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claims | 1. A method for fabricating a reactor component from a zirconium alloy comprising:securing a sufficient quantity of a zirconium alloy including 0.6-1.2 wt % Nb; 0.2-0.5 wt % Fe; 0.5-1.2 wt % Sn; and no more than 70 ppm Ni; the balance of the zirconium alloy being Zr and impurities;forging a slab of the zirconium alloy;thermally conditioning the slab;forming the reactor component from the slab using a final cold work process; andcompleting the reactor component, without additional annealing of the slab subsequent to the final cold work process, to obtain a final reactor product having residual cold work stress. 2. The method for fabricating a zirconium alloy strip for use as reactor component from a zirconium alloy according to claim 1, comprising:obtaining an ingot having an alloy composition including 0.6-1.2 wt % Nb, 0.2-0.5 wt % Fe, 0.5-1.2 wt % Sn and no more than 70 ppm Ni, the balance of the zirconium alloy being Zr and impurities;the ingot having an initial diameter Di and a mass Mi sufficient for forming the intended component;bringing the ingot to a hot working temperature THW;forging an initial slab from the heated ingot while maintaining the alloy at or near the hot working temperature with the thickness of the initial slab Ds being between 30% and 10% of the initial diameter of the ingot; bringing the initial slab to a first hot rolling temperature THR1;hot rolling the initial slab to form an intermediate slab with the thickness of the intermediate slab Dint being between 30% and 10% of the thickness of the initial slab;conditioning the intermediate slab at a first conditioning temperature Tcl, to adjust the microstructure and/or reduce stress;bringing the intermediate slab to a second hot rolling temperature THR2;hot rolling the intermediate slab to form a strip preform with the thickness of the strip preform Dsp being between 95% and 50% of the thickness of the intermediate slab;conditioning the strip preform to adjust the microstructure and/or reduce stress;β-quenching the strip preform;holding the quenched strip preform at a conditioning temperature Tc for a conditioning period; hot rolling the conditioned strip preform;annealing the rolled strip preform;cold rolling the annealed strip preform to achieve a thickness reduction of 15% to 50%;annealing the cold rolled strip preform in a non-oxidizing atmosphere;cold rolling the annealed cold rolled strip preform to a final thickness; andcutting the strip preform to the final strip dimensions. 3. The method for fabricating a reactor component from a zirconium alloy according to claim 1, wherein:the residual cold work stress is at least 2%. 4. The method for fabricating a reactor component from a zirconium alloy according to claim 3, wherein:the residual cold work stress does not exceed 10%. 5. The method for fabricating a reactor component from a zirconium alloy according to claim 1, wherein: the residual cold work stress is at least 10%. 6. The method for fabricating a reactor component from a zirconium alloy according to claim 1, wherein:the residual cold work stress is at least 25%. |
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description | The invention relates generally to a storage phosphor plate for the storage of X-ray information and a corresponding system or device for reading out the X-ray information. Furthermore, the invention relates to a corresponding radiography module or cassette for housing a system and storage phosphor plate for reading out the X-ray information. Generic storage phosphor plates and devices are used, in particular for medical purposes, in the field of computer radiography (CR). Here, X-rays are recorded in so-called storage phosphor layers, whereby the X-ray radiation passing through an object, for example a patient, is stored as a latent picture in the storage phosphor layer. In order to read out the stored picture, the storage phosphor layer is irradiated with stimulation light, and so stimulated into emitting emission light, the intensity of which is dependent upon the respectively stored picture information. The emission light is collected by an optical detector and converted into electric signals which can be further processed as required and shown on a monitor or on a corresponding display unit, such as eg. a printer. In certain applications, the storage phosphor layer is applied to a support layer which is partially transparent for the stimulation light so that the storage phosphor layer can be stimulated by irradiating with stimulation light from the side of the support layer. The problem can arise here that part of the stimulation light in the region of the upper boundary surface between the support layer and storage phosphor layer is reflected or dispersed back into the support layer by reflection and/or dispersion and reflected back in the direction of the storage phosphor layer on the lower boundary surface of the support layer. In such cases, in particular with support layers with a large thickness, regions of the storage phosphor layer are stimulated which are so far away from the region of the storage phosphor layer currently to be read out that the emission light emitted from them can no longer be collected. The consequence of this so-called advance read-out of individual regions is that with a subsequent, actual read-out of these regions, a reduced intensity of the emission light is obtained, and this leads overall to a detrimental effect upon the picture quality. It is the objective of the invention to provide a storage phosphor plate and a corresponding device and a radiography module for reading out this type of storage phosphor plate with which an improved picture quality can be achieved. The above and other problems in the prior art are solved by use of a storage phosphor plate for the storage of X-ray information, including a storage phosphor layer which stores the X-ray information and can be stimulated by stimulation light into emitting emission light, and a support layer on which the storage phosphor layer is located, the support layer being partially transparent for the stimulation light, and having a thickness d and an absorption coefficient k for the stimulation light, where (k times d)≧0.2. Due to the combination of a specific thickness of the support layer with the absorption properties for stimulation light of the same according to the invention, an efficient weakening of the light beams of the stimulation light relevant to the advance read-out is achieved, and so the picture quality improved. In particular, with relatively large thicknesses of the support layer with which the effect of the advance read-out has a particularly unfavourable effect upon the picture quality, using a support material with relatively small absorption coefficients, the advance read-out can be prevented, or at least greatly reduced. By using this type of relatively weakly absorbent support materials, the costs of appropriate support materials can be substantially reduced. In a preferred embodiment of the invention it is proposed that the thickness of the support layer comes within the range of between 1 mm and 10 mm. In this thickness range, the carrying capacity and mechanical stability of the support layer is sufficient for most applications. Any distortion of the storage phosphor layer positioned on the support layer is in this way sufficiently reduced so as to prevent any damage to the phosphor layer. The strongly pronounced effect of the advance read-out in this thickness range is prevented, or at least reduced, by the choice of the absorption coefficient of the support layer for stimulation light according to the invention. Preferably, the storage phosphor plate is self-supporting. The thickness of the support layer is chosen here as regards its length/width ratio such that it can be held at the edges along with the storage phosphor layer positioned on top of it, without it becoming substantially distorted. In this way, any additional mechanically stabilising layers or supports can be dispensed with so that the storage phosphor layer can be irradiated, unimpeded, with stimulation light on its lower side, i.e. from the transparent support layer. Preferably, the absorption coefficient of the support layer for the stimulation light is less than 1 mm−1 and greater than 0.02 mm−1. This makes it possible to use materials which require a relatively small degree of light weakening by absorption for the stimulation light, and are therefore correspondingly inexpensive. In a particularly preferred embodiment of the invention, the support layer includes a colouring which can partially absorb the stimulation light. This can be achieved, for example, by selecting an appropriately coloured glass or synthetic material for the support layer. The colouring here can either be distributed evenly over the whole thickness of the support layer or be contained in at least a first partial layer of the support layer. With the latterly specified alternative, the support layer preferably has two layers, namely one layer which does not substantially absorb the stimulation light, and an additional layer of colouring which partially absorbs the stimulation light. The desired absorption coefficient of the support layer can then be achieved simply by an appropriate choice of coloured layer. Preferably, the support layer has a lower and an upper boundary surface, the storage phosphor layer being located on the upper boundary surface and the at least one first partial layer being located in the region of the upper and/or lower boundary surface of the support layer. By locating the first partial layer in the region of the upper or lower boundary surface of the support layer, it is possible to particularly efficiently avoid or reduce the re-entry of dispersed radiation into the support layer or the reflection of the dispersed radiation on the lower boundary surface. In one variation of the invention, it is proposed that the support layer can partially absorb the stimulation light dependent upon polarisation of the same. This variation is advantageous when using polarised stimulation light, such as laser light. The absorption properties of the support layer are chosen here such that the originally polarised stimulation layer can pass through the support layer without any loss, and can stimulate the storage phosphor light located on the same into emitting emission light. The stimulation light thus dispersed on the upper boundary surface of the support layer is, however, no longer polarised as it was originally due to the dispersion process, and is absorbed by the support layer so that advance read-out of the storage phosphor layer is reduced or prevented. The absorption coefficient for stimulation light in the sense of the invention identifies in this variation the absorption coefficient for that portion of the stimulation light which does not have a preferred polarisation direction, i.e. is polarised isotropically. Preferably, the support layer has at least a second partial layer in which the stimulation light can be partially absorbed dependent upon polarisation of the same. The second partial layer is preferably located in the region of the lower boundary surface of the support layer. In this way, it is particularly easy to create a polarisation-dependent absorbent support layer. It is also preferred that the storage phosphor layer comprises a large number of oblong, in particular needle-shaped storage phosphor particles. These so-called needle phosphors are characterised by a particularly high intensity of stimulated emission light and so by a particularly high picture quality. Corresponding storage phosphor plates are also called Needle Image Plates (NIP). With the device according to the invention for reading out from the storage phosphor layer, the irradiation device for irradiating the storage phosphor layer with stimulation light is disposed on the side of the support layer facing away from the storage phosphor layer. The storage phosphor layer is therefore irradiated with stimulation light from the upper boundary surface of the support layer. The detection device for collecting emission light is preferably disposed on the side of the support layer facing towards the storage phosphor layer. In this way it is possible to carry out an efficient read-out of the storage phosphor layer in transmission geometry. In this way, a particularly high picture quality is achieved, with at the same time a very compact device, in particular in connection with oblong, needle-shaped storage phosphor particles which act like small light conductors for the stimulation and/or emission light. Further features and advantages of the invention are given in the following description of preferred embodiments and examples of applications, reference being made to the attached drawings, not necessarily drawn to scale. FIG. 1 shows a first example of an embodiment of the invention. The storage phosphor plate 1 includes a support layer 3 and a storage phosphor layer 2 located on top of the support layer. The storage phosphor layer 2 is preferably in the form of a so-called needle phosphor layer which includes a large number of oblong, in particular needle-shaped, storage phosphor particles. An irradiation device 6, in particular a laser or a laser diode line, serves to irradiate the storage phosphor layer 2 with stimulation light 4 which can stimulate the storage phosphor layer 2 into emitting emission light 5, the intensity of which is dependent upon the X-ray information stored in the storage phosphor layer 2. The emission light 5 emitted is detected with a detection device 7, in particular a photomultiplier or a line detector. The irradiation device 6 and the detection device 7 are preferably combined in a reading head (scan head) which is moved over the storage phosphor plate 1 in conveyance direction T so that the X-ray information stored in the storage phosphor layer 2 is successively read out. Alternatively however, the reading head can also be fixed. In this case, the storage phosphor plate 1 is moved past the reading head. The reading head is preferably in the form of a so-called line scanner, with which, at a particular point in time, one whole line of the storage phosphor layer 2 is respectively read out. In this case, the irradiation device 6 has a line light source, in particular in the form of laser diodes arranged in a line, and the detection device 7 includes a large number of light-sensitive detectors, in particular a photo diode or CCD array, arranged in a line. The support layer 3 is partially transparent for the stimulation light 4 so that part of the stimulation light 4 entering into the support layer 3 finally strikes the lower side of the storage phosphor layer 2, and can be stimulated into emitting emission light 5. However, only part of the stimulation light 4 striking the storage phosphor layer 2 is absorbed. Other parts of the stimulation light 4 are reflected on the upper boundary surface 11 of the support layer 3 or are dispersed on the storage phosphor layer 2, and partially arrive back at the support layer 3. These portions are shown for example in FIG. 1 by means of a first light beam 4′. The first light beam 4′ strikes the lower boundary surface 10 of the support layer 3, is at least partially reflected back to the storage phosphor layer 2, and finally strikes the lower side of the storage phosphor layer 2 once again. In the region where the reflected stimulation light 4′ strikes, the storage phosphor layer 2 is also stimulated into emitting emission light which, however, can not be collected by the detection device 7 due to the limited space of its aperture. The consequence of this so-called advance read-out is that the intensity of the emission light collected in a subsequent, actual read-out process in this region is lowered, and because of this, the quality of the X-ray picture read out is reduced. In order to reduce or avoid advance read-out, the support layer 3 is designed in such a way that it has a specific absorption coefficient k for the stimulation light 4 and 4′, and a specific thickness d, where the product of the thickness d and the absorption coefficient k is greater than or equal to 0.2, mathematically expressed as (k times d)≧0.2. The typical thickness d preferably lies within the range of between 1 and 10 mm. The absorption coefficient k for the stimulation light preferably lies within the range of between 0.02 and 1 mm−1, in particular between 0.02 and 0.4 mm−1. The maximum intensity of the stimulation light typically lies within the range of between 620 nm and 700 nm, in particular approximately 680 nm. With the above selected values for the thickness d and the absorption coefficient k, the first light beams 4′ which strike the lower boundary surface 10 of the support layer 3 at an angle α, which is greater than or equal to the limit angle of the total reflection, are weakened so that advance read-out caused by these first light beams 4′ is prevented. For a support layer 3 made from glass the limit angle of the total reflection is 41.8°. In this first embodiment, the support layer 3 is in the form of a glass plate which includes colouring which partially absorbs the stimulation light 4 and 4′. The colouring is chosen here such that light can be absorbed either in broad bands or only in certain wavelength regions. Suitable absorbent glass materials can be obtained, for example, from the companies Saint Gobain Glass (eg. glass type SGG Parsol) or Schott (eg. glass type NG11). With the second embodiment shown in FIG. 2, the colouring which partially absorbs the stimulation light 4 is contained in a first partial layer 8 of the support layer 3. The effectiveness of this type of support layer 3 design in avoiding advance read-out is substantially identical here to the first embodiment shown in FIG. 1. In the second embodiment too the product of the thickness d of the support layer 3 and the absorption coefficient k of the support layer 3 for stimulation light 4 is greater than or equal to 0.2. The absorption coefficient k identifies here the absorption behaviour of the whole support layer 3, and not only that of the absorbent colouring layer in the first partial layer 8. In this embodiment, the first partial layer 8 is located in the region of the lower boundary surface 10 of the support layer 3. Alternatively or in addition, the first support layer 8 can also be disposed in the region of the upper boundary surface 11 of the support layer 3. With the examples shown in FIGS. 1 and 2, the stimulation light 4 required directly for the read-out of the storage phosphor layer 3 in addition to the stimulation light 4′ reflected or dispersed on the upper boundary surface 11 is weakened by means of the absorbent support layer 3. In order to reduce or compensate this effect, the output of the irradiation device 6 and so also the intensity of the stimulation light 4 is correspondingly increased. With the third embodiment shown in FIG. 3, the support layer 3 includes a second partial layer 9 which can absorb the stimulation light 4 dependent upon polarisation of the same. The stimulation light produced by the irradiation device 6, in particular a laser or a laser diode line is linearly polarised and can substantially pass the second partial layer 9 without any absorption loss. Due to the dispersion of part of the stimulation light 4 in the storage phosphor layer 2, the polarisation of the light beams 4′ dispersed back into the support layer 3 is changed. The dispersed light is thus isotropically, i.e. direction-independently, polarised and as a result of this is absorbed to a large extent by the second partial layer 9 of the support layer 3. The dispersed stimulation light 4′ striking the lower boundary surface 10 of the support layer 3 is in this way greatly weakened so that reflection on the lower boundary surface 10 and finally advance read-out of the storage phosphor layer 2 is prevented or at least greatly reduced. In contrast with the examples of FIGS. 1 and 2, the third embodiment has the advantage that the linearly polarised stimulation light 4 can pass through the support layer 3 substantially without any loss of intensity, and because of this, the storage phosphor layer 2 can be stimulated with a high intensity without increasing the output of the irradiation device 6. Alternatively or in addition, the second partial layer 9, which can absorb the stimulation light 4 or 4′ dependent upon polarisation, is also disposed in the region of the upper boundary surface 11 of the support layer 3. FIG. 4 shows a fourth embodiment of the system or device for reading out the X-ray information which is housed in a radiography module 70. The radiography module 70 is preferably in the form of and manipulated like an X-ray cassette. The module 70 is essentially portable and can be inserted or integrated into different X-ray systems, such as an X-ray stand or an X-ray table for taking X-ray images. In order to read out the X-ray image stored in the storage phosphor plate 1, the radiography module 70 can remain in the X-ray system and does not, as with a conventional X-ray cassette, have to be removed from the X-ray system and introduced into a separate read-out station. The radiography module 70 includes a housing 77 in which the storage phosphor plate 1, the detection device 7 and the irradiation device are integrated. However in FIG. 4, the irradiation device 6 (see FIGS. 1 to 3) located on the lower side of the storage phosphor plate 1 is not visible. With the radiography module 70 shown, the storage phosphor plate 1 is disposed in the housing 77 such that it is fixed, i.e. the storage phosphor plate 1 is securely connected to the housing 77 by means of appropriate connection elements. The connection to the housing 77 here can be fixed or swinging, for instance, using appropriate suspension elements in order to dampen any external impacts to the housing 77 and transfer of the same to the storage phosphor plate 1. The reading head which includes the detection device 7 and the irradiation device (see description to FIG. 1 above) is movably mounted in the housing 77. In addition, in the region of the two long sides of the storage phosphor plate 1, guides 71 and 72 are disposed which serve as a mounting for the reading head, preferably in the form of an air bearing, and as guides. During read-out, the reading head is driven by an appropriate drive 73, such as a linear motor, and moved in conveyance direction T over the storage phosphor plate 1. In addition to the reading head, a deletion lamp 74 is provided which is also driven by the drive 73 and can be moved over the storage phosphor plate 1 in order to delete any information remaining in the storage phosphor layer which could still be present after read-out. Furthermore, a control device 75 is provided which controls or implements the read-out and deletion process as well as any signal processing processes. Interfaces 76 are provided on the control device 75 which are required for transferring energy, if required air pressure, control signals and/or image signals to or from the radiography module 70. |
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046844970 | description | DETAILED DESCRIPTION Cadmium oxide has been found by the inventor to be similar in chemical behavior to the lead and zinc oxides, but generally forms higher melting compounds than lead oxide. For example, cadmium silicate melts at about 1240.degree. C., whereas lead silicate melts at about 750.degree. C. A cadmium oxide/boron oxide eutectic melts at about 900.degree. C., whereas a lead oxide/boron oxide eutectic melts at about 500.degree. C. In accordance with the present invention, glasses suitable for use as a glaze on nuclear fuel elements and containing a burnable absorber can be made using cadmium oxide instead of lead oxide, except that such glazes must be fired at higher temperatures than the lead-based glazes. In particular, it has been further found that there are a group of glasses known as borosilicate glasses which include boron trioxide as a suitable glass forming component. Since cadmium oxide, like lead oxide, forms a series of glasses with silicon dioxide, the present invention broadly contemplates the substitution of cadmium oxide, wholly or in part, for the boron trioxide in these borosilicate glasses. Referring to the sole FIGURE, there is disclosed a nuclear fuel pellet 100 of fissionable material, that is, a material fissionable by neutrons of thermal energy such as U-235, U-233 and Pu-239. Coating the exterior of the nuclear fuel pellet 100 is a glaze 102 which includes a burnable absorber, which in accordance with the present invention, comprises an oxide of cadmium-113 isotope which has a neutron capture cross section of about 20,000 barns per atom. The cadmium-113 isotope is about five times more effective as a burnable absorber than the boron-10 isotope which has a neutron capture cross section of only about 3850 barns per atom. The glaze 102 containing cadmium-113 isotope is useful as a burnable absorber in effectively controlling the reactivity of a reactor core and ultimately extending the operating life cycle of the nuclear reactor. The camdium-113 isotope, as a constituent of the glaze 102 coating the nuclear fuel pellet 100, functions as a burnable absorber which burns out at a rate which reduces the negative reactivity introduced into the reactor by the cadmium-113 isotope at a rate approximately equal to the decline in excess reactivity due to fissionable material depletion. The glaze 102, in addition to containing the oxide of cadmium-113 isotope as a burnable absorber, contains any of the common constitutes of glass such as silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2 O.sub.3), boric oxide (B.sub.2 O.sub.3), sodium monoxide (Na.sub.2 O), potassium oxide (K.sub.2 O), lead monoxide (PbO), and mixtures thereof. However, in accordance with the present invention, it has been found that for the glaze 102 to be useful as a burnable absorber, the oxide of the cadmium-113 isotope should be present in greater than about 0.5 percent by weight. For example, the glaze 102 may contain cadmium oxide in the range of about 50 to 95 percent by weight; preferably in the range of about 70 to 95 percent by weight cadmium oxide; the preferred range being about 82 to 90 percent by weight cadmium oxide; and the balance being, for example, silicon dioxide. The use of boron-10 isotope as a burnable absorber in a coating on a nuclear fuel pellet contemplates a concentration of the order of 3.2 milligrams of natural boron per centimeter of pellet length. The corresponding quantity of cadmium-113 isotope is 11.0 milligrams of natural cadmium per centimeter of pellet length. When cadmium-113 isotope is substituted for the boron-10 isotope, such substitution would, for example, be approximately in the ratio of 11 parts by weight of cadmium to 3.2 parts by weight of boron. This substitution of the oxide of cadmium-113 isotope for the boron-10 isotope, increases the rate of burnout of the burnable absorber, reduces the amount of undesirable gases produced by the burnout of the boron, and produces a harder and more refractory glaze coating. In this regard, the cadmium-113 isotope produces no gaseous products as a result of neutron capture. Thus, the use of the oxide of cadmium-113 isotope as a burnable absorber burns out more rapidly than the boron-10 isotope and leaves less residual burnable absorber at any given time than that of the boron-10 isotope. Referring again to the sole FIGURE, a typical nuclear reactor pellet 100 of fissionable material, such as enriched uranium dioxide or mixed oxides, might be of the order of 0.5 inches (1.3 centimeters) in length. The nuclear fuel pellet 100 is expected to have a cadmium silicate glaze coating containing about 16 milligrams of the oxide of cadmium-113 isotope, i.e., about 87 percent cadmium by weight. However, greater or lesser amounts of cadmium oxide may be used in coating such nuclear fuel pellets as the present invention broadly relates to the use of cadmium oxide as a burnable absorber in a glaze for such nuclear fuel pellets, wherein cadmium-113 isotope is substituted, wholly or in part, for boron-10 isotope. Further, although there has thus far been described the use of the oxide of cadmium-113 isotope as a burnable absorber in a glaze for nuclear fuel pellets, it is also contemplated that a combination of two burnable absorbers, each having different neutron capture cross sections, may be incorporated into the glaze for controlling the reactivity of the reactor core and ultimately extending the operating life cycle of the nuclear reactor. The incorporation of more than one burnable absorber having different neutron capture cross sections, provides an extra degree of freedom for the nuclear engineer in the design of a reactor core. The two burnable absorbers burn out at different rates so that the reactivity of the reactor core can be controlled with more finesse. The use of such a sophisticated control can result in savings of fissionable material and produce more energy per unit of fissionable material loaded into a reactor core. In accordance with the present invention, a cadmium borosilicate glaze may contain from about 50 to 75 percent by weight cadmium oxide, two (2) to three (3) percent by weight boric oxide, three (3) to six (6) percent by weight potassium oxide and the balance silicon dioxide. The boron-10 isotope can also be present as sodium borate (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O). The glaze 102 is applied to the nuclear fuel pellet 100 by a dip coating process. Generally, the constitutes of the glaze 102 are ground to a fine powder and made into a thin slurry with water. The pellets 100 to be glazed are dipped into the slurry which can be thickened or thinned to produce the ultimate coating of the proper thickness. The wet glaze containing cadmium oxide is dried to about 70.degree. to 90.degree. C. and subsequently fired to melt the glaze to hard refractory coating upon cooling. However, it should be noted that the nuclear fuel pellet 100 may be dipped into the slurry one or more times as required to produce the ultimate coating thickness, each dip being followed by a drying step. Thus, several dips can be applied to provide greater coating thicknesses as required. The following example is illustrative of the present invention in applying a glaze 102 containing the oxide of cadmium-113 isotope as a burnable absorber of predetermined thickness to a nuclear fuel pellet 100 containing fissionable material. EXAMPLE I A cadmium silicate glaze composition for glazing nuclear fuel pellets in accordance with the present invention was prepared by grinding cadmium oxide powder and pure quartz powder in a porcelain ball mill with porcelain balls for 48 hours. The resulting mixed powders containing 89 percent by weight cadmium oxide, the balance silicon dioxide, was made into a slurry using water. Cylinders of uranium dioxide were dipped into the slurry and dried at about 70.degree. to 90.degree. C. and subsequently weighed. The dipping process was repeated until the cylinders had picked up the desired weight of dry slurry, that is, about 18 mg per 1.3 centimeters of cylinder length. The coated cylinders were fired at 1350.degree. C. in an inert atmosphere furnace for three (3) hours to produce ceramic cylinders with a nearly uniform coating of cadmium silicate glaze of about five (5) microns thick. The glaze cylinders were heated and cooled in the furnace at a rate less than 15.degree. C. per minute to prevent thermal shock to the cylinders. The furnace cycle was about two (2) hours for heat up, three (3) hours at glazing temperature, and twelve (12) hours for cool down. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made in the illustrative embodiments and that other arangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. In particular, although an exemplary application of the present invention would glaze nuclear fuel pellets (each having a generally cylindrical configuration with an approximately one-third inch diameter and an approximately one-half inch length) for placement in fuel rods which make up fuel assemblies, the glazing of nuclear fuel plates, columns or other nuclear fuel shapes is considered to be equivalent to the glazing of nuclear fuel pellets, which has been hereinbefore described. |
description | This application is a continuation-in-part of application Ser. No. 10/365,205 which was filed on Feb. 11, 2003 now abandoned and titled Method and Apparatus for Permanent and Safe Disposal of Radioactive Waste, and which has a priority date based on Provisional Patent Application No. 60/355,620, which has a filing date of Feb. 11, 2002. 1. Field of the Invention This invention relates to the apparatus for permanently disposing of high and low-level nuclear waste in subduction faults in oceans. 2. Description of the Prior Art One of the primary problems associated with the generation of electrical power via nuclear fusion is the disposal of radioactive waste. Uranium-fueled, light-water reactors, which are commonly used in the U.S., produce plutonium 239 as one of the waste byproducts. Not only is plutonium 239 extremely poisonous, it has a half-life of 24,400 years. That means that this element would be dangerous to man for about a quarter of a million years. Retrieval of high-level nuclear waste by terrorists is another potentially grave problem. Sophisticated terrorists may separate the plutonium from the waste in order to build thermonuclear weapons. Less sophisticated terrorists may simply use the high-level waste to build a dirty conventional bomb. Proposals for disposing of nuclear waste have included embedding the waste in a plastic binder and burying it, storing it above and below ground in special canisters and/or vaults, and encasing the material in a leakproof material and dropping it to the ocean floor. It has even been proposed that high-level nuclear waste be loaded aboard rockets and sent into outer space. None of these proposals provide safe permanent storage of the radioactive material. Nor are terrorists prevented from retrieving stored material. Any conventional disposal site will require round-the-clock security. What is needed is a disposal method and equipment that is both safe and permanent and, due to the nature of the process, will not require any further security once the waste has been packaged and placed. A primary object of the present invention is to provide a method for safe disposal of high and low-level radioactive waste. Radioactive waste is loaded into special containers and placed in suitable subduction zone locations where it will never be a hazard to life on the planet. Suitable subduction zones include the Aleutian Trench, the Juan De Fuca trench, the Peru-Chile Trench, the Kurile Trench, the Mariana Trench, the Ryukya Trench, the New Hebrides Trench, the Tonga Trench, the Kermadec Trench, and the Java Trench. The other two subduction zones-one in the Near East and the other on the China-India border-are not considered useful disposal locations, as they are not on an ocean floor and will not provide the same level of security as those subduction zones which are on an ocean floor. It is hypothesized that the majority of the internal heat of this planet comes from radioactive decay below the earth's crust. Therefore, placing the waste below the earth's crust will have no measurable effemct on the earth's interior temperature. The capacity of the earth's core is so vast as to be limitless for all practical purposes. The earth's interior has slow-moving currents of molten rock in its mantle that move in a direction toward the center of the earth in the vicinity of subduction zones. These currents will carry the containers down through the mantle until the currents slowly turn parallel to the surface of the earth's outer core. As the outer core is liquid iron, the radioactive waste will drop relatively quickly through this zone to the inner core until it lands on the surface of the inner core. That is where the waste will remain. These subduction faults provide a natural pathway for nuclear waste disposal with an increase in safety and security, at a fraction of the cost over the long term, as compared to the storage methods now being used and considered. Another primary objective of the present invention is to provide a disposal container that is designed for burial in sediment on the ocean floor near a subduction zone. To eliminate the possibility of leakage, the container must be of a pressure-equalizing design. These disposal containers are designed to be filled with high- or low-level radioactive waste, transported to the ocean floor next to a subduction zone, and buried in the mud. A key feature of the hardware is the ability to compensate for extreme increases in pressure without damage to the container. This is accomplished by creating a container that is essentially a piston within a cylinder, whereas the piston is free to move into the cylinder as far as necessary to equalize the pressures within and without. Some resistance to the equalization of pressures will occur as the spent fuel rods resist compression, but cuts made in the fuel rod bundles will cause their collapse within a certain delta of pressure. This has the advantage of insuring that any leak travels from outside to inside the container—therefore no contaimination external to the container will occur in the event of damage to the container or manufacturing flaw. Another primary objective of the present invention is to provide a method for transporting filled disposal containers to a subduction zone region. The method involves utilizing an unpressurized “submarine crawler” that can carry a number of containers and bury these in sediments on the sea floor. Once the containers are buried, this completes any action needed to completely eliminate them as a danger or hazard, as it they will be drawn slowly via tectonic forces at the subduction zone into the earth's serpentized mantle, and then into the mantle of the interior of the earth. Once there, the containers are unable to the surface due to the mass of the radioactive waste, which is considerably greater than that of the surrounding rock. Over many thousands of years, the containers will settle toward the earth's outer core due to local earthquake activity shaking the surrounding rock. Eventually, the waste will come to rest on the outer surface of the inner core of the earth. The invention will now be described in detail with reference to the attached drawing figures. It should be understood that the drawings are meant to be merely illustrative and are not necessarily drawn to scale. Referring now to FIG. 1, the present invention is designed to provide the nuclear power industry and other organizations that generate nuclear waste, including both low- and high-level waste, with a special container 10 for nuclear waste disposal. This container resists increasing temperatures by being made of stainless steel or other suitable material. Stainless steel starts to soften at 1100° C. and melts at 1400°-1500° C. Other materials may be used provided that the melting point is greater than that of stainless steel. Ceramic materials, for example, are a usable alternative to stainless steel. The container 10 includes a chamber body 11 having a cylindrical inner chamber; a piston plug 12 which slides within the cylindrical inner chamber, thereby compensating for increasing external pressures; a piston-plug retaining collar 13 which bolts to an upper end of the chamber body 11; and a bottom end cap 14, which bolts to and seals a lower end of the chamber body 11. Still referring to FIG. 1, the chamber body 11, which is the primary structure of the container 10, is thick-walled and generally axially symmetrical, having a large axially-aligned cylindrical inner chamber and a pronounced convex outer surface. The inside surface of the cylindrical inner chamber is coated with a layer of lead and then a layer of copper or other suitable material. The uppermost portion of the cylindrical inner chamber is slightly beveled so that when the piston plug 12 is installed within the cylindrical inner chamber, the copper and lead coating is partially peeled away as the piston plug enters the inner chamber. The piston plug 12 is a solid cylinder, rounded on the upper exposed end and having a generally flat piston shape to the opposite end which is inserted into the inner chamber during assembly. On the perimeter of the surface of the piston end is a curved cutting edge machined into the piston which is designed to scrape the lead and copper as the piston plug 12 moves further into the cylindrical inner chamber of the chamber body 11. The collar 13 bolts directly to the chamber body 11 and it locks the piston plug 12 within the chamber body 11. The end cap 14 is bolted to the lower end of the chamber body 11. During assembly, the end cap 14 is bolted to the lower end of the chamber body 11, the cylindrical inner chamber is filled, the piston plug 12 is installed, and the collar 13 is bolted to the upper end of the chamber body 11. Lead and copper O-rings filled with nitrogen can be used to provide an all-metal seal between the mating surfaces of the chamber body 11, the end cap 14, and the collar 13. Referring now to FIG. 8, an alternative free-drop container 20 is identical to the container 10 of FIG. 1, with two exceptions. Firstly, a penetrator end cap 21 replaces the end cap 14, bolting to the chamber body 11 in a like manner. The penetrator end cap 21 is shaped facilitate ground penetration at the end of the free-drop descent to the ocean bottom. Secondly, multiple tail fins 22, which can be mounted on the collar 13, are used to stabilize the descent of a free-dropped container 20. A preferred embodiment of the radioactive waste disposal process begins with the filling of the disposal containers with nuclear waste. The second step of the radioactive waste disposal process is the transport of the containers by ship or barge to pre-selected locations at a subduction fault zone on the ocean floor. Suitable subduction fault zones include the Aleutian Trench, the Juan De Fuca trench, the Peru-Chile Trench, the Kurile Trench, the Mariana Trench, the Ryukya Trench, the New Hebrides Trench, the Tonga Trench, the Kermadec Trench, and the Java Trench. The third step of the radioactive waste disposal process is burying the containers. A mother ship sends a remote-controlled submarine crawler with the containers down to the sediments at the bottom of the ocean over the fault. The crawler drills a hole in the mud for each container that is about 15-20 feet, plus the length of the container, deep, then drops a container into each hole. A covering of 15-20 feet of mud is sufficient mud to eliminate any trace of a radioactive signature at the burial site. Thus any nearby marine life will be protected. In order to avoid violation of international treaties, the disposal container is sealed inside a flexible polymeric covering so that the container, itself, is never in contact with the ocean environment during transit above and in the ocean. Burying the waste disposal container in a shallow hole is preferable to merely placing it on the seabed, although a free-drop container, having a penetrating end cap and stabilizing fins may be dropped from a surface ship. The layer of mud is advantageous because it protects the radioactive waste disposal container from the corrosive effects of seawater. The preferred material for the container is deemed to be stainless steel, but it can be made from a variety of materials, including ceramics. The mud also has the advantage of making retrieval by terrorists almost impossible. The mud makes it difficult both to locate and to extract the container from the seabed. Grappling and retrieving the rounded surface of the proposed container would be extremely difficult, and would require a major engineering effort. Once buried in mud, all support activity ceases other than general surveillance coverage of the broad area in which the containers rest. The amount of effort needed to even attempt to find and recover one of these containers would be huge and easily noticed by remote surveillance. The containers will quickly (geologically speaking) descend to the ocean bedrock and gradually be drawn into the subduction fault by the subducting motion of the oceanic bedrock. Being located in compressed clays and gravel, the containers will continue to travel downward at a faster rate than the surrounding sediments due to their greater mass. (Once in the earthquake zone, even a failure of the container will not release any radiation toward the surface as it will already be under the overhanging continental crust.) Nothing can reverse this process. The containers are drawn down, first, into the serpentized mantle, and then into the mantle, until the heat of the earth's interior starts to soften the metal of the containers in about 6 million years. When the metal fails, the released radioactive waste is carried still further down into the earth's mantle. After melting, the radioactive waste settles down through the mantle and through the outer core until it settles on the mountains of the inner core. Long before this happens, the radioactivity within the containers will drop to such a low level at a much shallower location, as to not be dangerous to anyone. Burying disposal containers filled with radioactive waste in holes drilled on the ocean floor in the mud adjacent to a subduction fault is a relatively economical process. A more detailed description of the drilling and insertion process will now be provided. The robot submarine seabed crawler can be roughly compared to a gigantic skeletonized Army battle tank without the turret but with an oil drilling rig in its place. The crawler has a pair of caterpillar treads similar to those of a tank. That is to say that each tread consists of a continuous roller belt running over cogged wheels. The drilling rig is positioned between the two treads. The crawler may incorporate ballast tanks which enable the machine to descend and ascend in water at a controlled rate. The crawler also serves as a dispenser magazine for multiple radioactive waste disposal containers. A vacuum assembly on the crawler draws mud and sediments into the central axis shaft during the drilling. When the drilling is finished, the drill bit and container are released and the drill/insertion shaft is retracted, the sediments that were drawn into the central axis shaft are now allowed to dump into the hole, burying the container. The shape of the disposal container (Items 10 or 20) allows it to slip from a high pressure area to a lower one as it travels through the sediments in a subduction fault region. The movement is analogous to squeezing a watermelon seed. There are no external projections on the container that might cause it to snag on the rock surrounding it. The preferred material of all parts except the lead and copper seal is stainless steel. Other materials may be used, depending upon specifications. Earthquake activity is the driving force that will propel the containers toward the earths center. The procedure of burying disposal containers filled with radioactive waste includes a number of steps. The first step is to identify an appropriate subduction fault in which to plant the containers. For example, the Aleutian Trench is approximately 1800 miles long by 150 miles wide, providing a huge amount of undersea real estate suitable for buried containers. All ocean-bottom subduction faults are suitable as disposal sites. Two major subduction faults are located on landmasses, one in the Middle East and the other in the area forming the border region between China and India. These are not suitable waste disposal sites due to (a) accessibility by terrorists and (b) the lack of immediate increase in pressure on the containers to maintain a tight seal. The second step is that of loading nuclear waste into a disposal container. This would most safely be performed at reactor sites. The third step is that of transporting the container to a port equipped with a mother ship. The preferred method would be by water, because if an accident were to occur, submergence in water would strengthen the container. Also, the surrounding water would act as an efficient shield, allowing time for recovery and blockading unauthorized water craft from the accident site. The fourth step is that of transporting the containers to a subduction fault on the mother ship, which carries a submarine seabed crawler. Each of a plurality of filed disposal containers is married to a disposable drill bit and then loaded on the submarine seabed crawler. The mother ship then travels to a subduction fault where it lowers the unmanned submarine seabed crawler to the sea floor. This is usually at a depth of between 5 and 7 miles. The fifth step involves selection of a drill bit/container assembly and connection of the drill-bit/container assembly to the drill/insertion shaft with automatic quarter-turn bolts. The sixth step involves drilling a hole in the sea floor sediments using the drill/insertion/container assembly. As the hole is drilled, the sediments are vacuumed into the interior of the axis shaft. When the proper depth is reached, the drill bit is released by reversing the quarter-turn bolts, which also releases the container. As the shaft is being retracted from the hole, the sediments in the center of the shaft are free to bury the container and the discarded drill bit. Once the drill/insertion shaft is completely retracted, it cycles onto another container pre-packaged with another drill bit, locks onto the new drill bit and the cycle repeats itself. |
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description | The present invention relates to a radiation image conversion panel that has a phosphor layer such as a stimulable phosphor layer formed by a vapor-phase deposition technique such as vacuum evaporation and achieves excellent sensitivity and sharpness, and a process suitable for producing the radiation image conversion panel. Upon exposure to a radiation (e.g. X-rays, α-rays, β-rays, γ-rays, electron beams, and ultraviolet rays), certain types of phosphors known in the art accumulate part of the energy of the applied radiation and, in response to subsequent application of exciting light such as visible light, they emit photostimulated luminescence in an amount that is associated with the accumulated energy. Called “storage phosphors” or “stimulable phosphors”, those types of phosphors find use in medical and various other fields. A known example of such use is a radiation image information recording and reproducing system that employs a radiation image conversion panel having a film (or layer) of the stimulable phosphor (which is hereinafter referred to as a “phosphor layer”). The radiation image conversion panel is hereinafter referred to simply as the “conversion panel” and is also called the stimulable phosphor panel (sheet). The system has already been commercialized by, for example, FUJIFILM Corporation under the trade name of FCR (Fuji Computed Radiography). In that system, a subject such as a human body is irradiated with X-rays or the like to record radiation image information about the subject on the conversion panel (more specifically, the phosphor layer). After the radiation image information is thus recorded, the conversion panel is scanned two-dimensionally with exciting light to emit photostimulated luminescence which, in turn, is read photoelectrically to yield an image signal. Then, an image reproduced on the basis of the image signal is output as the radiation image of the subject, typically to a display device such as a CRT display or on a recording material such as a photosensitive material. The conversion panel is typically prepared by the following method: Powder of a stimulable phosphor is dispersed in a solvent containing a binder and other necessary ingredients to make a coating solution, which is applied to a panel-shaped support (substrate) made of glass or a resin, with the applied coating being subsequently dried. As described in the patent documents to be referred to below, also known are conversion panels which are prepared by forming a phosphor layer on a substrate through vapor-phase deposition techniques (vacuum film deposition techniques) such as vacuum evaporation and sputtering. The phosphor layer formed by such vapor-phase deposition has superior characteristics in that it is formed in vacuo and hence has low impurity levels and that being substantially free of any ingredients other than the stimulable phosphor as exemplified by a binder, the phosphor layer has not only small scatter in performance but also features very highly efficient luminescence. A phosphor layer formed by vapor-phase deposition may often have a columnar crystal structure formed of columnar phosphor crystals. Various studies and propositions have been made to improve the characteristics of a conversion panel having a phosphor layer formed by vapor-phase deposition. To be more specific, JP 2003-302498 A refers to manufacture of a conversion panel having a phosphor layer of columnar crystals formed by vapor-phase deposition and discloses that proper control of the temperature of a substrate during the formation of the phosphor layer enables the phosphor layer formed to have a suitable column diameter and to be substantially uniform, whereby the thus obtained conversion panel can be of high image quality. JP 2004-233067 A discloses a similar conversion panel that has 50 to 4,000 columnar crystals per 100 μm2 of phosphor layer surface to achieve excellent photostimulated luminescence characteristics (luminescence intensity) and high sharpness. JP 2005-98716 A discloses a similar conversion panel that has a variation coefficient in columnar crystals of up to 50% and preferably up to 40% to achieve high sensitivity and less unevenness in the luminance of the photostimulated luminescence. EP 1359204 A also discloses a similar conversion panel having a variation coefficient in columnar crystals of 0.05 to 0.3. JP 2004-3955 A discloses a similar conversion panel which has a substrate whose surface is made uneven by a large number of protruding portions and in which columnar crystals are grown only from the protruding portions to be optically isolated from each other, thus achieving high sharpness. The conversion panels disclosed in those documents feature satisfactory sensitivity, photostimulated luminescence characteristics and sharpness. However, the requirements for the characteristics of conversion panels and particularly for their sensitivity and sharpness have become stricter than ever before and it is desired to produce conversion panels having more satisfactory sensitivity and sharpness. An object of the present invention is to solve the conventional problems as described above by providing a radiation image conversion panel which has a phosphor layer of columnar crystals formed by vapor-phase deposition and achieves high sensitivity and sharpness. Another object of the present invention is to provide a process for producing the radiation image conversion panel. In order to achieve the above objects, the present invention provides a radiation image conversion panel comprising: a substrate; and a phosphor layer of columnar crystals formed on the substrate by vapor-phase deposition, with a column diameter distribution of the columnar crystals having two or more peaks. The two or more peaks of the column diameter distribution preferably satisfy Expression:0.4R≦r≦0.8Rwherein R is a column diameter at a largest column diameter peak and r is a column diameter at any one of the remainder in the two or more peaks of the column diameter distribution. The phosphor layer preferably comprises a stimulable phosphor represented by a general formula “CsBr:Eu”. The present invention also provides a process for producing a radiation image conversion panel comprising the steps of: preparing a substrate on which two or more types of projections different in diameter are formed and satisfies Expression “0.4R≦r≦0.8R” where R is a diameter of a largest projection and r is a diameter of any one of the remainder in the two or more types of projections, thereby making a surface of the substrate uneven; and forming a phosphor layer on the uneven surface of the substrate by vapor-phase deposition. The radiation image conversion panel having the features described above according to the present invention has a structure in which two or more types of columnar crystals which are different in diameter exist to achieve high sensitivity and satisfactory sharpness (an image is reproduced with high sharpness). The radiation image conversion panel production process of the present invention enables radiation image conversion panels having such satisfactory characteristics to be produced in a consistent manner. On the pages that follow, the radiation image conversion panel and the process for producing the radiation image conversion panel according to the present invention are described in detail with reference to the preferred embodiments depicted in the accompanying drawings. FIG. 1 shows in concept an embodiment of the radiation image conversion panel of the present invention. A radiation image conversion panel of the present invention which is generally indicated by 10 (hereinafter referred to as a “conversion panel 10”) comprises a substrate 12, a phosphor layer 14, and a protective layer 20 entirely covering the phosphor layer 14 to hermetically seal it. In the illustrated case, the phosphor layer 14 and the protective layer 20 are preferably bonded together by an adhesive layer 18. There is no particular limitation on the structure of the radiation image conversion panel of the present invention but various structures may be used as long as the phosphor layer 14 has a columnar crystal structure formed by vapor-phase deposition and the diameter distribution of columnar crystals fulfills the conditions to be described below. For example, the adhesive layer 18 and the protective layer 20 may be omitted if the phosphor layer 14 has adequate moisture resistance. The protective layer 20 may be only bonded to the substrate 12 (or a frame member 32 to be described later) with the adhesive layer 18 instead of bonding together the protective layer 20 and the phosphor layer 14 such that the phosphor layer 14 may be covered and sealed with the protective layer 20. There is no particular limitation on the substrate 12 of the conversion panel 10 of the present invention but various types as used in conventionally known radiation image conversion panels are usable. Exemplary types include plastic plates and sheets (films) made of, for example, cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, and polycarbonate; glass plates and sheets made of, for example, quartz glass, alkali-free glass, soda glass, heat-resistant glass (e.g., Pyrex™); metal plates and sheets made of metals such as aluminum, iron, copper and chromium; and plates and sheets obtained by forming a coating layer such as a metal oxide layer on the surfaces of such metal plates and sheets. If desired, the substrate 12 may have on its surface a protective layer (protective layer for protecting the base body of the substrate 12), a reflective layer that reflects photostimulated luminescence, and even a protective layer that protects the reflective layer. In this case, the phosphor layer 14 is formed on top of these layers. As will be described later in detail, the substrate 12 used in the production process of the present invention has an uneven surface including a large number of columnar projections with two or more different diameters, and satisfies the following Expression:0.4R≦r≦0.8R(0.4≦r/R≦0.8)wherein R is the diameter of the largest projection and r is the diameter of another projection. The conversion panel 10 shown in FIG. 1 is produced by the production process of the present invention, and a substrate in which projections with two different diameters are formed on the whole surface to make the surface uneven is used for the substrate 12. In the conversion panel 10 of the present invention, the phosphor layer 14 is formed by a vapor-phase deposition technique such as vacuum evaporation and basically has a columnar crystal structure including columnar crystals isolated from each other. In the conversion panel 10 shown in FIG. 1, the columnar crystals grow from the surface of the substrate 12. However, this is not the sole case of the present invention. To be more specific, there are many cases where, in a phosphor layer formed by vacuum evaporation, particularly the one formed of a stimulable phosphor and in particular of an alkali halide-based stimulable phosphor to be described later, crystals initially grow in a spherical shape and further grow in a columnar shape to form columnar crystals according to the conditions under which the phosphor layer 14 is formed (conditions of film deposition). In such a case, the conversion panel 10 of the present invention may have a structure in which a spherical crystal layer having aggregated spherical crystals is formed on the surface of the substrate 12 and a columnar crystal layer is formed thereon. In the case where crystals grow in a spherical shape as described above, depending on the forming conditions of the phosphor layer 14, the spherical crystals very often stick to the surface of the substrate 12 to form aggregates (domains) before columnar crystals grow, and the columnar crystals are then formed from the domains. In such a case, the conversion panel 10 of the present invention may be of a structure in which a columnar crystal layer is formed on a domain layer having the domains, which is formed on a spherical crystal layer having aggregated spherical crystals, which in turn is formed on the surface of the substrate 12. As described above, the phosphor layer 14 is made up of the discrete columnar crystals. The conversion panel 10 of the present invention has two or more peaks (at which the profile changes from the upward direction to the downward direction) in the column diameter distribution of the columnar crystals constituting the phosphor layer 14. As FIG. 2 schematically shows the surface (the surface opposite from the substrate 12) of the phosphor layer 14, the illustrated conversion panel 10 is basically made up of two types of columnar crystals which are different in diameter, and as FIG. 3 schematically shows, the column diameter distribution has two peaks. A phosphor layer formed by a vapor-phase deposition technique such as vacuum evaporation and in particular a phosphor layer of a stimulable phosphor have very often a columnar crystal structure made up of columnar crystals. The column diameter distribution in the phosphor layer of the columnar crystals formed by vapor-phase deposition is a normal distribution and has therefore only one peak. As also described in JP 2003-302498 A, JP 2005-98716 A and EP 1359204 A, in each of the conventional conversion panels, it has been considered that the column diameter of the columnar crystals constituting the phosphor layer is preferably uniform, in other words, the column diameter distribution is preferably as narrow as possible, and therefore the phosphor layer has been produced so that the column diameter distribution is as narrow as possible. However, the inventor of the present invention has made intensive studies and as a result found that a phosphor layer has higher sensitivity and sharpness (a reproduced image has higher sharpness) in the structure in which the phosphor layer has two or more types of columnar crystals with different diameters, that is, in the state in which the column diameter distribution has two or more peaks than in the structure in which the phosphor layer has columnar crystals with uniform column diameter, that is, in the state in which the column diameter distribution has only one peak. It is not known why the presence of two or more peaks in the column diameter distribution enhances the sensitivity and sharpness of the conversion panel 10. According to the studies made by the inventor of the present invention, it is presumed that, in such a column diameter distribution, the structure includes two or more types of column crystals with different diameters in such a manner that columnar crystals with smaller diameters are present among columnar crystals with larger diameters, and as a result, the columnar crystals with larger diameters contribute to satisfactory sensitivity and the columnar crystals with smaller diameters embedded among the columnar crystals with larger diameters contribute to satisfactory sharpness. In the conversion panel 10 of the present invention, it is very difficult to directly measure the column diameters of the columnar crystals constituting the phosphor layer 14. Therefore, in the present invention, the column diameter distribution may be obtained, for example, by taking an electron micrograph of the surface of the produced phosphor layer 14 and measuring the column diameters of the columnar crystals on the electron micrograph. It is of course preferable to obtain the column diameter distribution through measurement of the column diameters over the entire surface of the phosphor layer 14, but it is not always necessary. The column diameter distribution over the entire surface of the phosphor layer 14 may be properly determined by taking electron micrographs at arbitrary 4 or 5 places with areas of about 1,000 to 100,000 μm2 on the surface of the phosphor layer 14 and measuring the column diameters. There is also no particular limitation on the pitch (step size of the column diameter) in the column diameter distribution. Too large a pitch does not bring about a proper column diameter distribution, whereas too small a pitch may increase an influence of noise or other factor. Therefore, it is preferable to obtain the column diameter distribution at a pitch of 0.1 μm and check the number of peaks. The shape of the columnar crystal (shape seen from the upper surface side (the layer surface side)=shape in the plane parallel to the surface of the substrate 12) is not necessarily a perfect circle. In such a case, another method may be used in which the major axis length and the minor axis length (lengths of the longest and shortest diagonals) are measured and the average of the two measurements is regarded as the column diameter of the columnar crystal (average column diameter=(major axis length+minor axis length)/2). In the conversion panel 10 of the present invention, there is no particular limitation on the column diameter (average column diameter) of the columnar crystal in the phosphor layer 14, and the column diameter is preferably in the range of 3 to 15 μm. The present invention preferably satisfies Expression:0.4R≦r≦0.8R(0.4≦r/R≦0.8)wherein R is the column diameter at the largest column diameter peak and r is the column diameter at another peak in the column diameter distribution of the columnar crystals. Such a structure can give preferable results, for example, in terms of keeping the columnar crystals discrete (maintaining the spaces among the columnar crystals) while achieving high PSL sensitivity through close packing of crystals. There is also no particular limitation on the coefficient of variation in the column diameter distribution of the columnar crystals of the phosphor layer 14 and the coefficient of variation is preferably between 0.05 and 0.3, with the range of 0.05 to 0.2 being particularly preferred. Such a structure can give preferable results, for example, in terms of keeping the columnar crystals discrete (maintaining the spaces among the columnar crystals) while achieving high PSL sensitivity through close packing of crystals. In the conversion panel 10 of the present invention, there is no particular limitation on the number of peaks in the column diameter distribution, as long as the number of peaks is at least 2. However, when the number of peaks is too large, the conversion panel 10 functions in the same manner as a common conversion panel in which the column diameter distribution has only one peak, and may not fully achieve the effects of the present invention. A drawback such as difficulty in controlling the crystal packing with the columnar crystals kept discrete (spaces among the columnar crystals maintained) may arise, so the number of peaks is preferably up to 15 and particularly 2 to 5. In the present invention, with respect to a valley between two peaks (at which the profile changes from the downward direction to the upward direction) and the two peaks between which the valley is sandwiched, it is preferable to have at least one peak satisfying the condition that the height (frequency) of the valley is up to 99% of the height of the lower peak (i.e., the relation between such valley and the two peaks between which the valley is sandwiched is found in one or more places). To be more specific, now referring to FIG. 3 showing a valley and two peaks between which the valley is sandwiched, the height h2 of the valley is preferably up to 99% of the height h1 of the lower peak. In other words, the conversion panel 10 of the present invention preferably has two or more peaks each adjacent to a valley whose height is up to 99% of the height of the peak in the column diameter distribution of the phosphor layer 14. Such a structure consistently ensures the effect of the present invention that satisfactory sensitivity and sharpness are obtained by the column diameter distribution with two or more peaks, and is therefore preferable. The columnar crystals constituting the phosphor layer 14 may be of any shape without any particular limitation, but a shape close to a perfect circle is preferable, and a shape of a polygon such as the one having four or more sides is more preferable, and a shape of a polygon such as the one having five or more sides is even more preferable. In addition, the average of the ratio (aspect ratio) AR of the major axis length to the minor axis length (major axis length/minor axis length=AR) in the columnar crystals constituting the phosphor layer 14 preferably satisfies Expression “1<AR<2” and more preferably “1<AR<1.5”. When the ratio AR of the major axis length to the minor axis lengthin the columnar crystals constituting the phosphor layer 14 takes a larger value, the packing fraction of the phosphor in the phosphor layer 14 may not be sufficient to obtain satisfactory adhesion strength between the substrate 12 and the phosphor layer 14. On the contrary, when the ratio AR of the major axis length to the minor axis length takes a smaller value, the packing fraction and as a result, the X-ray absorption capacity are increased to enable a high-quality radiation image to be obtained. In addition, a higher packing fraction facilitates stress relaxation in every direction to increase the adhesion strength between the substrate 12 and the phosphor layer 14. In particular, if at least 30% of the columnar crystals have a shape of a pentagon or a polygon having six or more sides when the phosphor layer 14 is seen from its surface side, a high-quality radiation image can be obtained while achieving sufficient adhesion strength between the substrate 12 and the phosphor layer 14. The phosphor layer 14 made up of the columnar crystals which preferably have a shape of a pentagon or a polygon with six or more sides and also satisfy the average of the ratio AR between the major axis length and minor axis length can be formed by the following process: The surface of the substrate 12 on which the phosphor layer 14 is to be formed is fully cleaned and is also subjected to plasma cleaning to be rendered sufficiently hydrophilic; and the phosphor layer 14 is formed while controlling the temperature of the substrate 12, that is, the temperature of the phosphor layer 14 or controlling the temperature at the time of vapor deposition for the phosphor layer 14 during its formation (film deposition). Exemplary methods that may be used to obtain columns with polygonal sections include a method in which projections and recesses are formed in the surface of the substrate 12 in a polygonal pattern and a method in which the substrate 12 is controlled to have a temperature of at least 100° C. while the degree of vacuum at the time of vapor deposition is controlled in the range of 0.1 to 3 Pa. The conversion panel 10 of the present invention has no particular limitation on the thickness of the phosphor layer 14 and it is preferably between 100 μm and 1500 μm, with the range of 500-1000 μm being particularly preferred. Adjusting the thickness of the phosphor layer 14 to lie within those ranges is preferred from various viewpoints including the image sharpness. In the case where the phosphor layer 14 in the conversion panel 10 of the present invention is made up of a stimulable phosphor including a phosphor and an activator, the stimulable phosphor may be used to form the whole of the phosphor layer 14. However, it is preferable to form in its lower part a matrix region that contains substantially no activator and form thereon a region of a stimulable phosphor containing an activator. For example, in the case where the stimulable phosphor is CsBr:Eu that contains Eu as an activator, the matrix region is substantially formed of only CsBr, whereas the stimulable phosphor region is formed of CsBr:Eu. The expression “contains substantially no activator” means that the content of an activator is up to 1.0×10−6 ppm and preferably no activator is completely contained. The matrix region acts as the stress relaxing layer, so the abovementioned structure enables the adhesion between the phosphor layer 14 and the substrate 12 to be more enhanced. In the present invention, there is no particular limitation on the phosphor used to form the phosphor layer 14, but various known phosphors as used in radiation image conversion panels may be used. In terms of readily achieving the effects of the present invention, stimulable phosphors containing a phosphor and an activator are advantageous, with alkali halide-based stimulable phosphors represented by the general formula “MIX·aMIIX′2·bMIIIX″3:cA” as disclosed in JP 61-72087 A being more advantageously used. In this formula, MI represents at least one element selected from the group consisting of Li, Na, K, Rb, and Cs. MII represents at least one divalent metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu, and Ni. MIII represents at least one trivalent metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, and In. X, X′, and X″ each represent at least one element selected from the group consisting of F, Cl, Br, and I. A represents at least one element selected from the group consisting of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu, Bi, and Mg, 0≦a<0.5, 0≦b<0.5, and 0<c≦0.2. Of these, an alkali halide-based stimulable phosphor in which MI contains at least Cs, X contains at least Br, and A is Eu or Bi is preferred, and a stimulable phosphor represented by the general formula “CsBr:Eu” is more preferred because they have excellent photostimulated luminescence characteristics and the effects of the present invention are advantageously achieved. Various other stimulable phosphors disclosed in, for example, U.S. Pat. No. 3,859,527, JP 55-12142 A, JP 55-12144 A, JP 55-12145 A, JP 56-116777 A, JP 58-69281 A, JP 58-206678 A, and JP 59-38278 A and JP 59-75200 A may also be advantageously used. The conversion panel 10 having the phosphor layer of a stimulable phosphor is not the sole case of the present invention, but the present invention may be advantageously used in various radiation image conversion panels having a phosphor layer including columnar phosphor crystals, such as a radiation scintillator panel having a phosphor layer including columnar crystals of a phosphor such as cesium iodide. In the conversion panel 10 of the present invention, the phosphor layer 14 is formed by various vapor-phase deposition techniques (vacuum film deposition techniques) including vacuum evaporation, sputtering, and CVD (chemical vapor deposition). Among these techniques, vacuum evaporation is a preferred method for forming the phosphor layer 14 from various viewpoints such as productivity. In the case of using a stimulable phosphor, it is preferred to form the phosphor layer 14 by two-source (multi-source) vacuum evaporation in which two film-forming materials, one for the phosphor and the other for the activator, are independently heated to evaporate. In the case of using CsBr:Eu as the stimulable phosphor, it is preferred to perform two-source vacuum evaporation which uses cesium bromide (CsBr) as the film-forming material for the phosphor and europium bromide (EuBrx; x is usually from 2 to 3, with 2 being preferred) as the film-forming material for the activator, respectively. When the phosphor layer 14 is formed by vacuum evaporation, there is no particular limitation on the heating method that can be employed in vacuum evaporation and the phosphor layer may be formed by electron beam heating using an electron gun or the like, or by resistance heating. If the phosphor layer is to be formed by multi-source vacuum evaporation, all film-forming materials may be heated to evaporate by the same heating means (such as electron beam heating). Alternatively, the film-forming material for the phosphor may be heated to evaporate by electron beam heating while the film-forming material for the activator, which is present in a very small amount, may be heated to evaporate by resistance heating. There is also no particular limitation on the conditions (of film deposition) under which the phosphor layer 14 is to be formed and they may be determined as appropriate for the type of the vapor-phase deposition method used, the film-forming materials used, the heating means, and other factors. The conversion panel 10 of the present invention is further described below. If the phosphor layer 14 including any one of the aforementioned various stimulable phosphors, particularly an alkali halide-based stimulable phosphor, more particularly a stimulable phosphor represented by the general formula “CsX:Eu”, and most particularly “CsBr:Eu” is to be formed by vacuum evaporation, a preferred procedure comprises first evacuating the system to a high degree of vacuum, then introducing an argon gas, a nitrogen gas or the like into the system to achieve a degree of vacuum between about 0.01 Pa and 3 Pa (which is hereinafter referred to as “medium degree of vacuum” for the sake of convenience), and heating the film-forming materials by resistance heating or the like to perform vacuum evaporation under such medium degree of vacuum. As already mentioned, the phosphor layer 14 in the conversion panel 10 of the present invention has discrete columnar crystals formed therein. The phosphor layer 14 that is formed by performing film deposition under the medium degree of vacuum, in particular, the phosphor layer 14 of an alkali halide-based stimulable phosphor such as CsBr:Eu has an especially satisfactory columnar crystal structure and is preferred in such terms as the PSL characteristics and the sharpness of the image that can be produced. The phosphor layer 14 as described above that has the columnar crystals of which the column diameter distribution has two or more peaks can be consistently produced by the production process of the present invention in which the substrate 12 which has an uneven surface including two or more types of columnar projections different in diameter and which satisfies Expression “0.4R≦r≦0.8R” wherein R is the diameter of the largest projection and r is the diameter of another projection, is used to form the phosphor layer on its surface by a vapor-phase deposition technique such as vacuum evaporation. In terms of further ensuring formation (by deposition) of the phosphor layer 14 having columnar crystals whose column diameter distribution has two or more peaks, and advantageously achieving the effects of the present invention by forming the phosphor layer 14 in such a manner that the column diameter distribution has two or more peaks, the projections of the substrate 12 are preferably formed in a state in which projections with diameters corresponding to the desired column diameter distribution are patterned, and the projections are more preferably formed in such a manner that the projections with different diameters are disposed in a predetermined array at predetermined intervals (at a predetermined pitch). As described above, the number of peaks in the column diameter distribution of the phosphor layer 14 is preferably up to 15. Therefore, preferably up to 15 types and more preferably 2 to 5 types of projections which are different in diameter are formed on the substrate 12. A technique is known in which a substrate having a large number of projections is used to advantageously produce discrete columnar crystals, thus forming a phosphor layer thereon by vapor-phase deposition. In such a process for forming the phosphor layer, in general, crystals preferentially grow from the projections and as a result, the columnar crystals can be advantageously formed in a discrete manner. For example, commonly assigned JP 2004-3955 A discloses the conversion panel that has very high sharpness and which has a phosphor layer formed on a substrate (support) having a large number of projections on its surface, with the phosphor layer being only formed of columnar crystals which have grown from the projections as the starting points and which have definite boundaries and are optically independent of each other. The column diameter of the columnar crystal having grown from the projection basically depends on the diameter of the projection. If the phosphor layer is formed under the same conditions, there is hardly a case where a columnar crystal having grown from a projection with a smaller diameter has a larger diameter than that of a columnar crystal having grown from a projection with a larger diameter. Therefore, the phosphor layer 14 in which the column diameter distribution has at least two peaks can be advantageously produced by using the substrate 12 with an uneven surface in which two or more types of projections with different diameters are formed in a pattern according to the desired column diameter distribution. A balance can also be suitably struck between columnar crystals with larger diameters and columnar crystals with smaller diameters if Expression “0.4R≦r≦0.8R” wherein R is the diameter of the largest projection and r is the diameter of another projection is satisfied. In the present invention, there is no particular limitation on the projection diameter, and the diameter is determined as appropriate within a range in which the column diameter of a columnar crystal growing from a projection depends on the diameter of the projection, because the diameter of a columnar crystal growing from a projection whose diameter is too large does not depend on the diameter of the projection but a plurality of narrow columnar crystals are formed on the projection. The phosphor layer 14 in which the column diameter distribution has two or more peaks can also be produced in the same manner by using a substrate formed by patterning projections of different sizes (different upper surface sizes) which are not cylindrical but prismatic and are preferably in the shape of a quadrangular prism or a prism whose cross section has five or more sides. In this case, the projection diameters R and r may be determined from the diagonal length (average of the largest length and the smallest length in the case where its cross section is not in the shape of a regular polygon). When a substrate on which not projections of different column diameters (sizes) but projections of an identical column diameter are formed and hence which has an uneven surface is used to form the phosphor layer, the projection diameter, projection pitch (center-to-center distance), spacing between adjacent projections, projection height, and ratio between the projection diameter and the pitch may be mutually adjusted to produce the phosphor layer 14 in which the column diameter distribution has two or more peaks. In the case where the phosphor layer 14 in which the column diameter distribution has two or more peaks is thus produced by adjusting the size, pitch, and height of the projections and other factors, the projection height is extremely important and need be set to 0.8 μm or less. As described above, the projections formed on the surface of the substrate 12 enable the columnar crystals to grow from the projections serving as starting points. The larger the height of the projection is, the more highly the projection is selected for the growth of the columnar crystal. If a projection formed on the surface of the substrate 12 has a height exceeding 0.8 μm and particularly a height of 1 μm or more, a crystal only grows from this projection. As a result, as shown in JP 2004-3955 A, columnar crystals of the same column diameter are densely formed on the projections serving as the starting points. On the other hand, if a projection has a height of up to 0.8 μm, the selectivity of the projection for the growth of a columnar crystal is reduced so that the columnar crystal may grow not from the projection but from the substrate surface (recess). However, projections are highly selected for the growth of columnar crystals, so the columnar crystals preferentially grow from the projections. Therefore, a columnar crystal growing from a projection serving as the starting point has a larger column diameter than that of another columnar crystal growing from the substrate surface except the projections. As a result, it is possible to produce the phosphor layer 14 in which the columnar crystals having grown from the projections and the columnar crystals having grown from the substrate surface except the projections are different in column diameter, and the column diameter distribution has two or more peaks. However, a substrate with too low projections functions in the same manner as a substrate having no projection, so the projection height need be set to at least 0.1 μm. Various known processing techniques may be used without any particular limitation for the method of forming such projections (projections and recesses) on the substrate 12. For example, a method may be suitably used in which a photolithographic technique as used in semiconductor manufacture is used to form a pattern corresponding to projections to be formed with a photoresist, and etching is carried out while the photoresist is masked, thereby forming a desired pattern of projections (projections and recesses) on the substrate 12. Alternatively, a method in which the surface of the substrate 12 is sandblasted to form a pattern of projections and recesses may be used. A method of forming the phosphor layer 14 by providing the temperature distribution to the substrate 12 may also be used for forming the phosphor layer 14 in which the column diameter distribution of the columnar crystals have two or more peaks. In general, a columnar crystal of a larger diameter grows at a higher substrate temperature. Therefore, the phosphor layer 14 in which the column diameter distribution of the columnar crystals has two or more peaks can be obtained, for example, by forming it in a state in which the substrate has point-like high-temperature portions and/or low-temperature portions. Various methods may be used for providing the temperature distribution to the substrate 12, and as an exemplary method, a substrate holder of a phosphor layer-forming apparatus (e.g., vacuum evaporation apparatus) is provided with a temperature adjusting means which is brought into contact with the back surface of a substrate to heat it or radiate the heat thereof, and the back surface of the substrate or the holder surface with which the substrate comes in contact is made uneven so that the substrate is brought into point contact with the holder to make the substrate 12 have a temperature distribution. The phosphor layer 14 formed on the substrate 12 in this manner is then annealed (subjected to thermal treatment) if necessary. Prior to forming the phosphor layer 14 on the substrate 12, the surface of the substrate 12 is preferably cleaned by plasma cleaning or the like. In its preferred embodiment, the illustrated conversion panel 10 has the protective layer 20 that covers the entire surface of the phosphor layer 14 to hermetically seal it. The phosphor layer formed by vapor-phase deposition, and particularly the phosphor layer of the alkali halide-based stimulable phosphor are highly hygroscopic and will readily deteriorate upon absorption of moisture. Therefore, in order to prevent the moisture absorption of the phosphor layer, it is preferable that, as shown in FIG. 1, the conversion panel 10 of the present invention be provided with the protective layer 20 that has moisture resistance (water impermeability) and entirely covers the phosphor layer 14 to hermetically seal it. Various types of material may be used for the protective layer 20 without any particular limitation as long as the material has sufficient moisture resistance. For example, the protective layer 20 is formed of 3 sub-layers on a polyethylene terephthalate (PET) film: an SiO2 film; a hybrid sub-layer of SiO2 and polyvinyl alcohol (PVA); and an SiO2 film. For formation of the protective layer 20 having 3 sub-layers of SiO2 film/hybrid sub-layer of SiO2 and PVA/SiO2 film on the PET film, the SiO2 films may be formed through sputtering and the hybrid sub-layer of SiO2 and PVA may be formed through a sol-gel process, for example. The hybrid sub-layer is preferably formed to have a ratio of PVA to SiO2 of 1:1. Other examples of the material that may be preferably used for the protective layer 20 include a glass plate (film); a film of resin such as polyethylene terephthalate or polycarbonate; and a film having an inorganic substance such as SiO2, Al2O3, or SiC deposited on the resin film. To construct the conversion panel 10 of the present invention, the phosphor layer 14 is entirely covered with the protective layer 20 that surrounds the entire circumference of the phosphor layer 14 and the adhesive layer 18 is applied to adhere the protective layer 20 to the substrate 12, whereby the protective layer 20 entirely covers the phosphor layer 14 to hermetically seal it. However, in a more preferred embodiment, the adhesive layer 18 is applied not only between the substrate 12 and the protective layer 20 but also to the surface of a columnar crystal layer 28 as shown in FIG. 4, so that the protective layer 20 is also adhered to the columnar crystal layer 28. This structural design helps prevent such problems as the floating of the protective layer 20, thus providing a highly durable conversion panel 10 that features even better mechanical strength. The adhesive layer 18 for the protective layer 20 is not limited in any particular way and various types may be employed as long as they have sufficient adhesive power. However, if the adhesive layer 18 is to be additionally provided on the surface of the columnar crystal layer 28 as shown in FIG. 4, it must have such optical characteristics as to permit sufficient transmission of photostimulated luminescence and exciting light. Another preferred embodiment of the present invention is schematically shown in FIGS. 4 and 5. A (radiation image) conversion panel 30 in those Figures has a frame member 32 (such as a square or rectangular frame) that surrounds the phosphor layer 14 in a direction parallel to the plane of the phosphor layer 14 (the substrate 12), and the protective layer 20 is adhered to the frame member 32 (and optionally the phosphor layer 14) such that the phosphor layer 14 is entirely sealed hermetically. To produce this conversion panel 30, the frame member 32 is first fixed to the substrate 12. In the preferred embodiment shown in FIG. 4, a groove 12a is formed in the surface of the substrate 12 and the frame member 32 is inserted into the groove 12a so that it is fixed to the substrate 12. This structural design is preferable since it not only improves the precision in the position of the frame member 32 but also provides greater ease in its positioning and other operations. Of course, the present invention is by no means limited to this embodiment and the frame member 32 may be fixed to the substrate 12 without providing the groove 12a. The frame member 32 may also be fixed by various other methods depending on the materials and shapes of the substrate 12 and the frame member 32 and they include the use of an adhesive, the use of a solder, and the fitting into the groove 12a if it is formed in the surface of the substrate 12. In the next step, with a mask applied, a suitable vapor-phase deposition technique such as vacuum evaporation is used to form the phosphor layer 14 as described above within the region surrounded by the frame member 32. When the formation of the phosphor layer 14 ends, annealing is optionally performed; the adhesive layer 18 is then formed on top of the frame member 32; both the frame member 32 and the phosphor layer 14 are covered with the protective layer 20, which is adhered to the frame member 32 by heat lamination or the like to entirely cover and hermetically seal the phosphor layer 14 with the frame member 32 and the protective layer 20 to thereby produce the conversion panel 30. Here again, the adhesive layer 18 may only be applied to the upper surface of the frame member 32 to adhere the frame member 32 to the protective layer 20, but as shown in FIG. 4, the adhesive layer 18 is preferably provided on the surface of the phosphor layer 14, too, so that the latter is adhered to the protective layer 20 by means of the adhesive layer 18. This is the same case as the embodiment shown in FIG. 1. By providing the frame member 32 and adhering the protective layer 20 to the member 32, the surface of the phosphor layer 14 and the adhering surface of the protective layer 20 as the latter seals the phosphor layer 14 can be made generally flush with each other and, hence, sealing by the protective layer 20 can be accomplished more easily and without damaging the phosphor layer 14. While the radiation image conversion panel and the process for producing the radiation image conversion panel according to the present invention have been described above in detail, the present invention is by no means limited to the foregoing embodiments and it should be understood that various improvements and modifications can of course be made without departing from the scope and spirit of the invention. On the following pages, the present invention is described in greater detail with reference to specific examples. It should of course be understood that the present invention is by no means limited to the following examples. Using europium bromide and cesium bromide as film-forming materials for the activator and the phosphor, respectively, two-source vacuum evaporation was carried out to prepare a conversion panel of the type shown in FIG. 1 which is generally indicated by 10 and has a phosphor layer 14. An aluminum plate having an area of 450×450 mm (thickness: 10 mm) was prepared. Over the whole surface of the aluminum plate (surface on which the phosphor layer is to be formed) were formed columnar projections, which had each a column diameter of 3.5 μm and a height of 0.5 μm and were centered on the points of intersection in a grid pattern with squares each having a side length of 5 μm (see FIG. 6A), thus obtaining the substrate 12. The projections (projections and recesses) were formed by photolithography. The substrate 12 was set on a substrate holder in a vacuum evaporation apparatus; in addition, the respective film-forming materials were set in specified positions and the surface of the substrate 12 was masked such that films would be deposited in the center area of the substrate 12 measuring 430×430 mm. The substrate holder was equipped with a heater that heats the substrate from its back surface (surface on which the phosphor layer was not to be formed). The film-forming materials were heated in a resistance heating apparatus using tantalum crucibles and a DC source capable of outputting a power of 6 kW. Installed above the crucibles was a shutter for shielding against the film-forming materials having evaporated therefrom. The crucible accommodating the film-forming material for the phosphor was furnished with a temperature measuring means. After setting the substrate on its holder, the vacuum chamber was closed and switched on to perform evacuation using a diffusion pump and a cryogenic coil. The shutter was in the closed state. When the degree of vacuum had reached 8×10−4 Pa, argon gas was introduced into the vacuum chamber to adjust the degree of vacuum to 2.6 Pa; then, the DC source was driven so that an electric current was applied to the crucibles to melt the film-forming materials they contained. Cesium bromide was melted at 670° C. As for europium bromide, the power was raised until its melting temperature was reached and a complete melt of europium bromide was formed; thereafter, the power input was reduced until the temperature was not high enough for the europium bromide to evaporate. The power to be delivered for melting the europium bromide was controlled in accordance with a preliminary experiment for its melting. At the point in time when 60 minutes had passed since the start of melting the film-forming materials, the shutter above the crucibles loaded with cesium bromide was opened so that the formation of the phosphor layer 14 (matrix region) on the surface of the substrate 12 by vapor deposition started (cesium bromide was vaporized at the temperature of 670° C.). As soon as the shutter was opened, the substrate 12 was heated to 160° C. with the heater. The power to be applied to the crucibles was adjusted such that the deposition rate of cesium bromide onto the substrate 12 could reach 6 μm/min. When the layer thickness reached 50 μm, the shutter was closed and the supply of argon gas was so adjusted that the pressure (Ar gas pressure) in the vacuum chamber would be 0.8 Pa; at the same time, the power to europium bromide (or its crucibles) was raised to the level at which the molarity ratio of Eu/Cs in the phosphor layer checked in advance would be 0.001:1. The shutter above the crucibles loaded with cesium bromide and europium bromide was opened to resume the formation of the phosphor layer 14 (start the vapor deposition of the stimulable phosphor). When the thickness of the phosphor layer 14 reached 700 μm, the DC source was switched off to stop the application of an electric current to the crucibles to end the formation of the phosphor layer 14. Subsequently, dry air was introduced into the vacuum chamber until the internal pressure became atmospheric and the phosphor layer was left to cool in the chamber as it was open to the atmosphere. After the end of the cooling, the substrate 12 (conversion panel 10) was detached from its holder and taken out of the vacuum chamber. The substrate 12 was annealed at 200° C. for 2 hours to prepare the conversion panel. As schematically shown in FIG. 7, the substrate 12 (region where the phosphor layer was formed) in the resulting conversion panel was horizontally and vertically divided into quarters, respectively, and images with an area of 50×60 μm were taken at 4 points of intersection near the corners of the substrate and at a point of intersection in the center of the substrate 12 to obtain electron micrographs. In each of the thus obtained five micrographs, the column diameter (average of the major axis length and the minor axis length) of the columnar crystals was measured, thus obtaining a column diameter distribution. The column diameter distribution was prepared at a pitch (step size) of 0.1 μm, and indicated by the frequency relative to the highest peak taken as 1. One of the electron micrographs of the conversion panel (print image obtained by outputting the image data of the micrograph) and its column diameter distribution are shown in FIGS. 8A and 8B, respectively. As shown in FIG. 8B, the column diameter distribution of the columnar crystals constituting the phosphor layer of the conversion panel has two peaks. The column diameter R at the largest peak in the diameter distribution of the columnar crystals is 3.7 μm and the column diameter r at the other peak in the diameter distribution of the columnar crystals is 2.96 μm, so r/R is 0.8 and is within the preferred range of the present invention. A conversion panel was prepared by repeating the procedure of Example 1 except that the projections having a height of 0.8 μm were formed on the substrate 12. The column diameter distribution of the prepared conversion panel was obtained in the same manner as in Example 1. One of the electron micrographs of the conversion panel and its column diameter distribution are shown in FIGS. 9A and 9B, respectively. As shown in FIG. 9B, the column diameter distribution of the columnar crystals constituting the phosphor layer of the conversion panel has two peaks. The column diameter R at the largest peak in the diameter distribution of the columnar crystals is 3.48 μm and the column diameter r at the other peak in the diameter distribution of the columnar crystals is 2.48 μm, so r/R is 0.71 and is within the preferred range of the present invention. On the same aluminum plate as used in Example 1, were formed columnar projections which had each a column diameter (diameter) of 3.5 μm and a height of 1 μm and were centered on the points of intersection in a grid pattern with squares each having a side length of 5 μm, and columnar projections which had each a column diameter of 2.5 μm and a height of 1 μm and were centered on the centers of the squares (see FIG. 6B). The column diameter R at the largest peak in the diameter distribution of the columnar projections is 3.5 μm and the column diameter r at the other peak in the diameter distribution of the columnar projections is 2.5 μm, so r/R is 0.71 and is within the preferred range of the present invention. The projections were formed in the same manner as in Example 1. A conversion panel was prepared by repeating the procedure of Example 1 except that the substrate 12 having two types of projections with different column diameters formed thereon was used. The column diameter distribution of the prepared conversion panel was obtained in the same manner as in Example 1. One of the electron micrographs of the conversion panel and its column diameter distribution are shown in FIGS. 10A and 10B, respectively. As shown in FIG. 10B, the column diameter distribution of the columnar crystals constituting the phosphor layer of the conversion panel has two peaks. The column diameter R at the largest peak in the diameter distribution of the columnar crystals is 3.33 μm and the column diameter r at the other peak in the diameter distribution of the columnar crystals is 2.44 μm, so r/R is 0.73 and is within the preferred range of the present invention. A conversion panel was prepared by repeating the procedure of Example 1 except that an aluminum plate with an area of 450×450 mm as used in Example 1 was used for the substrate without further processing (no projection was formed on the substrate surface). The column diameter distribution of the prepared conversion panel was obtained in the same manner as in Example 1. One of the electron micrographs of the conversion panel and its column diameter distribution are shown in FIGS. 11A and 11B, respectively. As shown in FIG. 11B, the column diameter distribution of the columnar crystals constituting the phosphor layer of the conversion panel has only one peak. A conversion panel was prepared by repeating the procedure of Example 1 except that the side length of each square in the grid pattern where a projection is to be formed, the diameter of the projection, and the height of the projection were set to 3 μm, 2.5 μm and 1 μm, respectively. The column diameter distribution of the prepared conversion panel was obtained in the same manner as in Example 1. One of the electron micrographs of the conversion panel and its column diameter distribution are shown in FIGS. 12A and 12B, respectively. As shown in FIG. 12B, the column diameter distribution of the columnar crystals constituting the phosphor layer of the conversion panel has only one peak. Each of the conversion panels prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was evaluated for its sensitivity (sensitivity for PSL (photostimulated luminescence)), sharpness (MTF) and detective quantum efficiency (DQE). (Sensitivity) Each of the conversion panels 10 was placed in a cassette shielded from light and exposed to about 1 mR of X-rays at a tube voltage of 80 kVp. After the exposure to X-rays, the conversion panel was taken out of the cassette in the dark and excited with semiconductor laser light (wavelength, 660 nm; 10 mV). The photostimulated luminescence emitted from the phosphor layer was measured with a photomultiplier tube after it was separated from the exciting light by passage through an exciting light cutoff filter (B410 of HOYA CORPORATION). The sensitivity was evaluated relative to the PSL sensitivity in Comparative Example 1 taken as 100. (Sharpness) Each conversion panel whose surface was closely attached to an MTF chart was placed in a cassette shielded from light and exposed to about 10 mR of X-rays at a tube voltage of 80 kVp. After the exposure to X-rays, the conversion panel was taken out of the cassette in the dark and a radiation image was read in the same manner as in the measurement of the photostimulated luminescence in the evaluation of the PSL sensitivity. The thus obtained radiation image was reproduced on a display to measure the MTF. The MTF was evaluated relative to that at 1 LP/mm. (DQC) Each conversion panel 10 whose surface was closely attached to an MTF chart was placed in a cassette shielded from light and exposed to about 1 mR of X-rays at a tube voltage of 80 kVp. After the exposure to X-rays, the conversion panel was taken out of the cassette in the dark and a radiation image was read in the same manner as in the measurement of the photostimulated luminescence in the evaluation of the PSL sensitivity. The thus obtained radiation image was reproduced on a display to measure the sharpness (MTF). On the other hand, each conversion panel 10 was placed in a cassette shielded from light and exposed to about 1 mR of X-rays at a tube voltage of 80 kVp. After the exposure to X-rays, the conversion panel was taken out of the cassette in the dark and a radiation image was read in the same manner as above. The thus obtained radiation image was reproduced on a display to measure the granularity (Wiener spectrum). DQE was calculated from the resulting sharpness and granularity. The DQE was evaluated relative to that at 1 LP/mm with the result of Comparative Example being taken as 100. The measurement results are shown in Table 1, below. TABLE 1Relative PSLMTFRelative DQEExample 11060.62104Example 21080.64111Example 31130.64116Comparative1000.60100Example 1Comparative930.6195Example 2 As shown in Table 1, the conversion panels of the present invention in which the column diameter distribution of the columnar crystals constituting the phosphor layer has two peaks are more excellent in sensitivity, sharpness and DQE (image quality) than the conventional conversion panels in Comparative Examples in which the column diameter distribution has only one peak, and therefore have satisfactory characteristics. From the foregoing results, the beneficiary effects of the present invention are apparent. |
