to said casing; (d) a motor disposed about said rotor and between said first and second bearings, said motor including a rotor section mounted to said central rotor for rotation therewith and a stator section mounted stationarily to said casing and about said rotor section, said motor being operable for rotatably driving said central rotor; (e) an impeller mounted to said one end of said central rotor in communication with said annular passage and rotatable with said rotor so as to create a lower pressure at said central inlet nozzle than at said peripheral outlet nozzle thereof for drawing reactor coolant fluid axially into said one casing end through said central inlet nozzle thereof and discharging reactor coolant fluid from said one casing end tangentially through said peripheral outlet nozzle thereof after movement in a main flowstream through said annular passage of said one casing end; and (f) a self-cooling arrangement defining a fluid flow loop in flow communication with said annular passage and in heat transfer relationship with said first and second bearings and said motor and being operable for diverting only a small fraction of the reactor coolant fluid from and back to said main stream through said annular passage to cool said bearings and motor. said inner loop portion includes an inner annulus; and said outer loop portion includes an outer annulus surrounding and spaced radially outwardly from said inner annulus. an outer annulus surrounding an exterior of said motor and defined by a portion of said casing surrounding and spaced outwardly from said motor exterior; and a plurality of channels extending between said outer annulus and said entry ports. said motor includes a rotor section mounted to said central rotor for rotation therewith and a stator section mounted stationarily to said casing and about said rotor section; and said loop includes an inner annulus defined by an annular clearance between said rotor and stator sections of said motor. a separator element mounted to said rotor for rotation therewith and extending across said flow loop for striking particles entrained in the flow of fluid in said loop and flinging the particles out of said loop; and an annular deadend cavity defined in said casing and surrounding the rotational path of said separator element of receiving and trapping particles flung therein by said rotating separator element. 2. The pump as recited in claim 1, wherein said fluid flow loop includes outer and inner loop portions, said outer loop portion being located farther radially outwardly from said central rotor than said inner loop portion. 3. The pump as recited in claim 2, wherein: 4. The pump as recited in claim 3, wherein said inner loop portion further includes lower and upper pathways defined along and past said lower and upper bearings, said upper pathways connecting in flow communication said inner annulus and said annular passage, said lower pathways connecting in flow communication said inner annulus and said outer annulus. 5. The pump as recited in claim 1, wherein said self-cooling arrangement includes a plurality of entry and exit ports to said loop defined in flow communication with said annular passage, said entry ports being located downstream of and at points of greater pressure in the main stream of fluid flow than said exit ports. 6. The pump as recited in claim 5, wherein said exit ports are defined through said impeller. 7. The pump as recited in claim 5, wherein said fluid flow loop includes outer and inner loop portions, said outer loop portion being located farther radially outwardly from said central rotor than said inner loop portion, said outer loop portion being connected at one end to said entry ports and said inner loop portion being connected at one end to said exit ports, said outer and inner loop portions being interconnected at respective other ends in flow communication with one another. 8. The pump as recited in claim 5, wherein said loop includes: 9. The pump as recited in claim 8, wherein: 10. The pump as recited in claim 1, wherein said self-cooling arrangement further includes a plurality of deflector elements mounted to said casing adjacent to and upstream of said entry ports for impeding particles entrained in the main stream of fluid flow from passing through said entry ports. 11. The pump as recited in claim 1, wherein said self-cooling arrangement further includes: |
description | This application claims the priority of U.S. Provisional Application No. 61/228,159, filed Jul. 24, 2009, which is incorporated herein by reference. The present invention relates to illumination systems and more particularly to illumination systems for hazardous underwater environments, including hazards such as nuclear radiation and/or contamination or in the ocean. A large number of reasons exist for lighting a large underwater environment including security, safety and illumination of work surfaces. Applications include oil drilling platforms, lighting around submarines and ships and for storage pools. In all applications it is desirable to use a high-efficiency, long-lifetime light source which can provide continuous lighting with minimal maintenance. Nowhere is the need for a low maintenance lighting system more pronounced than in nuclear refueling pools, spent fuel storage pools and in nuclear reactor vessels. These structures contain water, which is used to limit the transmittal of radiation. Service of the lighting systems in these areas takes excessive time, personnel may have limited access, and their service results in exposure of the maintenance personnel to radiation. Typically, these pools require a large number of lights for effective illumination. Traditionally, this lighting has been accomplished using 1000 W, 120 V incandescent spotlights or floodlights. These bulbs have lifetime ratings of 2,000 to 4,000 hours, and provide total light output of 17,000 lumens. At a lifetime of 4,000 hours, a particular light fixture will require 2.19 bulb changes per year, with maintenance personnel being exposed to radiation at each bulb change. A typical fuel storage pool uses 20 incandescent light fixtures. Thus, maintenance personnel may be subjected to short periods of radiation quite frequently for single bulb changes or to extended periods of exposure for “en mass” changes, if it is even possible to gain access to change the bulbs. Inside a nuclear containment structure, water is normally contained only in the immediate area of the reactor itself, i.e., the reactor pressure vessel. However, when the reactor is shut down for a refueling outage, it is necessary to fill the entire refueling cavity with water, to limit the transmittal of radiation as the fuel is being unloaded and loaded. The reactor cavity is typically flooded only during this refueling outage period, but it is necessary during this time to make sure that the cavity is properly illuminated. During this outage period, when maintenance is being performed on the reactor and when the fuel is being unloaded and loaded, it is costly and impractical to allocate maintenance personnel time for servicing the underwater lights. Additionally, some lamps may be installed in isolated areas where radiation flux can become quite high, such that access is available only for limited periods. The nuclear maintenance workers who are responsible for these areas are required to wear cumbersome PPE (Personal Protective Equipment) that makes high-dexterity repair work difficult or impossible. Every minute of radiation exposure is critical, excess radiation exposure is costly for plant owners, and personnel are limited in the cumulative amount of radiation exposure they can receive in a given time period. As a result of this challenging situation, in practice many of these short-lifespan lights remain failed rather than being continually serviced, often resulting in some of these critical structures being poorly illuminated. Even in areas where water is not introduced, a reliable, long-lasting light source is needed for replacement of the currently-used incandescent bulbs. A number of underwater lights are the subjects of patents, however, for various reasons, these lights are not suitable for use in nuclear environments, either as fixed lights or as drop lights. The submersible light assemblies of Olsson et al. (U.S. Pat. No. 4,683,523, issued Jul. 28, 1987, and U.S. Pat. No. 4,996,635, issued Feb. 26, 1991) have funnel-shaped housings with flared front portions designed for fixed attachment to submersible vehicles. The light sources are quartz-halogen lamps which require heat sinks, and the lamps themselves are fully isolated from water. The housings are relatively large and cumbersome and not adjustable in direction once attached. The light produced is generally projected in a narrow beam forward from the lens. Such a construction would not be suitable for the wide angle illumination needed in a nuclear pool or for the maneuverability required for a cable-suspended drop light. The underwater light of Poppenheimer (U.S. Pat. No. 4,574,337, issued Mar. 4, 1986) has a housing that is much larger than the small quartz-halogen lamp housed therein. The lamp is fully isolated from the water by an inner casing which is cooled by water that enters the outer housing. The light is projected forward in a generally narrow beam, resulting in the same limitations for use in nuclear applications as the lights of Olsson et al. The high-intensity light source described by Mula (U.S. Pat. No. 5,016,151, issued May 14, 1991) has a watertight housing with a second subhousing to isolate the lamp from the water. The flared shape of the housing places limitations on the maneuverability of such a device as a drop light. Finally, and most importantly, none of the above-described lights make provisions for rapid changeout of burned-out or damaged bulbs. The reliance on closed housing construction requires that any bulb changes be made out of the water, which is one of the main problems that must be overcome in a hazardous environment such as nuclear facility pools. Such changes are time-consuming and require multiple radiation exposures to effect a bulb replacement. Traditional incandescent underwater lamps used multiple small fasteners and sealing rings that necessitated a high level of dexterity for proper maintenance. If the entire lighting assembly were to be replaced to avoid multiple exposures, such changes could become very expensive due to the complex construction of the assemblies. Any facility which requires a large number of such light systems could find them to be prohibitively expensive to maintain High pressure sodium (HPS) lighting has been used extensively for street and parking area illumination, lighting in factories and for security lighting. The primary advantages of HPS lights are: 1) high efficiency, and 2) very long lifetime. Compared to a 1000 W incandescent bulb, an HPS bulb has a lifetime rating of 24,000 hours and provides a total light output of 140,000 lumens. U.S. Pat. No. 5,105,346, No. 5,213,410 and No. 5,386,355, each incorporated herein by reference, describe a lighting system and method for lighting hazardous underwater environments using HPS lamps in a modular configuration that provides for rapid replacement of the damaged or burned-out bulbs. The commercial version of this lighting system has received universal acceptance from major nuclear fuel manufacturers and has been installed in a large number of nuclear power plants worldwide. One drawback of HPS lighting is that its yellow-orange color temperature (˜2,200 K) is not ideal for human vision, which is optimized for white (5,500 K) light. While HPS lighting was the best option at the time the time of these patents, when using HPS lights in the underwater environment it can be difficult to discern objects and identify their true color due to the non-white color of the illumination. An additional drawback is that HPS lamps can take several minutes before reaching full intensity, which delays the user's ability to see clearly within the underwater environment in an emergency situation, if these lights were not previously turned on. The recent emergence of ultra-bright, white, high power light emitting diodes (LEDs) presents an alternative that can overcome some of the above-described drawbacks of HPS lighting. Key characteristics of these high power LEDs are excellent reliability and durability, instant turn on, longevity and good color. Furthermore, the efficiency (increased lumens per watt) of these LEDs provides a significant reduction in power consumption and, consequently, carbon emission. However, complexities are introduced over traditional lighting sources by their need for drivers and power factor correction. Despite these advantages, the major issue that has previously prevented the adoption of LED lighting is thermal management. While typical LEDs can be operated at temperatures up to 185° C., that high of an operating temperature is not conducive to long life and low maintenance. Some LED manufacturers specify a maximum operating temperature of 85° C. to ensure 70% luminance after an operating life of 50,000 hours. Failure to address the heat dissipation needs of LED lighting will lead to severe degradation, which reduces operational lifetime, reduces visible light output, and negatively affects the color rendering. U.S. Pat. No. 6,412,971 describes a LED array that has a large number of elements arranged with sufficient density to achieve a desired illumination intensity to replace conventional incandescent or HPS light sources without creating the environmental concerns of fluorescent bulbs. While the disclosed LED array solves many of the problems encountered with replacement of incandescent bulbs with LED arrays, it does not provide solutions for the special requirements of underwater operation, and particularly fails to address the problems involved in underwater operation in a hazardous environment such as a nuclear spent fuel pool or nuclear reactor. Accordingly, obstacles remain to realization of LED-based lighting fixtures for use in hazardous underwater environments such as nuclear reactors and spent fuel pools. The present invention is directed to providing such fixtures. It is an advantage of the present invention to provide a long-life LED-based light module that can be rapidly inserted into and removed from a lighting fixture that is located in a hazardous environment. In one aspect of the invention, a modular light unit for illuminating a hazardous underwater environment includes a housing having a front portion and a back shell portion, the front portion including a light transmissive window and a layered lighting assembly enclosed within the housing. The layered lighting assembly includes a printed circuit board comprising a dielectric layer. A plurality of electrically-conductive traces are formed on an upper surface of the dielectric layer. An array of LEDs is mounted on the printed circuit board (PCB) in electrical communication with the electrically-conductive traces. A thermal bridge abuts the underside of the PCB in thermal communication the LEDs, and a heat sink abuts the thermal bridge in thermal communication therewith. A thermally conductive potting material abuts the heat sink to fill all spaces between the heat sink and an inner surface of the back shell portion. A reflector array is disposed over an upper surface of the printed circuit board, the reflector array having a pattern corresponding to the array pattern of the LEDs so that the reflector array has a reflector corresponding to each LED of the plurality of LEDs. An underwater connector in electrical communication with the electrically-conductive traces provides releasable connection to an electrical cable for providing power to drive the plurality of LEDs. A quick-release mechanical fastener is attached to the housing for releasably attaching the modular light unit to a support structure installed within the hazardous underwater environment. In a preferred embodiment, the PCB is a metal core PCB which includes a metal base affixed to the underside of dielectric material. Where a metal core PCB is used, the metal base is preferably copper. The thermal bridge and the heat sink are preferably formed from copper and the housing is formed from stainless steel. In one embodiment, the heat sink includes a plurality of ribs that extend from a lower side of the heat sink, so that the potting material fills all spaces between the plurality of ribs and the inner surface of the back shell portion. According to a first embodiment of the present invention, an integrated LED module and