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abstract | A method of preparation of a map of areas on a sample that collects charge, and a method for using the map to selectively scan and modulate the intensity of the electron beam of a SEM so as to discriminate between the charging and non-charging areas of the sample. To generate the charging map, an image is first checked for saturation. The frame for the image is acquired by using digital scan control coupled with digital acquisition of the secondary electron detector signal. The next step is to perform a xe2x80x9cfast scanxe2x80x9d where the first frame is taken at the maximum frame rate that the system is capable of. A fast scan does not allow time for significant charge to collect on surfaces, and this provides a base level to subtract from a slower scan that allows charge to accumulate. Areas where the difference between the two is larger indicate areas of charge collection. A xe2x80x9cslow scanxe2x80x9d is then performed. The frames are then subtracted pixel-by-pixel in order to isolate the charging component of the image. After the pixel-by-pixel subtraction, the charging map is created. |
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description | This application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/EP2015/078808, filed Dec. 7, 2015, which claims the benefit of German Application No. 10 2014 118 623.0, filed Dec. 15, 2014. The entire contents of each of the foregoing patent applications are hereby incorporated by reference. 1. Technical Field The invention relates to a device for carrying out a leak test on a fuel rod capsule containing at least one fuel rod and test gas, the device comprising a test container which is designed for accommodating at least one fuel rod capsule and which is lowerable into a water-flooded pool of a nuclear plant. The invention further relates to a method for carrying out the leak test on the fuel rod capsule containing at least one fuel rod and test gas, using such a device. 2. Background and Relevant Art It is known that fuel rods of nuclear reactors may develop leaks during operation; i.e., water may penetrate into the fuel rods. As soon as a fuel rod with such a defect is identified, it is typically encapsulated underwater in a fuel rod capsule in order to counteract escape of radioactive fission products, in particular radioactive gases. The encapsulation of the fuel rod takes place at a sufficient depth that the opening and closing of the fuel rod capsule takes place by remote control by means of suitable manipulators. After the fuel rod capsule is opened and the fuel rod is inserted, the water that has penetrated into the fuel rod capsule is displaced by blowing in a test gas, and the fuel rod capsule is transferred into an encapsulation device. In this encapsulation device, the fuel rod situated in the fuel rod capsule is heated by passing hot test gas through the fuel rod capsule, thus evaporating the water present in the fuel rod. After the water vapor has been removed from the encapsulation device by drying the test gas or replacing the moist gas with dry test gas, the fuel rod capsule is closed and welded at the closure point. After the welded, and thus leak-tight, fuel rod capsule is removed from the encapsulation device, the fuel rod capsule must be further tested for leak-tightness. The fuel rod capsule containing the fuel rod is then optionally temporarily stored in a spent fuel pool filled with water before it can be transported to a final repository or a reprocessing plant. It is known to test the fuel rods per se or the fuel rod capsule containing the at least one fuel rod for leak-tightness. A method for testing the leak-tightness of fuel rods is known from DE 195 42 330 A1, for example, in which gases that escape from the fuel element are analyzed for their gaseous fission product content. WO 2007/071337 describes the testing of fuel rod capsules containing at least one fuel rod. The fuel rod capsule is introduced into a test container situated inside a flooded pool of a nuclear plant, beneath the water surface. Leaks are detected by means of an underwater camera, and a leak rate is estimated based on the number and size of the detected gas bubbles. Proceeding from this prior art, the object of the present invention is to improve the leak testing of fuel rod capsules in such a way that leak rates may be determined in a particularly accurate manner. With regard to the device, the object is achieved by the device for carrying out the leak test of the type mentioned at the outset, having the further features of Patent Claim 1. Advantageous embodiments of the invention are the subject matter of the subclaims. A device for carrying out a leak test on a fuel rod capsule containing at least one fuel rod and test gas includes a test container which is designed for accommodating at least one fuel rod capsule, and which is lowerable into a water-flooded pool of a nuclear plant. According to the invention, a mass spectrometer is fluidically connectable to the interior of the test container in such a way that the mass spectrometer may be supplied with a gas stream for detecting a concentration of the test gas that has diffused from the fuel rod capsule into the test container. The overall process of the leak testing, the same as the process of encapsulating the fuel rod, may thus be carried out underwater. For this purpose, the test container is lowered into the pool, for example a spent fuel pool, of a nuclear power plant. The fuel rod capsule contains, in addition to the at least one fuel rod, test gas that is under a known, predefined pressure. The test gas diffuses into the interior of the test container through leaks that may be present in the fuel rod capsule. The interior of the test container is connected to the mass spectrometer via lines, and optionally by valves situated in between, so that the test gas may be supplied to the mass spectrometer after a fluidic connection has been established. The selective detection of the test gas by means of the mass spectrometer allows a particularly accurate determination of the concentration of the test gas contained in the gas stream. The leak rate, which is derived from the concentration of the test gas determined in this way, is therefore more accurate. Helium is typically used as a test gas for leak testing according to common industry standards. However, as a departure therefrom, in the present application it has proven to be particularly advantageous to provide argon as the test gas. The mass spectrometer is therefore preferably designed for detecting the concentration of the argon that has diffused from the fuel rod capsule. After the fuel rods have been encapsulated in fuel rod capsules underwater, the presence of a certain amount of residual moisture within the fuel rod capsule cannot be ruled out. The same applies for the test container itself, which typically is flooded with water from the pool during introduction of the fuel rod capsule. Therefore, the interior of the fuel rod capsule or of the test container cannot be completely dried before the testing of the leak-tightness takes place. This is problematic in particular when a test of the leak-tightness is to take place by use of a mass spectrometrically detected concentration of helium that has diffused out, since helium and the hydrogen originating from the residual moisture have comparable atomic weights. The measuring results therefore have a relatively high level of inaccuracy if helium is used as the test gas. This problem may be avoided when argon, which has a greatly different atomic weight from hydrogen, is filled as test gas under a defined pressure inside the fuel rod capsule. Alternatively, some other inert gas may be used as the test gas. In one preferred exemplary embodiment, the test container has an evacuable design, such that an internal pressure that is reduced compared to a hydrostatic pressure caused by water surrounding the test container is settable in the interior of the test container. In other words, the interior of the test container may be insulated from the hydrostatic pressure of the surroundings, in particular by means of valve systems or the like, in such a way that the internal pressure inside the test container may be set to a value that is suitable for the leak testing, for example by means of vacuum pumps. This is desirable in particular for specifying defined criteria in determining the leak rates, whereby the pressure difference prevailing between the interior of the fuel rod capsule and the interior of the test container must be known. A suitable lowering of the internal pressure inside the test container with respect to the pressure prevailing inside the fuel rod capsule facilitates the diffusion of the test gas from the fuel rod capsule, so that the testing operation takes less time. The test container at a lower end preferably has a connection device that connects to the interior of the pool. The connection device is used as an outlet for water which is present in the test container and which has penetrated during introduction of the at least one fuel rod capsule. To this end, it is provided in particular to introduce a purge gas under pressure into the interior of the test container, the purge gas displacing the water and expelling it into the pool via the connection device, which is situated at the lowest point in the test container. For this purpose, the conveying of the purge gas to the test container may take place, for example, by means of a vacuum pump having an appropriate delivery rate. Emptying the test container of essentially all water is desirable in particular in exemplary embodiments that use argon as the test gas. Argon has comparatively good water solubility; thus, residual water remaining in the test container may significantly influence and skew the measuring results. The upper end of the test container is particularly preferably fluidically connectable to a first reservoir in which purge gas is storable under pressure. The purge gas in the first reservoir is under such high pressure that a test container filled with water may be completely flooded with purge gas by providing a fluidic connection between the first reservoir and the test container, for example by opening valves. For this purpose, the pressure inside the first reservoir must be higher than the hydrostatic pressure that is produced by the water surrounding the test container. A device designed in this way has a particularly simple and robust construction, since high-maintenance conveying devices, in particular vacuum pumps, for conveying the purge gas are avoided. The first reservoir is preferably fluidically connectable to a sampling point of the mass spectrometer. It is thus possible to flush lines, which connect the gas stream to the mass spectrometer, with purge gas and optionally dry them. In one refinement of the invention, a second reservoir is provided in which test gas is storable under pressure. The second reservoir may likewise be fluidically connected to the sampling point, for example via a suitable valve position. Supplying to the sampling point takes place for purposes of calibrating the mass spectrometer. The test gas is stored in the second reservoir under a known pressure and suppliable to the sampling point in a controlled manner, so that the calibration of the mass spectrometer takes place under defined conditions. The test gas includes the purge gas containing a small proportion of test gas. The concentration of the test gas contained in the purge gas is slightly above the detection limit of the mass spectrometer, so that the latter may be calibrated by the controlled supplying of test gas. At least one volume control valve is preferably [situated] between the sampling point and the first reservoir and/or between the sampling point and the second reservoir in order to set the volumetric flow of the purge gas or test gas. By means of the at least one volume control valve for the test gas, the volumetric flow is variable and settable to values in such a way that a precise calibration of the mass spectrometer is ensured. In addition, in one preferred exemplary embodiment the connection device provided at the lower end of the test container may be additionally used for controlled flooding of the test container with water from the pool. In this exemplary embodiment, the interior of the test container at an upper end is fluidically connectable to a sampling point of the mass spectrometer, for example by means of valve systems or the like, in such a way that conveying of the gas column, present in the test container, to the sampling point is made possible due to the introduction of water via the connection device. According to this embodiment, it is thus possible to utilize the hydrostatic pressure of the surrounding water to supply a gas column, present in the test container—and in the case of a leak, containing test gas—virtually completely to the mass spectrometer by flooding the test container in a controlled manner with water from the pool. In one specific exemplary embodiment, the connection device for the controlled flooding of the test container includes a gas exchange device. The gas exchange device includes an inner container over which the second container is pulled. Water from the pool, which may sometimes contain dissolved argon, is situated in the inner container. When the test container is blown out with purge gas, in particular nitrogen, purge gas is blown into the inner container, as the result of which a gas exchange takes place in the water. In this regard, in particular argon may be largely replaced by nitrogen. Due to blowing purge gas into the inner container, the surrounding second container is filled with purge gas. As a result, a hermetic separation from the surrounding pool is present due to the outer container. The volumes of the first and second containers may be dimensioned in such a way that, during the process of return flow (measuring phase) of the water present in the inner container into the test container, no water advances from the pool via the outer container to the inner container before the water level in the test container reaches the pool water level. This is meaningful in particular when argon is used as test gas, since dissolved argon may always be present in the water. A volumetric flow of the gas stream supplied to the sampling point of the mass spectrometer is preferably changeable, in particular controllable or regulatable, by means of an adjustment device, for example at least one further volume control valve or a vacuum pump. The withdrawal at the sampling point thus preferably takes place at constant pressure to avoid skewing of the measuring results. The pumping capacity of the vacuum pump and/or the outlet of the volume control valve may be appropriately varied for controlling or regulating the pressure at the sampling point. The adjustment device, in particular the further volume control valve or the vacuum pump, is particularly preferably connected to a pressure sensor for measuring the pressure at the sampling point. According to one possible exemplary embodiment, the test container is designed for accommodating only a single fuel rod capsule. In an alternative exemplary embodiment, the test container is dimensioned in such a way that multiple fuel rod capsules may be accommodated. The at least one fuel rod capsule is preferably introducible into the test container via a closeable opening on the end. For closing the fuel rod capsule, screw connections may be used, although integrally bonded weld connections in particular are also commonly used. The most accurate knowledge possible of the remaining state variables, in particular the temperature, is desirable for precisely determining the leak rate. Therefore, temperature sensors are preferably provided at various components of the device in order to detect the temperature. According to possible embodiments of the invention, the device includes components, in particular lines and/or line sections, that are situated inside the pool, underwater, and also outside the pool. Due to the decay heat of the fuel, a slightly increased, virtually constant temperature of approximately 30° C. to 40° C. prevails within the pool. Therefore, due to the cooler surroundings, the components situated outside the pool often have a lower temperature, which facilitates condensation of the gas stream while it is being supplied to the sampling point. However, such condensation may skew the measuring results. Therefore, a temperature that is as constant as possible preferably prevails in the entire area of the device. To ensure this, the components of the device situated outside the pool are provided, at least in sections, with thermal insulation. In one refinement of the invention, a heating device is provided, by means of which the components of the device situated outside the pool are heatable, at least in sections. In this way the temperature gradients that occur are at least reduced in order to prevent condensation in particular in the area of the sampling point. The temperature at the sampling point should preferably be set to the temperature present in the pool, by means of the heating device. With regard to the method, the object is achieved by a method for carrying out a leak test of the type stated at the outset, having the additional features of Patent Claim 15. In the method for carrying out the leak test on the fuel rod capsule containing at least one fuel rod and test gas, one of the above-described devices is used, so that reference is first made to the preceding embodiments. For testing the leak-tightness, the at least one fuel rod capsule is introduced into the test container that is lowered into the flooded pool of a nuclear plant. According to the invention, the gas stream containing test gas that has diffused from the fuel rod capsule into the test container is supplied to a mass spectrometer. In addition, a concentration of the test gas that has diffused from the fuel rod capsule into the test container is detected in the gas stream by means of the mass spectrometer in order to determine the leak rate. To this end, it is provided in particular that the leak rate is determined indirectly. To verify that an allowable leak rate has not been exceeded, the detected concentration of the test gas must remain below a predefined threshold value after a preset measuring period has elapsed (period of release of the test gas into the test container), whereby it must be ensured that the concentration of the test gas to be measured is above the detection limit of the mass spectrometer. In the case that argon is used as test gas, the detection limit of the mass spectrometer is typically between 10 parts per billion (ppb) and 1 part per million (ppm). The at least one fuel rod capsule is preferably introduced into the test container underwater, and the water that has penetrated into the test container is replaced by a purge gas. For this purpose, the purge gas is introduced into the test container under pressure. The purge gas preferably remains in the test container for a predefinable period of time before the gas stream containing the purge gas and the test gas that has diffused from the fuel rod capsule is supplied to the mass spectrometer. Under given criteria, which include the pressures and temperatures prevailing at the individual components, the leak rate may be determined from the detected concentration, and the tested fuel rod capsule may be classified with regard to its leak-tightness. In one particularly preferred exemplary embodiment, the test container is flooded with water from the pool in order to generate the gas stream. The test container is in particular flooded in a controlled manner after the predefinable time period has elapsed, in order to supply the gas stream containing test gas to the sampling point. The gas stream supplied to the sampling point of the mass spectrometer is preferably regulated with respect to its volume in such a way that a constant pressure prevails at the sampling point. In one preferred exemplary embodiment, a gas mixture containing a test gas and purge gas is supplied in a predefined mixing ratio to the sampling point in a controlled manner. For purposes of calibrating the mass spectrometer, the supplying of the gas mixture in the predefined mixing ratio may take place before start-up of the mass spectrometer. Components of the device, in particular lines and/or line sections, that are situated outside the pool are preferably heated, at least in sections, during operation. The occurrence of relatively large temperature gradients, which facilitate condensation in the gas stream, may be counteracted in this way. An inert gas may be used as the test gas. Argon is particularly preferably used as test gas. If the encapsulation of the fuel rods into the fuel rod capsules takes place in the same pool of the nuclear plant, it is provided to carry out the encapsulation and the leak testing at different locations within the pool. The reason is that argon has relatively good water solubility. Therefore, the measuring results may be skewed by argon-containing residual moisture remaining in the test container. This effect is at least minimized by a spatial separation of the operations that include the encapsulation and the leak testing. The water is preferably removed from the test container to the greatest extent possible. This may take place, for example, by using high-quality nitrogen as purge gas. FIG. 1 shows the schematic design of a device 1 for carrying out a leak test on a fuel rod capsule 3 containing at least one fuel rod 2 and test gas P according to a first exemplary embodiment of the invention. In the example shown, the fuel rod capsule 3 is filled with argon as test gas P. An internal pressure of approximately 2.5 to 3.5 bar is present within the fuel rod capsule 3. The fuel rod capsule 3 is introduced [into] a test container 4 situated in a pool 5 of a nuclear plant. The pool 5 is filled with water, and the test container 4 is lowered into the pool 5, beneath the water surface. The test container 4 has a closeable opening 6 on the end, through which the fuel rod capsule 3 may be introduced into the test container 4 underwater. A first temperature sensor 7 for measuring the temperature inside the test container 4 is situated in the area of the closeable opening 6. A connection device 8 which provides a connection to the interior of the pool is provided at the lower end of the test container 4. In the exemplary embodiment shown in FIG. 1, the connection device 8 includes a valve 9 and a gas exchange device 10. The connection device 8 that connects to the interior of the pool 5 is used as an outlet for water that has penetrated inside the test container 4. In addition, the connection device 8 allows controlled flooding of the test container 4 with water from the pool 5 in order to convey a gas column, present inside the test container 4, in the direction of a sampling point 13 for a mass spectrometer 14 via lines 11, 12. The device 1 includes components that are associated with an analysis unit 15 situated outside the pool 5. The components associated with the analysis unit 15 include in particular lines 12, 16, 17, 18 and a section of the line 11. In addition, the analysis unit 15 includes pressure sensors 19, 20, valves 21, 22, 23, 24, volume control valves 25, 26, 27, the sampling point 13, and the mass spectrometer 14. The components of the analysis unit 15 are provided with thermal insulation 28 to counteract in particular condensation in the gas stream while the leak test is being carried out. A second temperature sensor 29 is provided for detecting the temperature inside the analysis unit 15. The volume control valve 25 situated at the inlet to the sampling point 13 is connected to the pressure sensor 20 (illustrated by dashed lines). The pressure at the sampling point is controllable and in particular regulatable by means of the volume control valve 25 and the pressure sensor 20 in such a way that the supplying of the gas stream to the mass spectrometer 14 takes place at essentially constant pressure. Purge gas, which in the illustrated example is nitrogen, is stored under pressure in a first reservoir 30. An additional, second reservoir 31 contains test gas, which in the example shown here is nitrogen with a small proportion of argon as test gas P, under pressure. The sampling point 13 is suppliable via the lines 12, 17, 18 with purge gas or test gas in particular for purging or calibrating the mass spectrometer 14. For this purpose, the volumetric flow of the purge gas and test gas may be set by means of the volume control valves 22, 23. The method for carrying out the leak test on the fuel rod capsule 3 takes place using the device 1 shown in FIG. 1, as follows: First, all valves 9, 21, 22, 23, 24 are closed and the gas exchange device 10 is filled with water. The end-side opening 6 of the test container 4 is subsequently opened, and the fuel rod capsule 3 is introduced into the test container 4 underwater. The opening 6 of the test container 4 is then reclosed, and the water that has penetrated into the test container 4 is largely removed. This takes place by opening the valves 9, 21 and feeding purge gas from the first reservoir 30. The water present in the test container 4 is thus displaced, and ejected into the pool via the connection device 8. The test container 4 is adequately flushed with purge gas in order to sufficiently reduce the interior wetting of the test container 4 with water. Excess purge gas exits the device 1 via the connection device 8. During purging, purge gas is introduced into an internal first container of the gas exchange device 10 which contains water. In the process, a gas exchange of gases dissolved in the water takes place. In particular, dissolved argon may thus be replaced by nitrogen. In addition, a second container of the gas exchange device 10 which surrounds the first container is at least partially filled with purge gas during purging. The first and second containers of the gas exchange device 10 are dimensioned in such a way that no water from the pool 5 flows into the test container 4 during flooding of the test container. The valves 9, 21 are subsequently closed. A gas receiver which prevents overflow of water from the pool 5 remains in a dome area of the gas exchange device 10. The water present in the exchange device 10 is largely free of air and/or argon. The internal pressure inside the test container 4 is reduced after the valve 24 is opened. In the example shown here, the internal pressure is set to approximately 1 bar. The valve 24 is then reclosed. To increase the concentration of test gas P in the test container 4, a predefinable time period, which in the present case is one hour by way of example, is awaited before the gas column present in the test container 4 is supplied to the mass spectrometer 14 for analysis. During this time period, the valve 22 is opened and the line 12 is flushed with purge gas, so that no air can penetrate from the outside via an end-side outlet 32 of the line 12. The volume control valve 22 provided for supplying purge gas is set in such a way that compensation may take place via the volume control valve 25 situated at the inlet to the sampling point 13. In particular, the gas stream is adjusted in such a way that the pressure measured by the pressure sensor 20 remains at a virtually constant level during operation of the mass spectrometer 14. The calibration of the mass spectrometer 14 preferably takes place during the predefinable time period, which is used primarily for accumulating test gas P inside the test container 4. For this purpose, the valve 23 is first opened before the valve 22 is closed. The sampling point 13 is then in fluidic connection with the second reservoir 31, in which test gas P is stored under pressure. The volume control valve 23 is hereby set in such a way that compensation may take place by means of the further volume control valve 25, so that an essentially constant pressure is present at the sampling point 13. After calibration of the mass spectrometer 13, the valve 22 is first reopened before the valve 23 is closed. After the predefinable time period has elapsed, the valves 9, 24 are opened and the valve 22 is closed to allow water to flow from the pool 5 via the gas exchange device 10 into the test container 4. The water flows into the test container 4 due to the hydrostatic pressure, and transports the gas column present in the test container 4 in the direction of the sampling point 13. The mass spectrometer 14 detects the concentration of test gas P, in the present case argon, in the gas stream. The inertia of the measuring system, i.e., the minimum measuring time, should be taken into consideration. The volumetric flow is therefore compensated for in such a way that a constant pressure is present at the sampling point 13. The leak rate is calculated from the detected concentration, with inclusion of the measured pressures and temperatures. After the measurement, the valve 24 is reclosed, the test container 4 is opened, and the fuel rod capsule 3 is removed. FIG. 2 shows a device 1 for carrying out a leak test according to a second exemplary embodiment of the invention. The mode of operation of the exemplary embodiment shown corresponds essentially to the device in the first exemplary embodiment, so that reference is first made to this description. The exemplary embodiment shown in FIG. 2 has a vacuum pump 42 for supplying the gas stream to the mass spectrometer 14. In addition, valves 33, 34, 43 are provided, which are designed as ball valves for providing fluidic connections between lines 11, 12, 35, 36, 37, 40, 41, 43. The method for carrying out the leak test takes place using the device 1 of the second exemplary embodiment, illustrated in FIG. 2, as follows: The fuel rod capsule 3 is first introduced into the test container 4 via the end-side opening 6. For this purpose, the valve 33, designed as a ball valve, is opened in the direction of the test container 4. The valve 9 is likewise opened in the conducting direction. The fuel rod capsule 3 which is introduced into the test container 4 extends to just below the valve 33. The water that has penetrated into the test container 4 during insertion of the fuel rod capsule 3 is subsequently expelled from the test container 4. For this purpose, the valve 33 is first closed and the valve 9 is opened. A reservoir, in particular a gas cylinder, containing the purge gas under pressure is connected to an inlet 38. The valve 34 is set in such a way that the line 35 and the line 12 are fluidically connected to one another. The water is subsequently expelled from the test container 4, via the connection device 8, into the pool 5 by blowing in purge gas, in particular nitrogen. The line 35 is subsequently fluidically connected via the line 37, and by switching the valve 34, to the lines 36 and 40. The lines 36, 40 are likewise blown free by blowing in purge gas. When the test container 4 or the lines 35, 36, 37, 40 contain(s) only slight residual quantities of water, the valve 9 is closed. To generate a negative pressure in the test container 4, the valve 34 is first set in such a way that a fluidic connection is provided between the lines 11, 12. Correspondingly, the valve 39 is set in such a way that the lines 40, 41 are connected. The vacuum pump 42 is subsequently put into operation. After the required differential pressure between the interior of the fuel rod capsule 3 and the interior of the test container 4 is reached, the evacuation is discontinued, and the valve 39 is switched in such a way that the lines 40, 43 are fluidically connected to one another. The vacuum pump 42 continues operation even after the required negative pressure inside the test container 4 is reached, in order to continuously convey purge gas together with possible released portions of the test gas from the test container 4 to the mass spectrometer 14 and back again. The conveyed gas stream is analyzed for the contained proportions of test gas by means of the mass spectrometer 14. The leak rate is then determined from the measured concentration and the testing time, with inclusion of the other state variables. The invention has been described above with reference to preferred exemplary embodiments. However, it is understood that the invention is not limited to the specific design of the exemplary embodiments shown. Rather, based on the description, a competent person skilled in the art can derive variations without departing from the essential basic concept of the invention. List of reference numerals1device2fuel rod3fuel rod capsule4test container5pool6opening7temperature sensor8connection device9valve10gas exchange device11line12line13sampling point14mass spectrometer15analysis unit16line17line18line19pressure sensor20pressure sensor21valve22valve23valve24valve25volume control valve26volume control valve27volume control valve28insulation29temperature sensor30reservoir31reservoir32outlet33valve34valve35line36line37line38inlet39valve40line41line42vacuum pump43linePtest gas |
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summary | ||
abstract | The present invention provides a method for manufacturing a lens assembly of a microcolumn having a plurality of microlenses and a plurality of insulating layers alternately interposed between the microlenses. The method includes forming at least one first microlens assembly set (set—1) by anodic-bonding an insulating layer (101) and a microlens (102) together; layering a second microlens assembly set (set—2) on the first microlens assembly set (set—1); and scanning a laser beam, thus welding the first microlens assembly set (set—1) to the microlens of the second microlens assembly set (set—2). The method of the present invention further includes anodic-bonding the microlens assembly sets together. |
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052218422 | description | DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 a calibrator/irradiator unit 10 incorporating my invention is mounted on a platform 12 supported on a plurality of wheels 14, two of which are on casters. The overall dimensions of the unit and the platform are such that the assembly can be moved around essentially as desired and since the diameter of the calibrator/irradiator is approximately 32 inches, it is easily moved through 36 inch doorways. The calibrator/irradiator unit 10 includes a base 16 which contains among other things, a source drive system and other equipment discussed below. Supported on the base 16 is a large cylindrical container 18 which includes thick walls including lead shielding and a power operated cover or lid 20, also including heavy shielding. The cover 20 is hinged on one side of container 18 at hinge 22 and includes, on its top, a crossbar 24 having attached thereto a pair of damper rods 26,28 which cushion the closing of the cover which is lifted by an actuator connected to an electric motor, also discussed below. Within container 18 and carried along its axis is a cylindrical shielding structure 30 including a shielded radiation source rod. Also carried on the platform 12 is an instrument cabinet 32 including a control panel 34. FIG. 2 is a perspective view looking in the top of container 18 wherein the cylindrical structure 30 containing the source rod is shown and also a dosimeter rack 36 which includes openings 38 for receiving a large number of dosimeter units to be irradiated. Also shown in FIG. 2 is a cylindrical aluminum plate 39 which serves as a mechanical spacer and as a scatter shield as will be set forth in greater detail below. In this view only the portion inside the main shielding of container 18 is shown including a cylindrical wall 40 preferably of copper, approximately one-eighth inch thick which serves as a back scatter shield. FIGS. 3 and 4 illustrate closed and open positions of the lid 20 which closes the top of container 18. In FIG. 3 the cover 20 is shown closed against container 18. Also shown are the crossbar 24, damper rods 26 and 28 which are anchored at locations 42 and 44 respectively, on the platform 12, arm 46 which is part of the lid actuating structure, and hinge 22. Also shown is an upstanding centrally located cylindrical cap 21 in the center of the top of cover 20 which surrounds a corresponding cylindrical chamber accessible from the bottom of cover 20. FIG. 4, showing the cover 20 open, discloses a dosimeter rack 36 positioned in container 18, concentric with structure 30 containing the source rod. FIG. 5 is a side view, primarily in section, of the calibrator/irradiator described in FIGS. 1-4. Platform 12 is shown, supported on wheels 14 (two of which are on casters) with the platform 12 carrying the base 16 to which the cylindrical container 18 is fastened, as by means of bolts 48. An extension 50 of platform 12 supports one end of an actuator 52 actuated by an electric motor 54, said actuator being pivotally supported on a bracket and pin 56 and having its opposite end pivotally connected to arm 46. In this view it will be observed that a link 58 extends between the outboard end of arm 46 and cover 20. Operation of electric motor 54 and actuator 52 results in raising the cover 20 to the position shown in phantom, the actuator 52 pivoting around lower mounting bracket and pin 56 as required to raise cover 20. Cover 20 is quite heavy since it carries two layers of lead shielding 60, 62 bolted to a heavy steel lid and would have a possibility of slamming shut very quickly with possible injury to personnel should motor 54 happen to lose power unexpectedly. Damper rods 26, 28 (FIGS. 3 and 4) serve to prevent any such rapid closing. A top plate of base 16 is shown at numeral 64 to which is bolted a bottom plate 66 of container 18. Container 18 has an external cylindral wall 68 and an internal cylindrical wall 70 serving as a backscatter shield and which is preferably of copper 0.32 cm (1/8") thick, with the space 72 between the cylindrical walls being filled with lead to form the primary shielding layer. Additional lead shielding is shown at numeral 74 on the bottom of container 18. Fastened to base 16 as by bolts 76 is a cylindrical shield structure consisting of a lower member 78 and an upper member 80 which is axially aligned with and spaced from member 78 by means of the cylindrical scatter shield 39. A central bore 82 passes through the axis of members 78 and 80. Positioned in bore 80 and axially movable therein is a source rod 84 carrying a source of nuclear radiation 86 which, as shown, is aligned with the space between members 78 and 80. Each of members 78 and 80 includes a facing surface 88 and 90, respectively, in the form of flat conical surfaces preferably of aluminum, which surfaces, together with the heavy lead shielding in members 78 and 80, serve to provide a beam directing path for directing radiation outwardly, from source 86 along a path indicated by the dotted lines. The radiation is directed toward a vertical internal cylindrical surface of a rotatable member 92 which is shown carrying a plurality of dosimeters 94 which are to be irradiated. There are several types of dosimeter devices which it may be desired to irradiate and calibrate, some of which may hang on the inside surface of the wall of member 92 or they may be placed in one of a number of annular dosimeter racks 36, each of which has holes, grooves or other suitable support means for a given type of dosimeter. Member 92 is attached to a turntable structure 96 driven by an electric motor 98 as described below. When it is no longer desired to irradiate the dosimeters, the source rod 84 is translated downward, placing source 86 within the shielding of member 78. Those portions of rod 84 above and below the source 86 are of tungsten which is a very effective shielding material, so that radiation from source 86 is effectively contained and it is quite safe for personnel to open the cover 20 and remove and replace a dosimeter rack or perform other desired operations within the housing 18. Translation is effected by means of a pneumatic actuator 100. A pair of microswitches 102, 104 are operative at each end of the stroke to stop the movement. As shown in FIG. 5, the device has two positions, one being that shown where the source 86 is aligned with the beam path between members 88 and 90, and the other where rod 84 is moved downwardly to place source 86 in a position where its radiation is essentially completely shielded by the lead mass in member 78 plus the tungsten portions of rod 84. FIG. 6 is an enlarged view, partly in section, of a device very similar to that of FIG. 5, but with certain modifications which make it possible to supply multiple dose rates. In FIG. 6 those components which are, Or may be, the same as those of FIG. 5, are given the same numerals and the structure not shown is identical with that of FIG. 5. The electric motor 98 drives a sprocket 110 which drives a chain 112 wrapped around a turntable 96, the turntable also having sprocket teeth engaging the chain. Turntable 96 is pinned to rotatable member 92 as well as to a plurality of wheels 99 having "V" section rims and which ride on a member 101 extending radially from member 78. As will be apparent from the relative diameters of the sprocket 110 vs. the turntable 96, this assembly drives the turntable quite slowly relative to the rotational speed of the sprocket 110. Although the sources 86 and 118 radiate 360 degrees, the pattern is never totally uniform and it has been found that rotating the dosimeters provides greater uniformity in calibration. The pneumatic actuator 114 differs from actuator 100 in that it must locate source rod 116 in any of three desired axial positions: for selecting source 86, or source 118, or for moving rod 116 to a position where both sources are shielded. As the actuator approaches any of the desired positions, it operates one of microswitches 115, 117 or 119 to stop the translation of rod 116 at the desired position. Of the two radiation sources, source 118 may be several times stronger than source 86. When source 86 is aligned with the opening between surfaces 88 and 90, as shown, the dosimeters 94 are irradiated as described above. Source rod 116 may also be moved axially upwardly to align source 118 with the opening between surfaces 88 and 90 to thereby subject the dosimeters to a stronger radiation dose. The stronger, or different dosages are appropriate for different types of dosimeters. It will be apparent that the dosimeters 94 will be subject to radiation momentarily from the upper source 86 on upward or downward translation of source rod 116 even when it is desired to use source 118. Since the exposure to source 86 in either upward or downward travel is in the order of 0.1 sec or less, and since source 118 is, or may be, ten times stronger than source 86, the momentary exposure to source 86 becomes insignificant. The dosage of radiation to dosimeters 94 is also subject to variation through the operation of an attenuator in the form of a thin tungsten sleeve 120 movable axially downward to cover source 86 or 118, as shown, or upwardly to clear the beam path between surfaces 88 and 90. Sleeve 120 is fastened to a header member 122 which is, in turn, bolted to a rod 124 forming part of an actuator 126. Actuator 126 may be a solenoid or it may be a pneumatic actuator, and is carried within a cylindrical housing extension 128 bolted to member 80 and extending into the interior of cap member 21. The inside of cap member 21 is lined with lead shielding material 129. FIGS. 7 through 15 depict a number of typical dosimeter racks which are used with the devices of FIGS. 5 and 6. FIG. 7 is an enlarged portion of FIG. 2 showing a rack with holes for dosimeters which are generally cylindrical, a cross-section appearing in FIG. 8. FIGS. 9 and 10 are similar fragmentary plan and cross-sectional views of a rack for a different type of dosimeter. FIGS. 11 and 12 show a still different configuration of rack for still different types of dosimeters. FIG. 13 shows a generally cylindrical dosimeter installed in a rack like that of FIG. 7. FIG. 14 shows a still different dosimeter installing in a rack like that of FIGS. 9 and 10. FIG. 15 is a fragmentary sectional drawing similar to FIGS. 8, 10 and 12 and showing a dosimeter suspended as shown in FIGS. 5 and 6. FIG. 16 shows, in detail, the control panel 34 applicable to the embodiment of FIG. 6. Many of the functions described above are controlled from this panel which also includes a timer 130 which provides an LED display showing elapsed time of radiation and another display 132 showing remaining times for radiation. A switch 134 enables an operator to choose between manual setting and preset times. Completion of a preset time for radiation is indicated by illumination of a large indicator light 135 which may be accompanied by an audible signal such as a buzzer. A key operated power off-on switch is shown at numeral 136 with an indicator lamp 138 showing that power is on. The means for raising and lowering the cover 20 has been discussed in part above and panel 34 includes a three-position toggle switch 140 for raising or lowering the cover 20. Indicator lamps 142, 144 indicate that the cover is raised or lowered. Power to the turntable is indicated by lighting one or the other of lamps 146 or 150. When the turntable is energized as by turning toggle switch 148 from the "off" to the "on" position, an "on" indicator lamp 146 is lighted and when toggle switch 148 is turned to "off" position, the "off" lamp 150 is illuminated. The attenuator also is operated from panel 34 and includes an "on" indicator lamp 152, a toggle switch 154 for switching the attenuator either into a position over the radiation source (ON) or out of such position (OFF) respectively. When the attenuator sleeve 120 is in position over either source 86 or 118, lamp 152 is turned on. When sleeve 120 is retracted, lamp 156 is illuminated. Also forming part of the panel 34 is a switch 157 for turning on the compressor (not shown) which supplies air under pressure to a pneumatic actuator. In the event that air pressure is insufficient to operate the pneumatic actuator, a lamp 158 indicates such low pressure and the operator then is made aware that he should allow more time for the compressor to build up pressure before operating the source rod actuator 114 or that there is a malfunction in the pneumatic system. The source control part of the panel includes "irradiate" and "off" lamps 159 and 160, respectively, for source 186 which may be, for example, a 3 Ci source, and a momentary "OFF-ON" push button 162. Source 86, which may be a 2 mCi source is requested by a momentary "ON" push button 164 and when this source is in the "irradiate" position, a lamp 165 is illuminated. A second momentary OFF push button 166 is pushed to return the source 86 to shielded position. This will be indicated by illumination of an OFF lamp 167. An additional LOCAL-COMPUTER switch 168 is included to enable the operator to transfer control of some of the above functions to computer control which is not described herein since it forms no part of the present invention. FIG. 17 is a schematic diagram of the pneumatic system as arranged to operate a two position source rod and also a two position attenuator, if the attenuator is operated pneumatically. (It may also be operated by a solenoid.) Air under pressure from a compressor, not shown, is supplied to a quick disconnect type of connector 169, to a pressure switch 170, a filter 171, a regulator and gauge 172, a Watts oiler 174 and to a four way solenoid valve 176. When the solenoid valve is in one position, a supply of air is connected through a line 178 to an actuator or cylinder 100 to drive the rod 84 (FIG. 5) in one direction. Movement of the rod results in exhaust air being delivered through a line 180 to the solenoid which then exhausts the air to the atmosphere. Selection of movement to another position results in supplying air under pressure through line 178 to the opposite end of cylinder 100 with exhaust through line 180. Also receiving high pressure air through a line 182 is a second four way solenoid valve 184 having connections 186 and 188 to a pneumatic actuator 190 which operates attenuator sleeve 120. The solenoid valve 184 is, or may be, identical to solenoid valve 176 and includes means to alternately operate actuator 126 in one direction or the other. A schematic diagram of a modified pneumatic system is shown in FIG. 18. In this system no circuit for the attenuator is shown (although it may be included) and a second circuit is shown operating through a high pressure line 192 to drive a solenoid operated brake 194 forming part of the three position rod actuator 114. Even with microswitches 115, 117 and 119 a brake is desired to insure that the rod 116 moves quickly and will stop at the desired intermediate position without under or overshooting. Other components which are the same as those of FIG. 9 are given the same numerals. A Watts Oiler and regulator 196 is connected in line 192. In this system actuator 114 has three positions as set forth above and solenoid valve 176, responding to a request from the control panel moves to one of its four positions to drive o actuator 114 to the desired position. This brake is not required in the case of the actuator 100 which has only two positions. FIGS. 19A, 19B, and 19C are diagrams showing the electrical connections to the various switches and relays used in connection with the system thus far described. A power source is shown as 115 v.a.c., connected across lines 200 and 202. The power key switch 136 is connected across this supply as is a fuse 204. Closing of switch 136 illuminates lamp 138, and energizes the system shown on FIGS. 19A and 19B, the system of FIG. 19B being a continuation of that of FIG. 19A. This also energizes relay coil R1 and closes its contacts to provide power to the electronic timer 130, which circuit should be isolated such that it is protected from voltage surges from the switches and relays shown. When it is desired to operate the calibrator/irradiator and the power is turned on illuminating power lamp 138 and the source or sources installed, one will want to open the cover 20 to install a dosimeter rack 36. If the source or sources are in the lowered or shielded position microswitch 119 is closed as shown and coil R5 is energized closing contacts R5. Operating toggle switch 140 to the RAISE position will connect power through closed contacts R5 and N.C. contacts R4 to cause actuator 52, 54 to raise the cover. The cover will then continue to open until it has reached its full open position, at which point the COVER OPEN microswitch 141 is closed to energize coil R4 which opens N.C. contacts R4 to stop the actuator 52, 54 and to illuminate COVER OPEN lamp 142. Since switch 140 is a three position switch, the operator may decide to stop the raising or lowering of the cover 20 at any point in its travel which can be done by switching toggle switch 140 back to its middle position, thereby opening the circuit to the actuator 52, 54. When the dosimeter rack 36 is installed, operation of toggle switch 140 to the LOWER position will connect power through N.C. contacts R3 and causing the actuator 52, 54 to move in the opposite direction to close the cover 20. At approximately the point of closing, microswitch 143 is closed, energizing coil R3, opening N.C. contacts R3 and closing the circuit through N.O. contacts R3 to illuminate the COVER CLOSED lamp 144, which also closes a cover interlock. At the time it is desired to raise the source 86 or 118 to an irradiate position, a time is designated on the timer 130 if a timed irradiation is requested, and the timer PRESET/MANUAL switch 134 selected as desired. Before one of the switches 162 or 164 is activated, contacts R5 are closed, but contacts R6 and R7 are open. This puts power through R5 across the 3Ci OFF lamp 160 and across the 20mCi OFF lamp 167. Selecting the 3Ci source by closing switch 162 will energize relay coil R3Ci, closing contacts R3Ci which closes a circuit through solenoid valve 176 and causes actuator 114 to raise the source rod 116 to the 3Ci (Source 118) position. Microswitch 119 is opened and microswitch 115 is closed which energizes relay coil R7, turning on the 3Ci "Irradiate" lamp 159. Had the 20mCi source been chosen by switch 162, relay coil R20mCi will be energized which will energize solenoid valve 176 to cause actuator 114 to move to the intermediate position. This causes actuator 114 to reach brake microswitch 117 and energizing relay coil R6. The brake solenoid 194 is then energized to stop the rod 116 at the desired position Energizing relay coil R6 will close contacts R6 which will illuminate the 20mCi ON lamp 165. Since there is not a significant hazard in operating the turntable 92 with the cover either open or closed, no interlock is involved in turning it on. The switch 148, if in the OFF position closes the circuit through TURNTABLE OFF lamp 146. Changing the switch 148 to the ON position disconnects lamp 146, illuminates lamp 150, energizes the turntable motor 98 and energizes relay coil R2. When this invention is used with computer control, closing contacts R2 (FIG. 19C) informs an associated computer that the turntable is operating. In addition to the turntable switch 148 on the contact panel, there is a by-pass switch 212 located elsewhere on the system for blocking use of the turntable altogether. Some operators feel that the turntable operation is not necessary and by-pass switch 212 makes it possible to operate all other functions of the system even though the turntable switch 148 is in the "OFF" position. As indicated above, the N.O. relay contacts R3 must be closed to permit the source rod 116 to remain in an irradiating position. With contacts R3 closed, the operator may choose to place LOCAL-COMPUTER switch 168 in the LOCAL position. This is a double pole switch with contacts 168 and 168'. Placing the contacts in the LOCAL position connects the terminals marked "X" and power is connected through either of switches 148 or 212, switch 208 which is normally closed, through the timer 130 or the manual position of the preset-manned switch 134, through IRRAD switch 210 and relay coil R11. It will be observed that one contact position of the timer connects to the "CYCLE COMPLETE" lamp 135 and the sounding device or sonalert 215 thus providing both visible and audible indications that the requested timed cycle is complete. Operation in this mode is complete as described and the computer is, in effect, not connected to the system. The relay coil R12 is connected directly across power lines 200 and 202 in series with a switch 214 which responds to pressure in the pneumatic system. Should such pressure drop below a desired value, switch 214 will close energizing relay coil R12, closing relay contacts R12 and illuminating the "LOW PRESSURE" lamp 158. Where large numbers of batches of dosimeters 94 are to be calibrated, it is useful to connect the system to a computer which could be any IBM PC/XT/AT compatible computer. Those functions which involve significant hazards to personnel if not done correctly such as opening and closing the cover 20 are operated manually as described and are not operated through or by the computer. Turning the LOCAL-COMPUTER switch 168, 168' to the COMP position activates relay RC1 (FIG. 19C) which is a momentary switch to activate the sources and closes contacts RC1 and RC2 which remain continuously closed during the irradiation cycle. The several relays shown on FIG. 19C are, or may be, all connected through a single connector J. When RC2 is energized, it pulls in contacts R9 thereby closing a circuit through R10 and closing contacts R10. Relay RC1 also closes contacts R11. R11 is an interlock which will cut power to the sources and drop them to the shielded position should N.O. contacts R3 for any reason, become open. The contacts 168', when in the COMP position, connect relay coil R3Ci through contacts RC3 and relay coils R20mCi through relay coil RC4. One of RC3 or RC4 is selected through the computer, the irradiation timing sequence is then controlled through the computer. The remaining relay contacts shown on FIG. 19C are closed as described above with respect to functioning in the manual mode, closing of the respective relays tells the computer which of the various functions is in operation and it, through its interval clock, times each function and makes a record of each dosimeter irradiation cycle. While only a limited number of embodiments are shown and described herein, those skilled in the art will be aware of a number of possible modifications. While the turntable and its operation improve the accuracy of radiation, there may be those who consider the increment of improvement insufficient to justify the additional complexity. As stated above, while the actuators 100 and 114 are preferably pneumatic, other actuators such as that operating the cover and the attenuator may be either pneumatic or electrically operated. A number of switching arrangements are possible, but it must be borne in mind that an interlock must be included to present the cover from being opened when the sources 86 or 118 are in radiating position. Thus the above described embodiments are to be considered as merely descriptive of its principles and are not to be considered limiting. The scope of the present invention instead shall be determined from the scope of the following claims including their equivalents. |
042644135 | claims | 1. In a method for producing and confining a toroidal plasma having a cross-section elongated in the direction of the major toroidal axis, comprising the steps of pulsing electrical current around the poloidal circumference of a plasma confinement zone and initially producing a sharp-boundaried, toroidal, theta-pinch plasma having plasma current flow substantially limited to a current sheath at the surface of the toroidal plasma to generate a toroidal magnetic field component which is substantially absent from the plasma interiorly of the current sheath whereby an electromagnetic confining force is exerted on the plasma from the plasma surface, and subsequently relaxing said current sheath of the plasma while maintaining the plasma in a toroidal magnetic field to provide a toroidal diffuse-pinch plasma in which the plasma current is distributed over the cross-section of the plasma to generate a diffuse poloidal magnetic field component distributed throughout the plasma, the improvement comprising the steps of providing said diffuse-pinch plasma with a doublet or higher multiplet magnetic confinement configuration having one or more internal separatrices, and providing said initially formed, sharp-boundaried plasma with a current sheath having a contour corresponding to a flux surface of said doublet or higher multiplet diffuse pinch configuration. means for producing a toroidal, sharp-boundaried theta-pinch plasma in a toroidal plasma confinement zone having a current sheath at the outside surface of the plasma, and means for relaxing the current sheath of the sharp-boundaried plasma while maintaining a toroidal magnetic field in the plasma confinement zone to produce a toroidal diffuse-pinch plasma with a poloidal magnetic field distributed throughout the plasma, the improvement comprising means for providing said diffuse plasma with a doublet or higher multiplet magnetic confinement configuration having one or more internal separatrices, and means for shaping the current sheath of said initially formed sharp-boundaried plasma to conform to a flux surface of said doublet or higher multiplet magnetic confinement configuration. 2. A method in accordance with claim 1 wherein said plasma is a plasma selected from the group consisting of hydrogen plasmas, deuterium plasmas, tritium plasmas, and mixtures thereof. 3. A method in accordance with claim 1 wherein the plasma has an elongation ratio of at least three, and wherein a higher multiplet magnetic confinement configuration is employed having more than two internal separatrices. 4. A method in accordance with claim 1 wherein said doublet or multiplet configuration is provided through the use of a toroidal conducting shell surrounding said plasma confinement zone and having a doublet or higher multiplet contour. 5. A method in accordance with claim 1 wherein said doublet or multiplet magnetic confinement configuration is provided at least in part by conducting current through field shaping coils oriented parallel to the minor toroidal axis to provide a magnetic field component which combines with the toroidal and poloidal plasma field components to provide a doublet or higher multiplet field. 6. In an apparatus for producing and maintaining a toroidal plasma having a cross-section elongated in the direction of the major toroidal axis, comprising, 7. Apparatus in accordance with claim 6 wherein said doublet or higher multiplet magnetic confinement means comprises a conducting shell having a doublet or higher multiplet flux surface contour, and wherein said current sheath shaping means comprises said conducting shell and means for pulsing electrical current around said shell. 8. Apparatus in accordance with claim 6 wherein said doublet or higher multiplet magnetic confinement means comprises magnetic field generating coils oriented parallel to the minor toroidal axis, and means for selectively energizing said coils to provide a magnetic field in said confinement zone having one or more internal separatrices. 9. Apparatus in accordance with claim 6 further comprising toroidal field generating coils encircling the minor toroidal axis and electrical current supply means for said coils to control the .beta. ratio of the confined plasma. |
046612912 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is now described in more detail. In this specification, percent (%) to indicate the composition means wt% unless otherwise mentioned. The method of this invention for fixation of incinerator ash is applied to incinerator ash containing SiO.sub.2 and Al.sub.2 O.sub.3. Such ash is left after incineration of municipal waste, industrial waste, and waste from atomic energy facilities (such as atomic power plants, nuclear fuel reprocessing plants, and laboratories.) The last category includes wood, cloth, paper towel, computer printing paper, polyethylene film, ion exchange resin, rubber gloves, garbage, etc. According to this invention, incinerator ash is incorporated with NaOH or NaOH and an SiO.sub.2 -containing substance to make a mixture composed of 25 to 95% of SiO.sub.2, 2 to 10% of Na.sub.2 O, and more than 3% of Al.sub.2 O.sub.3. The content of Al.sub.2 O.sub.3 in terms of mol% in the mixture is less than the content of SiO.sub.2 in terms of mol%. Usually the content of Na.sub.2 O in incinerator ash is about 1% or less; and therefore the addition of NaOH is essential in this invention. Usually the content of SiO.sub.2 and Al.sub.2 O.sub.3 in incinerator ash is in the range of the above-mentioned composition; therefore, the addition of SiO.sub.2 is not essential in this invention. If the content is outside the above-mentioned range, it is necessary to adjust the content by adding an SiO.sub.2 -containing substance. Preferred examples of the SiO.sub.2 -containing substance include silica-stone powder, white clay powder, zeolite, soda glass, silicate glass, silica-containing glass, silica glass, sodium borosilicate glass, silica gel, and SiO.sub.2 -rich incinerator ash. The powder of SiO.sub.2 -containing substance should preferably be finer than 100 .mu.m in particle diameter; but it may contain coarse particles (greater than 100 .mu.m) up to 50% by volume. It is convenient to add NaOH in the form of aqueous solution because water is added to the mixture afterward, as mentioned below. According to this invention, more than 5 parts by weight, preferably 5 to 20 parts by weight of water is added to the mixture. The water should preferably be added in the form of aqueous solution of sodium hydroxide as mentioned above; but it may also be added alone. After the addition of water and mixing, the resulting mixture is subjected to hydrothermal reaction under a pressure of 70 kg/cm.sup.2 and up and a temperature of 150.degree. C. and up, whereby the fixing is accomplished. In other words, the hydrothermal reaction forms the three-dimensional skeleton structure (network) of at least partially hydrated alkali-containing aluminosilicate, whereby incinerator ash is fixed and metals (particularly heavy metals) in incinerator ash are sealed in the network. The following is an explanation of why the range of the content of SiO.sub.2, Al.sub.2 O.sub.3, and Na.sub.2 O is established as mentioned above. SiO.sub.2 takes part in forming the network of alkali-containing aluminosilicate. If the content is less than 25%, the network is not formed sufficiently and the fixed body is poor in strength. The upper limit of the content of SiO.sub.2 is established at 95%, because the lower limit of the content of Na.sub.2 O and Al.sub.2 O.sub.3 is 2% and 3%, respectively; therefore, it is not critical. The preferred content of SiO.sub.2 is 30 to 60%. Al.sub.2 O.sub.3 alone does not take part in forming the network; but it does by replacing a part of SiO.sub.2 in the network. Aluminum that has replaced Si in the network is negatively charged and attracts positively charged metal ions. If the content of Al.sub.2 O.sub.3 is less than 3 wt%, the network does not seal metal ions therein completely. If the content of Al.sub.2 O.sub.3 in terms of mol% is greater than that of SiO.sub.2 in terms of mol%, the network does not grow completely. Na.sub.2 O reacts with SiO.sub.2 and Al.sub.2 O.sub.3 during the hydrothermal reaction to accelerate the hydrothermal reaction and the formation of the alumino-silicate network. If the content of Na.sub.2 O is less than 2%, the reaction and network formation are not accelerated sufficiently. Conversely, if the content exceeds 10%, the aluminosilicate network is broken and the fixed body is weak and hence the network does not completely seal metal ions therein. The amount of NaOH in the mixture is expressed in terms of the content of Na.sub.2 O. In other words, NaOH in the mixture is assumed to be composed of Na.sub.2 O and H.sub.2 O, and the amount of H.sub.2 O derived from NaOH is combined with the water added separately and is not included in the weight of incinerator ash being disposed of. The amount of water to be added to the mixture is more than 5 parts by weight, preferably 5 to 20 parts by weight for 100 parts by weight of the mixture. If the amount of water is less than 5 parts by weight, the hydrothermal reaction does not proceed completely; and conversely if the amount of water exceeds 20 parts by weight, the resulting fixed body is so porous and weak that metals will leach out easily. The mixture may contain metal oxides such as Fe.sub.2 O.sub.3, Cr.sub.2 O.sub.3, MgO, CaO, TiO.sub.2, and K.sub.2 O in addition to the above-mentioned SiO.sub.2, Al.sub.2 O.sub.3, and Na.sub.2 O. Their amount and kind are not specifically limited; up to 40% is permissible without adverse effect on strength. In addition, the mixture may contain anions such as SO.sub.4.sup.--, Cl.sup.-, PO.sub.4.sup.--, CO.sub.3.sup.--, IO.sub.3.sup.-, and I.sup.- in an amount up to 20% in total. Where SO.sub.4.sup.-- is present in the form of gypsum (CaSO.sub.4), it accelerates the fixing reaction of incinerator ash. The method of this invention for fixation of iodine sorbent can be applied to the disposal of radioactive iodine originating from nuclear fuel reprocessing plants and atomic power plants. It can also be applied to the disposal of iodine of any origin. The sorbent used for the adsorption of iodine is a silver-loaded silicate adsorbent such as silver-loaded zeolite, silver-loaded mordenite, and silver-loaded silica gel. The amount of silver loaded is not specifically limited; but is is 5 to 50%, preferably 10 to 40%. Iodine is brought into contact with a silver-loaded adsorbent by using a common adsorber. The contact is accomplished by passing an iodine-containing fluid through a metal casing filled with a silver-loaded adsorbent. Upon contact with a silver-loaded silicate adsorbent, iodine is adsorbed by the adsorbent. A part of iodine passes into AgI and the remainder remains in the form simple substance or forms an instable bond with Ag. The amount of adsorbed iodine is not specifically limited; and the saturated adsorbent can be processed for fixation. In the practicing of the method of this invention for fixation of iodine sorbent, the sorbent which has adsorbed iodine may be crushed, if necessary. (Where the adsorbent is silica gel, it is desirable to crush it into power finer than 100 .mu.m in particle diameter because it is slow in fixing reaction and is hard to fix. Where the adsorbent is zeolite or mordenite, crushing is not advisable because it might give off a gas when crushed.) Subsequently, the adsorbent is incorporated with one or more than one of sodium hydroxide, potassium hydroxide, and barium hydroxide, preferably followed by thorough mixing. This mixing may be accomplished simultaneously with the above-mentioned crushing in a mill. The addition of an alkali metal hydroxide or alkaline earth metal hydroxide changes the physically adsorbed iodine into stable AgI or AgIO.sub.3 according to the following reaction formula. EQU 3I.sub.2 +60H.sup.- +6Ag.sup.+ .revreaction.AgIO.sub.3 +5AgI+3H.sub.2 O According to this invention, the mixture of the adsorbent that has adsorbed iodine and an alkali metal hydroxide or alkaline earth metal hydroxide is subjected to a hydrothermal reaction. Therefore, it is preferable to add water necessary for the reaction. Where barium hydroxide is used, the addition of water is not necessarily required because it contains a large amount of water of crystallization which is enough to permit the hydrothermal reaction to proceed. Where water is to be added, it is permissible to add water alone or in the form of aqueous solution of sodium hydroxide, potassium hydroxide, or barium hydroxide. The mixture of a silicate adsorbent that has adsorbed iodine and an alkali metal or alkaline earth metal hydroxide, said mixture containing water (and/or water of crystallization), undergoes hydrothermal reaction under a pressure of 70 kg/cm.sup.2 and up and at a temperature of 150.degree. C. and up, whereby the mixture is fixed. The hydrothermal reaction forms the three dimensional skeleton structure (network) of alkali-containing aluminosilicate which is at least partially hydrated. Through this reaction, the mixture composed mainly of silicate adsorbent is made into a compact strong solid and the iodine adsorbed onto the adsorbent is sealed in the network. During the hydrothermal reaction, sodium hydroxide, potassium hydroxide, or barium hydroxide reacts with SiO.sub.2 and Al.sub.2 O.sub.3 constituting the adsorbent, accelerating the hydration reaction and the reaction to form the network of aluminosilicate. If the amount of alkali hydroxide or alkaline earth metal hydroxide added is less than 1%, the reaction is not sufficiently accelerated; and if it is in excess of 30%, the network of aluminosilicate is broken and the fixed body is poor in strength and the sealing of iodine by the network is incomplete. The amount of water to be contained in the mixture should preferably be 2 to 20 parts by weight for 100 parts by weight of the mixture. If the water content is less than 2 parts by weight, the hydrothermal reaction does not proceed sufficiently. If the water content exceeds 20 parts by weight, the resulting fixed body is excessively porous (a large number of pores and a large pore diameter) and is so weak that iodine will leach out. The hydrothermal reaction for fixation of incinerator ash or iodine sorbent should be performed under a pressure of 70 kg/cm.sup.2 and above. The upper limit of the pressure is practically about 500 kg/cm.sup.2. Needless to say, the pressure should be higher than the vapor pressure of water at the reaction temperature so that the hydrothermal state is established. The hydrothermal reaction should be performed at 150.degree. C. and above; otherwise, the fixation reaction does not proceed and the resulting fixed body is very weak. The preferred temperature is 200.degree. to 350.degree. C. The hydrothermal reaction should be performed for 5 minutes to 1 hour. The reaction time may be extended where the reaction pressure and temperature are low and may be shortened where the reaction pressure and temperature are high. In the research by the present inventors, it was found that strong fixed bodies are obtained when the hydrothermal reaction is performed for a long time at as low a pressure and temperature as possible within the above-mentioned range. The hydrothermal reaction in this invention may be conveniently performed by using an apparatus made up of a cylinder and a piston fitted into one end thereof or two pistons fitted into both ends thereof, and a reaction chamber enclosed by the cylinder and piston(s). The mixture formed by adding water and mixing is filled in the reaction chamber, and it is compressed by the piston and heated simultaneously, whereby the hydrothermal reaction is performed. After a prescribed period of time, the reaction apparatus is cooled and the fixed body is discharged. What is important for the fixation reaction is that the mixture be heated under pressure during the reaction. Therefore, the pressurization and heating may be performed separately or simultaneously. FIG. 1 is a block diagram showing a procedure of fixing incinerator ash according to this invention by using the above-mentioned apparatus. In the first step, incinerator ash undergoes pretreatment for the removal of noncombustible materials such as bolts and wires and large aggregates. This pretreatment makes easy the subsequent steps. In the following steps, incinerator ash is weighed and a prescribed amount of NaOH aqueous solution is added with mixing. The resulting mixture is filled in the reaction apparatus for hydrothermal reaction under pressure and heating. After a prescribed period of time, the reaction apparatus is cooled and the fixed body is discharged. It is recommended that the charging of the mixture into the reaction apparatus be performed in several portions and each portion be compressed (temporarily) each time after charging. The temporary compression reduces the volume of individual portions charged, and consequently it is possible to fill a large amount of the mixture into the reaction apparatus or it is possible to reduce the capacity of the reaction apparatus for a certain amount of the mixture. The temporary compression may be achieved with about one-tenth the pressure employed for the fixing reaction. After all the mixture has been charged into the reaction apparatus by repeating the temporary compression as many times as the number of portions, the fixing reaction is started by applying the prescribed pressure. FIG. 2 is a block diagram showing a procedure of fixing iodine sorbent according to this invention. FIG. 1 and FIG. 2 are illustrative only and are not intended to limit the scope of this invention. According to one method of this invention, incinerator ash is incorporated with NaOH and optionally SiO.sub.2, followed by mixing, and the resulting mixture is subjected to hydrothermal reaction, whereby there is obtained a fixed body having the three-dimensional network of at least partially hydrated alkali-containing aluminosilicate. This fixed body holds metals therein. According to the other method of this invention, iodine is allowed to be adsorbed onto a sorbent and the resulting iodine sorbent is incorporated with a hydroxide of alkali metal or alkaline earth metal and optionally water, and the resulting mixture is subjected to hydrothermal reaction, whereby there is obtained a fixed body having the three-dimensional network of at least partially hydrated alkali-containing aluminosilicate. This fixed body holds iodine in the form of very stable compounds such as AgI and AgIO.sub.3. Therefore, the second method is very effective in fixing a sorbent which has adsorbed radioactive iodine. Both fixing of incinerator ash and fixing of iodine sorbent in this invention provide very compact and strong fixed bodies, which are stable over a long storage period, with very little leaching of metal ions or iodine. The fixed bodies thus produced are much smaller in volume than the incinerator ash or iodine sorbent. The volume reduction to one-sixth or below is possible in the case of incinerator ash. The heating and compressing apparatus required for the method of this invention is nothing special, and the additives required for the process are cheap. Thus the fixation according to this invention can be carried out at a low running cost. The method of this invention is easy to practice and is of practical use. The invention will be understood more readily by reference to the following examples; however, these examples are intended to illustrate the invention and not to be construed to limit the scope of the invention. EXAMPLE 1 An ash sample having the composition as shown in Table 1 was prepared by incinerating waste composed of softwood (10 wt%), cotton (34 wt%), computer printing paper (6 wt%), and polyethylene sheet (50 wt%). One kg of this ash sample was mixed with an aqueous solution of sodium hydroxide by spraying. (The amount and concentration of the NaOH solution are shown in the footnote to Table 2.) The mixture was subjected to hydrothermal reaction at 300 kg/cm.sup.2 and 300.degree. C. for 20 minutes, whereby the mixture was made into a fixed body. The apparatus for hydrothermal reaction is made up of a stainless steel cylinder, a pair of stainless steel pistons fitted into both ends of the cylinder, and a 2-kW heating wire (3 mm in diameter) wound around the cylinder. At the center of the cylinder, there is formed a thermocouple well which extends near (2 mm) to the inner surface of the cylinder. The reaction temperature is detected by a thermocouple inserted in this well. The cylinder is 100 mm in inside diameter and 160 mm in outside diameter and 300 mm long, and the piston is 120 mm long. A prescribed pressure was applied (in the compression direction) to the pistons by using an Instron type universal tester (made by Shimadzu Seisakusho Ltd.). The thus obtained fixed body was dipped in distilled water at 70.degree. C. for 24 hours and the rate of leaching was measured. The results are shown in Table 2. The above-mentioned experiment was repeated, except that the temperature of hydrothermal reaction was changed to 150.degree. C., 200.degree. C., and 350.degree. C. The results are shown in Table 2. EXAMPLE 2 Fixed bodies were produced in the same manner as in Example 1, except that the concentration and amount of NaOH solution and the reaction temperature were changed as shown in the footnote to Table 3. The fixed bodies were examined for the rate of leaching in the same manner as in Example 1. The results are shown in Table 3. EXAMPLE 3 Fixed bodies were produced in the same manner as in Example 1, except that the concentration and amount of NaOH solution and the reaction pressure were changed as shown in the footnote to Table 4. The fixed bodies were examined for the rate of leaching in the same manner as in Example 1. The results are shown in Table 4. (In the following examples, the rate of leaching was measured in the same manner as in Example 1.) EXAMPLE 4 Fixed bodies were produced in the same manner as in Example 1, except that the concentration and amount of NaOH solution and the reaction time were changed as shown in the footnote to Table 5. The fixed bodies were examined for the rate of leaching in the same manner as in Example 1. The results are shown in Table 5. EXAMPLE 5 Fixed bodies were produced in the same manner as in Example 1, except that 150 cc of 10N NaOH aqueous solution was added and the reaction temperature was varied in the range of 150.degree. to 350.degree. C. The fixed bodies were examined for compression strength. The results are shown in FIG. 3. EXAMPLE 6 Fixed bodies were produced in the same manner as in Example 1, except that 150 cc of 10N NaOH aqueous solution was added and the pressure for hydrothermal reaction was varied in the range of 100 to 500 kg/cm.sup.2. The fixed bodies were examined for compression strength. The results are shown in FIG. 4. EXAMPLE 7 Fixed bodies were produced in the same manner as in Example 6, except that 9N NaOH aqueous solution was used. The fixed bodies were examined for compression strength. The results are shown in FIG. 4. EXAMPLE 8 Fixed bodies were produced in the same manner as in Example 1, except that 150 cc of 10N NaOH aqueous solution was added and the pressure for hydrothermal reacttion was established at 500 kg/cm.sup.2 and the reaction time was changed in the range of 20 minutes to 60 minutes. The fixed bodies were examined for compression strength. The results are shown in FIG. 5. EXAMPLE 9 Fixed bodies were produced in the same manner as in Example 8, except that 8N NaOH aqueous solution was used. The fixed bodies were examined for comparison strength. The results are shown in FIG. 5. EXAMPLE 10 Fixed bodies were produced in the same manner as in Example 1, except that the concentration and amount of NaOH aqueous solutin were changed. The fixed bodies were examined for compression strength. The results are shown in FIG. 6. The results of the above-mentioned examples indicate that according to the method of this invention incinerator ash can be made into a small strong fixed body which is resistant to leaching. The volume of the incinerator ash is reduced to about one-sixth by the method of fixation. TABLE 1 ______________________________________ Properties and Composition of Incinerator Ash Items Values ______________________________________ Physical properties True density (g/cm.sup.3) (pycnometer method) 3.12 Bulk density (loose packing) (g/cm.sup.3) 0.34 (closest packing) (g/cm.sup.3) 0.59 Angle of repose 47.degree. Composition (wt %) Water 0.11 Loss on ignition 0.72 SiO.sub.2 36.41 Al.sub.2 O.sub.3 16.70 CaO 6.84 Fe.sub.2 O.sub.3 16.44 MgO 9.68 Na.sub.2 O 1.11 K.sub.2 O 0.66 Cr.sub.2 O.sub.3 0.15 TiO.sub.2 1.06 SO.sub.4.sup.- 3.33 Cl.sup.- 0.4 Others 6.31 Total 100.00 ______________________________________ TABLE 2 ______________________________________ Reaction Temperature and Rate of Leaching (*1) Reaction temperature (.degree.C.) Rate of leaching (g/cm.sup.3 .multidot. day) ______________________________________ 150 2.17 .times. 10.sup.-2 200 1.83 .times. 10.sup.-2 300 7.95 .times. 10.sup.-3 350 7.05 .times. 10.sup.-3 ______________________________________ Reaction pressure: 300 kg/cm.sup.2 - Reaction time: 20 min Amount of alkali aqueous solution added: 10N--NaOH 150 cc/1 kg incinerato ash (*2)(*3) (*1) The loss of weight per unit volume which takes place when the fixed body is dipped in distilled water at 70.degree. C. for 24 hours. The amount of distilled water is 8 cm.sup.3 per cm.sup.2 of the surface area of fixed body. This applies to Tables 2 and 3. (*2) The content of Na.sub.2 O is 6.71% if the amount of water added and the amount of water derived from NaOH are deducted. (*3) The amount of water added is 15.4 parts by weight for 100 parts by weight of ash and Na.sub.2 O in total. TABLE 3 ______________________________________ Reaction Pressure and Rate of Leaching No. Reaction pressure (kg/cm.sup.2) Rate of leaching (g/cm.sup.3 .multidot. day) ______________________________________ a 97 1.24 .times. 10.sup.-2 b 253 7.50 .times. 10.sup.-3 c 304 7.79 .times. 10.sup.-3 d 405 1.15 .times. 10.sup.-2 e 506 1.03 .times. 10.sup.-2 f 506 7.95 .times. 10.sup.-3 ______________________________________ Reaction temperature: 300.degree. C. Reaction time: 20 min Amount of alkali aqueous solution added: a, c, f = 10N--NaOH 150 cc/1 kg incinerator ash (The content of Na.sub.2 O is 6.71%, and the amount of water added is 15. parts by weight for 100 parts by weight of ash and Na.sub.2 O in total.) b, d, e = 8N--NaOH 150 cc/1 kg incinerator ash (The content of Na.sub.2 O is 4.66%, and the amount of water added is 15. parts by weight for 100 parts by weight of ash and Na.sub.2 O in total.) TABLE 4 ______________________________________ Reaction Pressure and Rate of Leaching No. Reaction time (min) Rate of leaching (g/cm.sup.3 .multidot. day) ______________________________________ g 20 7.95 .times. 10.sup.-3 h 20 1.03 .times. 10.sup.-2 i 30 1.72 .times. 10.sup.-2 j 45 1.33 .times. 10.sup.-2 k 60 7.83 .times. 10.sup.-3 l 60 1.08 .times. 10.sup.-2 ______________________________________ Reaction pressure: 300 kg/cm.sup.2 - Reaction temperature: 300.degree. C. Amount of alkali aqueous solution added: g, k = 10N--NaOH 150 cc/1 kg incinerator ash h, i, j, l = 8N--NaOH 150 cc/1 kg incinerator ash TABLE 5 ______________________________________ Amount of Alkali Added and Rate of Leaching Amount of NaOH Rate of leaching Water Na.sub.2 O aqueous solution (g/cm.sup.3 .multidot. day) (*1) (*2) ______________________________________ 4 N 150 cc 1.78 .times. 10.sup.-2 15.6 2.29 6 N 150 cc 1.86 .times. 10.sup.-2 15.5 3.79 8 N 150 cc 1.03 .times. 10.sup.-2 15.5 4.66 10 N 150 cc 7.95 .times. 10.sup.-3 15.4 6.71 4 N 100 cc 1.03 .times. 10.sup.-2 10.2 2.67 8 N 100 cc 6.53 .times. 10.sup.-3 10.4 4.18 10 N 100 cc 1.62 .times. 10.sup.-2 10.5 4.91 ______________________________________ Reaction temperature: 300.degree. C. Reaction time: 20 min Reaction pressure: 300 kg/cm.sup.2 - Amount of alkali aqueous solution added: 10N--NaOH 150 cc/1 kg incinerato ash (*2)(*3) (*1) The amount of water added for 100 parts by weight of ash and Na.sub. O in total. (*2) The content of Na.sub.2 O which is calculated by deducting the amoun of water added after the addition of NaOH aqueous solution. EXAMPLE 11 An iodine-adsorbed sorbent was prepared by allowing 10 kg of silver-loaded zeolite ("Silver Zeolite, Type III", a product of Rasa Industries Ltd., 10 to 16 mesh or 2 to 1.19 mm in particle diameter) and 2 kg of iodine to stand in a 20-liter closed container until iodine disappears by volatilization. One kg of this sorbent sample was mixed with 200 cc of 6N NaOH aqueous solution by spraying for 1 minute. The mixture was subjected to hydrothermal reaction at 300 kg/cm.sup.2 and 200.degree. C. for 30 minutes by using the same apparatus as used in Example 1, whereby the mixture was made into a fixed body. The thus obtained fixed body was examined for compression strength by using the same apparatus as used in Example 1. (Pressure was applied to both ends of the cylindrical fixed body.) The results are shown in Table 7. The thus obtained fixed body was dipped in distilled water at 70.degree. C. for 24 hours and the rate of iodine leaching was measured. The results are also shown in Table 7. The rate of leaching was calculated from the amount of iodine which had leached out when the fixed body was dipped in distilled water at 70.degree. C. for 24 hours. The amount of distilled water was 8 cm.sup.3 per cm.sup.2 of the surface area of fixed body. The methods used in this Example for measuring the compression strength and the rate of leaching are applied to the following Examples 12 to 16. EXAMPLES 12 to 14 Fixed bodies were produced in the same manner as in Example 11, except that the reaction pressure, temperature, and time were changed as shown in Table 6. The fixed bodies were examined for strength and the rate of leaching in the same manner as in Example 11. The results are shown in Table 7. EXAMPLES 15 and 16 Fixed bodies were prepared in the same manner as in Example 11, except that the sodium hydroxide was replaced by 6N aqueous solution of potassium hydroxide in Example 15 and barium hydroxide (Ba(OH).sub.2.8H.sub.2 O) crushed in the same particle size as the silver zeolite was used in an amount of 2 g for 9 g of the silver zeolite in Example 16. The reaction conditions are shown in Table 6. The fixed bodies thus obtained were examined for strength and the rate of leaching. The results are shown in Table 7. It is noted from Table 7 that according to the method of this invention iodine sorbent can be made into a very strong fixed body which is highly resistant to leaching. TABLE 6 ______________________________________ Reaction Conditions Ex- am- Amount Temper- ple added Pressure ature Time No. Additive (cc) (kg/cm.sup.2) (.degree.C.) (min) ______________________________________ 11 6N NaOH 200 300 200 30 12 6N NaOH 200 300 300 30 13 6N NaOH 200 300 400 30 14 6N NaOH 100 300 300 30 15 6N KOH 200 300 300 30 16 Ba(OH).sub.2.8H.sub.2 O 200 300 300 30 ______________________________________ TABLE 7 ______________________________________ Measured Values Example Compression strength Rate of leaching No. (kg/cm.sup.2) (g/cm.sup.2 /day) ______________________________________ 11 450 6 .times. 10.sup.-5 12 980 1 .times. 10.sup.-3 13 1200 2 .times. 10.sup.-3 14 1150 2.5 .times. 10.sup.-3 15 1050 9 .times. 10.sup.-4 16 1200 8 .times. 10.sup.-4 ______________________________________ |
description | Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. (First Embodiment) FIG. 1 is a conceptual diagram of a charged beam exposure apparatus according to the first embodiment. The charged beam exposure apparatus according to the first embodiment has an electron gun 1, a blanking aperture array 3, and a basic figure aperture array 5. The electron gun 1 is a charged beam generating source. xe2x80x9cCharged beamxe2x80x9d is an electron beam 9 and an ion beam. The following embodiment will explain the electron beam 9. The following explanation can be applied also to the ion beam in a manner that words are replaced. FIG. 1A is a conceptual diagram and does not show a lens system for simplification. A more concrete structure of optical system of the charged beam exposure apparatus shown in FIG. 1A is shown in FIG. 1B. FIG. 1B shows more detailed structure of the optical system of the charged beam exposure apparatus shown in FIG. 1A. The electron gun 1 contains a blanker 76. A voltage is applied to the blanker 76 by the electron gun control means 81 so that the electron beam is brought into on or off state. The electron beam 9 is controlled so as to have desired current density by the first lens 71 (condenser lens) so as to be emitted onto the first aperture 2. The electron beam 9 which passed through the first aperture 2 is emitted onto the second aperture 3 (blanking aperture array) by a first projection lens 74. Further, the electron beam 9 which passed through the second aperture 3 is emitted onto the third aperture 5 (basic figure aperture array) by a second projection lens 75. The first deflector (means) 4 is composed of four stages. The first deflector deflects the electron beam 9. The second deflector returns the electron beam 9 to an angle vertical to the third aperture. The third deflector returns the electron beam 9 which passed through the third aperture onto an optical axis, and the fourth deflector returns the electron beam 9 to a direction parallel with the optical axis. The electron beam 9 which is return to the optical axis is reduced and projected and exposed on the sample 7 by a second lens 72 (reduction lens and objective lens 9. The exposing position of the sample 7 is controlled by the second deflector (deflecting means: objective deflector) 6. As shown in FIG. 2, the blanking aperture array 3 of the first embodiment is a flat board which has a plurality of first aperture sections 8 having rectangular apertures and arranged in a lattice form so as to be close to each other. The first aperture sections are arranged cyclically. The xe2x80x9caperture sectionxe2x80x9d 8 is an iris of the electron beam 9. Moreover, as shown in FIGS. 3A and 3B, the blanking aperture array 3 has electrodes 10 which deflect the electron beam 9 passing through the first aperture sections 8 at the first aperture sections 8 respectively. The blanking aperture array 3 deflects the electron beam 9 at each aperture section so as to or not to emit the electron beam 9 onto a basic figure, namely, brings the beams into an on/off state. As shown in FIG. 1, the basic figure aperture array 5 of the first embodiment is a second flat board which is arranged parallel with the blanking aperture array 3. The basic figure aperture array 5 has second aperture sections A1 to A5 and B1 to B5 and C having basic figure apertures as shown in FIG. 4A. The second aperture section A1 or the like shapes the electron beam 9 which is about to pass or passed through the first aperture sections 8. The aperture section D is used to shape a variable shaped beam. xe2x80x9cAbout to pass or passedxe2x80x9d means that the electron beam first passes through the first aperture sections 8 and next through the second aperture section A1 or the like or the passing order may be reversed. More specifically, the blanking aperture array 3 and the basic figure aperture array 5 form two-stage apertures for the electron gun 1, but the blanking aperture array 3 or the basic figure aperture array 5 may be arranged on the side of the electron gun 1. xe2x80x9cThe basic figurexe2x80x9d is basically a desired pattern. As pattern of wirings in a semiconductor apparatus, xe2x80x9cthe basic figurexe2x80x9d may be set as follows. In the semiconductor apparatus, a width and intervals of wirings are uniform, and the wirings are bent at right angles. However, lengths of the wirings are different from one another. Here, the widths and the intervals of the wirings (or their ratio) are the same as a desired semiconductor apparatus, and the lengths of the wirings are set to a certain length. The pattern of such wirings is determined as xe2x80x9cbasic figurexe2x80x9d. As a result, in the case where the wiring pattern is short, one portion of the xe2x80x9cbasic figurexe2x80x9d is used, and in the case where the pattern is long, the xe2x80x9cbasic figurexe2x80x9d is used repeatedly and partially so that the wiring pattern can be represented by the xe2x80x9cbasic figurexe2x80x9d. The xe2x80x9cbasic figurexe2x80x9d is a figure which has a basic rule of the wiring pattern such as the width and interval of the wirings. The basic figure aperture array 5 having the basic figures draws a figure according to the basic rule, and lattice-shaped blanking aperture array 3 can cut unnecessary portion of the drawn figure. Namely, the length of the wiring in the wiring pattern can be shortened to a desired length. As a result, for example, since a pattern for each length of the wirings should not be prepared, a number of masks or the like can be reduced. The mask production cost can be reduced, and throughput in exposure can be improved. As shown in FIG. 1, the charged beam exposure apparatus has a first deflector 4 for emitting the electron beam 9 which passed through the first aperture sections 8 onto the second aperture section A1 or the like. A basic figure selection deflector which is called as the first deflector 4 emits the beam 9 which passed through the second aperture array 3 onto an arbitrary position on the basic figure aperture array to be the third aperture array 5. The charged beam exposure apparatus has a second deflector 6 for emitting the electron beam 9 which passed through the second aperture section A1 or the like onto an arbitrary position on a sample 7. The charged beam exposure apparatus has a second lens 72 for imaging the electron beam 9 which passed through the second aperture section A1 or the like on a surface of the sample 7. An objective deflector which is called as the second deflector 6 transfers the electron beam 9 which passed through the basic figure aperture array 5 onto an arbitrary position of the sample 7. The second lens 72 as an imaging lens system images the electron beam 9 which passed through the basic figure aperture array 5 on the sample. The xe2x80x9csamplexe2x80x9d 7 is a semiconductor substrate such as silicon (Si) to be used for producing a semiconductor apparatus, and a glass substrate to be used for a mask for exposure. As a result, the plural basic figures A1 to A5 and B1 to B5 and C can be used according to the pattern of a semiconductor apparatus. For example, as for the wiring pattern, the wiring pattern, where wirings in a vertical direction and wirings in a horizontal direction are combined, can be formed. Moreover, since the second lens 72 is provided, a refined pattern can be easily formed. The blanking aperture array 3 has the aperture sections 8 and the electrodes 10 according to LSI wiring pitch. Moreover, the basic figure aperture array 5 has basic figures according to the LSI wiring pitch. Here, the xe2x80x9cLSI wiring pitchxe2x80x9d is a repeating interval of the wirings of a large-scale integrated circuit (LSI) of the semiconductor apparatus. The aperture sections and the electrodes are allowed to correspond to the pitches so that the lengths of the wirings can be adjusted independently. Moreover, the basic figures are allowed to correspond to the pitches so that the basic figures can be used for the exposure of the wiring pattern. A ratio of the width of the first aperture sections 8 to the interval of the first aperture sections 8 is larger than a ratio of the width of the second aperture section A1 to the interval of the second aperture section A1. For this reason, shape of the basic figure A1 or the like can be prevented from being chipped due to shadow of the first aperture sections 8. The shapes of the apertures of the second aperture section A1 or the like are a wiring pattern on straight lines in the vertical and horizontal directions and a connection pattern having a right-angled portion connecting the vertical and horizontal wirings. The wiring pattern and the connection pattern are a plurality of patterns with different rotational directions and right, left, up and down inverted patterns. As the basic figure, wiring patterns on the straight lines of the vertical and horizontal directions are prepared. Further, connection patterns which have a right-angled portion connecting the wirings in the vertical and horizontal directions or connection patterns that the right angled portions can be composed by combinations are prepared. The connection patterns have a relation with right, left, up and down inverted patterns so as to be capable of coping with connection in every case of the wirings in the vertical and horizontal directions. The second aperture section A1 or the like includes first slits which are arranged parallel with the vertical sides of the rectangles so as to be opposed to one another with uniform intervals, and second slits which are parallel with the horizontal sides of the rectangles so as to be opposed to one another with uniform intervals. Here, the xe2x80x9cslitxe2x80x9d is an elongate aperture section, and it corresponds to the wiring pattern. As a result, the wiring pattern having arbitrary lengths in the vertical and horizontal directions can be obtained. As for the first slits, their lengths are equal with one another, and their both ends are arranged on the straight line, and a number of them is the same as a number of lines of lattice of the blanking aperture array 3. Moreover, as for the second slits, their lengths are equal with one another, their both ends are arranged on the straight line, and a number of them is the same as a number of rows of the lattice of the blanking aperture array 3. As a result, a plurality of wiring patterns can be formed by one beam emission. Further, as shown in FIG. 1A, the electron beam exposure apparatus of the first embodiment has the first lens 71 for controlling current density of the electron beam 9 emitted from the electron gun 1. The electron beam exposure apparatus of the first embodiment has a first aperture 2 for forming the shape of the electron beam 9 into a rectangle in order to prevent an excessive electron beam 9 from being emitted onto the second aperture array 3 or the like. In addition, the electron beam exposure apparatus has a sample stand 73 having driving means and sample stand driving control means 87. As a result, the sample 7 can be moved to a desired position. The electron beam exposure apparatus has electron gun control means 81, a central control device 82, second aperture array control means 83, first deflector control means 84, second deflector control means 86 and exposure data recording means 88. The central control device 82 controls the electron gun control means 81, the second aperture array control means 83, the first deflector control means 84, the second deflector control means 86, the sample stand driving control means 87 and the exposure data recording means 88 via a bus 85 so as to be capable of executing the exposure method. Data 94 for third aperture array, data 95 for sample and data 93 for second aperture array control for each shot of the electron beams 9 are recorded in the exposure data recording means 88. Data 94 for third aperture array include basic figure names as identifying tags which can identify the basic figures, and emitted positions of the electron beam 9 in the basic figures. The data 95 for sample include emitted positions of the sample 7 of the electron beam 9. The data 93 for second aperture array control include on/off information 93 showing existence/non-existence of deflection for each aperture section 8. The electron gun control means 81 controls the on/off state of the electron beam 9 emitted from the electron gun 1 at timing specified by the central control device 82. The second aperture array control means 83 sets all the aperture sections 8 to on or off state based on the data 93 for second aperture array control at timing specified by the central control device 82. The first deflector control means 84 applies a control voltage at timing specified by the central control device 82 so that the electron beam 9 can be emitted to a direction based on the data 94 for the third aperture array. The second deflector control means 86 applies a control voltage at timing specified by the central control device 82 so that the electron beam 9 can be emitted to a direction based on the data 95 for sample. The sample stand driving control means 87 moves the sample stand 73 at timing specified by the central control device 82 so that the electron beam 9 can be emitted to a direction based on the data 95 for sample. The electron beam 9 shot from the electron gun 1 passes through the first aperture 2, and is shaped into a desired shape on the second aperture array 3. The electron beam 9 is imaged on the third aperture array 5, and passes through the second deflector 6 and the imaging lens system 72 so as to be exposed in a desired position of the sample 7. In embodiments 1 and 2 explained below, an acceleration voltage of the electron beam 9 is 5 kV. FIG. 2 is an upper surface diagram of the blanking aperture array 3 according to the first embodiment. The aperture sections 8 are provided on the blanking aperture array 3. The aperture sections 8 are arranged according to the wiring pitch of the semiconductor apparatus (LSI). The aperture sections 8 are square, and they are arranged into square lattice form composed of 10 lines (L1 to L10) and ten rows (R1 to R10). Namely, their total number is 100 at the utmost. For example, when the wiring width and the wiring interval are 0.1 xcexcm and the wiring pitch is 0.2 xcexcm and a reduction rate from the array 3 to the sample 7 is ⅕, pitches of the aperture sections 8 in the line direction and the row direction on the array may be set to 1 xcexcm. As a result, all the one-hundred aperture sections 8 can be arranged within an area which is 10 by 10 xcexcm square. The two aperture arrays 3 and 5 have different functions. A position where the wirings are arranged is determined on the aperture array 3, and a shape in this position is determined on the aperture array 5. For this reason, a structure such that the shape cannot be controlled on the aperture array 5 is not permitted on the aperture array 3. More specifically, a ratio of the width of the aperture section 8 to a distance between the aperture sections 8 is set to be larger than the ratio of the width of the wiring to the intervals between the wirings. In the above example, since the ratio of the width of the wiring to the interval between the wirings is 1, the ratio of the width of the aperture section to the intervals between the aperture sections may be more than 1, but 4 or more is preferable. It is considered that the maximum value of the actual ratio is obtained when the arrangement is such that the interval between the aperture sections has a minimum machining dimension. Since the width of the wirings is generally set to the minimum machining dimension, the ratio becomes about 10 (1 xcexcm/0.1 xcexcm). Namely, the ratio becomes 10 which is obtained by multiplying an inverse number 5 of the reduction rate by the ratio 2 of the wiring pitch. FIG. 3A is an outside view of the second aperture array 3 according to the first embodiment. The second aperture array 3 has an aperture substrate 12, the aperture sections 8 which are opened in the aperture substrate 12, the electrodes 10 which are arranged on both sides so as to be opposed to one another across the aperture sections 8, and an I/O interconnection and terminal 77 connected with the electrodes 10. The I/O interconnection and terminal 77 is connected with the second aperture array control means 83 for outputting a control signal to be on/off information of the aperture sections 8. Moreover, a mask holder 15 for fixing the array 3 to the exposure apparatus may be arranged on a side surface of the array 3. FIG. 3B is a schematic sectional view of the second aperture array 3 according to the first embodiment. The aperture substrate 12 is composed of a silicon (Si) substrate 13, and an insulating film 14 which is arranged on a rear surface of the substrate 13. An electron beam deflection voltage which is a control signal from the second aperture array control means 83 is applied to the electrodes 10 via the I/O interconnection and terminal 77 provided on the mask holder 15. In the case where the deflection voltage is not applied to the electrodes 10, the electron beam 9 emitted onto the second aperture array 3 goes straight to the aperture sections 8 so as to be emitted onto the third aperture array 5. Meanwhile, in the case where the deflection voltage is applied to the electrodes 10, an electric field is generated between the electrodes 10 and 11, and the electron beam 9 is deflected so as not to be emitted onto the third aperture array 5. In such a manner, the existence/non-existence of the deflection due to the aperture sections 8 is controlled by the on/off information of the aperture sections 8 which is the control signal from the control means 83. The pattern form which is formed by a plurality of the aperture sections 8 on the on state is emitted onto the third aperture array 5. Here, the deflection voltage V for non-emission is about 30 V. FIGS. 4A to 4E are upper surface diagrams of the basic figure aperture array 5 according to the first embodiment. The basic figure aperture array 5 has aperture sections of the basic figures A1 to A5, B1 to B5 and C and a rectangular aperture section D. The basic figures A1 to A5 and B1 to B5 are composed of 10 apertures which have widths and are arranged with intervals according to the wiring pitch of the semiconductor apparatus. Their size is fit within the area which is 10 by 10 xcexcm square. The size is the same as the size such that the one-hundred aperture sections 8 are fit on the array 3. The same sizes are adopted in order to simplify the principle of the exposure, mentioned below. As a result, the positional relationship between the arrays 3 and 5 can be easily understood by overlapping the arrays 3 and 5. Therefore, the electron beam 9 is increased or reduced by a constant rate between the second aperture array 3 and the third aperture array 5 so that the basic figure which is increased or reduced by the same rate may be used for the size of the one-hundred aperture sections 8 of the array 3. There will be explained below a form of the basic figure A5. The basic figure A5 is composed of ten congruent rectangles. A length of the lateral side of the rectangle is 0.5 xcexcm, and a length of the longitudinal side is 10 xcexcm. The rectangles are arranged so that extended lines of the two lateral sides of the ten rectangles coincide with each other. Moreover, the rectangles are arranged with equal intervals, and the intervals are 0.5 xcexcm. This is because the width and the interval of the wirings are, for example, set to 0.1 xcexcm. A ratio of the length of the lateral side to the interval between the rectangles may be the same as the ratio of the width of the wirings to the interval between the wirings. The basic figure A1 is congruent with the figure below the figure A5 which is divided into two by a straight line connecting an upper-right angle of the right-end rectangle and a lower-left angle of the left-end rectangle. The basic figure A1 is arranged so as to be capable of being overlapped with the figure below the figure A5 by parallel movement. Here, in the case of xe2x80x9cbe capable of being overlappedxe2x80x9d, the arranging direction is limited and also the figures are congruent with each other. For this reason, except for a particularly necessary case, xe2x80x9ccongruentxe2x80x9d is not described according to the description of xe2x80x9cbe capable of being overlappedxe2x80x9d. The basic figure A2 can be overlapped with a figure which is obtained as axisymmetry of the figure A1 by only parallel movement of the obtained figure with respect to a parallel line with the longitudinal side of the rectangle of the figure A5. The basic figure A3 can be overlapped with a figure which is obtained as axisymmetry of the figure A1 by only parallel movement of the obtained figure with respect to a parallel line with the lateral side of the rectangle of the figure A5. The basic figure A4 can be overlapped with a figure which is obtained as axisymmetry of the figure A3 by only parallel movement of the obtained figure with respect to a parallel line with the longitudinal side of the rectangle of the figure A5. The basic figure B1 can be overlapped with the figure A1 by rotating the figure A1 through 90xc2x0 in the counterclockwise direction and moving it parallel. The basic figure B2 can be overlapped with the figure A2 by rotating the figure A2 through 90xc2x0 in the counterclockwise direction and moving it parallel. The basic figure B3 can be overlapped with the figure A4 by rotating the figure A4 through 90xc2x0 in the counterclockwise direction and moving it parallel. The basic figure B4 can be overlapped with the figure A3 by rotating the figure A3 through 90xc2x0 in the counterclockwise direction and moving it parallel. The basic figure B5 can be overlapped with the figure A5 by rotating the figure A5 through 90xc2x0 in the counterclockwise direction and moving it parallel. The basic figure C is obtained as an area where the figures A5 and B5 are overlapped with each other when the figure B5 is moved parallel so that the longer left side of the left-end rectangle of the figure A5 coincides with the shorter left side of the ten rectangles of the figure B5. The figure C forms a plug to be an inter-layer wiring when the multi-layer wiring is formed, but the figure C is provided in order to form a via hole when the plug is formed. In the above embodiment, the vertical and horizontal straight line patterns A and B and the plug C are shown as the basic figures, but another patterns may be used as the basic figures. FIG. 4B is a basic figure (A2+B1) which is formed by synthesizing the basic figures A2 and B1. Similarly, a basic figure (A1+B4) of FIG. 4C is formed by synthesizing the basic figures A1 and B4. A basic figure (A4+B2) of FIG. 4D is formed by synthesizing the basic figures A4 and B2. A basic figure (A3+B3) of FIG. 4E is formed by synthesizing the basic figures A3 and B3. In addition, a rectangular aperture section D of FIG. 4A is an aperture for VSB. A pattern which cannot be exposed by using the basic figures is conventionally provided for VSB exposure. In the case where the VSB exposure is carried out, it is necessary to image the second aperture array image on the third aperture array image. This point is similar to the conventional charged beam exposure apparatus, but in the case where only CP exposure is carried out, it is not always necessary to image the second aperture array image on the third aperture array image. On the contrary, it is necessary not to image edges of the aperture sections 8 of the second aperture array 3 on the third aperture array image. Namely, the image of the aperture sections 8 on the third aperture array 5 is slightly unfocused so that the images are slightly overlapped with each other. These optical conditions can be set arbitrarily by using the first projection lens 74, the second projection lens 75 and the like shown in FIG. 1B according to a pattern to be exposed. FIG. 5A is a diagram showing a positional relationship between the aperture sections 8 of the second aperture array 3 and the basic figure A5 of the third aperture array 5. The figure A5 is arranged so as to be overlapped with all the lines (L1 to L10) of the aperture sections 8. Moreover, the figure A5 is arranged so as to be overlapped with all the rows (R1 to R10). Two or more apertures of the basic figure are not overlapped with one aperture section 8. The sides of the square aperture sections 8 are parallel with the sides of the rectangles of the figure A5. The rectangle of the figure A5 is not arranged on three or more sides of the square of one aperture section 8. FIG. 5B is a diagram showing a positional relationship between the aperture sections 8 of the second aperture array 3 and the basic figure B3 of the third aperture array 5. The figure B3 is arranged so as to be overlapped with all the lines (L1 to L10) of the aperture sections 8. Namely, there is no line where the figure B3 does not exist. Moreover, the figure B3 is arranged so as to be overlapped with all the rows (R1 to R10). Namely, there is no row where the figure B3 does not exist. Two or more apertures of the basic figure are not overlapped with one aperture section 8. The sides of the square aperture sections 8 are parallel with the sides of the rectangles of the figure B3. The figure B3 is not arranged on three or more sides of the one square aperture section 8. At the time of drawing in exposure, selection is made from the apertures A1 to A5, B1 to B5 and C as the basic figures of the third aperture array 5, and the control voltage V is applied to each aperture section 8 so that the electron beam 9 which passes through the second aperture array 3 is deflected according to the pattern form which is desired to be drawn. The electron beam 9 passes through the second aperture array 3 and the third aperture array 5 so as to be emitted into the form of the pattern to be drawn on the sample 7. In such a manner, the basic figure apertures A1 to A5, B1 to B5, C, (A2+B1) and the like to be references are created so that one basic figure aperture A1 to A5, B1 to B5, C, (A2+B1) or the like can be applied to a plurality of patterns according to the beam 9 form of the second aperture array 3. As a result, in comparison with a number of CP apertures in the conventional CP system, a number of the apertures can be reduced. Due to this reduction, the mask cost can be reduced further than a mask in the electron-beam mask transfer system. In addition, since only the electron beam 9 required for the formation of the pattern on the first aperture 2 is emitted onto the second aperture array 3, an amount of the electron beam 9 to be emitted onto the aperture array 3 can be small. As a result, chromatic aberration can be prevented, and also contamination which easily occurs on the second aperture array can be avoided. The electron beam 9 passes through the aperture sections 8 also on the aperture array 3, and thus an amount of the electron beam 9 to be emitted onto the third aperture array 5 itself can be small. As a result, the preventive measures similar to the above are taken. An amount of the electron beam 9 to be emitted is suppressed so that a rise in temperature of the aperture arrays 3 and 5 is suppressed, and thermal expansion can be suppressed. For this reason, the patterns can be formed accurately. One hundred of the aperture sections 8 is a number which can be achieved sufficiently in the production technical field and in the technical field of voltage control for the electrodes 10. Here, the above second aperture array is composed of square lattices arranged on 10 linesxc3x9710 rows. However, for example, a number of the lies and a number of the rows may be set arbitrary such as 20 linesxc3x9715 rows. The arrangement of the aperture sections of the second aperture array may be set arbitrarily according to the basic figures. There will be explained below an exposure method by the above-described exposure apparatus. At first, layout data of the semiconductor apparatus are converted into exposure data which are applicable to the exposure apparatus. FIG. 6 is a flow chart showing an exposure data creating method according to the first embodiment. In the exposure data creating method according to the first embodiment, at step S1 layout data of the semiconductor apparatus are divided into a size of the basic figure aperture A1 or the like which takes reduction in exposure into consideration. At step S2 the divided layouts are classified as the basic figure aperture A1 or the like. At step S3 a portion where the divided layouts and the classified basic figure aperture A1 or the like are overlapped with each other is obtained by logic operation. Further, the data 93 for second aperture array control, which are on/off information about deflection due to the electrodes 10 of the second aperture array 3, are created based on the overlapped portion. Finally, drawing data 92 are created. The drawing data 92 have the data 95 for sample including a drawing position of the sample 7 as a position of the divided layouts in the layout of the semiconductor apparatus. Moreover, the drawing data 92 have the data 94 for the third aperture array which include a name of the classified basic figure aperture and if necessary an emitting position of the beam onto the basic figure aperture. The drawing data 92 have an address 96 for being capable of reading the data 93 for the second aperture array control. For this reason, the data 93 have correspondence to the data 92. Moreover, the data 94 and 95 and the address 96 have correspondence to each shot of the electron beam 9 for exposed. The drawing data 92 and the data 93 for the second aperture array control compose exposure data 91 for one shot. The exposure data 91 as well as a plurality of exposure data 97 and 98 having the same structure as the data 91 compose the exposure data (whole) of the semiconductor apparatus. Here, xe2x80x9cthe basic figure aperturexe2x80x9d is an iris which is cut into the shape of the basic figure. The xe2x80x9cposition of the divided layouts in the layout of the semiconductor apparatusxe2x80x9d is information which can reproduce the whole layout of the semiconductor apparatus by rearranging is obtained by rearranging the divided layouts. xe2x80x9cTaking reduction in exposure into considerationxe2x80x9d means that portions which are deformed due to the reduction are corrected so as to have correspondence to one another. xe2x80x9cThe name of the basic figurexe2x80x9d is a tag which can identify the basic figure from a plurality of the basic figures. As a result, since data showing forms of the basic figures may not be provided, an amount of data can be reduced, and a generating speed of the exposure data and a processing speed of exposure can be improved. In xe2x80x9cthe address 96 for being capable of reading the data 93 for the second aperture array control xe2x80x9d, the data 93 for the second aperture array control have correspondence to the position via the address 96. The exposure data creating method according to the first embodiment comprising the steps of: dividing chip data into a CP size; classifying the divided CP patterns as the basic figure A1 or the like in library; performing logic operation of the basic figure A1 or the like and the CP patterns and obtaining an overlapped portion; creating data B for beam on/off on the second aperture array 3; and creating drawing data A including position data of the CP patterns on the third aperture array 5, which are paired with the basic figure A1 or the like. Here, the xe2x80x9cCP sizexe2x80x9d is a range in which exposure can be carried out by one shot of the beam emission. The xe2x80x9cCP patternxe2x80x9d is a pattern which is divided based on the range. xe2x80x9cIn libraryxe2x80x9d means to prepare things for use object. The xe2x80x9clogic operation of the basic figure and the CP patternsxe2x80x9d is calculation which is carried out for each position of the area including the basic figure and the CP patterns in a state that the basic figure is overlapped with the CP patterns. In the logic operation, when both the basic figure and the CP patterns exist, 1 is put, and when not exist, 0 is put. As a result, since the forms of the basic figures should not be provided as data, an amount of data can be reduced, and the creating speed of the exposure data and the processing speed of the exposure can be improved. The exposure data 91 of the first embodiment has the data 93 for the second aperture array control showing on/off of the deflection of the aperture sections 8 on the second aperture array 3. The exposure data 91 has the drawing data 92. The drawing data 92 includes: the data 95 for sample of a drawing positions of the divided layouts in the layout of the semiconductor apparatus; the data 94 for the third aperture array of the name of the classified basic figure; and the address 96 for being capable of reading the first data. The data 95 and the data 94 and the address 96 have correspondence to one another. Such exposure data are recorded on a recording medium which is capable of being read by a computer. Here, the xe2x80x9crecording mediumxe2x80x9d includes media, which is capable of recording programs thereinto, such as a semiconductor memory, a magnetic disc, an optical disc and a magnetic tape. In order to prevent the data size from being enlarged, data showing the form of the basic figure A1 or the like can be omitted. Therefore, as for the pattern data whose file size is reduced by this method, design data can be downloaded or uploaded for short time by using a network such as internet. As a result, an order from the outside a company and a process on the outside a company which have been difficult can be carried out comparatively easily. A program for creating the exposure data according to the first embodiment has: the procedure for dividing the layout data of the semiconductor apparatus into a size of the basic figure aperture A1 or the like which takes reduction in the exposure into consideration; and the procedure for classifying the divided layouts as the basic figure aperture A1 or the like. Further, the program for creating the exposure data has: the procedure for obtaining an overlapped portion of the divided layouts and the classified basic figure aperture A1 or the like; and the procedure for creating the data 93 for the second aperture array control showing existence/non-existence of the deflection of the aperture sections 8 on the second aperture array 3. Further, the program for creating the exposure data has the procedure for creating the drawing data 92 having: the data 95 for sample showing a drawing position of the divided layouts in the layout of the semiconductor apparatus; the data 94 for the third aperture array of the name of the classified basic figure; and the address 96 for being capable of reading first data, wherein the position 95, the name 94 and the address 96 have correspondence to one another. The program for creating the exposure data is stored in a recording medium which can be read by a computer. As a result, the exposure data can be created easily and automatically by the computer. The exposure data creating method according to the first embodiment will be explained more specifically. (1) At step S1 of FIG. 6, the data of the layout in the semiconductor apparatus (chip data) are divided into sizes of the basic figure apertures A1 to A5, B1 to B5 and C taking reduction exposure into consideration. The divided layout for 1 block is shown in FIG. 8A. This layout is composed of layout patterns 16, 17 and 18 of the wirings arranged in the horizontal direction. A length of the pattern 17 is shorter. (2) At step S2 of FIG. 6 the divided layouts are classified according to the basic figures. The layout of FIG. 8A is for the wirings which are arranged in the horizontal direction and the outline of the layout is rectangular. For this reason, the basic figure B5 shown in FIG. 8B is selected from the basic figures of FIG. 4A. (3) At step S3 the logic operation is performed by the selected basic figure B5 corresponding to the divided layout (FIG. 8A) so that the overlapped portion is obtained. The data 93 for the second aperture array control (data B for beam on/off) of the aperture sections 8 on the second aperture array 3 are created. The created data 93 are recorded on the optical data recording means 88 in FIG. 1. A coordinate system which is composed of coordinate units 19 in the arrangement position having the same lines and rows as the aperture sections 8 on the second aperture array 3, is prepared. As shown in FIG. 8C, when the basic FIG. 5B is overlapped on the coordinate system, the FIG. 5B is arranged on all the coordinate units 19. Similarly as shown in FIG. 9A, the layouts 16 to 18 are overlapped on the coordinate system. No layout is arranged in the range of the lines 6 to 10 and the rows 6 to 8. As a result, the overlapped portion becomes display data 20 which shows xe2x80x9cno deflectionxe2x80x9d shown by xe2x80x9cxe2x96xa1xe2x80x9d in FIG. 9B. The non-overlapped portion becomes display data 21 which shows xe2x80x9cdeflectionxe2x80x9d shown by xe2x80x9cxc3x97xe2x80x9d. The display data 20 and 21 for each coordinate (L, R) are the data B for beam on/off (93). (4) Meanwhile, the drawing data A (92) are created. The drawing data A (92) are composed of a drawing position on the sample 7 (arrangement position of the divided layouts (FIG. 8A) in the whole layout of the semiconductor apparatus, namely, corresponding to the data 95), the basic figure name (corresponding to the data 94) according to the drawing position, and the address 96 for being capable of reading the data B (93) according to the drawing position. Here, the basic figure name according to the drawing position (corresponding to the data 94) is not limited to this, namely, and basic figure B5 or the like may be identified. Namely, the arrangement position on the third aperture array 5 and allocated identification number may be used. Moreover, the created data 92 are recorded on the exposure data recording means 88 of FIG. 1. The sequence returns to step S1 of FIG. 6 in (1) so that the exposure data 97 and 98 are created similarly until the divided layouts for 1 block do not exist. There will be explained below the latter half of the exposure method using the semiconductor apparatus using the created exposure data 91. FIG. 7 is a flow chart showing the exposure method according to the first embodiment. (5) At step S11 the central control device 82 calls the drawing positions 95 of the drawing data A (92) for the exposure data 91, 97 and 98 from the exposure data recording means 88. First, the case of the exposure data 91 will be explained below. (6) Next, at step S12 the central control device 82 calls the name of the basic figure B5 as the basic figure name 94 corresponding to the called drawing position 95 from the exposure data recording means 88. The name of the basic figure B5 is input into the first deflector control means 84. In addition, the central control device 82 calls the address 96 for being capable of reading the data B (93) corresponding to the called drawing position 95. The central control device 82 calls the data B (93) based on the addresses 96 and inputs the data B to the second aperture control means 83. The called data B (93) are the data explained with reference to FIG. 9B. As for the data 93, the display data 20 showing non-deflection are simplified and are shown in FIG. 10A as distribution 22 of the aperture sections 8 of non-deflection. (7) At step S13 the second aperture array control means 83 applies control voltage V for a deflection to the electrodes 10 of the second aperture array 3 based on the input data B (93). (8) At step S14 the first deflector control means 84 applies a control voltage to the first deflector 4 based on the input basic figure name. The control voltage is applied to the deflector 4 so that the electron beam 9 is led to the basic figure B5 in the array 5 of FIG. 4 based on the name of the basic figure B5 of the input data A. As a result, as shown in FIG. 10B, a mask due to the distribution 22 of the aperture sections 8 which do not deflect the electron beam 9 to its advancing path, and a mask due to the basic figure B5 are arranged. The electron beam 9 passing through both the masks has a form 23 shown in FIG. 10C. The form 23 coincides with the forms 16, 17 and 18 of FIG. 8A. (9) At step S15 the second deflector control means 86 inputs the drawing position 95 called into the central control device 82. The second deflector control means 86 applies a control voltage to the second deflector 6 to be a deflector for position specifying based on the called drawing position 95. (10) At step S16 the central control device 82 instructs the electron gun control means 81 to emit the electron beam 9 from the electron gun 1 to the first aperture 2. Here, the control voltages should be applied at steps S13 to S15 also when the electron beam 9 is emitted. An amount of the emitted electron beam 9 is sufficient for the exposure of the data A shaped into the form 23 shown in FIG. 10C to the drawing position 95. The emission of the beam 9 is stopped, and the application of the control voltages to the second aperture array 3 and the first and second deflectors 4 and 6 is stopped. More specifically, the beam 9 is emitted or is not emitted by a beam blanker 76, shown in FIG. 1B. (11) At step S17 a judgment is made as to whether or not the electron beam 9 is emitted to all drawing positions of the data A. Since the electron beam 9 is not emitted to the drawing positions 94 of the exposure data 97 and 98 in FIG. 6, the sequence returns to step S12 so that the steps S12 to S16 are executed for the drawing positions. After the execution, when the drawing position to which the beam is not emitted does not exist, the exposure method is ended. In the case where the chip is larger than the beam deflection area of the exposure apparatus, the sample stand 73 having the driving means on which the sample 7 is placed moves. This movement is carried out at the time of executing the step S15 or instead of the execution of the step S15. Namely, the sample stand driving control means 87 inputs the called drawing position 95 to the central control device 82. The sample stand driving control means 87 moves the sample stand 73 based on the called drawing position 95. Namely, in the case of the patterns 16 to 18 shown in FIG. 8A, these patterns 16 to 18 are created as CP apertures in the conventional method. In the first embodiment, the basic figure aperture B5 having a line and space pattern shown in FIG. 8B is prepared. The beam shape shown in FIG. 10A is formed on the second aperture array 3, and the beam is emitted onto the apertures B5 shown in FIG. 8B. As a result, the pattern having the same form as FIG. 8A can be obtained as the exposure pattern 23 of FIG. 10C. Various patterns can be drawn by changing the form of the beam which is not deflected on the second aperture array 3 based on the basic figures on the third aperture array 5. Moreover, the exposure (drawing) data are divided into the data A (92) and B (93) so that the data can be compressed. (Second Embodiment) Next, there will be explained below the creating method according to the second embodiment which is obtained by developing the exposure data creating method explained in the first embodiment. Moreover, there will be explained below the exposure method according to the second embodiment using the developed creating method. FIG. 11 is a flow chart showing the exposure data creating method according to the second embodiment. In the exposure data creating method according to the second embodiment, at step S4 data of the layout in the semiconductor apparatus are divided into a vertical line pattern and a horizontal line pattern which take reduction in the exposure into consideration. Next, at step S5 widths of the vertical line patterns are enlarged so that a first pattern, in which the adjacent vertical line patterns are integrated, is created. Further, widths of the horizontal line patterns are enlarged so that a second pattern, in which the adjacent horizontal line patterns are integrated, is created. At step S6 the first and second patterns are divided into the sizes of the basic figure apertures which take reduction in the exposure into consideration. At step S2 similarly to the case of FIG. 6, the divided first and second patterns are classified according to the basic figure apertures. At step S3 similarly to the case of FIG. 6, the overlapped portions of the divided first and second patterns and the classified basic figure apertures are obtained. The data 93 for the second aperture array control showing existence/non-existence of deflection at each aperture section on the aperture array are created. Moreover similarly to the first embodiment, the drawing data 92 are created. A wiring pattern which is obtained by combining the wirings in the vertical direction and the wirings in the horizontal direction can be formed by the exposure data creating method according to the second embodiment. There will be explained below in detail the exposure data creating method according to the second embodiment. (1) At step S4 the pattern in the chip data is divided into vertical component patterns and horizontal component patterns. As shown in FIG. 12, the wiring patterns 24 are arranged so as to connect lattice points 27 on vertical dotted lines 25 and the horizontal dotted lines 26, and are composed of vertical and horizontal straight lines and intersection points. The lattice points 27 are intersection points of the vertical dotted lines 25 and the horizontal dotted lines 26. The vertical and horizontal pitches of the lattice points 27 are 0.2 xcexcm. This pitch corresponds to the pitch of the wirings. The following method is used to divide the wiring patterns 24 into vertical and horizontal component patterns. The logic operation of the vertical dotted lines 25 shown in FIG. 13A and the horizontal dotted lines 26 shown in FIG. 13B is performed for the wiring patterns 24 so that overlapped portions of the patterns 24 and the dotted lines 25 and 26 are obtained. The portions shown by thick solid lines in FIG. 13C are the overlapped portions 28 and 30 of the vertical dotted lines 25 and the patterns 24. The thick horizontal dotted lines 29 are the patterns 24 which are not overlapped with the vertical dotted lines 25. Moreover, the portions 32 shown by the thick solid lines in FIG. 13D are the overlapped portions of the horizontal dotted lines 26 and the patterns 24. The thick vertical dotted lines 31 and 33 are the patterns 24 which are not overlapped with the horizontal dotted lines 26. As shown in FIGS. 13E and 13F, the thick solid lines 28, 30 and 32 which are the overlapped portions are extracted so as to be divided into three patterns 28, 30 and 32. (2) Next, at step S5 the patterns 28, 30 and 32 are subject to a thickening process. As shown in FIGS. 14A and 14B, the divided patterns 28, 30 and 32 are subject to the thickening process. At this time, a thickening amount is set to the same value as the value obtained by subtracting the wiring width (: 0.1 xcexcm) from the lattice point pitch of the wiring patterns 24. Both sides of the patterns 28, 30 and 32 are thickened by the same amount, i.e., 0.05 xcexcm (total: 0.1 xcexcm). According to this thickening process, as shown in FIGS. 14C and 14D, the wiring patterns 28, 30 and 32 are converted into patterns 33, 34 and 35 having polygonal form. (3) At step S6 the patterns 33, 34 and 35 which were subject to the thickening process are divided into sizes of the basic figure apertures A1 or the like. Here, the thickened polygonal patterns 33, 34 and 35 are divided into triangle and rectangle. The vertical component patterns are divided in the horizontal direction, and the horizontal component patterns are divided in the horizontal direction. As shown in FIGS. 15A and 15B, the thickened polygonal patterns 33 to 35 are divided into rectangles 42, 44 and 47 and triangles 41, 43, 45, 46 and 48. The wiring patterns 33 and 34 in the vertical direction are divided in the horizontal direction, and the wiring pattern 35 in the horizontal direction is divided in the vertical direction. (4) At step S2 the divided patterns are classified according to the basic figures A1 to A5 and B1 to B5 in the library shown in FIG. 4. The classification of the divided wiring patterns 41 to 45 in the vertical direction will be explained. At first, the wiring patterns 41 to 45 are pattern-matched with the basic figures A1 to A5 shown in FIG. 4. For example, as shown in FIG. 15C, the rectangular patterns 42 and 44 are classified as the basic figure A5. Moreover, the triangular patterns 43 and 45 are classified as the triangular basic figure A3, and the triangular pattern 41 is classified as the triangular basic figure A2. Similarly, the wiring patterns 46 to 48 in the horizontal direction are pattern-matched with the basic figures B1 to B5, and as shown in FIG. 15D, the rectangular pattern 47 is classified as the basic figure B5. The triangular pattern 46 is classified as the triangular basic figure B1, and the triangular pattern 48 is classified as the triangular basic figure B3. (5) At step S3 the logic operation of the classified basic figures and the divided rectangular and triangular wiring patterns is performed so that overlapped portions are obtained. The data B for beam on/off (93) of the second aperture array 3 are created. For example as shown in FIG. 16A, the rectangular pattern 42 has an overlapped portion in the range of lines L5 to L10 and the lows R1 to R2 with respect to the basic figure A5. Therefore, as for the data B (93) relating to the rectangular pattern 42, the display data showing non-deflection are set in the range of lines L5 to L10 and the rows of R1 and R2, and the display data showing deflection are set in the range of the lines L1 through 4 and rows R1 and R2 and the range of lines L1 to L10 and rows R3 to R10. Here, as to where in the basic figure A5 to overlap the pattern 42, this is not limited to the case where the pattern 42 is arranged on the upper-right end position shown in FIG. 16A. Therefore, the pattern 42 may be arranged so as to be overlapped on the coordinate units 19 of line L1 and row R1, line L1 and row R10, line L10 and row R10, or the pattern 42 may be arranged under only the condition that it is overlapped any position. In addition, as shown in FIG. 16B, the triangular pattern 43 has an overlapped portion in the range of lines L5 to L10 and rows R5 to R10 on the basic figure A3. Therefore, as the data B (93) relating to the triangular pattern 43, the display data showing non-deflection are set in the range of lines L5 to L10 and rows R5 to R10, and the display data showing deflection are set in the range of lines L1 to L10 and rows R1 to R4 and the range of lines L1 to L4 and rows R5 to R10. Here, when the patterns 42 and 43 which created the data B (93) explained with reference to FIGS. 16A and 16B are the patterns 42 and 43 in the area 33 of FIG. 15C, the patterns 42 and 43 are combined with each other so as to be capable of being overlapped in the range of lines L5 to L10 and rows R3 to R10 in FIG. 16B. In such a manner, one shot of the electron beam can be emitted instead of the case where two shots of the electron beams should be emitted. (6) Meanwhile, the drawing data A (92) are composed of the drawing positions 95 on the sample 7 (the arrangement positions of the divided layouts in the whole layout of the semiconductor apparatus), the basic figure names 95 classified at S2 according to the drawing positions 95, and the addresses 96 for being capable of reading the data B (93) set at step S3 according to the drawing positions 95. In such a manner, the exposure data 91, 97 and 98 are created as the drawing data A (92) and the data B for the second aperture array control (93). Next, the semiconductor apparatus is exposed based on the exposure data 91, 97 and 98. This exposure method is performed based on the flow chart in FIG. 7 similarly to the first embodiment. At the time of the exposure, the drawing data A (92) and the data B for the second aperture array control (93) are used. These data 92 and 93 act upon the electron beam exposure apparatus shown in FIG. 1 as follows. The data B for beam on/off (93) of the second aperture array 3 directly act upon the second aperture array 3 so as to actuate the deflectors 10 for aperture sections 8 on the second aperture array 3. As a result, the electron beam 9 having arbitrary form is emitted onto the third aperture array 5. The drawing data A (92) control the first deflector 4 and is used when the basic figure aperture A1 or the like is selected. Simultaneously, the drawing data A (92) control the second deflector 6 and the sample stand 73 and can carry out electron beam exposure on an arbitrary position of the sample 7. As a result, as shown in FIG. 17, synthesized images 55 to 62 of the second aperture array 3 and the third aperture array 5 are transferred onto the sample 7. As a result, the exposure of the wiring patterns 24 shown in FIG. 12 can be executed. (Third Embodiment) The third embodiment will explain the case where LSI type patterns are used as the basic figures of the basic figure apertures. In the third embodiment, the exposure apparatus used in the first embodiment is used. The characteristic of the third embodiment is that a lot of LSI type patterns 126 are arranged on the third aperture array (basic figure aperture array) 101 as shown in FIG. 18A. Here, the LSI type patterns 126 are patterns of parts composing an LSI circuit. The LSI chip is designed so that several hundred kinds of standard cell (SC) patterns are combined according to applications and are arranged. The third embodiment will explain the case where the SC patterns are the type patterns, namely, the basic figure patterns 126. SC patterns 103 to 105 shown in FIG. 18B are arranged on one basic figure pattern 102 in the plural basic figure patterns 126. FIG. 18B is one example, and a plurality of SC patterns having different forms (functions) are arranged in the basic figure patterns 126. The SC pattern 103 has patterns 106 to 108 such as gate electrode layer or the like. The SC pattern 104 has patterns 109 to 111. The SC pattern 105 has patterns 112 and 113. The SC patterns 103 to 105 compose SCs (units of SC patterns) having respective simple functions. The basic figure pattern 102 where the SC patterns 103 to 105 are connected also composes SCs having more complicated function. In the third embodiment, a second aperture array 114 shown in FIG. 19 can be used. The second aperture array 114 is also a blanking aperture array. The second aperture array 114 has aperture sections 115 having electrodes 10 being capable of deflecting the electron beam 9. The ten aperture sections 115 are arranged in the horizontal direction, on lines L1 to L10. Needless to say, the second aperture array 3 shown in FIG. 2 used in the first embodiment may be also used. The array 114 whose length cannot be adjusted in the vertical direction can be used because the design is normal so that the vertical lengths of SCs become uniform. Next, there will be explained below the exposure method according to the third embodiment. A Pattern 116 shown in FIG. 20A, for example, is exposed. The pattern 116 is composed of patterns 117 through 122 and 138. First, similarly to the first embodiment, according to FIG. 6, the exposure data are created. However, in the third embodiment, the step S1 and the step S2 are executed simultaneously. For example, the pattern 118 is selected, and the same pattern is retrieved from the basic figure pattern 126. As a result, the pattern 107 of FIG. 18B is detected. With this retrieval, the pattern 107 except for the SC pattern 103 (102) may be occasionally detected. Next, the pattern 108 which is the same as the pattern 119 adjacent to the pattern 118 detects the pattern 103 (102) which is adjacent to the previously detected pattern 107. The above steps are repeated so that the pattern 102, which has the same patterns 107 to 111 as the patterns 118 through 122, can be detected. Further, a judgment is made as to whether or not the same pattern as the pattern 138 exists on the right side of the pattern 111 in the pattern 102. Since not the pattern 138 but the pattern 112 exists on the right side of the pattern 111, the judgment is made that the same pattern as the pattern 138 does not exist on the right side of the pattern 111 in the pattern 102. Similarly, a judgment is made as to whether or not the same pattern as the 117 on the left side of the pattern 118 exists on the left side of the 107. In such a manner, the same patterns as the patterns 117 to 122 can be found from the patterns 106 to 111 in the pattern 102. This finding process corresponds to classification of the layout 116 at step S1 of FIG. 6 according to the patterns 117 to 122 and the pattern 138. Moreover, this finding procedure simultaneously corresponds to classification of the divided layouts 117 to 122 at step S2 according to the basic FIG. 102 having the patterns 106 to 111. The steps S1 and S2 are executed so that the drawing data 92 can be created. The basic figure names of the data 94 for the third aperture array of the drawing data 92 become identification symbol of the pattern 102. The emitting positions are the patterns 106 to 111. Moreover, the drawing position of the data 95 for sample is the arrangement position of the pattern 116 in FIG. 20A. The address 96 may be determined when the data 93 are input. Next, at step S3 the logic operation of the divided layouts 117 to 122 and the basic FIG. 102 is performed. As a result, the on/off information, where the aperture sections 115 on the lines L1 to L7 are which are the on-area 123 which does not deflect the beam 9, is stored as the data 93 for the second aperture array control. Moreover, the on/off information, where the aperture sections 115 on the lines L8 to L10 are the off-area 124 which deflects the beam 9, may be stored. Here, the creation of the exposure data is ended. Continuously, the latter of the exposure method is executed. The exposure method is executed according to FIG. 7 similarly to the first embodiment. First, at step S11 the drawing position 95 of the pattern 116 in FIG. 20A is called. At step S12, the basic figure name of the pattern 102 and the on/off information of FIG. 20B are called. The steps S13 to S16 are executed. The second aperture array 114 allows the beam to be emitted therethrough at only the necessary portion 123 as shown in FIG. 20B, and deflects the beam at the other portion 124. As a result, as shown in FIG. 20C, the formed beam 125 is emitted only to the patterns 106 to 111 on the SC pattern 102. As a result, the desired patterns 117 to 122 shown in FIG. 20A can be exposed. According to the third embodiment, the beam 9 is emitted only to the desired areas 106 to 111 of the cell pattern 126 on the aperture array 101, and the beam is not emitted to areas other than the desired areas 106 to 111. As a result, the plural cell patterns 103 to 105 are collective, and only the desired areas 103 and 104 are selected and the cell patterns are exposed. A number of the SC patterns arranged on the aperture array 101 can be reduced. (Comparative Example of Third Embodiment) As the comparative example of the third embodiment, FIGS. 21A and 21B show arrangements of the CP apertures 128 and 133 on the CP aperture arrays 127 and 132 of the prior art. In the case of the prior art shown in FIG. 21A, a beam 131 shaped by the first aperture is emitted onto a CP aperture 130. At this time, since the beam 131 is not emitted onto a CP aperture 129 which is another SC pattern, it is necessary to provide a wide interval between the SC patterns (apertures) 130 and the 129. For this reason, in the case where the same number of the CP apertures 128 as the third embodiment are mounted, it is necessary to enlarge the CP aperture array 127 and the beam deflection area. In addition, when the CP aperture array 132 has the same size as the third embodiment, as shown in FIG. 21B, only a small number of SC patterns 133 (apertures) can be mounted. A beam 136 shaped by the first aperture is emitted onto a CP aperture 135. At this time, since the beam 136 is not emitted onto a CP aperture 134 which is another SC pattern, it is necessary to provide a wide interval between the SC patterns (apertures) 135 and the 134. On the contrary, in the third embodiment, as shown in FIG. 18A, a lot of SC patterns 126 can be arranged with narrow intervals. (Fourth Embodiment) The fourth embodiment will explain the case where the basic figures of the basic figure apertures are oblique wiring patterns. Also in the fourth embodiment, the exposure apparatus used in the first embodiment is used. The feature of the fourth embodiment is that oblique wiring patterns 143 and 144 are arranged on a third aperture array (basic figure aperture array) 142 as shown in FIG. 22B. The oblique wiring pattern 143 is the oblique wiring pattern from the upper left to the lower right. The oblique wiring pattern 143 has eleven apertures R1 to R11. The oblique wiring pattern 144 is the oblique wiring pattern from the upper right to the lower left. The oblique wiring pattern 144 has eleven apertures L1 to L11. Here, the oblique wirings are wirings which are arranged in the LSI layout so as to form an angle with a set base line which is not parallel nor vertical with the base line. This base line may be a base line as a reference of stepping presumed at the time of exposure. In FIG. 22B, respective sides of the array 142 may be set as base lines. In this case, the oblique wiring patterns 143 and 144 are inclined 45xc2x0 with respect to the base lines. However, the inclined angle is not limited to 45xc2x0, and may be 30xc2x0 or 60xc2x0. Namely, the inclination can be set to an arbitrary angle. Moreover, some kinds of angles may be combined as to be 30xc2x0 and 60xc2x0. In the LSI layout, in addition to the wirings which are parallel with or vertical to the base lines, the oblique wirings are provided. The third aperture array 142 of FIG. 22B also has aperture 145 for a VBS exposure. Further, aperture sections 141 shown in FIG. 22A are formed on the second aperture array 140 used in the fourth embodiment correspondingly to the forms of the oblique wiring patterns 143 and 144 on the third aperture array 142. The aperture sections 141 and the oblique wiring pattern 143 can be arranged so as to establish a positional relationship shown in FIG. 23 due to reduction and enlargement. This positional relationship can be regarded as the same positional relationship as FIG. 5A. Moreover, the aperture sections 141 and the oblique wiring pattern 144 can be arranged so as to establish the same positional relationship as FIG. 23 due to reduction and enlargement. Next, there will be explained below the exposure method according to the fourth embodiment. For example, patterns 146 to 151 shown in FIG. 24A are exposed. In the fourth embodiment, as shown in FIG. 24B, the exposure is divided into two shot areas 152 and 153, and the aperture sections 141 on the second aperture array 140 are individually controlled so that the pattern 143 is exposed. Similarly to the first embodiment, the exposure data are created according to FIG. 6. At step S1, the layout patterns 146 through 151 are divided into the sizes of the basic figure apertures 143 and 144. As a result, as shown in FIG. 24B, the patterns 146 through 151 are divided in the areas 152 and 153. At step S2 since the divided layout patterns are oblique wirings from the upper left to the lower right, they are classified as the pattern 143 for the oblique wiring from the upper left to the lower right. The steps S1 and S2 are executed so that the drawing data 92 can be created. The basic figure names of the data 94 for the third aperture array of the drawing data 92 are identification symbols of the pattern 143. Moreover, the drawing positions of the data 95 for sample are an arrangement position of the patterns 146 to 151 in FIG. 24. The address 96 may be determined when the data 93 are input. Next, at step S3 the logic operation of the divided layouts 146 to 151 and the basic FIG. 143 is performed. As a result, the on/off information 93, which shows that the aperture sections 141 on R4 and L4 to L9, the aperture sections 141 on R6 and L2 to L11, the aperture sections 141 on R8 and L13 through L6 and the aperture sections 141 on R10 and L6 and L7 are on areas where the beam 9 is not deflected, is stored as the data 93 for the second aperture array control into the area 152. Similarly, the on/off information is stored into the area 153, and the creation of the exposure data is ended. Continuously, the latter half of the exposure method is executed. The exposure method is executed according to FIG. 7 similarly to the first embodiment. First, at step S11 the drawing positions 95 of the patterns 146 to 151 in FIG. 24A are called. At step S12 the basic figure name of the pattern 143 and the on/off information 93 are called. Steps S13 to S16 are executed. As shown in the area 152 of FIG. 24B, the second aperture array 140 allows the beam to transmit at necessary portions, and the other portions deflect the beam. The shaped beam is emitted only to R4, R6, R8 and R10 of the pattern 143. As a result, the oblique wiring patterns 146 to 151 shown in FIG. 24A can be exposed. (Modified Example of Fourth Embodiment) The modified example of the fourth embodiment will explain the case where the basic figures of the basic figure apertures are oblique wiring patterns. In the modified example of the fourth embodiment, the exposure apparatus used in the first embodiment is used. The feature of the modified example of the fourth embodiment is that oblique wiring patterns 163 and 164 are arranged on a third aperture array 162 as shown in FIG. 25B. The oblique wiring pattern 163 is an oblique wiring pattern from the upper left to the lower right. The oblique wiring pattern 163 has ten apertures R1 to R10. The oblique wiring pattern 164 is an oblique wiring pattern from the upper right to the lower left. The oblique wiring pattern 164 has ten apertures L1 to L10. The third aperture array 142 shown in FIG. 25B has aperture 145 for a VSB exposure. Further, aperture sections 161 shown in FIG. 25A are formed on a second aperture array 160 to be used in the modified example of the fourth embodiment correspondingly to the forms of the oblique wiring patterns 163 and 164 of the third aperture array 162. The aperture sections 161 and the oblique wiring pattern 163 can be arranged so as to establish a positional relationship shown in FIG. 26 due to reduction and enlargement. This positional relationship can be regarded as the same positional relationship as FIG. 5A. Moreover, the aperture sections 161 and the oblique wiring pattern 164 can be also arranged so as to establish a positional relationship shown in FIG. 26 due to reduction and enlargement. Next, there will be explained below the exposure method according to the modified example of the fourth embodiment. Similarly to the fourth embodiment, the patterns 146 to 151 shown in FIG. 24A are exposed. In the modified example of the fourth embodiment, as shown in FIG. 27, the exposure is divided into four shot areas 166 to 169, and the aperture sections 161 on the second aperture array 160 are individually controlled so that the pattern 163 is exposed. First, similarly to the first embodiment, the exposure data are created according to FIG. 6. At step S1 the layout patterns 146 to 151 are divided into the sizes of the basic figure apertures 163 and 164. As a result, as shown in FIG. 27, the layouts are divided in the areas 166 to 169. At step S2 since the divided layout patterns 146 to 151 are oblique wiring from the upper left to the lower right, they are classified as the oblique wiring pattern 163 from the upper left to the lower right. The steps S1 and S2 are executed so that the drawing data 92 can be created. The basic figure name of the data 94 for the third aperture array of the drawing data 92 is the identification symbol of the pattern 163. Moreover, the drawing position and the address 96 of the data 95 for sample may be determined similarly to the fourth embodiment. Next, at step S3 the logic operation of the divided layouts 146 to 151 and the basic FIG. 163 is performed. As a result, the on/off information 93, which shows that the aperture sections 161 on R1 and L4 to L8 and the aperture sections 161 on R3 and L2 to L8 and the aperture sections 161 on R5 and L3 to L6 and the aperture sections 161 on R7 and L6 and L7 are on areas which do not deflect the beam 9, is stored as the data 93 for the second aperture array control in the area 166, for example. Similarly, the on/off information is stored in the areas 167 to 169, and the creation of the exposure data is ended. Continuously, the latter half of the exposure method is executed. The exposure method can be executed according to FIG. 7 similarly to the fourth embodiment. The beam 9 shaped by the second aperture array 160 is emitted only to R1, R3, R5 and R7 of the pattern 163. As a result, the oblique wiring patterns 146 to 151 shown in FIG. 24A can be exposed. In such a manner, when some basic figure apertures to be reference are created, one basic figure aperture A1, 102, 143, 163 or the like can be applied to a plurality of patterns according to the beam shape of the second aperture arrays 3, 114, 140 and 160. Moreover, the exposure data are divided into the drawing data A (93) and the data B for the second aperture array control (93) so that the exposure data 91 can be compressed. The first embodiment to the fourth embodiment 4 are not limited to an acceleration voltage at the time of pattern exposure. In the first embodiment to the fourth embodiment, the acceleration voltage at the time of pattern exposure is 5 kV, but the acceleration voltage at the time of pattern exposure may be a low energy electron beam of 5 kV or less. Moreover, similarly the embodiments 1 through 4 can be applied to the case where the pattern exposure is carried out with the acceleration voltage of 5 kV or more. Further, the first embodiment to the fourth embodiment are not limited to types of the electron beam exposure apparatus. For example, a CP exposure type electron beam exposure apparatus, a variable shaping type electron beam exposure apparatus, multibeam type electron beam exposure apparatus, a disc beam type electron beam exposure apparatus or an electron-beam mask transfer system type electron beam exposure apparatus can be combined with the first embodiment to the fourth embodiment so as to be capable of being used. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. |
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description | This application claims priority to the following U.S. patent applications: U.S. Provisional Patent Application No. 61/260,585 filed Nov. 12, 2009 for “Medical Isotope Production on Demand”; U.S. Provisional Patent Application No. 61/265,383 filed Dec. 1, 2009 for “System for On-Demand Production of I-131”; U.S. Provisional Patent Application No. 61/405,605 filed Oct. 21, 2010 for “Techniques for On-Demand Production of Medical Isotopes Such as Mo-99/Tc-99m.” This application is also related to U.S. patent application Ser. No. 12/944,694 filled contemporaneously herewith for “Techniques for On-Demand Production of Medical Radioactive Iodine Isotopes Including 1-131” (inventor Francis Yu-Hei Tsang). The entire disclosures of all the above mentioned applications, including all appendices and attachments, are hereby incorporated by reference for all purposes. The present invention relates generally to the generation of unstable, i.e., radioactive, nuclear isotopes (often referred to as radioisotopes), and more particularly to techniques for generating medical isotopes such as molybdenum-99 (Mo-99) and its decay daughter technetium-99m (Tc-99m), and radioactive iodine such as iodine-131 (I-131). Radioisotopes, in very small doses, are widely used in clinical therapy (radiation treatments) for such diseases as cancer and hyperthyroidism, as well as diagnostics using the ability to image regions where radioisotopes concentrate in the subject's body. Currently, nearly 80% of all nuclear imaging procedures utilize Tc-99m, making it a very important isotope for diagnostic medicine. Molecules and proteins that concentrate in specific areas of the body can be tagged with Tc-99m, which decays to a ground state through emission of a low energy gamma-ray, and observed from outside the body using gamma-ray cameras or detectors. This method allows “active” areas, or regions where the Tc-99m tagged compound concentrates, to be observed in 3-D from outside the body. With a high demand for medical procedures involving the use of Tc-99m and I-131, a demand that is only expected to increase as the U.S. population ages, reliability of the Tc-99m and I-131 supplies is critical. A major obstacle to a reliable source is the fact that 100% of the U.S. supply is imported from foreign reactors. The U.S supply is sourced almost entirely from the NRU Reactor in Canada (Chalk River) and the HFR in the Netherlands, and both reactors are over 40 years old. The rapid decay of the Mo-99 means that product must be shipped and used immediately with no long term storage possible. Any interruptions in supply, even brief periods such as a reactor shutting down for maintenance, can cause shortages and patient treatment delays. Real shortages have occurred as recently as 2007 and 2008 when the NRU Reactor and HFR, respectively, were shut down for a period of time. Traditional methods rely on thermal fission of targets made of highly enriched uranium (HEU). HEU is uranium that has been processed to greatly increase the percentage of fissionable U-235 above the approximately 0.7% level, found in naturally occurring uranium, to levels above 93%. Thermal fission refers to the irradiation of a target by low-energy (“thermal”) neutrons, causing fission to occur. Currently, the U.S. exports more than 50 kg of HEU having more than 93% U-235 to at least five foreign nuclear reactors for irradiation and extraction of the Mo-99/Tc-99m and other medical isotopes. The proliferation potential and hazards associated with shipping fresh HEU and spent HEU are obvious, but current production of Mo-99/Tc-99m relies on this process. The spent HEU target material is also a threat because only between 1-3% of the U-235 in the HEU target is burned up and the remaining target material can still contain 92% enriched U-235. Also, because of the low burn-up, after three-year storage, the HEU target materials can be essentially contact handled, meaning that due to its relatively low burn up, the amount of long-lived fission products in the spent HEU target material are minimal. The spent HEU target can be handled and processed relatively easy with minimal shielding materials to protect the proliferators. Alternative techniques have been proposed, but they are thought to be significantly less cost effective and many technical challenges remain. One such proposal is to transition to a lower level of enrichment of the U-235 target (LEU), say below 20% U-235, but this still presents the same problems as HEU, including the need for a nuclear reactor. Another method proposed is to utilize neutron capture in Mo-98, which can be mined as ore. However, natural molybdenum contains on the order of 24.1% Mo-98, so targets are likely to require enrichment prior to irradiation. Other techniques proposed for production of Mo-99 include causing (p, 2n) or (p, pn) reactions in an Mo-100 target using a proton accelerator (cyclotron). Again, natural molybdenum contains on the order of 9.64% of Mo-100, so targets for cyclotrons are also likely to require enrichment prior to irradiation. It has also been proposed to cause (γ, f) reactions on U-235 or LEU, or U-238 or a combination of all three materials via bremsstrahlung radiation produced from a high-energy electron accelerator. The proposed alternative methods using particle accelerators all have similar problems: They all require large and enriched isotopic targets. They all require heat removal from the targets during irradiation, which represents a technical challenge. The Mo-99 produced must be purified to remove unused molybdenum isotopes and other fission products and activation by-products. They all require development of fast dissolution methods for the metallic targets. Treatment and disposal of the waste fission products and waste uranium present significant challenges (for LEU). Embodiments of the present invention provide techniques for the production of radioisotopes. Radioisotopes that are useful in the field of medicine are sometimes referred to as medical isotopes, although some stable isotopes have potential medical uses and are sometimes referred to as stable medical isotopes. The techniques provided by the invention overcome at least some of the problems discussed above. Embodiments do not rely on a nuclear reactor far from the delivery site, but can be implemented as relatively small stand-alone devices that can be widely distributed. In describing embodiments of the invention, the following terms are sometimes used: Non-enriched uranium (“NEU”); Neutron-reflecting material; Fast neutrons; Fast neutron fission reactions; and Neutron generator.As will now be discussed, these terms are defined broadly. The term “non-enriched uranium” (“NEU”) is intended to cover naturally occurring uranium or depleted uranium, in addition to any uranium that contains at least as much U-238 as naturally occurring uranium (99.27%) and no more U-235 than naturally occurring uranium (0.72%). Depleted uranium is normally understood to mean uranium that has less than the naturally occurring amount of U-235 (0.72%), but depleted uranium that is used for commercial and military purposes more commonly has less than 0.3% U-235. The definition of NEU is not limited to any form of the uranium, so long as the isotope content meets the above criteria. The NEU material, also referred to as the NEU feedstock or the NEU target, can be in the form of bulk solid material, crushed solid material, metallic shavings, metallic filings, sintered pellets, liquid solutions, molten salts, molten alloys, or slurries. The NEU, whatever its form, can also be mixed with other material that is compatible with the intended use. The term “neutron-reflecting material” is intended to cover material that reflects or scatters neutrons. While it is preferred that the scattering be elastic, or largely so, this is not necessary for the definition. Further, while some of the embodiments use neutron-reflecting material formed into solid structural shapes such as plates, spherical shells, cylindrical shells, tubes, and the like, the term is intended to cover material that includes small particles such as powders, pellets, shavings, filings, and the like. The term “fast neutron” is often used to distinguish thermal neutrons, which Wikipedia characterizes as having energies of “of about 0.025 eV.” Wikipedia also characterizes fast neutrons as having energies “greater than 1 eV, 0.1 MeV or approximately 1 MeV, depending on the definition.” For present purposes, the term “fast neutron” will mean a neutron with an energy above 800 keV (i.e., 0.8 MeV), which is a threshold for fission in U-238. However, embodiments of the present invention can use neutrons of higher energies, say 10-20 MeV, or possibly 12-16 MeV. Higher-energy neutrons, say in the 20-100 MeV range, can also be used. The term “fast neutron fission” is intended to cover the fission reactions that are caused by neutrons with energies that are above the threshold of 800 keV. The reaction representation (m, f) is used for simplicity. The term “neutron generator” is intended to cover a wide range of devices and processes for generating neutrons of the desired energies. Wikipedia defines neutron generators as follows: Neutron generators are neutron source devices which contain compact linear accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains either deuterium, tritium or a mixture. Fusion of deuterium atoms (D+D) results in the formation of a He-3 ion and a neutron with a kinetic energy of approximately 2.45 MeV. Fusion of a deuterium and a tritium atom (D+T) results in the formation of a He-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV.Fusion of a triton and a tritium atom (T+T) results in the formation of a He-4 ion and two neutrons. These two neutrons can have an energy range from below 0.1 eV to ˜9.33 MeV. As used in this application, however, the term “neutron generator” is defined more broadly to include any device that would provide a sufficient number of neutrons of the desired energies. This could include, for example, but is not limited to, the following. A dense plasma focusing device can use deuterium or tritium plasma to produce 2.45 MeV neutrons, 14.1 MeV neutrons, or neutrons covering a broad spectrum (below 0.1 eV to ˜9.33 MeV). An electron accelerator can be used to send high energy electrons from an electron beam onto a converter material, e.g., tantalum (Ta), tungsten (W), etc., thereby converting the electron energy into bremsstrahlung radiation. This bremsstrahlung radiation can then be used to interact with neutron-rich materials to produce neutrons via (γ, n) interactions. For example, irradiating the beryllium isotope Be-9 with γ rays can produce a beryllium isotope with a lower atomic mass and one or two neutrons (the reactions being denoted Be-9(γ, n)Be-8, or Be-9(γ, 2n)Be-7). A proton accelerator such as a cyclotron can be used to send high energy protons into materials such as carbon, beryllium, or lithium, for example, to produce neutrons via C-12(p, n)N-12, or Be-9(p, n)B-9 reactions, for example. In short, embodiments of the present invention use fast-neutron-caused fission of depleted or naturally occurring uranium targets in an irradiation chamber. A generic term for such uranium is non-enriched uranium (“NEU”). U-238, is fissionable in that it can be made to fission when struck by fast neutrons, i.e., neutrons having energies above a fission threshold. It is not fissile in that it cannot sustain a chain reaction. This is because when U-238 undergoes fission, neutrons resulting from the fission are generally below the energy threshold to cause more U-238 fission. The purpose of causing fission is to generate and extract fission products that are, or decay to, desired radioisotopes. Embodiments will be described in the context of extracting Mo-99/Tc-99m, but this is exemplary. Since the fission products include radioactive iodine isotopes, some embodiments can also extract radioactive iodine isotopes as well. In this application, the term “fission product” will be used as set forth in the NRC glossary (http://www.nrc.gov/reading-rm/basic-ref/glossary.html), which defines “fission products” as “[t]he nuclei (fission fragments) formed by the fission of heavy elements, plus the nuclide formed by the fission fragments' radioactive decay.” Thus the term is used more broadly than a definition that would cover only the nuclei resulting directly from the fission reaction. This interpretation is consistent with the glossary at http://www.nuclearglossary.com (“The Language of the Nucleus”), which defines “fission product” as “[a]residual nucleus formed in fission, including fission fragments and their decay daughters.” The term “fission fragment” is defined as “[a]nucleus formed as a direct result of fission. Fission products formed by the decay of these nuclides are not included.” The term “primary fission product” is said to be a synonym for “fission fragment.” Embodiments of the present invention operate to enhance fast fission in NEU targets by having neutrons undergo scattering or reflection after passing through a region of NEU. This is accomplished by having the target material interspersed with what is referred to as “neutron-reflecting” material, which reflects or scatters neutrons so that the neutrons travel a longer path before leaving the target material. This provides more opportunities for the neutrons to cause fission reactions with the NEU target material. Thus, a given neutron tends to have multiple interactions (e.g., scattering events) with U-238 nuclei before it causes a fission reaction or leaves the region or regions occupied by NEU target material without being absorbed by the U-238. After a number of scattering events within the NEU target material, a neutron's energy will drop below the fission threshold. The target material can be interspersed with neutron-reflecting material according to a number of different geometrical arrangements. The particular form of feedstock typically depends on the geometry of the irradiation chamber, the characteristics of the fission products that are to be extracted, and the manner of extracting the fission products. A preferred feedstock is in the form of depleted uranium. Depleted uranium is a byproduct of uranium enrichment and contains over 99.7% of U-238 as compared to natural uranium, which contains about 99.3% of U-238. As well as maintaining the neutron energy above a fast fission threshold, it is preferred to maintain a sufficiently high neutron energy to minimize neutron absorption by U-238. When a neutron with slower energy is captured by U-238, Pu-239 is produced after subsequent decay of the excited U-238 atom. Using fast neutron sources instead, the probability of fission of U-238 becomes orders of magnitude higher than the probability of capture, resulting in greatly reduced production of Pu-239. In one set of embodiments, the NEU and neutron-reflecting material are formed as alternating layers of NEU and neutron-reflecting material. The layers can take the form of spherical shells, cylindrical shells, flat plates and the like, with a fast neutron generator disposed near the center. In these embodiments, the irradiation chamber is generally spherical, generally cylindrical, or generally rectangular. Other geometries such as polygonal cylinders and polyhedrons are also possible, and may allow easier fabrication. In another set of embodiments, the NEU occupies a plurality of parallel elongate regions with each region surrounded by neutron-reflecting material. The surrounding neutron-reflecting material can be formed as a plurality of tubes, and solid rods or crushed NEU can be disposed in the tubes. The NEU and surrounding neutron-reflecting material can occupy a cylindrical region with a hollow center for the fast neutron generator. Thus, in this set of embodiments, the irradiation chamber is generally cylindrical (circular or polygonal base). In other embodiments, the NEU and neutron-reflecting material can both be formed as relatively small objects (say a few centimeters in size), and mixed in solid form or in a slurry. The slurry can be circulated in tubes surrounding the neutron generator. Embodiments where the NEU is in molten form, whether or not interspersed with neutron-reflecting material, can also be circulated. Circulating the NEU results in even irradiation of all the NEU in the chamber. In an aspect of the invention, a method for producing radioisotopes comprises introducing NEU material into a an irradiation chamber, irradiating the NEU material with neutrons having energies above 800 keV to cause fast fission reactions to occur in the NEU material and generate fission products, and extracting the fission products from the NEU material. The irradiation chamber has one or more walls formed of neutron-reflecting material, and at least some neutrons from the irradiating are reflected from at least one of the one or more walls, thereby increasing the path length over which those neutrons are in the NEU material. The increased path length increases the probability that those neutrons in the NEU material will cause fast fission reactions. In some embodiments, the NEU material in the irradiation chamber occupies a single spatially contiguous region, while in other embodiments, the NEU material in the irradiation chamber occupies multiple spatially disjoint regions. The one or more walls formed of neutron-reflecting material can comprise at least one internal wall of the irradiation chamber, or an outer wall that surrounds all the NEU material in the irradiation chamber, or both. In another aspect of the invention, a method for producing radioisotopes comprises providing a volume of NEU material, interspersing the NEU material with neutron-reflecting material, surrounding the volume of NEU material with additional neutron-reflecting material, surrounding the additional neutron-reflecting material with neutron-absorbing material, and irradiating the NEU material with neutrons having energies above a fission threshold to cause fast fission reactions to occur in the NEU material and generate fission products. For at least some neutrons, the neutron-reflecting material prolongs the time that those neutrons remain within the volume of NEU material, thereby increasing the number of fast fission reactions caused by those neutrons before those neutrons encounter the neutron-absorbing material. The method can also include extracting the fission products from the NEU material. Depending on the reactions and the products, the extraction may or may not require removing the NEU material from the irradiation chamber. In another aspect of the invention, apparatus for producing radioisotopes comprises a fast neutron generator and a plurality of spaced shells made of neutron-reflecting material. The shells surround the neutron generator and include an outermost shell, and the spacing between adjacent shells provides a number of regions configured to receive NEU for irradiation by neutrons generated by the neutron generator. The outermost shell can be thicker than the remaining shells. In another aspect of the invention, apparatus for producing radioisotopes comprises a fast neutron generator, an irradiation chamber having one or more regions into which NEU can be introduced, and one or more neutron-reflecting regions disposed in or around the irradiation chamber. The one or more neutron-reflecting regions are configured to increase the path length traveled by at least some neutrons from the neutron generator before those neutrons leave the irradiation chamber. In some embodiments, the apparatus can also comprise an outer containment vessel having one or more walls made of neutron-absorbing material to absorb neutrons passing out of the outermost shell. The walls of the outer containment vessel can be spaced from the outermost shell to limit the likelihood that neutrons scattered or reflected from the walls of the outer containment vessel will encounter the outermost shell. In some embodiments, the irradiation chamber is of spherical configuration, the one or more neutron-reflecting regions include a plurality of spaced concentric spherical shells, including an outermost shell, of neutron-reflecting material, the shells surround the neutron generator, and the space between adjacent shells defines at least one of the one or more regions into which NEU can be introduced. In some embodiments, the irradiation chamber is of cylindrical configuration with an outer wall having a portion formed as a cylindrical shell, the one or more neutron-reflecting regions include one or more tubes of neutron-reflecting material, and the bores of the one or more tubes define at least one of the one or more regions into which NEU can be introduced. In some embodiments, the irradiation chamber is of cylindrical configuration with an outer wall having a portion formed as a cylindrical shell, the one or more neutron-reflecting regions include a plurality of spaced coaxial cylindrical shells of neutron-reflecting material, and the space between the cylindrical shells of neutron-reflecting material defines at least one of the one or more regions into which NEU can be introduced. In some embodiments, the irradiation chamber is of rectangular configuration with an outer wall having a portion formed as a rectangular shell, the one or more neutron-reflecting regions include a plurality of spaced plates or rectangular shells of neutron-reflecting material, and the space between the plates or rectangular shells of neutron-reflecting material defines at least one of the one or more regions into which NEU can be introduced. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings, which are intended to be exemplary and not limiting. Overview of Embodiments FIG. 1 is a stylized high-level schematic of a radioisotope generator 10 according to an embodiment of the present invention, and is used to illustrate salient features that can be viewed as generic to the various embodiments discussed below. The main components of radioisotope generator 10 include an irradiation chamber 15, a fast neutron generator 20, and, for preferred embodiments, one or more neutron-reflecting elements 25. The irradiation chamber is configured to accept a charge of what is referred to as non-enriched uranium (“NEU”). As mentioned above, the NEU can be in any suitable form, including elemental metal, salt, alloy, molten salt, molten alloy, slurry, or other mixture, and can assume any one of a number of shapes and states, as will be described below. For purposes of generality, the NEU is shown as a plurality of arbitrary-shaped bodies 30 (stippled for clarity). The irradiation chamber is generally provided with mechanisms for introducing NEU into, and removing NEU from, the irradiation chamber, such as one or more fill ports 35a and one or more empty (drain) ports 35b. In some embodiments, it is desired to flow gas through the irradiation chamber, and to this end the chamber can be provided with one or more gas inlet ports 40a and one or more gas outlet ports 40b. FIG. 1 also shows a neutron-absorbing outer containment chamber 45 surrounding the irradiation chamber. In representative embodiments, this outer containment chamber is an entirely separate structure from the irradiation chamber and can be built on site prior to installation of the radioisotope generator. Containment chamber 45 can be built as a concrete vault or bunker and lined with special neutron-absorbing material such as borated polyethylene. It is preferred that the outer containment chamber be significantly larger than the irradiation chamber so that the irradiation chamber subtends a relatively small solid angle at any point on walls of the outer containment chamber. This tends to reduce the likelihood of any slow neutrons scattered by the outer containment chamber walls getting back inside the irradiation chamber. The walls of irradiation chamber 15 preferably include at least a layer of neutron-reflecting material, and so the combination of irradiation chamber 15's layer of neutron-reflecting elements, and neutron-reflecting elements 25 can be considered to define one or more neutron-reflecting regions disposed in or around the irradiation chamber. Some of the embodiments to be described below include separate neutron-reflecting elements inside the chamber, which may have the effect of subdividing the chamber into disjoint regions occupied by NEU material, while other embodiments provide a single contiguous region occupied by NEU material. For generality, FIG. 1 shows the NEU as separate disjoint bodies, but the case of a single contiguous body of NEU material should be considered to fall within the scope of the invention. In keeping with the schematic nature of FIG. 1, the neutron-reflecting elements and the NEU bodies are shown as sparsely populating the irradiation chamber. In most embodiments, however, the regions of NEU material will generally fill hollow regions within the irradiation chamber so as to be surrounded by neutron-reflecting material. However, this does not preclude their being hollow portions of the chamber having neither neutron-reflecting material nor NEU material. Embodiments of the present invention are not limited to any particular type of neutron generator. Representative systems can use a portable and compact accelerator that can accelerate and direct charged particles, or neutral particles, or deuterons, or tritons to targets that can be used to produce neutrons with energies that are above the 800 keV fast neutron fission threshold energy of U-238. The target materials can be elements, compounds, or solutions. Other target materials also can contain materials or compounds that are enriched with tritium atoms. Specifically, the fusing of deuterium atoms with tritium atoms produces 14.1-MeV neutrons which are used to cause fast fission reactions in the uranium atoms. When tritons are accelerated and fused with targets enriched with tritium atoms, the produced neutrons can encompass energies from below 0.1 eV to ˜9.3 MeV. Suitable neutron generators are commercially available, for example from Adelphi Technology Inc. 2003 East Bayshore Rd, Redwood City, Calif. 