composite heat transfer mechanism, enclosed by a metal housing and an optical window. In a preferred embodiment, the housing is stainless steel, more preferably 316-type stainless steel, however other stainless steel types as well as aluminum or other metals may be used for applications where the need to support decontamination is not as critical, i.e., in non-nuclear settings. The integrated LED module includes a plurality of high power LEDs, preferably emitting white light, mounted in an array on a metal core printed circuit board (PCB). The module also includes an array of reflectors that is positioned above the PCB, with one reflector associated with each LED. A composite heat transfer assembly includes stacked components in which the metal core circuit board is bonded to a thermal bridge. Heat generated by the LEDs is transferred from the thermal bridge to the module housing via a heat sink and high-efficiency heat transfer potting compound. The potting compound is in contact with the interior surface of the housing. In a first embodiment, a heat sink with an upper surface in contact with the back surface of the thermal bridge has ribs extending from its lower surface which are surrounded by a thermally conductive potting compound. The potting compound provides heat transfer between the heat sink and the inner surface of module housing. An underwater connector attached to the housing provides electrical connection from a power supply for driving the LEDs. The heat transfer assembly maintains the LEDs at appropriate operating temperatures when the lamp is submerged in water of temperatures of 50° C. or less. This environment allows the LEDs to operate at steady-state temperatures that optimize operating life (e.g., 30,000 hours or more). The integrated LED lamp module provides output illumination that is comparable to a conventional 1000 W HPS lamp. An important advantage of the LED module is that the emitted light has a higher color temperature than HPS lamps, which provides improved visibility for human users. In addition, unlike the HPS lamps, the LED lamp is dimmable. In a second embodiment of the integrated LED lamp module, the same components as in the first embodiment are used with a modified heat sink that does not have fins. In this embodiment, the larger volume of heat sink material provides a sufficiently uniform dispersal to minimize hot spots. The heat sink is attached by potting compound to the interior surfaces of the housing. All lamp internals are sealed and their exposure to water is avoided through a combination of the materials and fastening means used to assemble the housing and the potting compound. The lamp mechanical design allows easy installation and removal of the entire module. By reducing the time required for installation and removal, the radiation exposure to maintenance workers is decreased and the ALARA (“As Low As Reasonably Achievable”) radiation exposure minimization principle is practiced. Radiation exposure by maintenance workers is minimized due to the reduced frequency of maintenance interventions being required. All external portions of the light assembly are designed for use in hazardous environments, through the use of materials and geometries that can easily be easily decontaminated. This easily-serviced underwater light for use in a hazardous underwater environment can be constructed using either of the above-described modular lamp constructions. A rapid-change light module for use in a hazardous underwater environment can be constructed using either of the above-described modular lamp constructions. As used in the present description, the term “LED” refers to a solid state chip or die (light emitting diode chip) that converts electricity into light as well as a packaged light emitting diode, as known in the art, which includes a LED chip, a primary lens, and a thermal pad for heat transfer from the LED chip. For some applications of the invention, LED may also include laser diodes. FIGS. 1a-1c illustrate an exemplary light head 100 that can be constructed using the LED-based modular lamp components that are described in more detail below. The integrated lamp module 100 includes a housing 130 formed by the combination of a rear shell 120 and a front cover 140 which includes an optical grade window. For nuclear reactor applications, the rear shell 120, and any other exposed metal used in housing 130 is preferably stainless steel. Selection of an appropriate type of stainless steel is within the level of skill in the art, and will be based on the selected material's ability to undergo decontamination procedures without excessive surface damage or structural degradation. In the preferred embodiment, type 316 stainless steel is used. For non-nuclear applications, appropriate metals may include other types of stainless steel, aluminum or other metals. As seen in FIG. 1c, fins or ribs may be formed to extend away from the rear shell to enhance heat dissipation from the module. Visible through, and enclosed by the optical grade window 142 of front cover 140, is a LED array and a reflector array, which are described in more detail below. In one embodiment, the optical grade window 142, typically made from acrylic or other polymer suitable for the intended application, is a flat plate sealed to a frame around its edges to complete a water-tight enclosure when assembled to rear shell 120. In this case, the frame and window together define the front portion 140 of housing 130. The frame may be formed from the same metal as the rear shell 120, e.g., type 316 stainless steel, or may be formed from the same material as the window. Alternatively, the frame and window may integrally formed by machining or molding a single piece of acrylic (or other appropriate light-transmitting material). In any of these configurations, the front portion 140 may be attached to the back portion 120 by bolts, screws or other appropriate fasteners. Screws 15 are shown in FIG. 2 as an example. One or more O-rings 17 (one is shown in FIG. 2) may be located in channels formed in one or both of the abutting edges or surfaces of the back shell 120 and front cover 140 to ensure a watertight seal. An underwater connector 146 may be located on the back, as shown in FIG. 1b, or a side of the housing 130, with appropriate internal connections (not shown) to the PCB to conduct power to the light-emitting elements. In a preferred embodiment, the connector will be wet-mateable. Such connectors are commercially-available from a number of sources including Sub-Conn Inc. (North Pembroke, Mass.) and Bowtech Products, Ltd. (Aberdeen, UK), among others. Appropriate connectors should be made from materials that tolerate radiation exposure. Connector 146 provides electrical communication with a corresponding connector disposed at the end of a cable (not shown) which is electrically connected to an external power source that is appropriate for driving the lighting module. In one embodiment, the housing 130 may be attached via pivoting fasteners 154 to a bail or yoke 148 to allow adjustment of the angle of illumination. The fasteners will preferably have a locking capability to stabilize the lighting module once the desired angle has been achieved. Such fasteners are known in the art. Yoke 148 has a socket 150 and a quick release mechanical fastener, e.g., a hole for mating with a spring-biased button, or a bayonet mounting on the end of a pole 160 (indicated by dashed lines in FIG. 1a). The quick release fastener allows the entire modular assembly 100 to be rapidly attached to or removed from a pole, similar to the one shown in FIG. 1 of U.S. Pat. No. 5,386,355, which is incorporated herein by reference. (The ballast illustrated in the '355 patent would not be required.) While any number of quick-release attachment means may be used, employing the same connectors that are used in a pre-existing installation has the advantage that the LED-based modular lighting assembly can easily replace existing HPS fixtures similar to those described in the '355 patent. In this application, the ballast assembly shown in the HPS fixture could be replaced by a LED driver, which may be enclosed in a watertight housing in a configuration similar to the ballast shown in the '355 patent. Alternatively, the LED driver(s) may be included within the housing of the modular light assembly 100. The ability to attach the inventive LED-based light module to an existing pole installation that may have been previously used with a HPS fixture will further assist in minimizing radiation exposure of maintenance personnel. After removal of the lamp module 100, the module may be taken to a maintenance shop for decontamination and replacement of damaged or spent LEDs by opening the housing, removing the entire internal assembly, and replacing it with a new internal assembly. Referring to FIGS. 2 and 3, the internal assembly of the integrated LED lamp is shown and includes a plurality of LEDs 10 mounted in an array on a printed circuit board (PCB) 12. Exemplary illustrations of different array patterns of LEDs are shown in FIGS. 1a and 1c, and FIG. 3. Typical numbers of LEDs in an array can range from several dozen, e.g., 80 LEDs in the exemplary 4×20 array of FIG. 3, to several hundreds, as in the 437 LEDs in the exemplary 19×23 array in FIGS. 1a and 1c. More or fewer LEDs may be used, and other patterns may be selected based on specific lighting requirements for the desired application and the light output of the individual LEDs. Selection of appropriate LED numbers and arrangements is within the level of skill in the art. A plurality of copper traces 4 printed on the upper surface of the PCB 12 serve as the electrical connection to each of the LEDs for delivering power for operation. In the preferred embodiment, PCB 12 is a metal core board (MCPCB). FIG. 3 illustrates the structure of the MCPCB, which is formed by laminating a thermally conductive dielectric layer 13, e.g., G10 epoxy or similar, and a high thermal conduction metal base 14. In the preferred embodiment, the metal base 14 is copper, although aluminum or other metals may be used. Openings 11 formed through dielectric layer 13 allow direct contact between the LED thermal pads and metal base 14 for optimal heat conduction. As illustrated in FIG. 3, the metal base has small pedestals formed on its upper surface to extend though the openings 11 in the dielectric layer 13 to contact the thermal pad of the LEDs. An alternative approach would be to make the openings 11 of a size and shape sufficient to allow the thermal pad of the LED to extend through the dielectric layer to directly contact the flat upper surface of the metal base 14. An example of this approach is described in U.S. Pat. No. 7,262,438 of Mok et al., which is incorporated herein by reference. In either approach, the thermal pad of the LED may be attached to the metal base 14 by a thermally conductive bonding agent. In yet another alternative embodiment, the PCB 12 may omit the metal core, in which case the PCB could be formed from FR-4, which is known in the art. In this embodiment, the PCB would be formed in a manner similar to that described by Mok et al., and as illustrated in FIG. 3, however, the thermal pads of the LEDs 10 would extend through the PCB 12 to contact the upper surface of the thermal bridge 16. Thermal bridge 16 uniformly conducts the heat from the LEDs 10 toward heat sink 20. To avoid creation of hot spots, PCB metal base 14 (if used), thermal bridge 16 and heat sink 20 preferably have uniform, flat contact surfaces. To achieve the desired flatness, both thermal bridge 16 and heat sink 20 may be formed by milling metal bar stock. The bar stock should be of relatively high purity without inclusions to enhance uniform conduction. In the preferred embodiment, both the thermal bridge and heat sink are formed from copper, but other thermally conductive metals and alloys may be used as appropriate for the type of LEDs used and the particular lighting application. The thermal bridge 16 may be attached directly to the base of the MCPCB 12 by a thermally conductive adhesive, thus eliminating the need for multiple heat sinks on top of the surface mounted components. Use of a thermally conductive adhesive between the different contact surfaces may be able to compensate for minor variations in surface flatness, however, in general, the adhesive will preferably have a uniform thickness, again to avoid creation of potential hot spots. Heat sink 20, which abuts the back side of thermal bridge 16, conducts the heat transferred from the packaged LED through the PCB 12 and thermal bridge to the back shell 120 of housing 130. In the first embodiment shown in FIG. 4, the heat sink 20 may include a plurality of ribs 22 extending from its back side (the side opposite the front portion of the module). The spaces between the ribs 22, as well as any spaces between the ribs and the inner surface of the back shell 120, are filled with a high heat transfer potting compound 24. Such compounds are commercially-available from a number of sources, including Durapot™ 810, an alumina based, thermally conductive potting compound and adhesive available from Contronics Corp. (Brooklyn N.Y.). In a second embodiment shown in FIG. 5, the heat sink 26 is formed as a solid block, without ribs. A high heat transfer potting compound 24 fills the space between a solid heat sink 24 and the inner surface of back shell 120. A reflector array 160 with a plurality of conical or parabolic reflectors 162 is positioned over the front face of the PCB 12. The number of reflectors 162 and their spacing match that of the LED array so that when the reflector array and LED array are aligned, each LED 10 is centered within the bottom opening of its corresponding reflector to maximize the amount of light that is directed through the window. The LED lighting system described above can be maintained at its safe operating temperature when the lamp is subjected to water temperatures of 50° C. or lower. When operated within its safe operating temperature, the inventive LED lighting system will achieve an average of 50,000 life hours. The integrated LED lamp provides an output illumination comparable to conventional 1000 W HPS lamps while providing a higher color temperature than conventional HPS lamps. The modular design of the inventive lighting system allows easy installation and removal. When used in nuclear reactors, the time required for installation or removal is minimized, decreasing radiation exposure to RAD workers and promoting the ALARA (As Low As Reasonably Achievable) principle. For ease of description, elements of the invention have been described herein as having “upper” and “lower”, “front” and “back” sides or surfaces. These and other position-related adjectives are intended to indicate relative location only in the layered assembly and are not intended to limit the invention to use in a particular orientation. Thus, for example, reference to the upper surface of a printed circuit board means the surface on which electrical components (LEDs) are attached, as illustrated in FIGS. 2-5. This does not mean that the PCB will only be used in a horizontal orientation with the LEDs facing upward, as will be readily apparent from FIGS. 1a-1c. The foregoing description of preferred embodiments is not intended to be limited to the specific details disclosed herein. Rather, the present invention extends to all functionally equivalent structures, methods and uses as fall within the scope of the appended claims. |
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047939630 | abstract | The improved fuel assembly has a plurality of elongated corner posts extending longitudinally between and releasably and rigidly interconnecting top and bottom nozzles so as to form a rigid structural skeleton of the fuel assembly. Additionally, a plurality of transverse grids are supported at axially spaced locations along the corner posts and a plurality of fuel rods are supported by the grids. Certain groups of the fuel rods are spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the top and bottom nozzles. A cluster assembly having a cluster plate with a plurality of elongated rods is adapted to be removably supported on the top nozzle with its rods extending through the channels. The rods can be a plurality of guide thimbles in the case of one cluster assembly, or a plurality of oversized fuel rods in the case of another cluster assembly. The provision of cluster assemblies allows a unique scheme for loading fuel in the reactor core. Cluster assemblies containing burnt fuel can be loaded into fuel assemblies containing fresh fuel and vice versa. Also, a guide fixture mounting guide rods and a pair of comb devices mounting locking bars are utilized to depress springs within the cells of the grids in order to load fuel rods into the grid cells without scratching their exterior surfaces. |