94063, Halliburton, 10200 Bellaire Blvd. Houston, Tex. 77072, and Schlumberger Technology, 300 Schlumberger Dr., Sugar Land, Tex. 77478. The operation of radioisotope generator 10 can be summarized as follows. Neutron generator 20 provides neutrons above a fission threshold for U-238. The purpose of causing fission is to generate and extract one or more fission products that are, or decay to, desired radioisotopes. FIG. 2 shows the decay products of Mo-99 (Z=42), which is one of the primary fission products, and is also produced through the decay chain. Mo-99 constitutes ˜6% of the fission yield. Mo-99 will decay, with a half-life of 66 hours, to Tc-99 (12.5%) and Tc-99's metastable isomer Tc-99m (87.5%) (both Z=43). Both Mo-99 and Tc-99m can be recovered with chemical extraction processes and/or electrochemical separators. Embodiments will be described in the context of extracting Mo-99/Tc-99m. The neutrons are preferably maintained above energies where the neutron-absorption cross section for U-238 remains negligible. Thus, the NEU target does not breed plutonium (Pu-239). Other fission products include I-129, I-131, I-132, and I-133, which can also be recovered with chemical extraction processes and/or electrochemical separators. The purpose, and operation, of the neutron-reflecting material is to increase the path length traveled by at least some neutrons from the neutron generator before those neutrons leave the irradiation chamber. Thus, as a neutron exits a region of NEU material, possibly having undergone one or more scattering interactions therein, it is reflected or scattered to enhance the likelihood that it will encounter additional NEU material and therefore have an increased chance to initiate a fission reaction. Iron is an example of an element that can act as neutron-reflecting material. In specific embodiments, stainless steel is used both for its structural and neutron-reflecting properties. For neutron energies above 800 keV, each scattering event with iron causes the neutron to lose about 0.56 MeV in energy. Thus, after a sufficient number of scattering events (depending on initial energy), the neutron will fall below the fast fission threshold. Overview of Relevant Properties of Uranium and Fission Reactions The literature concerning the properties of uranium and the physics of nuclear fission is vast, and is well understood by those skilled in the nuclear physics and engineering fields. For the sake of completeness, a short overview of the relevant aspects of this vast store of knowledge will be outlined to provide context for the description of embodiments of the present invention. As discussed above, embodiments of the present invention use depleted or naturally occurring (i.e., non-enriched uranium or NEU) targets. Naturally occurring uranium is about 99.27% U-238, 0.72% U-235, and 0.0055% U-234Depleted uranium is the by-product of the process of enriching naturally occurring uranium to achieve a higher proportion of U-235. Thus the depleted uranium contains significantly less U-235 and U-234 than natural uranium (say less than a third as much). There is no fundamental reason why embodiments of the present invention could not use pure U-238, but as a practical matter, that would be much more expensive. Further, as discussed above, embodiments of the present invention irradiate NEU, largely containing U-238, with fast neutrons to cause fission. The most common nuclear reactors, on the other hand, irradiate U-235 with thermal neutrons to cause fission. Both U-235 and U-238 will undergo fission when struck with fast neutrons, but the characteristics are different. First is the difference in fission cross section as a function of neutron energy for the two isotopes. U-235's fission cross section for fast neutrons is at least 250 times lower than for thermal neutrons. That is the reason why a nuclear reactor is used to produce Mo-99 using targets enriched with U-235, since the neutrons within a nuclear reactor are typically thermalized. Thermal neutrons cannot cause fission in U-238. Second is the nature of the reaction. U-235 is fissile, meaning that it can sustain a chain reaction when a critical mass is present, since the neutrons resulting from the fission reactions have energies where U-235's fission cross section is high. U-238, on the other hand, while fissionable, is not fissile. While U-238 can be made to fission when struck with fast neutrons, most of the neutrons resulting from the fission reactions have energies that are not sufficiently high to cause additional U-238 fission. FIG. 3 is a graph of U-238's fission cross section and neutron capture cross section as functions of neutron energy. This graph was generated using the tools provided at http://atom.kaeri.re.kr/cgi-bin/endfplot.pl. U-238 also has a reaction path where it absorbs a neutron and, after two beta decays, becomes Pu-239. While this reaction path may be desirable in breeder reactors, embodiments of the invention seek to reduce the probability of neutron absorption by maintaining neutron energies in a range where the cross section for fission far exceeds the cross section for neutron absorption. For example, as can be seen in the graph of FIG. 3, the two cross sections are equal at a neutron energy of ˜1.3 MeV, while at 2.2 MeV, the fission cross section is ˜20 times larger. Accordingly, it is preferred to minimize or eliminate materials that would act as moderators. As can be seen from the graph of U-238's fission cross section as a function of neutron energy, the fission cross section plateaus between 1 and 2 MeV, the neutron capture cross section is rapidly falling off in this range of energies. It should be understood that a fast neutron can transverse its entire path through the NEU without causing a fission reaction. This fast neutron also can be scattered or reflected from U-238 nuclei. The neutron-reflecting or scattering material is used to enhance the probability that a fast neutron will ultimately interact with a U-238 nucleus and cause a fission reaction before its energy drops below the 800 keV threshold. Once this fast neutron interacts with U-238 and causes a fission reaction, this neutron essentially is gone. There will be 2-3 neutrons born after the fission reaction (prompt neutrons), and some of these neutrons can cause some addition fission in the NEU if their energies can stay above the 800 keV threshold. Overview of Representative Geometrical Configurations FIG. 4 is a simplified oblique view of a radioisotope generator 10sphere having a spherical irradiation chamber according to an embodiment of the present invention. Fill port 35a is shown, but drain port 35b would be hidden from view. The chamber is preferably fabricated in at least two sections, which is signified by an equatorial line (the hidden half being shown in phantom). The equatorial line also denotes the intersection of a horizontal plane that is designated by a section line 6-6. For simplicity, gas inlet port(s) 40a and gas outlet port(s) 40b are not shown. FIG. 5 is a simplified oblique view of a radioisotope generator 10cyl having a cylindrical irradiation chamber according to an embodiment of the present invention. Again, fill port 35a is shown, but drain port 35b would be hidden from view. Also, gas inlet port(s) 40a and gas outlet port(s) 40b are not shown. Shown in phantom is the intersection of a horizontal plane that is designated by a section line (also 6-6). The cylindrical wall of irradiation chamber 15 need not be fabricated in multiple sections, although it can be. In such a case, the phantom line designating the intersection of the horizontal plane could be drawn in solid on the visible portion of the cylindrical wall. FIG. 6 is a simplified cross-sectional view that applies to either of radioisotope generators 10sphere and 10cyl, and is taken along line 6-6 in FIGS. 4 and 5. For the spherical embodiment 10sphere, neutron-reflecting elements 25 are formed as a plurality of spaced concentric spherical shells that surround neutron generator 20. For the cylindrical embodiment 10cyl, neutron-reflecting elements 25 are formed as a plurality of spaced coaxial cylindrical shells that surround neutron generator 20. In both embodiments, NEU bodies or regions 30 partially or fully occupy the spaces between neutron-reflecting shells 25. The drawing is simplified in that it doesn't show holes in the neutron-reflecting shells that allow NEU material introduced in one region to find its way to other regions. Further, it is contemplated that there may be bulkheads, again not shown, that maintain the spacing between the shells and provide additional structural strength. For both embodiments, the outermost neutron-reflecting shell, which is shown as being thicker than the radially inward shells, at least partially defines irradiation chamber 15. While a plurality of regions for NEU are shown, some embodiments can have only one region (spherical or cylindrical shell as the case may be). Furthermore, the outermost neutron-reflecting shell need not be thicker than the inner one or ones. Radially outward of the outermost neutron-reflecting shell is a biological shield 50, which is used to block ionizing radiation such as alpha particles, electrons, and gamma rays that might leak out of the neutron-reflecting shell. Biological shield 50 also can be considered to partially define irradiation chamber 15. Such a shield can be made of materials such as lead, iron, borated polyethylene, or a combination of any or all of such materials. While specific dimensions do not form a part of the invention, some representative dimensions, or at least factors that can be considered in specifying particular dimensions will be discussed. For example, the NEU can be formed in a single layer on the order of 30 to 50 cm thick, or a combination of multiple layers on the order of 10 cm thick and separated by stainless steel layers on the order of 0.5 cm thick. In this way, when the neutron energy falls below 1 MeV after multiple scattering events, the neutron will leak out of the outermost layer of the NEU. A distance of containment chamber 45's walls from irradiation chamber 15 on the order of 2.5 meters is representative. FIG. 7 is a is a simplified oblique view of a radioisotope generator 10rect having a rectangular-prism-shaped irradiation chamber according to an embodiment of the present invention. Again, fill port 35a is shown, but drain port 35b would be hidden from view. Also, gas inlet port(s) 40a and gas outlet port(s) 40b are not shown. Shown in phantom is the intersection of a horizontal plane that is designated by a section line 8-8. FIG. 8 is a simplified cross-sectional view of the radioisotope generator shown in FIG. 7 and is taken along line 8-8 in FIG. 7. In this embodiment, neutron-reflecting elements 25 are formed as a plurality of spaced parallel plates, some of which are cut away or shortened to provide a cavity for neutron generator 20. NEU bodies or regions 30 partially or fully occupy the spaces between neutron-reflecting plates 25. FIG. 9 is a simplified cross-sectional view of a radioisotope generator 10rod where the NEU is in the form of rods 55, one of which is shown enlarged. As can be seen, each rod comprises a tubular shell of neutron-reflecting material 25 surrounding a bore 44 containing NEU 30. The rods are shown as circular in cross section, but polygonal tubes can also be used. A circular cross section is generally preferred since that is generally the most common and would be more economical to manufacture and operate. A circular cross section has the additional advantages of the greatest structural integrity and efficiency for the propagation of fast neutrons. The tubes are shown disposed in a cylindrical irradiation chamber, but there is no requirement. As schematically drawn, rods are laid out in an octagonal array, and so an octagonal irradiation chamber could also be used. The rods could also be distributed along a set of concentric circles so that their axes would lie in concentric cylindrical surfaces. Process Overview FIG. 10 is a process schematic for the generation of radioisotopes according to an exemplary embodiment of the present invention. Each block in the schematic represents an operation, but many of the blocks also represent a physical piece of apparatus. The connector lines represent logical flow as well as material flow, so the figure can also be viewed as a flowchart. The production can be considered to begin with providing an initial supply of NEU (operation 60), which in this exemplary embodiment is depleted uranium. This exemplary embodiment uses NEU in granular form, and so NEU is then subjected to a grinding operation 65 and a sorting operation 70 that rejects undersized pieces of NEU. The pieces meeting the desired size criteria are sent to an inventory 75 of NEU in a suitable form or state, and the undersized pieces are diverted to bypass the inventory and are subjected to further processing as will be described below. Grinding and sorting operations 65 and 70 can also be used for recycling NEU as will be described below. For the sake of this exemplary embodiment, a suitable form would be NEU that had been ground or crushed to “pebbles” of desired nominal size, say on the order of no less than 0.64 cm (¼-inch) in the smallest dimension and no more than 12.7 cm (½-inch) in the largest dimension. The NEU is loaded into the radioisotope generator, say by gravity through fill port(s) 35a (not shown in FIG. 10), and irradiated for a suitable period of time with neutrons of a suitable energy (operation 80). In one exemplary embodiment, the NEU is irradiated with 3.5×1013 neutrons/second for 20 hours using 14.1-MeV neutrons. This provides a balance between production and decay. For the example of a single 30-cm spherical shell of NEU having an outer diameter of 182.88 cm (6 feet), the mass of the NEU would be on the order of 22,000 kg. After irradiation, the NEU, which now contains fission products, including the desired fission products and other fission products, is removed from the radioisotope generator, say by gravity through drain port(s) 35b (not shown in FIG. 10), subjected to a radioisotope recovery operation 85 to provide the desired fission product, in this case Mo-99. The recovered Mo-99 is then subjected to a quality control testing operation 90, is used to charge a Tc-99m generator (operation 95), and the Tc-99m generator is set for shipment to an end user (operation 100). By way of example, a single generator may contain 6 curies and would be used to prepare a large number of individual patient doses that might be on the order of 10-30 microcuries per patient. The NEU from which the Mo-99 has been recovered is subjected to a separate recovery operation 105 to remove the other fission products, some of which may be desirable radioisotopes, and is then subjected to yet another recovery operation 110 to recover the NEU for recycling. As will be described below, the recovery operations can use ionic liquids, and more specifically room-temperature ionic liquids (RTILs). The recovered NEU provided by recovery operation 110 is returned to be subjected to grinding and sorting operations, which can be the same grinding and sorting operations 65 and 70 used for the NEU that is originally provided to the system. As for the originally provided NEU, the sorting operation rejects undersized pieces of NEU. The pieces meeting the desired size criteria are returned to the NEU inventory, and the undersized pieces are diverted to bypass the inventory and irradiation chamber. The irradiation and fission can also give rise to various fission products in a gaseous state. These gaseous fission products include fission products that are themselves gases (e.g., xenon and kryton), and iodine (e.g., I-129, I-131, I-132, I-133, etc.), which is a solid, but easily sublimates. In some traditional systems using HEU, the HEU target elements are encapsulated. Thus, these gaseous fission products would be trapped in the encapsulated target elements, and the gaseous fission products would be captured after irradiation in connection with the Mo-99 recovery. Additionally, to the extent that gaseous fission products leaked out of the target, the iodine would dissolve in the water that acted as a coolant and moderator. In this exemplary embodiment, the gaseous fission products (i.e., fission gases and sublimated iodine) are extracted during irradiation. Thus, while the Mo-99 is recovered on a batch basis, the gaseous fission products can be collected on a continuous basis. As will be discussed below, some of the fission gases and iodine remain trapped within the NEU matrix and are recovered on a batch basis. In this exemplary embodiment, the irradiation chamber is provided with one or more gas inlet ports 40a and one or more gas outlet ports 40b (shown schematically in FIG. 1). Further, provision is made for fluid communication between the gas inlet and outlet ports and the NEU in the irradiation chamber. An inert carrier gas (e.g., argon) is introduced into an inlet port and circulated through the irradiation chamber where it mixes with the gaseous fission products. The gas exiting an outlet port of the irradiation chamber is subjected to a scavenging operation 115 to remove the gaseous fission products before the gas is reintroduced into an inlet port of the irradiation chamber. The gases removed by scavenging operation 115 are subjected to one or more recovery operations 120, one of which is shown. This can be a standard chemical extraction processes or a standard electrochemical separation. In this exemplary embodiment, it is desired to extract iodine (with I-131 often being the radioisotope of greatest interest), which can be captured in a silver zeolite trap, and the remaining gaseous fission products captured in HEPA filters for disposal. The iodine (including I-131) is then subjected to a quality control testing operation 125, packaged in suitable quantities (operation 127), and set for shipment to an end user (operation 130). References Burger—2004 (“HWVP Iodine Trap Evaluation”), Chapman—2010 (“Radioactive Iodine Capture in Silver-Containing Mordenites through Nanoscale Silver Iodide Formation”), and Wang 2006 (“Simulating Gaseous 131I Distribution in a Silver Zeolite Cartridge Using Sodium Iodide Solution”) provide additional background for the iodine recovery. The field of isotope extraction and separation is well developed, and Mo-99 recovery process 85 could use techniques such as chemical extraction processes and/or electrochemical separation processes. For example, generalized procedures for the recovery of Mo-99 from HEU have been developed in connection with nuclear-reactor-based operations. The HEU is normally encapsulated in a dispersion-type target with aluminum cladding, and the HEU can take the form of mini fuel plates or pins. After irradiation (typically 10-12 days), the targets are removed from the reactor and cooled for several hours in the pool adjacent to the reactor before being transported to the processing hot cell. The targets are then dissolved in nitric acid, with the possible addition of mercury (II) nitrate (Hg(NO3)2) to assist the dissolution of the aluminum. Following dissolution, the solution is fed to an alumina or polymer column, and the Mo-99 is adsorbed on the column with minor amounts of other components including heavy metals. Once the column is loaded with the Mo-99, the column is washed with nitric acid and then water, and then Mo-99 is stripped from the column using an ammonium-hydroxide solution. Purification is carried out to remove as much of the heavy metals as possible. Some producers have to carry out many purification steps in order to reduce the heavy metal concentrations to the level to meet FDA requirements. Chapter 2 of Reference NRC—2004 (“Medical Isotope Production without Highly Enriched Uranium”) provides a description of Molybdenum-99/Technetium-99m production and use, with a description of the dissolution and Mo-99 recovery at pages 25-30. In this exemplary embodiment, Mo-99 recovery process 85 uses ionic liquids, and more specifically room-temperature ionic liquids (RTILs). The recovery process includes a series of sub-processes, as will now be described. Initially, the NEU (including the fission products) that is unloaded from the irradiation chamber is dissolved in an RTIL (operation 135), and the Mo-99 is recovered from the solution (operation 140). Recovery operation 140, for this exemplary embodiment, entails electrodepositing the Mo-99 onto an anode. The recovered Mo-99 is then removed from the anode (operation 145). For sacrificial anodes, this can entail dissolving or otherwise destroying the anode with a higher charge. In the case of a permanent anode, this can include techniques such as scraping. References Pemberton—2008 (“Solubility and Electrochemistry of Uranyl Carbonate in a Room Temperature Ionic Liquid System”) and Pemberton—2009 (“Solubility and Electrochemistry of Uranium Extracted into a Room Temperature Ionic Liquid”) provide addition background. The above description of the iodine recovery was somewhat simplified, and will be explained in greater detail below. In many circumstances, some of the fission gases and some of the iodine fission product remain trapped in the NEU, and are released during Mo-99 recovery. To recover desired radioisotopes, provision is made to scavenge fission gases and sublimated iodine released during the Mo-99 recovery, to extract the iodine (including I-131), to subject the recovered iodine to quality control testing, to package the iodine, and to set the packaged iodine for shipment. This is shown schematically in phantom blocks associated with the NEU dissolution (operation 135). These blocks correspond generally to scavenging operation 115, recovery operation(s) 120, quality control testing operation 125, packaging operation 127, and setting for shipment operation 130 that are performed during irradiation of the NEU. While these blocks represent operations that are performed at different times, one or more may be implemented using the same apparatus that is used to perform these operations during irradiation. This is denoted by the legend “(One or more could be shared with irradiation chamber).” That possibility is also denoted schematically by a dashed arrow from NEU dissolution operation 135 to the gas scavenging operation 115 that is associated with irradiating the NEU (operation 80). Specific Embodiment with Cylindrical Irradiation Chamber with Parallel NEU Rods FIG. 11A is a perspective view of a radioisotope generator according to a specific embodiment having a cylindrical irradiation chamber in which are disposed parallel cylindrical NEU rods. FIG. 11B is a perspective, cutaway view of the radioisotope generator shown in FIG. 11A with the cover and the outer cylinder removed, exposing the tube assemblies and neutron generator. FIG. 11C is a perspective cutaway view of the radioisotope generator shown in FIG. 11A taken from a different view to show additional details of the tube assembly and the neutron generator. Generation and Recovery of Radioactive Iodine Isotopes Including I-131 As mentioned above, the irradiation and fission give rise to various fission products, and some of these are in gaseous states. Radioactive iodine 131 (sometimes referred to as 131I, radioiodine 131, or simply I-131) is not a fission gas, but readily sublimates, and so is one of these gaseous fission products, and is an important radioisotope to be recovered. Embodiments of the invention are designed with the production and recovery of I-131 and other radioactive iodine isotopes in mind. An iodine isotope of major interest is I-131, but the fission products include a number of other radioactive iodine isotopes and other elements that decay to radioactive iodine. Properties and Uses of I-131 I-131 (atomic number Z=53, 78 neutrons) has a half-life of 8.02 days and used for a variety of applications. These include diagnostic and therapeutic thyroid applications (in either a solution or capsule form), industrial tracers, and various research applications such as antibody labeling. I-131 is also used to label antibodies for therapeutic applications in the treatment of cancers. Examples of its use in radiation therapy include the treatment of thyrotoxicosis and thyroid cancer. When a small dose of I-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal (GI) tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland's cells. Diagnostic tests exploit the mechanism of absorption of iodine by the normal cells of the thyroid gland. As an example I-131 is one of the radioactive isotopes of iodine that can be used to test how well the thyroid gland is functioning. FIG. 12 shows the decay products of I-131, which is one of the primary fission products, and constitutes on the order of 3% of the total fission yield. In short, the I-131 decays to xenon 131, or Xe-131 (Z=54, 77 neutrons), emitting a beta particle (β−), a gamma (γ) ray, and a neutrino (ν) in the process. The primary emissions of I-131 decay are 364-keV γ rays (81% abundance) and 606-keV β− particles (89% abundance). As shown in more detail in FIG. 12, the decay is actually a two-step process where the I-131 first decays by beta decay to one of a number of excited states of Xe-131, emitting β− particle and a neutrino in the process, and Xe-131 in the excited state falls to a metastable state (Xe-131m), emitting a γ ray in the process. The first step occurs with a half-life of about 8 days, while the second step is, for present purposes, immediate. FIG. 12 is simplified in that only two of the excited states are shown, a first that is 637 keV above the metastable state, and a second that is 364 keV above the metastable state. The beta decay to the first state results in beta particles having a range of energies between zero and a maximum of 333 keV, while the beta decay to the second state results in beta particles having a range of energies between zero and a maximum of 606 keV. The remaining energy is carried off by the neutrino. In 82% of the decays to the metastable state, a 364-keV gamma ray is emitted, and in 7% of decays the decays to the metastable state, a 637-keV gamma ray is emitted. Other decay mechanisms make up the other 11% of decays to the ground state. The metastable isomer Xe-131m has a half life of 11.93 days, and undergoes an isomeric transition to the stable isotope Xe-131 by the mechanism of internal conversion, ejecting a single 164-keV electron in the process. Xe-131 is one of xenon's nine stable isotopes, and constitutes 21.2% of naturally occurring xenon. FIG. 12 shows I-131 as a fission product, which includes some I-131 nuclei which are primary fission product (fission fragments) and also includes some nuclei that are decay products of other fission products. For example, fission fragments and fission products in the chain include: indium 131 (In-131, Z=49, 82 neutrons), which beta decays with a half-life of less than a second to tin 131 (Sn-131, Z=50, 81 neutrons); Sn-131, which beta decays with a half-life of less than a minute to antimony 131 (Sb-131, Z=51, 80 neutrons); Sb-131, which beta decays with a half-life of 23 minutes to two isomers of tellurium 131 (Te-131 and Te-131*, Z=52, 79 neutrons); Te-131, which beta decays with a half-life of 25 minutes to I-131 (Z=53, 78 neutrons); and (Te-131*, which undergoes an isomeric transition with a half-life on the order of 30 hours to Te-131, which beta decays to I-131 as above).The total of the I-131 fission fragments and the I-131 decay products make up on the order of 3% of the total fission yield. Properties and Uses of Other Radioactive Iodine Isotopes As noted above, the fission products include a number of iodine isotopes in addition to I-131. The longer-lived radioactive fission products include the following (also shown are half-lives and fission yield): I-129 (1.59 million years, 0.54%); I-131 (8.042 days, ˜3%); I-132 (2.29 hours (metastable isomer 1.4 hours), 4.31%); I-133 (20.8 hours (metastable isomer 9 seconds), 6.77%); I-134 (52.6 minutes, 7.87%); and I-135 (6.6 hours, 6.54%).At least some of these isotopes have applications in imaging and/or medical therapy (the most useful are believed to be I-131, I-132, and I-133). Embodiments of the present invention also can produce radioactive iodine isotopes up to I-142. Depending on the application, it is believed that the radioactive iodine produced by embodiments of the present invention will have lower dose requirements than pure I-131 produced by other techniques. I-130 (12.4 hours (metastable isomer 8.9 minutes)) is not a fission product since it is not a fission fragment and would only be produced in a decay chain from Te-130, except that Te-130 has a half life on the order of 2.5×1021 years. Radioactive iodine isotopes below I-127 are not fission fragments and are not decay chain products since they are blocked by stable elements. Other radioactive iodine isotopes are short-lived (hours or minutes) and occur in very small amounts, and can be ignored as a practical matter. I-129 accounts for 0.54% of the primary fission yields and has a half-life of 15.9 million years, thus being essentially stable. It is possible to separate these radioactive iodine isotopes, and depending on the application, there may be reasons to do so. I-132 and I-133 are additional radioactive iodine isotopes that are of interest. The I-132 production scheme is as follows. indium 132 (In-132, Z=49, 83 neutrons), which beta decays with a half-life of less than a second to tin 132 (Sn-132, Z=50, 82 neutrons); Sn-132, which beta decays with a half-life of 40 seconds to two isomers of antimony 132 (Sb-132 and Sb-132*, Z=51, 81 neutrons); Sb-132 and Sb-132*, which beta decay with respective half-lives of 4.2 minutes and 2.8 minutes to tellurium 132 (Te-132, Z=52, 80 neutrons); Te-132, which beta decays with a half-life of 3.2 days to two isomers of iodine 132 (I-132 and I-132*, Z=53, 79 neutrons); I-132, which beta decays with a half-life of 2.28 hours to xenon 132 (Xe-132, Z=54, 78 neutrons); and (I-132*, which undergoes an isomeric transition with a half-life of 1.4 hours to I-132, which beta decays to Xe-132 as above).The total of the I-132 fission fragments and the I-132 decay products make up on the order of 4.31% of the total fission yields. The I-133 production scheme is as follows. indium 133 (In-133, Z=49, 84 neutrons), which beta decays with a half-life of less than a second to tin 133 (Sn-133, Z=50, 83 neutrons); Sn-133, which beta decays with a half-life of 1.4 seconds to antimony 133 (Sb-133, Z=51, 82 neutrons); Sb-133, which beta decays with a half-life of 2.5 minutes to two isomers of tellurium 133 (Te-133 and Te-133*, Z=52, 81 neutrons); Te-133, which beta decays with a half-life of 12.4 minutes to two isomers of iodine 133 (I-133 and I-133*, Z=53, 80 neutrons); (Te-133*, which undergoes an isomeric transition with a half-life of 55.4 minutes to Te-133); I-133, which beta decays with a half-life of 20.8 hours to two isomers of xenon 133 (Xe-133 and Xe-133*, Z=54, 79 neutrons); (I-133*, which undergoes an isomeric transition with a half-life of 9 seconds to I-133, which beta decays to Xe-133 and Xe-133* as above; and Xe-133, which beta decays with a half-life of 5.24 days to cesium 133 (Cs-133, Z=55, 78 neutrons); and (Xe-133*, which undergoes an isomeric transition with a half-life of 2.19 days to Xe-133, which beta decays to Cs-133 as above).The total of the I-133 fission fragments and the I-133 decay products make up on the order of 6.7% of the total fission yields. Where the end result of the iodine decay is an inert isotope of xenon (e.g., Xe-131, Xe-132, and Xe-133), there is no problem. Otherwise, the processing may entail additional operations. If the end result is not a stable xenon isotope, it may be desirable to separate it out, for example using electrochemical techniques or ion-exchange chromatography (ion chromatography). This would be the case for relatively long-lived radioactive substances or for undesirable stable substances such as barium, cerium, and cesium. Some short-lived radioactive substances can be addressed by allowing the extracted iodine additional time so the radioactive end result substance can decay to a stable substance or a radioactive substance that is susceptible of separation. For example, I-133 decays to stable Cs-133, but I-135 and I-137 decay to radioactive cesium isotopes, which are considered undesirable for both imaging and therapeutic applications. Since the irradiation cycle is on the order of 20 hours, one approach is to let the collected radioactive iodine decay for about a day (˜4 half-lives for I-135, and more than 1000 half-lives for I-137) so that the radioactive cesium can be electrochemically separated or separated through ion-exchange chromatography from the iodine solution. As a result, the resulting iodine solution would contain mainly I-127 (non-radioactive), I-129, I-131, I-132, and I-133, which could be used both for both therapeutic and imaging applications. I-132 has a relatively short half-life—2.29 hours with an isomeric transition of I-132* of 1.39 hours. Since I-132's half-life is short, that means it decays quickly within the body, so that there is no lingering radioactivity after the procedure and the dosage is much lower than other iodine imaging isotopes. Radioisotope Generator Tailored for Generation of I-131 and Other Radioactive Iodine Isotopes Any of the above irradiation chamber designs can be adapted to enhance the extraction of the gaseous fission products (including I-131 and other radioactive iodine isotopes, which sublimate to a gaseous state). In particular, as mentioned above, it is desired to withdraw the gaseous fission products from the irradiation chamber during irradiation by introducing an inert carrier gas (e.g., argon, which is inert and relatively cheap due to its large natural occurrence), circulating it through the irradiation chamber to mix with the fission gases, and exhausting the gas mixture for further processing. FIG. 13 is a simplified cross-sectional view of a radioisotope generator such as that shown in the sectional view of FIG. 6 (e.g., radioisotope generator 10sphere or 10cyl), with additional details relating to the circulation of gas through the irradiation chamber. Shown explicitly are gas inlet port(s) 40a and gas outlet port(s) 40b. Gas venting layers 150 (shown in heavier solid lines) are provided along surfaces of the NEU layers, and radially extending gas venting channels 155 provide gas communication paths between gas venting layers 150 and the inlet and outlet ports. Additional ways to increase the circulation of the carrier gas in the irradiation chamber include providing apertures in bulkheads and other structural elements. For embodiments using NEU in tubes, the tube walls can be provided with holes that are generally smaller than the smallest expected size of the NEU granules. A pump 160 exhausts the gases from irradiation chamber 15 and the gases are subjected to the scavenging and iodine recovery operations described above. The irradiation chamber is preferably maintained at a slight negative pressure during operation. As discussed above, some of the iodine and gaseous fission products can remain trapped in the uranium matrix, and are recovered in connection with the recovery of Mo-99 and other materials after the NEU is removed from the irradiation chamber. Providing the NEU in a granular form tends to increase the amount of iodine and fission gases that can escape from the uranium matrix during irradiation and be recovered on a continuous basis. References The following references are incorporated by reference. Burger_2004L. L. Burger, R. D. Scheele, “HWVP Iodine Trap Evaluation,” PacificNorthwest National Laboratory Report PNNL-14860 (September 2004)Chapman_2010Karena W. Chapman, Peter J. Chupas, and Tina M. Nenoff, “RadioactiveIodine Capture in Silver-Containing Mordenites through NanoscaleSilver Iodide Formation,” J. Am. Chem. Soc., 2010, 132 (26), pp 8897-8899(publication date (web) Jun. 15, 2010)DOI: 10.1021/ja103110yNRC_2009Medical Isotope Production without Highly Enriched Uranium, Nuclearand Radiation Studies Board, Division of Earth and Life Studies,National Research Council of the National Academies, The NationalAcademies Press, Washington, D.C. (2009). Dissolution and Mo-99Recovery are discussed at pages 25-30.http://www.nap.edu/openbook.php?record_id=12569Pemberton_2008Wendy J. Pemberton, Kenneth R. Czerwinski, David Hatchett,“Solubility and Electrochemistry of Uranyl Carbonate in a RoomTemperature Ionic Liquid System,” presented Sep. 25, 2008 in theRadiochemistry in the Advanced Nuclear Fuel Cycle session of the 42ndWestern Regional Meeting of the American Chemical Society, LasVegas, NV (Sep. 23-27, 2008)Pemberton_2009Wendy J. Pemberton, Kenneth R. Czerwinski and David H Hatchett,“Solubility and Electrochemistry of Uranium Extracted into a RoomTemperature Ionic Liquid,” Actinides 2009, San Francisco, CA, July2009Wang_2006Wei-Hsung Wang, Kenneth L. Matthews, II, “Simulating Gaseous 131IDistribution in a Silver Zeolite Cartridge Using Sodium Iodide Solution,”Health Physics: May 2006 - Volume 90 - Issue 5 - pp S73-S79DOI: 10.1097/01.HP.0000203812.30182.7bConclusion and Potential Advantages In conclusion it can be seen that embodiments of the present invention can provide safe, efficient, economical techniques for producing medical isotopes. Embodiments of the present invention can be characterized by one or more of the following attributes, alone or in any combination: Using neutron-reflecting material maximizes the neutron population above the fast fission threshold of U-238 within the NEU layer or layers, enhancing the fast fission process in the NEU material. Maintaining the neutron energy above ˜1 MeV while in the NEU minimizes neutron capture, and hence the decay to Pu-239. U-238 can be used as a primary fissionable material rather than enriched U-235, which is used by traditional nuclear-reactor-based methods. Depleted uranium, a byproduct from the enrichment process that is already stored at the Department of Energy (DOE) sites, can be utilized efficiently. This greatly reduces the cost of Mo-99/Tc-99m production and I-131 production due the more relaxed regulatory requirements concerning natural uranium or depleted uranium. The radioisotope generator according to embodiments of the present invention can be widely deployed, thereby allowing radioisotope generation closer to the end users for use as diagnostic, therapeutic, and research medical radioisotopes in imaging centers, hospitals, and medical research institutions. Embodiments of the present invention eliminate or reduce the need to export HEU to foreign nuclear reactors and subsequently import radioisotopes such as Mo-99/Tc-99m and radioactive iodine isotopes. A suite of radioactive iodine radioisotopes is produced. The integrated iodine dose from all the iodine radioisotopes produced is larger than systems producing only 1-131. Because some of the radioisotopes have much shorter half-lives than I-131, the produced radioisotope iodine potentially has a broader applicability than I-131 alone—lower dose. While the above is a complete description of specific embodiments of the invention, the above description should not be taken as limiting the scope of the invention as defined by the claims. |
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06069937& | claims | 1. An illumination apparatus for illuminating an object, the apparatus comprising: a) an excitation energy light generation unit for generating excitation energy light rays; b) a target member having a curved surface and a plurality of X-ray sources provided on said curved surface that emit X-rays simultaneously when irradiated by said light rays, wherein said target member is positioned relative to said light generation unit so that at least some of said light rays intercept said curved surface; and c) an illumination optical system that images said X-rays from said plurality of X-ray sources onto the object. a) the illumination apparatus of claim 1; and b) an image-forming optical system adjacent the object to be illuminated. a) providing a target member having a curved surface; b) irradiating said curved surface at a plurality of locations with excitation energy light rays; c) emitting X-rays simultaneously from said plurality of locations; and d) imaging said X-rays onto the object. a) directing excitation energy light to a plurality of locations on a curved surface; b) transforming said light to X-rays at said plurality of locations simultaneously; and c) imaging said X-rays onto the object. 2. An illumination apparatus according to claim 1, wherein said curved surface is cylindrical. 3. An illumination apparatus according to claim 1 or claim 2, wherein said target member is tape-shaped, and is provided along said curved surface. 4. An illumination apparatus according to claim 1 or claim 2, wherein said target member is particulate, and a plurality of target members form said curved surface. 5. An illumination apparatus according to claim 1 or claim 2, wherein said target member comprises a liquid. 6. An illumination apparatus according to claim 1 or claim 2, wherein said target member comprises a gas. 7. An illumination apparatus according to claim 1, wherein said target member comprises a material selected from the group of materials consisting of: tin, antimony, lead, tungsten, tantalum, and gold. 8. An illumination apparatus according to claim 1, wherein said excitation energy light generation unit includes a laser. 9. An illumination apparatus according to claim 1, wherein said excitation energy light generation unit includes an electron beam unit. 10. An illumination apparatus according to claim 1, wherein said illumination optical system includes a reflector. 11. An illumination apparatus according to claim 1, wherein said illumination optical system includes an optical element for creating a plurality of excitation energy light beams. 12. An optical exposure apparatus capable of forming an image of an object, the apparatus comprising: 13. A method of illuminating an object comprising the steps of: 14. A method according to claim 13, wherein said step d) involves providing an illumination optical system adjacent said target member and imaging said X-rays through said illumination optical system. 15. A method of illuminating an object, comprising the steps of: |
045270660 | abstract | The invention is directed to a concrete shielding housing for receiving and storing a transportable fuel element container which is suitable for storage and filled with spent nuclear reactor fuel elements. The outer dimensions of the fuel element container are somewhat smaller than the clear interior dimensions of the concrete shielding housing. The concrete shielding housing includes a pallet-like base which can be moved about from one location to another with the aid of a suitable vehicle such as a fork-lift truck. The housing also includes the concrete shielding wall placeable upon the base, and a cover which can be placed atop the upper end of the concrete shielding wall. At least one air inlet opening is provided at the lower region of the concrete shielding housing and, at the upper region thereof, there is provided at least one air outlet opening. The plan profile of the base is smaller than the plan profile of the concrete shielding wall so that the surface water which accumulates on the concrete shielding housing from falling rain can run off to the ground without hindrance. In addition to the advantageous runoff of the surface water from the concrete shielding housing, this configuration permits the transport corridors in the container storage area to be made narrower. |
summary | ||
abstract | A method for scanning an object in an X-ray security inspection system, wherein the X-ray security inspection system comprises an ingoing tunnel equipped with radiation-shielding curtains, an X-ray section and an outgoing tunnel equipped with radiation-shielding curtains, the method comprising: passing the object through the ingoing tunnel at a first rate of speed and with a first extent of separation between successive objects; passing the object through the X-ray section at a second rate of speed and with a second extent of separation between successive objects; and passing the object through the outgoing tunnel at a third rate of speed and with a third extent of separation between successive objects; wherein the second rate of speed is less than the first rate of speed and the third rate of speed, and wherein the second extent of separation between successive objects is less than the first extent of separation between successive objects and the third extent of separation between successive objects. |
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048511811 | abstract | In a light water moderation type nuclear reactor with the once-through method, the reactor core is divided into a central area and a peripheral area by a partition member, a first fuel assembly is arranged in the central area (high conversion area) and a second fuel assembly is arranged in the peripheral area. The ratio (r.sub.H/U) of the number of hydrogen atoms to that of uranium atoms in the central area is smaller than that of the ratio in the peripheral area and the second fuel assembly in the peripheral area is formed of fuel rods of the first fuel assembly having been previously burned in the central area and moved into the peripheral area. The plutonium production increases and uranium consumption is reduced during the first half of the lifetime of the fuel rods in the high conversion area with the take-up burn up increasing during the second half of the lifetime of the fuel rods in the burner area. |
042016258 | summary | The present invention concerns a process for producing .sup.52 manganese by a nuclear reaction in which a target having a metal atom content is bombarded with accelerated ions of small mass, after which the .sup.52 manganese formed from the metal atoms by nuclear reaction is isolated by means of a chemical separation process. .sup.52 Manganese is of interest in the field, along others, of nuclear medicine; for example, for the diagnosis and/or therapy of blood diseases. According to the known process of production (Radioisotope Production and Quality Control, IAEA, Vienna, 1971, Technical Report No. 128, p. 805), the .sup.52 manganese isotope is produced by bombarding chromium or iron with protons or deuterons. In this process, along with the desired .sup.52 manganese, the isotope .sup.54 manganese is also produced. .sup.54 Manganese is undesired, however, because it has a substantially longer half-life (312 days) than .sup.52 manganese (5.7 days), so that on account of the higher radiation exposure of the patient, limits are imposed on its use in nuclear medicine. .sup.54 Manganese can be separated out of an isotope mixture with .sup.52 manganese only with great difficulty and at great expense. THE PRESENT INVENTION It is an object of the present invention to provide a process by which .sup.52 manganese can be obtained in a relatively simple manner. Briefly, a target containing vanadium is bombarded with .sup.3 helium ions and the .sup.52 manganese produced thereby is isolated chemically from among the target materials. .sup.52 Manganese is formed from vanadium by .sup.3 helium bombardment by the following nuclear reactions: EQU .sup.50 V(.sup.3 He,n).sup.52 Mn; Q=8,3 MeV EQU .sup.51 V(.sup.3 He,2n).sup.52 Mn; Q=-2,7 MeV .sup.50 V and .sup.51 V are contained in natural vanadium to the extent respectively of 0.25% and 99.75%. According to a particularly simple manner of carrying out the process of the invention, the target is simply constituted by a vanadium foil, which is then dissolved in acid after the .sup.3 He bombardment. The .sup.52 manganese is then chemically isolated from the solution. The nuclear reaction of vanadium with .sup.3 helium ions suited for the production of .sup.52 manganese takes place also in the presence of other substances, so that it is also possible to utilize a target in which vanadium is present in an alloy or in a chemical compound, in which case, the accompanying chemical elements should not produce any disturbing or interfering reactions upon .sup.3 helium bombardment. Since .sup.52 manganese is produced from both .sup.50 V and .sup.51 V upon .sup.3 He bombardment, it is possible to use for the production of .sup.52 manganese according to the invention, a vanadium-containing target of which the vanadium has an isotope distribution that varies from the natural isotope distribution in vanadium. Measurements of the radioactivity immediately after the .sup.3 He irradiation show the presence of short-living nuclides as .sup.52m Mn, .sup.51 Mn, .sup.49 Cr and .sup.52 V. The decay of .sup.51 Mn with a half-life of 46 minutes yields the likewise radioactive .sup.51 Cr having a half-life of 27.7 days which should be absent in the prepared .sup.52 Mn. Therefore a delay period for the substantial decay of .sup.51 Mn is preferred between the irradiation of the target and the chemical separation of manganese. After such a delay the high purity of the .sup.52 Mn can be perceived. .sup.3 He ions having an energy of about 14 MeV are preferred for the .sup.3 He bombardment of the target. |
051606950 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The current invention of apparatus is based on the use of the ICC effect, which can be created or reached only by operation at or above a certain set of conditions of the primary ion flow system. The invention of the ICC effect, itself, is derived from a new understanding of the dynamics of ion flow and interaction in the flow regime around the central core of a converging colliding-flow system. Its principles will work as well for cylindrical converging flow as for spherical flows, but attention here is limited to the spherical case, as this will always yield the largest degree of density increase and the most favorable conditions for the attainment of fusion reactions of interest for power generation. Finally, the ICC effect can be attained in ANY system of spherical converging flow of charged particles or of an ion/electron mixture, in which the ions are injected or caused to move radially inward at high energies (e.g. at energies >1 keV) by some means, whether this is achieved by the use of ion guns (as in the method of Hirsch/Farnsworth.sup.4,6), or by electric grids (as by inversion of the electric fields from those of Elmore et al.sup.2), or by acceleration by virtual cathodes (as from well formation by electron injection, as in the method of Bussard.sup.1). The attainment of the desired ICC method of operation requires that conditions for ion acoustic oscillations be achieved at small radius in the core, where the ion density increases naturally due to geometric convergence of the cross-cavity flow of ions through the spherical system. In the normal flow of ions with non-zero transverse (or angular) momentum in such a system, conservation of total momentum and total energy of the ions results in increasing deviation from purely radial motion as the ions move to smaller radii. At some finite radius, the ion radial velocity (v.sub.r) will reach zero, and the ion will orbit around the center and proceed out the other side of the system, if no resonant oscillatory effects (of the type of interest here) are present. The only deviation from single particle motion will result from Coulomb collisions with other ions similarly orbiting past the core region. In order that these be sufficient to create useful fusion reaction rates it has been shown.sup.1 that ion flow recirculation through the core must be the order of 1E3 to 1E4 times the ion injection current, and corresponding electron recirculation ratios must be in the range of 1E5 to 1E6. With the ICC method, these recirculation ratios may be greatly reduced, typically to values of one-hundredth to one-ten-thousandth of those required for useful operation without the ICC effect. This is a result of the unique compaction of ion density that occurs in the central core of the system when the conditions for initiation of the ICC effect are obtained. For initiation of resonant coupling of ion flow motion with radial ion acoustic waves (here called "S" waves), and thus with other ions resonantly coupled with (or trapped in) such waves, these conditions require that the rate of change of mean free path for ion acoustic wave/particle collisions be small over one wavelength in the radial direction. For resonance with azimuthal-tangential (transverse) motion (here called "T" waves) it is necessary that the fractional rate of change of ion/wave collisional mean free path be equal to the fractional rate of change of radial position of the ions trapped within the collisiondiffusion core set up by these wave structures. The collision mean free path (.lambda..sub.pi) will be the distance traveled by an ion at maximum speed (v.sub.i) in the core region over one cycle of oscillation at ion acoustic wave frequency (f.sub.pi), thus .lambda..sub.pi =(v.sub.i /f.sub.pi). Pure ion/ion oscillations can occur in regions where the ion density exceeds the electron density. Since this will frequently be the case in the core boundary of such converging spherical ion flows, oscillations of this type will appear at the ion/ion acoustic wave frequency and ion particle speed of EQU v.sub.i =(2E.sub.w /m.sub.i).sup.0.5 and f.sub.ii =(n.sub.i Z.sup.2 e.sup.2 /.pi.m.sub.i).sup.0.5 (1) In addition, hybrid ion/electron oscillations will occur in the core and at the core boundary, where electron radial speeds are comparable to ion speeds. These ion/electron oscillations, also called ion-acoustic waves, will occur at a modified electron plasma frequency, f.sub.ie of EQU f.sub.ie =(n.sub.i Z.sup.2 e.sup.2 /.pi.m.sub.e).sup.0.5 =f.sub.ii (m.sub.i /m.sub.e).sup.0.5 (2) Defining a.sub.ij =1 for ion/ion waves and a.sub.ij =(m.sub.e /m.sub.i).sup.0.5 for ion/electron waves, allows both of these ion-acoustic oscillation frequencies to be written simply as f.sub.pi =f.sub.ii /a.sub.ij. Here E.sub.w is the energy of ions in the core region, m.sub.e is electron mass, m.sub.i is the ion mass, n.sub.i is ion particle density, and Z is the ionic charge in units of the electronic charge e, given by e=4.8E-10 cgs units (statcoulombs). Using these, the ion/wave collision mean free path at the core surface can be written as ##EQU1## where the ion density at the collisional core boundary has been written as n.sub.c, and the numeric form is for E.sub.w in eV and n.sub.c in ions/cm.sup.3. Now, the conditions for coherency of resonant oscillation (described above) are just EQU (d.lambda..sub.pi /dr).sub.c <<1 (4a) for S-wave radial resonant coupling, and EQU (dLN.lambda..sub.pi /dLNr).sub.c =1 (4b) for T-wave azimuthal-tangential coupling where LN denotes the natural logarithm (log to the base e=2.71828), and the expressions are to be evaluated at the boundary (r.sub.c) of the acoustic wave core, within which the particles are constrained in their motion by collision diffusion processes between wave-trapped ions with each other and with the resonantly-driven ion acoustic waves. In addition, a fundamental requirement for existence of any ion acoustic waves within the core boundary is simply that the mean free path be less than the boundary radius, thus (.lambda..sub.pi).sub.c <r.sub.c, which gives equivalent conditions to those of Eq. (3), above. Applying these to the functional forms given above for the mean free path gives the conditions for ion/wave coherency and oscillation-initiation in terms of the ion energy, charge state, core boundary density, and radius of the acoustic wave core boundary. The minimal condition for acoustic S-wave initiation requires that the ion density be EQU n.sub.c >(2.pi.E.sub.w /Z.sup.2 e.sup.2 r.sub.c.sup.2)(a.sub.ij) (5) at the core boundary. Indeed, this condition determines whether or not and where such a boundary will be (i.e. at what r.sub.c it will be found, given other parameters). With this it is possible to determine the minimum input ion injection power (P.sub.inj) required to produce the desired ICC condition. The total power is just the injected surface ion current density (j.sub.io) taken over the injection surface at radius (R), and the ion energy (E.sub.w). For purposes of comparison, it is convenient to write this in terms of an equivalent electron injection power, based on an injection surface electron density (n.sub.eo) with current density (j.sub.eo =n.sub.eo v.sub.eo), where v.sub.eo is electron velocity at energy E.sub.w. The injection ion density at this surface is less than the electron density by the factor G.sub.j, the electron recirculation ratio. Thus the injection power can be written as P.sub.inj =4.pi.R.sup.2 (E.sub.w v.sub.eo n.sub.io /k.sub.s G.sub.j), where the power is in watts for E.sub.w in eV, and k.sub.s =6.28E18 charges/sec per amp of current. In order to use this in the S-wave criterion of Eq. (5), it is necessary to write the surface ion density in terms of ion density in the core region. This can be done by use of the (1/r.sup.2) geometric scaling of spherically convergent flow, n.sub.io =n.sub.c (r.sub.c /R).sup.2. With this the S-wave condition leads to a minimum requirement on injection power for resonant wave initiation as EQU P.sub.inj .gtoreq.(a.sub.ij) (2.pi.E.sub.w k.sub.e /Z.sup.2 e.sup.2)* (4.pi.E.sub.w /G.sub.j k.sub.s) (2E.sub.w k.sub.e /m.sub.e).sup.0.5 (watts) (6) for E.sub.w in eV. Here m is electron mass in gm, and k.sub.e is a conversion constant for energy (k.sub.e =1.6E-12 erg/eV), and other parameters are as before. Reducing this numerically gives EQU P.sub.inj .gtoreq.5.21E-3(a.sub.ij)(E.sub.w.sup.2.5 /Z.sup.2 G.sub.j) (watts) (7) which is independent of the core radius, r.sub.c. Thus, S-waves can be initiated at any core radius at which it is possible to do so, if sufficient driving power is supplied to the system. Note that the electron recirculation ratio (G.sub.j) is related to the ion recirculation ratio (G.sub.i) for ion-injection-driven systems simply by the square root of the ratio of ion to electron mass; i.e. G.sub.i =G.sub.j (m.sub.e /m.sub.i) =G.sub.j (a.sub.ij). Typically, ion current recirculation ratios will be less than electron ratios by a factor of the order of 70-100. As an example, for the mode a.sub.ij =1, if G.sub.j =1E4 (so that typically G.sub.i .apprxeq.100-130), Z.sup.2 =2, and E.sub.w =1E4 eV, the injection power required would be only P.sub.inj =2.6 kwe. At E.sub.w =1E5 eV, this becomes P.sub.inj =82.2 kwe. And, if G.sub.j =1E3, G.sub.i .apprxeq.10-13, the power levels would be only ten-fold higher. These power levels are all very much smaller than those required to drive ion- or electron-driven spherically convergent flow systems without the ICC process. In reference to FIG. 4a, these S-waves involve exchange of energy between ion radial kinetic energy 700 (whether or not ion motion is purely radial or is partially tangential) and radial wave electric fields 720 (E.sub.r), resulting from and associated with the ion acoustic wave fields, with wavelength .lambda..sub.pic 710. Such oscillations 720 are shown in FIG. 4a along the radial path of an ion 730 inside the critical core radius r.sub.c 740. In reference to FIGS. 4b and 5a, the second type of waves are azimuthal-tangential T-waves 750, with wavelength .lambda..sub.pic 760, set up by exchange of energy between ion tangential kinetic energy 770 and azimuthal-tangential wave E.sub..theta. fields 750. These waves appear as quasi-hexagonal-conical cellular repetitive structures 800 of width .lambda..sub.pic 810 on the surface 820 of the core sphere at r.sub.c, as shown in FIG. 5a (which also shows a cross-section 830 of two such cells), because the ion motion azimuthally is isotropic in angle in any given surface shell. The cells are not rigid as suggested in the figure, but are formed of ion density concentrations due to the ion-acoustic oscillations. These waves are then like an array of azimuthal honeycomb cells extending over that radial depth of core over which the criterion for their generation is satisfied. This criterion is that the fractional change in coupling length (mean free path, or wavelength is .lambda..sub.pic) is identically equal to the fractional change in radial position with decreasing radius into the core. This condition preserves azimuthal coherency with changing radial position and allows the establishment of the shell-like honeycomb E.sub..THETA. field structures, in which ions collide with electric fields due to acoustic waves azimuthally, and scatter off each other. Here, as for S-waves, if the density outside the ICC core scales as the inverse square of radius, the initiation condition is also independent of radius, as before. However, to create these waves it is necessary to have an azimuthal driver. The only driver available is that due to conservation of transverse momentum in ion flow to and through the potential well, as indicated in FIG. 4b. As previously discussed, this limits the ion motion so that ions can not approach the system center closer than a momentum-limited radius (r.sub.o) given by the square root of the ratio of mean transverse energy (E.sub.t) at the system injection surface (R) to the maximum radial energy (E.sub.r) at injection or at the deepest point of the potential well, (r.sub.o /R)=(E.sub.t /E.sub.r).sup.0.5. The ICC effect will be initiated at a radius comparable to or larger than that of the transverse-ion-momentum convergence limit <r.sub.o >=(r.sub.o /R). Ions approaching the central core region will all arrive with paths which lie between the two extremes of pure radial motion (transverse momentum is zero), or of pure azimuthal motion (with no radial component). Ions moving along radial paths can initiate radial (S) waves, while those following the second limiting path can initiate transverse or azimuthal (T) waves. Of course, ions with a combination of both motions (radial and azimuthal, as indicated in FIG. 4a) are capable of initiating either or both types of resonant acoustic waves in the core region. In either case, if the conditions of this process are met in accordance with the invention, the ions will drive resonantly-coupled acoustic oscillations in the core and will be trapped in the core by the acoustic wave structures thus produced. This process can be seen by imagining a core made of surface-packed quasi-conical honeycomb ion density structures 840 over the entire core surface at the acoustic wave initiation radius r.sub.c 850, as shown in cross-section in FIG. 5b. An ion 860 entering one of the honeycomb "cells" will be scattered internally from the cell "walls" (which are actually the ion density waves associated with the acoustic wave resonant structure) and will be internally reflected 870 to the opposite wall, or may pass through a wavefront, being deflected into an adjoining cell 880, in which it is again reflected or scattered into still another cell region. The mean free path of such scattering collisions/deflections is exactly the ion acoustic wavelength at the local conditions of ion density and energy. This is always very small compared to the Coulomb scattering collision mean-free-path (mfp) for ion/ion energy exchange and, in systems of interest, small compared to the core dimension. In these circumstances, it is evident that the motion of particles inside the ICC core will be of a diffusive character, with each particle undergoing many collisions before it can traverse the core and exit again to the extra-core region, and thence return to the radial circulating flow of the overall device. Since the particles are thus trapped by short (mfp) collisions, their density will build up inside the core to values very much larger than those that would be expected from simple Coulomb-collisional interactions without acoustic wave resonant coupling (i.e. without the ICC process and effect). Exact analysis of the motion and density distribution of such wave-trapped particles within the core is complex, as the deposition of ions within the core, from the external flow system, is approximately given by an ion source term of the form S(r).apprxeq.j(r)/.lambda..sub.s (r) where the uncollided deposition current density is given crudely by EQU j(r)=j.sub.c (r.sub.o /r).sup.2 EXP[-(r.sub.o -r)/.lambda..sub.s (r)] (8) Here j.sub.c =(nv).sub.c is the ion flux (radially) incident on the acoustic wave ICC core surface at r =r.sub.c, .lambda..sub.s (r) is the average scattering mfp of ions to radius r within the core, and r is the ion-momentum-limited convergence radius, as before. Use of this expression as a source term in the normal wave equation is further complicated by the fact that the scattering mfp is, itself, a function of radial position, and should be written as an integral expression over the range r.sub.o .fwdarw.r. It varies with the density variation of the ions across the ICC core, and will act to trap particles increasingly as their density increases within the core (due to the decrease in .lambda..sub.s (r) as density increases with decreasing r). A simpler model that gives an approximation to the particle density distribution can be invoked by treating the incoming particles as being deposited from the external ion flow into the critical core with a volumetric source term distribution given more simply by S(r).apprxeq.(j.sub.c /.lambda..sub.pic) [n(r)/n.sub.c ].sup.0.5 within this core. This model ignores the increasing trapping effect mentioned above, and will give results generally less favorable (i.e. less density increase) than the real situation. However, it is useful to illustrate the nature of behavior of the system and to provide some lower bounds on the performance potential of the ICC process. With this model the description of ion density follows from the conservation equation EQU D.sub.r .gradient..sub.r.sup.2 [n(r)V.sub.i ]+S(r)=0 (9) where the diffusion coefficient is D.sub.r (r)=.lambda..sub.pr /3=(1/3)[2.pi.E.sub.w /Z.sup.2 e.sup.2 n(r)].sup.0.5. Using S(r) as above, this reduces to the simple wave equation EQU .gradient..sub.r.sup.2 [n(r)]+B.sup.2 [n(r)]=0 (10) Here the constant is defined in terms of density and energy parameters in the system as B=(.sqroot.3/.lambda..sub.pic), and the density variation is found to be EQU n(r)=nSIN(Br)/(Br) (11) where the density (n.sub.o) is that at the center of the ICC core. This variation 900 is shown across the core region in FIG. 6a. Matching boundary conditions at the edge of the core with the ion density variation 910 outside the core requires that the ion density, in this diffusion model, go to zero at some hypothetical "extrapolation distance" (.delta.) 920 outside the core radius, r=r.sub.c, as shown in FIG. 6a. This condition requires that the wave equation constant, above, be also defined geometrically as B=[N.sub.R .delta./(r.sub.c +.delta.)], where N.sub.R is an integer equal to the number of core surface acoustic wavelengths contained in the core radius. The offset .delta. can be shown to be approximately .delta..apprxeq.(.pi./6).lambda..sub.pic =0.52 .pi..sub.pic. Equating these two expressions for B gives a simple relationship between ICC core dimension, extrapolation distance and ion density and energy as EQU .delta.=(N.sub.R .pi./3).lambda..sub.pic -r.sub.c from which (12a) EQU r.sub.c =[(N.sub.R .pi./3)-0.8][.lambda..sub.pic ] (12b) Since the onset conditions for S-waves are independent of radius, this simply shows that any radius r.sub.c >.lambda..sub.pic is capable of sustaining such waves. In actual fact, however the N.sub.R =1 condition is favored as the fundamental mode of density variation across the core. This will be attained at a radius as small as r.sub.c .gtoreq.1.29 .lambda..sub.pic, or for a density such that EQU n.sub.c .gtoreq.2.pi.(a.sub.ij).sup.2 /(Zer.sub.c).sup.2 =7.27E7(a.sub.ij)[E.sub.w /(Zr.sub.c).sup.2 ] (13) for n.sub.c in ions/cm.sup.3, E in eV and r.sub.c in cm. For example for E.sub.w =1E5 eV, Z.sup.2 =2, and r.sub.c =1.0 cm, then n.sub.c .gtoreq.3.63E12/cm.sup.3 for ICC operation if a.sub.ij =1 (ion/ion) or n.sub.c .gtoreq.8.43E10/.sqroot.A /cm.sup.3 for ICC if (ion/electron) acoustic oscillations with ions of mass number A dominate the core. The core convergence radius is determined by transverse momentum considerations external to the core, and is generally greater than the minimum r.sub.c cited above. However, for this condition the critical density for onset of ICC acoustic waves still is as given by Eq. (13). If this density is attained at this radius, the ICC effect will appear; and conversely. Once initiated, the actual ion acoustic wavelengths found within the core r<r.sub.c will decrease with increasing density as r.fwdarw.0, so that many such spherical waves will be found within the core envelope, under the N.sub.R =1 fundamental mode. Higher mathematical order core density wave modes are possible, in principle, but practically only as small amplitude superpositions on the fundamental mode. Note that, if n(r) varies as 1/r.sup.m in the region external to the ICC core and internal to the surface at radius R at which ions enter the system with energy E.sub.w, the system surface ion density must be EQU n.sub.io .gtoreq.7.27E.sub.7 (a.sub.ij)[E.sub.w r.sub.c.sup.m-2 /Z.sup.2 R.sup.m .pi. (14) for initiation of ion acoustic waves and the ICC effect. For a typical variation with m=2 in the previous example case, for R=100 cm this yields n.sub.io .gtoreq.3.63E8/cm.sup.3 for a.sub.ij =1, or N.sub.io .fwdarw.8.43E6/.sqroot.A /cm.sup.3 otherwise. If n(r) varies as m=3 these values are all lowered by a factor of 100. Initiation of T-waves follows a slightly different criterion (as given in Eq. (4), above), that leads to the result that the critical radius for onset of ion acoustic T-waves depends upon the functional form of the ion density variation in the region just outside the ICC core. It is found that this critical radius is as follows ##EQU2## Thus T-waves will be created as the ion current density azimuthal flow reaches a critical value. This is set both by the level of recirculating ion current flow outside the core and by the fractional transverse momentum of ions converging to the core region. Using a (typical) inverse-square geometric convergence the azimuthal ion acoustic wavelength is found to be ##EQU3## where .lambda..sub.pio is the acoustic wavelength calculated for conditions at the internal cavity outer radius, R, where the ion density is n.sub.io. Since the ion density at the surface is related to the injection power and the ion recirculation ratio (G.sub.i), and thus to the equivalent electron recirculation ratio, G.sub.j, it is possible to write the T-wave acoustic wavelength in terms of injection power, for E.sub.w in eV, P in watts, and all dimensions in cm, as EQU .THETA..sub.p.THETA. =7.22E-2 (E.sub.w.sup.2.5 /P.sub.inj G.sub.j).sup.0.5 (a.sub.ij)(cm) (17) The number of surface cells must fit within the core circumference, thus the condition to be satisfied is N.sub.T (.lambda..sub.p.THETA.)=2.pi.(r.sub.c), where N.sub.T is the (integer) number of cells around the core circumference. It is readily shown that the total number (N.sub.o) of quasi-hexagonal cells that can be fitted on the surface of the spherical core is given by the formula N.sub.o =0.3675 N.sub.T.sup.2 ; so that N.sub.T =16 gives a total number of cells of N.sub.o .apprxeq.72, for example. The smallest practical tangential cell number for resonant fundamental modes is N.sub.T =8, with N.sub.o =24. (It is noted that this simple formula for N.sub.o breaks down at N.sub.T =4; geometric considerations for tetrahedral symmetry gives N.sub.o =8 for such a resonant surface structure, but discreteness argues against coherency.) Using this and the simple integer condition above, the injection power can be related to the recirculation factor, the ion energy, and the acoustic wavelength, as previously in Eq. (6) for S-waves. The critical equation giving the power injection criterion for onset of T-waves is then EQU P.sub.inj =5.9E-3(a.sub.ij)(E.sub.w.sup.2.5 /Z.sup.2 G.sub.j) (watts) (18) which is seen to be closely comparable to the criterion for S-wave initiation, as given by Eq. (7). Thus, T-wave-trapped ions can serve to supply the core, as discussed above in connection with the wave equation description of the in-core ICC diffusion process. Once started, such acoustic waves will readily propagate into the core and will be maintained by resonant coupling with the stream of inflowing ion momentum, both azimuthal and radial. Incoming particles will be trapped in acoustic wave structures, and will diffusively move through the core, building up density until a level is reached at which their outward diffusion-limited flow exactly balances the inooming flux. Ions esoaping from this inertial-collisional-compression (ICC) core will be emitted isotropically into the extracore region. Thus azimuthally-isotropic incoming ions will be replaced by azimuthally-isotropic emitted ions, with no net change in transverse momentum content of the ion population. Ion energy within the core will remain sensibly the same as that at entry, since little energy is stored in the oscillating ion acoustic wave fields (as previously shown). The net flux into the core must be equal to that leaving from the ICC effect region at r.apprxeq.r.sub.c. This latter is just D.sub.c .gradient..sub.r [v.sub.i n(r)].vertline..sub.rc while the former is the average flow of ions into radius r.sub.c from the flow system outside the ICC core. Taking a cosinusoidal distribution of transverse momentum at the core boundary gives an average radial in-flow speed of (2/.pi.)v.sub.i. With this, equating ion fluxes from both sides of the core boundary surfaoe r.sub.c yields the ratio of core maximum (central) density to surface density as given approximately by EQU (n.sub.o /n.sub.c)=(r.sub.c /D.sub.c)=3r.sub.c /.pi..sub.pic (19) where the subscript c indicates parameters evaluated at boundary conditions of the ICC core, at r=r.sub.c, and .lambda..sub.pic is given by Eq. (3) for each choice of a.sub.ij. The functional form for n(r), given by Eqs. (3) and (11), can be integrated over the core volume, from which approximate (for .nu..sub.pic <<r.sub.c) integrated average <n.sub.o > and mean-square <n.sub.o.sup.2 > values of core ion density are found to be EQU <n.sub.o >/n.sub.c =(3/.pi..sup.2)(n.sub.o /n.sub.c) (20) and EQU <n.sub.o.sup.2 >/n.sub.c.sup.2 =(3/2.pi..sup.2)(n.sub.o /n.sub.c).sup.2 ( 21) The mean-square value is of interest in estimating fusion reaction rate densities and core power, since the fusion reaction density is given by EQU q.sub.f =(b.sub.ij)(<n.sub.o.sup.2 >)(.sigma.v.sub.i) (22) where b.sub.ij =0.25 if the reacting particles are alike, and is 0.5 if they are of different species, with equal density in the system. The fusion power is this rate density times the energy released per fusion (E.sub.f), over the core volume EQU P.sub.f =(q.sub.f E.sub.f)(4.pi./3)(r.sub.c) (23) The increase in fusion rate due to the ICC process, over that expected from conventional Coulomb collisions and geometric convergence in spherical flow systems, is then just the density enhancement factor given by Eq. (21), above. This is shown in FIG. 6b for typical parameter ranges of interest. In this the variation across the core is shown for successively larger values 930, 940, 950 of .lambda..sub.pic. The ICC process thus can yield greatly increased output from any spherical flow system, by design for operation at the appropriate density, current, and input power and voltage conditions, as required to initiate the ICC effect. The magnitude of this increase in potential output is suggested by the data in Table 1, following. This shows the range of ratios of integrated average density and of mean-square density normalized to core boundary density, n.sub.c, and to ICC core radius r.sub.c, for an ion collision energy of E.sub.w =1E5 eV, an average charge of Z.sup.2 =2, and for a.sub.ij =1 and with a.sub.ij =(1/61) as for D ions. The lower values given have been corrected slightly for approximations used in obtaining Eqs. (20, 21). TABLE 1 __________________________________________________________________________ POTENTIAL INCREASE IN AVERAGE AND MEAN-SQUARE DENSITY DUE TO ICC Core Boundary Average Core Density Mean-Square Density Density (<n.sub.o >/n.sub.c) (1/r.sub.c), (1/cm) (>n.sub.o.sup.2 >/n.sub.c.sup.2) (1/r.sub.c.sup.2), (1/cm.sup.2) n.sub.c, (1/cm.sup.3) aij = 1 aij = (1/61) aij = 1 aij = (1/61) __________________________________________________________________________ 1E9 -- 1.0-1.9 -- 2.2-4.5 1E10 -- 3.5-5.0 -- 22.3-44.6 1E11 -- 8.7-16 -- 223-446 1E12 1.3-2.0 23-45 0.6-1.2 2.2-4.5E3 1E13 3.0-5.0 73-147 6-12 2.2-4.5E4 1E14 7.4-15 230-460 60-120 2.2-4.5E5 1E15 20-40 730-1470 600-1200 2.2-4.5E6 1E16 62-120 2.3-4.6E3 0.6-1.2E4 2.2-4.5E7 1E17 195-400 0.7-1.5E4 0.6-1.2E5 -- __________________________________________________________________________ Note that the ion/ion mode (a.sub.ij =1) yields no useful increase for densities below about 1E12, and that the formulae give unrealistic values for the highest densities in the ion/electron mode (a.sub.ij =1/61). It is also important to note that the average density would be higher by the square root of the ratio (1E5/E.sub.w), and the mean-square density by the ratio, itself, if ion energy less than 1E5 eV were used. Thus, if the ion energy sought were only 1E4 eV (10 keV), for example, the mean-square values, and the comparative fusion rate densities would all be larger by a factor of ten than the tabulated values. Also, larger charge will yield larger densities in direct proportion to the ratio Z/.sqroot.2, thus multiply-charged fuels (e.g. .sup.11 B) will be ICC compressed more than will those with single charges (e.g. D,T). Finally, it is possible to show conditions for net power generation in fusion systems operating under the ICC concept. A lower bound criterion for net power generation is given by comparison of minimum required injection P.sub.jmn of the system from Eqs. (7,18) and fusion power generation capability from Eqs. (22,23). Combining these (using the S-wave criterion of Eq. (7)) gives a (maximum) "base power gain potential" (G.sub.o) for the system of ##EQU4## for cgs units, as before, with E.sub.f in MeV and E.sub.w in eV, .sigma..sub.f in cm.sup.2. Here the function F(A)=[(A.sub.1 +A.sub.2)/A.sub.1 A.sub.2 ] a factor near unity to account for fuel ions of differing mass number, A.sub.1,A.sub.2 (for DD, F(A)=1, for D.sup.3 He or DT, F(A)=0.91, and for p.sup.11 B, F(A)=1.04). As an example of the potential of the ICC process consider a case using D and T (b.sub.ij =0.5, F(A)=0.91) as the fusion fuels ) in an (ion/electron) ion-acoustic mode (a.sub.jj 1/61) system with core at r=0.5 cm, Z.sup.2 =2, n.sub.c =1E14/cm.sup.3, E.sub.w =2E4 eV, a fusion cross-section .sigma..sub.f =2.0E-24 cm.sup.2, E.sub.f =17.6 MeV, and an electron recirculation ratio of G.sub.j =300, equivalent to an ion recirculating current ratio of only about G.sub.i =4.4. For these conditions, Eq. (24) gives the base power gain as G.sub.o =(P.sub.fus /P.sub.jmn) =184. Such a device could be operated in a pulsed mode to attain high peak power densities, if continuous ICC operation requires excessive input power. As a second example, consider an ion-acoustic mode case using fuels p and .sup.11 B (a.sub.ij =1/143), with r.sub.c =1.8 cm, Z.sup.2 =5.5, core boundary ion density n.sub.c 4E13/cm.sup.3, ion energy of E.sub.w =3E5 eV, .sigma..sub.f =0.2E-24 cm.sup.2, E.sub.f =8.7 MeV, and G.sub.j =2E3 (ion current recirculation ratio G.sub.i =20-26). For this case the base power gain is still as high as G.sub.o =112. Note that the equivalent electron current recirculation ratio in each of these cases is less than that of conventional spherically-converging flow schemes.sup.1,4-10 by a factor of the order of 100- 1000, for the same general level of potential power gain performance. This can be rewritten in terms of the ion energy, system momentum convergence limit and size, current recirculation ratio, and injection (or ion accelerating drive) power, for any given fuel combination, as EQU G.sub.o =3.45E23(G.sub.j.sup.4 P.sub.inj.sup.3 /<r.sub.c >R)* (Z.sup.4 E.sub.f .sigma..sub.f b.sub.ij A.sup.1.5 F(A)/E.sub.w 7.5) (25) where <r >=(r.sub.c /R) and R is the major radius of the inner cavity of the ICC machine. For fixed injection power P.sub.inj, G.sub.o varies inversely with radius R. However, if the ion injection surface power density p.sub.inj =P.sub.inj /4.pi.R.sup.2 is kept fixed, the system base gain varies with the fifth power of the radius, R, as EQU G.sub.o =6.84E26(b.sub.ij)(R.sup.5 G.sub.j.sup.4 p.sub.inj.sup.3 /<r.sub.c >)* (Z.sup.4 E.sub.f .sigma..sub.f b.sub.ij A.sup.1.5 F(A)/E.sub.w 7.5) (26) For this constraint condition and any specified parameter values, there is then always a value of R at which the base gain can be made unity or greater. For the case of DT fuel at ion energy of E.sub.w =2E4 eV, with Z.sup.2 taken to be 2, the system base gain becomes ##EQU5## If R=100 cm, G.sub.j =2E3 (G.sub.i =28), P.sub.inj 32 2E6 watts, and <r.sub.c >=1E-2, the base gain is then G.sub.o (DT)=61.8. Reducing the radius to 25 cm and decreasing the equivalent electron recirculating current ratio to G.sub.j =1000, holding the other parameters at their original values, still yields a base gain of 15.5. All of these levels of potential performance are 100-1000 times better, higher, or more readily attainable than for their counterparts in conventional spherical electrostatic well systems; a direct result of employing the novel ICC effect and process in their design and description. It is of some interest to note that the results of the experiments of Hirsch, which yielded anomalously high neutron production rates from a system using six opposed ion injection beams, might be a result of the phenomena described above. The parameters that characterized Hirsch's experiments.sup.5 (beam energy and current, beam diameter, ion energy in the central core region, and system core dimensions) were not all well known, and neither Hirsch.sup.5, nor Black.sup.8, nor Baxter and Stuart.sup.9 were able to explain these results. However, a liberal interpretation of Hirsch's reported data can be made that yields conditions in the central quasi-spherical core (formed at the intersection of the six ion beams) that are slightly beyond those minimally required for the onset of the ICC process effect. The regimes of operation of the ICC process and the probable regime of the Hirsch experiments are depicted in FIG. 7. The ICC allowed region, labeled 1000, occurs between the "V" defined by any one of a selected vertical line corresponding to different critical radii r.sub.c, and any one of the positive sloping straight lines 1, 2, . . . 5. The allowed region thus extends to the right of the vertical line, for a given vertical line choice r.sub.c, (a more positive X value), and to the upper portion, (corresponding to more positive Y value), of the selected positively sloped line, 1, 2, etc. The vertical lines corresponding to a selected value of r.sub.c are plotted on the X axis from constraint equation (5) above and represent density per unit well depth. The parameter Y, in units of power per cm.sup.5, is taken from combining constraint equations (5) and (7), and is evaluated for exemplary values of E.sub.w and G.sub.j as seen in the bottom block portion of FIG. 7. The lines 1, 2, etc are defined using selected combinations of the ion energy at the core or well depth E.sub.w and the electron current recirculation ratio G.sub.j. In some cases, there are more than one pair of values for E.sub.w and G.sub.j in a given block, e.g., line 3, and in such cases the graphic results do not differ significantly from one pair to the next as represented by the small circles next to the lines labeled 3 and 4. Thus, a representative allowed regime for the ICC process, could be that defined by the "V" between line 1 and r.sub.c =1cm. In accordance with equations (5) and (7), the appropriate values of density and injection power may be calculated to produce the ICC operation for any point selected within the "V". ine 1015, defining region 1020 in the upper right protion of the graph, has been drawn in FIG. 7 to represent a reasonable choice of an operation regime not too close to the boundary regions where small pertubations may result in instability. FIG. 7 also indicates the range 1010 over which Hirsch's experiments might have operated. The slight overlap shown over a restricted range of parameters is far from the range of conditions desired for ICC effective operations, as shown at 1020 in FIG. 7. Electrode Arrangements It will be understood that any means of accelerating ions radially inward in a manner that minimizes transverse motion may be employed to provide a densification of ions towards the center of a spherical (or cylindrical) geometry, and that such acceleration at current and voltage (particle energy) conditions described here as required for the initiation of the collisional-diffusion processes of the ICC effect, can result in the onset of this effect. However, the nature of this effect allows the invention of special apparatus for the achievement of the process and conditions required for its attainment that are uniquely simple and devoid of extensive complex structure. These are all based on use of minimal wire frame or sheet conductor or distributed point conductor electrode grid systems, g1, g2, 1100 (FIG. 8) to provide spherical (or cylindrical) radial electric field gradients for acceleration of ions to the system center, g0, the whole being surrounded by and contained within a concentric outer electron-reflective bounding wall or surface 1110, as shown in cross-section in FIG. 8. (It is noted that FIG. 8 represents a cross sectional view for either a spherical or cylindrical system). In this circumstance, a system of spherical colliding flow of ions (and electrons) can be devised in which the ion-accelerating fields are provided by simple grids of large transparency, and system power consumption is kept small by avoiding the use of electric currents to create high magnetic fields. FIG. 9 shows an example of one such electrode system for ion acceleration, using a minimal curvilinear tetrahedral wire frame geometry with two nested grids, g1 1200 and g2 1210. FIG. 10 shows a nested set of three orthogonal circles 1300, 1310 (a curvilinear octahedron or "great circle" geometry), FIG. 11 indicates a set of "tennis ball seam" continuous curvilinear electrodes, 1400, 1410, and FIG. 12 shows (in cross-section) a concentric array of point conductor "buttons", 1500, 1510 acting as electrodes. Note in each figure that there are two concentric spherical surfaces at radii rg1 and rg2, on which the inner g1 and outer g2 electrodes are located, around a central point g0, and that the electrodes in one surface match those in the other in angular position. This is always so in order to minimize curvature in the electrostatic field that is maintained between the two electrodes, in order that the accelerating force on ions in the interelectrode space be made as nearly perfectly radial as possible. The closer the ions can be made to follow exact radial motion, the less will be their transverse momentum content and the smaller will be their minimum convergence radius, r (related to the ICC core radius r.sub.c by Eqs. (15), which show that r.sub.o .ltoreq.r.sub.c .ltoreq.2r.sub.o). This is important in achieving conditions for onset of the ICC effect, which requires that the surface current density at r.sub.c exceed certain levels (previously described and defined) in order to initiate collisional phenomena that cause ion density to increase within this radius. If the ions have large transverse momentum content, the total current required for ICC onset will be excessively large, and the system will not practically reach the appropriate conditions. Thus, the choice of means to accelerate ions inward is critical; pure radial acceleration is the preferred mode. One such means is to make use of the minimal wire frame or button electrode structures discussed above, in which spherical symmetry of the field is maintained by the rapid azimuthal flow of electrons around the spherical surface, on surfaces of equipotential. Transverse (angular) electron flow will occur naturally along equipotential surfaces containing these grid structures, as observed in experiments of Litton and vanPassen.sup.14 on wire-frame hollow cathodes with highly non-uniform electron injection means. Alternatively, inner and outer (first and second) grids can be made of mesh screening (e.g. in the fashion of "chicken wire" screening), if of reasonable transparency. Note, in this regard, that ion current recirculation ratios required to provide net base gain above unity with the ICC effect, are only on the order of 10-100. Thus, screen grids with 1-10% solidity can be used for this function. However, the loss of electrons circulating in the system will also be governed by the solidity/transparency of these grids, and by losses due to collisions with the external boundary surface of the system, outside the ion-accelerating-grid region. Electron losses constitute a power loss to the system, which may exceed that due to requirements of ion injection power to initiate the ICC effect. There is thus an incentive to construct high-transparency grid systems, in order to minimize internal electron losses. Electron losses external to the ion-accelerating-grids may also be reduced by use of a third (outer) grid provided around the inner two, in order to decelerate electrons escaping outward from the ion-accelerating region of the inner two grids. If this outer grid is biased at negative potential relative to the next inner grid it will prevent or reduce electron losses from the system due to their collision with external wall/boundary structures. This is not necessary for initiation of the ICC effect, but is useful for conservation of electrons (and thus for preserving electron recirculating current). The fractional solidity (f.sub.s) of the wire frame grids is determined by the total area on the grid frame sphere at radius R subtended by the total length (L) of wire structure, divided by the spherical area, itself; this is just f.sub.s =Ld/4.pi.R.sup.2, where d is the diameter of the wire, or width of the grid frame sheet if metal sheet conductors are used. The total length of conductor in each of the three wire frame geometries of FIGS. 9, 10, and 11 is found as L=3.84(.pi.R), 6(.pi.R) and .sqroot./2(.pi.R) for the curvilinear tetrahedron, octahedron, and "tennis ball seam", respectively, and their corresponding solidity fractions are f.sub.2 =0.96(d/R), 1.5(d/R) and 0.708(d/R). Thus, if d=0.1 cm is the grid wire or sheet thickness, and the inner grid surface radius is at R=100 cm, the solidity fraction will be of the order of 1E-3, and the allowed ion and electron current recirculation ratios can be G.sub.i .apprxeq.(1/f.sub.s ).apprxeq.1E3. Larger wires or closer spacing will reduce the allowable recirculation ratios. The transparency of rod or button electrode arrays is generally greater than that attainable with continuous wire frame or sheet electrode systems, for the same degree of "stiffness" of the overall structure. For example, the solidity fraction of an array of N buttons, each of radius r.sub.b, is f.sub.s =Nr.sub.b.sup.2 /4.pi.R.sup.2 ; for N=6 (at the vertices of an octahedron) and r.sub.b =0.2 cm, the solidity fraction will be f.sub.s =3.2E-6 in a system with R=100 cm. Within the two inner grids the electron current flow should be at approximately the same speed (although somewhat larger) as that of the ions, so that the usual factor of (m.sub.i /m.sub.e).sup.0.5 .apprxeq.70-100 increase in electron current above the ion current flow is not present. Outside the outermost grid (of the inner two comprising the ion acceleration grid system), electron current reflux will tend to the higher value ratio. It is here that wall and grid collision losses (with an outer third grid or external wall) can result in excessive power losses to the system, as mentioned above. These can be inhibited in a variety of ways, such as by the use of electron-reflective surface magnetic fields, as proposed by Limpaecher.sup.15, or by polyhedral fields as proposed by Bussard.sup.1,12, or by "magnetic insulation" as proposed by Hirsch.sup.10, or by an electrostatic potential bias of sufficient magnitude on the wall surface, or by any other means well known in the art. If necessary, by these means the external electron losses may be suppressed and electron recirculation ratio may be kept high enough to allow net power to be generated from such devices as limited only by the base gain (G.sub.o) limits of the ICC process, itself. It is important to note that no net current flow paths should be allowed on or in the two ion accelerating grid structures, in order to ensure that there be no magnetic fields around these wires. The reason for this is that the motion of ions (and electrons) through the grid spacing can be affected by any significant fields due to grid wire currents, in such a way as to introduce curvature and non-radial motion to the ion paths, and thus to reduce their ability to converge to the smallest possible core radius. This can be avoided by utilizing dual parallel grid conductors, electrically connected in counter-current fashion, so that any grid wire current flows (from particle collisions with the grid structure) will yield cancelling magnetic fields from each grid conductor pair. With such an array of grid wires, the device can be started by applying the ion accelerating voltage across the inner two grid conductor systems. The innermost grid must be biased negatively relative to the outer accelerating grid, so that ions will be attracted towards the system center. Conversely, electrons in the inter-grid space will be accelerated away from the center, and will collide with neutral atoms within this space, thus ionizing them. The ions so produced will be accelerated through the innermost grid and will converge towards the core region, while the electrons so produced will be accelerated outward through the outer accelerating grid. The energy of the ions created in this manner will vary from near zero energy (those created by collisions very near to the inner grid) to the maximum energy of the full grid accelerating potential (those created by collisions very near to the outer grid). The energy distribution from this inter-grid volume will be weighted by the square of the ratio of the radius of birth position to the inner grid radius, so that more ions will be found at high energy, above the mean, than at low energy. Even though the ions have differing energy and radial momentum, the spherical flow geometry ensures that all collisions will occur very near to the system geometric center, with the result that such two-body ion/ion collisions between ions of differing energies can not distort the ion energy distribution from that imparted in the initial inter-grid ionization and acceleration process. Neither slow nor fast ions can be collided with in a manner to make their energy change in the system frame of reference. The mean ion energy in the system will be less than the inter-grid accelerating potential energy, thus, if a mean ion energy of E.sub.w is desired in the core region of the system, the grid potential difference should be set higher than E.sub.w. Electrons must be made available to the ions entering the space within the innermost grid, in order to prevent the buildup of an excessive virtual anode potential by ion compaction at the system center. This can be done by allowing electrons to be emitted from the inner grid, in the fashion of Hirsch.sup.5,6, which then follow the ions in their inward path; attracted by their space charge. Alternatively, electrons recirculating in the region external to the ion accelerating grids, and within the accelerating grid space will likewise be attracted by the space charge induced by ion motion, and can thus provide a source for the central region. By these means the ion kinetic collisional energy, which is preserved within the ICC collision-diffusion core--and forms the basis for the fusion reaction collisions therein--can be kept to a reasonable (large) fraction of the ion injection energy, thus maintaining efficient use of the injection power required for ICC initiation. Fuel ions which undergo fusion will disappear from the system, as their fusion products are too energetic to be captured by the ion accelerating fields that drive the ICC machine in the first place. These fusion products will escape from the active core region and will travel radially outwards until intercepted by structure or decelerated by externally-provided electric fields. Fuel ion makeup can be accomplished by injection of neutral atoms of the fuel, by use of neutral-particle beams or by supersonic gas injection nozzles, so that they are directed towards a region of the system where it is desired that they be ionized by collisions with in-situ ions or with electrons already oscillating in the system. This method is simple, readily controllable, and allows adjustment of the ion density and energy distribution to levels somewhat different from those which arise naturally at and during startup of the device. For example, placement of the injected fuel into the outer sections of the ion accelerating grid space will cause the mean ion energy to rise from its natural half-accelerating-potential value, because nearly all of the injected atoms will be ionized near the outer accelerating grid, and thus will gain maximum energy from the ion accelerating grid potential system. As was seen in the previous discussions, it is possible to create base system gain values well in excess of 30-100 by use of the ICC effect with very modest ion current recirculation ratios in systems of reasonable size (R.ltoreq.100 cm). It was further shown that the minimum power required for ICC process onset could be as low as 20-800 kw. Thus small devices with large fusion power output (e.g. 1 m radius, 100 kw in, 10 Mw out) appear possible by this novel invention. And, as for other electrostatic confinement concepts, the ICC machine can work as well with non-radiative fuels (fusion fuels that do not produce neutrons) as with the easier-to-burn neutron-producing fuels, so is well-suited to use in normal radiation-free human environments. In addition, since the fusion products from such non-radiative fuels are all charged particles with very high particle energies, they can all be slowed down by electric potentials provided by additional grid systems external to the ion accelerating grids and the core, and thus create electrical energy in external circuits by direct conversion within the ICC machine. Such direct conversion can be made very efficient (above 70% of the particle energy can appear directly as electricity), thus such devices offer promise for use in a wide array of civil, industrial, urban, airborne, and space-based systems. The ICC effect and process allows any spherically-convergent ion and electron flow system to work at performance levels vastly greater than heretofore imagined. This fact allows the conception of new and novel means for exploitation of this effect, which employ minimal grid conductor structures in simple geometries, capable of high power gain, with small power input and large power output from fusion reactions between ions supplied to the system. REFERENCES 1. R. W. Bussard, "Method and Apparatus for Controlling Charged Particles," U.S. Pat. No. 4,826,646, issued May 2, 1989 2. W. C. Elmore, J. L. Tuck, and K. M. Watson, "On the Inertial-Electrostatic Confinement of a Plasma", Phys.Fluids, Vol.2, No.3, pp.239-246 (May-June 1959) 3. H. P. Furth, "Prevalent Instability of Nonthermal Plasma", Phys. Fluids, Vol. 6, No. 1, pp. 48-53 (January 1963) 4. P. T. Farnsworth, U.S. Pat No. 3,258,402, "Electric Discharge Device for Producing Interactions Between Nuclei," issued June 28, 1966, and U.S. Pat. No. 3,386,883, "Method and Apparatus for Producing Nuclear Fusion Reactions," issued June 4, 1968 5. Robert L. Hirsch, "Inertial-Electrostatic Confinement of Ionized Fusion Gases", Jour. Appl. Phys., Vol 38, No. 11, pp. 4522-4534 (October 1967) 6. R. L. Hirsoh, U.S. Pat. No. 3,530,036, "Apparatus for Generating Fusion Reactions," and R. L. Hirsch and Gene A. Meeks, U.S. Pat. No. 3,530,497, "Apparatus for Generating Fusion Reactions," both issued Sept. 22, 1970 7. T. J. Dolan, J. T. Verdeyen, D. J. Meeker, and B. E. Cherrington, "Electrostatic-Inertial Plasma Confinement," Jour. Appl. Phys., Vol. 43, No. 4, pp. 1590-1600 (April 1972) 8. W. M. Black, "Theory of potential well formation in an electrostatic confinement device," Jour. Appl. Phys,Vol. 45, No. 6, pp. 2502-2511 (June 1974) 9. D. C. Baxter and G. W. Stuart, "The effect of charge exchange on ion guns and an application to inertial-electrostatic confinement devices," Jour. Appl. Phys., Vol. 53, No. 7, pp. 4597-4601 (July 1982) 10. Robert L. Hirsch, "U.S. Pat. No. 3,664,920, "Electrostatic Containment in Fusion Reactors," issued May 23, 1973 11. L. C. Marshall and H. Sahlin (eds.), "Electrostatic and Electromagnetic Confinement of Plasmas and the Phenomenology of Relativistic Electron Beams," Proceedings of a conference held March 4-7, 1974, publ. as Vol. 251 of the Annals of the New York Acad. of Sci., New York, 1975 12. R. W. Bussard, "Magnetic Inertial-Electrostatic Confinement: A New Concept For Spherical Conversion-Flow Fusion," technical paper sub. for publ. to Fusion Technology, Sept. 27, 1989 13. R. W. Bussard, et al, "Preliminary Research Studies of a New Method for Control of Charged Particle Interactions,"PSR Report No. 1899, Nov. 30, 1988, Final Report under Contract No. DNA001-87-C-0052, Defense Nuclear Agency 14. James Litton, Jr. and H. L. L. van Paassen, "Electron Beam Production From Perforated Wall Hollow Cathode Discharges," in the Proceedings of the 23rd Conference on Physical Electronics, pp. 185-194 (1963) 15. Rudolf Limpaecher, U. S. Pat. No. 4,233,537, "Multicusp Plasma Containment Apparatus," issued Nov. 11, 1980 |
description | This application claims the benefit of provisional patent application No. 61/167,677, filed Apr. 8, 2009, which is incorporated herein by reference. This disclosure relates to workpiece handling, and more particularly to dual sided workpiece handing. Differing processing tools accept a workpiece and perform different processing steps depending on the type of tool. One type of a processing tool is an ion processing tool where a workpiece is treated with ions. An ion processing tool may include a plasma assisted doping (PLAD) tool or a beamline tool. A PLAD tool includes a process chamber where plasma is generated. One or more workpieces are positioned in the process chamber and biased to attract ions from the plasma. The ions may provide for precise material modification to the workpiece. The workpiece may include but not be limited to, magnetic disks, semiconductor wafers, flat panels, solar panels, and polymer substrates. A beamline tool includes an ion source and an extraction electrode assembly to extract a well defined ion beam from the ion source. One or more beamline components known in the art may control, modify, and direct the ion beam with desired characteristics towards a surface of a workpiece. The workpiece for the beamline tool may also include, but not be limited to, magnetic disks, semiconductor wafers, flat panels, solar panels, and polymer substrates. The ion beam may be distributed across a surface of the workpiece by ion beam movement, workpiece movement, or a combination of the two. Many workpieces to be treated by such process tools are single sided workpieces in that there is only one side or surface of the workpiece subject to treatment. For example, the front surface of a conventional semiconductor wafer is treated with ions but the rear surface is not. However, some workpieces are dual sided workpieces that have front and opposing rear sides to be treated. For example, a magnetic disk used in a conventional hard disk drive may require ion treatment on both sides of the disk. Conventional wafer handling equipment in an ion processing tool accepts a dual sided workpiece for processing and treats only a first side of the workpiece. If a second opposing side of the same workpiece also needs to be treated, it is removed from the ion processing tool which is typically under vacuum while processing. Once removed from the tool and the vacuum condition, the workpiece would then need to be reoriented, and then inserted back into the ion processing tool with its second opposing side now positioned for treatment. One drawback with this conventional equipment and method is the substantial time to perform the removal and reinsertion steps. This additional time negatively impacts throughput performance or the number of workpieces that can be processed over a given time period. Another drawback is that these removal and reinsertion steps necessarily involve workpiece handling operations which is an inherent factor in reliability of the entire processing operation. Accordingly, there is a need in the art for improved dual sided workpiece handling that overcomes the above-described inadequacies and shortcomings. According to a first aspect of the disclosure a method is provided. The method includes positioning at least one dual sided workpiece on an assembly in a process chamber to expose a first side of the at least one dual sided workpiece, treating the first side of the at least one dual sided workpiece, reorienting a portion of the assembly in the process chamber to expose a second side of the at least one dual sided workpiece, the second side opposing the first side, and treating the second side. According to another aspect of the disclosure, a processing apparatus is provided. The processing apparatus includes: a process chamber defining an enclosed volume; a dual sided workpiece assembly disposed in the enclosed volume, the dual sided workpiece assembly comprising a base portion and a flip portion coupled to the base portion, the flip portion having a support surface configured to support at least one dual sided workpiece, and wherein the flip portion is configured to rotate about a flipping axis; and a controller configured to control the dual sided workpiece assembly to expose a first side of the at least one dual sided workpiece to treatment in the process chamber and to expose a second side of the at least one dual sided workpiece to treatment by rotating the flip portion about the flipping axis, the second side opposing the first side. The present disclosure will now be described in more detail with reference to exemplary embodiments as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility. FIG. 1 is a block diagram of a processing apparatus 100 illustrating in cross sectional view a dual sided workpiece handling assembly 124 consistent with one embodiment of the disclosure. Although the processing apparatus 100 is further described herein as a plasma doping apparatus, a dual sided workpiece assembly 124 consistent with the disclosure may also be disposed in the process chamber of other processing tools such as etch tools, deposition tools, and beam line ion implanters. The beamline ion implanter may include an ion source know in the art from which a well defined ion beam is extracted. One or more beamline components known in the art may control, modify, and direct the ion beam with desired characteristics towards a surface of a dual sided workpiece. The process chamber of the beamline ion implanter may also be referred to in the art as an end station. Furthermore, a plasma doping apparatus can perform many differing material modification processes using ions on a treated workpiece. One such process includes directing ions towards a magnetic disk workpiece for use in hard drives to alter the magnetic characteristics of desired regions of the disk. Another process includes directing ions towards a semiconductor wafer workpiece with sufficient energy to implant the ions into a semiconductor material. The processing apparatus 100 of FIG. 1 is illustrated as a stand alone system, but alternatively may be part of a cluster tool including other processing apparatuses. FIG. 2 is a perspective view of the dual sided handling assembly 124 of FIG. 1. In general, the dual sided workpiece handling assembly 124 is configured to enable opposing sides of one or more dual sided workpieces to be treated in situ without removing the workpieces from the process chamber 102 between treatment of each side. For example, each workpiece 220, 222 shown in phantom in FIG. 1 may have a first side 220A, 222A and a second opposing side 220B, 222B. Ions 103 may be accelerated towards the first sides 220A, 222B during treatment of the same. A portion of the assembly 124 may then be reoriented to expose the second opposing sides 220B, 222B to the ions 103. The dual sided workpieces 220, 222 remain in the process chamber 102 during a time interval between the treating of the first sides 220A, 222A and second sides 220B, 222B. The processing apparatus 100 may include a process chamber 102, a gas source 188, a vacuum pump 180, a plasma source 106, a bias source 190, a controller 118, a user interface system 116, and the dual sided workpiece handling assembly 124. The process chamber 102 defines an enclosed volume 105. A gas source 188 provides a gas to the enclosed volume 105 of the process chamber 102. A vacuum pump 180 evacuates the process chamber 102 through the exhaust port 176 to create a high vacuum condition within the process chamber. The vacuum pump 180 may include a turbo pump, and/or a mechanical pump. An exhaust valve 178 controls the exhaust conductance through the exhaust port 176. The plasma source 106 is configured to generate the plasma 140 in the process chamber 102. The plasma source 106 may be any plasma source known to those in the art such as an inductively coupled plasma (ICP) source, a capacitively coupled plasma (CCP) source, a microwave (MW) source, a glow-discharge (GD) source, or a helicon source, or a combination thereof. The bias source 190 provides a bias signal to the dual sided workpiece handling assembly 124 and each workpiece supported thereby. The bias source 190 may be a DC power supply to supply a DC bias signal or an RF power supply to supply an RF bias signal depending on the type of plasma source 106. In one embodiment, the DC bias signal is a pulsed DC bias signal with ON and OFF periods to accelerate ions 103 from the plasma 140 to the workpieces during the ON periods. Controlling the duty cycle and amplitude of such a pulsed DC bias signal can influence the dose and energy of the ions 103. The controller 118 can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller 118 also includes communication devices, data storage devices, and software. The user interface system 116 may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the processing apparatus 100 via the controller 118. The controller 118 may receive signals from the user interface system 116 and/or one or more components or sensors of the processing apparatus 100 and control various components of the apparatus 100. For clarity of illustration, the controller 118 is illustrating as communicating with only the dual sided workpiece assembly 124 to control the same. Those skilled in the art will recognize that the controller 118 may receive signals from all of the components of the processing apparatus 100 and control the same, e.g., control the bias source 190, the vacuum pump 180, the plasma source 106, etc., in response to differing conditions and instructions. With reference to FIG. 2, the dual sided workpiece assembly 124 may be fixed to a portion of the process chamber 102 and generally include a base portion 218 and a flip portion 248. The base portion 212 supports the flip portion 248 and enables the flip portion 248 to flip 180° about a flipping axis 272 as indicated by arrow 274. The base portion 218 may include a support rod 138 coupled to a pair of opposing upstanding arms 126, 128. The arms 126, 128 may further support the flip portion 248 and have a length sufficient to permit the flip portion 248 to flip 180° about the flipping axis 272 without contacting other components such as the support rod 138. The base portion 218 may also be configured to allow for rotation of the flip portion 248 about a rotational axis 140 to facilitate alignment of the workpieces 220, 222, 224, 226 with other robots and openings (not illustrated). The rotational axis 140 may be orthogonal to a workpiece plane 193 defined by the carrier 202 that supports the workpieces 220, 222, 224, 226. The flip portion 248 in the embodiment of FIG. 2 includes a carrier 202 having four pockets to accept four dual sided workpieces 220, 222, 224, 226. The pockets may also allow for good thermal contact of the workpieces 220, 222, 224, 226 to the carrier 202 for thermal control. The dual sided workpiece assembly 124 may also have passageways (not illustrated) for transporting cooling fluid of a cooling system there through for thermal control. The workpieces 220, 222, 224, 226 are illustrated as magnetic disks for use in a conventional hard disk drive. Alternative embodiments may have only one pocket for one workpiece or any plurality of pockets. The carrier 202 may be supported and secured by a guide rail 221 having an opening and a slot to accept and secure the carrier 202. The guide rail 221 may have mechanical features such as protrusions and/or indents to further secure the carrier 202 once fully inserted into the opening of the guide rail 221. The guide rail 221 and carrier 202 may form part of a gimbal mechanism to facilitate the rotation of the carrier 202 about the flipping axis 272. The carrier 202 may be shaped similar to a conventional 300 millimeter (mm) diameter semiconductor wafer. That is, the carrier 202 may have a disk shape with about a 300 mm diameter so that existing wafer handling equipment designed to accommodate 300 mm semiconductor wafers can readily handle a similarly shaped carrier 202. Turning to FIG. 3, a plan view of one slot 284 of the carrier 202 of FIG. 2 is illustrated in more detail. The slot 284 has a pair biasing members such as the pair of springs 302, 304. The springs 302, 304 both secure the workpiece 222 within the slot 284 and also complete an electrical path 308 from the biasing source 190 to the workpiece 222. Hence, the springs 302, 304 advantageously serve a dual role. The workpiece 222 of FIG. 3 is shown in phantom as it enters the opening of the slot 284 and is urged in the direction of the arrow 310. The workpiece 222 is also shown in solid lines at its secured position fully within the recess of the slot 284 and further retained and supported by the outward bias of the pair of springs 302, 304. In operation, four dual sided workpieces 220, 222, 224, 226 may be urged into respective slots of the carrier 202. The dual sided workpieces 220, 222, 224, 226 may be magnetic disks. As each workpiece is urged into a respective slot of the carrier 202 with sufficient force, a pair of springs 302, 304 may be compressed to enable the full insertion of the workpiece. For example, FIG. 3 illustrates the workpiece 220 in solid lines fully inserted into the slot 284. The springs 302, 304 are outwardly biased to serve a dual role of further securing the workpiece 222 in the slot 284 while also providing an electrical path 308 for a biasing signal from the bias source 190. Each slot of the carrier 202 may also have similar springs 302, 304. Associated wafer handling equipment and robots may transfer the carrier 202 with the workpieces 220, 222, 224, 226 fully engaged in respective slots to a secure position within the guide rail 221 of the flip mechanism 248. Such a carrier 202 can improve throughput as multiple workpieces 220, 222, 224, 226 can be loaded in batches rather than one at a time. Alternatively, a turntable having one or more machined pockets may be used in the flip portion 248 in lieu of the carrier 202. As opposed to the carrier 202, the turntable may be permanently fixed in the flip portion 248 of the assembly 124. The pockets of the turntable allow for retention of associated workpieces with sufficient electrical contact to receive a biasing signal from the bias source 190. Once the carrier 202 is secured in the guide rail 221 and associated wafer handling equipment is withdrawn from the process chamber 102, the gas source 188 may supply an ionizable gas to the process chamber 102. Examples of an ionizable gas include, but are not limited to, BF3, BI3, N2, Ar, PH3, AsH3, B2H6, H2, Xe, Kr, Ne, He, SiH4, SiF4, GeH4, GeF4, CH4, CF4, AsF5, PF3, and PF5. The plasma source 106 may generate the plasma 140 by exciting and ionizing the gas provided to the process chamber 102. The dual sided workpiece handling assembly 124 may hold the workpieces 220, 222, 224, 226 to expose a first side 220A, 222A, 224A, 226A of each to the plasma 140. The bias source 190 may provide a bias signal to each workpiece 220, 222, 224, 226 to attract the ions 103 towards the first side 220A, 222A, 224A, 226A of the workpieces. When the workpieces 220, 222, 224, 226 are the illustrated magnetic disks for use in hard drives, the ions 103 alter the magnetic characteristics of desired regions of the disks. Once a first side of each workpiece 220, 222, 224, 226 is processed, the dual sided workpiece handling assembly 124 may reorient the workpieces in the process chamber 102 to expose a second opposite side of each workpeiece to the plasma 140. To reorient the workpieces, the controller 118 may instruct the dual sided workpiece handling assembly 124 to flip the carrier 202 by 180° about the flipping axis 272 thus allowing the second opposing side of the workpieces (e.g., sides 220B and 222B of workpieces 220, 222) to be treated by the ions 103. The assembly 124 may have one or more electromechanical actuators (not illustrated) to facilitate such flipping. During a time interval between treating the first side and second side of the workpieces, the workpieces 220, 222, 224, 226 remain in the process chamber 102. Furthermore, the controller 118 may instruct the vacuum pump 180 and associated system to maintain a vacuum condition in the process chamber 102. This vacuum condition may be maintained during the treating of the first side 220A, 222A, 224A, 226A of the workpieces 220, 222, 224, 226 and the second opposing side of the workpieces, as well as the time interval between the treating of the first and second side. Accordingly, there is provided a method that enables both sides of a dual sided workpiece to be treated in situ within a process chamber. The dual sided workpieces may therefore be processed quickly and reliably. The throughput of a processing apparatus such as an ion implanting apparatus may therefore be improved compared to a conventional apparatus that removes each workpiece from the process chamber, reorients the workpieces, and then reinserts the same with the opposing side positioned for treatment. The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein. |
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053609743 | description | DETAILED DESCRIPTION OF THE INVENTION The assembly of FIG. 1 is used in a scanning probe microscope. It includes a frame 10 which provides a reference surface with respect to which a dual quad flexure carriage 12 is mounted. The dual quad flexure carriage 12 provides a surface upon which a scanning probe tip (not shown) is received and offers movement of the scanning probe tip with respect to the frame 10 in either an X or Y direction. A pair of piezo actuators 14 (available as the DPTC actuator and manufactured by Queensgate Instruments Inc.) are attached to adjacent sides of the dual quad flexure carriage 12 such that the one end of the piezo actuator 14 bears against a side of the dual quad flexure carriage 12. The second end of each piezo actuator 14 is attached to a holder block 16, which in turn is fastened to the frame 10. The actuators are commercial units combining precision piezo stack actuators with capacitive position feedback sensors to produce motion linearities to +/-0.15% of full range. In the preferred embodiment, a one dimensional (1D) flexure 17 is interposed between a first end of the piezo actuator 14 and the respective side of the dual quad flexure carriage 12, and between a second end of the piezo actuator 14 and the respective holder block 16. The nature and mechanics of one dimensional flexures are known, as illustrated for example, in U.S. Pat. No. 4,667,415. The preferred embodiment further provides for a bearing 18 that is interposed between the second end of the piezo actuator 14 and the 1D flexure 17. In this embodiment, the 1D flexure elements allow a very small rotation about the flexure line without friction. A pair of spring assemblies 20 are attached to adjacent sides, and opposite piezo actuators 14, of the dual quad flexure carriage 12 such that a first end of each spring assembly 20 bears against a side of the dual quad flexure carriage 12 and a second end is fastened to the frame 10 by a block 16 or similar support means. Each spring assembly 20 thus urging the dual quad flexure carriage 12 against the piezo actuator and maintaining the entire assembly in a compressed state. The preferred embodiment of compression of the invention is one in which the piezo actuator 14, carriage 12 and spring assembly 20 combination with support means are maintained substantially at 20 lbs. pressure. Referring now to FIG. 2, it can be seen that the dual quad flexure carriage 12 consists of a unitary flexure assembly which comprises a base 24, an intermediate carriage 22, and an inner carriage 26. The dual quad flexure carriage 12 further comprises four outer flexures 28 and four inner flexures 29. The intermediate carriage 22 is supported off of the base 24 by the four outer flexures 28. The intermediate carriage 22 and base 24 are each quadrilaterals that, along with the four outer flexures 28, form a first parallelogram. Similarly, the inner carriage 26 is suspended from the intermediate carriage 22 by the four inner flexures 29. The inner carriage 26 and intermediate carriage 22 likewise are quadrilaterals that, along with the four inner flexures 29, form a second parallelogram. As further illustrated in FIG. 2, the second parallelogram is smaller than the first parallelogram and is disposed within the first parallelogram such that the intermediate carriage 22 offers a common plane to each parallelogram. In turn, the inner carriage 26 provides a surface for receiving a scanning probe assembly (not shown). The unitary construction of the dual quad flexure carriage 12 provides inherent geometric integrity of matched flexure pairs. The unitary construction of the dual quad flexure carriage 12 along with the matched flexure pairs further offer extremely flat horizontal motion and natural thermal stability. That is, if otherwise constructed with discrete components, the dual quad flexure carriage 12 could result in a structure with unmatched flexure pairs, and a structure lacking the benefits the flatness and thermal stability. The feature of the dual quad flexure carriage 12 providing the property of flat motion is illustrated in FIG. 3. Each inner flexure 29 is double cantilevered between the inner carriage 26 and the intermediate carriage 22. Further, each outer flexure 28 is double cantilevered between the base 24 and the intermediate carriage 22. FIG. 3 illustrates a partial view of the dual quad flexure carriage 12 in a typical deflected condition. As shown in FIG. 3, a lateral force tends to urge the inner carriage 26 in the direction of the force and upward, toward the intermediate carriage 22. Likewise the same lateral force, tends to urge the intermediate carriage 22 downward toward the base 24. Provided the dimensions of both flexures 28, 29 and all cantilever and end conditions are the same, a lateral force applied to the dual quad flexure carriage 12 deflects each flexure 28, 29 the same amount. The upward motion of the inner carriage 26 toward the intermediate carriage 22 is then exactly canceled by the downward motion of the intermediate carriage 22 toward the base 24, thereby resulting in a flat horizontal motion of the inner carriage 26, as well as the entire dual quad flexure carriage 12, Further, the horizontal motion of the inner carriage 26, as well as the deflection of the flexures 28, 29 is dependent on the direction of the force applied. That is, the resulting displacement of the inner carriage 26 is limited to the direction of the force on the dual quad flexure carriage 12. Still however, one significant attribute of the system is that the dual quad flexure carriage 12 moves along one planar axis with minimum displacement along a second planar axis. The dual quad flexure carriage 12 rotates about the fixed 1D flexures 17 of each piezo actuator 14. Because of the large dimension of the piezo actuators 14 versus the scanning motion, displacement off a linear axis is small: less than 5 nm for the full 75 micron range, and less than 1 Angstrom for a useful 10 micron scan. Thermal stability is also a property of the matched flexure 28, 29 pairs. Assuming both flexures 28, 29 in one corner of the dual quad flexure carriage 12 are subjected to the same ambient temperature, each will grow at the same rate (up and down) thereby canceling any net vertical motion of the inner carriage 26. Because of this differential property of the beam pair configuration, each of the four flexure pairs may be subjected to different ambient temperatures (within a few degrees) without theoretically affecting the inner carriage vertical position. This provides a measure of immunity to thermal gradients. To further minimize thermal effects, in the preferred embodiment, the dual quad flexure carriage 12 is made from annealed super invar which has a thermal coefficient of expansion better than two orders of magnitude below that of steel. To further minimize thermal effects, the matched flexures 28, 29 are set in close proximity to one another. This increases the likelihood of both flexures 28, 29 maintaining a same temperature. For thermal stability it is sufficient that each matched flexure 28, 29 pair be maintained at equal temperature; different pairs may be at different temperatures. Although the preferred embodiment of the invention is one in which the dual quad flexure carriage 12 comprises two nested parallelograms, alternate embodiments may include any means whereby two geometrically similar structures are nested with a common reciprocating surface. The two similar structures further being displaced, one from the other, by a flexure means; the combination providing a single, unitary structure. In so doing, the arrangement provides for flat motion as well as natural thermal stability as described in the preferred embodiment of the present invention. The scanner subsystem electronics are shown in FIG. 4. Each piezo actuator 14 is driven by a servo controller to commanded positions. This controller implements a predominantly integral control law and, combined with high precision feedback sensors, provide piezo actuator 14 linearity. In the preferred embodiment, analog command signals are delivered to the servo controllers over an interconnect plane from a multichannel digital to analog conversion board. This high resolution converter/driver receives the position command information in digital form over a high speed serial channel from the system controller. The system controller originates XY position coordinates as part of its task of overall motion coordination and data collection. High resolution, 18 bit conversions are necessary to achieve small command voltage differences that result in the high resolution motion required of the scanner. Noise on the analog side directly contributes to the overall noise floor that becomes the lower limit of the motion resolution. This design is implemented to minimize that noise. All analog components are packaged in close proximity, and signals are distributed over backplanes instead of cables. The analog package is uniformly shielded, and all analog cable runs have been eliminated. While the invention has been described above in connection with a preferred embodiment therefore as illustrated by the drawings, those of skill in the art will readily recognize alternative embodiments of the invention can be easily produced which do not depart from the spirit and scope of the invention as defined in the following claims. |
abstract | A nuclear powered quantum dot light source, having a holder having at least a portion that is a radiolucent and a mixture of quantum dots, a radionuclide, and a radiolucent binder material into which the quantum dots and radionuclide are located. Alpha and/or beta particles from the radionuclide energize the quantum dots and cause them to give off light at one or more predetermined wavelengths. |
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claims | 1. A method of forming graphical representations of fuel bundle groups, comprising:selecting, with a computer interface, a graphical representation of a nuclear reactor core;creating a loading map, with the computer interface, using the graphical representation of the nuclear reactor core, the loading map representing the nuclear reactor core; andexecuting a grouping operation on the loading map by performing at least one of,assigning, by a user with the computer interface, at least one fuel bundle within the loading map into one of a plurality of bundle groups, the assigning being based on a user-selected symmetry and a user-selected fuel bundle characteristic, andusing an automated process available on the computer interface to automatically assign at least one fuel bundle within the loading map into one of the plurality of bundle groups, the automated assigning being based on a user-selected symmetry and a user-selected fuel bundle characteristic. 2. The method of claim 1, wherein the associated fuel bundle characteristic is a fuel bundle type, the fuel bundle type being one of a fresh fuel bundle, a reinserted fuel bundle, and a lock fuel bundle, a locked fuel bundle being an unmovable fuel bundle. 3. The method of claim 1, wherein each of the plurality of bundle groups includes an associated symmetry. 4. The method of claim 3, wherein the associated symmetry is one of rotational and mirror. 5. The method of claim 3, wherein the associated symmetry is based on equally divided and symmetric portions of the core. 6. The method of claim 5, wherein the associated symmetry is one of octant, quadrant, and semi. 7. The method of claim 1, wherein the fuel bundle characteristics are a constraint on fuel bundle placement in an optimization function. 8. The method of claim 7, wherein the constraint is fuel bundles in a given bundle group may only be exchanged with other fuel bundles in the given bundle group. 9. The method of claim 1, wherein the bundle groups are a constraint in a user-based, trial and error process. 10. The method of claim 9, wherein the constraint is fuel bundles in a given bundle group may only be exchanged with other fuel bundles in the given bundle group. 11. The method of claim 1, wherein the plurality of bundle groups include a first bundle group with a first associated symmetry attribute and a second bundle group with a second associated symmetry attribute. |
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056051719 | claims | 1. An illumination source comprising a porous silicon having a source of electrons on the surface and/or intersticies thereof. 2. The illumination source of claim 1, wherein said porous silicon has a total porosity in the range of from about 50% to about 90% by volume. 3. The illumination source of claim 1, wherein said porous silicon has a pore size distribution in the range of from about 1 to about 100 nanometers. 4. The illumination source of claim 1, wherein a sufficient quantity of said source of electrons is present to provide radiation of not less than about 10 millicuries/cm.sup.3. 5. The illumination source of claim 1, wherein a sufficient quantity of said source electrons is present to provide radiation in the range of from about 10 to about 100 millicuries/cm.sup.3. 6. The illumination source of claim 1, wherein said electron source is tritium. 7. The illumination source of claim 1, wherein said porous silicon is optically transparent. 8. The illumination source of claim 1, wherein said porous silicon has a thickness in the range of from about 10 to about 50 microns. 9. The illumination source of claim 8, and further comprising a photovoltaic device in optical proximity thereto. 10. The illumination source of claim 8, and further comprising an optoelectronic mechanism operatively connected thereto for converting light from said illumination source to an electrical signal. 11. An illumination source comprising a tritiated porous silicon. 12. The illumination source of claim 11, wherein said porous silicon has a porosity in the range of from about 50% to about 90% by volume. 13. The illumination source of claim 11, wherein the porous silicon has pores not exceeding about 100 nanometers. 14. The illumination source of claim 11, wherein the porous silicon has a pore size distribution in the range of from about 1 to about 100 nanometers. 15. The illumination source of claim 11, wherein there is sufficient tritium in said porous silicon to provide radiation of not less than 10 millicuries/cm.sup.3. 16. The combination of a photovoltaic device and an illumination source of tritiated porous silicon. 17. The combination of claim 16 wherein said tritiated porous silicon has a total porosity in the range of from about 50% to about 90% by volume. 18. The combination of claim 16, wherein said porous silicon has a pore size distribution in the range of from about 1 to about 100 nanometers. 19. The combination of claim 16, wherein said porous silicon is optically transparent. 20. The combination of an illumination source of tritiated porous silicon with one or more microelectro-mechanical systems. 21. The combination of claim 20, wherein said porous silicon has a total porosity in the range of from about 50% to about 90% by volume. 22. The combination of claim 20, wherein said porous silicon is optically transparent. 23. The combination of claim 20 wherein said systems include one or more of electronic sensors, actuators, micropumps and microvalves. |
046631291 | abstract | A method and apparatus for providing radionuclides of bismuth-212 and lead-212. Thorium-228 and carrier solution starting material is input to a radiologically contained portion of an isotopic generator system, and radium-224 is separated from thorium-228 which is retained by a strongly basic anion exchange column. The separated radium-224 is transferred to an accessible, strongly acidic cationic exchange column. The cationic column retains the radium-224, and natural radioactive decay generates bismuth-212 and lead-212. The cationic exchange column can also be separated from the contained portion of the system and utilized without the extraordinary safety measures necessary in the contained portion. Furthermore, the cationic exchange column provides over a relatively long time period the short lived lead-212 and bismuth-212 radionuclides which are useful for a variety of medical therapies. |
claims | 1. An electron beam exposure apparatus comprising:a column for irradiating an electron beam to a sample;a sample chamber having a vacuum exhaustion unit for controlling an internal unit to a vacuum atmosphere;a stage, arranged in said sample chamber, for holding and moving the sample; anda first mounting for elastically supporting said column with respect to said sample chamber. 2. The electron beam exposure apparatus according to claim 1, further comprising:an interferometer, arranged in said sample chamber, for measuring a position of said stage; anda first fixing member for fixing said interferometer to said column. 3. The electron beam exposure apparatus according to claim 2, wherein said stage performs aligning based on a measurement result of said interferometer. 4. The electron beam exposure apparatus according to claim 2, wherein said column comprises a correction system for correcting an orbit of an electron beam based on a measurement result of said interferometer. 5. The electron beam exposure apparatus according to claim 2, further comprising:an optical system, arranged outside said sample chamber, for supplying said interferometer with measurement light; anda second fixing member for fixing said optical system to said column. 6. The electron beam exposure apparatus according to claim 1, further comprising a first bellows partition connected to said column and said sample chamber in a way to seal a gap between said column and said sample chamber. 7. The electron beam exposure apparatus according to claim 1, further comprising a first magnetic shield unit for attenuating magnetism that passes through the gap between said column and said sample chamber. 8. The electron beam exposure apparatus according to claim 7, wherein said first magnetic shield unit is configured in a way that a magnetic shield provided on an external wall portion of said column and a magnetic shield provided on an upper wall unit of said sample chamber do not come in contact with each other, and respectively have large areas facing each other. 9. The electron beam exposure apparatus according to claim 1, further comprising:a stage base; anda second mounting for elastically supporting said stage base with respect to a base member. 10. The electron beam exposure apparatus according to claim 9, further comprising:a second bellows partition connected to said sample chamber and said second mounting in a way to seal an opening of said sample chamber provided for said second mounting; anda second magnetic shield unit for attenuating magnetism that passes through the opening of said sample chamber provided for said second mounting. 11. The electron beam exposure apparatus according to claim 9, further comprising:a second displacement sensor for measuring a relative displacement between said stage base and said base member;a second accelerometer for measuring acceleration of said stage base; anda second actuator for changing a relative displacement between said stage base and said base member based on a measurement result of said second displacement sensor and a measurement result of said second accelerometer. 12. The electron beam exposure apparatus according to claim 9, further comprising a reaction force receiver for dissipating reaction force to said base member, said reaction force being received by said stage base at the time of acceleration or deceleration of said stage. 13. The electron beam exposure apparatus according to claim 12, wherein said reaction force receiver comprises a strut fixed to said base member, a reaction force transmission member fixed to said stage base, and a linear motor arranged between the strut and the reaction force transmission member,said apparatus further comprising:a third bellows partition connected to said sample chamber and said reaction force transmission member in a way to seal an opening of said sample chamber provided for said reaction force transmission member; anda third magnetic shield unit for attenuating magnetism that passes through the opening of said sample chamber provided for said reaction force transmission member. 14. The electron beam exposure apparatus according to claim 9, further comprising a counter mass mechanism for moving a counter member so as to cancel reaction force, which is received by said stage base at the time of acceleration or deceleration of said stage. 15. The electron beam exposure apparatus according to claim 14, wherein movement of said stage and movement of said counter member are realized by respective electromagnets, and directions of magnetic flux of the electromagnets are opposite to each other. 16. The electron beam exposure apparatus according to claim 1, further comprising a second mounting for elastically supporting said sample chamber with respect to a base member. 17. The electron beam exposure apparatus according to claim 16, further comprising a reaction force receiver for dissipating reaction force to said base member, said reaction force being received by said sample chamber at the time of acceleration or deceleration of said stage. 18. A device manufacturing method comprising:a step of exposing the sample by said electron beam exposure apparatus according to claim 1; anda step of developing the sample which has been subjected to exposure. 19. An electron beam exposure apparatus comprising:a column for irradiating an electron beam to a sample;a sample chamber having a vacuum exhaustion unit for controlling an internal unit to a vacuum atmosphere;a stage, arranged in said sample chamber, for holding and moving the sample; anda mounting for elastically supporting said column with respect to a base member; and further comprising: a first displacement sensor for measuring a relative displacement between said column and said sample chamber; a first accelerometer for measuring acceleration of said column; and a first actuator for changing a relative displacement between said column and said sample chamber based on a measurement result of said first displacement sensor and a measurement result of said first accelerometer. 20. A device manufacturing-method comprising:a step of exposing the sample by said electron beam exposure apparatus according to claim 19; anda step of developing the sample which has been subjected to exposure. |
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description | This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-382394, filed Dec. 27, 2002, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The invention relates to lithography using a charged particle beam. More specifically, the invention relates to a stage phase measurement method for a charged particle beam exposure apparatus for measuring the phase of a mask stage coordinate system for a specimen stage coordinate system of a charged particle beam exposure apparatus; a demagnification measurement method for a charged particle beam exposure apparatus for measuring the demagnification for image projection onto a mask specimen surface; a control method for a charged particle beam exposure apparatus for performing control corresponding the measured phase and demagnification; and a charged particle beam exposure apparatus. 2. Description of the Related Art With increasingly fined semiconductor devices, studies and research are being made regarding charged particle beam exposure apparatuses for exposure patterns. Demagnification lenses and objective lenses are used to demagnify and transferring a mask pattern onto a specimen. The mask pattern is demagnified by these lenses and the pattern is rotated by a magnetic field, so that the phase of the pattern to be transferred onto the surface of the specimen is varied concurrently with deflection in demagnification. The apparatus is designed by taking both the rotation and the demagnification into account, and the apparatus is designed so that the rotation is performed at a desired demagnification. Practically, however, design errors and manufacture errors disable obtaining the condition concurrently allowing the desired demagnification and the desired rotation to be exhibited. A process for measuring the demagnification and pattern rotation angle is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-22349. A rotational error of the pattern is correctable by using a rotation stage that carries the mask. However, since no means is provided to correct the movement direction of a mask stage X and the movement direction of a mask stage Y, the system phase of the mask stage coordinate system remains mismatched with the specimen stage coordinate system. Because of assembly errors, design errors, and lens system adjustment errors, the mask stage coordinate system has errors for the specimen stage coordinate system; and generally, it does not have means for adjusting the errors. While an XY mask stage should be mounted to one more θ stage to adjust the phase of an XY mask stage, since the construction is thereby completed and free space in an electrooptical housing is insufficient, it is difficult to mount the XY mask stage. When moving a desired mask pattern with the mask stage to the vicinity of the beam, if such errors as those described above are zero, the movement position can be determined in accordance with pattern design values. However, a problem arises in that an accurate movement position of the pattern cannot be known, so that accurate movement cannot be implemented. Regarding a demagnification measurement method, using a design distance D between two opening portions provided in the mask and a distance d between individual beam specimen surface positions formed in the opening portions, the demagnification has been obtained by way of “demagnification M=d/D”. However, errors such as those occurring in the manufacture of the opening portions and distortion undesirably influence the calculation result. In a case where the manufacture error is 50 nm and the distance between the opening portions is 500 μm, the case results in causing an error of 0.01% (50 nm/500 μm×100). When performing scan-exposure of a 300 μm mask pattern by using the demagnification, there arises the problem of causing an image-dimensional error of as large as 30 nm (i.e., 300 μm×0.01%=30 nm). Further, a problem arises in that an accurate pattern cannot be imaged onto the specimen since no method is available to measure the phase of the mask stage coordinate system with respect to the problem of demagnification measurement errors and the specimen stage coordinate system. A demagnification measurement method for a charged particle beam exposure apparatus, according to an aspect of the present invention, comprises: measuring a first stage position of a mask stage of the charged particle beam exposure in accordance with a mask stage coordinate system with an opening portion of a mask placed on the mask stage being situated in a first opening position; irradiating a first charged particle beam to a first irradiation position on a surface of a specimen through the opening portion of the mask, the first charged particle beam being shaped through the opening portion and then passing through an objective lens system; measuring the first irradiation position in accordance with a specimen stage coordinate system; moving the mask stage to a second stage position to situate the opening portion of the mask in a second opening position different from the first opening position; measuring the second stage position of the mask stage in accordance with the mask stage coordinate system; irradiating a second charged particle beam to a second irradiation position on the surface of the specimen through the opening portion of the mask moved together with the mask stage, the second charged particle beam being shaped through the opening portion situated in the second opening position and then passing through an objective lens system; measuring the second irradiation position in accordance with the specimen stage coordinate system; and calculating a demagnification of the objective lens system from the first and second stage positions and the first and second irradiation positions. A stage phase measurement method for a charged particle beam exposure apparatus, according to another aspect of the present invention, comprises: measuring a rotation angle of a pattern of a charged particle beam shaped through a mask placed on a mask stage of the charged particle beam exposure apparatus and then irradiated on a surface of a specimen through an objective optical system; correcting rotation of the pattern by rotating the mask corresponding to the measured rotation angle; measuring a first stage position of the mask stage in accordance with a mask stage coordinate system after correcting the rotation with an opening portion of the mask being situated in a first opening position; irradiating a first charged particle beam to a first irradiation position on the surface of the specimen through the opening portion of the mask, the first charged particle beam being shaped through the opening portion and then passing through an objective lens system; measuring the first irradiation position in accordance with a specimen stage coordinate system; moving the mask stage to a second stage position to situate the opening portion in a second opening position different from the first opening position; measuring the second stage position of the mask stage in accordance with the mask stage coordinate system; irradiating a second charged particle beam to a second irradiation position on the surface of the specimen through the opening of the mask moved together with the mask stage, the second charged particle beam shaped through the opening portion situated in the second opening position and then passing through the objective lens system; measuring the second irradiation position in accordance with a specimen stage coordinate system; and calculating a phase difference between the specimen stage coordinate system and the mask stage coordinate system from the first and second stage positions and the first and second irradiation positions. A control method for a charged particle beam exposure apparatus, according to another aspect of the present invention, comprises: measuring a first stage position of a mask stage of the charged particle beam exposure apparatus in accordance with a mask stage coordinate system with an opening portion of a mask placed on the mask stage being situated in a first opening position; irradiating a first charged particle beam to a first irradiation position on a surface of a specimen through the opening portion of the mask, the first charged particle beam being shaped through the opening portion situated in the first opening position and then passing through an objective lens system of the exposure apparatus; measuring a first irradiation position in accordance with a specimen stage coordinate system; moving the mask stage to a second stage position to situate the opening portion in a second opening position different from the first opening position; measuring the second stage position of the mask stage in accordance with the mask stage coordinate system; irradiating a second charged particle beam to a second irradiation position on the surface of the specimen through the opening portion of the mask moved together with the mask stage, the second charged particle beam being shaped through the opening portion situated in the second opening position and then passing through the objective lens system; measuring the second irradiation position in accordance with a specimen stage coordinate system; and obtaining a demagnification of the objective lens system from the first and second stage positions and the first and second irradiation positions; adjusting the demagnification of the objective lens system corresponding to the obtained demagnification; measuring a rotation angle of a pattern of the charged particle beam shaped through the mask and then irradiated on the surface of the specimen via the objective optical system, after the adjusting; correcting the rotation of the pattern by rotating the mask corresponding to the measured rotation angle; measuring a third stage position of the mask stage in accordance with a mask stage coordinate system after correcting the rotation with the opening portion of the mask being situated in a third opening position; irradiating a third charged particle beam to a third irradiation position on the surface of the specimen through the opening portion situated in the third opening position, the third charged particle beam being shaped through the opening portion situated in the third opening position and then passing through an objective lens system; measuring the third irradiation position in accordance with a specimen stage coordinate system; moving the mask stage to a fourth stage position to situate the opening portion in a fourth opening position different from the third opening position; measuring the fourth stage position of the mask stage in accordance with the mask stage coordinate system; irradiating a fourth charged particle beam to a fourth irradiation position on the surface of the specimen through the opening portion situated in the fourth opening position, the fourth charged particle beam being shaped through the opening portion situated in the fourth opening position and then passing through the objective lens system; measuring the fourth irradiation position in accordance with a specimen stage coordinate system; and obtaining a phase difference between the specimen stage coordinate system and the mask stage coordinate system from the third and fourth stage positions and the third and fourth irradiation positions; and moving the mask stage by correction in accordance with the phase difference. A charged particle beam exposure apparatus according to another aspect of the present invention, comprises: a radiating unit configure to radiate a charged particle beam; an XY mask stage on which a mask having an opening is placed and which moves the mask stage in X and Y directions of a mask stage coordinate system; a mask stage measuring unit configured to measure a position of the XY mask stage in accordance with the mask stage coordinate system; a deflector which deflects the charged particle beam and changes the position of the charged particle beam on a surface of the mask; an objective lens system which demagnifies a pattern of the charged particle beam shaped through the mask and irradiates the specimen with the charged particle beam; a specimen stage on which the specimen is placed and which moves the specimen in X and Y directions of a specimen stage coordinate system; an objective deflector which deflects the charged particle beam and changes the position of the charged particle beam on a surface of the specimen; an irradiation position measuring unit configure to measure an irradiation position of the charged particle beam on the surface of the specimen in accordance with the specimen stage coordinate system; and a demagnification measuring unit configure to measure a demagnification of the objective lens system on the basis of two positions of the XY mask stage measured at different opening positions respectively and a position of the charged particle beam on the surface of the specimen that was shaped through the opening of each of the opening positions. A charged particle beam exposure apparatus according to another aspect of the present invention, comprises: a radiate unit configure to radiate a charged particle beam; an XY mask stage on which a mask having an opening is placed and which moves the mask in X and Y directions of a mask stage coordinate system; a θ mask stage which rotates the mask in an XY plane of the mask stage coordinate system; an opening position measuring unit configure to measure a position of the opening in accordance with the mask stage coordinate system; a deflector which deflects the charged particle beam and changes the position of the charged particle beam on a surface of the mask; an objective lens system which demagnifies a pattern of the charged particle beam shaped through the mask and irradiates a specimen with the charged particle beam; a specimen stage on which the specimen is placed and which moves the specimen in X and Y directions of a specimen stage coordinate system; an objective deflector which deflects the charged particle beam and changes the position of the charged particle beam on a surface of the specimen; an irradiation position measuring unit configure to measure an irradiation position of the charged particle beam on the surface of the specimen in accordance with the specimen stage coordinate system; a rotation angle measuring unit configure to measure a rotation angle of the pattern of the charged particle beam in the objective lens system; a phase measuring portion configure to measure a phase of the mask stage coordinate system with respect to the specimen stage coordinate system based on a position of the XY mask stage measured at two opening positions respectively and a position of the charged particle beam on the surface of the specimen that was shaped through the opening of each of the opening positions; and a driving unit configure to drive the XY mask stage and the θ mask stage corresponding to the measured phase. An embodiment according to the present invention will be described herein below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an electron beam exposure apparatus according to the embodiment of the present invention. A beam emitted from an electron gun 1 is imaged through an illumination lens 2, a projection lens 19, and a demagnification lens (objective lens system) 8, and is finally imaged on a main surface of an objective lens (objective lens system) 9. An image of a first shaping aperture 4 is formed onto a mask 6, and an image thus formed is created on the specimen surface through the demagnification lens 8 and the objective lens 9. An opening portion 21 is provided in the first shaping aperture 4. The dimensional shape of the opening portion 21 is a rectangle having one side of 80 μm, for example. The electron beam emitted from the electron gun 1 can be deflected through a blanking deflector 3, and the beam position on the first shaping aperture 4 can thereby be changed. Referring to FIG. 2, the mask 6 is mounted over a θ stage 20, and the θ stage 20 is mounted on an X stage 14 and a Y stage 15, whereby the mask 6 can be moved. The mask 6 is moved by the X stage 14 and the Y stage 15 in X and Y directions. The positions of the X stage 14 and the Y stage 15 are under positional control of a laser measurement apparatus (laser interferometer) 31. An opening portion 22 is provided in the mask 6, as shown in FIG. 2. In accordance with programs stored in a storage medium 35, a CPU 34 acquires the position of the opening portion 22 from the measurement result of the laser measurement device 31. The dimensional shape of the opening portion 22 is smaller than the size of the first shaping aperture image formed on the mask 6. The dimensional shape of the opening portion 22 is a rectangle having one side of 40 μm, for example. The electron beam shaped through the opening portion 21 of the first shaping aperture can be deflected through a shaping deflector 5, and the beam position on the mask 6 can thereby be changed. The beam passed through the objective lens 9 can be deflected by an objective deflector 18. A marking table 10 is provided on an XY specimen stage 11 and is movable in the X and Y directions in the specimen stage coordinate system. The position of the XY specimen stage 11 is under positional control of a laser measurement device (laser interferometer) 32. As shown in FIG. 3, a cross mark 17 provided on the marking table 10 is made from a beam-reflecting material different from a material of a base 24. For example, the base 24 is made of silicon, whereas the mark 17 is made of a material such as gold or tungsten, for example. The beam position on the marking table 10 can be changed by the objective deflector 18. A beam detector 23 detects electrons reflected from the marking table 10 and secondary electrons. A function is provided that moves the mark 17 to the optical axis position, scans the electron beam to be projected onto the mark 17 by using the objective deflector 18, and then detects the irradiation position of the electron beam in accordance with the distance between the mark and the electron beam, which has been obtained through calculation performed by taking a signal detected by the beam detector 23 into a mark signal processor 33 and a stage position measurement value of the laser measurement device 32. The CPU 34 executes the above-described function in accordance with programs stored in the storage medium 35. In FIG. 1, reference numeral 17 denotes an objective aperture, reference numeral 12 denotes a lens imaging system, and reference numeral 13 denotes a shaped-image imaging system 13. A mask stage phase measurement method and an objective-lens-system demagnification measurement method according to the present embodiment will now be described hereinbelow by using FIGS. 4A, 4B, and 5. The mask stage phase measurement and the objective-lens-system demagnification measurement are executed by the CPU 34 in accordance with programs stored in the storage medium 35. Also, control of the X, Y, and θ mask stages 14, 15, and 20 corresponding to the measurement results is executed by the CPU 34 in accordance with programs stored in the storage medium 35. When measuring a mask stage phase, a rotation angle θ mp of the mask pattern formed through the demagnification lens 8 and the objective lens 9 is preliminarily measured. The θ stage 20 is driven in accordance with the measurement result to bring the mask pattern into to the state in which it is not rotated on the specimen. A method of measuring a mask-pattern rotation angle as θ mp is described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-22349. However, the measurement of the rotation angle θ mp is not necessary in the event of obtaining only the demagnification. The opening portion 22 on the mask 6 is moved to a position A by using the shaping deflector. The positions of the X mask stage 14 and the Y mask stage 15 are measured by a laser measurement device in accordance with the mask stage coordinate system, and the position A of the opening portion 22 is measured from the results thereof. The electron beam shaped through the first shaping aperture opening portion 21 is deflected by the shaping deflector 5 to the opening portion 22 on the mask. The electron beam is deflected to a position where the opening portion 22 is covered overall, as shown in FIG. 4A. The electron beam shaped through the opening portion 22 arrives at a position “a”, as shown in FIG. 4B. The position “a” is measured by a mark scan process performed in accordance with the specimen stage coordinate system. The mark scan process is described in, for example, reference document (S. Nishimura: Jpn. J. Appl. Phys. Vol. 36 (1997), pp. 7517–7522: Evaluation of Shaping Gain Adjustment Accuracy Using Atomic Force Microscope in Variably Shaped Electron-Beam Writing Systems) and Jpn. Pat. Appln. KOKAI Publication No. 10-270337. Subsequently, the opening portion 22 of the mask 6 is moved to a position B (FIG. 4A). The positions of the X mask stage 14 and the Y mask stage 15 are measured by a laser measurement device in accordance with the mask stage coordinate system, and the position B is measured from the results thereof. The electron beam is deflected by the shaping deflector to the opening portion 22 in the position B. The beam shaped through the opening portion 22 is then irradiated to a position b (FIG. 4B) on the specimen. In a manner similar to the above, the position b is measured by the mark scan process in accordance with the specimen stage coordinate system. The electron beam is irradiated to the two positions without altering the settings of the demagnification lens 8, the objective lens 9, and the objective deflector 18. The distance between the position A and the position B of the opening portion on the mask 6 is represented by L. Likewise, the distance between the beam position “a” and the beam position b of each specimen surface is represented by 1. In this case, the relationship can be expressed as “demagnification η=1/L.” In addition, the phase difference between a line segment connecting between the position A and the position B and an Xm axis of the mask stage coordinate system is represented by θ1. Likewise, the phase difference between a line segment connecting between the position “a” and the position b and the X axis of the specimen stage coordinate system is represented by θ2. In this case, a phase θ of the mask stage coordinate system for the specimen stage coordinate system can be expressed as “θ2-θ1” (FIG. 5). The phase differences θ1 and θ2 are thus obtained based on the Xm axis and the X axis. However, the phase differences θ1 and θ2 may be obtained based on a Ym axis and the Y axis. Still alternatively, the phase differences θ1 and θ2 may be obtained based on straight lines having the same tilts in the individual coordinate systems. In addition, according to the above description, the opening positions A and B are individually obtained. However, only the positions of the X mask stage 14 and the Y mask stage 15 may be measured by the laser measurement device in the state in which the opening portions are individually situated in the opening positions A and B. The positional relationship between the two opening positions can be known and the distances and phase differences can be obtained from the X mask stage 14 and the Y mask stage 15 in the individual opening positions. The positions of the X mask stage 14 and the Y mask stage 15 can be accurately obtained. In the present embodiment, the measurement is performed by way of measurement of the positions of the X mask stage 14 and the Y mask stage 15, so that the measurements are each obtained with a measurement accuracy of 1 nm or less (accuracy of an actual measurement device recently used). Accordingly, also the measurement accuracy of the distance L of each of the positions A and B is 1 nm or less. When the distance L is 500 μm, the error is 50 nm in the conventional case. However, in the present invention, the measurement can be implemented with the accuracy of 1 nm or less, so that the demagnification measurement error is 0.0002% (1 nm/500 μm×100). Therefore, in the case where a pattern of 300 μm is imaged on the mask, a linewidth accuracy or positional accuracy of 0.6 nm (i.e., 300 μm×0.0002×0.01=0.6 nm) can be implemented. Where the measurement accuracy of the irradiation position “a” and the irradiation position b is 1 nm (measurement accuracy of a recent exposure apparatus) and the distance is 50 μm, the phase measurement error is 1/50,000 rad (=0.02 mrad). Where the movement amount of the mask stage is 100 mm, the difference at both ends is as extremely small as 2 μm (100 mm×0.02/1,000). As such, the positional movement accuracy of the pattern on the mask 6 is exhibited with a high value of 2 μm. Further, since the differing phase is corrected and the mask stage is moved, when exposure is performed while the mask stage is being moved, the overall deflection range of Y of the shaping deflection becomes effectively usable as a scan width. A control method for the charged particle beam exposure apparatus, which is configured by combining the above-described demagnification measurement and the stage phase measurement will now be described hereinbelow with reference to FIG. 6. Using the method described above, processing is performed to measure a demagnification η (step S101). Then, the measured demagnification η is compared with a desired demagnification η0 (step S102). If the result is not η=η0, the lens system is adjusted so that the desired demagnification can be obtained (step S103). If the measured demagnification η has become the demagnification η0, processing proceeds to next step S104. The arrangement may be such that if a required demagnification has reached an allowable error range, processing shifts to next step S104. Using a well known process, processing is performed to measure a rotation angle η mp of a pattern of an electron beam that has been shaped through a mask and has traveled through the objective lens system (step S104). The process to be used to measure the rotation angle η mp is selected from those of the type that does not rely on the phase difference between the mask stage coordinate system and the specimen stage coordinate system. Then, the η stage 20 is driven corresponding to the rotation angle η mp, and the rotation of the pattern is thereby corrected (step S105). Subsequently, using the above-described method, processing is performed to measure a phase η of the specimen stage coordinate system for the mask stage coordinate system (step S106). When moving the mask stage, after correction is made corresponding to the phase η, and the mask stage is moved (step S107). Where the mask pattern coordinate system is based on (Xm, Ym) and the mask stage coordinates are based on (X, Y), moving the mask stage to satisfy the following relationship enables the mask stage to be moved in conformity with the phase of the specimen stage:ΔX=ΔXm×cos θ+ΔYm×sin θΔY=ΔYm×cos θ−ΔXm×sin θ By performing the movement correction of the XY mask stage, the mask can be moved to an accurate position. Then, by performing adjustment of the demagnification, correction of the rotation angle of the pattern, and movement correction of the mask stage according to the phase θ, the pattern can be accurately imaged on the specimen. The present invention is not limited to the embodiment described above. While having been described by reference to the exemplified electron beam exposure apparatus, the present invention can be adapted also to an ion beam exposure apparatus. In addition, while the stage position is measured by the laser interferometer, there is no limitation thereto; and any other devices may be used as long as they are capable of defining the stage coordinates with high accuracy. The process of measuring the irradiation position of the electron beam is not limited to the mark scan process. For example, as shown in FIG. 7, a process is available in which scan is performed with an electron beam over a mark M sized smaller than a scan range, and the center of gravity of a screen-image object is obtained to thereby measure the beam position. The mark M may be arbitrary, as shown in FIG. 7. A range R larger than the mark M is beam-scanned to thereby obtain data of the screen-image object. The beam position can be obtained by obtaining the data of the screen-image object. The present invention can be practiced by making various other changes without departing from the scope of the invention. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. |
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claims | 1. Method for irradiating a target (102) with a beam (105) approaching target points, involving the following steps:Measuring at least one of the parameters relating to the position of the beam and the intensity of the beam, changing the beam as a function of the at least one measured parameter, particularly as a function of a variance relating to the at least one measured parameter, characterized in that the at least one measured parameter is measured at the most once per target point;wherein the approach of the successive target points is determined by the elapsed time or by the extraction profile. 2. Method according to claim 1, wherein the position of the beam (105) is measured at the most once per target point. 3. Method according to claim 1 or 2, wherein the irradiation process is designed a multiple irradiation with at least two scans, wherein in each of the scans target points are approached successively. 4. Method according to claim 3, wherein the target (102) is moved. 5. Method according to any one of the preceding claims, wherein the at least one measured parameter is measured at the most once for at least two target points. 6. Method according to any one of the preceding claims, wherein the points in time of the measurement of the at least one measured parameter is determined by the elapsed time. 7. Method according to any one of the preceding claims, wherein the beam position is measured as far in the direction of the source of the beam (104) that the cross-section of the beam (105) corresponds to at the most 80% of the cross-section of the beam directly before the target. 8. Method according to any one of the preceding claims, wherein the width of the beam (105) is measured with a beam width measuring module. 9. Device for irradiating a target (102) with a beam (105) approaching target points comprising a measuring device (116, 117) for measuring at least one of the parameters relating to the position (117) of the beam (105) and the intensity (116) of the beam (105), and comprising a sequence control system (112) designed to change the beam (105) as a function of the at least one measured parameter, particularly as a function of a variance relating to the at least one measured parameter, characterized in that the device is designed to measure the at least one measured parameter at the most once per target point;wherein the approach of the successive target points is determined by the elapsed time or by the extraction profile. 10. Device according to claim 9, wherein several measuring devices are connected in series. 11. Device according to claim 9 or 10, designed to perform a method in accordance with claims 1 to 10. 12. Control system (112) for controlling a device in accordance with any one of claims 9 to 11. |
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062748777 | claims | 1. An electron beam exposure apparatus for forming a pattern on a substrate by exposure using a plurality of electron beams, comprising: an electron beam source for generating a plurality of electron beams in accordance with a pattern to be exposed; a reduction electron optical system for imaging the plurality of electron beams emitted by said electron beam source on the substrate; a scanning unit for scanning the plurality of electron beams on the substrate; and a correction unit for correcting imaging positions of the plurality of electron beams on the basis of correction data corresponding to a distribution of the plurality of electron beams. an electron source; a plurality of elementary electron optical systems for forming intermediate images of said electron source; and a control unit for controlling whether each of said plurality of elementary electron optical systems forms an intermediate image of said electron source. said scanning unit divides an exposure region on the substrate into a plurality of fields, switches the field to be exposed by said main deflector, and scans the plurality of electron beams in each field using said sub deflector, and a constant correction amount for imaging positions of the plurality of electron beams is maintained while a pattern is drawn on each field. the number of electron beams coming from the subarray corresponding to an object to be corrected; a distance between the subarray corresponding to the object to be corrected, and another subarray that outputs the electron beams; and the number of electron beams coming from the other subarray. imaging a plurality of electron beams, which are emitted by an electron beam source in accordance with a pattern to be exposed, via a reduction electron optical system, and scanning the plurality of electron beams on the substrate; and correcting imaging positions of the plurality of electron beams on the basis of correction data corresponding to a distribution of the plurality of electron beams in synchronism with the scan. an electron source; a plurality of elementary electron optical systems for forming intermediate images of said electron source; and a control unit for controlling whether each of said plurality of elementary electron optical systems forms an intermediate image of said electron source. a constant correction amount for imaging positions of the plurality of electron beams is maintained while a pattern is drawn on each field. the number of electron beams coming from the subarray corresponding to an object to be corrected; a distance between the subarray corresponding to the object to be corrected, and another subarray that outputs the electron beams; and the number of electron beams coming from the other subarray. inputting data that defines a pattern to be exposed on a substrate; and generating correction data used for correcting imaging positions of a plurality of electron beams on the basis of the input data. inputting data that defines a pattern to be exposed on a substrate; and generating correction data used for correcting imaging positions of a plurality of electron beams on the basis of the input data. an electron beam source which generates a plurality of electron beams in accordance with a pattern to be exposed; a reduction electron optical system which images the plurality of electron beams emitted by said electron beam source on the substrate; a scanning unit which scans the plurality of electron beams on the substrate; and a correction unit which corrects imaging positions of the plurality of electron beams on the basis of a distribution of the plurality of electron beams. an electron source; a plurality of elementary electron optical systems which form intermediate images of said electron source; and a control unit which controls whether each of said plurality of elementary electron optical systems forms an intermediate image of said electron source. said scanning unit divides an exposure region on the substrate into a plurality of fields, switches the field to be exposed by said main deflector, and scans the plurality of electron beams in each field using said sub deflector, and a constant correction amount for imaging positions of the plurality of electron beams is maintained while a pattern is drawn on each field. the number of electron beams coming from the subarray corresponding to an object to be corrected; a distance between the subarray corresponding to the object to be corrected, and another subarray that outputs the electron beams; and the number of electron beams coming from the other subarray. 2. The apparatus according to claim 1, wherein said correction unit adjusts a focal point position of said reduction electron optical system on the basis of the correction data. 3. The apparatus according to claim 1, wherein said electron beam source comprises: 4. The apparatus according to claim 3, wherein said correction unit adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system on the basis of the correction data. 5. The apparatus according to claim 3, wherein said correction unit adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system, and a focal point position of said reduction electron optical system on the basis of the correction data. 6. The apparatus according to claim 3, wherein a subarray is formed by a matrix of a plurality of elementary electron optical systems and an entire array is formed by a matrix of a plurality of subarrays. 7. The apparatus according to claim 6, wherein said correction unit corrects imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of the correction data. 8. The apparatus according to claim 6, wherein said correction unit commonly corrects imaging positions of electron beams coming from all the elementary electron optical systems of the entire array by adjusting a focal point position of said reduction electron optical system on the basis of the correction data, and adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of differences between the common correction amount and appropriate correction amounts. 9. The apparatus according to claim 1, wherein said scanning unit comprises a main deflector and a sub deflector for deflecting electron beams emitted by said electron beam source, 10. The apparatus according to claim 1, wherein said correction unit dynamically corrects imaging positions of the plurality of electron beams emitted by said electron beam source on the basis of the correction data. 11. The apparatus according to claim 10, wherein said correction unit corrects the imaging positions of the plurality of electron beams on the basis of the correction data each time a positional relationship between the plurality of electron beams emitted by said electron beam source and the substrate is settled. 12. The apparatus according to claim 6, wherein the correction data is a function having, as variables, at least: 13. The apparatus according to claim 6, wherein the correction data is a function having, as a variable, at least a spacing of electron beams emitted by said electron source. 14. The apparatus according to claim 1, further comprising a calculation unit for generating correction data used for correcting imaging positions of the plurality of electron beams on the basis of data that defines the pattern to be exposed on the substrate. 15. An electron beam exposure method for forming a pattern on a substrate by exposure using a plurality of electron beams, comprising the steps of: 16. The method according to claim 15, wherein the correcting step includes the step of adjusting a focal point position of said reduction electron optical system on the basis of the correction data. 17. The method according to claim 15, wherein said electron beam source comprises: 18. The method according to claim 17, wherein the correcting step includes the step of adjusting imaging positions of the intermediate images in an axial direction of said reduction electron optical system on the basis of the correction data. 19. The method according to claim 17, wherein the correcting step includes the step of adjusting imaging positions of the intermediate images in an axial direction of said reduction electron optical system, and a focal point position of said reduction electron optical system on the basis of the correction data. 20. The method according to claim 17, wherein a subarray is formed by a matrix of a plurality of elementary electron optical systems and an entire array is formed by a matrix of a plurality of subarrays. 21. The method according to claim 20, wherein the correcting step includes the step of correcting imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of the correction data. 22. The method according to claim 20, wherein the correcting step includes the step of commonly correcting imaging positions of electron beams coming from all the elementary electron optical systems of the entire array by adjusting a focal point position of said reduction electron optical system on the basis of the correction data, and adjusting imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of differences between the common correction amount and appropriate correction amounts. 23. The method according to claim 15, wherein an exposure region on the substrate is divided into a plurality of fields, the field to be exposed is switched by a main deflector, and the plurality of electron beams in each field is scanned using a sub deflector, and 24. The method according to claim 15, wherein the correcting step includes the step of dynamically correcting imaging positions of the plurality of electron beams emitted by the electron beam source on the basis of the correction data. 25. The method according to claim 24, wherein the correcting step includes the step of correcting the imaging positions of the plurality of electron beams on the basis of the correction data each time a positional relationship between the plurality of electron beams emitted by the electron beam source and the substrate is settled. 26. The method according to claim 20, wherein the correction data is a function having, as variables, at least: 27. The method according to claim 20, wherein the correction data is a function having, as a variable, at least a spacing of electron beams emitted by said electron beam source. 28. The method according to claim 15, further comprising a step of generating correction data used for correcting imaging positions of the plurality of electron beams on the basis of data that defines the pattern to be exposed on the substrate. 29. A method of generating data for controlling an electron beam exposure apparatus of claim 1, comprising the steps of: 30. The method according to claim 29, wherein the correction data generation step includes a step of generating the correction data on the basis of a distribution of electron beams that make up the plurality of electron beams emitted by an electron beam source. 31. The method according to claim 29, wherein the correction data generation step includes a step of generating the correction data for correcting the imaging positions of the plurality of electron beams when a positional relationship between the plurality of electron beams and the substrate is settled. 32. A computer readable program for generating data for controlling an electron beam exposure apparatus of claim 1, comprising the steps of: 33. The program according to claim 32, wherein the correction data generation step includes a step of generating the correction data on the basis of the number of electron beams that make up the plurality of electron beams emitted by an electron beam source. 34. The program according to claim 32, wherein the correction data generation step includes a step of generating the correction data on the basis of a distribution of electron beams that make up the plurality of electron beams emitted by an electron beam source. 35. The method according to claim 32, wherein the correction data generation step includes a step of generating the correction data for correcting the imaging positions of the plurality of electron beams when a positional relationship between the plurality of electron beams and the substrate is settled. 36. A method of manufacturing a device using an electron beam exposure apparatus of claim 1 in some steps. 37. A method of manufacturing a device using an electron beam exposure method of claim 15 in some steps. 38. An electron beam exposure apparatus which forms a pattern on a substrate by exposure using a plurality of electron beams, comprising: 39. The apparatus according to claim 38, wherein said correction unit adjusts a focal point position of said reduction electron optical system on the basis of the distribution of the plurality of electron beams. 40. The apparatus according to claim 38, wherein said electron beam source comprises: 41. The apparatus according to claim 40, wherein said correction unit adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system on the basis of the distribution of the plurality of electron beams. 42. The apparatus according to claim 40, wherein said correction unit adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system, and a focal point position of said reduction electron optical system on the basis of the distribution of the plurality of electron beams. 43. The apparatus according to claim 40, wherein a subarray is formed by a matrix of a plurality of elementary electron optical systems and an entire array is formed by a matrix of a plurality of subarrays. 44. The apparatus according to claim 43, wherein said correction unit corrects imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of the distribution of the plurality of electron beams. 45. The apparatus according to claim 43, wherein said correction unit commonly corrects imaging positions of electron beams coming from all the elementary electron optical systems of the entire array by adjusting a focal point position of said reduction electron optical system on the basis of the distribution of the plurality of electron beams, and adjusts imaging positions of the intermediate images in an axial direction of said reduction electron optical system in units of subarrays on the basis of differences between the common correction amount and appropriate correction amounts. 46. The apparatus according to claim 38, wherein said scanning unit comprises a main deflector and a sub deflector which deflect electron beams emitted by said electron beam source, 47. The apparatus according to claim 38, wherein said correction unit dynamically corrects imaging positions of the plurality of electron beams emitted by said electron beam source on the basis of the distribution of the plurality of electron beams. 48. The apparatus according to claim 47, wherein said correction unit corrects the imaging positions of the plurality of electron beams on the basis of the distribution of the plurality of electron beams each time a positional relationship between the plurality of electron beams emitted by said electron beam source and the substrate is settled. 49. The apparatus according to claim 43, wherein the distribution of the plurality of electron beams is expressed by a function having, as variables, at least: 50. The apparatus according to claim 43, wherein the distribution of the plurality of electron beams is expressed by a function having, as a variable, at least a spacing of electron beams emitted by said electron source. |
summary | ||
summary | ||
056378785 | claims | 1. A method for the electron-beam irradiation of gemstones for color enhancement comprising the steps of: placing the gemstones in an oscillating means provided with coolant means; circulating a coolant through said coolant means; initiating an oscillating motion along a horizontal y-axis in said oscillating means; directing an oscillating electron-beam produced by an electron-beam source having the power of about 10 kW to about 500 kW onto the gemstones and wherein the oscillating electron beam is along a z-axis; maintaining the circulation of coolant through said coolant means until the gemstones are cooled to ambient temperature; and removing uniformly colored gemstones. placing the topaz stones in an oscillating means provided with coolant means; circulating a coolant through said coolant means; initiating an oscillating motion along a horizontal y-axis in said oscillating means; directing an oscillating electron-beam produced by an electron-beam source have the power of 50 kW at between about 3 MeV to 5 MeV to provide a dosage of between 4 to 25 girarads for a period of about 24 hours onto the topaz stones and wherein the oscillating electron beam is along a z-axis; maintaining the circulation of coolant through said coolant means until the topaz stones are cooled to ambient temperatures; and removing uniformly colored topaz stones. 2. The method of claim 1 wherein said gemstones are selected from diamonds, beryl, quartz, tourmaline, sapphire, and dark pearls. 3. The method of claim 1 wherein said gemstone is topaz. 4. The method of claim 1 wherein said electron-beam radiation is produced from an electron-beam source having the power of between 3 MeV to 5 MeV to provide a dosage of between about 4 to 25 gigarads for a period of about 15 to 500 hours. 5. The method of claim 1 wherein the rate of oscillation for said oscillating means is from about 5 to about 20 feet per minutes. 6. The method of claim 1 wherein said cooling means is a fluid. 7. The method claim 6 wherein said fluid is water. 8. A method for E-beam irradiation of topaz stones for color enhancement comprising the steps of: |
044252951 | claims | 1. A method for generating steady-state toroidal current in a toroidal plasma comprising the steps of: preparing a toroidal plasma immersed in a toroidal magnetic field, and injecting rf energy into said plasma such that the rf energy comprises a spectrum of waves traveling substantially in a toroidal direction either substantially parallel or substantially anti-parallel to said toroidal magnetic field, said waves having substantially no parallel momentum, where said rf energy is phased such as to increase preferentially the cyclotron motion of electrons traveling in one of said toroidal direction said electrons satisfying the resonance condition .omega.-k.sub..parallel. v.sub..parallel. =n.phi..sub.e, where .omega. is the wave frequency, k.sub..parallel. is the wave parallel wavenumber, v.sub..parallel. is the electron parallel velocity, .omega..sub.e is the electron gyrofrequency, n is an integer, and said electrons being selected from the group consisting essentially of electrons substantially on the magnetic axis or having an energy in the range of 10 to 50 times the thermal electron energy. means for preparing a toroidal plasma immersed in a toroidal magnetic field, and means for injecting rf energy into said plasma such that the rf energy comprises a spectrum of waves traveling substantially in a toroidal direction either substantially parallel or substantially anti-parallel to said toroidal magnetic field, said waves having substantially no parallel momentum, where said rf energy is phased such as to increase preferentially the cyclotron motion of electrons traveling in one of said toroidal direction said electrons satisfying the resonance condition .omega.-k.sub..parallel. v.sub..parallel. =n.OMEGA..sub.e, where .omega. is the wave frequency, k.sub..parallel. is the wave parallel wavenumber, v.sub..parallel. is the electron parallel velocity, .OMEGA..sub.e is the electron gyrofrequency, n is an integer, and said electrons being selected from the group consisting essentially of electrons substantially on the magnetic axis or having an energy in the range of 10 to 50 times the thermal electron energy. 2. Method according to claim 1 wherein said plasma is prepared in a tokamak device wherein said generated toroidal current is of long duration and of sufficient intensity so that it provides a poloidal magnetic field sufficient for steady-state confinement of said plasma. 3. Method according to claim 2 where said rf energy is carried by the extraordinary plasma waves which are launched into the high-field side of said tokamak by means of waveguides carrying waves with electric field polarized substantially perpendicular to said toroidal magnetic field, wherein said waves have frequency .omega. in the range .OMEGA..sub.2 /2<.omega.<.OMEGA..sub.e, where .OMEGA..sub.e is the cyclotron frequency of resonant electrons in said toroidal magnetic field at some interior location in the plasma. 4. Method according to claim 3 wherein the axes of said waveguides are titled in the vertical plane as well as in the horizontal plane, so that said rf energy is preferentially absorbed by faster electrons than would be possible without said tilt, where said faster electrons typically have energy in the range of 10 to 50 times the thermal electron energy. 5. Method according to claim 2 wherein said rf energy is carried by the ordinary plasma wave which are launched into the low-field side of the tokamak by means of waveguides carrying waves with electric field polarized substantially parallel to said toroidal magnetic field, wherein said waves have frequency .omega. greater than .OMEGA..sub.e. 6. Method according to claim 5 wherein the axes of said waveguides are titled in the vertical plane as well as in the horizontal plane, so that said rf energy is preferentially absorbed by faster electrons than would be possible without sald tilt, where said faster electrons typically have energy in the range of 10 to 50 times the thermal electron energy. 7. Method according to claim 4 wherein said rf energy is carried by the extraordinary plasma wave. 8. Method according to claim 6 wherein said rf energy is carried by the ordinary plasma wave. 9. A system for generating steady-state toroidal current in a toroidal plasma comprising: 10. System according to claim 9 wherein said plasma is prepared in a tokamak device wherein said generated toroidal current is of long duration and of sufficient intensity so that it provides a poloidal magnetic field sufficient for steady-state confinement of said plasma. 11. System according to claim 10 where said rf energy is carried by the extraordinary plasma waves which are launched into the high-field side of said tokamak by means of waveguides carrying waves with electric field polarized substantially perpendicular to said toroidal magnetic field, wherein said waves have frequency .omega. in the range .OMEGA..sub.e /2<.omega.<.OMEGA..sub.e, where .OMEGA..sub.e is the cyclotron frequency of resonant electrons in said toroidal magnetic field at some interior location in the plasma. 12. System according to claim 11 wherein the axes of said waveguides are tilted in the vertical plane as well as in the horizontal plane, so that said rf energy is preferentially absorbed by faster electrons than would be possible without said tilt, where said faster electrons typically have energy in the range of 10 to 50 times the thermal electron energy. 13. System according to claim 10 wherein said rf energy is carried by the ordinary plasma wave which are launched into the low-field side of the tokamak by means of waveguides carrying waves with electric field polarized substantially parallel to said toroidal magnetic field, wherein said waves have frequency .omega. greater than .OMEGA..sub.e. 14. System according to claim 13 wherein the axes of said waveguides are tilted in the vertical plane as well as in the horizontal plane, so that said rf energy is preferentially absorbed by faster electrons than would be possible without said tilt, where said faster electrons typically have energy in the range of 10 to 50 times the thermal electron energy. 15. System according to claim 12 wherein said rf energy is carried by the extraordinary plasma wave. 16. Method according to claim 14 wherein said rf energy is carried by the ordinary plasma wave. |
abstract | Fluid element device including fluid elements arranged in a matrix configuration having rows and columns with the level of fluid in each fluid element being controllable by electric force. The fluid elements include capillary tubes having electrode segments electrically insulated from one another such that each segments is receivable of a different voltage. A first voltage delivery circuit applies voltage to selected fluid elements in one or more rows of fluid elements and a second voltage delivery circuit applies voltage to selected fluid elements in one or more columns of fluid elements. The fluid level rises in the selected fluid elements to which voltage is applied by both the first and second voltage delivery circuits. The capillary tubes are structured and arranged such that the level of fluid in the selected elements can be retained independent of the application of voltage by the first and second voltage delivery circuits. |
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053902211 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a pertinent detail of a portion of a reactor core is shown. Control rod drive housing H has fuel support casting C supported thereon. Fuel support casting C includes arm 16 which orients casting C with respect to pin 14 in core plate P. Core plate P divides high pressure lower plenum L from core R, preserving the necessary pressure differential barrier to cause the controlled circulation within the many individual fuel bundles of the reactor. Fuel support casting C includes four apertures 20 onto which four fuel bundles B at their respective lower tie plate assemblies T are placed. Each lower tie plate assembly T is disposed to cause its inlet nozzle N to communicate to one of the apertures 20 of the fuel support casting. Fuel support casting C also includes apertures through which control rods 22 penetrate to the interstices of the four fuel bundles sitting on top of the fuel support casting C. Since the action of the control rods is not important with respect to this invention, further discussion of this aspect of the reactor will not be included. Each fuel bundle includes a plurality of upstanding fuel rods 42 surrounded by a channel 44. Spacers 46 surround the fuel rods 42 discretely at several elevations and constitute locations where debris can be trapped, dynamically fretted by the passing coolant, and cause damage to fuel rods 42. Accordingly, and in this disclosure, the filter of this invention is located in any of the illustrated plenums to the rod supporting grid G of the lower tie plate (See FIGS. 2, 3 and 4), or in the fuel support casting C. In the following illustrations, the debris catchers of this invention will be illustrated with location in the lower tie plate flow plenum between the inlet orifice or nozzle N and the rod supporting grid G. Remembering further that only four out of a possible 750 fuel bundles are illustrated, it will be understood that the pressure drop across core plate P is important. Accordingly, a review of the pressure drop within a boiling water nuclear reactor can be instructive. First, and through an orifice (not shown) in the fuel support casting C, an approximate 7 to 8 psi pressure drop occurs at typical 100% power/100% flow operating conditions. This pressure drop is utilized to ensure uniform distribution of bundle coolant flow through the many (up to 750) fuel bundles within a boiling water nuclear reactor. Secondly, at in the lower tie plate of the fuel bundles on each fuel support casting C, approximately 11/2 psi of pressure drop occurs. This pressure drop is a result primarily of the changes in flow velocity and direction occurring through this complex geometry structure. Finally, and as the coolant rises and generates steam within the fuel bundle, approximately 10 to 12 psi of pressure drop is incurred. This pressure drop is distributed throughout the length of the fuel bundle--and is important to the operating stability of both the individual fuel bundles and the collective fuel bundles constituting the core of the nuclear reactor. The reader should understand that the summary of pressure drop given above is an over simplification. This is a very complex part of the design and operation of a nuclear reactor. Having said this much, one point must be stressed. Flow resistance within the individual fuel bundles of a boiling water must remain substantially unchanged. Accordingly, if apparatus for preventing debris entrainment into the fuel bundles is going to be utilized, appreciable change in overall fuel bundle flow resistance should be avoided. Regarding the overall performance of a debris catcher or trap, such structure must be capable of trapping particles small enough to be entrained but large enough to enter through the lower tie plate grid G and in between the fuel rods 42. Such a structure must be structurally sound and especially avoid any failure resulting in loose parts. It is desired that the structure trap and retain debris particles. At the same time, adverse flow conditions into the fuel bundle should not be generated. Finally, the filter should be such that it is not possible under any circumstances for the filter to become clogged and cause appreciable obstruction to the total flow into the fuel bundle B. Accordingly, and in the description of the specific embodiments that follow it will be seen that we utilize a filter structure that does not constitute a continuum of structure across the particular flow plenum being utilized. In each case--assuming that the perforate portions of the filter become complete clogged--it will be seen that unobstructed water coolant flow paths are preserved to the fuel rods. The following designs direct debris particles into screen or mesh paths that intercept only a fraction of the total flow path. This minimizes pressure drop. At the same time, solid portions can be incorporated to the mesh structures to impart required resistance to failure. Referring to FIG. 2, a side elevation section schematic of a lower tie plate assembly T is shown. This lower tie plate includes four walls 52 defining a substantially square volume with tapered substantially conical wall 54 truncated at inlet nozzle N. Nozzle N includes a bail 60 over the nozzle forming the lower most structure of the fuel bundle. In the structure illustrated in FIG. 2, there is included a debris collector ring 70. Ring 70 fastens interiorly of plenum P surrounding nozzle N and projects upwardly into the volume of plenum P. As will be realized hereafter, ring 70 forms between the inside of conical wall 54 and the outside surface of ring 70 a trap for debris. Secondly, located above or preferably within nozzle N is static swirl vane 80. Swirl vane 80 imparts an upwardly spiralling flow to coolant flowing through nozzle N into plenum P. Such spiral flow classifies heavier debris to the outside of ring 70 with the lighter coolant flowing upwardly through rod supporting grid G. Finally, mesh pick off filter 90 including horizontal portion 92 and downward depending ring 94 is placed centrally of the structure. Preferably, the structure is perforate for allowing fluid flow through the mesh pick off structure; it will be understood that portions of this structure can be solid if desired. Operation is easy to understand. Water coolant including debris enters nozzle N and has a swirling motion imparted by a static swirl vane 60. Above the static swirl vane there is an open central flow path. Heavier debris--typically metal particles having 8 to 10 times the density of water--are classified to the exterior of plenum P and trapped--either by ring 70 or overlying mesh pick off filter 90. Debris is retained at these locations. At the same time, the open central flow path is not obstructed by a continuum of filter structure. Obstruction of the filter structure causing impeding of flow to the fuel rods 42 cannot occur. It is anticipated that the length of pitch of static swirl device 80 will be adjusted for optimum performance. Further, dimension of debris collector ring 70 and mesh pick off filter 90 will likewise be adjusted for optimum trapping of debris. It is to be noted that upon cessation of flow, debris trapped at mesh pick off filter 90 will fall. In such a fall, trapping of the debris will occur at ring 70. Thus, and in the case of the illustrated fuel bundle B, with removal of the fuel bundle removal of the debris will occur. Referring to FIG. 3, a structure similar to FIG. 2 is illustrated with the exception of cone deflector 100. This deflector peripherally diverts fluid to the plenum periphery at the cone 100. This cone can be constructed of mesh and/or solid material. Cone 100 extends beyond ring 70 and terminates in depending mesh ring 102. Depending mesh ring 102 is outside of ring 70. Operation is easy to understand. Debris entraining water coolant is deflected at cone 100 with debris being trapped either at debris collector ring 102 or the mesh pick off filter. Debris falling from either location--either during coolant flow or after coolant flow has ceased--will fall into the outside of ring 70 and be trapped by ring 70 within lower tie plate T. Referring to FIG. 4, a structure similar to that illustrated in FIGS. 2 and 3 is illustrated in which upper filter layer 124 and lower filter layer 114 impart the circuitous flow path to the passing fluid. Lower filter structure 114 includes cone filter 110 having a solid central ring 11 to define a central flow path. A peripherally sloping perforate cone 110 truncated at the central flow paths extends to perforate ring 113. Upper filter layer 124 consists of peripheral annular perforate filter section 120 and central inverted conical basket 122. Conical basket 122 includes an inverted perforate cone section 126 and a depending perforate ring section 127. In operation, it will be seen that the disclosed design includes offset over-under placement of layered traps for debris particles. At the same time, open flow passages are preserved so that complete debris or corrosion clogging of the filter cannot occur. The sloped profile of the filter assists migration of the trapped debris to the collecting corners of the upper filter layer 124. Debris falling from these upper layer 124 corners is either trapped by lower filter layer 114 or optional ring 70. In the schematic of the apparatus herein illustrated, a ring, cone, and annulus structure is shown. The reader will understand that a straight structure across plenum P having the overall side elevation of the ring structure illustrated could as well be used. |
046577327 | claims | 1. A high temperature nuclear reactor barrier system comprising a plurality of barriers to prevent a release of radioactivity wherein; a first barrier comprises a coating over fissionable material in reactor fuel elements; a second barrier comprises a graphite matrix in which said fuel elements are embedded; a third barrier comprises a pressure vessel metal liner; a fourth barrier comprises in combination a concrete body of a prestressed concrete pressure vessel, a plurality of closure devices affixed to passages in the concrete pressure vessel, wherein said closure devices include inner and outer covers defining intermediate spaces therebetween, said inner covers forming a primary gas seal, and a plurality of conduits connected to said intermediate spaces for removing exhaust leakage of primary gas passing into said intermediate space; means for retention of fission products in said conduits, wherein said means for retention of fission products is a filter and further comprising means for exhausting filtered gas in said conduits outside said prestressed concrete pressure vessel, said means for exhausting comprises an exhaust stack attached to said conduits downstream from said filter and extending outside said prestressed concrete pressure vessel; and wherein the conduits are positioned within the concrete body of the prestressed concrete pressure vessel up to their connection with the exhaust stack. a reactor enclosed in a prestressed concrete pressure vessel wherein said pressure vessel exhibits a plurality of passages; a barrier system comprises a plurality of barriers to prevent a release of radioactivity wherein; a first barrier comprises a coating over fissionable material in spherical fuel elements utilized by said reactor; a second barrier comprises a graphite matrix in which said fuel elements are embedded; a third barrier comprises a metal liner clad to an interior surface of said pressure vessel; and a fourth barrier comprises in combination, a concrete body of the prestressed concrete pressure vessel, a plurality of closure devices affixed to the outer passages, said closure devices include inner and outer covers defining defining intermediate spaces therebetween, said inner covers forming primary gas seals, a plurality of conduits connected to said intermediate spaces for removing exhaust leakage of primary gas passing into said intermediate space; means for retention of fission products in said conduits wherein said means for retention of fission products is a filter and further comprising means for exhausting filtered gas in said conduits outside said prestressed concrete pressure vessel; and wherein the filters are located in the concrete body of the prestressed concrete pressure vessel. a first barrier comprises a coating over fissionable material in reactor fuel elements; a second barrier comprises a graphite matrix in which said fuel elements are embedded; a third barrier comprises a pressure vessel metal liner; and a fourth barrier comprises in combination a concrete body of a prestressed concrete pressure vessel, a plurality of closure devices affixed to passages in the concrete pressure vessel, wherein said closure devices include inner and outer covers defining intermediate spaces therebetween, said inner covers forming a primary gas seal, a plurality of conduits connected to said intermediate spaces for removing exhaust leakage of primary gas passing into said intermediate space, and means for retention of fission products in said conduits wherein said means for retention of fission products is a filter and further comprising means for exhausting filtered gas in said conduits outside said prestressed concrete pressure vessel, and wherein the filters are located in the concrete body of the prestressed concrete pressure vessel. 2. A barrier system as in claim 1, wherein the prestressed concrete pressure vessel operates as a protective installation which can withstand collision with aircraft. 3. A high temperature reactor installation comprising: 4. A high temperature reactor installation as in claim 3, wherein said means for exhausting comprises an exhaust stack attached to said conduits downstream from said filter and extending outside said prestressed concrete pressure vessel. 5. A high temperature reactor installation as in claim 4, wherein the conduits are positioned in the concrete body of the prestresed concrete pressure vessel up to their connection with the exhaust stack. 6. A high temperature reactor installation as in claim 3, wherein the prestressed concrete pressure vessel operates as a protective installation which can withstand collision with aircraft. 7. A high temperature nuclear reactor barrier system comprising a plurality of barriers to prevent a release of radioactivity wherein: 8. A barrier system as in claim 7, wherein said means for exhausting comprises an exhaust stack attached to said conduits downstream from said filter and extending outside said prestressed concrete pressure vessel. 9. A barrier system as in claim 8, wherein the conduits are positioned within the concrete body of the prestressed concrete pressure vessel up to their connection with the exhaust stack. 10. A barrier system as in claim 7, wherein the prestressed concrete pressure vessel is a protective installation which can withstand an aircraft collision. |