048037168 | claims | 1. An x-ray diagnostics installation comprising: means for generating an x-ray beam having a central ray directed at an examination subject; x-ray film disposed in the path of said x-ray beam after said examination subject for recording radiation from said means for generating attenuated by said examination subject; means disposed between said examination subject and said x-ray film for generating an electrical signal corresponding to the exposure time; a secondary radiation grid also disposed between said examination subject and said x-ray film having lamellae; means for moving said secondary radiation grid perpendicularly with respect to said central ray of said x-ray beam; and control means for controlling the speed of movement of said secondary radiation grid dependent on said exposure time including means for integrating said signal corresponding to the exposure time, and wherein said signal corresponding to said exposure time is also supplied as a control signal for said means for moving said secondary radiation grid, such that the speed of said secondary radiation grid is controlled for all exposure times to avoid imaging said lamellae of said secondary grid on said x-ray film. |
summary | ||
claims | 1. A multilayer mirror comprising:a layer of a first material;a layer of silicon;the layer of the first material and the layer of silicon forming a stack of layers;wherein only an exposed region of the layer of silicon comprises a modification that is arranged to improve robustness of the exposed region of the layer of the silicon. 2. The multilayer mirror of claim 1, wherein the modification is arranged to improve the robustness of the exposed region of the layer of the silicon by at least one of:reducing a reactivity of the exposed region of the layer of silicon with hydrogen or atomic hydrogen; andimproving a sputtering resistance of the exposed region of the layer of silicon. 3. The multilayer mirror of claim 2, wherein the reactivity of the exposed region of the layer of silicon with hydrogen or atomic hydrogen is reduced by at least one of:one or more implanted materials provided on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; anda passivation layer covering, or forming part of, the exposed region of the layer of silicon. 4. The multilayer mirror of claim 2, wherein the sputtering resistance of the exposed region of the layer of silicon is improved by at least one of:one or more implanted materials provided on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; anda passivation layer covering, or forming part of, the exposed region of the layer of silicon. 5. The multilayer mirror of claim 1, wherein the modification comprises at least one of:one or more implanted materials comprising at least one of boron, nitrogen and nitride, provided on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; anda passivation layer covering, or forming part of the exposed region of the layer of silicon. 6. The multilayer mirror of claim 5, wherein the passivation layer comprises one or more of a nitride layer, a silicon nitride layer, a boron glass layer, or a silicon oxynitride layer. 7. The multilayer mirror of claim 1, wherein the exposed region of the layer of silicon is a peripheral region of the layer of silicon or a sidewall of the layer of silicon. 8. The multilayer mirror of claim 1, wherein:the multilayer mirror comprises at least one of a plurality of layers of the first material and a plurality of layers of silicon, such that:the plurality of layers of silicon are separated by a layer of the first material, orthe plurality of layers of the first material are separated by a layer of silicon. 9. The multilayer mirror of claim 1, wherein a plurality of exposed regions of the layer or layers of silicon comprises the modification. 10. The multilayer mirror of claim 1, wherein a majority or substantially all of the exposed region or regions of the layer or layers of silicon comprise the modification. 11. A lithographic apparatus comprising:an illumination system configured to generated a beam of radiation;a patterning device configured to modulate the beam;a projection system configured to direct the modulated beam onto a target portion of a substrate; andmultilayer mirror within one of the illumination or projection system, the multilayer mirror comprising:a layer of a first material;a layer of silicon;the layer of the first material and the layer of silicon forming a stack of layers;wherein only an exposed region of the layer of silicon comprises a modification that is arranged to improve robustness of the exposed region of the layer of the silicon. 12. A method comprising:forming a stack of layers including a layer of a first material and a layer of silicon; andmodifying only an exposed region of the layer of silicon to improve robustness of the exposed region of silicon. 13. The method of claim 12, wherein the modifying comprises:reducing a reactivity of the exposed region of the layer of silicon with hydrogen or atomic hydrogen; or improving a sputtering resistance of the exposed region of the layer of silicon. 14. The method of claim 13, wherein the reactivity of the exposed region of the layer of silicon with hydrogen or atomic hydrogen is reduced by at least one of:implanting one or more material on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; andproviding a passivation layer that covers, or forms part of, the exposed region of the layer of silicon. 15. The multilayer mirror of claim 13, wherein the sputtering resistance of the exposed region of the layer of silicon is improved by at least one of:implanting one or more material on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; andproviding a passivation layer that covers, or forms part of, the exposed region of the layer of silicon. 16. The method of claim 12, wherein modifying comprises at least one of:implanting one or more material on a surface of the exposed region of the layer of silicon, or within the exposed region of the layer of silicon; andproviding a passivation layer that covers, or forms part of, the exposed region of the layer of silicon. |
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039731316 | description | DESCRIPTION OF THE INVENTION In FIG. 1, a borehole 20 is shown traversing earth formations 21. A steel casing 22 is cemented in place by a column of cement 23 which prevents fluid migration between formations. The casing is filled with a well control fluid 24 such as water, drilling mud or the like. The well tool or sonde 25 is an elongated, fluid-tight enclosure sized to be passed through the well bore. In the well tool 25 is a pulsed source 26 of high energy neutrons (14 MeV) and, above the source 26 is a detector 27 for detecting gamma rays. The pulsed neutron source 26 can be a neutron generator tube such as the Philips type operating from the principle of the deuterium-tritium reaction. The gamma ray detector 27 may be a photomultiplier tube and detector crystal for detecting gamma rays resulting from fast or thermal neutron interaction with the earth formations 21 surrounding the well bore 20. A radiation shield 28 of iron, tungsten or other suitable material is interposed between the neutron accelerator 26 and the detector 27. The detector crystal may comprise a thalium doped, sodium iodide or cesium iodide or other like activated material which can be optically coupled to a photomultiplier tube. The radiation shield 28 reduces the probability of direct irradiation of the detector by neutrons emitted by the source 26. The detector 27 produces voltage pulses proportional in height to the intensity of the scintillation light flashes, where the intensity of the light flashes is proportional to the energy of the gamma ray causing the light flash. The source 26 is repetitively pulsed to produce bursts of high energy (14 MeV) neutrons. Both the source 26 and detector 27 are associated with a downhole electronic cartridge 29 which controls the operation. The tool 25 is supported in the well bore by an electrical armored cable 30 which houses the electrical conductors, in this case, coaxial conductors as noted above. The cable passes over a surface pulley 32 and electrically connects to the surface instrument 31. A mechanical or an electrical linkage 33 is used to illustrate the connection of the pulley 32 to the surface recorder instrumentation 31 so that a record of the measurements as a function of tool depth can be obtained. Referring now to FIG. 2, the various wave forms will explain the time difference between thermal neutron decay time gamma ray measurements and carbon/oxygen ratio gamma ray measurements. As shown in FIG. 2A, a carbon/oxygen system employs a background gamma ray time gate 35A, an inelastic neutron interaction time gate 35B for obtaining carbon/oxygen measurements and a capture gamma ray time gate 35C for calcium/silicon lithology measurements. These time gates are within 50.mu.s of the occurrence of the neutron burst at a time t.sub.o. That is to say, in a C/O measurement, neutron pulses at a repetition frequency of up to 20 KHz are employed. On the other hand, a thermal neutron decay time log is developed by use of time gates 36(A - C) which are usually chosen to extend for up to several hundred microseconds after the neutron burst time t.sub.o. In thermal neutron decay time logging, neutron pulse repetition frequency is usually about 1 KHz. From this illustration, it can be seen that the gating times and pulse repetition rates for these types of measurements are much different. Moreover, in C/O ratio measurements, the neutron pulse duration is about 5 microseconds where in thermal neutron decay time measurements, it is usually about 40 microseconds duration. For further details of a carbon/oxygen system, reference may be made to U.S. Pat. Nos. 3,780,303, 3,780,302 and 3,780,301. With regard to a thermal neutron decay time logging system, reference may be made to U.S. Pat. No. 3,842,264 for further illustration and explanation. In FIG. 2C, a timing sequence is illustrated for a thermal neutron decay time log. Repetitive bursts of neutron 37 at a frequency of 1 KHz are generated and between each burst 37, the gates 36A and 36B (FIG. 2B) sample the gamma rays detected. After 944 of such bursts, the system operates for a 55 ms period (equal to 55 neutron bursts) to open the gate 36C and sample background gamma rays. The background gamma ray count is scaled in time and subtracted from the measurements of gates 36A and 36B to derive the thermal neutron decay time for the formations. Referring now to FIG. 2D, a pulse 38 having a width W repeats at a time interval T. The pulse 38 is representative in the unshaded time period 38A of the ionization time in the neutron generator while the shaded time period 38B is representative of the time of a neutron burst. One of the purposes of the present invention is the provision for selecting both the repetition rate or frequency and the width W of the ion source pulse. Referring now to the system of FIG. 3, in the downhole tool is the D-T accelerator tube 26 which generally includes a deuterium replenisher 26A, an ion source 26B and a target 26C. The target 26C is connected to a negative high voltage power supply 69. The pulse width and pulse repetition rate of the generator tube can be controlled by the ion source 26B. In the illustrated form of this invention, four channels representing individually controlled pulse repetition frequencies and pulse widths are shown although it will be appreciated that more or less channels can be employed. The frequency for each channel is based upon a master clock circuit 40 which can be operated, for example, at 20 KHz. The clock 40 inputs to a divider circuit 41 which provides an output of 10 KHz. The divider circuit 41 inputs to a second divider circuit 42 which provides an output of 1 KHz. The divider circuit 42 inputs to a third divider circuit 43 which provides an output of 100 Hz. Thus, the circuitry includes four separate frequency outputs, i.e., 20 KHz, 10 KHz, 1 KHz and 100 Hz. The outputs of clock 40 and the divider circuits 41 and 43 respectively are input to one-shot multivibrator circuits 44, 45 and 46. The output of the divider circuit 42 inputs to a background synchronization pulse generator circuit 47 which, in turn, inputs to a one-shot multivibrator 48. Each one-shot multivibrator has a predetermined output pulse configuration which is different and which governs the duration W of the ion source pulse width. Thus, one-shots 44 - 46 and 48 provide four different pulse durations W for the neutron generator tube 26. The outputs of the one-shot multivibrators 44 - 46 and 48 are respectively coupled to AND gates 50 - 53 and the outputs of the gates are connected to a NOR circuit 54. By selecting one of the AND gates 50 - 53 for operation, one of the predetermined pulse durations W and pulse repetition frequencies is selected. The NOR circuit 54 passes any of the gate outputs to an ion source switch circuit 55 which controls the ion source 26B of the generator 26. The gate selection for AND gates 50 - 53 is made by one of latch circuits 57 - 60. The latch circuits generally function in responding to an input signal to provide a fixed condition output signal which, in effect, opens a gate to permit passage of pulses from a one-shot multivibrator. The latch circuits only reset when the power is discontinued. A separate latch circuit 61 is used to condition the switch circuit 55 to an "on" condition. Each of the latch circuits 57 - 61 has its input connected to a decoder circuit 62. The decoder circuit 62 has a plurality of channels which respond individually to different control signal frequencies. For example, a control signal frequency f.sub.1 would produce an output to latch circuit 61, a control signal frequency f.sub.2 would produce an output to latch circuit 60 and so forth. The various control signal frequencies fs are supplied to the decoder 62 by a conductor 63 coupled to the inner shield conductor of the triaxial cable 64. A D.C. power invertor 66 for the tool is also connected to the conductor 63 and receives power from a surface power supply 83. The triaxial cable's outer armor layer is electrically grounded. The center conductor 65 of the cable is connected to the detector 27 and supplies operative D.C. power for the detector. Gamma Ray data pulses from the detector 27 are conducted to the surface on the center conductor of the triaxial cable. The conductor 65 also receives a positive sync pulse from the background synchronization circuit 47 and a negative sync pulse from a synchronization generator circuit 67. Operating voltage for the target 26C of the neutron generator 26 is provided by a negative 125 Kv high voltage power supply 69. A low voltage power supply 71 is connected via an output voltage switching circuit 70 to the high voltage power supply 69. As will be subsequently discussed, the high voltage produced by the supply 69 is controlled by the input voltage supplied by the low voltage power supply 71. The switch 70 is controlled by an input signal on conductor 72 from the decoder 62. The switching input signal on the conductor 72 is controlled by a control signal frequency input to the decoder 62. Reviewing the system, a control signal frequency signal f.sub.1 first operates the latch 61 which turns the ion source switch 55 to an "on" condition (this condition shown in FIG. 2D as the time from I to F). A second selected control frequency frequency signal f.sub.2 operates the latch circuit 57 which in turn, opens the gate 50. Thereafter, the one-shot 44 is triggered by the clock 40 and turns the switch 55 to an "off" condition (this condition shown in FIG. 2D as the time from F to I) for a set time period. Thus, the duration W of the ion source control pulse 38 is controlled by the one-shot circuit 44. The sync circuits 67 and 47 indicate the occurrence of certain events. The sync circuit 67 produces negative sync pulses for each burst of neutrons at the time I (see FIG. 2D). The sync circuit 47 indicates for thermal decay logging when the background gamma rays are to be counted. This system also has the ability of varying the neutron output at different levels while the tool is operating in a borehole. This feature is important because for certain logs, pulse pile up (i.e., a too high instantaneous counting rate