description | The present invention relates generally to the field of electromagnetic trap systems and more particularly to trapping and cooling the trapped object using a parallel dipole line trap system. Various kinds of electromagnetic trap systems are very important in physics. They allow isolation of particles or matter that enable many kinds of precision measurements and exploration of fundamental phenomena. Examples are the Penning trap, quadrupole ion trap, optical trap and magneto-optic-trap. The uses of these electromagnetic trap systems have broad applications for fundamental physics and technology. The Penning trap allows high precision measurement of fundamental parameters such as the electron gyromagnetic factor. The magneto-optic-trap (MOT) system allows trapping and cooling of atoms to remarkably low temperature. This system allows the creation of a new state of matter such as a Bose-Einstein condensate. Active cooling systems similar to the cold atom system in a MOT can also be achieved for a macroscopic object. An example is the active cold-mirror system in the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment that allows precision interferometric measurements by lowering the vibration noise floor. Therefore, realizing an active cooling system in an electromagnetic trap has a broad and fundamental interest in physics. According to an embodiment, a method for decreasing the motion of a levitated diamagnetic rod trapped between a pair of dipole line magnets, the method comprising: measuring a displacement signal of a diamagnetic rod based on a light source and one or more photodetectors; calculating a velocity signal and a drive polarity, based on the displacement signal, by a differentiator circuit wherein the velocity signal is sent to a proportional-integral-derivative (PID) control loop, wherein the PID control loop generates an output signal; responsive to a positive drive polarity, adjusting a first electrode based on the output signal; and responsive to a negative drive polarity, adjusting a second electrode based on the output signal. According to another embodiment, an apparatus for decreasing random motions of a levitated diamagnetic cylinder, the apparatus comprising: a vacuum chamber; a plurality of dipole line magnets disposed within the vacuum chamber; a light source disposed within the vacuum chamber; one or more photodetectors disposed within the vacuum chamber; a diamagnetic rod disposed within the vacuum chamber; a second electrode and a first electrode disposed within the vacuum chamber and connected to an external power source; a control computer comprising a proportional-integral-derivative (PID) control loop; an input circuit connected to the one or more photodetectors, a differentiator circuit and inputs associated with the PID control loop; a differentiator circuit to calculate the velocity signal; and an output circuit connected to the first electrode, the second electrode and outputs associated with the PID control loop. According to another embodiment, a system for decreasing random motions of a levitated diamagnetic cylinder, the system comprising: a vacuum chamber; a plurality of dipole line magnets disposed within the vacuum chamber; a light source disposed within the vacuum chamber; one or more photodetectors disposed within the vacuum chamber; a diamagnetic rod disposed within the vacuum chamber; a second electrode and a first electrode disposed within the vacuum chamber and connected to an external power source; a control computer comprising a proportional-integral-derivative (PID) control loop; an input circuit connected to the one or more photodetectors and inputs associated with the PID control loop; a differentiator circuit to calculate the velocity signal; an output circuit connected to the first electrode, the second electrode and outputs associated with the PID control loop; and a test server connected to the control computer over a network. Embodiments of the present invention recognize that improvements to precision measurements of existing magnetic traps or the creation of new states of matter can be made by using a parallel dipole line (PDL) trap system. A PDL trap system can trap a diamagnetic object. The trap consists of a magnetic parallel dipole line system made of a pair of transversely magnetized (or diametric) cylindrical magnets or dipole line magnets that naturally attract each other and align their magnetization. A diamagnetic cylindrical object such as graphite can be trapped at the center. Detailed description of embodiments of the claimed structures and methods are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the claimed structures and methods that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments is intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the methods and structures of the present disclosure. References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described. The key discovery and the central feature of the PDL trap is the existence of a field confinement effect that forms a “camelback magnetic energy potential” along the longitudinal (z-axis); i.e. a magnetic field enhancement near the edge of the dipole line which occurs when the length of the system is larger than a critical length, i.e. L>LC, where, in an experimental context using the diametric magnet system, LC˜2.5 a where a is the radius of the magnet. This camelback potential effect is a natural effect of electromagnetism found in a system of two lines of transverse dipoles whose length is beyond the critical length. (See Gunawan et al., “The one-dimensional camelback potential in the parallel dipole line trap: Stability conditions and finite size effect”, J. Appl. Phys. 121, 133902 (2017)). By adding a pair of drive electrodes around the trapped object one could manipulate the position of the trapped object. This makes the PDL trap serve as a functional electromagnetic trap device where one could trap, drive and detect the trapped object in the trap. In a mechanical oscillator, the vibration amplitude is given as z n = 4 k B T Qm ω 0 3 ( 1 ) here kB is the Boltzmann constant, Q is the quality factor, m is the mass of the object and w is the angular frequency of the oscillator and T is the temperature. For example, a PDL trap could have system parameters: rod radius b=0.65 mm, length l=10 mm, density ρ=1750 kg/m3, camelback oscillation frequency f=0.64 Hz, and oscillator quality factor Q=15,000 (in vacuum) at room temperature T=298 K. Then we have: zn=27 pm/Hz0.5. The phonon populations in the system can be calculated as: N = k z z _ n 2 2 ℏω 0 = m ω 0 z _ n 2 2 ℏ , where z _ n 2 = z n 2 f BW ( 2 ) Assuming an operation bandwidth fBW˜1 Hz in the system (quenching all sidebands), then the starting phonon population (before cooling is activated) is approximately: N˜3.2×108. This phonon population N is proportional to zn2 and to the “effective” temperature T. Therefore, by activating the electromagnetic cooling system, the vibration amplitude can be quenched and the effective temperature, T, is reduced. The present embodiment also utilizes a PDL trap system with a graphite rod as the trapped object. The system is equipped with a pair of electrodes (see FIG. 2A), differential photodetectors and a feedback loop electronic circuit using a proportional-differential-integral (PID) system. The differential photodetectors detect the displacement of the rod and the signal is fed to the differential amplifier, a differentiator and PID feedback controller and electrode voltage drive the electrodes to counteract the movement of the rod. As a result, smaller vibrations are obtained. Thus the present embodiment describes a system to decrease the physical motions of a trapped object. Since the effective rod temperature is proportional to the square of the vibration amplitude, the object effective temperature is lowered, even if the surrounding ambient temperature is not. This cooling effect is important as it allows a lower displacement noise floor (zN) that will benefit many applications using PDL traps such as seismometer, inclinometer and gravimeter allowing them to measure a smaller range of signals or achieving better measurement accuracy. FIG. 1 is a functional block diagram illustrating a PDL trap data processing environment, generally designated 100, in accordance with one embodiment of the present invention. FIG. 1 provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments may be implemented. Many modifications to the depicted environment may be made by those skilled in the art without departing from the scope of the invention as recited by the claims. PDL trap data processing environment 100 includes magnetic trap control server 110 and magnetic trap device 120, all interconnected over network 103. Network 103 can be, for example, a telecommunications network, a local area network (LAN), a wide area network (WAN), such as the Internet, or a combination of the three, and can include wired, wireless, or fiber optic connections. Network 103 can include one or more wired and/or wireless networks that are capable of receiving and transmitting data, voice, and/or video signals, including multimedia signals that include voice, data, and video information. In general, network 103 can be any combination of connections and protocols that will support communications between magnetic trap control server 110, magnetic trap device 120, and other computing devices (not shown) within PDL trap data processing environment 100. Magnetic trap control server 110 can be a standalone computing device, a management server, a web server, a mobile computing device, or any other electronic device or computing system capable of receiving, sending, and processing data. In other embodiments, magnetic trap control server 110 can represent a server computing system utilizing multiple computers as a server system, such as in a cloud computing environment. In another embodiment, magnetic trap control server 110 can be a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), a desktop computer, a personal digital assistant (PDA), a smart phone, or any other programmable electronic device capable of communicating with magnetic trap device 120, and other computing devices (not shown) within PDL trap data processing environment 100 via network 103. In another embodiment, magnetic trap control server 110 represents a computing system utilizing clustered computers and components (e.g., database server computers, application server computers, etc.) that act as a single pool of seamless resources when accessed within PDL trap data processing environment 100. Magnetic trap control server 110 includes magnetic trap control component 111 and database 112. Magnetic trap control component 111 enables the present invention to control magnetic trap device 120. In the depicted embodiment, magnetic trap control component 111 resides on magnetic trap control server 110. In another embodiment, magnetic trap control component 111 can reside on magnetic trap device 120. Database 112 is a repository for data used by magnetic trap control system 111. In the depicted embodiment, database 112 resides on magnetic trap control server 110. In another embodiment, database 112 may reside elsewhere within PDL trap data processing environment 100, provided that magnetic trap control system 111 has access to database 112. A database is an organized collection of data. Database 112 can be implemented with any type of storage device capable of storing data and configuration files that can be accessed and utilized by magnetic trap control server 110, such as a database server, a hard disk drive, or a flash memory. Database 112 uses one or more of a plurality of techniques known in the art to store a plurality of information regarding experimentation runs. For example, database 112 may store information about measurements from various cycle runs of the trap. Magnetic trap device 120 enables the present invention to measure and cool the trapped object. In the depicted embodiment, magnetic trap device 120 consists of several components (refer to FIG. 2) that work in tandem to conduct various experiments to measure and cool trapped objects such as diamagnetic rods. FIGS. 2A, 2B and 2C are diagrams depicting a front view, a side view and top view, respectively, of the magnetic trap device 120. The magnetic trap device comprises of light source 201, a first and second electrodes (ground) on the left and first and second electrodes (bias) on the right in FIG. 2A, one or more first electrodes 202 and one or more second electrodes 211 in FIG. 2B. Also there is diamagnetic rod 203, pair of dipole line magnets 204, a differential photodetector pair 205, differential amplifier 208, differentiator 209, proportional-integral-derivative (PID) controller 207 and electrode voltage drive 206. Light source 201 of the present invention provides the capability to use light as a source of illumination. In an embodiment, light source 201 provides the mechanism to measure the position and motion of a trapped object such as a graphite rod. The light source could be broadband or monochromatic from infrared to ultraviolet (UV) such as a light emitting diode. To minimize the diffraction limit the preferred wavelength of the light source is a short wavelength such as those found in ultraviolet (UV), provided the light source does not damage or ionize the trapped object. First electrode 202 and second electrode 211 of the present invention provide the capability to drive the motion of the graphite rod. There are two distinct electrodes that are located on the opposite ends, along the longitudinal axis, of the diamagnetic rod 203. For the purposes of the description hereinafter, the term “left” electrode and “right” electrode shall relate to the disclosed structures and method, as oriented in the drawing figures. “Left” electrode shall be synonymous with the term, first electrode 202. “Right” electrode shall be synonymous with the term, second electrode 211. Referring to FIG. 2C, top view, on the arrangement of the two electrodes, first electrode 202 has two connections, one for the bias (V1) and one for ground. Second electrode 211 has two connections, one for the bias (V2) and one for ground as denoted in FIG. 2C. It is noted throughout this disclosure that both electrodes will contain at least one connection for the bias (V1,V2) and one for the ground. It is further noted that the ground for the two electrodes may be tied to the ground of dipole line magnet 204. In an embodiment, first and second electrodes (ground) and first and second electrodes (bias, 202 and 211) are arranged in an “enclosing electrode” configuration (see FIGS. 4A and 4B). The advantage of the “enclosing electrode” configuration is that it has a high capacitance due to close proximity between the two capacitor plates and hence, a low voltage operation. However, due to the physical structure design, this configuration is more difficult to fabricate and miniaturize. In another embodiment, first and second electrodes 202 and 211 and ground electrodes are arranged in an “open” electrode configuration (see FIGS. 5A and 5B, 5C and 5D, 5E and 5F). There are three types of “open” electrode designs, Types I, II, and III. These three types have a common advantage of being easier to fabricate than the enclosing electrode configuration. In another embodiment (referring to FIGS. 5A and 5B), Type I has non-magnetic metallic foils partially wrapped around the magnets with an insulating layer in between. Type I has a disadvantage compared to the enclosing electrode configuration of having a lower capacitance and hence, a higher voltage operation. In addition, the field lines are going from the first electrode 202 or the second electrode 211 to ground, transverse to the rod, which induces a sideways torsional motion to the diamagnetic rod. An interesting feature of Type II is that the left and right drive electrodes have a common ground. In yet another embodiment (referring to FIGS. 5C and 5D), Type II has non-magnetic metallic foils partially wrapped around the magnet with an insulating layer, insulator 210, in between the foils and magnet. Type II has a disadvantage compared to the enclosing electrode configuration of having a lower capacitance and hence, a higher voltage operation. An interesting feature of Type II is that the left and right drive electrodes have no common ground. The magnets are grounded together. In addition to being easier to fabricate, Type II has minimal effects from sideways torsional motions because the field lines go symmetrically from the first electrode pair to the neighboring ground or from the second electrode pair to the neighboring ground, or between the electrodes if the two electrodes have different voltages. In yet another embodiment (referring to FIGS. 5E and 5F), Type III has overhanging electrodes parallel and displaced from the diamagnetic rod. Type III has a disadvantage compared to the enclosing electrode configuration of having a slightly lower capacitance and hence, a slightly higher voltage operation. The magnet serves as a common ground. In addition to being easier to fabricate, Type III has minimal effects from sideways torsional motions because the field lines go from the electrodes to the magnet or between the electrodes if the two electrodes have different voltages. Diamagnetic rod 203 of the present invention is used as the trapped object. In an embodiment, diamagnetic rod 203 is made from a material with a high ratio of magnetic susceptibility to mass density, such as graphite. The pair of dipole line magnets 204 of the present invention provides the magnetic field to levitate and trap a diamagnetic object. In an embodiment, dipole line magnets 204 are made from transversely magnetized (or diametric) cylinder magnets. It is noted that the orientation of the magnets' magnetization is transverse (perpendicular) to the axes of the magnetic cylinders as shown in FIG. 2A. A pair of differential photodetectors 205 of the present invention provides the capability for sensing the rod displacement. In an embodiment, a pair of differential photodetectors 205 is used to receive light from light source 201 as the light passes around the diamagnetic rod 203. It is noted that the use of a lens is permissible since the lens can collimate the light source towards the pair of differential photodetectors 205. Electrode voltage drive 206 of the present invention provides the capability to apply the drive voltage to the first electrode 202 and second electrode 211. In an embodiment, electrode voltage drive 206 processes incoming signals from differential photodetector 205 and PID controller 207. Electrode voltage drive 206 will produce the voltage that drives both first electrode 202 and second electrode 211. PID controller 207 of the present invention provides the capability to process the velocity signal produced by the differentiator 209. The In an embodiment, PID controller 207 processes the velocity signal denoted by v(t). PID controller 207 can be tuned with at least three parameters, the proportional, integral, and differential gain settings. It is noted that the displacement signal, s(t) and the velocity signal, v(t), are non-transitory signals and are not to be construed as transitory signals. Differential amplifier 208 of the present invention provides the capability to process and amplify the signal from a pair of differential photodetectors 205. In an embodiment, differential amplifier 208 processes the photocurrent difference between the photodetector elements and amplifies it to produce a displacement signal, s(t), to be used by differentiator 209 and PID controller 207 to control both first electrode 202 and second electrode 211. Differentiator 209 of the present invention provides the capability to create a velocity signal based on output from differential amplifier 208. Differentiator 209 can be implemented by a standard circuit using a single operational-amplifier (op-amp) and a resistor-capacitor (RC) feedback network. In an embodiment, both differentiator 209 and PID controller 207 work in tandem to optimally minimize the motion of diamagnetic rod 203. FIG. 3 is a flowchart depicting the operational steps of the magnetic trap control component 111, within data processing environment 100 of FIG. 1, in accordance with an embodiment of the present invention. Differential photodetectors 205 detect the diamagnetic rod 203 displacement (step 302). In an embodiment, light source 201 transmits a light around diamagnetic rod 203 towards a pair of photodetectors that forms a differential photodetector setup 205. The difference in the light flux detected by the two photodetectors is proportional to the displacement of the cylindrical rod. The displacement signal, s(t), is amplified by differential amplifier 208 (step 303). It is noted that users may wish to monitor the displacement signal separately since PID loop controller manages the movement based on the displacement and velocity signal. Differentiator 209 receives the displacement signal (step 304). The displacement signal is differentiated by differentiator 209 to produce the velocity signal, v(t), (step 305). PID controller 207 processes the velocity signal (from step 305) and produces an output signal to the electrode voltage drive 206. In an embodiment, the detected signal, s(t), is amplified by differential amplifier 208, and the signal is fed to the differentiator 209, PID controller 207 and eventually to electrode voltage drive 206. The PID controller 207 feedback system processes any deviation in the velocity signal, v(t), of the diamagnetic rod. It is noted that users may wish to monitor the velocity signal separately since PID loop controller manages the movement based on the displacement and velocity signal. Electrode voltage drive 206 determines which direction to adjust or drive the electrodes (decision block 308). Diamagnetic rod 203 is adjusted based on the polarity of the signal. In an embodiment, electrode voltage drive 206 will process the velocity signal v(t), to apply bias drive voltage to either the first electrode 202 or second electrode 211. The first electrode 202 will pull the diamagnetic rod 203 towards it when energized. The second electrode 202 will pull the diamagnetic rod 203 towards it when energized. Electrode voltage drive 206 adjusts first electrode 202 (step 310). If the diamagnetic rod is moving to the right (positive velocity) then the electrode voltage drive 206 will energize the first electrode with a bias voltage to pull the diamagnetic rod 203 towards the left (negative direction). Electrode voltage drive 206 adjusts second electrode 211 (step 312). If the diamagnetic rod is moving to the left (negative velocity) then electrode voltage to drive 206 will energize the second electrode with a bias voltage to pull diamagnetic rod 203 towards the right (positive displacement). Furthermore, PID controller 207 continuously monitors the velocity signal v(t), generated by the system. Based on the velocity signals, PID controller 207 may adjust diamagnetic rod 203 to reach a steady state position or zero velocity. Consequently, if diamagnetic rod 203 reaches a steady state position, then the system reaches the base effective temperature. FIG. 4A depicts (front view) one embodiment, the “enclosing electrodes”, of first electrode (ground) and first electrode (bias) 202 enclosure configuration, in accordance with an embodiment of the present invention. FIG. 4B depicts (top view) one embodiment, the “enclosing electrodes”, of first electrode 202 and second electrode 211 enclosure configuration, in accordance with an embodiment of the present invention. FIG. 5A depicts (front view) another embodiment, the “non-enclosing electrodes” (TYPE I), of ground electrode and first electrode (bias) 202 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 5B depicts (top view) another embodiment, the “non-enclosing electrodes” (TYPE I), of first electrode 202 and second electrode 211 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 5C depicts (front view) another embodiment, the “non-enclosing electrodes” (TYPE II), of first electrode (bias) 202 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 5D depicts (top view) another embodiment, the “non-enclosing electrodes” (TYPE II), of first electrode 202 second electrode 211 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 5E depicts (front view) another embodiment, the “non-enclosing electrodes” (TYPE III), of first electrode (bias) 202 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 5F depicts (top view) another embodiment, the “non-enclosing electrodes” (TYPE III), of first electrode 202 and second electrode 211 non-enclosing configuration, in accordance with an embodiment of the present invention. FIG. 6 depicts a block diagram of components of the magnetic trap control server 110, designated as 600, in accordance with an embodiment of the present invention. It should be appreciated that FIG. 6 provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments can be implemented. Many modifications to the depicted environment can be made. Magnetic trap control server 110 can include processor(s) 604, cache 616, memory 606, persistent storage 608, communications unit 610, input/output (I/O) interface(s) 612 and communications fabric 602. Communications fabric 602 provides communications between cache 616, memory 606, persistent storage 608, communications unit 610, and input/output (I/O) interface(s) 612. Communications fabric 602 can be implemented with any architecture designed for passing data and/or control information between processors (such as microprocessors, communications and network processors, etc.), system memory, peripheral devices, and any other hardware components within a system. For example, communications fabric 602 can be implemented with one or more buses. Memory 606 and persistent storage 608 are computer readable storage media. In this embodiment, memory 606 includes random access memory (RAM). In general, memory 606 can include any suitable volatile or non-volatile computer readable storage media. Cache 616 is a fast memory that enhances the performance of processor(s) 604 by holding recently accessed data, and data near recently accessed data, from memory 606. Program instructions and data used to practice embodiments of the present invention, e.g., magnetic trap control component 111 and database 112, can be stored in persistent storage 608 for execution and/or access by one or more of the respective processor(s) 604 of magnetic trap control server 110 via memory 606. In this embodiment, persistent storage 608 includes a magnetic hard disk drive. Alternatively, or in addition to a magnetic hard disk drive, persistent storage 608 can include a solid-state hard drive, a semiconductor storage device, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), a flash memory, or any other computer readable storage media that is capable of storing program instructions or digital information. The media used by persistent storage 608 may also be removable. For example, a removable hard drive may be used for persistent storage 608. Other examples include optical and magnetic disks, thumb drives, and smart cards that are inserted into a drive for transfer onto another computer readable storage medium that is also part of persistent storage 608. Communications unit 610, in these examples, provides for communications with other data processing systems or devices, including resources of client computing device 120. In these examples, communications unit 610 includes one or more network interface cards. Communications unit 610 may provide communications through the use of either or both physical and wireless communications links. Magnetic trap control component 111 and database 112 may be downloaded to persistent storage 608 of magnetic trap control server 110 through communications unit 610. I/O interface(s) 612 allows for input and output of data with other devices that may be connected to magnetic trap control server 110. For example, I/O interface(s) 612 may provide a connection to external device(s) 618 such as a keyboard, a keypad, a touch screen, a microphone, a digital camera, and/or some other suitable input device. External device(s) 618 can also include portable computer readable storage media such as, for example, thumb drives, portable optical or magnetic disks, and memory cards. Software and data used to practice embodiments of the present invention, e.g., magnetic trap control component 111 and database 112 on magnetic trap control server 110, can be stored on such portable computer readable storage media and can be loaded onto persistent storage 608 via I/O interface(s) 612. I/O interface(s) 612 also connect to a display 620. Display 620 provides a mechanism to display data to a user and may be, for example, a computer monitor or the lenses of a head mounted display. Display 620 can also function as a touchscreen, such as a display of a tablet computer. FIG. 7 is a flowchart, designated as 700, depicting operational steps of an alternative method for the parallel dipole line trap, in accordance with another embodiment of the present invention. PID controller 207 is tuned to begin the sequence. In an embodiment, PID controller 207 is tuned in order to ensure the integrity and accuracy of the feedback loop. Differential photodetectors 205 measure the diamagnetic rod 203 displacement (step 702). In an embodiment, light source 201 transmits a light around diamagnetic rod 203 towards a pair of photodetectors that forms a differential photodetector 205 setup. The difference in the light flux detected by the two photodetectors is proportional to the displacement of the cylindrical rod. The displacement signal is amplified by differential amplifier 208 and then differentiated by a differentiator 209 to produce the velocity signal. The PID controller 207 processes the velocity signal and produces an output signal to the electrode voltage drive module. In an embodiment, the detected signal, s(t), is amplified by differential amplifier 208, and the signal is fed to the differentiator 209, PID controller 207 and eventually to electrode voltage drive 206. The PID controller 207 feedback system processes any deviation in the velocity signal v(t) of the diamagnetic rod. Diamagnetic rod 203 is adjusted based on the polarity of the signal from the PID controller. In an embodiment, electrode voltage drive 206 will process the incoming signal to apply a bias drive voltage to either the first electrode 202 or second electrode 211. First electrode 202 will pull the diamagnetic rod 203 towards it when energized with a bias voltage. Second electrode 202 will pull the diamagnetic rod 203 towards it when energized. The bias voltage may be either positive or negative voltage with respect to ground. If the diamagnetic rod is moving to the right (positive velocity) then the electrode voltage drive 206 will energize the first electrode with a bias voltage to pull the diamagnetic rod 203 towards the left (negative direction) (step 706). If the diamagnetic rod is moving to the left (negative velocity) then electrode voltage drive 206 will energize the second electrode with a bias voltage to pull diamagnetic rod 203 towards the right (positive displacement) (step 708). Furthermore, the differentiator 209 continuously monitors the velocity signal v(t), generated by the system. Based on the velocity signals, PID controller 207 may adjust diamagnetic rod 203 to reach a steady state position or zero velocity. Consequently, if diamagnetic rod 203 reaches a steady state position, then the system reaches the base effective temperature. The programs described herein are identified based upon the application for which they are implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program nomenclature herein is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature. The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention. The computer readable storage medium can be any tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire. Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device. Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention. Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions. These computer readable program instructions may be provided to a processor of a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks. The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks. The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, a segment, or a portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. |
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claims | 1. A system for controlling a solution nuclear reactor comprising:(A) a solution nuclear reactor having a nuclear reactor vessel and a homogenous fissile solution disposed therein;(B) one or more standpipes located in at least one low worth area of the nuclear reactor vessel, the one or more standpipes having an open end located at a level below a solution level of the homogenous fissile solution contained in the nuclear reactor vessel of the solution nuclear reactor so that the homogenous fissile solution is free to move both into and out of the one or more standpipes;(C) at least one gas system, wherein the at least one gas system is in fluidic communication with the one or more of the standpipes and is configured to adjust a pressure within the one or more standpipes,wherein a fluid level of the homogeneous fissile solution in the one or more standpipes is controlled via the pressure exerted within the one or more standpipes by the at least one gas system. 2. The system of claim 1, wherein the at least one gas system utilizes at least one gas that is selected from nitrogen, helium, oxygen, hydrogen, air, or combinations of two or more thereof. 3. The system of claim 1, wherein the at least one gas system utilizes at least one gas that is selected from nitrogen, helium, air, or combinations of two or more thereof. 4. The system of claim 1, wherein the homogenous fissile solution in the solution nuclear reactor remains homogenous as the fluid level of the homogenous fissile solution in the one or more standpipes is altered. 5. The system of claim 1, wherein the reactivity in the solution nuclear reactor is controlled without the use of any mechanical movement of any design feature within the nuclear reactor vessel. 6. The system of claim 1, wherein the reactivity coefficients of the solution nuclear reactor are not permitted to become positive. 7. The system of claim 1, wherein any failure of the system results in a fail-safe condition. 8. The system of claim 1, wherein any inadvertent pressurization or depressurization of the one or more standpipes containing homogenous fissile solution results in the solution nuclear reactor being in, maintaining, and/or achieving a fail-safe condition. |
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046560009 | abstract | A nuclear reactor having a reactor vessel adapted to be supplied with a coolant, a reactor core disposed in the reactor vessel and including a plurality of fuel assemblies, a plurality of control rods adapted to be inserted into the reactor core and a plurality of control rod driving devices for driving the control rods into and out of the reactor core. A plurality of tubular coolant passage members are disposed above the fuel assemblies so as to receive the heated coolant discharged from the fuel assemblies, so that the heated coolant flows upwardly through the tubular coolant passage members. The tubular coolant passage members provide a chimney effect which enhances the upward flow of the coolant and, hence, increases the flow rate of coolant flowing through the reactor core. In consequence, a greater cooling effect is obtained and the range of power controllable by the control rods is widened. In consequence, the construction of the reactor is simplified and the size is decreased due to elimination of coolant recycling system in the reactor vessel. |
abstract | A spacer for a fuel element of a boiling water reactor contains cells that are formed by inner partitions, which are disposed in a crisscross manner, and by outer partitions, which surround the inner partitions in a frame-like manner. A guiding device is placed on the spacer and contains a flow-through opening, which is located in an outer partition. The guiding device also contains a guiding element which, when viewed in the direction of flow of the coolant, is located in front of the flow-through opening, and is situated at a distance from the inner side of the outer partition, and interacts with the flow-through opening like a venturi nozzle. |
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abstract | An intensity modulator for controlling the intensity of ions, such as protons, controllably block a portion of sub-areas of an area beam to control the average intensity within that sub-area. A fan beam is then created by a focusing process that reforms the area beam while blurring intensity variations in each sub-area to a corresponding beamlet in the fan beam of uniform intensity. |
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claims | 1. A system for visual inspection of a nuclear reactor, the system comprising:a submersible remotely operated vehicle (SROV) system that is movable to an area within a nuclear vessel, the SROV system including a maneuverable inspection camera assembly for visual inspection of nuclear vessel components, the inspection camera assembly being maneuverable in relation to the SROV system;a control system located in an area remote from the area within the nuclear vessel, the control system configured to control the movement of the SROV system and the maneuvering of the inspection camera assembly;a cable suspending the inspection camera assembly from the SROV; anda first motor configured to vertically raise and lower the inspection camera assembly on the cable to and from the SROV; andan attachment mechanism connected to the SROV system, the attachment mechanism including,a suction device configured to impart a suction force on a surface of the nuclear vessel components in order to adhere the SROV system to the surface,at least one wheel configured to impart a friction force on the surface in order to move the SROV while the suction device is in operation. 2. The system of claim 1, wherein the SROV system includes at least one discharge device attached to the inspection camera assembly, the at least one discharge device configured to discharge cleaning fluid to an inspection area. 3. The system of claim 2, wherein the control system is further configured to control the discharge of the cleaning fluid, and the control system is connected to the SROV system via a control cable. 4. The system of claim 3, wherein the control system includes:a first display unit configured to display the visual inspection performed by the inspection camera assembly;at least one second display unit configured to display a position of the SROV system within the nuclear vessel;a valve system configured to control pressure and flow of the cleaning fluid discharged via the at least one discharge device; andan operational control unit configured to permit a user to control at least one of the movement of the SROV system, the maneuvering of the camera assembly, and the valve system,the operational control unit configured to display tracking information based on the position of the SROV system within the nuclear vessel. 5. The system of claim I, wherein the SROV system includes a plurality of propulsive devices configured to move the SROV system to the area within the nuclear vessel, the plurality of propulsive device being remotely controlled by the control system. 6. The system of claim 5, wherein the plurality of propulsive devices permit the SROV system to move horizontally, vertically, rotationally about an axis of the SROV system. 7. The system of claim 1, wherein the SROV system includes:a frame assembly having a vertical structure;an arm assembly connected to the vertical structure driven via a second motor, wherein the arm assembly is movable about an axis of the second motor, the second motor being remotely controlled by the control system. 8. The system of claim 7, wherein,the inspection camera assembly is connected to the arm assembly via the cable,the second motor being remotely controlled by the control system. 9. The system of claim 1, wherein the inspection camera assembly includes a camera manipulator having tilt and pan mechanisms, and an inspection camera, the inspection camera being connected to the camera manipulator, the tilt and pan mechanisms permitting the inspection camera to be moveable with respect to the camera manipulator, the camera manipulator being remotely controlled by the control system. 10. The system of claim 1, wherein the SROV system includes:a first positional camera for viewing a first perspective of the SROV system within the nuclear vessel;a second position camera for viewing a second perspective of the SROV system within the nuclear vessel. 11. The system of claim 1, wherein the SROV system includes:an attachment mechanism configured to attach the SROV system to the area of the nuclear vessel and permit the SROV system to move to different positions on the area. 12. The system of claim 11, wherein the area of the nuclear vessel is one of a shroud and Reactor Pressure Vessel (RPV) flange. 13. The system of claim 12, further comprising:an observation camera positioned on the RPV flange. 14. The system of claim 1, wherein the SROV system includes:an integrated calibration system configured to calibrate an inspection camera of the inspection camera assembly. 15. A submersible remotely operated vehicle (SROV) system for visual inspection of a nuclear reactor, the SROV system comprising:a device that is movable to an area within a nuclear vessel, the device including a maneuverable inspection camera assembly for visual inspection of nuclear vessel components, the inspection camera assembly being maneuverable in relation to the device, the movement of the device and the maneuvering of the inspection camera assembly being remotely controlled;a cable suspending the inspection camera assembly from the SROV; anda first motor configured to vertically raise and lower the inspection camera assembly on the cable to and from the SROV; andan attachment mechanism connected to the SROV system, the attachment mechanism including,a suction device configured to impart a suction force on a surface of the nuclear vessel components in order to adhere the SROV system to the surface,at least one wheel configured to impart a friction force on the surface in order to move the SROV while the suction device is in operation. 16. The SROV system of claim 15, further comprising:at least one discharge device attached to the inspection camera assembly, the at least one discharge device configured to discharge cleaning fluid to an inspection area. 17. The SROV system of claim 15, further comprising:a plurality of propulsive devices configured to move the device to the area within the nuclear vessel, the plurality of propulsive devices being remotely controlled. 18. The SROV system of claim 17, wherein the plurality of propulsive devices permit the device to move horizontally, vertically, rotationally about an axis of the device. 19. The SROV system of claim 15, further comprising:a mechanism configured to maneuver the inspection camera assembly. 20. The SROV system of claim 19, wherein the mechanism is configured to drive a cable that is connected to the inspection camera assembly to move the inspection camera assembly. 21. The SROV system of claim 20, further comprising:a cable retraction mechanism configured to maintain a tautness of the cable. 22. The SROV system of claim 15, further comprising:a frame assembly having a vertical structure;an arm assembly connected to the vertical structure driven via a second motor, wherein the arm assembly is movable about an axis of the second motor, the second motor being remotely controlled. 23. The SROV system of claim 22, wherein,the inspection camera assembly is connected to the arm assembly via the cable,the second motor is remotely controlled. 24. The SROV system of claim 15, wherein the inspection camera assembly includes a camera manipulator having tilt and pan mechanisms, and an inspection camera, the inspection camera being connected to the camera manipulator, the tilt and pan mechanisms permitting the inspection camera to be moveable with respect to the camera manipulator, the camera manipulator being remotely controlled. 25. The SROV system of claim 15, further comprising:a first positional camera for viewing a first perspective of the device within the nuclear vessel;a second position camera for viewing a second perspective of the device within the nuclear vessel. 26. The SROV system of claim 15, further comprising:an attachment mechanism configured to attached the device to the area of the nuclear vessel and permit the device to move to different positions on the area. 27. The SROV system of claim 15, further comprising:an integrated calibration system configured to calibrate an inspection camera of the inspection camera assembly. 28. The system of claim 1, further comprising:a submersible cable retraction mechanism configured to support the cable and the submersible inspection camera assembly,the cable retraction mechanism including a pulley to maintain a tautness of the cable above the SROV system. 29. The system of claim 1, wherein the control system includes,a first camera configured to view the visual inspection performed by the inspection camera assembly,at least one second camera configured to view a position of the SROV system within the nuclear vessel,an operational control unit configured to display tracking information based on the position of the SROV system within the nuclear vessel. |
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abstract | A novel specimen holder for specimen support devices for insertion in electron microscopes. The novel specimen holder of the invention provides mechanical support for specimen support devices and as well as electrical contacts to the specimens or specimen support devices. |
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050948024 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is generally related to a nuclear reactor fuel assembly and in particular to a debris filter used with the fuel assembly. 2. General Background Commercial nuclear reactors include multiple fuel assemblies. Each fuel assembly is comprised of a number of fuel rods radially spaced apart in a parallel array by grid assemblies spaced along the length of the fuel rods. Each grid assembly is formed in an eggcrate design by multiple metal strips that criss-cross at right angles to form individual cells for each of the fuel rods. The strips are provided with tabs that project into the cells against the fuel rods. The tabs serve the purposes of holding the fuel rods in their respective radial positions and providing maximum surface area contact of the fuel rods with coolant flowing through the cells. Control rod guide thimble tubes also extend through selected cells in the grid assembly and are attached at their upper and lower ends respectively to an upper end fitting and a lower end fitting. The upper and lower end fittings are also commonly referred to in the industry as nozzle plates since they are rigid plates that provide structural integrity and load bearing support to the fuel assembly and are provided with flow apertures therethrough for coolant flow. The lower end fitting or nozzle plate is positioned directly above openings in the lower portion of the reactor where coolant flows up into the reactor to the core. The ligaments between apertures in the end fittings coincide with the ends of the fuel rods and limit upward or downward movement of the fuel rods. Debris such as metal particles, chips, and turnings is generated during manufacture installation, and repair of the reactor, piping, and associated cooling equipment. The size and complexities of the equipment prevent location and removal of all such debris before operations are commenced. Also, some of this debris may not become loose matter in the system until the system is put into operation. It has bee recognized that this debris presents a greater problem to the system than previously thought. These small pieces of debris have been found to lodge between the walls of the grid cells and the fuel elements. Movement and vibration of the lodged debris caused by coolant flow results in abrasion and removal of cladding on the fuel rods. This in turn leads to detrimental effects such as corrosion of the fuel rods and failure to retain radioactive fission gas products. Such damage, although not critical to safety of the surrounding environment, can reduce operating efficiency by the need to suspend operation while replacing damaged fuel rods. It can be seen that a need exists for a debris filter capable of filtering debris of a size which may lodge between the grid cell walls and the fuel rods. An important consideration besides that of filtration is that a substantial coolant pressure drop across the filter must be avoided in order to maintain an adequate coolant flow over the fuel rods for heat removal therefrom. Patented approaches to this problem of which applicant is aware include the following. U.S. Pat. Nos. 4,684,495 and 4,684,496 disclose debris traps formed from a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for coolant flow through the trap. U.S. Pat. No. 4,828,791 discloses a debris resistant bottom nozzle which is a substantially solid plate having cut-out regions in alignment with inlet flow holes in the lower core plate. Separate criss-cross structures fixed to the plate extend across the cut-out regions to act as a debris trap. U.S. Pat. Nos. 4,664,880 and 4,678,627 disclose debris traps mounted within a bottom nozzle that define a hollow enclosure with an opening so as to form a debris capturing and retaining chamber. U.S. Pat. No. 4,652,425 discloses a trap for catching debris disposed between the bottom nozzle and the bottom grid. The structure forms multiple hollow cells that receive the fuel rod lower end plugs with dimples in each cell for catching debris carried into the cells by the coolant flow. SUMMARY OF THE INVENTION The present invention provides a solution to the above problem in the form of a screen attached to the lower end fitting or nozzle plate. The lower end fitting is formed from a substantially square base having interconnecting ribs between the walls with openings thereon which receive control rod guide tubes. Legs extending downward from each corner support the end fitting on the lower reactor internals. A stamped screen sized to match the lower end fitting and provided with flow holes sized to filter debris is attached to the lower end fitting. |
050698630 | abstract | A transfer system moves fuel assemblies along a track extending through a transfer tube within a containment wall in a nuclear power plant between the auxiliary building side and the containment building side. A car carries a basket for the assemblies. Two winches are located on the auxiliary building side above the water level existing over the track during refueling operations. The winches operate respective pairs of cables, driving the car in either direction. Four sheaves respectively direct the cables to the horizontal direction along the track. One pair of cables is secured to a yoke on the car to drive the car away from the containment building. Two horizontal sheaves are located near the containment end of the transfer tube. The other two cables extend horizontally along the track from the vertical sheaves to the horizontal sheaves, redirecting them to extend horizontally in the reverse direction. These return cables are secured to the yoke to drive the car toward the containment building. The winches are operated under the control of a programmable limit switch to move the car selectively between one end position in which the car is within the auxiliary building, and the other end position in which the car is principally within the containment building with at least the car yoke located over the track within the transfer tube and to the auxiliary building side of the horizontal sheaves. |
description | Embodiments relate to buildings, rooms, power consumption, resource utilization, and to decision and estimation techniques. Embodiments also relate to graphical user interfaces and remote metering. Embodiments yet further relate to the fields of system modeling, linear regression, and local regression. Buildings use and consume a variety of resources such as electricity, water, gas, and steam. These resources are more commonly referred to as utilities. Many facilities control utility consumption through a system of controllers. For example, thermostats placed around a building can regulate the temperature of regions within the building. Utilities are often metered at the point where they enter buildings and readings of the meters indicate how much of the utility has been consumed. In many systems, a person reads the meter at two different times and then determines the buildings consumption during the period encompassed by those two times. More recently, remote metering capabilities have removed the person from the process. Meters can be connected to a communications network such that computers can remotely query the meters. Those practiced in the art of linear regression and local regression are familiar with modeling techniques such as LOESS. A data set can contain numerous samples of the values of independent variables and of dependent variables that depend on those independent variables. Techniques such as LOESS can produce a model of the data set. When given values for the independent variables, the model can produce an estimates of the dependent variables and their variances. The variance estimates are an indication of how “noisy” the dependent variable estimates are. In an effort to conserve resources, historical data can be examined in an effort to determine trends in utility consumption. Systems and methods for analyzing resource utilization are needed. The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. It is therefore an aspect of the embodiments to obtain load measurements indicative of resource utilization within the regions of a building. Time stamping the load measurements and storing them results in a database of historical load measurements. It is also an aspect of the embodiments to measure the values of independent variables such as outside air temperature, date, time of day, occupancy, and workday versus non-workday. The independent variable measurements can also be time stamped and stored in the database with the caveat that time and date data typically time stamps itself. As such, the database contains historical data. The historical data is a record over time of resource usage and of independent factors that can affect resource usage. Deploying multiple sensors throughout a building allows measurements to be made in the various regions and rooms within the building. It is a further aspect of the embodiments that a similar data selector can be supplied with a selection of independent variable measurements. The similar data selector then obtains similar historical data from the database indicating resource usage during similar time periods. Note that a similar time period is one having similar conditions in general but not necessarily occurring during a similar time of day. For example, submitting “noon and 40 degrees outside” to the similar data selector can result in the return of all the load measurements for every building region when the temperature was between 35 and 45 degrees and the time was between 11 AM and 1 PM. It is a further aspect of the embodiments that the similar historical data is analyzed to produce baseline mean estimates and baseline variance estimates. The baseline mean estimate for a region is an indication of what the load measurement is expected to be based on prior observations. The baseline variance is an indication of how precise the baseline mean estimate is. The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. In general, the figures are not to scale. A system for utility base lining records historic values of utility loads for regions within a facility. The system also records historic values of independent variables such as outside temperature, time, date, workday versus non-workday, and occupancy. A similar data selector seeks out similar times in the past and submits the data from those times to a base line estimator that produces a baseline mean estimate and a baseline variance estimate. Differences between the current load and the baseline mean estimate can trigger alarms or investigations to determine why the utility load has changed. More specifically, the error is the difference between the baseline mean estimate and the current load. The ratio between the magnitude of the error and the baseline variance estimate indicates if the current load is anomalous and, if so, the magnitude of the anomaly. The local data selector can have a built in bias for more recent data. In such a case, the estimates are not sensitive to slowly drifting load. Otherwise, false alarms can occur when the utility load drifts over time. Detecting drift or immunity to drift can help reduce false alarms or help in the investigation of alarms. A graphical user interface (GUI) can present an easily understood representation of the regions, load estimation errors, load anomaly severity, alarms, and detected drift. FIG. 1 illustrates a system producing baseline mean and variance estimates 113 for the regions of a facility in accordance with aspects of the embodiments. A building 100 is divided into five regions 101-105. Each region has a sensor 106 that senses utility load such as electrical energy use, amount of heating, amount of cooling, or some other utility. The load sensors produce load measurements 108. Independent factors can affect the utility load. The independent factors can be observed as independent variables. For example. regions can have occupancy monitors 107 that detect the number of people in a region. An occupancy monitor can be part of an access control system, a system that detects people, a system that detects something people carry such as RFID tags, or some other system. An outdoor thermometer 114 can measure outside temperature. A clock 109 can supply a measurement of the current date and time. The independent variable sensors produce independent variable measurements 110 including outside temperature, occupancy, date, and time. The load measurements 108 and the independent variable measurements 110 can be stored as historical data 112 in a database 111. A similar data selector 115 accepts a recent measurement 118 and produces similar historical data 116. The recent measurement 118 is a recently acquired set of independent variable measurements 110. The similar data selector 115 gathers similar historical data 116 which is historical data from past times that were similar to the recent measurement 118. A baseline estimation module 117 analyzes the similar historical data 116 to produce baseline estimates 113. The baseline estimates 113 predict what the utility load should be based on the recent measurement 118. A linear regression model 119 can produce such an estimate. Those practiced in the art of linear algebra are familiar with linear regression. Furthermore, a weighted linear regression analysis is applied in many LOESS implementations after the selection of similar historical data. The baseline estimates 113 can be stored in the database for later processing, for visualization, or detection of anomalous energy demands. Some systems, such as certain LOESS implantations, select similar historical data and also weight the similar historical data. As such, the more similar a particular historical data record is to the recent measurement, the more heavily it is weighted. The more heavily that data is weighted more greatly it effects the baseline estimates. More recent historical data can be weighted more heavily because the recent measurement contains a time and date. The recent data is closer along the time axis. This weighting can lead to a degree of drift immunity. FIG. 2 illustrates a system producing similar historical data in accordance with aspects of the embodiments. A trigger 203 such as a periodic pulse, message, or command can cause load sensors 201 to produce load measurements 202 and independent variable sensors 204 to produce independent variable measurements 110. A clock 109 produces time 205 and date 206 measurements. An outdoor thermometer 114 measures outdoor temperature 207. An occupancy monitor 107 measures occupancy 208. The load measurements 202 and the independent variable measurements 110 can be stored in a historical data record 209 in the historical data 112. The date 206 can be used to set the workday or non-workday variable. For example, the trigger 203 can be periodic occurring every 10 minutes. The historical data 112 would thereby include independent variable measurements 110 and load measurements 202 taken at ten minute intervals. Note that the listed set of independent variables is an example of some of the influencing factors that can affect utility load. Baseline estimates can be produced when given the listed independent variables, a subset of them, or a different set of independent variables. A recent measurement 212 is presented to the similar data selector 115. Here, the recent measurement is that it is 12 AM on a workday with an outside temperature of 25 with seven people in the region. Here the similar data selector 115 is a distance based similar data selector. The independent variables in the database can be formed into historical vectors. In a similar manner, the recent measurement can also be formed in a vector. The similar data selector can then use a distance measure, such as Euclidean distance, to choose the historical data that is close to, and thereby similar to, the recent measurement. Similarity measure is not limited to being derived from Euclidean distance; it could be defined using various techniques. FIG. 3 illustrates a system detecting drift in accordance with aspects of the embodiments. Independent variable measurements 110 and load measurements are periodically stored as historical data. The independent variable measurements also result in the recent measurement 118. The recent measurement 118 is input to the similar data selector 312. The similar data selector 312 also accepts a reference period 313. The reference period can be produced by a reference period selection module. For example, the desired reference period can be “one year ago”. In such an example, the reference period selection module can obtain the current date from the independent variable measurements 110 and produce the desired reference period 313 that is then passed to the similar data selector 312. The similar data selector 312 can then produce similar reference period data 308 containing historical data obtained from times during the reference period. Note that certain weighted LOESS implementations can simply receive a past date. The weighted LOESS implementation can then simply weight historical data more strongly if it was taken near the past date. Passing the similar reference period data to the baseline estimation module results in which eventually leads to the production of reference period baseline estimates 311. The reference period baseline estimates 311 are baseline estimates produced from the reference periods historical data. A differencer 306 calculates the error 307 as the difference between the load measurement 310 and the reference period baseline mean estimate 311. The error can be stored in the database for future use. A drift detection module 301 examines the error 307 to determine the occurrence of baseline drift. Baseline drift occurs when the utility load changes slowly over time. For example, a heater may become less efficient over a long period of time and cause the utility load to slowly increase. Recall that the baseline estimation module can be immune to slowly drifting load measurements. Detecting slowly drifting loads, however, can supply crucial information leading to the maintenance of slowly clogging filters or a degrading heater. The illustrated drift detection module 301 is a rule based drift detection module 301. It has two rules. A first rule 302 finds drift when the error is greater than 10% for 10 days from 8 PM to 12 PM. The second rule 303 finds drift when the error exceeds 100 W for 10 days. For example, if the reference period is one year in the past, then the second rule tends to detect drift exceeding 100 Watts per year. Either rule can give rise to a drift alarm 304. A drift alarm can contain data such as the affected region 211 and the drift amount 305. The drift amount 305 can be the average error over an interval of time. FIG. 4 illustrates a graphical user interface 400 presenting load estimation errors 401 and detected drift 402 in accordance with aspects of the embodiments. The GUI 400 can be presented on a computer monitor or similar display. As can be seen in comparison with FIG. 1, the GUI 400 can be a representation of the facility and the regions within the facility. Each region contains text fields identifying the region and showing the load estimation error 401. Another text field can appear to indicate drift 402. FIG. 5 illustrates a portion of a graphical user interface 500 presenting load estimation errors and detected drift in accordance with aspects of the embodiments. Here, only the representation of region 2 is illustrated. Alternatively, the entire facility can be shown with each region presented. Two chart lines are shown. The load line 501 indicates the actual measured utility load. The estimate line 502 indicates the baseline estimates. The vertical axis corresponds to load whereas the horizontal axis corresponds to time. The error can be observed as the amount of separation between the load line 501 and estimate line 502. Arrows 503 indicate that drift has been detected and at what time it was detected. FIG. 6 illustrates a distance based similar data selector 605 in accordance with aspects of the embodiments. A historical data record 209 can be converted into a historical vector 601. In some embodiments, the historical data records are historical vectors that are stored as vectors in the database. Those familiar with linear algebra can convert a group of numbers, such as those in a historical data record 209, into a historical vector. Similarly, the recent measurement 118 can be expressed as a measurement vector 602. The similar data selector 605 can choose data based on the minimum distance between the historical vector 601 and the measurement vector 602. The distances are calculated by distance calculators. Distance calculator 1 can calculate a Euclidean distance while only considering the values for occupancy and outside temperature. Distance calculator 2 can calculate a distance while considering only the values for time and workday v. non-workday (a flag). The similar data selector can choose all historical data within a threshold value for distance calculator 1 603 and within a different threshold value for distance calculator 2 604. It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. |
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046363521 | summary | FIELD OF THE INVENTION The present invention relates to an improved nuclear fuel rod with a burnable plate which will prevent corrosive attack of the rod cladding by fissile materials released during operation of a reactor employing the rods. BACKGROUND OF THE INVENTION It is well-known that the process of nuclear fission involves the disintegration of the fissionable fuel material, usually enriched uranium dioxide, into two or more fission products of lower mass number. Among other things, the process also includes a net increase in the number of available free neutrons which are the basis for a self-sustaining reaction. When a reactor has operated over a period of time the fuel assembly with fissionable material must ultimately be replaced due to depletion. Inasmuch as the process of replacement is time consuming and costly, it is desirable to extend the life of a given fuel assembly as long as practically feasible. For that reason, deliberate additions to the reactor fuel of parasitic neutron-capturing elements in calculated small amounts may lead to highly beneficial effects on a thermal reactor. Such neutron-capturing elements are usually designated as "burnable absorbers" if they have a high probability (or cross-section) for absorbing neutrons while producing no new or additional neutrons or changing into new absorbers as a result of neutron absorption. During reactor operation the burnable absorbers are progressively reduced in amount so that there is a compensation made with respect to the concomitant reduction in the fissionable material. The life of a fuel assembly may be extended by combining an initially larger amount of fissionable material as well as a calculated amount of burnable absorber. During the early stages of operation of such a fuel assembly, excessive neutrons are absorbed by the burnable absorber which undergoes transformation to elements of low neutron cross-section which do not substantially affect the reactivity of the fuel assembly in the latter period of its life when the availability of fissionable material is lower. The burnable absorber compensates for the larger amount of fissionable material during the early life of the fuel assembly, but progressively less absorber captures neutrons during the latter life of the fuel assembly, so that a long life at relatively constant fission level is assured for the fuel assembly. Accordingly, with a fuel assembly containing both fuel and burnable absorber in carefully proportioned quantity, an extended fuel assembly life can be achieved with relatively constant neutron production and reactivity. The incorporation of burnable absorber in fuel assemblies has been recognized in the nuclear fuel as an effective means of increasing fuel capacity and thereby extending core life. Burnable absorbers are used either uniformly mixed with the fuel (i.e., distributed absorber) or are placed discretely as separate elements in the reactor, as separate burnable absorber rods, so arranged that they burn out or are depleted at about the same rate as the fuel. Thus, the net reactivity of the core is maintained relatively constant over the active life of the core. Among the various burnable absorbers that have been mixed with fuel as a distributed absorber, gadolinium oxide has been found to be an excellent absorber due to its extremely high thermal absorption cross-section. Enriched uranium dioxide, with a high U-235 isotope content, and gadolinium oxide, as a mixture, has thus previously been used as nuclear fuel pellets. The use of separate bodies or pellets of a burnable poison in conjunction with nuclear fuel pellets has also been proposed. In U.S. Pat. No. 3,334,019 for example, the use of poison plates containing boron or a boron compound, dysprosium or samarium, cadmium or europium, has been proposed, where these plates are disposed between fuel elements containing fissile material. The purpose of the interspersing of poison plates between the fuel elements is to control the tendency of the reactivity of a reactor to change during its life. Also, in U.S. Pat. No. 3,119,747, a fuel element is described wherein wafers of a burnable poison are disposed on either side of a fuel body, and cylinders of a moderator, such as graphite, are disposed between the wafers and the respective end fixtures for the fuel element. As discussed above, during operation of the reactor, fissile materials are released from the fuel pellets. These released materials, which include volatile materials, cause a problem of stress corrosion and possible failure of the metallic tubular cladding. This phenomenon is generally described as "pellet-clad interaction" (PCI). The chemical reaction of the metallic tubing with volatile fissile materials such as iodine, cadmium, or other volatile elements, coupled with cladding operating stresses can produce stress corrosion cracking of the metallic cladding or tubing and eventual penetration of the wall of the tube. Attempts have been made to prevent such pellet-clad interaction, such as by coating the inside wall of the tubing with a protective coating, and co-extruding a pure zirconium barrier on the inner portion of the zircaloy tubular wall. Such procedures are objectionable because of the high costs associated therewith. It is an object of the present invention to provide a nuclear fuel rod that is so constructed as to eliminate or minimize pellet-clad interaction. It is another object of the present invention to provide a nuclear fuel rod that incorporates the eliminating or minimizing of pellet-clad interaction failures into a burnable poison concept. BRIEF SUMMARY OF THE INVENTION An improved nuclear fuel rod comprising a metallic tubular cladding containing a plurality of nuclear fuel pellets, contains a plurality of ceramic wafers that are a sintered mixture of a natural or depleted uranium dioxide and gadolinium oxide. The wafers are each disposed between a major portion of the adjacent fuel pellets and freeze out volatile fission products released by the fuel pellets and minimize or prevent pellet-clad interaction failures. The wafers have diameter substantially the same as the diameter of the fuel pellets and a thickness of about 10-100 mils. The gadolinium oxide is present in an amount of between 1-8 percent by weight of the mixture. The wafers are formed by mixing a natural or depleted uranium dioxide with the gadolinium oxide and sintering the mixture to form ceramic wafers. |
048428051 | summary | The present invention relates to detecting when anti-reactive elements, i.e. neutron-absorbing elements, fall into the core of the reactor in a nuclear fission power station. The invention is more particularly applicable to the case where the fall to be detected is the fall of one of the "control clusters" which are used for regulating and controlling the nuclear power, i.e. the power generated by the reaction. Such clusters are distributed over the horizontal section of the core. They are moved vertically in both directions under the control of an appropriate mechanism situated above the core so as to cause their absorbant rods to penetrate to a greater or lesser extent into the core. For safety reasons, position detectors are disposed to indicate the position of each cluster at any moment. Unfortunately, these detectors can only be situated, in practice, facing the suspension elements to which the clusters are attached, and not actually facing the clusters themselves. An attachment defect can therefore cause a cluster to fall accidentally without said fall being indicated by said detectors. Such a fall gives rise to a local drop in nuclear power, and thus to a drop in the overall power of the core. The presence of a power-regulating loop means that said drop is rapidly compensated by other control clusters being raised. However, in addition to other drawbacks, there then appears a distortion in the neutron flux which slows down combustion of the fuel elements in the vicinity of the fallen cluster and accelerates combustion in the other fuel elements. In addition, the scope of possible action which can be taken on the reaction is reduced. This is the main reason why it is desirable to detect when such accidental falls occur as quickly and as reliably as possible so as to perform an emergency stop on the reactor and then re-establish normal operation. In prior power stations this detection is performed by detection means which are used simultaneously for other types of accident. More precisely, these means detect the excessive temperatures caused by the appearance of steam pockets at various points in the core along the component rods of the fuel elements. When a cluster has fallen accidentally, the first time the nuclear power rises to a certain level after said fall such an excess temperature or steam pocket appears along a fuel element whose combustion has been accelerated by the flux distortion. Different automatic protection means then give rise to an emergency reactor stop. The cause of this stop is then determined and the consequences of the accident are repaired before the reactor is put back into service. This has the drawback, particularly if the anti-reactivity of the fallen cluster is relatively low, that a fairly long period of time may elapse before the nuclear power is raised high enough to trigger the above-described stop procedure. The combustion rate of some of the fuel elements can then be very different from the norm. A particular aim of the present invention is to provide more rapid and more certain detection of the fall of an anti-reactive element such as a control cluster, even when a fallen cluster gives rise to only a small variation in the nuclear power by virtue of its position and/or by virtue of its low anti-reactivity. Another aim of the invention, by virtue of such detection, is to provide better protection for the reactor of a power station against the damaging consequences of continuing the nuclear reaction in normal service after such a fall. The invention also aims at achieving these results in a simple, and cheap manner which avoids unfavorable secondary effects, an in particular which avoids unnecessary emergency stops of the reactor in the power station. To satisfy these aims, the present invention provides, in particular a method of detecting the fall of an anti-reactive element into the reactor of a nuclear power station, said method being characterized by the fact that variations are monitored firstly in the nuclear power of the reactor under the control of a loop for regulating said power and secondly of at least one external parameter related to events outside the reactor and used in calculating the power reference value which is supplied to said regulation loop in order to control the reactor, said fall being detected by the fact that a rapid drop in said power is detected while no large external parameter variation is detected with a predetermined time relationship to said rapid drop. Naturally, such a time relationship must be adapted to each of the external parameters that is selected for monitoring. The time relationship is chosen so as to show that the drop in nuclear power is the result of a variation in the external parameter. The term "result" is used to cover both the case where it is directly caused by said variation, and the case where it is caused by the same original cause as said variation. The appropriate time relationship is often simply that the time interval between the two events should be less than a predetermined value. It will also be understood that the words "rapid" and "large" have a quantitative meaning herein which depends on the power station to which the invention is applied: a drop in power is said, herein, to be "rapid" if it falls within the range of power drop rates which follow the accidental falls that are to be detected. A variation in an external parameter is said to be "large" if the rapidity and/or the amplitude thereof make it capable of giving rise to such a rapid drop in the nuclear power. Further, it must be understood that the above-mentioned reference power value may itself be used as an external parameter in accordance with the invention, since it is representative of the external parameters from which it is derived. The present invention also provides a nuclear power station having a reactor protected against the fall of an anti-reactive element, said reactor comprising: a core containing fissile fuel elements for maintaining a nuclear reaction providing nuclear power; PA1 a cooling fluid circuit having a branch passing through said core to remove said power in the form of heat and to enable said heat to be utilized outside the reactor; PA1 measurement means for continuously measuring the current nuclear power of the reactor; PA1 anti-reactive regulation elements suitable for reversibly reducing said power; and PA1 regulation drive means controlled by said power measurement means in order to cause said regulation elements to penetrate to a greater or lesser extent into said core depending on whether the current nuclear power is greater than or less than a power reference value, in such a manner as to constitute a nuclear power regulation loop and to enable the reactor to be controlled by varying said reference value, with any reaction of said loop giving rise to transient power variations before settling if possible; PA1 at least one anti-reactive element being suspended above a passage into said core such that an accidental fall of said element causes it to penetrate into the core, thereby initiating a rapid decrease in nuclear power, followed by a reaction from said regulation loop, which reaction is accompanied by transient variations in said power prior to said power settling back on its value prior to said fall; PA1 said reactor further including stop means under the control of a reactor stop signal; and PA1 accident detection means for providing such a reactor stop signal after an accident in the core, in particular such a fall of an anti-reactive element, and thus for protecting the reactor against the damage which would result if said reaction were to continue without the accident being repaired; PA1 said power station further including: PA1 a power outlet member receiving inlet thermal power from another branch of said cooling fluid circuit and providing variable and/or interruptible outlet power to a load; and PA1 at least one nuclear power regulating system receiving the values of parameters external to the reactor such as parameters relating to the operation of said power outlet member, and generating said power reference value in response thereto in order to continuously match the current nuclear power to variations in said parameters so that if such a variation is large it is capable of causing a rapid variation in nuclear power; PA1 said power station being characterized by the fact that said accident detection means comprise a circuit specifically for detecting the fall of an anti-reactive element, said circuit being suitable for detecting firstly rapid drops in nuclear power and secondly said large variations in at least one said external parameter, and for providing a said reactor stop signal when such a drop in nuclear power is detected with no such external parameter variation in a predetermined time relationship with said drop. PA1 Said circuit for detecting a fall comprises: PA1 a nuclear power monitoring circuit comprising differentiating means receiving a measurement signal representative of said power and delivering a derivative signal which is differentiated with respect to time; and PA1 threshold means receiving said derivative signal and delivering a signal representative of a rapid drop in nuclear power when said power drops at a rate greater than a predetermined rate; PA1 at least one external parameter monitoring circuit, each such circuit including differentiator means receiving a measurement signal representative of such a parameter and delivering a derivative signal; and PA1 threshold means receiving the, or each, said derivative signal and providing a signal representative of large variation in an external parameter when any such derivative signal leaves a predetermined range; and PA1 a logic circuit having its inputs connected to said monitoring circuits in order to provide said reactor stop signal on receiving a signal representative of a rapid drop in nuclear power without receiving a signal representative of a large variation in an external parameter. PA1 said logic circuit comprising means for logically adding the output signals from said monitoring circuits. PA1 said logic circuit providing said reactor stop signal when said signal representative of a rapid drop in the current nuclear power is present and none of said delayed and nondelayed signals representative of a large variation in an external parameter is simultaneously present. PA1 said cooling fluid circuit includes cooling loops each of which comprises a primary pressurized water circuit and a secondary water and steam circuit, the primary circuit cooling said core, the secondary circuit including at condenser and a steam generator heated by said primary circuit, each of said circuits including a pump for circulating water; PA1 said means for measuring nuclear power are chambers sensitive to neutron flux and disposed in said core; PA1 said anti-reactive regulation elements are control clusters each comprising a plurality of vertically-suspended rods that penetrate to a greater or lesser extent into passages in said core, each of said cluster simultaneously constituting one of said anti-reactive elements capable of suffering an accidental fall; PA1 said power outlet member comprising at least one steam turbine driven by the steam from at least one of said secondary cooling fluid circuits and driving an alternator; PA1 said load being an electricity supply grid fed from said alternator; PA1 control means being provided on said cooling fluid secondary circuit to control the steam pressure at the inlet to the turbine as a function of the turbine speed and/or the electrical conditions at the alternator outlet, in such a manner as to constitute a regulation loop for the turbine-alternator assembly; and PA1 circuit breaking means are provided to isolate the alternator from the grid in the event of a grid fault or when necessary for power station operation. PA1 the cooling fluid circuit comprises two to four cooling loops; PA1 the means for measuring the nuclear power comprise measurement chambers installed along two orthogonal diameters of the core symmetrically relative to said diameters; and PA1 said accident detection means include, inter alia, means for detecting excessive temperatures and/or excessive steam in the core. (In accordance with the invention, the said means for detecting an accidental fall are provided in addition to said means for detecting excessive temperature and/or steam). PA1 when the power station is voluntarily or automatically isolated from the grid; PA1 when the grid suffers an electric fault requiring a rapid reaction from the power station but not requiring isolation; or PA1 when the turbine is tripped, i.e. when an automatic device turns off its steam feed because of an anomaly. It appears in the context of the present invention that the rapid power drop phenomenon which accompanies such an accidental fall can be used for reliably detecting such a fall provided solely that, when such a power drop is detected, it is possible to establish whether or not it constitutes a part of the transient variations in power which accompany any large variation in an external parameter. More precisely, such knowledge makes it possible to trigger a stop on the basis of a power drop rate threshold which is sufficiently low to ensure that any dangerous fall of an anti-reactive element gives rise to such a stop even if the element in question has relatively low anti-reactivity. This knowledge makes it possible to eliminate the danger which accompanies the selection of such a low threshold, which danger is that relatively large variations in external parameters will give rise to pointless emergency stops which are damaging to exploitation of the power station. This knowledge is made possible by the fact that it is possible to establish simply and with a limited margin of error the time relationships which exist between large easily-detected variations in certain external parameters, and the rapid drops in nuclear power that these variations may give rise to. Preferably, in accordance with the present invention, the following additional dispositions are also adopted: Said circuit for detecting a fall comprises a plurality of said circuits for monitoring external parameters each detecting variations in a corresponding external parameter, Said circuit for detecting a fall comprises at least one delay means for delaying the measurement signal or a signal derived from the measurement signal of at least one of said external parameters in order to provide at least one signal representative of a large variation in an external parameter which signal is delayed relative to another non-delayed signal representative of a large variation in the same parameter; The above disposition makes it possible to take account of a possible time lapse between a variation in an external parameter and some of the nuclear power drop stages which are caused by said variation. The invention is particularly applicable to well known PWR type power stations having the following dispositions: Conventionally, in such a power station: In such a power station, the present invention makes it possible firstly to stop the reactor reliably in the event of a control cluster falling, even if said cluster has relatively low anti-reactivity or if its position is such that it gives rise to a relatively low variation in nuclear power on falling. The invention also makes it possible, simultaneously, to avoid pointlessly stopping the reactor, in particular: The present invention is still more applicable to the case where said pump for the primary cooling fluid circuit is driven by a motor fed with electricity from said alternator such that the speed of said pump varies with the speed of said alternator and said turbine. In such a case it seems advantageous for saidcircuit for detecting a fall to include two of said circuits for monitoring large variations in external parameter, one of said circuits detecting variations in steam pressure at the inlet to the turbine, and the other detecting variations in the speed of the pump in said primary circuit. |
claims | 1. A method for charge neutralization of a charged particle beam, comprising:a) maintaining a sample under an initial low pressure within a chamber;b) injecting a gas into the chamber directly onto a small portion of the sample creating a micro-environment on the small portion of the sample, the micro-environment having a gas concentration higher than elsewhere on the sample, while the sample outside the small portion is maintained closer to the initial low pressure; andc) passing the charged particle beam through the micro-environment and onto the small portion of the sample for promoting charge neutralization in the micro-environment. 2. The method for charge neutralization of claim 1, wherein the gas concentration of the micro-environment is sufficient for promoting charge neutralization in the micro-environment. 3. The method for charge neutralization of claim 2, further comprisingmonitoring the pressure of the chamber prior to passing the charged particle beam. 4. The method for charge neutralization of claim 2, further comprisingmonitoring charging events within the chamber; andadjusting the gas injection into the chamber for promoting charge neutralization in the micro-environment. 5. The method for charge neutralization of claim 4, wherein adjusting the gas injection into the chamber includes varying a gas flow rate, a gas flow pressure, a position of a nozzle delivering the gas, or a combination thereof. 6. The method for charge neutralization of claim 1, wherein the charged particle beam is an ion beam. 7. The method for charge neutralization of claim 1, wherein the gas includes a non-reactive gas. 8. The method for charge neutralization of claim 1, wherein the gas includes a mixture of a non-reactive gas and a reactive gas. 9. The method of charge neutralization of claim 8, wherein the non-reactive gas and the reactive gas are injected into the chamber using independent gas delivery tubes. 10. The method of charge neutralization of claim 8, wherein the non-reactive gas and the reactive gas are pre-mixed and injected into the chamber using a single gas delivery tube. 11. The method for charge neutralization of claim 1, wherein injecting the gas into the chamber comprises:delivering the gas through a gas nozzle, the gas nozzle including:a hollow body for receiving the gas,a frusto-conically shaped aperture extending through the hollow body for receiving the charged particle beam; anda gas outlet orifice concentric with the frusto-conically shaped aperture for delivering the gas from the hollow body to the small portion of the sample. 12. The method for charge neutralization of claim 11, wherein the gas outlet orifice delivers the gas at a high gas flux at the small portion of the sample while maintaining a reduced gas flux near the charged particle beam. 13. The method for charge neutralization of claim 12, wherein the frusto-conically shaped aperture is defined by a top opening having a first area and a bottom opening having a second area, the second area being smaller than the first area to provide a large escape angle for secondary charged particles ejected from a sample surface. 14. The method for charge neutralization of claim 11, wherein the frusto-conically shaped aperture is angled to allow at least two charged particle beams. 15. The method for charge neutralization of claim 11, wherein the hollow body is shaped to form a gas reservoir around the gas outlet orifice. 16. The method for charge neutralization of claim 1, further comprising:detecting secondary particles milled from a sample surface; andmonitoring progress in milling the sample. 17. The method for charge neutralization of claim 16, further comprising:introducing an electrostatic or an electromagnetic field to improve yield of the secondary particle detection. 18. The method for charge neutralization of claim 17, wherein the electrostatic or the electromagnetic field alters the speed and/or a trajectory of the secondary particles. 19. The method for charge neutralization of claim 18, further comprising:providing a heating or a cooling element to control a sample temperature during a gas assisted editing of the sample. 20. The method for charge neutralization of claim 19, wherein the sample temperature is controlled to optimize enhancement or retardation of the gas assisted editing of the sample. |
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description | 1. Field of the Invention The present invention is directed to an apparatus and a method for generating monochromatic X-ray radiation, of the type using an X-ray source, a monochromator and a slit collimator that are arranged relative to one another so that X-rays of a specific energy among the X-rays emanating from the X-ray source are reflected at the monochromator and emerge through the slit of the slit collimator. 2. Description of the Prior Art Monochromatic X-ray radiation is especially desired particularly in some areas of medical technology, for example in mammography, since it enables the imaging of body details with higher contrast than polychromatic radiation, with which parts of the X-ray spectrum are always absorbed in the patient under examination, thereby increasing the radiation dose for the patient without contributing to the image. A reduction of the dose for the patient therefore can be achieved with monochromatic radiation. Also, by a designational utilization of monochromatic X-ray radiation at a specific energy, materials such as contrast agents in medical technology are especially well emphasized in an X-ray image. When, for example, iodine is employed as a contrast agent that is injected into the body of a patient, monochromatic radiation with an energy of approximately 33 keV should be employed so that the tissue structures having the iodine appear especially clearly in generated X-ray images. An apparatus and a method for generating monochromatic X-ray radiation are disclosed in German OS 199 55 848. As can be seen from FIG. 1 herein, which shows an apparatus according to German OS 199 55 848, the apparatus has an X-ray source 1 (merely indicated here), a monochromator 2 as well as a slit collimator 3. The monochromator 2 is arranged at an angle—referred to as the Bragg angle—relative to the focus F of the X-ray source 1 so that only X-rays with a specific energy are reflected at the monochromator 2 at this angle. These X-rays subsequently pass through the slit of the slit collimator 3 and form a fan-shaped, monochromatic X-ray beam 4 having an aperture angle 5. After penetrating an examination subject 6, the X-ray beam 4 is incident on an X-ray detector 7. Since the aperture angle 5 usually amounts to only approximately 1°, the X-ray source 1, the monochromator 2 as well as the slit collimator 3 must be rotated around an axis 8 intersecting the slit collimator 3 in order to scan the examination subject 6 with the fan-shaped, monochromatic X-ray beam 4 and acquire a planar X-ray image of the examination subject 6. It is disadvantageous that comparatively long exposure times are required. An object of the present invention is to provide an apparatus and a method of the type initially described with which the production of an X-ray image of an examination subject with monochromatic X-ray radiation is simplified. According to the invention, this object is achieved by an apparatus and a method wherein an X-ray source, a monochromator and a slit collimator are arranged at an angle relative to one another such that only X-rays of a specific energy among the X-rays emanating from the X-ray source are reflected at this angle at the monochromator and emerge through the slit of the slit collimator, and for scanning an examination subject to be charged with monochromatic X-rays, the monochromator is adjustable relative to the X-ray source and the slit collimator on a predefined path such that the condition for the reflection angle required for the reflection of X-rays remains substantially satisfied during the adjustment and essentially only X-rays of the specific energy pass through the slit of the slit collimator. The monochromator is thus adjusted relative to the X-ray source and the slit collimator so that only X-rays of a specific energy proceed through the slit of the slit collimator, so an angular range, and thus an examination subject, can be scanned with the generated, fan-shaped monochromatic X-ray beam due to the adjustment of the monochromator relative to the slit collimator. In this way, an X-ray exposure of an examination subject can be acquired relatively simply with monochromatic X-ray radiation. In versions of the invention the monochromator is a monochromator crystal, preferably a highly oriented, pyrolytic graphite crystal, referred to as an HOPG crystal. When X-ray radiation emitted by the X-ray source strikes such an HOPG crystal at the Bragg angle (the Bragg angle for a photon energy of, for example, 17 keV amounts to 6.1°) the HOPG crystal reflects monochromatic X-ray radiation of this energy at this angle in the direction toward the slit of the slit collimator. A fan-shaped beam of monochromatic X-rays ultimately passes through the slit collimator. According to another version of the invention, the monochromator can be a multi-layer system, for example Göbel mirrors, that reflects X-rays. In further versions of the invention the monochromator is adjustable along a substantially elliptical path, and the focus of the X-ray source in a preferred embodiment located substantially in one focus of the ellipse defining the elliptical path, and the slit of the slit collimator is substantially located in the other focus of the ellipse. As a result of the adjustment of the monochromator on an elliptical path, the Bragg condition for the reflection of X-rays of a specific energy remains essentially met. However, the reflected, monochromatic X-radiation passes through the slit of the slit collimator at various angles, so the scan effect is achieved. The present invention is a modification of the method and apparatus that were initially described and is shown in FIG. 1. X-rays emanating from the focus F of the schematically indicated X-ray source 1 strike the monochromator 2, at which they are diffracted and reflected. X-rays of a specific energy are selectively reflected at a specific angle at the monochromator 2. The slit collimator 2 is arranged such relative to the monochromator 2 and the X-ray source 1 so that only X-rays of this specific energy can pass through the slit of the slit collimator 3 and form a fan-shaped beam 4 of monochromatic X-rays having an aperture angle 5. After the monochromatic X-ray beam 4 has penetrated through an examination subject 6, it strikes an X-ray detector 7. Since, as already mentioned, the aperture angle 5 only amounts to approximately 1°, only a small strip of the examination subject 6 is penetrated by the monochromatic X-ray beam 4. For generating a planar X-ray image of the examination subject 6, the apparatus composed of the X-ray source 1, monochromator 2 and slit collimator 3 must be rotated around the axis 8 shown in FIG. 1. In order to avoid this rotation around the axis 8, which involves a relatively long exposure time for acquiring a planar X-ray exposure of the examination subject 6, in accordance with the invention the monochromator 2 is adjusted relative to the X-ray source 1, or the focus F of the X-ray source 1, and relative to the slit collimator 3 in order to acquire a planar X-ray exposure of the examination subject 6, as shown in FIG. 2. As an example, FIG. 2 shows three positions I, II and III of the monochromator 2 relative to the focus F of the X-ray source 1 and relative to the slut collimator 3. The adjustment of the monochromator 2 relative to the X-ray source 1 and the slit collimator 3 ensues such that the condition for the reflection angle Θ required for the reflection of X-rays of a specific energy at the monochromator 2 remains substantially satisfied during the entire adjustment motion of the monochromator 2 relative to the X-ray source 1 and the slit collimator 3, and thus substantially only X-rays of the specific energy can pass through the slit of the slit collimator 3. As shown in FIG. 2 for the three positions I, II and III of the monochromator 2, the X-ray beam emanating from the focus F of the X-ray source 1 strikes the monochromator 2 at the angle Θ, and X-rays of a specific energy are reflected at the angle Θ at the monochromator 2 and pass through the slit of the slit collimator 3 as a fan-shaped beam 4 of monochromatic X-radiation. When, accordingly, the monochromator 2 is continuously adjusted from its initial position I shown in FIG. 2 into its final position III shown in FIG. 2 during the acquisition of an X-ray exposure of the examination subject 6, then the fan-shaped, monochromatic X-ray beam 4 sweeps an angular range φ that suffices in order to scan the examination subject 6. When, for example, the apparatus for generating monochromatic X-radiation is provided for employment in mammography, then an X-ray source 1 that has an anode 9 of molybdenum is usually employed. In this case, the monochromator 2 is arranged or adjustable such relative to the focus F of the X-ray source 1 and the slit of the slit collimator 3 such that a reflection angle Θ of the X-ray radiation (Bragg angle) is adhered to at which X-ray radiation having an energy of approximately 17.5 keV is selected, this corresponding to the energy of the Kα line of molybdenum. Given this arrangement, essentially only X-rays of this energy pass through the slit of the slit collimator 3, which preferably has a width of approximately 50 μm. The monochromator 2 is a monochromator crystal, preferably an HOPG crystal (highly oriented pyrolytic graphite crystal). As indicated in FIG. 2, the HOPG crystal 2 is preferably adjusted along an elliptical path, with the focus F of the X-ray source 1 situated in one focus of the ellipse defining the elliptical path and the slit of the slit collimator 3 situated in the other focus of the ellipse. The duration of the adjustment motion of the HOPG crystal 2 from its initial position I into its final position III essentially corresponds to the duration for the acquisition of a planar X-ray exposure or to a whole-numbered fraction of this duration. When, for example, the distance of the slit of the slit collimator 3 from the focus F of the X-ray source 1 amounts to 10 cm and the HOPG crystal 2 is moved from its initial position I, in which it is situated approximately 1 cm in front of the focus F of the X-ray source 1, into its final position III wherein it is situated approximately 1 cm in front of the slit of the slit collimator 3, then an exit angle range φ of approximately 12.8° occurs given a Bragg angle of Θ=8°. Given a distance of 80 cm of the slit of the slit collimator 3 from the plane of the X-ray detector 7, thus, a region of 18 cm can be swept on the X-ray detector 7. This corresponds to the standard X-ray film width. FIG. 3 shows a schematic top view of an adjustment mechanism 10 for the HOPG crystal 2. In the exemplary embodiment shown in FIG. 3, the HOPG crystal 2 is provided with four rods 11 through 14 that are guided in guide rails 15 and 16 at both sides of the monochromator 2. The adjustment of the rods 11 through 14 in the guide rails 15 through 16 ensues electromotively (in a way that is not shown). The adjustment is controlled by a conventional computer device that is not shown and that is suitably programmed for the aforementioned control. Compared to the known method and apparatus initially described, the inventive apparatus and method have the advantages that an examination subject can be scanned with a fan-shaped beam of monochromatic X-radiation in a comparatively short time using a less complex apparatus. Planar detectors, for example X-ray films, X-ray image intensifiers or solid-state detectors can be employed. As an alternative to HOPG crystals, other monochromator crystals or multi-layer systems, for example Göbel mirrors, that reflect X-rays can be employed as the monochromator. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art. |