of gamma rays) in the detector system must be minimized by reducing the neutron output. Generally the neutron output may be reduced by changing the source-to-detector spacing. This action is normally prohibited in a borehole because of the need for maximum shielding. In the present system the neutron output is changed by varying the target voltage (and hence target current). Since the neutron output is related to the target current or voltage, the magnitude of these currents can be stepped down electronically to correspond to predetermined percentages of the maximum neutron output. For the system shown in FIG. 3, the neutron output is reduced by changing a 50 volt input voltage in supply 71 to change the negative 125 KV high voltage target voltage supplied by power supply 69. This is accomplished by sending a selection control signal to the 50 volt power supply switch 70. This switch 70 is programmed to reduce the target voltage by reducing the input voltage from the low voltage power supply 71 to the high voltage power supply 70 in predetermined steps. Once the proper level of voltage is selected, the switch 70 holds that position until the tool power is shut off or additional selection control signals are received to reposition the switch. The switch 70 is programmed to reset itself automatically once a cycle of different levels of voltages has been completed. This feature allows the operator to observe the response at several levels and choose the best neutron output for his application. Turning now to the surface equipment, an encoder for developing the various control signal frequencies is connected to the inner shield conductor 63. The center conductor 65 is connected to a cable box circuit 84 which separates sync pulses and data signals from power supply voltages. D.C. power for operation of the detector 27 is supplied by the surface detector power supply 85. Data pulse signals and sync pulses from the tool are supplied via a conductor 86 to an amplifier 87 and automatic gain control circuit 88 which linearizes the signals. An output from the AGC circuit 88 passes through a log selector switch 89, in the position shown, to linear gates 90, 91 and 92. The linear gates serve to pass the signal in an unchanged condition or prevent passage therethrough. In other words, the pulse height information in the data pulses is not disturbed. Each of the gates 90 - 92 is connected to a buffer memory circuit 94. A linear gate selector switch 95 is disposed between the log selector switch 89 and the linear gates 90 and 91 and can be operated to disconnect the gates 90 and 91 from the log selector switch 89. Output from the amplifier 87 is supplied to a first single channel analyzer 93. The single channel analyzer 93 responds only to the voltage height of the sync pulse from the sync pulse generator 67 and triggers digital gates 96, 97 and 98. The amplitude of the sync pulses is chosen such that data pulses will not trigger an analyzer. The digital gates 96 - 98 serve to open the respective linear gates 90 - 92 for passage of data pulses therethrough at desired time intervals for a particular type of log. The digital gate is manually adjustable to provide square wave output voltage levels of variable duration and initiation time. Between the analyzer 93 and gates 97 and 98 is a digital gate selector switch 99 which can be operated to disconnect the output of these digital gates from the analyzer 93. The output of cable box circuit 84 is also connected to a single channel analyzer 101 which is set to detect positive sync pulses only from the downhole sync generator circuit 47. The sync pulses from generator 67 are still negative on conductor 86 prior to their entry into amplifier 87 and are thus discriminated against by analyzer 101. A background switch 100 connects the output of either the analyzer 93 or the analyzer 101 to the digital gate 98. The output of the buffer memory 94 is supplied to a computer 102 for deriving the desired ratio thermal neutron decay time, or neutron gamma ray log measurements from the gamma ray data. The recorder 103 provides a log or record as a function of depth. With the tool in the hole for a thermal neutron decay time log, the encoder 82 at the surface provides the frequency control signal to the downhole decoder 62 to operate latch 61 which supplies a voltage to the ion source switch 55 and the ion source 26B. This is a condition for a continuous logging operating such as N- .gamma. logging. To operate in a pulse node for a thermal neutron decay log, a frequency control signal is used to operate the latch 59. All of the AND gates 50, 52 and 53 are closed while the output of the latch 59 opens the AND gate 52. Referring to FIG. 4 for details of the background sync circuit 47 of FIG. 3 may be seen. The 1 KHz output from the divider circuit 42 is supplied to the counter 75 and is passed through the gate 79 to the one-shot circuit 48 of FIG. 3. The one-shot circuit 48 output controls the duration of the neutron pulse generated by generator tube 26. The sync circuit 67 provides a negative sync pulse on conductor 65 for each operation of the one-shot circuit 48. Referring again to FIG. 4, when the counter 75 counts 944 neutron input pulses, the decoder circuit 76 sets flip-flop 77 which intercepts the initiating pulse to the one-shot circuit 48 via gate 79. The pulse generator 78 in response to the setting of the flip-flop 77 provides a positive sync pulse on the conductor 65 indicating the initiation of a background gamma ray counting period. Upon counter 75 reaching a count of 1000 pulses, the decoder 80 resets the flip-flop 77 so that the neutron pulsing is resumed. Both positive and negative sync pulses and the detected gamma ray pulses are transmitted via cable center conductor 65 to the surface equipment. In the surface equipment, the background switch 100 is in position to connect the analyzer circuit 101 to the gate 98. All other surface switches are in the position shown. The negative sync pulse from circuit 67 is detected and operates gates 96 to provide a time gate 36A (FIG. 2B) and operates gate 97 to provide a time gate 36B (FIG. 2B) so that the detected pulses pass through the gates 90 and 91 to the buffer memory 94 during the open times 36A and 36B. When the positive sync pulse from circuit 47 arrives, it activates analyzer 101 and the gate 98 is operated for the open period of the time gate 36C (FIG. 2B). The buffer memory 94 provides input data to a computer 102 which calculates macroscopic thermal neutron decay time or capture cross-section values. For operation to obtain a C/O log after the thermal decay log is recorded, the tool is repositioned as desired in the bore hole. The electrical power is interrupted to drop out the latchs 59 and 61. Frequency control signals from the surface encoder 82 then are sent to operate the latchs 61 and 57 in sequence. This conditions the neutron generator 26 and opens the gate 50. The subsequent pulses from clock 40 operate the one-shot circuit 44 at 20 KHz frequency and hold the pulse duration of the ion source to 20 microseconds. Negative sync pulses from the circuit 67 are repetitively supplied to the surface equipment. At the surface, the background switch 100 is in the illustrated position. Thus, for each sync pulse, the gates 96, 97 and 98 produce the gating time pulses 35 (A-C) for sampling the gamma ray data pulses input to the linear gates 90, 91 and 92. The data pulses from gates 90, 91 and 92 are transmitted to the memory 94 where they are available to the computer 102 and buffer for processing and subsequent recording by the recorder 103. The linear gate switch 95 can be operated by movement to disconnect the linear gates 90 and 91 from receiving inputs from the AGC circuit 88. The log selection switch 89 can be operated then to couple data pulses directly to the buffer memory 94 by a conductor 105. In this manner a conventional neutron gamma ray log may also be provided, if desired. To change the voltage on the generator 26, a frequency control signal is transmitted to the decoder 62 which, via a conductor 72, operates the step function switch 70. For each step function, the voltage of the high votlage power supply 69 can be increased or decreased. For example, the power supply 69 can be 125 Kv and the low voltage power supply 71 can provide 5 volt increments. With a six-position switch, the voltage to the target of generator 26 can be increased five steps to 125 Kv and then revert on the sixth step to 100 Kv. While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. |
046541942 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the illustrative embodiment depicted in the accompanying drawings, there is shown in FIG. 1 an inlet nozzle assembly, comprehensively designated 10, constructed in accordance with this invention. This inlet nozzle assembly 10 forms the lower end of a fuel assembly and is suitably connected at the upper end thereof to the lower portion of a duct tube (not shown)in a manner well known in the art. As used herein, the terms upper, lower, top, bottom, vertical, horizontal and the like are applied only for convenience of description with reference to FIG. 1 and, while oriented in such an attitude in a fast breeder nuclear reactor, should not be taken as limiting the scope of this invention. The inlet nozzle assembly 10 comprises an elongated shell 11 provided with a reduced diameter lower portion 12 having a solid bottom portion 13 terminating in a cylindrical post 14. The post 14 is sized and adapted to fit into a complementary shaped cavity formed in the supporting structure for the reactor core. The sizing of the post 14 and the associated cavity assures precise positioning of each of the many fuel assemblies located within the several hexagonal rows of the reactor core. Except for the solid bottom portion 13, the shell 11 is hollow throughout and is formed with an elongated chamber portion 15 of uniform cross section which then tapers downwardly to form a throat portion 16 and terminates in a lower chamber portion 17 of lesser cross sectional dimension than the major chamber portion 15. A shoulder or seat 18 is formed between the juncture of chamber portion 15 and throat 16 for supporting several internal components, including an orifice plate assembly 20, a shield block 21, a shield plug 22, and a diffuser 23, each of which will hereinafter be described in detail. A plurality of elongated slots 25 are formed in the lower portion 12 of shell 11 just above the solid portion 13 to provide inlet passages for the coolant adapted to be directed upwardly through the nozzle assembly 10 and the fuel assembly duct attached thereto. The orifice plate assembly 20 comprises a plurality of orifice plates 26, 27, and 28 stacked in a vertically back-to-back relation. While 3 such plates are shown in the embodiment illustrated in FIG. 1, the present invention envisions the use of any nuaber of orifice plates as dictated by the flow requirements for a specific fuel assembly. Indeed, a significant feature of the present invention is the selective use of differently orificed plates to realize the flow pattern desired in a particular fuel assembly to obtain optimum coolant flow therethrough without pressure increases and without impacting neutron shielding. For example, where greater coolant flow is desired without significantly increasing pressure, one of the plates, say plate 28 for example, can be removed. Where impeded coolant flow is desired, additional plates can be added to the assembly 20, as desired or required. The plates 26-28 are formed with one or more flow through openings or orifices 30, 31 and 32, respectively, which can be offset from each other to establish the desired flow path in a particular assembly. Also, the shape of the plates can vary. For example, as shown in FIGS. 1 and 2, the plates 26 and 28 are provided with annular body portions having peripheral rims or flanges 33 and 35, respectively, while the plate 27 interposed therebetween is formed as a circular disk. As mentioned earlier, these orifice plates are placed in a vertically stacked relation with the lowermost plate supported and resting on the seat 18. The shield block 21 is seated on the orifice plate assembly 20 and comprises a generally cylindrical body 36 having a central bore 37 therethrough provided at one end with a tapered inlet opening 38 adjacent to the orifice plate assembly 20 and at the other end with a recess 40 forming the outlet of block 21. The shield block 21 serves as a neutron shield to impede the neutron flux generated within the associated fuel assembly from passing onto the nuclear core's supporting structure. The shield plug 22 further inhibits neutron flux flow and comprises a generally cylindrical body 41 having a tapered nose 42 projecting downwardly into recess 40 of shield block 21. The opposite ends of body 41 are formed with radial flanges 43 and 45 extending radially outwardly into engagement with the inner wall surface of shell 11. These flanges 43 and 45 define an annular space 46 between body 41 and the shell wall for the passage of coolant from the lower end to the upper end of the plug 22. The lower flange 43 seats on the upper end of shield block 21 while the upper flange 45 serves as a seat for the diffuser 23. All of the parts of the nozzle assembly including the shield block and shield plug are preferably made from amterials that are resistant to degradation in molten sodium in a high neutron flux. Typically this material may be an alloy such as stainless steel. A plurality of circumferentially spaced, tapered channels 47 are formed on the lower end of body 41 and provide passages for the flow of coolant from outlet recess 40 of shield block 21 to the annular passage defined by space 46. Likewise, circumferentially spaced, tapered channels 48 are formed at the opposite or upper end of body 41 to provide passages for the flow of coolant from space 46 upwardly to the diffuser 23. The upper end of body 41 is formed with a tail portion 50 having an outwardly flared sidewall 51 for uniformly dispersing the coolant upwardly and outwardly into diffuser 23. The diffuser 23 functions to disperse or distribute the upwardly flowing coolant into the duct (not shown) of the fuel assembly for uniform flow about the multiplicity of fuel pins contained therein. The diffuser 23 comprises a generally cylindrical body 52 seated on the upper flange 45 of shield plug 22. The lower end of body 52 is recessed, as at 53, and accommodates the tail portion 50 of plug 22. A central axial bore 55 is formed in body 52. Also, a plurality of bores 56 are formed in body 52 in a circumferential array about the central bore 55 in radially spaced relation thereto. The bores 55 and 56 flare gradually outwardly, as at 57 and 58, for directing the coolant uniformly upwardly through the fuel assembly duct (not shown). The outer surface of body 52 is foraed with a threaded portion 60 for engagement with the internal threads provided at the upper end of shell 11. In assembling the nozzle assembly 10, the several orifice plates forming the plate assembly 20 are placed within shell 11 and positioned against the seat 18. The shield block 21 and shield plug 22 are successively placed within the shell 11 in a vertical stacked relation against the orifice plate assembly 20 and against each other. Next, the diffuser 23 is threaded into place in bearing relation against the stacked components to tightly secure the same against the seat 18. Completing the assembly 10 are a pair of laterally spaced support plates 61 (only one of which is shown in FIG. 1) secured to the adjoining housing 11 by pins 62. These support plates are formed with slots 63 for receiving support bars (not shown) onto which the lower ends of individual fuel pins (also not shown) are secured. FIGS. 3 and 4 illustrate another form of an inlet nozzle assembly 10' of this invention which is very similar to the form described above with the exception that the shell 11' is foreshortened and the lower portion 12' of the nozzle assembly containing the orifice plate assembly 20 is detachably connected to the shell 11'. The remaining structural elements are identical to those described above and the same numerals primed are utilized to identify similar parts. The detachable lower portion 12' is provided at its upper end with a bell formation 65 having internal threads 66 engageable with external threads formed on the lower end of shell 11'. One or more set screws 67 are threaded into suitable tapped bores 68 formed in bell formation 65 and received within a recess 70 formed in the lower end of shell 11'. As best shown