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abstract | A method for producing 229Th includes the steps of providing 226Ra as a target material, and bombarding the target material with alpha particles, helium-3, or neutrons to form 229Th. When neutrons are used, the neutrons preferably include an epithermal neutron flux of at least 1×1013 n s−1·cm−2. 228Ra can also be bombarded with thermal and/or energetic neutrons to result in a neutron capture reaction to form 229Th. Using 230Th as a target material, 229Th can be formed using neutron, gamma ray, proton or deuteron bombardment. |
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abstract | The present invention relates to a nuclear reactor (1), in particular a liquid-metal-cooled reactor, provided with a separation structure (5) between hot header (6) and cold header (7), narrower in the upper portion (16) for containment of the headers of the fuel assemblies and wider in the lower element (14) at the active part (4) of the core, with a variously shaped connecting element (15) between the lower element (14) and the upper element (16), and with heat exchangers (11) positioned between the upper portion (16) of said separation structure (5) and the reactor vessel (2), which engage on the connecting element (15) via vertical ducts (20) for being fed with hot primary fluid leaving the core (4). |
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abstract | An object of the invention is to embody a small and inexpensive passage selector, which can be applied by commonly using an index device even if the number of detector passages is changed, and which is easy to make inspection and maintenance. The passage selector of a reactor in-core nuclear-measuring apparatus of the invention includes: a drive motor; an index device that is driven by the drive motor and that makes a rotary output of a predetermined index number; a central rotating shaft that is driven to rotate by the index device and that causes a passage selecting guide tube to be located in opposition to any detector passage; and a speed-increasing and decreasing device that is interposed between an output shaft of the index device and the central rotating shaft, and that adjusts the index number of the central rotating shaft. |
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abstract | A first robotic assembly transfers articles from carriers on a transport mechanism at a loading area to a first load conveyor. The conveyor transfers the articles to a process conveyor which moves the articles through a target region at a substantially constant speed. The process conveyor then transfers the articles to a second load conveyor. A second robotic assembly then transfers the articles to article carriers on the transport mechanism at an unloading area. The load and process conveyors may be divided into two tracks. First and second radiation sources respectively disposed at first and second gaps in the process conveyor in the target region respectively irradiate the articles in both tracks in opposite directions from positions above and below the articles. Articles on the tracks may be (a) diverged on the first load conveyor to separate the articles from the dividers, (b) converged on the process conveyor to minimize the width of the radiation sources and (c) diverged on the second load conveyor. If one of the radiation sources is not operative, the other source may irradiate the opposite sides of the articles during article movements sequentially on the first tracks of the first load conveyor, the process conveyor and the second load conveyor and then sequentially on the second tracks of the first load conveyor, the process conveyor and the second load conveyor. The articles are inverted during their transfer from the first track of the second load conveyor to the second track of the first load conveyor. |
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description | This application claims priority of German Application No. 10 2006 053 579.0, filed Nov. 10, 2006, the complete disclosure of which is hereby incorporated by reference. The invention is directed to a laser protection arrangement for application in laser material processing. In laser material processing, hazards can arise on one hand through the direct action of laser radiation on humans or sensitive objects, e.g., as a result of faulty control, and on the other hand through materials in gaseous, liquid or particulate form which are ablated in the course of processing. Quantities of laser irradiation which are harmless to humans are specified as a function of radiation properties (wavelength, output or pulse energy, time modulation, active time period) in national and international guidelines. The danger posed by ablated material is usually not laser-specific and is regulated in general rules for the handling of hazardous gaseous substances such as aerosols and dust particles. Particular risks occur, for example, in the processing of organic materials (e.g., natural and synthetic materials such as textiles, leather, composite materials), where even small concentrations of burned up waste can be hazardous to health. This is particularly true of the fine particles of inorganic materials. In industrial installations, hazards are generally averted through suitable enclosure of lasers and processing objects (workpieces) and the mechanical installations (e.g., articulated-arm robots, gantries) which adjust and modify the relative position of the beam and workpiece programmably in a booth which allows neither radiation nor ablated material to exit during operation of the laser. In this case, a suitable exhaust, possibly provided with filters, is generally used. Enclosures of this type which are known from the prior art can be classified into passive enclosures and active enclosures or laser protection walls. Passive laser protection walls, including windows and doors, are designed such that they withstand full laser irradiation, such as can occur from incorrect orientation of the beam, over a given period of time without impairment of the protective action. It is disadvantageous that booths comprising passive laser protection walls not only occupy a relatively large space but are also heavy and engender high investment and operating costs. Also, the required exhaust capacities (and, consequently, the expenditure on exhaust) increase with the size of the booth. Because of the size and great bulk, the laser material processing installations can only be used at various locations by a relatively large expenditure. These disadvantages are particularly pronounced in medium-size laser processing installations (in the power range of about 100 W to about 1 kW) which it would be desirable to integrate into flexible processing chains. In contrast to the above-mentioned passive laser protection walls, active laser protection walls not only passively prevent penetration of the laser radiation through their dimensioning and material characteristics, but also switch off the laser radiation immediately when the laser radiation strikes the laser protection wall. Accordingly, the requirements for booth walls (including windows and doors) can be eased by reducing the maximum possible storage of radiation before a safety cutoff. By reducing the wall thickness and/or the use of other wall materials, wall mass and cost can be reduced with the booth geometry remaining the same. Further, modified booth constructions can be used in which the walls enclose only the immediate surroundings of the respective processing location more or less flexibly. A great many solutions for active laser protection walls are known from the prior art. DE G 89 08 806 U1, which is based on a prior art according to which the laser processing process must be attentively observed by the worker so that the emergency switch can be actuated in case of anomaly, describes a protective arrangement for a laser processing machine comprising side walls, which surround the work area and which are at least partly movable, and an emergency cutoff. A current-carrying conductor, e.g., in the form of loops, acting with the emergency cutoff as a safety fuse is integrated in the side walls. The conductor is advantageously arranged in a zigzag manner between composite disks, i.e., an inner, transparent synthetic resin disk and an outer glass disk. The conductors of a plurality of side walls can be connected in series or individually to the emergency cutoff. A shield according to GB-A 1595201 is formed by two layers which are at a distance from one another and define a closed chamber, and one of the layers can be destroyed by the laser. EP 0 157 221 B1 discloses a laser protection arrangement which is distinguished from the above arrangement in that the shield is transportable and freestanding and the chamber is filled with a gaseous medium and a sensor is provided which reacts to the gas flow following the destruction of a layer. The pressure in the chamber can diverge from atmospheric pressure (also vacuum pressure) and the sensor reacts to changes in pressure in the chamber. Alternatively, the chamber can contain a detectable gas and the sensor detects this gas. The sensor can be connected to an alarm device or a cutoff. DE 199 40 476 A1 shows a laser protection wall which has at least one sensor, e.g., a heat sensor or a light sensor, that detects laser radiation. DE 36 38 874 A1 is directed to a two-layer viewing window in a protective device with an electric conductor running between the layers. When the laser burns a hole in the inner layer, the conductor, which is part of a safety cutoff for controlling the laser source, melts and the laser is switched off before it can also penetrate the outer layer. Alternatively, the change in resistance of the conductor resulting from an increase in temperature is measured and an acoustic or optical warning signal is generated. The conductor is arranged, e.g., in a wavy or zigzagging shape, at distances which are less than the beam diameter at the point of incidence. A similar device is disclosed in U.S. Pat. No. 4,710,606. EP 0 321 965 B1 discloses a laser protection wall of transparent material which directs the impinging laser radiation to an integrated illumination device, e.g., a photodiode, that generates an electric signal depending on the illumination intensity. A laser protection wall of this kind has the advantage that no fine-meshed net of conductor wires is required and that there is no destruction and therefore no need for replacement. All of the active laser protection walls mentioned above have in common that they have a laser radiation-sensitive element, i.e., an element which undergoes a state change when acted upon by the laser radiation, which results in the laser being switched off. The laser radiation-sensitive element forms either a closed surface or a grid-shaped or net-like surface within or on a side of the laser protection wall, wherein the grid spacing or net mesh size is not greater than the beam diameter of any possibly impinging laser beam. In almost all of the solutions mentioned above, the laser radiation-sensitive element, e.g., a safety fuse or a chamber-enclosing layer, is at least partially destroyed when acted upon by laser radiation so that the laser protection wall must be exchanged in order to restore safety. The dependability of the solutions in which the laser radiation-sensitive element, e.g., a transparent surface for conveying the laser radiation to a radiation sensor, is not destroyed appears questionable. It is the primary object of the invention to provide a laser protection arrangement comprising at least one laser protection wall which works dependably and which must be replaced after being struck by laser radiation in order to maintain absolute safety. The invention is based on the idea of carrying out the two functions of an active laser protection wall, namely, first, to cause the laser to be immediately switched off after the impingement of laser radiation and, second, to ensure a passive laser protection in order to store the amount of impinging radiation before cutoff, by materially separate means, i.e., by a device for active protection and a device for passive protection. The device for passive protection can be any conceivable passive laser protection wall which is designed such that it can store the impinging amount of radiation before the safety cutoff. It is preferably designed in such a way that it does not undergo any irreversible changes in doing so. The device for active protection is a foil which is either itself a laser-sensitive element or is incorporated in or arranged on a laser-sensitive element. According to the invention, the foil, hereinafter laser protection foil, is arranged in front of the passive laser protection wall in the radiation direction. In general, it is damaged when struck by laser radiation and must subsequently be exchanged to restore safety. On the other hand, the laser protection wall arranged behind it need not be exchanged, which economizes on costs and resources. Compared to all of the solutions for active laser protection walls known from the prior art, a laser protection arrangement which comprises a passive laser protection wall with a laser protection foil arranged in front of it according to the invention is appreciably cheaper in the long term and safety can be restored more quickly and more simply. By dividing the two above-mentioned functions of the laser protection arrangement between two materially separate devices, a further advantage is achieved in that the entire work space of the laser need not necessarily be enclosed; that is, in order for laser radiation exiting from the work space to be contained in all instances, the work space is completely surrounded by the laser foil, but a passive laser protection wall need not necessarily be arranged behind the laser protection foil in every spatial direction, e.g., toward the shop ceiling, but only in the areas in which the laser radiation could affect persons or sensitive objects at a dangerous intensity. For some constructions of the laser protection foil, the surface area of a passive laser protection wall to accompany it need not be taken into account already during manufacture, so that it can also be stocked in an unfinished state and cut to the required dimensions as needed. This makes exchange even cheaper and simpler. It is advantageous that the unimpaired functionality of the laser protection foil can be checked at any time. This can be achieved for the individual constructions of the laser protection foil either by an obvious destruction or can be indicated by means of a sensor signal. The invention will be described more fully in the following with reference to a number of embodiment examples shown in the drawings. A laser protection arrangement according to the invention (FIG. 1) which prevents a laser beam of a laser material processing installation from exiting its work area comprises a passive laser protection wall 1, a laser protection foil 3, at least one sensor 4, and a threshold switch 5 by which a laser 2 of the laser material processing installation is connected to an energy source 6. A plurality of laser protection arrangements of the type mentioned above can be assembled to form a laser protection booth so that a plurality of threshold switches 5 are connected in series between the laser 2 and the energy source 6. In a first embodiment example, the laser protection foil 3 is a thin foil of expandable material with a thickness between 0.2 mm and 2 mm and is stretched in an expanded state in front of or on a passive laser protection wall 1 located behind it. At least one expansion sensor which senses tensile strain is provided on the laser protection foil 3. The laser protection foil 3 is preferably expanded in only one direction, and the expansion sensor is an expansion measurement strip which adheres to the foil in the expansion direction. When struck by laser radiation, the foil is destroyed at the point of incidence and a tear forms proceeding from the point of incidence and extending substantially perpendicular to the expansion direction and leads to a reduction in the tensile strain in the foil. When the tensile strain falls below a predetermined threshold, the laser 2 is switched off by a threshold switch 5 communicating with the expansion measurement strip and the laser 2. Because the laser protection foil 3 is stretched in front of the laser protection wall 1 in a positive or frictional engagement only by holding elements, the destroyed laser protection foil 3 can be removed simply by loosening the holding elements and replacing it with a new laser protection foil 3. Since the laser protection foil 3 can be finished in any size, a passive laser protection wall 1 can be covered by an individual large laser protection foil 3 or by a plurality of correspondingly small laser protection foils 3. Exchange is facilitated by the latter alternative. A laser protection arrangement with a laser protection foil 3 according to the first embodiment example is particularly advantageous for forming laser protection booths in many different configurations which completely enclose the work space of the laser material processing installation. A laser protection booth of the type mentioned above basically comprises a plurality of side walls of the same height which stand vertically and are connected to one another by their longitudinal sides so as to form a closed base and a ceiling closing at the top. A door and frequently also a window are integrated in the side walls. In order to optimally adapt the base of the booth to the work space of the laser material processing installation, it is often useful to construct the booth in different widths. In the laser protection walls of the prior art, this led to the problem that a replacement had to be stocked for every width so that safety could be restored immediately when needed. A laser protection foil 3 according to the first embodiment example can be stocked on a roll in unfinished state by the meter, cut immediately before use as needed, and provided with an expansion measurement strip. The laser protection foil 3 can also be used by itself as a ceiling without a passive laser protection wall 1 arranged behind it. In this case, it is also preferably stretched only in one direction regardless of the shape of the ceiling area which is basically identical to the shape of the base area. The laser protection booth is accordingly reduced in mass, while nevertheless ensuring that no gases occurring during processing can penetrate to the outside and that the laser 2 is switched off when laser radiation exits the work space due to faulty control. The shop ceiling, which is often located above the ceiling of the laser protection booth, is far enough away from the laser 2 that the radiation intensity cannot cause any damage when striking the shop ceiling. For laser processing installations whose work space is substantially higher than the size of a person for whom the protection is provided in particular, a laser protection side wall can also be constructed in such a way that the passive laser protection wall 1 ends, e.g., at a height of 2.20 m and the total height is lengthened by an open frame, the laser protection foil 3 being clamped in the open frame. The laser protection foil 3 need not be stretched by holding elements which are located at the passive laser protection wall 1, but can also be erected, e.g., in a freestanding frame in front of the passive laser protection wall 1. In a second embodiment example, at least one electric conductor path is embedded in or arranged on the laser protection foil 3. The conductor paths are arranged in a finished laser protection foil 3 in such a way that the distance between two adjacent conductor paths is always smaller than the diameter of a laser beam at the point of incidence in order to ensure than the conductor path is struck regardless of where the laser beam strikes the laser protection foil 3. The conductor paths are connected by one end to a current source or voltage source and by the other end to a measurement device via contacts. In principle, one conductor path per laser protection foil 3 is sufficient. It is preferably arranged in a sine-shaped or zigzag shape. When the laser beam strikes a conductor path, its resistance changes first due to heating and melts when acted upon again by radiation. The increase in resistance or drop in current or voltage is measured and if the measured quantity exceeds or falls below a predetermined threshold value the laser 2 is switched off by a threshold switch 5. In a third embodiment example, optical fibers are embedded in the laser protection foil 3 instead of electric conductor paths. To direct the radiation to a radiation detector connected to the fiber ends independent of the angle of incidence of the laser beam, the fiber has a fiber cladding surrounding a fiber core. This fiber cladding is destroyed in a locally limited manner when struck by laser radiation so that the laser radiation enters into the optical fiber and can be directed to the radiation sensor. To ensure that the radiation is reliably coupled into the fibers, the fibers can be arranged using a knitting technique so that they take up a large angle relative to the surface of the laser protection foil 3. In a fourth embodiment example, optical fibers which are embedded in the laser protection foil 3 are supplied with a modulated laser radiation which is detected by a sensor. When the optical fibers, particularly plastic fibers in this instance, are destroyed, a change in the detected signal is perceived. A laser protection foil according to the invention can also comprise electrically or optically conducting layers instead of electric or optical conductor paths. Accordingly, for example, a fifth embodiment example for a laser protection foil 3 is a plastic foil which is provided with an electrically conductive layer on one side and with electric conductor paths on the other side. Current flows through both of these or a voltage is applied to both. When struck by laser radiation, the plastic foil located therebetween melts locally so that the layer and the conductor path come into contact with one another and cause a short circuit. In a sixth embodiment example, the material of the laser protection foil 3 is a material that is transparent to the laser radiation and is coated on both sides with a highly reflective layer. An impinging laser beam destroys the highly reflective layer due to its energy density at the point of incidence, is then dispersed in the transparent material and strikes a radiation sensor integrated in the transparent material. Embodiment examples two to five basically show laser protection foils in which the foil itself forms only one layer. They differ from a laser protection foil 3 according to the first embodiment example in that additional elements are provided and in that the laser protection foil 3 can be glued to the passive laser protection wall 1 or arranged thereon by means of some other material engagement. Although this may be time-consuming to exchange, no additional holding elements or tensioning elements are necessary. The laser protection foil 3 can be placed on any curved passive laser protection walls 1. According to a seventh embodiment example, the laser protection foil 3 is a double-foil which is formed by at least one gas-filled hollow chamber, and the laterally adjoining foil layers are advantageously connected to one another in more than one place by webs so as to keep the hollow chambers flat even under above-atmospheric pressure. A pressure transducer is connected in or to every hollow chamber. The gas pressure in the hollow chambers is higher than the ambient pressure so that when a hollow chamber is destroyed the internal pressure drops and when the measured pressure falls below a threshold value a threshold switch 5 connected to the pressure transducer switches off the laser 2. A laser protection foil 3 is preferably formed by only one hollow chamber. In this way, only one pressure transducer is needed. It is also conceivable to measure sound signals generated by the destruction of the hollow chamber which is under pressure and to use the sound signal as a signal for switching off the laser 2. A sound signal of this kind is also detectable when a stretched laser protection foil 3 according to the first embodiment example is destroyed and could also be used as a switching signal. In an eighth embodiment example, the hollow chambers are filled with a special gas which exits and can be detected when the hollow chamber is destroyed. For this purpose, it is advantageous when the hollow chamber has the greatest possible volume so that the exiting gas can be detected by a gas detector as quickly as possible. In particular, laser protection foils 3 according to the seventh and eighth embodiment examples afford the possibility of collapsible, freestanding booths. For this purpose, each of the individual, e.g., four, side walls which are joined to one another lengthwise preferably comprises only one hollow chamber with an inlet valve by which the hollow chambers are filled with gas at the setup location. In the hazardous area, which does not generally extend in height substantially beyond the maximum height of a person, passive laser protection walls 1 are added to the laser protection foils 3. A laser protection booth of the type mentioned above is an economical and time-saving protection solution particularly for occasional use of lasers in certain locations. In a ninth embodiment example, the laser protection foil 3 is a bubble foil, i.e., it comprises a plurality of small hollow chambers. In this case, in contrast to the first and seventh embodiment examples, a series of acoustic signals is initiated when a laser beam moves over the laser protection foil 3 due to faulty control. In order to prevent defects in the individual chambers or bubbles from being overlooked, the latter are advantageously separated from one another by thin channels or by walls with poor permeability to gas. For example, the bubbles can be arranged in a honeycomb structure with semipermeable dividing walls. While the chamber pressure is increased so sharply by a sudden impingement of laser radiation that a shock wave is initiated, which also destroys neighboring chambers or bubbles, any other kind of defect in a chamber or a bubble becomes noticeable in that the pressure in the entire laser protection foil drops due to the pressure equilibrium taking place. When switching off a laser as a consequence of acoustic signals, it is important that these signals differ significantly from the sounds generated by laser material processing. The signals are reinforced by one or more suitably arranged microphones and initiate a cutoff. The microphones must be distributed in such a way that at least one microphone is always reached by an airborne or structure-borne sound sufficiently quickly after the impingement of the laser pulse. While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention. 1 passive laser protection wall 2 laser 3 laser protection foil 4 sensor 5 threshold switch 6 energy source |
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047626739 | description | DETAILED DESCRIPTION The present invention provides a burnable poison rod that is of the normal length of such rods but which acts in the manner of a part-length burnable poison rod. The rod, as is conventional, comprises a metallic tube or cladding that is formed from stainless steel or a zirconium alloy such as zircaloy. The rod has upper and lower closure means in the form of end plugs. Positioned within the cladding is a neutron absorber or burnable poison which absorbs excess neutrons. These neutron absorbers are known in the art, and include boron, such a boron carbide or a boron carbide-aluminum oxide mixture, gadolinium, samarium, europium and the like. A preferred neutron absorber comprises borosilicate glass in the form of a tube which fits within the tubular cladding. In the burnable poison rod of the present invention, the neutron absorber is spaced from the bottom closure means of the rod by a neutron moderating spacing means which may be in the form of a solid mass or a contained liquid mass. Neutron moderators are materials which will slow down neutrons, but do not absorb the same as do neutron absorbers, and are also known in the art. In embodiments of the present invention where a solid mass of a neutron moderator is used as the neutron moderating spacing means, graphite, carbon, or beryllium, or the like are usable. In embodiments of the present invention where a liquid neutron moderating means is used, the lower closure means or end plug has an aperture therein and the side wall of the lower section of the cladding has apertures therein, such that the lower section is filled with coolant of the reactor, such as water. An intermediate or sealing plug is provided to seal the lower section of the burnable poison rod from the neutron absorber contained therein. The liquid coolant will flow into the lower section of the rod and is contained therein to act as a neutron moderator. While actual continuous flow of the water through the rod is not effected, the apertures prevent stagnation of the contained water. In FIG. 1, there is illustrated an embodiment of the burnable poison rod of the present invention. As illustrated, the rod 1 has a tubular metallic cladding 3 and upper and lower closure means 5 and 7 respectively. Positioned within the tubular cladding 3 is a neutron absorber 9 such as a borosilicate tube. Centered within the borosilicate tube 9 is a stainless steel spacer tube 11, the tube 11 having a radially outwardly directed flange 13 therein, upon which the bottom end 15 of the borosilicate tube 9 will rest. A neutron moderating spacing means is provided within the metallic cladding 3, which spacing means comprises a solid mass 17, of cylindrical shape, of a neutron moderating material. This neutron moderating spacing means 17 positions the borosilicate glass tube 9 in spaced relation to the lower closure means 7 and acts to moderate fast neutrons. The length of the cylinder of neutron moderator 17 is determined by the distance from the lower closure means that it is desired to position the neutron absorber, or borosilicate glass tube 9. Another embodiment of the present invention is illustrated in FIG. 2. As illustrated, the rod 21 has a tubular metallic cladding 23 and upper and lower closure means 25 and 27 respectively. Positioned within the tubular cladding 3 is a neutron absorber 29, shown as a borosilicate glass tube. As with the previous embodiment, a stainless steel spacer tube 31 may be centered in the borosilicate tube 29, the spacer tube having an outwardly directed flange 33 thereon, upon which the bottom end 35 of the borosilicate tube will rest. A neutron moderating spacing means is provided within the metallic cladding 23 which comprises a lower section 37 of the rod adapted to contain water or other neutron moderating liquid, the lower section 37 sealed from the neutron absorber 29 by means of a sealing plug 39. The sealing plug 39 may divide the cladding into separate sections along its length as illustrated, or it may fit within grooves in the interior wall of the cladding. The lower closure means 27 comprises an end plug having an axial aperture 41 therethrough which communicates with the interior of the lower section 37 of the tubular cladding 23. A plurality of apertures 43 are also provided through the wall of the cladding 23 at the lower section 37 thereof. The apertures 41 and 43 provide for the containment of water or other liquid coolant within the lower section 37 to act as a neutron moderator, while the sealing plug 39 positions the neutron absorber in spaced relationship to the lower closure means 27. The burnable poison rods of the present invention are usable in a nuclear fuel assembly using conventional handling equipment. As illustrated in FIG. 3, a nuclear fuel assembly 51 includes an array fuel rods 53 held in spaced relationship to each other by grids 55, 57 and 59 (only three of which are shown in FIG. 3) spaced along the fuel assembly length. Each fuel rod includes nuclear fuel pellets 61 and a spring 63 located in the plenum of each fuel rod, and the ends of the rods are closed by end plugs 65, all in a conventional manner. To control the fission process, a multiplicity of control rods 67 or burnable poison rods 69, are reciprocally movable in control rod guide tubes or guide thimbles located at predetermined positions in each selected fuel assembly in the reactor. The guide thimbles are attached to the grids 55, 57 and 59. The reactor includes a top nozzle 71 and a bottom nozzle 73 to which opposite ends of the control rod guide thimbles are attached to form an integral assembly capable of being conventionally handled without damaging the assembly components. Typically, the guide thimbles have sleeves for weld compatibility with the upper 55 and lower 59 grids and with the top 71 and bottom 73 nozzles. In this case, a sleeve 75 is used to join the guide thimble 77 to the upper grid 57 and the top nozzle 71. Each guide thimble 77 extends the full length of the fuel assembly 51 between the top nozzle 71 and the bottom nozzle 73. The sleeve 75 only extends from the top nozzle 71 to the upper grid 55, and the sleeve 79 only extends from the bottom nozzle 73 to the lower grid 59. The guide thimble 77 is attached to the sleeve 75 by a bulge fit. The guide thimble 77 is attached to the sleeve 79. As illustrated, the top nozzle is square in cross section and comprises a housing 81 having an upper plate 83 spaced from a (lower) adapter plate 85. Assembly hold-down springs 87 attached to opposite sides of upper plate 83 are held in place by bolts 89 and are adapted to be compressed when the reactor upper core plate (not shown) is placed in position. The top nozzle further includes a rod cluster control assembly 91 comprising an internally threaded cylindrical member 93 having radially extending flukes or arms 95. A connector 97 interconnects each control rod 67 or burnable poison rod 69 with the arms, the arrangement being such that the rod cluster assembly positions the control rods and burnable poison rods vertically in the rod guide thimbles to thereby control the fission process in the assembly. There has been described a burnable poison rod which contains a neutron absorber spaced from the bottom closure means of the rod by a neutron moderating spacing means. The use of the neutron moderating spacing means axially positions the neutron absorber within the rod at a spaced location from the bottom closure for the rod, minimizes the displacement of the neutron moderator, and maintains a proper overall length for the burnable poison rod required for compatability with existing rod handling equipment. |
claims | 1. A method of creating charged beam drawing data used for a charged beam drawing apparatus to draw a pattern on a drawing area of a sample by irradiating a charged beam onto the sample, the method comprising:selecting a charged beam drawing apparatus which divides the drawing area into two or more hierarchical fields including a plurality of main fields, a plurality of subfields which are lower in layer than the plurality of main fields and a plurality of unit fields which are lower in layer than the plurality of subfields, and draws a pattern using the unit field as a drawing unit, as the charged beam drawing apparatus to draw the pattern;dividing design data corresponding to the pattern to be drawn on the drawing area into a plurality of first design data corresponding to the plurality of main fields, dividing each of the plurality of first design data into a plurality of second design data corresponding to the plurality of subfields, and dividing each of the plurality of second design data into a plurality of third design data corresponding to the plurality of unit fields;evaluating quality of resist resolution to a predetermined dimension on each of the plurality of unit fields;creating a table which relates the plurality of unit fields to the quality of the resist resolution based on an evaluation result acquired by the evaluating the quality of the resist resolution;judging whether or not each of the plurality of third design data corresponds to data having the predetermined dimension and corresponds to a pattern falling in the unit field which the quality of the resist resolution is rejectable based on the predetermined dimension and the table; andconverting data judged to correspond to the data among the plurality of third design data into first drawing data after performing a coordinate conversion so that the data fall in the unit field which the resist resolution is acceptable, and converting data judged not to correspond to the data among the plurality of third design data into second drawing data without performing the coordinate conversion. 2. The method of creating charged beam drawing data according to claim 1,wherein the hierarchical fields are two hierarchical fields including the plurality of main fields, the plurality of subfields and divided subfields as the plurality of unit fields, or three hierarchical fields including the plurality of main fields, the plurality of subfields, subsubfields which are lower in layer than the plurality of subfields and divided subfields as the plurality of unit fields. 3. A charged beam drawing method using a charged beam drawing apparatus to draw a pattern on a drawing area of a sample by irradiating a charged beam onto the sample, the method comprising:selecting a charged beam drawing apparatus which divides the drawing area into two or more hierarchical fields including a plurality of main fields, a plurality of subfields which are lower in layer than the plurality of main fields and a plurality of unit fields which are lower in layer than the plurality of subfields, and draws a pattern using the unit field as a drawing unit, as the charged beam drawing apparatus to draw the pattern;dividing design data corresponding to the pattern to be drawn on the drawing area into a plurality of first design data corresponding to the plurality of main fields, dividing each of the plurality of first design data into a plurality of second design data corresponding to the plurality of subfields, and dividing each of the plurality of second design data into a plurality of third design data corresponding to the plurality of unit fields;evaluating quality of resist resolution to a predetermined dimension on each of the plurality of unit fields;creating a table which defines a unit field having an acceptable resist resolution and a unit field having a rejectable resist resolution among the plurality of unit fields based on an evaluation result acquired by the evaluating the quality of the resist resolution;judging whether or not each of the plurality of third design data corresponds to data having the predetermined dimension and corresponds to a pattern falling in the unit field which the quality of the resist resolution is rejectable based on the predetermined dimension and the table; andconverting data judged to correspond to the data among the plurality of third design data into first drawing data after performing a coordinate conversion so that the data fall in the unit field which the resist resolution is acceptable, and converting data judged not to correspond to the data among the plurality of third design data into second drawing data without performing the coordinate conversion. 4. The charged beam drawing method according to claim 3,wherein the evaluating the quality of the resist resolution to the predetermined dimension on each of the plurality of unit fields is performed in real time based on a shape of the charged beam which is irradiated from the plurality of unit fields. 5. The charged beam drawing method according to claim 3,wherein the hierarchical fields are two hierarchical fields including the plurality of main fields, the plurality of subfields and divided subfields as the plurality of unit fields, or three hierarchical fields including the plurality of main fields, the plurality of subfields, sub-subfields which are lower in layer than the plurality of subfields and divided subfields as the plurality of unit fields. 6. The charged beam drawing method according to claim 4,wherein the hierarchical fields are two hierarchical fields including the plurality of main fields, the plurality of subfields and divided subfields as the plurality of unit fields, or three hierarchical fields including the plurality of main fields, the plurality of subfields, sub-subfields which are lower in layer than the plurality of subfields and divided subfields as the plurality of unit fields. 7. A charged beam drawing apparatus to draw a pattern on a drawing area of a sample by irradiating a charged beam onto the sample, the pattern being drawn using a unit field as a drawing unit, the charged beam drawing apparatus comprising:a first dividing section configured to divide the drawing area into two or more hierarchical fields including a plurality of main fields, a plurality of subfields which are lower in layer than the plurality of main fields and a plurality of unit fields which are lower in layer than the plurality of subfields,a second dividing section configured to divide design data corresponding to the pattern to be drawn on the drawing area into a plurality of first design data corresponding to the plurality of main fields, dividing each of the plurality of first design data into a plurality of second design data corresponding to the plurality of subfields, and dividing each of the plurality of second design data into a plurality of third design data corresponding to the plurality of unit fields;a resolution evaluating section configured to evaluate quality of resist resolution to a predetermined dimension on each of the plurality of unit fields;a table creating section configured to create a table which relates the plurality of unit fields to the quality of the resist resolution based on an evaluation result acquired by the evaluating the quality of the resist resolution;a judging section configured to judge whether or not each of the plurality of third design data corresponds to data having the predetermined dimension and corresponds to a pattern falling in the unit field which the quality of the resist resolution is rejectable based on the predetermined dimension and the table;a coordinate converting section configured to convert a coordinate of data judged to correspond to the data among the plurality of third design data into a coordinate so that the data fall in the unit field which the resist resolution is acceptable,a first data converting section configured to convert the third design data whose coordinate is converted by the coordinate converting section into a first drawing data;a second data converting section configured to convert data judged not to correspond to the data among the plurality of third design data into a second drawing data without performing the coordinate conversion; anda drawing section configured to draw the pattern by referring to drawing data including the first and second drawing data and irradiating the charged beam onto the sample, the drawing section drawing patterns in the subfields by referring to the first drawing data using the unit field as a drawing unit for each of the plurality of subfields, and in a case where there exists a pattern not being drawn in the subfields, the drawing section drawing the pattern not being drawn on a desired position in the subfields by referring to the second drawing data and by moving the sample, or by referring to the second drawing data and by adjusting a deflection position of the charged beam on the subfields. 8. The charged beam drawing apparatus according to claim 7,wherein the resolution evaluating section performs the resist resolution evaluation in real time based on an a shape of the charged beam which is irradiated from the plurality of unit fields. 9. The charged beam drawing apparatus according to claim 7,wherein the hierarchical fields are two hierarchical fields including the plurality of main fields, the plurality of subfields and divided subfields as the plurality of unit fields, or three hierarchical fields including the plurality of main fields, the plurality of subfields, sub-subfields which are lower in layer than the plurality of subfields and divided subfields as the plurality of unit fields. 10. The charged beam drawing apparatus according to claim 8,wherein the hierarchical fields are two hierarchical fields including the plurality of main fields, the plurality of subfields and divided subfields as the plurality of unit fields, or three hierarchical fields including the plurality of main fields, the plurality of subfields, sub-subfields which are lower in layer than the plurality of subfields and divided subfields as the plurality of unit fields. 11. A semiconductor device manufacturing method comprising:preparing a sample including a substrate and a resist film formed on the substrate; anddrawing a pattern on the resist film by a charged beam drawing method according to claim 3. 12. The semiconductor device manufacturing method according to claim 11, further comprising:forming a resist pattern by developing the resist film on which the patterns are drawn; andetching the substrate using the resist pattern as a mask. |
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summary | ||
summary | ||
abstract | A radioisotope-powered energy source comprising: a flexible center substrate coated with the radioisotope, wherein the substrate comprises upper and lower surfaces; and two substantially identical sequences of layers bonded to each other and to the upper and lower surfaces via electrically insulating mesh barriers, wherein each sequence comprises the following layers bonded together in a y-direction in the following order: a first low-density alpha particle impact layer, a first high-density beta particle impact layer, a second low-density alpha particle impact layer, a second radioisotope-coated substrate, a third low-density alpha particle impact layer, a second high-density beta particle impact layer, and a photovoltaic layer. |
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052767183 | claims | 1. A control blade for use in nuclear reactors comprising: an upper structure means; a lower structure means; a central tie means disposed between said upper structure means and said lower structure means; a wing means having a plurality of wings connected to each other by said central tie means in such a manner that a plurality of said wings are disposed to form a cross-shaped lateral cross section; and neutron absorber means enclosed in at least a major portion of a multiplicity of accommodiating holes formed in a widthwise direction of each wing and in line disposed in a lengthwise direction of said wing, said wing means being arranged in such a manner that each of said wings is constituted by a plate member made of hafnium metal, a hafnium alloy composed of hafnium and zirconium or titanium or an alloy the main component of which is zirconium or titanium, said neutron absorber menas comprising a long-lived type neutron absorber which is enclosed in said accommodating holes formed in a front insertion portion of said wing which is exposed to a large amount of neutrons and made of hafnium, metal a main component of which is hafnium, a silver-indium-cadmium alloy; and a neutron absorber which in inserted into at least a major portion of residual accommodating holes and which contains a boron compound, and a mixture of a material containing a boron compound and at least one hydrogen absorber composed of at least one of zirconium particles and hafnium powder being enclosed in said accommodating holes among said accommodating holes for accommodating said neutron absorber containing a boron compound disposed in a range from the front insertion portion, which is exposed to a large amount of neutrons, to 1/4L of a height L of an effective core portion from the front insertion portion of a nuclear reactor, said neutron absorber means further including at least one of: a gap between said long-lived type neutron absorber and a covering pipe; a sleeve around said long-lived type neutron absorber; and an oxide film on a surface of said long-lived neutron absorber. an upper structure means; lower structure means; a central tie means for establishing a connection between said upper structure means and said lower structure means; a sheath plate means connected to said central tie means and having a U-shaped lateral cross section to constitute wings disposed to form a cross-shaped lateral cross section; and a neutron absorber rod means accommodated in said sheath plate means in line, wherein said neutron absorber rod means is constituted by inserting said long-lived type neutron absorber made of hafnium metal, metal the main component of which is hafnium or a silver-indium-cadmium (Ag-In-Cd) alloy into a covering pipe said neutron absorber rod means further including at least one of: a gap between said long-lived type neutron absorber and said covering pipe; a sleeve around said long-lived type neutron absorber; and an oxide film on a surface of said long-lived neutron absorber. an elongated covering pipe; a plug means for sealing two end portions of said covering pipe; and a neutron absorber means accommodated in said covering pipe, said neutron absorber means comprising a long-lived type neutron absorber enclosed in one side of said covering pipe, which is exposed to a large amount of neutrons, and made of hafnium metal, alloy a main component of which is hafnium or a silver-indium-cadmium alloy and a neutron absorber enclosed in a residual region and composed of a boron compound, and wherein said long-lived type neutron absorber is enclosed in said covering pipe and wherein said neutron absorber means further includes at least one of: a gap between said long-lived type neutron absorber and said covering pipe; a sleeve around said long-lived type neutron absorber; and an oxide film on a surface of said long-lived neutron absorber. an upper structure means; a lower structure means; a central tie means disposed between said upper structure means and said lower structure means; a wing means having a plurality of wings connected to each other by said central tie means in such a manner that a plurality of said wings are disposed to form a cross-shaped lateral cross section; said wing means including at least first, second, third and fourth regions, and wherein said second through fourth regions include accommodating holes formed in a widthwise direction of each wing; and wherein said second region includes at least one of said accommodating holes having a tubular member inserted therein, said tubular member formed of zirconium. 2. A control blade for use in nuclear reactors according to claim 1, wherein said accommodating holes formed in said wing and disposed in a range from the front insertion portion, which is exposed to a large amount of neutrons, to 1/4.multidot.L are filled with said material which contains a boron compound and which is surrounded by a pure zirconium sheet. 3. A control blade for use in nuclear reactors according to claim 1, wherein said accommodating holes, which is formed in said wing and in which said long-lived type neutron absorber is enclosed, are filled with said long-lived type neutron absorber which is surrounded by a zirconium sheet. 4. A control blade for use in nuclear reactors according to claim 1, wherein said long-lived type neutron absorber to be inserted into a shape such as a thread having projections and pits on the outer surface thereof. 5. A control blade for use in nuclear reactors according to claim 1, wherein the length of said long-lived type neutron absorber to be inserted into each of said accommodating holes formed in said wing is shorter than the depth of said accommodating hole and at least a hydrogen absorber composed of at least either zirconium particles or hafnium powder is enclosed in a space of said accommodating hole in a range which corresponds to said length shortened. 6. A control blade for use in nuclear reactors according to claim 1, wherein said long-lived type neutron absorber to be inserted into each of said accommodating holes formed in said wing is divided into a plurality of short neutron absorber elements, a gap is formed in at least a portion between said neutron absorber elements and at least a hydrogen absorber composed of at least either zirconium particles or hafnium powder is charged into said gap. 7. A control blade for use in nuclear reactors according to claim 1, wherein said long-lived type neutron absorber to be inserted into each of said accommodating holes formed in said wing is longitudinally divided into a plurality of pieces in parallel to the axial direction of said accommodating hole and projecting portions are formed for the purpose of creating gaps between said pieces. 8. A control blade for use in nuclear reactors according to claim 1, wherein said long-lived type neutron absorber to be inserted into each of said accommodating holes formed in said wing is longitudinally divided into a plurality of pieces in parallel to the axial direction of said accommodating hole and zirconium strip is interposed between said pieces. 9. A control blade for use in nuclear reactors according to claim 1, wherein an oxide film is formed on the surface of said long-lived type neutron absorber to be inserted into each of said accommodating holes formed in said wing. 10. A control blade for use in nuclear reactors according to claim 1, wherein an oxide film is formed on the inner surface of said accommodating holes, in which said neutron absorber containing a boron compound is enclosed, among said accommodating holes formed in said wing. 11. A control blade for use in nuclear reactors according to claim 1, wherein at least a hydrogen absorber composed of at least either zirconium particles or hafnium powder is enclosed in at least one accommodating hole among said accommodating holes formed in a range of 3 cm or more and as well as 35 cm or shorter from the front insertion portion of said wing. 12. A control blade for use in nuclear reactors according to claim 1, wherein a zirconium tubular member is inserted to form a gas plenum into at least one accommodating hole among said accommodating holes formed in a range of 3 cm or more and as well as 35 cm or shorter from the front insertion portion of said wing. 13. A control blade for use in nuclear reactors according to claim 1, wherein a long-lived type neutron absorbing rod made of hafnium metal, metal the main component of which is hafnium or an Ag-In-Cd alloy, which extends in the lengthwise direction of said wing, is disposed on the outer portion of each of said accommodating holes disposed in a range of at least 1/4.multidot.L from the front insertion portion of said wing, the major portion of said neutron absorbing rod being covered with a zirconium sleeve. 14. A control blade for use in nuclear reactors according to claim 1, wherein a long-lived type neutron absorbing rod made of hafnium metal, metal the main component of which is hafnium or an Ag-In-Cd alloy, which extends in the lengthwise direction of said wing, is disposed on the outer portion of each of said accommodating holes disposed in a range of at least 1/4.multidot.L from the front insertion portion of said wing and a zirconium strip is disposed between said neutron absorbing rod and each of said accommodating holes. 15. A control blade for use in nuclear reactors according to claim 1, wherein hafnium particles are enclosed in a range of 1 to 2 cm from the outer end portion of each of said accommodating holes disposed in at least a range of 1/4.multidot.L from the front insertion portion of said wing toward the inside of the wing. 16. A control blade for use in nuclear reactors according to claim 1, wherein zirconium tubular member is inserted into each of said accommodating holes among said accommodating holes formed in said wing and accommodates said neutron absorber containing a boron compound disposed at least a range of 1/4.multidot.L from the front insertion portion of said wing, which is exposed to a large amount of neutrons and zirconium particles and said boron compound mixed are enclosed in said tubular member. 17. A control blade for use in nuclear reactors comprising: 18. A control blade for use in nuclear reactors according to claim 17, wherein said neutron absorber rod means is inserted into a predetermined region in said covering pipe in such a manner that a boron compound is mixed with at least a hydrogen absorber composed of at least either zirconium particles or hafnium powder. 19. A neutron absorbing rod comprising: 20. A neutron absorbing rod according to claim 19, wherein a hydrogen absorber composed of at least either zirconium particles or hafnium powder is mixed and enclosed with said neutron absorber among said neutron absorbers composed of said boron compound to be enclosed in said covering pipe in a predetermined region, which is exposed to a large amount of neutrons. 21. A neutron absorbing rod according to claim 19, wherein said neutron absorber, among said neutral absorbers composed of said boron compound to be enclosed in said covering pipe, in a predetermined region which is exposed to a large amount of neutrons is enclosed in an unsealed type inner pipe accommodated in said covering pipe. 22. The control blade of claim 17, wherein a gap is provided between said long-lived type neutron absorber and said covering pipe, and wherein said long-lived type neutron absorber comprises a rod having at least one of a plurality of projections and a thread formed thereon, thereby maintaining said gap between said long-lived type neutron absorber and said covering pipe. 23. The control blade of claim 17, wherein a gap is provided between said long-lived type neutron absorber and said covering pipe, and wherein said covering pipe includes a plurality of inward projections disposed upon an inner surface thereof, thereby maintaining said gap between said long-lived type neutron absorber and said covering pipe. 24. The control blade of claim 19, wherein a gap is provided between said long-lived type neutron absorber and said covering pipe, and wherein said long-lived type neutron absorber comprises a rod having at least one of a plurality of projections and a thread formed thereon, thereby maintaining said gap between said long-lived type neutron absorber and said covering pipe. 25. The control blade of claim 19, wherein a gap is provided between said long-lived type neutron absorber and said covering pipe, and wherein said covering pipe includes a plurality of inward projections disposed upon an inner surface thereof, thereby maintaining said gap between said long-lived type neutron absorber and said covering pipe. 26. A control blade for use in nuclear reactors comprising: 27. The control blade of claim 26, wherein said first region includes at least one accommodating hole having a tubular member disposed therein formed of zirconium, and wherein said at least one accommodating hole of said second region further includes zirconium disposed inside of said tubular member. 28. The control blade of claim 27, wherein said third region includes a plurality of said accommodating holes, and wherein said plurality of accommodating holes of said third region include zirconium tubular members disposed therein and a long-lived neutron absorber rod disposed inside of said zirconium tubular member. 29. The control blade of claim 28, wherein said fourth region includes a plurality of accommodating holes having a high reactivity neutron absorber and zirconium disposed therein. 30. The control blade of claim 26, wherein said third region includes a plurality of said accommodating holes, and wherein said plurality of accommodating holes of said third region include zirconium tubular members disposed therein and a long-lived neutron absorber rod disposed inside of said zirconium tubular member. 31. The control blade of claim 30, wherein said fourth region includes a plurality of accommodating holes having a high reactivity neutron absorber and zirconium disposed therein. 32. The control blade of claim 31, wherein said first through fourth regions extend along a length of said control blade which is in the range of 1/4L to 3/4L of a height L of an effective core portion from a front insertion portion of a nuclear reactor, and wherein said control blade further includes a fifth region having a plurality of accommodating holes disposed therein, and wherein accommodating holes of said fifth region contain a boron compound. |
claims | 1. A method for producing uniform activity targets, comprising:arranging a plurality of targets in a holding device having an array of compartments, each target being assigned to a compartment based on a known flux of a reactor core so as to facilitate an appropriate exposure of the targets to the flux based on target placement within the array of compartments, the holding device including a plurality of target plates and a shaft extending through the plurality of target plates, the shaft structured to unite the plurality of target plates, each target plate having a first surface and an opposing second surface, the first surface having the array of compartments, the target plates arranged such that the first surface of one target plate faces the second surface of an adjacent target plate;positioning the holding device within the reactor core to irradiate the targets; andirradiating the plurality of targets within the holding device. 2. The method of claim 1, wherein the targets are radially arranged such that more of the plurality of targets are grouped together in compartments that are at a greater radial distance from a center of the holding device relative to compartments that are at a lesser radial distance from the center of the holding device. 3. The method of claim 1, wherein the targets are axially arranged such that more of the plurality of targets are grouped together in compartments in axial portions of the holding device that are subjected to higher flux during irradiation relative to compartments in the axial portions of the holding device that are subjected to lower flux during the irradiation. 4. The method of claim 1, wherein more of the plurality of targets are grouped together in compartments that are in closer proximity to the flux during irradiation relative to compartments that are farther to the flux during the irradiation. 5. The method of claim 1, wherein targets of the same isotope are grouped together in one or more compartments. 6. The method of claim 1, wherein the plurality of targets includes different types of targets that are formed of different materials. 7. The method of claim 6, wherein the targets are arranged in the array of compartments based on their self-shielding properties. 8. The method of claim 7, wherein targets with lower self-shielding properties are grouped together in one or more compartments relative to targets with higher self-shielding properties. 9. The method of claim 7, wherein targets with higher self-shielding properties are separated from each other so as to be grouped in different compartments relative to targets with lower self-shielding properties. 10. The method of claim 6, wherein the targets are arranged in the array of compartments based on their different cross sections. 11. The method of claim 10, wherein targets having lower cross sections are arranged in one or more compartments that are in closer proximity to the flux during irradiation relative to compartments that are farther to the flux during the irradiation. 12. The method of claim 6, wherein the different types of targets are grouped together in one or more compartments. 13. The method of claim 1, wherein a number of targets in a compartment is increased so as to decrease a resulting activity of each target in the compartment after irradiation. 14. The method of claim 1, further comprising:waiting a predetermined period of time for impurities to decay after irradiation prior to collecting the irradiated targets. 15. A method for producing uniform activity targets, comprising:positioning targets within a holding device according to a determined target loading configuration, the determined target loading configuration being based on a required flux for each target in conjunction with a known environment of a reactor core that is used to irradiate the targets, the holding device including a plurality of target plates and a shaft extending through the plurality of target plates, the shaft structured to unite the plurality of target plates, each target plate having a first surface and an opposing second surface, the first surface having an array of compartments, the target plates arranged such that the first surface of one target plate faces the second surface of an adjacent target plate; andirradiating the targets within the holding device. 16. The method of claim 15, wherein the determined target loading configuration is in a form of a ring pattern. 17. The method of claim 15, wherein the determined target loading configuration corresponds to a shape of the target plates of the holding device. 18. The method of claim 15, wherein the determined target loading configuration results in a target being subjected to uniform flux. 19. The method of claim 15, wherein the determined target loading configuration results in a target being subjected to non-uniform flux. 20. A method for producing uniform activity targets, comprising:arranging a plurality of targets in a holding device having an array of compartments, each target being assigned to a compartment based on a known flux of a reactor core so as to facilitate an appropriate exposure of the targets to the flux based on target placement within the array of compartments, the holding device including a plurality of target plates and a shaft extending through the plurality of target plates, the shaft structured to unite the plurality of target plates, each target plate having a first surface and an opposing second surface, the first surface having the array of compartments, the target plates arranged such that the first surface of one target plate faces the second surface of an adjacent target plate;positioning the holding device within the reactor core to irradiate the targets, the targets being formed of different natural or enriched isotopes and arranged by isotope type, cross section, and self-shielding properties; andirradiating the plurality of targets within the holding device. |
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summary | ||
abstract | The present disclosure provides an adjustable collimator for collimating a beam of energy emitted from a focal spot of a beam source. The collimator is particularly intended for collimating an x-ray beam of a computed tomography scanner after the x-ray beam has passed through a patient being scanned. The collimator includes two elongated parallel plates arranged side by side to define a collimating slit between the plates. At least one of the plates is movably relative to the other plate for varying a width of the collimating slit. The collimator also includes a movable cam operatively arranged with respect to the at least one movable plate such that movement of the cam in a first direction causes the width of the collimating slit to increase, while movement of the cam in a second direction causes the width of the collimating slit to decrease. |
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055241280 | description | DETAILED DESCRIPTION Neutronic and Thermal Hydraulic Feedback The BWR core consists of a large number of vertically oriented fuel bundles, exhibiting radially independent hydraulic behavior, that are coupled at their inlet and exit via the reactor upper and lower plenums. The fuel bundles are oriented in an array having the general shape of a right circular cylinder. Each fuel bundle has an open lattice of nuclear fuel pins enclosed by a flow channel through which water is pumped upwardly from the lower plenum to the upper plenum; the water functions both as a coolant and a neutron moderator. The presence of boiling within these fuel channels makes them susceptible to reactor coolant density-wave instabilities. Pressure perturbations at the core inlet cause flow disturbances that travel up the fuel channels as time-varying coolant density waves. These waves result in local deviations from the steady-state axial pressure drop distribution. The local pressure drop in a fuel bundle is highly dependent on void fraction. Since the coolant voiding increases axially with greater core elevation, the highest void fraction is found at the channel outlet. The effect of density waves on total channel pressure drop is therefore effectively delayed in time--the void sweeping time--until the perturbation is felt at the channel exit. When the channel pressure drop time delay (phase lag) nears 180.degree. out of phase with the channel inlet flow variations, the fuel assembly can become thermal-hydraulically unstable. Thus the thermal-hydraulic stability margin of a fuel channel is dependent on the phase lag caused by void sweeping time, and the gain which is dependent on the channel void distribution. An additional complexity is introduced in BWR stability because of the reactor power dependency on coolant density. Local void reactivity (.rho..sub..nu.) responds to the time-varying density wave described above. The reactivity change affects local neutron flux (o.sub.dV), and is manifested after a time delay (fuel thermal time constant) as changes in fuel cladding surface heat flux and ultimately in local coolant voiding. This mechanism can also provide positive feedback to density wave oscillations. The neutronic feedback gain is dependent on how closely the fuel thermal time constant approximates the void sweeping time, and on the local void fraction. For point kinetics models, void reactivity is related to void fraction and local neutron flux by: ##EQU1## The flux-squared dependency of reflects the feedback contribution of the relatively high power fuel bundles on core stability, which increases non-linearly with power. The two feedback mechanisms, thermal hydraulic and neutronic, are coupled in a BWR core and produce oscillations in both core flow and thermal power. These oscillations can affect margins to fuel thermal safety limits. In addition, core instabilities can occur even when neither feedback mechanism alone is sufficient to generate reactor power oscillations. The feedback mechanisms described above are illustrated in FIG. 1. Parameters Affecting Stability Predicting and controlling reactor stability in an operational setting, where the fuel and core designs are fixed, is difficult. Commonly used operational parameters for measuring core thermal-hydraulic and neutronic behavior do not provide sufficient insight into the basic mechanics of reactor stability. Thus, a more fundamental approach is needed to permit development of a functional stability control. Coupled neutronic-thermal hydraulic instability is a phenomenon only found in boiling water reactors. This is because only BWR's have significant bulk coolant boiling in the core during normal reactor operations. It is observed that BWR stability performance is dominated by the core void distribution for a given core design: EQU DR.sub.core =f{void distribution}, (2) where DR.sub.core is the core decay ratio. When a BWR is maneuvered throughout its power-flow operating domain, five global variables can have a significant influence on void distribution: core flow, core power, axial flux shape, radial flux shape, and core coolant inlet subcooling. This relationship is illustrated in FIG. 2, in which AP.sub.i : axial power shape PA1 RP.sub.j : radial power shape PA1 P: core thermal power PA1 W: core flow PA1 DHS: core inlet subcooling PA1 W=core flow rate PA1 DHS=core inlet subcooling PA1 P=total core thermal power PA1 DHS in (BTU/lb) PA1 P in (MW.sub.th) DR.sub.core, which is influenced by the core void distribution, is therefore related to the following variables: EQU DR.sub.core =f{AP.sub.i,RP.sub.j,P,W,DHS} (3) Differentiating equation (3) yields: ##EQU2## The usefulness of equation (4) is severely limited, however. First, although the behavior of all terms except ##EQU3## is generally understood, it is difficult to establish the partial derivatives for reasonable changes in the variables. This is due to the interdependency of these five parameters in an operational environment. During reactor startup, for example, the core radial power shape is constantly changing in response to control rod withdrawals executed to increase reactor power. This interdependence must be recognized in the development of a successful stability control. Second, no unique relationship between AP.sub.i and DR.sub.core and has been demonstrated. Analysis demonstrates that examination of the axial power shape alone cannot provide effective and reliable control of reactor stability. For example, consider the two cases depicted in FIGS. 3 (bottom peaked average axial power) and 4 (top peaked average axial power). These figures show two hypothetical reactor states that differ only in their axial power shapes and core inlet subcooling (RP.sub.j,P, and W remain constant). When core inlet subcooling (DHS) is low and bulk coolant saturates at elevation `a`, DR.sub.Shape 1 <DR.sub.Shape 2. However, when core inlet subcooling is high and bulk coolant saturates at elevation `b`, then DR.sub.Shape 1 >DR.sub.Shape 2. This example illustrates the difficulty of determining relative reactor stability margins based on changes in axial power shape alone. The development of a simple, reliable stability control based on a direct independent assessment of each parameter in equation (3) therefore does not appear to be feasible. The variables are either interdependent, or their influence on DR.sub.core cannot be resolved. To proceed, the observation that the voided region of the core determines reactor stability, must be revisited. Axial Power Shape Effects To simplify the discussion, a radial collapse of the core, as depicted in FIG. 5, will be initially assumed. For an average fuel channel, equation (3) is simplified to: EQU DR.sub.core =f{AP.sub.i,P,W,DHS} (5) The presence of voids in the coolant flowing through the average channel divides the core into two distinct regions: the single-phase region below the bulk saturation elevation (1o), and the two-phase region above the bulk saturation elevation (2o). As a first order approximation, subcooled boiling is ignored. These separated regions can be directly related to the feedback mechanisms driving reactor instability, described above. FIG. 6 illustrates the relationship between the separated regions of the core, and the stability feedback mechanisms. The thermal hydraulic feedback is dependent on void sweeping time and core void fraction. Both of these parameters are dependent on the location of the bulk coolant saturation elevation (i.e. the elevation of the average boiling boundary). This elevation determines the two-phase column length which, for a given coolant flow rate (W), defines the void sweeping time and therefore pressure drop feedback phase lag. The location of the bulk coolant boiling boundary, in conjunction with the axial power shape in the two-phase region, also determines the core void fraction for a given reactor state condition (P, W, and DHS). The magnitude of the core void fraction helps determine the feedback gain. Thus, by resolving the location of the core average boiling boundary, the specific effects that the axial power shape has on reactor stability can be elicited. The neutronic feedback is related to the core void fraction and the axial flux shape in the two-phase region (AP.sub.i.sup.2o). No significant neutronic feedback can occur in the single-phase region because moderator density variations are small. Again, knowledge of the bulk coolant saturation elevation is critical to evaluating this feedback mechanism. Since void reactivity is dependent on local flux squared (see Equation 1), AP.sub.i.sup.2o can have a significant impact on stability margin if axial flux peaks high in the voided region of the core. These concepts, as illustrated in FIG. 6, lead to the observation that the two phase column length and neutron flux shape in the two-phase region of a reactor core are the major factors influencing reactor stability: ##EQU4## where L.sub.xo is phase column length. The separation of the 1o and 2o regions of the core is dependent on identifying the average axial bulk coolant saturation elevation, Z.sub.bb. On a core-average basis, this boiling boundary is a function of: EQU Z.sub.bb =f{AP.sub.i,P,W,DHS} (7) The issue of how AP.sub.i is related to DR.sub.core is now resolved. AP.sub.i has two distinct impacts on the stability feedback mechanisms. First, the integrated AP.sub.i at the core bottom determines the location of Z.sub.bb and thus the 2o column length. Second, the AP.sub.i above Z.sub.bb influences the void reactivity feedback: EQU .rho..sub.84 =f{AP.sub.i,i>Z.sub.bb } (8) Without knowledge of the location of Z.sub.bb (which is not available independent of P,W, and DHS), the impact of axial power shape on each stability feedback mechanism is indeterminate. The expression that relates core average boiling boundary, Z.sub.bb, to the core average parameters important to stability is: ##EQU5## where C is a constant. (See Section on Implementation and Plant Experience for derivation of this equation.) Variations in each parameter of Equation (9) result in an appropriate change in the core average boiling boundary as tabulated in Table 2.1. TABLE 1 ______________________________________ Limiting Changes in Z.sub.bb Parameter Value Boiling Height ______________________________________ W << W.sub.nom Z.sub.bb .fwdarw. O W >> W.sub.nom Z.sub.bb .fwdarw. H.sub.core P << P.sub.nom Z.sub.bb .fwdarw. H.sub.core P >> P.sub.nom Z.sub.bb .fwdarw. O DHS << DHS.sub.nom Z.sub.bb .fwdarw. O DHS >> DHS.sub.nom Z.sub.bb .fwdarw. H.sub.core AP.sub.i = top peak Z.sub.bb .fwdarw. H.sub.core AP.sub.i = btm peak Z.sub.bb .fwdarw. O ______________________________________ where: X.sub.nom = nominal value H.sub.core = core height Radial Power Shape Effects One variable that can significantly influence stability but is not captured within the Z.sub.bb expression, is the radial power shape, RP.sub.j. This parameter was initially collapsed by performing a radial averaging of the fuel channels. In fact, the boiling boundary of each fuel assembly lies above or below the core average, depending on the assembly's relative thermal hydraulic condition (see FIG. 5). The hot channel boiling boundary, Z.sub.bb.sup.ch, is usually located below the core average because of its high power output. Therefore, the hot channel is expected to be thermal-hydraulically less stable than an average channel. To identify the parameters important in controlling hot channel stability, the fraction of core power, f, required for coolant saturation in an average channel can be written as follows: ##EQU6## where N is the number of fuel assemblies in the core. Define w=average channel active flow, and p=average channel power, such that: ##EQU7## The fraction of power required for coolant saturation for the hot channel (f.sub.ch) can be written as follows: ##EQU8## Comparing the hot channel power fraction, f.sub.ch, to the core average bundle power fraction, f, the following observations can be made: EQU DHS.sub.ch =DHS, EQU P.sub.ch =RP.sub.j.sup.ch .times.p, and EQU W.sub.ch .congruent.w, (13) where RP.sub.j.sup.ch is hot channel radial peaking. The single most important factor relating the core average to the hot channel power fraction required for saturation is RP.sub.j.sup.ch, or: ##EQU9## As discussed above, the axial power shape also affects boiling boundary elevation. Hot channels are generally completely uncontrolled, and therefore the hot channel axial power shape, RP.sub.j.sup.ch, can be significantly more bottom peaked than the average channel. However, to a large extent, power sharing among adjacent fuel assemblies ameliorates these effects. Reducing the average power at the core bottom will limit the length of the hot channel two phase column length. The influence of the high power fuel bundles on the stability of the entire reactor core can be disproportionally large, as has been noted. Therefore, an effective stability control must limit the hot channel decay ratio, DR.sub.ch. Identification of Stability Control The capability to resolve the influence of core axial power shape on coupled neutronic-thermal hydraulic feedback mechanisms is achieved by dividing the axial flux into two components. These components are defined by the bulk coolant saturation elevation which provides the basis for a reliable, effective stability control. If the core average boiling boundary, Z.sub.bb, is maintained sufficiently high, then the core will remain stable (DR.sub.core <<1) during normal reactor operations in regions susceptible to power oscillations. When Z.sub.bb is sufficiently high, then variations in all parameters that affect stability will produce only second order effects on DR.sub.core and may be ignored if existing fuel thermal limits are not exceeded. The foregoing permits the terms of equation 4 to be evaluated at Z.sub.bb : EQU .gradient.DR.sub.core .vertline..sub.Z.spsb.bb.sbsb.high .apprxeq.0(15) Reactor stability is assured with a high boiling boundary primarily because of the consequences of a short two-phase column on the thermal hydraulic and neutronic feedback mechanisms. The effect of variations in the two-phase axial power shape cannot render the core unstable at sufficiently high boiling boundaries. The Z.sub.bb concept also addresses the interdependence of the important parameters affecting stability. For a constant boiling boundary, a change in one stability parameter forces a compensating change in the others (see Equation 9). Finally, a high boiling boundary limits the influence of radial power shape, RP.sub.j on stability. A significantly low integrated axial power in the core bottom is required to generate a high boiling boundary. Because of power sharing among fuel bundles, this low average power in the core bottom limits the hot channel two-phase column length and therefore maintains its relative stability. Unusual control rod configurations that support sufficient power sharing among a group of adjacent high power bundles could potentially threaten core stability, even at high core average boiling boundaries. However, this situation, where a highly skewed power shape exists, is not compatible with maintenance of existing fuel thermal limits while operating with the stability control in place. DERIVATION OF STABILITY CONTROL LIMIT A stability control limit is only useful operationally if adherence to the limit can be determined using currently defined core parameters, and can be accomplished during necessary reactor maneuvers. The Z.sub.bb stability control, which only utilizes core average parameters and obviates the need for radial constraints, will be employed to define the stability limit. Assuming that 100% of core power is deposited in the active fuel channel flow (conservative, since actual value is approximately 98%), the fraction of core power (f) required for coolant saturation is: ##EQU10## where: F.sub.af =Active core flow fraction at off-rated conditions or following unit conversion: ##EQU11## where: W in (10.sup.6 lb.sub.m /hr) The core axial plane where this fraction of core power occurs is dependent upon the average axial power shape. For a core divided into n axial nodes, generating a relative nodal axial power AP.sub.i, the axial power distribution is assumed to be normalized as follows: ##EQU12## The axial elevation where the integral of the average axial power (from the bottom of the fuel) equals f defines the core average bulk coolant boiling boundary (Z.sub.bb): ##EQU13## The relationship of the core average boiling boundary to all core average parameters that are important to stability, is illustrated in FIG. 7. To control the core average boiling boundary during reactor operations, the boiling boundary (Z.sub.bb) can be compared to a predetermined minimum elevation limit, (Z.sub.bb). This boiling boundary stability control is enforced by requiring the actual boiling boundary (Z.sub.bb) to exceed the limit, Z.sub.bb : EQU Z.sub.bb .gtoreq.Z.sub.bb. (20) This expression is now converted from an elevation limit into a core power fraction limit. Specifically, the core power fraction up to the boiling boundary limit, Z.sub.bb, must be less than the power fraction required for bulk coolant saturation: ##EQU14## Thus, the power required for coolant saturation must be larger than the actual power generated up to elevation Z.sub.bb and therefore the boiling boundary will occur, on a core average basis, above Z.sub.bb. The stability control is now normalized, by defining a limit of Fraction of Core Boiling Boundary (FCBB) as follows: ##EQU15## This normalized limit should satisfy the condition: EQU FCBB.ltoreq.1.0 (23) Adherence to the FCBB limit ensures that the actual core average boiling boundary, Z.sub.bb, is equal to or higher than Z.sub.bb. Use of the boiling boundary concept provides a powerful mechanism for operational control of reactor stability. Its strength is derived from two significant features. First, the control explicitly incorporates all reactor parameters that have a significant influence on stability. This means that the stability control can be reliably and effectively used by itself, without concern for changes in other parameters. Second, the stability control is readily derived from core average parameters normally available to a reactor operator. In fact, the normalized stability control limit, FCBB, can easily be incorporated into core monitoring computer software for automatic display to reactor operators. These two features permit quick and efficient evaluation of core stability during reactor maneuvering. For example, the change in Z.sub.bb, caused by the repositioning of control rods, is reflected in FIG. 8. Control rod pattern 1 represents a bottom peaked power shape with an associated boiling boundary Z.sub.bb 1 that is assumed to cause FCBB>1.0. To rectify this situation, control rod pattern 2 is adopted. This change raises the boiling boundary to Z.sub.bb 2 where Z.sub.bb 1>Z.sub.bb 2, in order that FCBB<1.0. The effect of raising the boiling boundary is a shortened two-phase column length, which improves the reactor stability margin as outlined in above. IMPLEMENTATION AND PLANT EXPERIENCE Background A typical core power and flow operating map for a reactor is shown in FIG. 9. The lightly shaded area in the figure labelled "instability region" is representative of the operating domain region susceptible to power oscillations. Its shape is consistent with the influence of core power and flow on reactor stability. A generic calculational procedure, described in BWR Owners Group, Long Term Stability Solutions Licensing Methodology, GE Nuclear Energy Licensing Topical Report NEDO-31960, June 1991, has been selected for establishing the boundary of the region susceptible to power oscillations. Alternative methods of accounting for the different modes of oscillation may be used. The procedure uses a stability criterion that accounts for susceptibility to the fundamental and higher order harmonic modes of power oscillations, based on calculated values for core and hot channel decay ratios. Implementation The stability control, Fraction of Core Boiling Boundary (FCBB), Significantly increases the margin to reactor instability near the operating region susceptible to power oscillations. In general, it is assumed that the instability region shown in FIG. 9 will be avoided during controlled reactor maneuvers in order to decrease the possibility of reactor power oscillations. The presence of conditions conducive to power oscillations outside this region is, however, still possible. Examples of such conditions include low feedwater temperature, unfavorable xenon conditions and skewed axial and radial flux distributions. Application of the stability control, FCBB, in a defined area outside the region susceptible to power oscillations provides protection not only during normal operation, but also under extreme operating conditions. In addition, the use of FCBB outside the region susceptible to instabilities addresses the problem of uncertainty in the location of this region boundary. Resolution of this issue is possible since conformance to FCBB provides significant stability margin. In effect, state points at the boundary of the susceptible region that satisfy the FCBB limit will result in reactor conditions well within the stability criterion. An operating domain region is defined to be outside the region susceptible to instabilities where FCBB is applied. An example of this controlled region is shown in FIG. 9. The size of the controlled region can be determined by requiring that reasonably limiting reactor conditions at the controlled region boundary, with no stability controls enforced, will conform to the stability criterion. The target elevation of the core average boiling boundary, Z.sub.bb, is used to define the operating limit, FCBB (see Equation 22). The FCBB limit is normalized such that conformance to Z.sub.bb during controlled reactor maneuvers is ensured if FCBB does not exceed 1.0. As an example., for a core model consisting of 25 nodes, each 6.0 inches high, and with Z.sub.bb =4.0 feet, FCBB requires: ##EQU16## If during controlled reactor operations FCBB exceeds 1.0, the boiling boundary is below Z.sub.bb and corrective action is needed. The most effective way to decrease FCBB is by insertion of shaping control rods. These rods will suppress the power at the bottom of the core and shift the boiling boundary upward (See FIG. 8). The FCBB limit in conjunction with other fuel operating limits provides adequate protection from reactor instabilities. However, as a matter of good operating practice, non-uniform control rod patterns should be avoided. This includes control rods in deep position for reactivity control, as well as shallow position for Z.sub.bb control. Control rod dispersion that is radially non-uniform may lead to situations where small regions in the core become neutronically decoupled, exhibiting a low Z.sub.bb and potentially reducing the stability margin of the reactor. Inserting control rods used for reactivity control as far as possible into the core can also increase the stability margin of the reactor. This insertion minimizes the power generated at the core top, which weakens the neutronic feedback. In summary, control rod distribution patterns that are radially uniform in the core should be used for both the shaping and the reactivity control rods. The shaping control rod inventory should be set to achieve the target Z.sub.bb. The reactivity control rod inventory should be set to minimize the power peaking in the core top. Placing control rods at other intermediate positions should be avoided to the extent practicable. As the reactor startup is initiated, Z.sub.bb is at the top of the core, where bulk saturation is first achieved. Subsequently, Z.sub.bb is moved downward in the core as control rods are being withdrawn and reactor power increases. As the rated operating condition is approached, the bulk saturation elevation in the core is lowered and Z.sub.bb settles below Z.sub.bb. Reactor instability is not a concern, however, because of the high core flow rate. For some reactor designs, the controlled region of FIG. 9 can be completely avoided, and application of stability controls is not required. However, if entry into the controlled region is unavoidable, FCBB, and therefore Z.sub.bb, can be enforced to preclude instabilities. Since Z.sub.bb is initially very high in the core, the startup path can be planned such that Z.sub.bb will not fall below Z.sub.bb prior to maneuvering through the controlled region. This strategy will eliminate unnecessary and untimely control rod maneuvers to satisfy the FCBB limit. Upon exiting the controlled region, the shaping control rods can be withdrawn to achieve the target rod pattern for rated conditions, allowing Z.sub.bb to fall below Z.sub.bb. Plant Experience The core average boiling boundary control's effects on reactor stability performance has been assessed for reactor conditions and with control rod patterns consistent with normal operational practices. The results of this assessment suggest that a core average boiling boundary limit of about 4.0 feet (about one-third of the typical core height of about 12 feet) is not only an effective control, but that it is also feasible. This conclusion is supported by actual plant data. Startup data from a US BWR plant was evaluated to assess the implementation feasibility of a Z.sub.bb limit of 4.0 feet. The data was selected at the most challenging core power and flow state point along the startup path. This state point is achieved during a required reactor recirculation pump upshift from slow to high speed at minimum core flow conditions. A summary of selected actual conditions from one operating cycle is provided in Table 2. TABLE 2 ______________________________________ Exposure Shut down Secondary Z.sub.bb (GWD/MT) (days) Rods (ft) ______________________________________ 1. 0.1 >14 used 4.3 2. 1.4 <1 none 2.9 3. 2.0 >9 none 2.5 4. 5.4 >1 used 4.9 ______________________________________ The table represents operating state points with different xenon conditions (shutdown duration prior to startup), cycle exposures and control rod patterns. The secondary control rods remain inserted early in the startup and are typically withdrawn prior to achieving the final rod pattern at rated power. The purpose of the secondary rods is power shaping during the startup to compensate for non-equilibrium xenon conditions. They may be withdrawn before or after the recirculation pump upshift. As expected, the Z.sub.bb values in Table 1 are directly related to the use of the shaping secondary rods. No correlation is observed (or expected) in relation to xenon condition or cycle exposure. The operating conditions shown in Table 2 were specified without any consideration of Z.sub.bb. They represent typical operating conditions for the fuel cycle. Moreover, additional analysis based on actual reactor operating conditions demonstrated that Z.sub.bb values of 5.0 feet, at varying cycle conditions from beginning to end of cycle, are achievable. Thus, a Z.sub.bb limit of 4.0 feet can be operationally consistent with typical plant operations near the region susceptible to reactor instability. Details of State Points 1 and 3 in Table 1 are provided to demonstrate the difference between low and high Z.sub.bb startups. FIG. 10 depicts the core average boiling boundary, Z.sub.bb, of State Point 3 as a function of the actual startup path. The operating map is shown as a reference on the core power and flow plane. As expected, Z.sub.bb starts high in the core when power is low, and decreases to about 2.0 feet when the 100% recirculation flow control-line is reached. The secondary control rods are withdrawn early in the startup path, which results in a Z.sub.bb of 2.5 feet at the recirculation pump upshift conditions. The corresponding control rod pattern, with quarter-core symmetry, is shown in FIG. 11. The axial power shape, with the actual indicated, is shown in FIG. 12. In this case Z.sub.bb is below the target Z.sub.bb limit of 4.0 feet. In contrast, FIG. 13 depicts the core average boiling boundary, Z.sub.bb, of State Point 1 as a function of the actual startup path. Here, the secondary rods are withdrawn late in the startup path. This results in a Z.sub.bb value over 4.0 feet at the recirculation pump upshift conditions. The control rod pattern is shown in FIG. 14 and the axial power shape in FIG. 15. In this case Z.sub.bb is above the target Z.sub.bb limit of 4.0 feet. The FCBB limit, with Z.sub.bb set at 4.0 feet, has been implemented successfully in an operating US BWR. Implementation of the FCBB limit did not result in any significant additional burden to the operating staff. It has created and maintained significant stability margin throughout the reactor startup path, without any need for reliance on a stability monitoring system, on-line instability predictions, or pre-startup analysis. Industry experience has clearly demonstrated the need for an effective stability control that can readily be applied to reactor operations. The core average boiling boundary control fulfills this need. BWR stability performance is dominated by the core void distribution. All global core parameters must be considered in defining the location of the bulk coolant saturation elevation that marks the beginning of the voided core region. However, the two-phase column length and neutron flux shape in the two-phase region of a core are the major factors influencing reactor stability. The two-phase column length determines the void sweeping time and therefore the pressure drop phase lag. It also limits the core void fraction that controls the thermal hydraulic and neutronic feedback gains. The core average boiling boundary provides a convenient parameter for expressing the relative lengths of the single-phase and two-phase columns in a reactor core. When defined using core average parameters, the equation incorporates all the factors important to reactor stability for a radially collapsed core. The effects of varying radial core power shapes can be controlled through use of the boiling boundary parameter in conjunction with existing fuel thermal limits. When the core average boiling boundary is raised sufficiently, the core remains very stable during reactor maneuvering in a defined power-flow operating domain region. In addition, variations in all parameters affecting stability become secondary and may be ignored. Thus, a single parameter stability control has been developed that captures all significant factors affecting reactor stability. Use of this control can guide plant operations in a practical manner, to assure adequate stability margins during reactor maneuvering. The ability to utilize this stability control has been demonstrated analytically, and verified during reactor startups with a large BWR. In accordance with the foregoing, the flow diagram of FIG. 16 illustrates the method of the invention. In step 10, a region in core power--core flow space is determined, in which the control method is to be implemented. This control region is preferably adjacent a predetermined instability region, as illustrated in FIG. 9. In step 12, a target value of core elevation is determined. In step 14, the actual average boiling boundary elevation in the core is determined. In step 16, the actual average boiling boundary elevation is compared with the target value. In the preferred embodiment, step 16 is carried out by computing the power generated in the core below the target elevation, the power required for coolant saturation, and forming their ratio FCBB. In step 18, the reactor (if it is in the control region determined in step 10) is controlled so that the actual average boiling boundary elevation is greater than the target elevation; with the preferred embodiment for step 16, the controlling 18 is performed so that FCBB is equal to or less than one. The controlling step 18 may be implemented by positioning shaping control rods. Steps 14, 16, and 18 are preferably performed repetitively in a control loop to maintain stability. The block diagram of FIG. 17 illustrates a preferred apparatus for carrying out the invention, which merely requires modification of the software in a core monitoring computer already used with the reactor. The core monitoring computer 20 receives signals from core monitoring instruments 22 via I/O interface 24. Digital data 32 representing these signals and parameters derived therefrom are stored in memory 28 under control of CPU 26. Memory 28 also includes a stability control algorithm 30 in accordance with the invention, such as an algorithm for calculating FCBB. The algorithm 30 is executed by CPU 26 using the monitored core parameters 32 stored in memory 28. Core monitoring computer 20 includes an operator I/O 36 coupled to CPU 26, which may comprise a keyboard and a visual display. Algorithm 30 may include portions for controlling a display, such as to display the actual and target boiling boundary elevations or to display FCBB. CPU 26 is coupled to reactor controls 38, such as means for positioning control rods, via I/O interface 34. Algorithm 30 may include means for automatically operating the reactor controls to maintain the stability control conditions described herein. Alternatively, the apparatus may merely output information to the operator regarding stability conditions, and the operator may independently determine and effect appropriate reactor control. While a preferred embodiment of the invention has been disclosed, variations will no doubt occur to those skilled in the art without departing from the spirit and scope of the invention. |