in FIG. 4, the set screw 67 is formed with a head 71 disposed inwardly of the outer surface of bell formation 65 and can be swaged or crimped into an adjacent groove formed in the bell formation 65 to lock the screw 67 in place. Disassembly can be readily accomplished by drilling out the set screw crimp and/or turning the screw 67 with sufficient torque to decrimp the head. This detachable arrangement for the lower portion of the nozzle assembly facilitates quick and easy removal and/or replacement of the orifice plates without disturbing the other components. Moreover, the orifice assembly 20 can be formed integral with the shell lower portion 12' and the mating connections of members 11' and 12' can be formed to preclude inadvertent installation of a high flow fuel assembly with a low flow nozzle arrangement and vice versa. A suitable annular seal 72 is provided in a groove 73 formed between the aating surfaces of shell 11' and nozzle portion 12' to provide leaktight pressure sealing therebetween. FIGS. 5 and 6 illustrate still another form of an inlet nozzle assembly 10" of this invention which depicts a specially configurated shield block 21' and orifice plate 75 used in conjunction therewith. The shield block 21' comprises a generally cylindrical body 76 having an inlet opening 77 defined by a tapered or converging wall 78 and which communicates with a central passage 80. An insert 81 is threaded into a tapped counterbore 82 formed in body 76 and is provided with a longitudinal bore 83 communicating with passage 80. The insert 81 is formed at one end with a central embossment 84 extending downwardly into passage 80 and at the other end with a divergent outlet 85 for accomaodating the tapered nose 42 of shield block 22 and defining therewith a diverging conical passage 86. The shield block body 76 is provided with an annular well 87 concentric with the axis of passage 80 and defines therebetween a relatively thin cylindrical wall portion 88. The upper edge 90 of the wall portion 88 serves as a stop or seat for the lower face of insert 81. Wall portion 88 is formed with a plurality of circumferentially spaced, longitudinal slots 91 extending from the upper edge 90 inwardly into wall portion 88. These slots 91 provide passage for undesirable particulates into the well 87 which traps and collects such particulates therein. The orifice plate 75 comprises a central hub portion 92 having a plurality of circumferentially spaced, curved vanes 93 projecting radially therefrom and terminating in an annular rim 95. These vanes 93 impart a high speed cyclonic flow to the coolant flowing upwardly therethrough. As the rotating or spiraling coolant moves upwardly past orifice plate 75, the rate of spiraling is accelerated by virtue of the tapered wall section 78. This high speed swirling action produces a centrifugal force causing the heavier particles entrained in the coolant to be swept upwardly along the wall defining passage 80. The momentum induced in these particles causes them to be guided into the area between embossment 84 and wall portion 88 and ejected through the several slots 91 into the well 87. The engagement of the lower face of insert 81 against wall portion 88 isolates the well 87 from the coolant flow stream to retain the particles in well 87. The coolant flowing upwardly through bore 83 is diffused radially outwardly through the conical passage 86. In this manner, particulates can be effectively separated in the shield block 21' of a nozzle assembly and retained therein until removal of the assembly during refueling and/or replacement thereof. Moreover, the outer configuration of the shield block 21' and orifice plate 75 can be readily substituted for the block 21 and any of the orifice plates hereinbefore described in connection with FIG. 1. From the foregoing, it is apparent that the objects of the present invention have been fully accomplished. As a result of this invention, a new and improved inlet nozzle assembly is provided for optimizing coolant flow to the associated fuel assembly while adequately shielding the permanent core supporting structure. The inlet nozzle assembly is comprised of a plurality of easily replaceable internal components arranged in a stacked back-to-back relation for fabrication simplicity and ease of non-destructive replacement. By the provision of a plurality of orifice plates having differently sized and configurated openings, optimum coolant flow design for specific fuel assemblies can be achieved. By providing the shield block with an annular well in conjunction with a specially configurated, vane-type orifice plate, particulates can be effectively removed from the coolant flow stream. Also, the provision of a separable threaded lower nozzle section adjacent the orifice plate assembly facilitates replacing and substituting plates of differently configurated orifices to extend the useful life of a fuel assembly. |
summary | ||
058928073 | abstract | A fuel assembly for a pressurized water reactor having a fuel rod with a high strength cladding tube including an inner tubular layer of a zirconium alloy with alloying components of molybdenum and 3 to 6 weight percent bismuth, the balance zirconium. |
abstract | An X-ray fluorescence analyzer device comprises an X-ray source and a sample window. Between the X-ray source and the sample window there are a collimator plate with a plurality of microscopic pores and an annular plate comprising material essentially opaque to X-rays. The annular plate defines an area transparent to X-rays. The pores in said collimator plate let through collimated X-rays radiated by said X-ray source towards said sample window. The area transparent to X-rays in said annular plate spatially limits in a transverse direction a beam of X-rays radiated by said X-ray source towards said sample window. |
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description | This is a continuation application, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/050558, filed Jan. 14, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent applications DE 10 2012 201 131.5 filed Jan. 26, 2012, DE 10 2012 203 347.5 filed Mar. 2, 2012, and DE 10 2012 210 409.7 filed Jun. 20, 2012; the prior applications are herewith incorporated by reference in their entireties. The invention relates to a container, a device and a method for the gas-tight encapsulation of a fuel rod or of a fuel rod section. For transportation and/or storage purposes, defective fuel rods or fuel rod sections are inserted in a vacuum-tight and a fluid-tight fashion into containers or capsules such as are known for example from German patent DE 196 40 393 B4, from European patent application EP 1 248 270 A1, from European patent EP 1 600 982 B1, and from international patent disclosure WO 2010/084122 A1. Since the encapsulation of a fuel rod or of a fuel rod section is performed as close as possible to the original storage location, that is to say underwater within the fuel element storage basin, it is inevitable that water infiltrates into the open container during the insertion of the fuel rod or fuel rod section. The water must however be removed from the fuel rod container because, owing to decay heat, the water would evaporate and lead to an inadmissibly high internal pressure. For this reason, the closure elements used in the containers known from German patent DE 196 40 393 B4, from European patent application EP 1 248 270 Al and from European patent EP 1 600 982 B1 have a duct via which gas can be injected such that the water situated in the container is expelled. In the case of the closure plugs known in each case from German patent DE 196 40 393 B4 and from European patent application EP 1 248 270 A1, a coaxial duct is provided in each closure plug, in which coaxial duct there is arranged a spring-loaded valve which, by way of a closing element, closes off the duct in fluid-tight fashion. For the expulsion of the water, the closing elements are raised from their valve seat by a ram, and via a duct that is then opened, a gas is injected and the water is expelled via the likewise open duct of the oppositely situated closure element. In the case of the two known containers, the expulsion of the water takes place when the closure elements are, as a result of a screwing, welding or deformation process, situated in their final assembled position in which they close off the container in a fluid-tight fashion. In the container known from European patent EP 1 600 982 B1, a closure element is provided which can be screwed onto an external thread of the container and in which a seal element is mounted in axially displaceable fashion. In an intermediate position of the closure element, in which the closure element is not yet fully tightened, a parting joint exists between the sealing surface of the sealing element and the face surface, which interacts with the sealing surface to form a sealing pairing, of the hollow cylindrical container part, which parting joint communicates with a lateral ventilation opening in the closure element and, in the intermediate position, fluidically connects the exterior to the scavenging chamber of the hollow cylindrical container part. In order, in the case of the closure elements known from German patent DE 196 40 393 B4, from European patent application EP 1 248 270 A1 and from European patent EP 1 600 982 B1, to permit both an expulsion of the water situated in the container and also, in a final assembled state, reliable fluid-tight closure of the container, the closure elements are of multi-part and relatively complex construction. Furthermore, the handling thereof involves a correspondingly high level of manipulation effort. In the case of the container known from international patent disclosure WO 2010/084122 A1, there is provided as a closure element a cap which is pushed onto a hollow cylindrical container part and connected to the face surface thereof in cohesive fashion. The closure of the container is performed in a fluid-tight chamber. Before the closure, that is to say when the cap has not been mounted onto the hollow cylindrical container part, the liquid situated in the chamber is drawn out, and a vacuum-drying process is subsequently performed. Owing to the fact that, within the container equipped with a fuel rod, narrow gaps are present between the fuel rod and the internal wall of the container, it is in some circumstances possible for residual water to remain in the container. The invention is therefore based on the problem of specifying a container for the gas-tight encapsulation of a fuel rod or of a fuel rod section, the closure element of which container is of simple construction and permits a simple and reliable fluid-tight, that is to say gas-tight and liquid-tight, closure of the container. The invention is furthermore based on the object of specifying a device and a method by which a container containing a fuel rod or fuel rod section can be closed with the least possible residual water content. Accordingly, the container has a hollow cylindrical container part which, at its two free ends, is closed off in fluid-tight fashion by a respective unipartite closure plug. The closure plug is provided with a duct which fluidically connects the scavenging chamber of the container part to the exterior exclusively in an intermediate position which is assumed during the assembly process before an end position is reached and in which the closure plug projects out of the container part by an axial projecting length. Since the closure plug is of unipartite form, the closure plug can be of technically very simple form and produced with little outlay. Since, furthermore, the duct situated in the closure plug fluidically connects the scavenging chamber of the container part to the exterior only when the closure plug is situated in an intermediate position, no additional closing elements are required within the duct, such that the duct, too, can be manufactured in a simple manner by way of bores or recesses. Within the context of the present invention, the expression “closure plug” should be understood to mean that, for the insertion of the closure plug into the hollow cylindrical container part, only a “plugging” action is required, that is to say a pushing-in action in the axial direction and no rotational movement. The intermediate position is a position in which the closure plug has already been pushed into the hollow cylindrical container part but has not yet reached the end position in which it closes off the hollow cylindrical container part in fluid-tight fashion by a cohesive or form locking connection. In one advantageous embodiment of the invention, the duct has a first duct section which runs parallel to the longitudinal axis of the closure plug from an inner face side of the closure plug and which issues into a second duct section, the latter running transversely with respect to the longitudinal axis and extending from a shell surface of the closure plug. A duct of this type can be produced in a simple manner by way of bores in a longitudinal or transverse direction respectively. To hold the closure plug securely in the intermediate position, detent devices are provided on the closure plug and/or hollow cylindrical container part on the outer circumference and/or on the inner circumference respectively, which detent devices detachably fix the closure plug in the intermediate position. If the closure plug, in the fully assembled position, is seated by way of an annularly encircling flange on a face surface of the hollow cylindrical container part, it is possible for the closure plug and hollow cylindrical container part to be connected to one another in a fluid-tight fashion, in a simple manner from a manufacturing aspect, by an annularly encircling weld seam or brazed seam between the flange and the face surface. As an alternative to a cohesive connection of this type, the closure plug may also be fixed in a fluid-tight fashion in the hollow cylindrical container part by a shrink-fit connection. With regard to the device, the device has a first and a second processing chamber, the processing chambers being arranged spaced apart from one another on a common system axis. The first and second processing chambers are furthermore provided with a first and second opening, respectively, for receiving a free end, which issues into the processing chamber, of the container, such that the first and second processing chambers, when a container is arranged between them, can be fluidically connected to one another exclusively via the container itself. The first processing chamber has an inlet and the second processing chamber has an outlet for a scavenging gas, wherein each processing chamber has means for closing the container in gas-tight fashion. Since the first and second processing chambers, when a container is arranged between the processing chambers, can be fluidically connected to one another exclusively via the container itself, it is sufficient for scavenging gas to be injected exclusively into the first processing chamber, which scavenging gas is then inevitably forced through the hollow cylindrical container part via openings situated in the closure plug, and passes exclusively through the container part into the second processing chamber. As a result, the water situated in the container part is reliably expelled. It is thus not necessary for a scavenging gas line to be connected directly to a duct arranged in the closure plug. In one advantageous embodiment of the device, the processing chambers are arranged so as to be displaceable along the system axis. In this way, the container can be arranged between the processing chambers. By displacement of the processing chambers, the free ends of the container are guided through the openings so as to project into the processing chambers. In a particularly advantageous embodiment of the invention, each processing chamber is provided with a pressure ram which annularly surrounds the opening and which can be advanced in the direction of the system axis toward the opening and by which, by way of an advancing movement in the direction of the system axis, a force with a component acting transversely with respect thereto is exerted on a sealing ring which is arranged on the opening and which surrounds the opening. By means of this measure, the container can in a simple manner be connected in a fluid-tight fashion to the respective processing chamber by use of the opening, such that the processing chambers are mechanically connected to one another exclusively by the container. In an alternative embodiment of the device, the first and second processing chambers are rigidly connected to one another along the system axis by a connecting pipe which projects by way of its face-side ends into the first and second processing chambers. The container can be inserted into the connecting pipe such that the container projects by way of its free ends beyond the connecting pipe. The construction of the device is simplified by means of this measure because the processing chambers no longer need to be mounted so as to be displaceable relative to one another. In a further advantageous embodiment, the inlet and outlet are formed by an inlet pipe and an outlet pipe respectively, which issue into the first and second processing chambers respectively and the central axes of which coincide with the system axis and between which the connecting pipe is arranged in each case with an axial spacing, such that, between the face sides facing toward one another, there remain a first and a second free space respectively. Here, the connecting pipe can be connected in a fluid-tight fashion to the inlet pipe and to the outlet pipe by a first and second sleeve, respectively, which is arranged so as to be axially displaceable into a first position, wherein the first and second sleeves are displaceable into a second position in which the first and second free spaces are open to the first and second processing chambers respectively. In this embodiment, it is no longer necessary for the scavenging gas to be conducted through the processing chambers because, in the latter, a fluid-tight duct that serves as a scavenging chamber is created by the inlet and outlet pipe and the connecting pipe, such that, during the insertion of the container into the device, which takes place under water, no water can infiltrate into a working chamber of the processing chamber, which working chamber is situated outside the scavenging chamber and in which working chamber the tools required for the fluid-tight closure of the container are situated. It is preferable for a sealing element to be arranged between the container and connecting pipe, which sealing element can be set such that the inlet pipe and outlet pipe are fluidically connected to one another exclusively via the container. In order, in addition to the expulsion of the water from the container by the scavenging gas that is forced in, to also remove any water that has infiltrated into a defective, non-sealed fuel rod or into fuel rod sections and thus into the fuel matrix, it is provided in one advantageous embodiment of the device that the inlet and outlet can be connected to one another, via a bypass line that runs outside the processing chambers, in such a way that a closed gas circuit is formed, wherein, in the gas circuit, there are arranged a pump and a heating device for respectively circulating and heating a heating gas situated in the gas circuit. In this way, the water bound in the fuel matrix can be evaporated, and the fuel matrix dried. If each processing chamber has a pressure ram for exerting a pressure force that acts in the direction of the system axis, the closure plug of a container can be pushed into the hollow cylindrical container part in a particularly simple manner. If each processing chamber has a welding head which is mounted such that it can be rotated about, and advanced toward, the system axis, the closure plug can be welded to the hollow cylindrical container part without it being necessary for the container part to be set in rotational motion for this purpose. Furthermore, if each processing chamber contains a cleaning brush which is mounted such that it can be rotated about, and advanced toward, the system axis, the parts to be welded can be cleaned in situ before the welding process, and the quality of the weld seam can thus be improved. The outlay in terms of construction is furthermore reduced if the welding head and cleaning brush are arranged on a common rotary ring. With regard to the method, the object of the invention is achieved by a method using the device according to the invention and the container according to the invention. The method includes the following method steps: a) introducing a free end of the container part, which is equipped with the closure plug in the intermediate position and which contains the fuel rod or the fuel rod section, through the first opening into the first processing chamber, and introducing the opposite free end through the second opening into the second processing chamber, such that the first and second processing chambers are fluidically connected to one another exclusively via the container part itself; and b) injecting a scavenging gas into the first processing chamber, and expelling the water situated in the container part and in the processing chambers that are fluidically connected to one another via the container part, through the build-up of a positive pressure. In a particularly advantageous embodiment of the invention, after the expulsion of the water, heating gas is pumped through the container part, in order thereby to additionally reduce the water content in the container part by evaporation of the water. In other words: no vacuum drying takes place. If the heating gas is furthermore circulated in a closed gas circuit until a final value is attained at which the moisture content increases no further, it is possible from the moisture content to determine the absolute amount of water, which is gaseous during recirculation of the heating gas, situated within the container, such that precise statements can be made regarding the remaining water content in the container after the closure of the container. The closure plug is subsequently pressed into the container part as far as the end position and is connected in fluid-tight fashion to the container part. The closure plug is preferably cohesively connected to the container part by an annularly encircling weld seam or brazed seam, or is alternatively fixed in fluid-tight fashion in the container part by a shrink-fit connection. 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 container, a device and a method for encapsulating a fuel rod or a fuel rod portion in a gas-tight manner, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a container 2 having a hollow cylindrical container part 8 which is open at its face or end sides 4 and 6. At the face sides 4, 6, a respective unipartite closure plug 10 has been partially pushed in as far as an intermediate position. Each closure plug 10 has a head part 11 and a cylindrical shank 12, the outer diameter of which is only slightly smaller than the inner diameter of the container part 8. The head part 11 has an annularly encircling flange 13, an outer diameter of which corresponds to the outer diameter of the container part 8. In the intermediate position, the closure plug 10 projects beyond the hollow cylindrical part 8 by an additional projecting length s in relation to the end position of the closure plug 10, such that a part of the shank 12 situated below the head part 11 is situated outside the container part 8. Each closure plug 10 is provided with a duct 14 which, in an intermediate position, fluidically connects an interior 15 to the exterior 16. A sintered metallic filter element 18 is arranged in the cylindrical container part 8 at that free end which is situated at the bottom during handling, which filter element 18 prevents coarse particles from being able to escape from the still-open container 2 after the container has been equipped with a fuel rod 20 or fuel rod section indicated by dashed lines in FIG. 1. If it is the intention to encapsulate a defective fuel rod 20 into which water has infiltrated, the fuel rod has previously been opened in the region of its two end plugs, and the gaseous radioactive fission products contained therein, which escape through the openings, have been discharged in a targeted fashion. The duct 14 which, in the intermediate position, is fluidically connected to the exterior 16 is formed, in the example, by a central first duct section 24, which runs along a longitudinal central axis 22 and extends from a face side 23 facing toward an interior 15 and which is in the form of a blind bore, and by at least one second duct section 26, a through bore in the example, which runs perpendicular to the first duct section 24, wherein the first duct section 24 issues into the second duct section 26. The location or locations at which the second duct section(s) 26 intersect(s) a shell surface 27 of the closure plug 10, that is to say the issuing openings of the one or more second duct sections 26, is/are arranged in that region of the shank 12 of the closure plug 10 which is situated outside the container part 8 when the closure plug 10 is in the intermediate position. The shank 12 of the closure plug 10 is equipped, between its face side 23 that projects into the container part 8 and the one or more issuing openings, with an annular recess or groove 28 which serves for receiving a securing ring 30. The hollow cylindrical container part 8 is likewise equipped, on its inner surface in the region of the free ends, with a respective annularly encircling turned-in portion 32 into which the securing ring 30 inserted into the groove 28 engages with detent action when the closure plug 10 is inserted into the hollow cylindrical container part 8. The securing ring 30 and groove 28 accordingly serve as detent devices that detachably fix the closure plug 10 in the intermediate position. At its face side 33 facing away from the hollow cylindrical container part 8, the closure plug 10 is provided with a threaded bore 34 which serves for the screwed engagement of a bar-type tool that is used for handling the closure plug 10. A groove 36 (indicated by dashed lines) that runs perpendicular to the threaded bore 34 serves as a torque support as a bar-type tool (not illustrated in the figure) is screwed into the threaded bore 34. FIG. 2 shows the container 2 with the upper closure plug 10 in an end position in which it has been pushed deeper into the container part 8, by the distance s, until the flange 13 has set down by way of its sealing surface on the face surface of the hollow cylindrical container part 8 and the issuing openings of the one or more second duct sections 26 are situated within the container part 8. In the end position, the flange 13 is welded to the face sides 4 of the container part 8 along an annularly encircling weld seam 40, such that the closure plug 10 closes off the container part 8 in fluid-tight fashion. As per FIGS. 3A, 3B, a device for closing off the container 2 illustrated in FIG. 1 in a gas-tight fashion at both sides contains a first (upper) processing chamber 50 (FIG. 3A) and a second (lower) processing chamber 52 (FIG. 3B). The first and second processing chambers 50, 52 are spaced apart from one another and are arranged such that they can be positioned on a common, vertically oriented system axis 53 and such that they can be displaced relative to one another along the system axis 53. The first and second processing chambers 50, 52 are provided with first and second insertion openings 56, 57 which face toward one another and which are formed by first and second guide sleeves 54, 55 and which are arranged opposite one another in the direction of the system axis 53 and through which the container part 8 equipped with the fuel rod 20 or a fuel rod section is, by way of its face-side free ends and the closure plugs 10 pre-mounted there in the intermediate position, inserted and oriented such that the longitudinal central axis 22 of the container part 8 and the system axis 53 of the device coincide. After the face-side ends of the container part 8 equipped with the pre-mounted closure plug 10 have been inserted through the insertion openings 56, 57, the first and second processing chambers 50, 52 are closed off in fluid-tight fashion in the region of the insertion openings 56, 57 by virtue of a sealing ring 60 which annularly surrounds the container 2 being subjected, by virtue of an annular pressure ram 64 likewise equipped with an elastic sealing ring 62 being advanced axially in the direction of the system axis 53, to a force with a component acting perpendicular to the system axis 53, such that the sealing ring 60 is pressed against the outer circumference of the container part 8 and against the inner edge of the insertion opening 56, 57, thus closing a gap situated between the container part 8 and the insertion opening 56 and 57 respectively. In the assembled position, in which the closure plugs are still situated in the intermediate position, the first and second processing chambers 50, 52 are fluidically connected to one another exclusively via the container part 8. The first processing chamber 50 has an inlet 66 via which scavenging gas G, for example argon Ar, can be injected at high pressure. At its bottom side, the first processing chamber 50 is provided with an outlet 67 which has a valve 68 which is closed for the purpose of building up an internal pressure. The second processing chamber 52 is provided, on its bottom side, with a siphon which serves as an outlet 69 for the scavenging gas G. In each processing chamber 50, 52, a rotary ring 70 is mounted so as to be rotatable about the system axis 53, on which rotary ring a cleaning brush 72 and a welding head 74 are mounted, such that they can be advanced toward the system axis 53, by use of a respective rocker arm 76 and 78. The rotary ring 70 is driven, via a pinion 80, by an encapsulated motor 82. An observation camera 90 makes it possible to monitor the work operations to be performed for the closure of the container. In each of the first and second processing chambers 50 and 52, opposite the opening 54 or 56 respectively, there is arranged a pressure ram 92 actuated by a stroke-action cylinder 91, by which pressure ram the closure plug 10 can be subjected to a pressure force acting in the direction of the system axis 53. After insertion of the container part 8 equipped with the closure plug 10 in the intermediate position into the first and second processing chambers 50, 52 as far as a stop formed in each case by the pressure ram 92, the openings 56 and 57 are closed off. Subsequently, with a valve 68 open, the scavenging gas G is introduced at high pressure into the first processing chamber 50. The first processing chamber 50 is brought into a dry state in this way. After the closure of the valve 68, the scavenging gas G then flows through the container part 8 equipped with the closure plugs 10 in the intermediate position and expels, via the outlet 69, water situated in the container part 8 and in the second processing chamber 52. If gas bubbles rise from the outlet 69, this is an indication that the first and second processing chambers 50, 52 and the container part 8 no longer contain water. If a valve is installed in the outlet 69, it is possible, after the closure of the valve, for the supply of scavenging gas G to be stopped and for the positive pressure prevailing in the processing chambers 50, 52 to be dissipated. The cleaning brushes 72 are subsequently advanced and, by a rotational movement of rotary rings 70, the face surfaces on the face sides 4, 6 of the container 2 and the sealing surfaces of the flanges 13 are cleaned. After cleaning has been performed, the cleaning brushes 72 are retracted, and the pressure rams 92 are actuated, which pressure rams push the closure plugs 10 into the container 2 until the sealing surface of the flange 13 sets down on the respective face surface of the hollow cylindrical container part 8. After the sealing plugs 10 have been pushed in, welding heads 74 are advanced and, by a rotational movement of the rotary ring 70, the closure plug 10 is welded to the hollow cylindrical container part 8 along an annular weld seam 40 (see FIG. 2). As an alternative to this, the closure plug 10 and container part 8 may also be brazed with one another along an annular brazed seam. Instead of a cohesive connection of this type, a shrink-fit connection may also be provided by virtue of the ends of the container 2 being inductively heated and the closure plugs 10 being pushed into the ends that have been expanded in this way. After the ends have cooled, the closure plug is fixed in fluid-tight fashion in the container part 8. After the welding has been performed, the pressure rams 64 are retracted, the container 2 is received in a holder, and at least one of the processing chambers 50, 52 is axially displaced such that the container 2 can be withdrawn. In the exemplary embodiment as per FIGS. 4A and 4B, the two processing chambers 50, 52 are connected to one another rigidly, and in fluid-tight fashion with respect to the outside, by a connecting pipe 100. The connecting pipe 100 projects by way of its face-side ends into the first and second processing chambers 50 and 52 respectively. The container 2 with its closure plugs 10 inserted in an intermediate position is inserted into the connecting pipe 100. In the intermediate position, the interior 15 of the container 2 is fluidically connected to the exterior. The cylindrical container part 8 of the container 2 projects beyond the connecting pipe 100 at both sides. In the first and second processing chambers 50, 52, there are arranged an inlet pipe 102 and an outlet pipe 104 respectively, the central axes of which coincide with the system axis 53, and which form the inlet 66 and the outlet 69 for the scavenging gas G. The connecting pipe 100 is arranged between the inlet pipe 102, which issues into the first processing chamber 50, and the outlet pipe 104, which issues into the second processing chamber 52, with an axial spacing a to each, such that, between the face sides facing toward one another, there remains a first and a second free space 106 and 108 respectively. In the working position illustrated in FIGS. 4A and 4B, the inlet pipe 102 and connecting pipe 100, and the connecting pipe 100 and outlet pipe 104, are connected to one another in fluid-tight fashion by a first and a second sleeve 110 and 112 respectively, the sleeves being axially displaceable and mounted so as to be rotatable about the system axis 53, and form a rectilinear, relatively narrow scavenging chamber 113 which is fluidically separated from a first and a second working chamber 114, 115 respectively, in which the tools and drives required for the closure of the container 2 are situated, of the first and the second processing chamber 50, 52 respectively. The connecting pipe 100 is provided, on its inner circumference at its face-side end projecting into the first processing chamber 50, with an adjustable seal element 116, in the example an inflatable sealing ring, by which, after the container 2 has been inserted into the connecting pipe 100, a gap chamber 118 situated between the container 2 and the connecting pipe 100 can be closed such that the scavenging gas G flowing in the scavenging chamber 113 flows exclusively through the container 2, and the inlet pipe and outlet pipe 102 and 104 respectively are fluidically connected to one another exclusively via the container 2. Owing to the connecting pipe 100 connected in fluid-tight fashion to the processing chambers 50, 52, it is adequate for the gap to be closed by a single sealing element 116 in order to achieve the desired guidance of the scavenging gas G through the container 2. By a stroke-action cylinder 119 arranged in each of the first and second processing chambers 50, 52, it is possible for the first and second sleeve 110 and 112 respectively to be axially displaced such that the first and the second free space 106 and 108 respectively can be opened or closed with respect to the first and the second processing chamber 50, 52 respectively. Those ends of the inlet pipe 102 and of the outlet pipe 104 which project out of the processing chambers 50, 52 are provided, in each case, with a connection piece 120 onto which there is sealingly mounted a stroke-action cylinder 122 which, like the stroke-action cylinder 91 in the exemplary embodiment of FIGS. 3A and 3B, drives a pressure ram 124 which is displaceable axially in the direction of the system axis 53 and by which the closure plugs 10 can be pushed into their final position. A gas supply line 128 is connected via a valve 126 to the inlet pipe 102, via which gas supply line the scavenging gas G can be introduced at high pressure into the inlet pipe 102 in order to expel the water situated in the container 2. The water emerging into the outlet pipe 104 is then discharged via a water expulsion line 132 that can be closed off by a valve 130. The inlet pipe 102 and outlet pipe 104 are connected via two-way valves 134 and 136 to a bypass line 138 which connects the inlet pipe 102 and outlet pipe 104 to one another in a closed gas circuit. In the bypass line 138 there are arranged a pump 140 and a heating device 142 by which a heating gas H situated in the bypass line 138 can be pumped through the inlet pipe 102, the container 2 and the outlet pipe 104 in order thereby to dry the fuel rod 20 situated in the container 2. During the drying process, the valves 126 and 130 are closed. For the precise positioning of the container 2, the second sleeve 112 is provided with a radially extendable stop element 143, on which the container part 8 is seated by way of its lower face side 6. The first and second sleeves 110, 112 are provided in each case with an annularly encircling flange which serves as a support for the welding head 74 and the cleaning brush 72 and which is simultaneously configured as a rotary ring 70 which meshes with a pinion 146 driven by a motor 145, such that the cleaning brush 72 and welding head 74 can be rotated about the system axis 53. By use of temperature sensors 150, pressure sensors 152 and moisture sensors 154, the temperature T, the pressure P and the humidity X in the inlet pipe 102 and in the outlet pipe 104 are measured in order to be able to detect the progression of the drying process. The drying process is ended when the moisture content in the heating gas H attains a final value at which the moisture content rises no further and there is accordingly no longer any liquid water situated in the gas circuit. For a known volume of the container 2, it is possible for the absolute amount of water situated within the container 2 in the gaseous phase to be determined, and for adherence to specifications with regard to the maximum admissible water content to be reliably monitored. To achieve complete evaporation of the water, the volume of the gas circuit is several times greater than the volume of the hollow chamber situated in the container 2 when a fuel rod 20 has been inserted therein. The mode of operation of the device during the encapsulation of a defective fuel rods 20 provided with openings in the region of its ends will be explained in more detail below. Firstly, the device is opened. For this purpose, the upper stroke-action cylinder 122 arranged on the inlet pipe 102 is dismounted from the device. Before the dismounting process, the first and second sleeves 110 and 112 have been displaced into the position shown in FIGS. 4A and 4B, in which they produce a fluid-tight connection between the inlet pipe 102 and the connecting pipe 100 and between the connecting pipe 100 and the outlet pipe 104, such that the water that infiltrates, as a result of the dismounting of the, into the scavenging chamber 113 formed from the inlet pipe 102, connecting pipe 100 and outlet pipe 104 cannot pass into the processing chambers 50, 52. Furthermore, the working chamber 114, which surrounds the scavenging chamber 113, of the processing chambers 50, 52 is permanently charged with scavenging gas (not illustrated) in order to thereby additionally prevents the infiltration of water. The container 2 loaded with the fuel rod 20 is subsequently inserted, by a handling tool not illustrated in FIG. 4A, into the connecting pipe 100 until the container sets down on the extended stop element 143. Thereafter, the stroke-action cylinder 122 is mounted in fluid-tight fashion onto the connection piece 120 again. The processes explained below take place with the device in a working position as illustrated in FIGS. 4A and 4B. After the stroke-action cylinder has been mounted, scavenging gas G is, by virtue of the valve 126 being opened, introduced at high pressure into the inlet pipe 102 and forced through the interior, and with a valve 136 open, the water situated in the scavenging chamber 113 is initially expelled. Through subsequent pressurization of the inflatable seal 116 with a compressed gas, the gap between the connecting pipe 100 and container part 8 is closed, such that the scavenging gas G flows exclusively through the container 2, with water being expelled from the latter in this way. During the process, via openings that may have previously been provided on the top and bottom ends of the fuel rod 20 (not illustrated), water is also removed from the fuel rod 20. The gas flow is maintained until the humidity X measured by the humidity sensor 154 arranged on the outlet pipe 104 falls below a predefined threshold value and signals an adequate level of dryness. Subsequently, any water still situated in the bypass line 138 is expelled by virtue of the valve 136 being opened and the pump 140 being set in operation. The valves 128 and 130 are subsequently closed. Subsequently, for the purpose of drying the fuel rod 20, the heating device 140 is set in operation. The pump 140 drives the scavenging gas G, which is situated in the scavenging chamber 113, via the heating device 142. In the heating device 142, the scavenging gas G is heated and passes, as heating gas H, via the thermally insulated water expulsion line 132 to the scavenging chamber 113 and to the lower closure plug 10 of the container 2. From here, the heating gas H passes into the interior of the container 2 and to the filter element 18. By virtue of the heating gas H being conducted in this direction, residual water is blown out of the filter element 18, such that the heating gas H can pass through more easily. By the heating gas H flowing along the fuel rod 20, the water situated therein in the fuel matrix is evaporated, is released into the container 2 via the openings provided previously on the top and bottom ends of the fuel rod 20, and is transported with the heating gas H into the scavenging chamber 113 via the upper closure plug 10. From there, the moisture-laden heating gas H is supplied via the valve 134 back to the pump 140. The gas circuit is thus closed. The temperature T of the heating gas H is detected by the temperature sensors 150 and is fed, via a distributor 156, to an evaluation and control unit which is not illustrated in the figures and which controls the pump 140 and heating device 142 and regulates the temperature T to a predefined target value. The evaluation and control unit also controls the other active components in the device—valves, pump, processing devices, stroke-action cylinder, motor drives etc. The passage of the heating gas H in the container 2 is monitored by the pressure sensors 152. The heating gas H is circulated in the gas circuit until the upper and lower humidity sensors 154 register adequate saturation. This is an indication that all of the water in the fuel matrix has evaporated and no further water is being released. At this point, the heating and circulation of the heating gas H can be terminated. By opening the valve 126, fresh scavenging gas G can flow in. By cyclically opening and closing the valve 130, the scavenging gas G is alternately discharged via the water expulsion line 132 or conducted through the container 2. Finally, the valves 130, 134, 136 are closed and pressure equalization between the scavenging chamber 113 and working chamber 114, 115 of the processing chambers 50, 52 is performed. The valve 126 is subsequently closed. Thereafter, the first sleeve 110 is pushed onto the connecting pipe 100 by the stroke-action cylinder 122, such that the free space 106 is open to the interior of the first processing chamber, and the brush 72 and welding head 74 situated at the level of the face side 4 of the container part 8. Following the actuation of the brush advancement, that is to say the application of the brush 72 to the contact surfaces to be cleaned, the first sleeve 110 is set in rotation, and thus the brush 72 is also moved around the container 2, by virtue of the pinion 146 being driven. After the cleaning process, the brush 72 is retracted into the initial position again. Subsequently, the stroke-action cylinder 122 is actuated, and, by the piston rod thereof, the upper closure plug 10 is pushed onto the container part 8. Thereafter, the welding head 74 is advanced radially and moved around the container 2 by rotation of the first sleeve 110. The working position is illustrated in FIG. 5A. After the welding process, the upper welding head 74 is also moved into the initial position again, and the sleeve 110 is also moved into the initial position again. The cleaning and welding in the second processing chamber 52 subsequently takes place analogously, wherein, before the displacement of the second sleeve 112 into the position required for the cleaning and welding processes, the stop element 143 is retracted. FIG. 5B likewise shows a situation in which the welding head 74 is situated in a working position. For the withdrawal of the closed container 2, the device is opened. For this purpose, the pressure ram 124 of the upper stroke-action cylinder 122 is retracted and is thereafter dismounted from the device. As a result of the dismounting process, the scavenging chamber 113 of the device is flooded with water. The container 2 is then gripped by a bar-type tool, the inflatable sealing element 116 is ventilated, and the pressure ram 124 of the lower stroke-action cylinder 122 is moved into the initial position again. The drying process illustrated in conjunction with FIGS. 4A, 4B, 5A, and 5B may basically also be performed in the case of the device illustrated in FIGS. 3A and 3B by virtue of the device being supplemented by the heating circuit illustrated in FIGS. 4A, 4B, 5A and 5B. |
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description | FIG. 1 is a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A side wall 16 extends from bottom head 12 to top head 14. Side wall 16 includes a top flange 18. Top head 14 is attached to top flange 18. A cylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud 20 is supported at one end by a shroud support 24 and includes a removable shroud head 26 at the other end. An annulus 28 is formed between shroud 20 and side wall 16. A pump deck 30, which has a ring shape, extends between shroud support 24 and RPV side wall 16. Pump deck 30 includes a plurality of circular openings 32, with each opening housing a jet pump assembly 34. Jet pump assemblies 34 are circumferentially distributed around core shroud 20. Heat is generated within core 22, which includes fuel bundles 36 of fissionable material. Water circulated up through core 22 is at least partially converted to steam. Steam separators 38 separates steam from water, which is recirculated. Residual water is removed from the steam by steam dryers 40. The steam exits RPV 10 through a steam outlet 42 near vessel top head 14. The amount of heat generated in core 22 is regulated by inserting and withdrawing control rods 44 of neutron absorbing material, such as for example, hafnium. To the extent that control rod 44 is inserted into fuel bundle 36, it absorbs neutrons that would otherwise be available to promote the chain reaction which generates heat in core 22. Control rod guide tubes 46 maintain the vertical motion of control rods 44 during insertion and withdrawal. Control rod drives 48 effect the insertion and withdrawal of control rods 44. Control rod drives 48 extend through bottom head 12. Fuel bundles 36 are aligned by a core plate 50 located at the base of core 22. A top guide 52 aligns fuel bundles 36 as they are lowered into core 22. Core plate 50 and top guide 52 are supported by core shroud 20. FIG. 2 is a perspective view, with parts cut away, of jet pump assembly 34. An inlet nozzle 54 extends through side wall 16 of RPV 10 and is coupled to a jet pump assembly 34. Jet pump assembly 34 includes a thermal sleeve 56 that extends through nozzle 54, a lower elbow (only partially visible in FIG. 2), and a riser pipe 58. Riser pipe 58 extends between and substantially parallel to shroud 20 and RPV side wall 16. Riser braces 60 stabilize riser pipe 58 within RPV 10. Riser pipe 58 is coupled to two jet pumps 62 by a transition assembly 64. Each jet pump 62 includes a jet pump nozzle 66, a suction inlet 68, an inlet mixer 70, and a diffuser 72. Jet pump nozzle 66 is positioned in suction inlet 68 which is located at a first end 74 of inlet mixer 70. Diffuser 72 is coupled to a second end 76 of inlet mixer 72 by a slip joint 78. Because of their large size, both inlet mixer 70 and diffuser 72 are formed from multiple cylindrical sections. Circumferential weld joints 80 join the cylindrical sections together. FIG. 3 is a side view of an inspection apparatus 82 in accordance with an embodiment of the present invention. Inspection apparatus 82 includes a frame structure 84 configured to attach to top flange 18 of reactor pressure vessel 10. Frame structure 84 includes an elongate frame member 86, an attachment frame member 88 extending from a first end portion 90 of elongate frame member 86, and a support wheel 92 coupled to a second end portion 94 of elongate frame member 86. Attachment frame member 88 is configured to attach to top flange 18 of reactor pressure vessel 10 when reactor pressure vessel top head 14 is removed. Particularly, attachment frame member 88 includes a bolt opening 96 sized to receive a RPV top head bolt 98. When inspection apparatus 82 is installed in RPV 10, support wheel 92 engages side wall 16 of RPV 10. A lifting eye 100 is attached to first end portion 90 of frame member 86 to facilitate lifting inspection apparatus 82 into position in RPV 10. An elongate track 102 is attached to frame member 86. Track 102 extends from first end portion 90 to second end portion 94 of frame member 86. A trolley 104 is movably coupled to track 102 and is movable along the length of track 102. A first motor 106 is attached to trolley 104 and is operatively coupled to track 102. Operation of first motor 106 causes trolley 104 to move along track 102. A second motor 108 is mounted on trolley 104 and is operatively coupled to a first end 110 of a flexible drive cable 112. Particularly, second motor 108 is coupled to a gear box 114 which is coupled to a drive shaft 116 by a shaft coupling 118. Drive shaft 116 is attached to first end 110 of flexible drive cable 112. A tool head 120 is coupled to a second end 122 of flexible cable 112. Operation of second motor 108 rotates drive cable 112 around the longitudinal axis of drive cable 112. Operation of first motor 106 causes trolley 104 to move along track 102 which causes tool head 120 to be moved to various positions in RPV 10. Typically, frame structure 84 is attached to RPV 10 so that frame member 86 is positioned vertically along RPV side wall 16. Consequently, the movement of trolley 104 along vertically orientated track 102 changes the vertical location of tool head 120 in RPV 10. A motion controller (not shown) is operatively coupled to trolley 104 and monitors the movement and position of tool head 120. Any known suitable motion controller can be used. FIG. 4 is a side view of tool head 120 of inspection apparatus 82. Tool head 120 includes a first portion 124 coupled to a second portion 126 by a first flexible U-joint 128, and a probe subassembly 130 coupled to second portion 126 by a second flexible U-joint 132. A calibration sleeve 133 is coupled to the end of probe subassembly 130. Probe subassembly 130 includes a probe housing 134 and three probe arms 136 (one shown) pivotably coupled to housing 134 at a first end 138 of each probe arm 136. Each probe arm 136 includes a sensor 140 coupled to a second end 142 of each probe arm 136. Inspection apparatus 82 includes an insertion subassembly 144 that couples to suction inlet 68 of jet pump 62. Insertion subassembly 144 is sized to receive tool head 120 and connected flexible drive cable 112 and guide tool head 120 into jet pump 62 through suction inlet 68. Insertion subassembly 144 includes an elongate tube portion 146, a location cone 148 attached to a first end 150 of tube portion 146, and an attachment clamp 152 attached to a second end 154 of tube portion 146. Attachment clamp 152 is configured to clamp to jet pump 62 at suction inlet 68. Particularly, attachment clamp 152 includes a plate 156 coupled to tube portion 143. Plate 156 includes a notch 158 sized to receive a side wall 160 of jet pump 62. Attachment clamp 152 further includes an engagement arm 162 pivotably coupled to plate 152, and a ratchet assembly 164 coupled to engagement arm 162. Engagement arm 162 is moved into engagement with jet pump side wall 160 by tightening ratchet assembly 164. Referring to FIGS. 5 and 6, probe arms 136 are pivotably movable between a first position (shown in FIG. 5) where probe arms 136 are parallel to the longitudinal axis of probe subassembly 130, and a second position (shown in FIG. 6) where probe arms 136 are at an angle to the longitudinal axis of probe subassembly 130. In the second position, sensors 140 contact the inner surface of jet pump 62 to inspect weld joints 80. A pneumatic cylinder 166, located in tool head second portion 126 is operatively coupled to probe arms through probe support arms 168. Support arms 168 are pivotably coupled to probe arms 136 between a first end 170 and a second end 172 of probe arms 136. Support arms 168 are also slidably coupled to probe housing 134 and operatively coupled to pneumatic cylinder 166. The activation of pneumatic cylinder 166 causes support arms 168 to slide along a track 174 attached to probe housing 130 which causes probe arms 136 to move between the first position (see FIG. 5) and the second position (see FIG. 6). Sensors 140 are ultrasonic transducer probes or eddy current transducer probes. Particularly, probe subassembly 130 can contain any combination of ultrasonic transducer probes and/or eddy current transducer probes depending on the desired inspection, i.e., volumetric inspection and/or surface inspection. Calibration sleeve 133 includes a notch on the inner surface to check the parameters of an eddy current signal, and a notch on the outer surface to check the parameters of an ultrasonic transducer signal to ensure optimal working parameters during weld inspection. A complete calibration of sensors 140 is done before installation of inspection apparatus 82 into jet pump 62. To inspect weld joints 80, inspection apparatus 82 is installed in RPV 10 by securing attachment frame member 88 to RPV top flange 18 with a top head bolt 98. After installation, elongate frame member 86 is in a vertical position with support wheel 92 engaging RPV side wall 16. Insertion subassembly 144 is installed on jet pump 62 by positioning tube portion 146 in suction inlet 68 with jet pump side wall 160 located in notch 158 of plate 156. Ratchet assembly 164 is then tightened to move engagement arm into engagement with sidewall 160 to clamp insertion subassembly 144 in place. Probe subassembly 304 is then positioned adjacent the jet pump weld joint 80 that is to be scanned by activating first motor 106 to move trolley 104 along track 102 causing flexible drive cable 112 and tool head 120 to extend from the bottom of frame structure 84 and move vertically downward toward insertion subassembly 144 mounted on jet pump 62. Tool head 130 is inserted into location cone 148 and is guided through tube portion 146 and into jet pump 62. At the predetermined vertical position adjacent to weld joint 80, first motor 106 is stopped. Probe arms 136 are then extended by activating pneumatic cylinder which causes support arms 168 to slide along track 174 which causes probe arms 136 to pivot into scanning position with sensors 140 in contact with the inner surface of side wall 160 of jet pump 62. To scan weld joint 80, second motor 108 is activated to rotate flexible drive cable 112 around its axis which causes sensors 140 to move circumferentially around weld joint 80. A data acquisition system (not shown) is used to record the scan data from sensors 140. Second motor 108 is stopped when the scan is complete. Probe arms 136 are then retracted at least partially so that sensors 140 are not in contact with side wall 160. First motor then actuated to move trolley 104 which causes probe subassembly 130 to move to a different location adjacent an other weld joint 80. Probe arms 136 are then extended as described above and the desired weld joint 80 is scanned as described above. To remove inspection apparatus 82 from RPV 10, probe arms 136 are fully retracted and trolley 104 is moved vertically upward to cause tool head 130 to exit jet pump 62 through tube portion 146 of insertion subassembly 144. After tool head 130 has been fully retracted, insertion subassembly 1044 is removed from jet pump 62 by loosening ratchet assembly 164 which causes engagement arm 162 to move away from side wall 160 of jet pump 62. Insertion subassembly 144 can then be lifted from jet pump 62. Frame structure 84 is then removed by removing top head bolt 98 and lifting frame structure from RPV 10 by utilizing lifting eye 100. The above described inspection apparatus 82 performs ultrasonic and/or eddy current examinations of jet pump weld joints 80 from inside jet pump inlet mixer 70 and diffuser 72 in nuclear reactor 10 without having to disassemble jet pump 62. Also inspection apparatus 82 is remotely operable and can scan multiple weld joints 80 with a single insertion into jet pump 62. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. |
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056365128 | claims | 1. A nuclear thermal rocket engine comprising: a rocket propellant source; a nuclear reactor including an inlet for receiving propellant from said propellant source, fuel assemblies for heating said propellant, an outlet coupled to said fuel assemblies for discharging said heated propellant therefrom and a recycling port disposed between said fuel assemblies and said outlet; a primary feed system including a line coupling said rocket propellant source to said nuclear reactor inlet and a pump coupled to said line for pumping said propellant through said line; and an auxiliary feed system including a bypass line having an inlet receiving heated propellant from said recycling port, a first outlet for returning a first portion of said heated propellant to said rocket propellant source and a second outlet for returning a second portion of said heated propellant to a fluid line between said nuclear reactor inlet and said fuel assemblies, said auxiliary feed system further including means for withdrawing heat from propellant flowing through said bypass line. a rocket propellant source; a nuclear reactor including an inlet for receiving propellant from said propellant source, fuel assemblies for heating said propellant, an outlet coupled to said fuel assemblies for discharging said heated propellant and a recycling port disposed between said fuel assemblies and said outlet; a primary feed system including a line coupling said rocket propellant source to said nuclear reactor inlet and a pump coupled to said line for pumping said propellant through said line; and an auxiliary feed system including a bypass line having an inlet for receiving heated propellant from said recycling port and an outlet for directing a substantial portion of said heated propellant to said primary feed line downstream of said propellant source and upstream of said nuclear reactor inlet, said auxiliary feed system further including means for withdrawing heat from propellant flowing through said bypass line. a rocket propellant source; a nuclear reactor including an inlet for receiving propellant from said propellant source, fuel assemblies for heating said propellant, an outlet coupled to said fuel assemblies for discharging said heated propellant and a recycling port disposed between said fuel assemblies and said outlet; a primary feed system including a line coupling said rocket propellant source to said nuclear reactor inlet and a pump coupled to said line for pumping said propellant through said line; an auxiliary feed system including a bypass line having an inlet for receiving heated propellant from said recycling port and an outlet for directing a portion of said heated propellant to said primary feed line, said auxiliary feed system further including means for withdrawing heat from propellant flowing through said bypass line; and a controllable valve coupled to said bypass line between said turbine and said recuperator, the valve being adapted to selectively control propellant flow such that a first: portion of said propellant flows through said recuperator to said radiator and a second portion of said propellant flow bypasses said recuperator and flows directly to said radiator. 2. The rocket engine of claim 1 further including a recuperator coupled to said bypass line and to said primary feed line between said pump and said nuclear reactor inlet, the recuperator being adapted to transfer heat from propellant flowing through said bypass line to propellant flowing through said primary feed line. 3. The rocket engine of claim 1 further including an electric pump coupled to said primary feed line between said pump and said propellant source for receiving said propellant from said propellant source and pumping said propellant to said nuclear reactor inlet, said auxiliary feed system providing power to said electric pump. 4. The rocket engine of claim 2 wherein said auxiliary feed system includes a turbine and a compressor coupled to said bypass line for pumping said second portion of said heated propellant from said recycling port to said nuclear reactor, said first portion of said heated propellant being allowed to flow back into said propellant source. 5. The rocket engine of claim 4 further including a valve coupled to said bypass line between a discharge side of said turbine and said recuperator, said valve being adapted to eject a portion of said propellant into space to decrease fluid pressure at said discharge side of said turbine. 6. A nuclear thermal rocket engine comprising: 7. The rocket engine of claim 6 further including a turbine and a compressor coupled to said bypass line for pumping propellant from said recycling port to said primary feed line. 8. The rocket engine of claim 6 further including a recuperator coupled to said primary feed line between said pump and said nuclear reactor inlet and to said bypass line between said turbine and said compressor, the recuperator being adapted to transfer heat from propellant flowing through said bypass line to propellant flowing through said primary feed line. 9. The rocket engine of claim 8 wherein the withdrawing means includes a radiator for withdrawing a substantial portion of the heat from said propellant and discharging said portion of said heat into space. 10. A nuclear thermal rocket engine comprising: |
claims | 1. A segmented lattice rack for storing fuel components from nuclear power stations, having walls made of plates, the plates being orthogonally joined, forming a lattice defining numerous cell cavities, longitudinally coupled forming a sandwich, comprising: a) a central part of a material formed from neutronic poisons, coinciding with an active part of the stored fuel component, comprising: a plurality of intermediate units ( 4 )-( 8 ) which in one direction have successive parallel plates grooved on both sides, over which other grooved orthogonal plates are orthogonally installed and in both directions, which coincide with the center of the former and protrude above and below; where said lattices are coupled at a relative displacement of 90xc2x0, such that on one plane there is a discontinuity in height in one or other direction, but when piled, rotated with respect to each other, they couple forming conduits; and two end units ( 3 ) and ( 9 ), formed by parallel plates with a width equivalent to the difference between the two plates of the central units, arranged in a plane, so that they overlap the protruding part of the former, to finish the assembly on a same plane, closing the conduits; b) two end zones coinciding with a non-active part of the stored radioactive component, formed by two sets of lattices ( 1 )( 2 ) and ( 10 )( 11 ), the latter welded to a cover or end plate, providing rigidity to the rack. 2. The rack of claim 1 , in which the plates are joined to each other by angle welding ( 17 ) forming a rigid assembly. claim 1 3. The rack of claim 1 , in which the lattices is tied together by means of thin, pretensioned strips ( 14 ) welded to the lower and upper lattices. claim 1 4. The rack of claim 1 , in which the plates of the central part are of stainless steel, and are fitted forming a double wall ( 18 )( 19 ) having a gap filled with a material ( 20 ) chosen from the group comprising boron treated water and Boral dispersion of boron carbide in aluminium. claim 1 5. The rack according to claim 1 , in which the plates of the central part comprise an assembly formed by a stainless steel plate ( 21 ) and a boron treated steel plate ( 22 ). claim 1 6. The rack of claim 1 , in which the plates of the central part are of boron treated steel. claim 1 7. The rack of claim 1 , further comprising a lower part serving as a support to the bottom of the pool, in which plates of this area are of normal stainless steel, joined to each other and to adjacent components by means of welding. claim 1 |
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