claims | 1. A method of achieving a magnification calibration reference with a pitch accuracy of ±0.01 nm suitable for precision magnification calibration of imaging instruments comprising the steps of selecting a holographic diffraction grating with a nominal pitch size appropriate for a magnification range to be calibrated; selecting a substrate on which a number of grating lines has been sufficiently reproduced; using an optical goniometer with an angular measurement accuracy of 1 arc second; selecting 435.835 nm wavelength mercury line; performing a series of measurements at several locations on a grating; calculating a standard mean deviation from these measurements; calculating a diffraction angle obtained with said goniometer and mercury line; calculating a diffraction pitch using Bragg's formula: λ=2d*sin θ; and calibrating a magnification of an imaging instrument with the use of the calculated diffraction pitch. |
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claims | 1. A container for storing a hazardous waste item, said container comprising:a) a RFID tag comprising an antenna, a transceiver operable at a low radio frequency not exceeding 15 MHz, a data storage device, a microprocessor operable to control data flow between said data storage device and said transceiver, and an energy source for providing energy to said transceiver, said data storage device, and said microprocessor;b) an encasement structure surrounding said waste item and said RFID tag, said encasement structure comprising a cementitious composition. 2. A container as set forth in claim 1, wherein said radio frequency does not exceed 1 MHz. 3. A container as set forth in claim 1, wherein said data storage device is operable to store information selected from data for identifying said container, pedigree data about said container, and pedigree data about said waste item. 4. A container as set forth in claim 1, wherein said energy source comprises an energy storage device. 5. A container as set forth in claim 1, wherein said energy source comprises a tag coil operable for energization thereof as a result of inductive coupling of said tag coil to an external coil. 6. A container as set forth in claim 5, said energy source further comprising an energy storage device and an AC-to-DC converter, operable to charge said energy storage device from AC energy induced in said tag coil. 7. A container as set forth in claim 1, wherein said antenna comprises a loop antenna characterized by dimensions comparable to dimensions of said waste item. 8. A container as set forth in claim 1, wherein said waste item comprises a multigallon steel drum holding plutonium. 9. A container as set forth in claim 1, said RFID tag being encased in a protective shell before said disposing step c). 10. A container as set forth in claim 1, said RFID tag comprising a condition sensor operable to sense a condition experienced by said RFID tag, said condition sensor being operable for communication with said microprocessor for storage, in said data storage device, of data that defines said condition. 11. A container as set forth in claim 10, said container further comprising an indicator device operable to emit a signal at said low radio frequency upon a said condition beyond a selected threshold level. 12. A container for storing a dangerous waste item, said container comprising:a) an inner layer surrounding said waste item, said inner layer comprising an unhydrated cementitious composition;b) a RFID tag comprising an antenna, a transceiver operable at a low radio frequency not exceeding 15 MHz, a data storage device, a microprocessor operable to control data flow between said data storage device and said transceiver, and an energy source for providing energy to said transceiver, said data storage device, and said microprocessor;c) an outer layer surrounding said inner layer and said RFID tag, said outer layer comprising a hydrated cementitious composition. 13. The container of claim 12, wherein the container is a steel drum holding plutonium or other nuclear waste. 14. A system for accessing information about a hazardous waste item during shipment and storage thereof, said system comprising:i) a container for storing said hazardous waste item, said container comprising:a) a RFID tag comprising an antenna, a transceiver operable at a low radio frequency not exceeding 15 MHz, a data storage device, a microprocessor operable to control data flow between said data storage device and said transceiver, and an energy source for providing energy to said transceiver, said data storage device, and said microprocessor;b) an encasement structure surrounding said waste item and said RFID tag, said encasement structure comprising a cementitious composition; andii) a field antenna operable to send an interrogation signal to said RFID tag at said low radio frequency and to receive data signals at said low frequency from said RFID tag. 15. A system as set forth in claim 14, said system further comprising a WOW, (write-once-only), data storage device, said WOW being in communication with said field and operable to store, in an unalterable manner, said data signals from said RFID tag. 16. A method for accessing information about a hazardous waste item during shipment and storage thereof, said method comprising: i) surrounding said waste item and an RFID tag in a container, said container comprising a cementitious composition, said RFID tag comprising a tag antenna, a transceiver operable at a low radio frequency not exceeding 15 MHz, a data storage device, a microprocessor operable to control data flow between said data storage device and said transceiver, and an energy source for providing energy to said transceiver, said data storage device, and said microprocessor; ii) disposing a field antenna in spaced adjacency to said container, iii) receiving data signals, (e.g., representing a condition experienced by said RFID tag), of said low radio frequency, at said field antenna and transmitting them to computing device; iv) storing information based upon said data signals; in a data storage apparatus. 17. A method as set forth in claim 16, said RFID tag comprising a condition sensor operable to sense a condition experienced by said RFID tag, said condition sensor being operable for communication with said microprocessor for storage, in said data storage device, of data that defines said condition, said receiving step iii) further comprising the steps of interrogating said RFID tag with a said low radio frequency interrogation signal to obtain said data signals representing said data that defines said condition. 18. A method as set forth in claim 16, further comprising the step of safeguarding said data storage apparatus. 19. A method of containing a hazardous waste item, said method comprising the steps of: a) disposing an inner layer of powdered hydraulic cement around a waste item; b) compressing said inner layer of powdered hydraulic cement around said waste item to form a compressed inner layer; c) disposing, adjacent said compressed inner layer, an RFID tag comprising an antenna, a transceiver operable at a low radio frequency not exceeding 15 MHz a data storage device, a microprocessor operable to control data flow between said data storage device and said transceiver, and an energy source for providing energy to said transceiver, said data storage device, and said microprocessor; d) positioning an outer layer of cement paste around said compressed inner layer of powdered hydraulic cement; and e) hydrating and curing the outer layer of cement paste without substantial hydration of said compressed inner layer of powdered hydraulic cement. 20. A method as set forth in claim 19, said RFID tag being encased in a protective shell before said disposing step c). 21. A method as set forth in claim 19, said disposing step c) further comprising a step of disposing a loop antenna adjacent said compressed inner layer, said loop antenna being operable for communication with said transceiver, said loop antenna having dimensions that are substantially comparable to said waste item; and said transceiver, data storage device, microprocessor, and energy source being encased in a protective shell. 22. The method of claim 19, wherein the transceiver is operable at a radio frequency of 128 KHz. |
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summary | ||
description | The present invention claims priority to U.S. Provisional Patent Application No. 60/842,868, filed Sep. 6, 2006, the entirety of which is hereby incorporated by reference. The present invention relates generally to the field of storing and/or transporting high level waste, such as spent nuclear fuel rods, and specifically to apparatus and methods of storing and/or transporting spent nuclear fuel rods in a dry and hermetically sealed state. In the operation of nuclear reactors, hollow zircaloy tubes filled with enriched uranium, known as fuel assemblies, are burned up inside the nuclear reactor core. It is necessary to remove these fuel assemblies from the reactor after their energy has been depleted to a predetermined level. Upon depletion and subsequent removal from the reactor, these spent nuclear fuel (“SNF”) rods are still highly radioactive and produce considerable heat, requiring that great care be taken in their subsequent packaging, transporting, and storing. Specifically, the SNF emits extremely dangerous neutrons and gamma photons. It is imperative that these neutrons and gamma photons be contained at all times subsequent to removal from the reactor core. In defueling a nuclear reactor, the SNF is removed from the reactor and placed under water, in what is generally known as a spent fuel pool or pond storage. The pool water facilitates cooling of the SNF and provides adequate radiation shielding. The SNF is stored in the pool for a period of time that allows the heat and radiation to decay to a sufficiently low level so that the SNF can be transported with safety. However, because of safety, space, and economic concerns, use of the pool alone is not satisfactory where the SNF needs to be stored for any considerable length of time. Thus, when long-term storage of SNF is required, it is standard practice in the nuclear industry to store the SNF in a dry state subsequent to a brief storage period in the spent fuel pool. Dry storage of SNF typically comprises storing the SNF in a dry inert gas atmosphere encased within a structure that provides adequate radiation shielding. Systems that are used to store SNF for long periods of time in the dry state typically utilize a hermetically sealable and transportable canister or similar structure that serves as a vessel for the transfer and storage of the SNF. One such canister, known as a multi-purpose canister. (“MPC”), is described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999, the entirety of which is hereby incorporated by reference. Typically, the SNF is loaded into an open canister that is submerged under water in a fuel pool. Once loaded with SNF, the canister is removed from the pool, placed in a staging area, dewatered, dried, hermetically sealed and transported to a storage facility. An example of a canister drying method can be found in U.S. Pat. No. 7,096,600, to Krishna P. Singh, issued Aug. 29, 2006, the entirety of which is hereby incorporated by reference. Because a typical canister does not by itself provide the necessary radiation shielding properties, canisters are often positioned within large storage containers known as casks/overpacks during all stages of transportation and/or storage. An example of a canister transfer and storage operation can be found in U.S. Pat. No. 6,625,246, to Krishna P. Singh, issued Sep. 23, 2003, the entirety of which is hereby incorporated by reference. A dry storage canister (“DSC”) provides the confinement boundary for the stored SNF. Thus, the structural and hermetic integrity of the DSC is extremely important. An existing DSC is sold in the United States by Transnuclear, Inc. of Columbia, Md. under the tradename NUHOMS. The NUHOMS DSC is a single-walled vessel with two top closure lids, including an inner top lid and an outer top lid. The closure lids are welded to a canister body after the SNF has been loaded into it. In the United States, the practice of using two closure lids to create a double confinement barrier only at the field welded closure location is motivated by the fact that field welds are generally less sound than those made in the factory. However, in other countries, the creation of a double confinement barrier only at the field welded closure does not meet nuclear regulatory mandates. For example, Ukrainian regulatory practice calls for a double confinement boundary all around the SNF. To meet this dual-confinement requirement, the NUHOMS DSC comprises a hermetically-sealed fuel tube in which SNF rods in the form of a fuel bundle (half of a fuel assembly) is placed. These fuel tubes are positioned within the main cavity of the NUHOMS DSC. However, the body of the NUHOMS DSC remains a single-walled cylindrical vessel. The fuel tube concept of the NUHOMS DSC meets the basic Ukrainian regulation that a double confinement boundary exist all around the SNF. However, as will be discussed in greater detail below, it has been discovered that this design suffers from a number of significant drawbacks and engineering design flaws. It is an object of the present invention to provide an apparatus for transporting, storing and/or supporting high level radioactive waste. It is another object of the present invention to provide an apparatus for transporting, storing and/or supporting spent nuclear fuel. A further object of the present invention is to provide and apparatus for storing spent nuclear fuel that essentially precludes the potential of radiological release to the environment. A yet further object of the present invention is to provide an apparatus for storing, transporting and/or supporting spent nuclear fuel in a dry state. Another object of the present invention is to create a system of storing spent nuclear fuel with two independent containment boundaries around the entirety of the spent nuclear fuel stored therein that contain radiological matter, such as gases and/or particulates. A further object of the present invention is to provide an apparatus for storing spent nuclear fuel with two independent radiological containment boundaries that facilitate heat removal via conformal contact therebetween. A still further object of the present invention is to provide a canister for storing spent nuclear fuel having two independent radiological containment boundaries surrounding a cavity. Another object of the present invention is to provide an improved fuel basket for supporting spent nuclear fuel. A still further object of the present invention is to provide a vented fuel tube for holding high level radioactive waste. Yet another object is to provide a fuel basket that can efficiently accommodate both poison rods and spent nuclear fuel. These and other objects are met by the present invention, which one aspect can be a canister for storing and/or transporting spent nuclear fuel rods comprising: a first shell forming a cavity for receiving spent nuclear fuel rods; a first plate connected to the first shell so as to form a floor of the cavity; a first lid enclosing the cavity; the first shell, the first plate and the first lid forming a first hermetic containment boundary about the cavity; a basket for supporting a plurality of spent nuclear fuel rods positioned within the cavity; a second shell surrounding the first shell so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell; a second plate connected to the second shell; a second lid; and the second shell, the second plate and the second lid forming a second hermetic containment boundary that surrounds the first radiation containment boundary. In another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first pressure vessel comprising a first shell forming a first cavity for receiving spent nuclear fuel rods, a first plate connected to the first shell so as to enclose a first end of the first cavity, and a first lid connected to the first shell so as to enclose a second end of the first cavity; a second pressure vessel comprising a second shell forming a second cavity, a second plate connected to the second shell so as to enclose a first end of the second cavity, and a second lid connected to the second shell so as to enclose a second end of the second cavity; and the first pressure vessel located within the second cavity so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell. In yet another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first metal pressure vessel having an outer surface and forming a cavity for receiving spent nuclear fuel rods; a second metal pressure vessel having an inner surface; and the first pressure vessel located within the second pressure vessel so that a substantial entirety of the outer surface of the first metal pressure vessel is in substantially continuous surface contact with the inner surface of the second metal pressure vessel. in still another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first structural assembly forming a cavity for receiving spent nuclear fuel rods, the first structural assembly forming a first gas-tight containment boundary surrounding the cavity; a second structural assembly surrounding the first structural assembly, the second structural assembly forming a second gas-tight containment boundary surrounding the cavity; and wherein the first structural assembly and second structural assembly are in substantially continuous surface contact with one another. In yet another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a plurality of disk-like grates, each disk-like grate having a plurality of cells formed by a gridwork of beams; and means for supporting the disk-like grates in a spaced arrangement with respect to one another and so that the cells of the disk-like grates are aligned. In a further aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; the gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams; and wherein the first, second and third series of parallel beams are arranged in the ring-like structures so as to intersect and form a plurality of cells. In another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; and the gridwork of beams forming a first set of cells having a first shape and a second set of cells having a second shape. Referring to FIG. 1, a dual-walled DSC 100 according to one embodiment of the present invention is disclosed. The dual-walled DSC 100 and its components are illustrated and described as an MPC style structure. However, it is to be understood that the concepts and ideas disclosed herein can be applied to other areas of high level radioactive waste storage, transportation and support. Moreover, while the dual-walled DSC 100 is described as being used in combination with a specially designed fuel basket 90 (which in of itself constitutes an invention), the dual-walled DSC 100 can be used with any style of fuel basket, such as the one described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999. In fact, in some instances it may be possible to use the dual-walled DSC 100 without a fuel basket, depending on the intended function. Furthermore, the dual-walled DSC 100 can be used to store and/or transport any type of high level radioactive waste and is not limited to SNF. As will become apparent from the structural description below, the dual-walled DSC 100 contains two independent containment boundaries about the storage cavity 30 that operate to contain both fluidic (gas and liquid) and particulate radiological matter within the cavity 30. As a result, if one containment boundary were to fail, the other containment boundary will remain intact. While theoretically the same, the containment boundaries formed by the dual-walled DSC 100 about the cavity 30 can be literalized in many ways, including without limitation a gas-tight containment boundary, a pressure vessel, a hermetic containment boundary, a radiological containment boundary, and a containment boundary for fluidic and particulate matter. These terms are used synonymously throughout this application. In one instance, these terms generally refer to a type of boundary that surrounds a space and prohibits all fluidic and particulate matter from escaping from and/or entering into the space when subjected to the required operating conditions, such as pressures, temperatures, etc. Finally, while the dual-walled DSC 100 is illustrated and described in a vertical orientation, it is to be understood that the dual-walled DSC 100 can be used to store and/or transport its load in any desired orientation, including at an angle or horizontally. Thus, use of all relative terms through this specification, including without limitation “top”, “bottom”, “inner”and “outer”, are used for convenience only and are not intended to be limiting of the invention in such a manner. The dual-walled DSC 100 dispenses with the single-walled body concept of the prior art DSCs. More specifically, the dual walled DSC 100 comprises a first shell that acts as an inner shell 10 and a second shell that acts as an outer shell 20. The inner and outer shells 10, 20 are preferably cylindrical tubes and are constructed of a metal. Of course, other shapes can be used if desired. The inner shell 10 is a tubular hollow shell that comprises an inner surface 11, an outer surface 12, a top edge 13 and a bottom edge 14. The inner surface 11 of the inner shell 10 forms a cavity/space 30 for receiving and storing SNF. The cavity 30 is a cylindrical cavity formed about a central axis. The outer shell 20 is also a tubular hollow shell that comprises an inner surface 21, an outer surface 22, a top edge 23 and a bottom edge 24. The outer shell 20 circumferentially surrounds the inner shell 10. The inner shell 10 and the outer shell 20 are constructed so that the inner surface 21 of the outer shell 20 is in substantially continuous surface contact with the outer surface 12 of the inner shell 10. In other words, the interface between the inner shell 10 and the outer shell 20 is substantially free of gaps/voids and are in conformal contact. This can be achieved through an explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process that bonds the inner shell 10 to the outer shell 20. The continuous surface contact at the interface between the inner shell 10 and the outer shell 20 reduces the resistance to the transmission of heat through the inner and outer shells 10, 20 to a negligible value. Thus, heat emanating from the SNF loaded within the cavity 30 can efficiently and effectively be conducted outward through the shells 10, 20 where it is removed from the outer surface 22 of the outer shell via convection. The inner and outer shells 10, 20 are preferably both made of a metal. As used herein, the term metal refers to both pure metals and metal alloys. Suitable metals include without limitation austenitic stainless steel and other alloys including Hastelloy™ and Inconel™. Of course, other materials can be utilized. The thickness of each of the inner and outer shells 10, 20 is preferably in the range of 5 mm to 25 mm. The outer diameter of the outer shell 20 is preferably in the range of 1700 mm to 2000 mm. The inner diameter of the inner shell 10 is preferably in the range of 1700 mm to 1900 mm. The invention, however, is not limited to any specific size and/or thickness of the shells 10, 20. In some embodiments, it may be further preferable that the inner shell 10 be constructed of a metal that has a coefficient of thermal expansion that is equal to or greater than the coefficient of thermal expansion of the metal of which the outer shell 20 is constructed. Thus, when the SNF that is stored in the cavity 30 and emits heat, the outer shell 20 will not expand away from the inner shell 10. This ensures that the continuous surface contact between the outer surface 12 of the inner shell 10 and the outer surface 21 of the outer shell 20 will be maintained and a gaps will not form under heat loading conditions. The dual-walled DSC 100 further comprises a first lid that acts as an inner top lid 60 for the inner shell 10 and a second lid that acts as an outer top lid 70 for the second shell 20. The inner and outer top lids 60, 70 are plate-like structures that are preferably constructed of the same materials discussed above with respect to the shells 10, 20. Preferably the thickness of the inner top lid 60 is in the range of 100 mm to 300 mm. The thickness of the outer top lid is preferably in the range of 50 mm to 150 mm. The invention is not, however, limited to any specific dimensions, which will be dictated on a case-by-case basis and the radioactive levels of the SNF to be stored in the cavity 30. Referring now to FIG. 2, the inner top lid 60 comprises a top surface 61, a bottom surface 62 and an outer lateral surface/edge 63. The outer top lid 70 comprises a top surface 71, a bottom surface 72 and an outer lateral surface/edge 73. When fully assembled, the outer lid 70 is positioned atop the inner lid 60 so that the bottom surface 72 of the outer lid 70 is in substantially continuous surface contact with the top surface 61 of the inner lid 60. During an SNF underwater loading procedure, the inner and outer lids 60, 70 are removed. Once the cavity 30 is loaded with the SNF, the inner top lid 60 is positioned so as to enclose the top end of the cavity 30 and rests atop the brackets 15. Once the inner top lid 60 is in place and seal welded to the inner shell 10, the cavity 30 is evacuated/dried via the appropriate method and backfilled with nitrogen, helium or another inert gas. The drying and backfilling process of the cavity 30 is achieved via the holes 64 of the inner lid 60 that form passageways into the cavity 30. Once the drying and backfilling is complete, the holes 61 are filled with a metal or other wise plugged so as to hermetically seal the cavity 30. Referring now to FIGS. 1 and 3 concurrently, the outer shell 20 has an axial length L2 that is greater than the axial length L1 of the inner shell 10. As such, the top edge 13 of the inner shell 10 extends beyond the top edge 23 of the outer shell 20. Similarly, the bottom edge 24 of the outer shell 20 extends beyond the bottom edge 13 of the inner shell 10. The offset between the top edges 13, 23 of the shells 10, 20 allows the top edge 13 of the inner shell 10 to act as a ledge for receiving and supporting the outer top lid 70. When the inner lid 60 is in place, the inner surface 11 of the inner shell 10 extends over the outer lateral edges 63. When the outer lid 70 is then positioned atop the inner lid 60, the inner surface 21 of the outer shell 20 extends over the outer lateral edge 73 of the outer top lid 70. The top edge 23 of the outer shell 20 is substantially flush with the top surface 71 of the outer top lid 70. The inner and outer top lids 60, 70 are welded to the inner and outer shells 10, 20 respectively after the fuel is loaded into the cavity 30. Conventional edge groove welds can be used. However, it is preferred that all connections between the components of the dual-walled DSC 100 be through-thickness weld. The dual-walled DSC 100 further comprises a first plate that acts as an inner base plate 40 and a second plate that acts as an outer base plate 50. The inner and outer base plates 40, 50 are rigid plate-like structures having circular horizontal cross-sections. The invention is not so limited, however, and the shape and size of the base plates 40, 50 is dependent upon the shape of the inner and outer shells 10, 20. The inner base plate 40 comprises a top surface 41, a bottom surface 42 and an outer lateral surface/edge 43. Similarly, the outer base plate 50 comprises a top surface 51, a bottom surface 52 and an outer lateral surface/edge 53. The top surface 41 of the inner base plate 40 forms the floor of the cavity 30. The inner base plate 40 rests atop the outer base plate 50. Similar to the other corresponding components of the dual-walled DSC 100, the bottom surface 42 of the inner base plate 40 is in substantially continuous surface contact with the top surface 51 of the outer base plate 50. As a result, the interface between the inner base plate 40 and the outer base plate 50 is free of gaseous gaps/voids for thermal conduction optimization. An explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process can be used to effectuate the contact between the base plates 40, 50. Preferably, the thickness of the inner base plate 40 is in the range of 50 mm to 150 mm. The thickness of the outer base plate 50 is preferably in the range of 100 mm to 200 mm. Preferably, the length from the top surface of the outer top lid 70 to the bottom surface of the outer base plate 50 is in the range of 4000 mm to 5000 mm, but the invention is in no way limited to any specific dimensions. The outer base plate 50 may be equipped on its bottom surface with a grapple ring (not shown) for handling purposes. The thickness of the grapple ring is preferably between 50 mm and 150 mm. The outer diameter of the grapple ring is preferably between 350 mm and 450 mm. Referring now to FIGS. 2 and 4 concurrently, the inner shell 10 rests atop the inner base plate 40 in a substantially upright orientation. The bottom edge 14 of the inner shell 10 is connected to the top surface 41 of the inner base plate 40 by a through-thickness single groove (V or J shape) weld. The outer surface 12 of the inner shell 10 is substantially flush with the outer lateral edge 43 of the inner base plate 40. The outer shell 20, which circumferentially surrounds the inner shell 10, extends over the outer lateral edges 43, 53 of the inner and outer base plates 40, 50 so that the bottom edge 24 of the outer shell 20 is substantially flush with the bottom surface 52 of the outer base plate 50. The inner surface 21 of the outer shell 20 is also connected to the outer base plate 50 using a through-thickness edge weld. In an alternative embodiment, the bottom edge 24 of the outer shell 20 could rest atop the top surface 51 of the outer base plate 50 (rather than extending over the outer later edge of the base plate 50). In that embodiment, the bottom edge 24 of the outer shell 20 could be welded to the top surface 51 of the outer base plate 50. When all of the seal welds discussed above are completed, the combination of the inner shell 10, the inner base plate 40 and the inner top lid 60 forms a first hermetically sealed structure surrounding the cavity 30, thereby creating a first pressure vessel. Similarly, the combination of the outer shell 20, the outer base plate 50 and the outer top lid 70 form a second sealed structure about the first hermetically sealed structure, thereby creating a second pressure vessel about the first pressure vessel and the cavity 30. Theoretically, the first pressure vessel is located within the internal cavity of the second pressure vessel. Each pressure vessel is engineered to autonomously meet the stress limits of the ASME Code with significant margins. Unlike the prior art DSC, all of the SNF stored in the cavity 30 of the dual-walled DSC 100 share a common confinement space. The common confinement space (i.e, cavity 30) is protected by two independent gas-tight pressure retention boundaries. Each of these boundaries can withstand both sub-atmospheric supra-atmospheric pressures as needed, even when subjected to the thermal load given off by the SNF within the cavity 30. Referring now to FIG. 5, the dual-walled DSC 100 is illustrated having a fuel basket 90 positioned within the cavity 30 in a free-standing orientation. The fuel basket 90 serves to hold and support a plurality of SNF rods (which are located within fuel tubes 91) in the desired arrangement and maintains the desired separate locality. The fuel basket 90 comprises a plurality of disk-like grates 92 arranged in a stacked and spaced orientation. The separation between the disk-like grates 92 is accomplished via a plurality of vertically oriented tie-rods that pass through the cells of the disk-like grates 92. Once the tie rods are in place, one of the disk-like grates 92 is slid into position. Tubular sleeves that can not pass through the cells are then placed over the tie-rods and above the disk-like grates 92 in place. The next disk-like grates 92 is then slid down the tie rods. However, because the tubular sleeves can not pass through the disk-like grates 92, the two disk-like grates 92 are maintained in the spaced relation. The grates 92 are disc-like frames comprising a ring 185 and a plurality of series of beams 182, 183, 184. The outer surface 186 of the ring 185 is in surface contact with the inner surface II of the inner shell 10. The outer diameter of the disk-like grate 92 is preferably 1700 mm to 1900 mm. The outer diameter, however is dependent upon the size of the cavity 30. In the illustrated embodiment, the number of grates 92 is nine, and the thickness of each grate 92 is preferably between 1 mm and 10 mm. However, the invention is not so limited, so long as the SNF rods are adequately supported within the cavity 30. Referring now to FIGS. 5 and 6, concurrently, the fuel basket 90 further comprises a plurality of ventilate fuel tubes 91. As will be discussed in greater detail below, when assembled, the ventilated fuel tubes 91 are inserted through the cells 180 of the stack of grates 92, which are aligned. The ventilated fuel tubes 91 form cylindrical cavities 193 (FIG. 9) in which the SNF rods will reside. Preferably, the fuel cells 180 around the outer perimeter of the grates 92 (i.e. the slots 180 nearest to the inner surface 11 of the inner shell 10) remain free of SNF rods. Referring now to FIG. 7, the grates 92 also comprise a plurality of smaller cells 95 (referred to below as poison rod cells 181) for slidably receiving poison rods 93. The poison rods 93 are provided between the loaded fuel tubes 91 to control reactivity in necessary cases. The number of poison rods 93 is selected to ensure that the computed keff of the SNF rods at maximum design basis initial enrichment, with no credit for burnup, and with the inclusion of all uncertainties and biases is less than 0.95. However, in some embodiments, the poison rods 93 may not be required at all. The pitch P between each of the ventilated fuel tubes 91 is between 100 mm and 150 nm. The invention is not so limited however, and the pitch between the ventilated fuel tubes 91 is affected by both the size of the cavity 30 and the number and location of the poison rods 93, and the radioactivity of the load to be stored. Referring now to FIG. 8, a top view of one of the grates 92 is illustrated. The grate 92 is a honey-comb grid like structure. The grates 92 comprise a ring structure 185, a first series of substantially parallel beams 182, a second series of substantially parallel beams 183 and a third series of substantially parallel beams 184. The ring structure 185 encompasses the a first, second and third series of substantially parallel beams 182-184. The entire grate 92 can be constructed of a metal, such as steel or aluminum, or any of the materials discussed above. The first, second and third series of substantially parallel beams 182-184 are arranged within the ring structure 185 so that each one of the series of beams 182-184 intersects with the other two series of beams 182-184. The intersection of the series beams 182-184 forms a gridwork that results in an array of fuel cells 180 and an array of poison rod cells 181. More specifically, the general outline of the fuel cells 180 is created by the intersection of the first and second series of beams 182, 183 while the poison rod cells 181 are created by the intersection of the third series of beams 184 with the first and second series of beams 182, 183. When assembled, the fuel cells 180 receive the fuel tubes 91 while the poison rod cells 181 receive the poison rods 93. As can be seen the poison rod cells 181 are smaller and of a different shape than the fuel cells 180. The relative arrangement of first, second and third series of substantially parallel beams 182-184 with respect to one another is specifically selected to create hexagonal shaped fuel cells 180 and triangular shaped poison cells 181. Of course, additional series of beams and/or arrangement can be used to create cells that have different shapes, including octagonal, pentagonal, circular, square, etc. The desired shape may be dictated by the shape of the fuel tube and SNF fuel assembly to be stored. The series of beams 182, 183, 184 are rectangular strips (i.e., elongated plates) having notches (not visible) strategically located along their length to facilitate assembly. More specifically, notches that extend into the edges of the beams for at least ½ the height of the beams are provided. The notches are arranged on the beams 182-184 so that when the beams 182-184 are arranged in the desired gridwork, the notches of the bottom edge of some beams 182-184 are aligned with the notches on the top edge of the remaining beams 182-184. The beams 182-184 can then slidably mate with one another via the interaction between the notches. The beams 182, 183, 184 are then welded to each other at their intersecting points via tungsten inert gas process. While the beams 182-184 are illustrated as strips, the invention is not so limited and other structures may be used to form the gridwork, such as rods. Referring now to FIG. 9, the structure of the poison rods 93 and the ventilated fuel tubes 91 will be described. In the illustrated embodiment, the poison rods 93 are hollow tubular members having a cavity 196 for receiving a neutron absorbing material. For example, the hollow tubular member can be constructed of a stainless steel and filled with boron-carbide powder. In other embodiment, the poison rods 93 can be constructed of a monolithic material, such as a metal matrix material, such as metamic. The outer diameter of the poison rods 93 is between 20 mm and 40 mm and the inner diameter is between 10 mm and 40 mm. The invention is not so limited, however. When assembled in the DSC 100, the poison rods 93 are of a sufficient length so as to extend along the full height of the SNF rods stored within the fuel tubes 91. Turning now to the fuel tubes 91, the ventilated fuel tubes 91 are designed to allow for ventilation of heat emitted by the SNF rods stored therein. The ventilated fuel tube 91 comprises a tubular body portion 191 and a ventilated cap portion 192. The tubular body portion 191 forms a cavity 193 for receiving the SNF rods, e.g., in the form of fuel bundles (half fuel assemblies). Preferably, the ventilated fuel tubes 91 have a horizontal cross sectional profile such that the cavity 193 accommodates no more than one fuel bundle. However, this is not limiting of the invention. The outer and inner diameter of the tubular body portion 191 of the ventilated fuel tube 91 is preferably between 75 mm and 125 mm, but the invention is not so limited. The tubular body portion 191 comprises a closed bottom end 194 and open top end 197. The closed bottom end 194 is a tapered and flat bottom. As will be discussed in further detail below, the tapering of the closed bottom end 194 allows for better air flow through the dual walled DSC 100. In an alternative embodiment, the closed bottom end 194 could further comprise holes and/or vents for improved air flow and heat removal. The ventilated cap portion 192 is connected to the open top end of the body portion 191 once the cavity 193 is filled with the SNF rods. The cap portion 192 is a non-unitary structure with respect to the tubular body 191 and removable therefrom. The caps 192 prevent any of the solid contents from spilling out during handling operations in the processing facility. The caps 192 of the tubes 91 comprise one or more openings 195 that provide passageways into the cavity 193 from the cavity 30. The openings 195 are covered with fine-mesh screen (not visible) so as to prevent any build-up of pressure in the fuel tube 191 while containing any small debris within the cavity 193 of the tube 91. It has been discovered that one inherent flaw in the design of the NUHOMS DSC is that the hermetically sealed fuel tube creates a mini-pressure vessel around the SNF rods stored therein. Because of the small confinement space/volume available in the hermetically sealed fuel tube of the NUHOMS DSC, even a small amount of water or release of plenum gas from the inside of the SNF rods can raise the internal pressure in the fuel tube steeply, rendering it susceptible to bursting. As a result, the integrity of the fuel tube of the NUHOMS DSC as a pressure vessel can not be assured when used to store previously waterlogged SNF rods that contain micro-cracks with a high level of confidence. The ventilated fuel tubes 91 of the present invention, on the other hand, prevent pressure build-up by allowing ventilation with the larger cavity 30 via the opening 195 in the cap 192 The openings 195 are generally triangular in shape, but can be circular, rectangular or any other shape, so long as the proper venting is achieved. Referring again to FIG. 5, when the ventilated fuel tubes 92 are positioned in the dual walled DSC 100, a plenum exists between the top of the ventilated fuel tubes 91 and the bottom surface 62 of the inner top lid 60. As mentioned previously, it is also preferable that the perimeter of the grid plate 92 remain free of fuel tubes 91. Whereas the present invention has been described in detail herein, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of the present invention. It is also intended that all matter contained in the foregoing description or shown in any accompanying drawings shall be interpreted as illustrative rather than limiting. |
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051223341 | claims | 1. A zirconium-base alloy having improved creep strength, comprising Zr and an amount of Ga effective to improve creep strength of the alloy, Ga being present in amounts up to 1 wt.%. 2. The alloy of claim 1, wherein Ga is present in amounts up to 0.5 wt. %. 3. The alloy of claim 1, wherein Ga is present in amounts up to 0.25 wt. %. 4. The alloy of claim 1, wherein Ga is present in amounts of 0.1-0.25 wt. %. 5. The alloy of claim 1, wherein Ga is present in amounts of 0.25-0.5 wt. %. 6. The alloy of claim 1, further comprising up to 0.5 wt. % oxygen. 7. The alloy of claim 6, wherein oxygen is present in amounts of 0.1-0.25 wt. %. 8. The alloy of claim 6, wherein oxygen is present in amounts of 0.12-0.18 wt. %. 9. The alloy of claim 1, further comprising up to 1 wt. % Sn. 10. The alloy of claim 9, wherein Sn is present in amounts of 0.1-0.7 wt. %. 11. The alloy of claim 9, wherein Sn is present in amounts of 0.25-0.5 wt. %. 12. The alloy of claim 1, further comprising at least one of Fe, Cr and V in a total amount of up to 1 wt. %. 13. The alloy of claim 12, wherein Fe is present in amounts up to 0.5 wt. %. 14. The alloy of claim 12, wherein Fe is present in amounts of 0.1-0.5 wt. %. 15. The alloy of claim 12, wherein Fe is present in amounts of 0.25-0.4 wt. %. 16. The alloy of claim 12, wherein Cr is present in amounts up to 0.5 wt. %. 17. The alloy of claim 12, wherein Cr is present in amounts of 0.1-0.5 wt. %. 18. The alloy of claim 12, wherein Cr is present in amounts of 0.15-0.25 wt. %. 19. The alloy of claim 12, wherein v is present in amounts up to 0.5 wt. %. 20. The alloy of claim 12, wherein V is present in amounts of 0.15-0.4 wt. %. 21. The alloy of claim 12, wherein V is present in amounts of 0.2-0.3 wt. %. 22. The alloy of claim 5, further comprising 0.1-0.25 wt. % oxygen, 0.1-0.7 wt. % Sn, 0.1-0.5 wt. % Fe, 0.15-0.4 wt. % V, 0-0.5 wt. % Cr, balance Zr and unavoidable impurities. 23. The alloy of claim 22, wherein oxygen is present in amounts of 0.12-0.18 wt. %, Sn is present in amounts of 0.25-0.5 wt. %, Fe is present in amounts of 0.25-0.4 wt. %, V is present in amounts of 0.2-0.3 wt. %, and Cr is present in amounts of 0.15-0.25 wt. %. 24. A structural component for use in nuclear reactors and made of a zirconium-base alloy, the alloy including an amount of Ga effective to improve creep strength of the alloy, Ga being present in amount up to 1 wt.%. 25. The structural component of claim 24, wherein the alloy includes up to 1 wt. % Ga, up to 0.5 wt. % oxygen, up to 1 wt. % Sn and up to 1 wt. % in total of Fe, Cr and V. 26. The structural component of claim 24, wherein the alloy consists essentially of up to 0.5 wt.% Ga, 0.1-0.25 wt. % oxygen, 0.1-0.7 wt. % Sn, 0.1-0.5 wt. % Fe, 0.1-0.5 wt. % V, 0-0.5 wt. % Cr, balance Zr and unavoidable impurities. 27. The structural component of claim 26, wherein oxygen is present in amounts of 0.12-0.18 wt. %, Sn is present in amounts of 0.1-0.3 wt. %, Fe is present in amounts of 0.25-0.4 wt. %, V is present in amounts of 0.15-0.35 wt. %, and Cr is present in amounts of 0-0.25 wt. %. 28. The structural component of claim 24, wherein the alloy consists essentially of up to 0.5 wt.% Ga, 0.1-0.25 wt. % oxygen, 0.1-0.7 wt. % Sn, 0.1-0.5 wt. % Fe, 0-0.5 wt. % V, 0.1-0.5 wt. % Cr, balance Zr and unavoidable impurities. 29. The structural component of claim 28, wherein oxygen is present in amounts of 0.12-0.18 wt. %, Sn is present in amounts of 0.1-0.3 wt. %, Fe is present in amounts of 0.25-0.4 wt. %, V is present in amounts of 0-0.25 wt. %, and Cr is present in amounts of 0.1-0.3 wt. %. 30. The structural component of claim 24, wherein the structural component comprises a fuel tube. 31. The structural component of claim 30, wherein the fuel tube is liner-free. 32. The structural component of claim 30, wherein the fuel tube includes a Ga-free inner liner of zirconium. 33. The structural component of claim 24, wherein the structural component comprises a component of a fuel assembly. |
043022960 | claims | 1. In a pool-type nuclear reactor which uses liquid sodium as a coolant, comprising a vertically extending main reactor vessel; a generally horizontally extending structural load bearing arrangement located within and extending across said vessel; a reactor core located directly on top of and being supported by said arrangement; a first plenum located within and generally horizontally across said vessel above said load bearing arrangement and core for containing a relatively turbulent supply of liquid sodium; and a second plenum located within said vessel above and directly adjacent to said load bearing arrangement around said core such that the latter and said second plenum together separate said first plenum and load bearing arrangement from one another, said second plenum containing a stagnant quantity of sodium serving as a thermally insulating fluid barrier between the first plenum and said load bearing arrangement. 2. A reactor as in claim 1 wherein said second plenum has substantially no net flow of sodium therethrough and achieves temperature stratification of the sodium therein as a result of variations in density of the sodium due to a temperature gradient. 3. A reactor as in claim 1 wherein said second plenum includes a horizontal baffle for reducing thermal currents within the second plenum due to irregular temperature gradients between the sodium in the first plenum and the structural arrangement. 4. A reactor as in claim 1 wherein said second plenum includes a horizontal baffle forming a top wall of the second plenum, said first plenum being located generally above said baffle, said sodium in the second plenum being in fluid and temperature communication across the horizontal baffle with the sodium in said first plenum. 5. A reactor as in claim 7 wherein said first plenum receives hot sodium discharging upward from the reactor core during operation. 6. A reactor as in claim 1 wherein the sodium in said first plenum has a temperature greater than about 800.degree. F. 7. A reactor as in claim 1 wherein said second plenum includes means separating the latter into a first sub-plenum adjacent said first plenum and a second sub-plenum adjacent said load bearing arrangement, said sub-plenums being in fluid communication with one another sufficient to eliminate any pressure drop therebetween. 8. A reactor as in claim 1 wherein said first and second plenums are in sufficient fluid communication with one another to eliminate any pressure drop therebetween while maintaining the stagnant nature of the sodium within the second plenum. 9. A reactor as in claim 1 including a third plenum containing a relatively tubulent supply of liquid sodium lower in temperature than the sodium in said first plenum, said third plenum being located within said vessel adjacent said load bearing arrangement opposite said second plenum whereby said stagnant quantity of sodium in said second plenum also serves as a thermally insulating fluid barrier between the first plenum and third plenum. 10. In a pool-type nuclear reactor which uses liquid sodium as a coolant, said reactor comprising: a vertically extending main reactor vessel; a reactor core located within said vessel; a generally horizontally extending structural load bearing arrangement located within and extending across the vessel below said core for supporting the latter; an upper generally horizontally extending plenum located with said vessel above said load bearing arrangement and around a top section of said core for containing a supply of hot liquid sodium; a generally horizontally extending lower plenum located within said vessel below said structural arrangement for containing a supply of cooler liquid sodium; means including at least one heat exchanger and one circulation pump for providing a continuous stream of liquid sodium from said lower plenum through said core and thereafter to and through said heat exchanger and into said upper plenum whereby the sodium in each of the upper and lower plenums is in a state of turbulence; and an intermediate plenum located within said vessel between said upper plenum and said load bearing arrangement and around said core for containing a stagnant quantity of sodium serving as a thermally insulating fluid barrier between the upper plenum on one side thereof and the load bearing arrangement and lower plenum on the other side thereof, said upper plenum and intermediate plenum being in sufficient fluid communication with one another to eliminate any pressure drop therebetween while maintaining the stagnant nature of the sodium within the intermediate plenum, regardless of the turbulence in the upper plenum. |
description | FIG. 1 is a schematic, partial cross section, illustration of a boiling water reactor 100 including a reactor pressure vessel (RPV) 102. RPV 102 has a generally cylindrical shape and is closed at one end by a bottom head 106 and at its other end by removable top head (not shown). A top guide 108 is spaced above a core plate 110 within RPV 102. A shroud 112 surrounds core plate 110 and is supported by a shroud support structure 114. An annulus 116 is formed between shroud 112 and the wall of RPV 102. A baffle plate 118, which has a ring shape, extends around RPV 102 between shroud support structure 114 and the wall of RPV 102. RPV 102, of course, is filled with water. RPV 102 is shown in FIG. 1 as being shut down with many components removed. For example, and in operation, many fuel bundles and control rods (not shown) are located in the area between top guide 108 and core plate 110. In addition, and in operation, steam separators and dryers and many other components (not shown) are located in the area above top guide 108. Top guide 108 is a latticed structure including several top guide beams 126 defining top guide openings 128. Core plate 110 includes several recessed surfaces 130 which are substantially aligned with top guide openings 128 to facilitate positioning the fuel bundles between top guide 108 and core plate 110. Fuel bundles are inserted into the area between top guide 108 and core plate 110 by utilizing top guide openings 128 and recessed surfaces 130. Particularly, each fuel bundle is inserted through a top guide opening 128, and is supported horizontally by core plate 110 and top guide beams 126. The fuel is supported vertically at the core plate by structure not shown. FIG. 2 is a perspective view of a forged upper shroud section 200, with a portion cut away, in accordance with one embodiment of the present invention. Upper shroud section 200 may be machined from a single piece rectangular cross-section ring forging and includes a circular flange 202 and a cylindrical shell 204. Openings and slots 206 are machined into flange 202 to align and support the shroud head. A groove 208 is machined along an inside surface 210 of cylinder section 200, and groove 208 may be used to support top guide grid (not shown). An end 212 of cylinder section 200 is machined with a weld prep for attachment to the core section of the shroud 213. FIG. 3 is a view of forged upper shroud section 200 through line Axe2x80x94A shown in FIG. 2. The thickness of section 200 is governed by the nominal inside diameter of the shroud and the outside diameter of flange 202. The height of section 200 is limited by the size of available ring forgings. The height is also governed by the need to locate the attachment weld of upper shroud section 200 in an area with acceptable fluence levels. The thickness of flange 202 is selected to provide adequate strength to carry the loads from the shroud head. Flange 202 is also stiffened by the use of an integral gusset 214 which spans between flange 202 and cylinder shell or section 204. The thickness of shroud cylinder section 204 is selected to carry the loads from the shroud head and the radial loads from the top guide grid. The above described upper shroud section is fabricated from a single piece forging and therefore, fewer welds are required with such upper shroud section as compared to known upper shroud section. In addition, the present upper shroud section provides the same flow barrier as the welded upper sections, provides a flange to which the shroud head may be bolted and supported, provides a groove to which the top guide grid may be attached without the need for a ledge or flange, and the number to total shroud welds is reduced because of the single piece design. Reducing the number of welds minimizes cracking which can occur in shroud welds and also reduces the number of welds which must be inspected during the construction and life of the shroud. From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims. |
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claims | 1. An integrated passive cooling containment structure for a nuclear reactor, the integrated passive cooling containment structure comprising:a concentric arrangement of an inner steel cylindrical shell and an outer steel cylindrical shell, an inner surface of the inner steel cylindrical shell defining a lateral boundary of a containment environment of the nuclear reactor that is configured to accommodate the nuclear reactor, an outer surface of the inner steel cylindrical shell and an inner surface of the outer steel cylindrical shell defining inner and outer diameters, respectively, of an annular gap space between the inner steel cylindrical shell and the outer steel cylindrical shell;a concrete donut structure at a bottom of the annular gap space, such that the concrete donut structure fills a lower region of the annular gap space that is between the outer steel cylindrical shell and the inner steel cylindrical shell and extends upwards into the annular gap space from the bottom of the annular gap space; anda plurality of concrete columns spaced apart azimuthally around a circumference of the annular gap and extending in parallel from a top surface of the concrete donut structure to a top of the annular gap space;wherein the outer steel cylindrical shell, the inner steel cylindrical shell, the plurality of concrete columns, and the concrete donut structure at least partially define one or more coolant channels in the annular gap space, the one or more coolant channels extending from the top surface of the concrete donut structure to the top of the annular gap space,wherein the outer steel cylindrical shell includes one or more coolant supply ports at a bottom of the one or more coolant channels, the one or more coolant supply ports configured to couple with a coolant source via one or more coolant fluid supply conduits, such that the one or more coolant supply ports are configured to direct a coolant fluid into a bottom region of the one or more coolant channels such that the coolant fluid rises through the one or more coolant channels towards a top of the one or more coolant channels, according to a change in coolant fluid buoyancy based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment via the inner steel cylindrical shell. 2. The integrated passive cooling containment structure of claim 1, whereintwo or more concrete columns, of the plurality of concrete columns, each have a radial diameter, in a radial direction of the annular gap space, that equals a radial distance of the annular gap space between an inner diameter and an outer diameter of the annular gap space over at least a portion of a vertical height of each of the two or more concrete columns, such that the two or more concrete columns azimuthally partition at least a portion of the annular gap space into two or more isolated coolant channels that extend vertically through at least the portion of the annular gap space, andthe outer steel cylindrical shell includes two or more coolant supply ports that are each configured to direct coolant fluid into a separate coolant channel of the two or more isolated coolant channels. 3. The integrated passive cooling containment structure of claim 2, further comprising:one or more steel partitions isolating a concrete column of the plurality of concrete columns from an adjacent coolant channel of the one or more coolant channels. 4. The integrated passive cooling containment structure of claim 1, whereinone or more concrete columns, of the plurality of concrete columns, have a radial diameter, in a radial direction of the annular gap space, that is less than a radial distance of the annular gap space between an inner diameter and an outer diameter of the annular gap space, such that the one or more concrete columns are isolated from directly contacting one or more of the inner steel cylindrical shell or the outer steel cylindrical shell. 5. The integrated passive cooling containment structure of claim 1, further comprising:a cap structure that seals the top of the annular gap space to define the top of the one or more coolant channels, the cap structure including one or more coolant outlet ports configured to direct coolant flowing to the top of the one or more coolant channels to a coolant return via one or more coolant return conduits. 6. The integrated passive cooling containment structure of claim 1, wherein the plurality of concrete columns and the concrete donut structure are a single, uniform piece of concrete. 7. The integrated passive cooling containment structure of claim 1, wherein the plurality of concrete columns and the concrete donut structure each include self-consolidating concrete. 8. The integrated passive cooling containment structure of claim 1, wherein the inner steel cylindrical shell and the outer steel cylindrical shell each include corrosion resistant steel or steel coated with a corrosion resistant coating. 9. A method for forming the integrated passive cooling containment structure of claim 1, the method comprising:forming a steel annulus structure, the steel annulus structure including a concentric arrangement of an inner steel cylindrical shell and an outer steel cylindrical shell, an inner surface of the inner steel cylindrical shell defining a lateral boundary of a containment environment of a nuclear reactor, an outer surface of the inner steel cylindrical shell and an inner surface of the outer steel cylindrical shell defining inner and outer diameters, respectively, of an annular gap space between the inner steel cylindrical shell and the outer steel cylindrical shell;forming a concrete donut structure at a bottom of the annular gap space, such that the concrete donut structure fills a lower region of the annular gap space;forming a plurality of concrete columns spaced apart azimuthally around a circumference of the annular gap space and extending in parallel from a top surface of the concrete donut structure to a top of the annular gap space, such that the outer steel cylindrical shell, the inner steel cylindrical shell, the plurality of concrete columns, and the concrete donut structure at least partially define one or more coolant channels in the annular gap space, the one or more coolant channels extending from the top surface of the concrete donut structure to the top of the annular gap space; andinstalling one or more coolant supply ports at a bottom of the one or more coolant channels, the one or more coolant supply ports configured to couple with a coolant source via one or more coolant fluid supply conduits, such that the one or more coolant supply ports are configured to direct a coolant fluid into a bottom region of the one or more coolant channels such that the coolant fluid rises through the one or more coolant channels towards a top of the one or more coolant channels, according to a change in coolant fluid buoyancy based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment via the inner steel cylindrical shell. 10. The method of claim 9, whereinthe forming the steel annulus structure includes installing one or more steel partitions in the annular gap space to define an inner laterally-closed space, that extends from the top surface of the concrete donut structure to the top of the annular gap space, within the annular gap space, andthe forming the plurality of concrete columns includes filling the inner laterally-closed space with concrete to form one concrete column of the plurality of concrete columns. 11. The method of claim 9, further comprising:mounting the nuclear reactor in the containment environment such that the nuclear reactor is structurally supported in the containment environment by the integrated passive cooling containment structure via at least the concrete donut structure. 12. A nuclear plant, comprising:a reactor building structure;the integrated passive cooling containment structure of claim 1, wherein the integrated passive cooling containment structure is located within an interior of the reactor building structure and defines a void space between the reactor building structure and an exterior of the integrated passive cooling containment structure; anda nuclear reactor located within the containment environment that is at least partially defined by the inner surface of the inner steel cylindrical shell of the integrated passive cooling containment structure. 13. The nuclear plant of claim 12, whereinthe integrated passive cooling containment structure further includes a cap structure that seals the top of the annular gap space to define the top of the one or more coolant channels, the cap structure including one or more coolant outlet ports configured to direct coolant flowing to the top of the one or more coolant channels to a coolant return via one or more coolant return conduits; andthe nuclear plant further includes a coolant reservoir that is both the coolant source and the coolant return. |
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046876235 | abstract | Each of the either normally closed or normally open switches, in an n out of m voted power interface circuit having parallel connected groups of serially connected switches, is shunted by a high impedance resistor to form a leakage path through each group of switches. A detector associated with each group of switches, and responsive to the change of impedance produced by actuation of a resistor shunted switch in the group, generates an output signal, preferably a one bit digital signal, indicative of the state of the switches in the group in response to a sequence of test signals which selectively actuate fewer switches than are required to actuate the load controlled by the power interface. Compensation for large variations in supply voltage is provided by incorporating each group of switches into a resistance measuring bridge circuit in which the digital output signal is generated by a comparator connected across the bridge. Preferably, the bridge circuits share common reference voltage generating legs. |
047537698 | claims | 1. In a nuclear reactor having a pressure vessel, a cover for said vessel, a sleeve (20) secured to the cover and projecting therethrough, upper internals insertable into and movable from said vessel, having a guide tube (18) in alignment with said sleeve, a drive shaft (22) formed with circumferential grooves and linearly movable along said guide tube, and a control cluster connectable by means of a remotely controlled tool to a lower end of said drive shaft, a device for retaining said drive shaft in locked condition within said upper internals, said device comprising (a) a base member (28) fixedly secured to an upper portion of said upper internals; (b) a plurality of spaced apart grippers (34) distributed about the axis of said base member (28) and each mounted about a pin carried by said base member for pivotal movement about a horizontal axis between a position of engagement with said drive shaft and a released position free from engagement with said drive shaft; (c) slide means (42) axially movable with respect to said base member between a higher position and a lower position, said slide means having a mechanical interconnection with said grippers such as to cause pivotal movement of said grippers into engagement with one of the grooves of said drive shaft when moved to said upper position; and (d) resilient means (44) arranged to exert an upwardly directed force on said slide means tending to engage said grippers into said shaft; (e) wherein said slide means is so dimensioned with respect to said base member as to be held by said sleeve at a position sufficiently remote from said upper position for maintaining the grippers out of engagement whatever the temperature prevailing in the reactor and consequently whatever the variations of relative position of the sleeve and the upper internals due to differential thermal expansion. 2. The device of claim 8, wherein said resilient means comprise three springs compressed between the base member and the slide means, distributed about the axis. 3. The device of claim 2, wherein said springs are circumferentially distributed about said axis and alternating with said grippers. 4. The device of claim 8, wherein each of said grippers is in the form of a bell crank lever having one arm formed with at least one latching tooth and another arm having a terminal ball emprisoned in the slide means. 5. The device of claim 8, wherein each of said sleeves is provided with a tulip shaped end piece arranged for engaging said slide means and which constitutes heat protection means. |
055442072 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of the present invention will firstly be explained. FIG. 1 is a perspective view showing a magnetic yoke having an appropriate length and cross-sectional area of the magnetic path and an exciting coil, the magnetic yoke being placed closely in contact with the interior of the pressure vessel of a nuclear reactor, the pressure vessel being shown in a fragmentary sectional view. In FIG. 1, the reference numeral 101 designates a magnetic yoke, the numeral 102 an exciting coil, the numerals 103a and 103b the portions of the magnetic yoke 101 adapted to be closely placed in contact with the pressure vessel of the nuclear reactor, the numeral 104 the inner wall surface of the pressure vessel of the nuclear reactor, the numeral 105 an overlay clad of the inner wall of the pressure vessel of the nuclear reactor and the numeral 106 a vessel section of the pressure vessel of the nuclear reactor. FIG. 2 is a sectional view taken along the line C--C' which passes through the center of the magnetic yoke 101 shown in FIG. 1. In FIGS. 1 and 2, the overlay clad 105 is made of non-magnetic stainless steel while the vessel section 106 is made of a low carbon, ferromagnetic low alloy steel. In the condition shown in FIGS. 1 and 2, if an exciting current is caused to flow through the exciting coil 102 and the magnetic yoke 101 is magnetized thereby, the magnetic fluxes flow as shown in FIG. 3 from the magnetic yoke 101 to the overlay clad 105 of the non-magnetic stainless steel and the vessel section 106 of the low carbon steel. In FIG. 3, the reference numerals 301a through 301i designate the flow of the magnetic fluxes, the symbol g the thickness of the overlay clad 105, the symbol l the length in the direction of the line C--C' of the closely contract portion 103a of the magnetic yoke 101 placed closely in contact with the pressure vessel of the nuclear reactor and the symbol x the distance in the direction of the line C--C' from the half point of l as the reference. In this case, the spatial distribution Hv(x) of the magnetic field component orthogonally crossing with the inner wall surface 104 of the pressure vessel of a nuclear reactor is represented by the curve 401 in FIG. 4. And it is to be noted that the medium value h of the spatial distribution Hv(x) at the point x=0, and the half value width W.sub.1/2 indicating the distance between two points in the direction of x where the magnitude of the spatial distribution Hv(x) are h/2 varies only along with the thickness g of the overlay clad 105 if the geometrical dimension and the magnetic characteristics of the material of the magnetic yoke 101 and of the pressure vessel of the nuclear reactor are determined, and such a relation can be as shown in FIG. 5. This relation can be readily predetermined by using a static magnetic field analysis method such as the definite element method, the boundary element method or the like. Accordingly, if the measured value .sup.m h or .sup.m W.sub.1/2 respectively of the medium value h or the half value width W.sub.1/2 of the spatial distribution Hv(x) of the magnetic field are obtained by measuring the distribution of the magnetic field, the value .sup.m g of the thickness of the overlay clad 105 can be known. The first embodiment of the present invention based on the above-mentioned principle is illustrated in FIG. 6. In FIG. 6, reference numerals identical to those shown in FIG. 1 designate; the same components as those designated by the same reference numerals shown in FIG. 1. The present embodiment is characterized in that a plurality of magnetic field sensors 601 are disposed along the straight line defined on the inner wall surface 104 of the pressure vessel of the nuclear reactor by the central plane C--C' of the magnetic yoke in the system shown in FIG. 1. FIG. 7 is a sectional view taken along the line C--C' passing through the center of the magnetic yoke 101 shown in FIG. 6. The spatial distribution of the magnetic field component orthogonally crossing with the inner wall surface 104 of the pressure vessel of the nuclear reactor is measured by a group of the magnetic field sensors 601. Then, the thickness of the overlay clad 105 can be obtained from the medium value h or the half value width W.sub.1/2 of the measured spatial distribution of the magnetic flux component, by using the relationship between the medium value h or the half value width W.sub.1/2 and the thickness g of the overlay clad 105 which has been determined in advance by the static field analysis. For the magnetic field sensors comprising the group of the magnetic field sensors 601, such comparatively cheap elements as Hall elements, magnetic resistance elements or the like can be used. The second embodiment of the present invention based on the above-mentioned principle is illustrated in FIG. 8. The present embodiment is characterized in that one magnetic field sensor 801 is used in place of a plurality of the magnetic field sensors 601 as a group employed in the first embodiment shown in FIG. 6 in such a manner as the magnetic field sensor 801 is travelled on the inner wall surface 104 of the pressure vessel of the nuclear reactor so as to measure the spatial distribution of the magnetic field. In FIG. 8, reference numerals identical to those shown in FIG. 6 designate identical components to those designated by the same reference numerals as those shown in FIG. 6. According to the present embodiment, a clearance g.sub.o is required to allow the magnetic field sensor 801 to travel therethrough. However, since the clearance g.sub.o can be incorporated in the computation process to the static magnetic field analysis and then the relation between the medium value h or the half value width W.sub.1/2 of the distribution of the magnetic field and the thickness g of the overlay clad 105 can be predetermined, there will be no problems. The present invention having been described in a detailed by referring to certain preferred embodiments, it will be understood that changes and the modifications can be made within the spirit and the scope of the claims of the present invention. |
description | Referring to FIG. 1, a sample fuel assembly is illustrated. The example fuel assembly has a top nozzle 100, a bottom nozzle 106, a plurality of fuel rods 102 between the top and bottom nozzles 100, 106 and guide tube sleeves 104 interspersed between the plurality of fuel rods. During lifting of the fuel assembly, load is carried by the guide tube sleeve 104 to prevent stress from damaging the fuel rods. Industry experience has shown, however, that the guide tube sleeves 104 are susceptible to defects from, for example stress corrosion cracking, therefore affecting the only load path for a lifted assembly. As a result, a damaged fuel assembly is not lifted, hampering maintenance activities. Alternatively, an elaborate handling apparatus, such as a strongback, is used to lift the assembly. Referring to FIG. 2, a cross-section of a fuel assembly structural reinforcement 10 is illustrated. The fuel assembly structural reinforcement 10 is composed of an actuator 12 which is connected to a sleeve 16. The actuator 12 may be shaped as illustrated with a flat upper surface and a beveled edge 14 to allow a flush fit or a near flush fit during installation of the fuel assembly structural reinforcement 10. The actuator 12 may also be configured in another geometric shape such as a block for example. The actuator 12 and the sleeve 16 may be configured as one piece or may be separate pieces as shown. The reinforcement 10 may also be constructed from carbon steel or corrosive resistant materials. The actuator 12, the sleeve 16 and reinforcement 10 may also be made from a variety of materials such as, for example, stainless steel to provide sufficient structural load carrying capacity during anticipated use. Such anticipated uses include not only dead weight of the lifted fuel assembly, but also any attachments to the fuel assembly, forces from hydraulic drag during movement, seismic loading and impact loadings, among other loadings. The materials chosen for use may also be selected to allow for superior corrosion resistance and to limit foreign materials, such as rust or corrosion products, from entering the moderating fluid of a fuel pool during installation. The sleeve 16 defines It an interior volume 36. In the interior volume 36, an upper section 38 is positioned such that the upper section 38 is snugly arranged in the sleeve 16. The installation of the sleeve 16 in the upper section 38 may be by several methods including press fitting. The installation of the sleeve .16 may also be accomplished through welding to provide a sufficient structural attachment The upper section 38 is provided such that an inner adjusting body 20 is positioned partially internally to the upper section 38. The inner adjusting body 20 extends from the upper section 38 through the connection 18 through to the main body 22 and into the lower section 26. The inner adjusting body 20 may be configured as a rod or other shape and have a top 30 and a bottom 32. The inner adjusting body 20 ray be configured with a connection, such as a threaded screw type connection, to allow the inner adjusting body 20 to move upon force exerted on the actuator 12. In the exemplary embodiment illustrated, rotation of the actuator 12 may be used to cause a rotation of the inner adjusting body 20, consequently moving the body 20 up the main body 22 and the lower section 26. The screw thread arrangement between the adjusting body 20 and the main body 22 and/or actuator 12 and the adjusting body 20 may be configured with any desired number of threads per unit length measurement thereby allowing fine or coarse adjustment. The number and configuration of the screw threads are chosen to provide an adequate holding capacity for the reinforcement 10. The reinforcement 10 may be designed to nuclear single failure proof criteria, such as, for example, with a factor of safety of 10 to 1. The inner adjusting body 20 may also be configured to move in an opposite direction thereby loosening the reinforcement 10. Other configurations are possible and the example embodiment shown is merely illustrative in nature. The upper end fitting and the reinforcement 10 may be designed such that the fitting is captured in the interior volume 36. The fitting may be captured by several arrangements such as a screw connection. The connection established between the reinforcement 10 and the upper end fitting may be designed as a single failure proof connection to allow a single reinforcement 10 to carry the load of the entire fuel assembly. Alternatively, the reinforcement 10 may be designed for a lesser load such that multiple installed reinforcement 10 units share the load of the assembly. Optional markings may be provided on the actuator 12 to allow visual identification of the capacity of the reinforcement 10. The interior volume 36 may be designed such that with the rod 20 and the mandrel 28 in the fully retracted position, a sufficient volume 36 exists for attachment of an upper end fitting or lifting device to be used. The overall length of the fuel assembly structural reinforcement 10 may be such that it is configured to provide a repair for differing length fuel assemblies including allowances for changes in length of the fuel assembly from such factors as radiation exposure and temperature. The reinforcement 10, thus, may be adapted in length and overall shape to fit a variety of fuel assemblies such as pressurized water and boiling water reactor types from various manufacturers. At the bottom 32 of the inner adjusting body 20, a mandrel 28 is attached to actuate a holding body 34 for the inner adjusting body 20. The mandrel 28 may be shaped in a variety of configurations, such as a wedge or a ball, and as such the example embodiment shown is purely illustrative. The mandrel 28 may be attached to the inner adjusting body 20 by forming the mandrel 28 at the same time as the inner adjusting body 20 or alternatively the mandrel 28 may be welded, brazed or positively connected by another arrangement. The holding body 34 may be configured such that a sufficient amount of material may be positioned to allow the fuel assembly structural reinforcement 10 to have a sufficient sheer capacity for anticipated loadings during lifting of an attached fuel assembly. To provide this necessary sheer capacity, the holding body 34 may be configured with a receiving edge 24 with a steep angle, permitting extension of the lower section 26 upon actuation of the inner adjusting body 20. As will be apparent to those skilled in the art, the lower section 26 may be configured with slots such that movement of the mandrel 28 towards the actuator 12 will allow the lower section 26 to expand in a consistent manner. Referring to FIG. 3, a fuel assembly structural reinforcement 10 is shown in a mandrel 28 retracted position. Actuation of the actuator 12 allows the mandrel 28 to be drawn to the actuator end of the reinforcement 10. Retraction of the mandrel 28 places a force upon the lower section 26 causing the lower section 26 to extend in an outward direction as measured from the central axis of the reinforcement 10. The extension of the lower section 26 may then be used as a contacting surface to allow load to be transmitted from the bottom nozzle (for example) along the reinforcement 10 thereby creating a secondary load path. The overall shape of the reinforcement 10 may be a tube or other geometry which will allow for ease of installation into the instrument tube. In a typical installation the external diameter of the reinforcement 10 may be 0.405 inches and the internal diameter 0.215 inches. Other configurations are possible wherein the reinforcement may have an external diameter between 0.1 inches to 1 inch and an internal diameter between 0.05 inches to 0.95 inches. Operationally, the fuel assembly structural reinforcement 10 is used to provide a secondary load path for a fuel assembly. A fuel assembly which has been identified as potentially exhibiting stress corrosion cracking in a guide tube or some other load path feature may be reconfigured to provide a secondary load path using the fuel assembly structural reinforcement 10. A hole is machined through the grillage of the top nozzle of a fuel assembly to provide access to the instrument tube. The fuel assembly structural reinforcement 10 is inserted into the hole that has been created such that the reinforcement 10 may extend from the top nozzle 100 to the bottom nozzle 106. As the actuator 12 at the top of the reinforcement 10 is rotated, for example, the screw and thread arrangement allows the inner adjusting body 20 to be xe2x80x9cpulled upxe2x80x9d into the main body 22 and the actuator 12 is placed in contact with the top nozzle. The shape of the mandrel 28 located at the bottom 32 of the inner adjusting body 20 causes the receiving edge 24 to contact the exterior of the holding body 34. Further tightening of the actuator 12 causes the lower section 26 to extend outwardly to provide, for example, a locking finger arrangement thereby contacting the structure of the fuel assembly and providing a secondary load path for the fuel assembly when it contacts the structural support such as a lower nozzle as well as finding the actuator 12 to the top nozzle. As will be apparent to those skilled in the art, further rotating of the inner adjusting body 20 will allow further deflection of the lower section 26, providing a larger potential contact surface. It will also be apparent to those skilled in the art that several reinforcements 10 may be used in order to provide needed structural support if a single reinforcement 10 would not provide the necessary load carrying capability. The present invention allows the reinforcement 10 to be inserted into the fuel assembly and then placed in a retracted state to prevent removal of the reinforcement 10 back through the insertion area. The present invention provides several advantages over conventional methods and apparatus for repairing fuel assemblies. Simple machinery is used to prepare a potentially damaged fuel assembly for installation of the reinforcement 10 such as, for example, a conventional drill. Moreover, the simple configuration of the present invention allows the reinforcement 10 to be installed underwater, protecting operators or machinists from unnecessary radiation exposure. The reinforcement 10 may be installed through use of a robot, crane or other mechanical device such that workers may install the reinforcement from a remote location, i.e. a location away from the reinforcement thereby potentially limiting radiation exposure to workers. Reduced installation time for the reinforcement 10 provides production of a speedy secondary load path saving economic expense for the installer and plant refueling time for the owner. The reinforcement 10 may also be left in place allowing a permanent fix for future moves unlike a special lifting device which must be installed and removed at every move. The installation of the reinforcement 10 does not add significant weight to the assembly eliminating costly analysis for movement of a fuel assembly over safety significant structures or components. Additionally, the reinforcement 10 may be readily installed by, craftpersons eliminating potential human error inherent in costly and complicated devices. All materials used for the reinforcement may be constructed of materials in conformance with high quality requirements of the nuclear industry. All connections, such as for example, welds may be inspected with any type of inspection technique such as magnetic particle inspection or liquid penetrate inspection for example, to determine the presence of defects in the materials used. Both the connections and the materials used may also allow for varying operational temperature considerations which may be present during lifting such as directly after reactor shutdown or after prolonged cooling of an assembly. The materials chosen also may be selected to prevent or limit galvanic reaction with fuel assembly materials. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments, thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense. |
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044951426 | claims | 1. A monitoring system for monitoring the state of the core of a nuclear reactor, comprising: a first pipe communicated at its both ends with the gas layer in a nuclear reactor container housing a nuclear reactor vessel; gas transferring means provided in said first pipe; first means provided in said first pipe for measuring a level of the radioactivity of iodine; second means provided in said first pipe at the downstream side of said first means for measuring a level of the radioactivity of noble gas; a second pipe communicated at its both ends with a space which is to be filled with the coolant in the liquid state discharged out of said nuclear reactor vessel; means disposed in said second pipe for transferring said coolant in the liquid state; third means disposed in said second pipe for measuring a level of the radioactivity of iodine in the coolant in the liquid state; judging means for determining, upon receipt of the outputs from said first means, second means and third means, a condition of fuel rods in said nuclear reactor vessel; and means for displaying the condition of the fuel rods as determined by said judging means. 2. A monitoring system as claimed in claim 1, wherein said judging means determines as the condition of the fuel rods at least one of occurrence of perforation and melt down of the fuel rods in response to the outputs of said first, second and third measuring means and a ratio of the output of the second measuring means to the sum of the outputs of the first and third measuring means. 3. A monitoring system for monitoring the condition of a nuclear core, comprising iodine gas measuring means for measuring a level of the radioactivity of the iodine in the gas in a nuclear reactor container housing a nuclear reactor vessel and for providing an output indicative thereof, noble gas measuring means for measuring a level of the radioactivity of noble gas in the nuclear reactor container and for providing an output indicative thereof, iodine liquid measing means for measuring a level of the radioactivity of iodine in the coolant which has been discharged from the inside of the nuclear reactor vessel to the space inside the nuclear reactor container in a liquid state and for providing an output indicative thereof, judging means for determining as a condition of fuel rods in the reactor core at least one of the occurrence of perforation and the occurrence of melt down of the fuel rods in accordance with the outputs of the iodine gas measuring means, iodine liquid measuring means and noble gas measuring means, and a ratio of the output of the noble gas measuring means to the outputs of the iodine gas and liquid measuring means, and display means for displaying the condition of the fuel rods determined by the judging means. 4. A monitoring system as claimed in claim 3, wherein the ratio of the output of the noble gas measuring means to the outputs of the iodine gas and liquid measuring means is a ratio of the output of the noble gas measuring means to the sum of the outputs of the iodine gas and liquid radiation measuring means. 5. A monitoring system as claimed in claim 4, wherein the judging means determines the condition of the occurrence of perforation of the fuel rods in accordance with the relationship of the sum of the outputs of the noble gas measuring means and the outputs of the iodine gas and liquid radiation measuring means to a first value and in accordance with the relationship of the ratio to a second value. 6. A monitoring system as claimed in claim 5, wherein the judging means determines the condition of occurrence of melt down of fuel rods at least in accordance with the relationship of the sum of the outputs of the noble gas measuring means and the outputs of the iodine gas and liquid radiation measuring means to a third value. 7. A monitoring system as claimed in claim 6, wherein said nuclear reactor container is a container of a boiling water reactor including a dry well and a pressure suppression chamber, the judging means determining as a condition of the fuel rods whether the perforation of the fuel rods is continuously spreading after the occurrence of a loss of coolant accident (LOCA), the noble gas, and iodine gas and liquid measuring means continuously measuring the level of the radioactivity in the pressure suppression chamber, the judging means determining that the perforation of the fuel rods is not spreading when the level of the radioactivity in the pressure suppression chamber decreases in accordance with the equation EQU C=.SIGMA.Cio.multidot.exp(-.lambda.i.multidot.t) 8. A monitoring system for monitoring the condition of a nuclear reactor core comprising: first means for measuring a level of the radioactivity of iodine in a gas layer within a nuclear reactor container housing a nuclear reactor vessel; second means for measuring a level of the reactivity of noble gas in said nuclear reactor container; third means for measuring a level of the radioactivity of a liquid layer within said nuclear reactor container; judging means including a first means responsive to outputs of said first, second and third measuring means for summing the outputs of said first, second, and third measuring means and for comparing the sum with a first predetermined value, and a second means responsive to the outputs of said first, second and third measuring means for providing a ratio between the output of said second measuring means and a sum of the outputs of said first and third measuring means and for comparing the ratio with a second predetermined value; and display means for displaying conditions of fuel rods in accordance with the results of the comparisons. 9. A monitoring system as claimed in claim 8, wherein said nuclear reactor container is a container of a boiling water reactor comprising a drywell and a pressure suppression chamber. 10. A monitoring system as claimed in claim 9, wherein said judging means determines as a condition of the fuel rods an occurrence of a perforation of the fuel rods and whether the perforation of the fuel rods is continuously spreading after the occurrence of a loss of coolant accident (LOCA), said first, second and third measuring means continuously measuring the level of the radioactivity in the pressure suppression chamber, said judging means determining that the perforation of the fuel rods is not spreading when the level of the radioactivity in the pressure suppression chamber decreases in accordance with the equation, EQU C=.SIGMA.Cio.multidot.exp(-.lambda.i.multidot.t) 11. A monitoring system as claimed in claim 8, wherein said third means measures a level of the radioactivity of iodine in the liquid layer. 12. A monitoring system as claimed in claim 8, wherein said judging means includes a third means responsive to the outputs of said first, second and third measuring means for providing a ratio between the output of said second measuring means and a sum of the outputs of said first and third measuring means and for comparing the ratio to a third predetermined value, and a fourth means responsive to the outputs of said first, second and third measuring means for summing the outputs of said first, second and third measuring means and for comparing the sum with one of a fourth and fifth predetermined value in dependence upon the comparison of the ratio with said third predetermined value. 13. A monitoring system as claimed in claim 10, wherein said judging means includes a fifth means responsive to the outputs of said first, second and third measuring means for summing the outputs of said first, second and third measuring means and for comparing the sum with a sixth predetermined value in dependence upon the results of the comparison of the sum with said fifth predetermined value. |
062663925 | claims | 1. A soller slit comprising a plurality of metal foils stacked with a constant interval between adjacent ones of said metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein each said metal foil being prepared by sintering a metal material such that surfaces thereof having high harmonic surface roughness. oxide material is formed on both surfaces of each said metal foil by oxidizing said metal foil and said oxide material has high harmonic surface roughness. said metal foils are prepared by sintering a metal material such that surfaces thereof have high harmonic surface roughness. oxide material is formed on both surface of each said metal foil by oxidizing said metal foil and said oxide material has high harmonic surface roughness. 2. A soller slit as claimed in claim 1, wherein the surface roughness has RMS value in a range from 20 nm to 1 .mu.m, preferably from 20 to 50 nm. 3. A soller slit as claimed in claim 2, wherein said metal material is tungsten or molybdenum. 4. A soller slit as claimed in claim 1, wherein said metal material is tungsten or molybdenum. 5. A soller slit comprising a plurality of metal foils stacked with a constant interval between adjacent ones of said metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein 6. A soller slit as claimed in claim 5, wherein the surface roughness has RMS value in a range from 20 nm to 1 .mu.m, preferably from 20 nm to 50 nm. 7. A soller slit as claimed in claim 6, wherein said metal foils are formed from brass. 8. A soller slit as claimed in claim 5, wherein said metal foils are formed from brass. 9. A method for manufacturing a soller slit including a plurality of metal foils stacked with a constant interval between adjacent ones of said metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein 10. A method for manufacturing a soller slit including a plurality of metal foils stacked with a constant interval between adjacent ones of said metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein |
062529234 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an isometric view and FIG. 2 is a top view of a spent nuclear fuel container 10 having multiple spent nuclear fuel assemblies 12 stored therein. The fuel assemblies 12 extend substantially the entire axial length of the container 10. A neutron absorbing material 14, such as boral neutron poison or borated stainless steel, is located around the spent nuclear fuel assemblies 12 within the container 10. The container 10 may be of any desired size and, for example, typically has a length of about 190 inches and an outer diameter of about 66 inches, with a capacity for twenty-one to twenty-four pressurized water reactor spent nuclear fuel assemblies of forty-four to seventy-four boiling water reactor spent nuclear fuel assemblies 12. The spent fuel assemblies 12 may be from a pressurized water reactor (PWR) or a boiling water reactor (BWR). A circular lid (not shown) is typically double welded or otherwise multiply sealed to the top of the container 10 in a known manner to seal the container after the spent fuel assemblies have been loaded. As shown in FIG. 1, in one embodiment an array of detectors 30 is placed adjacent the container 10. In accordance with the preferred embodiment of the present invention, the detectors 30 are used to simultaneously measure neutron and .gamma.-ray flux, as more fully described below. In an alternative embodiment, temperature sensors may be used in addition to the neutron and .gamma.-ray detectors 30 to measure a temperature profile of the container 10. The neutron detectors 30 may be mounted on a strip 16 or other suitable support structure that allows placement of the detectors 30 adjacent or within the canister 10 in the desired locations. The strip 16 includes wires or other suitable electrical conductors for transmitting signals generated by the neutron detectors 30. A wire 18 or other suitable conductor transmits the signals from the strip 16. The strip 16 preferably comprises a flexible material such as an insulating plastic resistant to high temperatures and radiation, which facilitates placement of the arrays 30 adjacent the container 10. The neutron and .gamma.-ray detectors and the (optional) thermal sensors might alternatively be located inside the container. As shown in FIG. 3, the sealed spent nuclear fuel container 10 may be stored inside a concrete cask 20 having a base 22 and lid 24. The base 22 and lid 24 surround and contain the cask 20 according to the specific manufacturer's design. In one example shown, a ventilation opening 26 is provided in the lid 24. A cover assembly 28 is placed over the lid 24 and rests on the cask 20. The area between the inner wall of the cask 20 and outer wall of the container 10 defines an annular region in which the neutrons and .gamma.-ray detectors 30 are positioned. In a preferred design, a thin steel annular heat shield may be used between the canister and cask. The neutron and .gamma.-ray detectors 30 are held in the desired location in relation to the container 10 by the strip 16. In a preferred embodiment, the wire 18 extends through the ventilation opening or another suitable penetration 26 to the exterior of the cask 20 in order to transmit the signals generated by the neutron and .gamma.-ray detectors 30. In accordance with the present invention, the neutron and .gamma.-ray detectors 30 are used to monitor the flux of energetic neutrons and .gamma.-ray emitted by the spent nuclear fuel assemblies 12. The detector array may be periodically interrogated, such as once every few months. By performing this interrogation when the spent nuclear fuel container 10 is put into storage, a baseline profile of neutron flux and .gamma.-ray flux versus container height is established. Subsequent variations from this profile can be used to determine several parameters of interest. For example, if an unforeseen event were to introduce water into the container, some neutron absorbing materials 14, e.g., boral neutron poison, which typically extends within the container 10 over the entire length of the fuel assemblies 12, might decompose over a period of decades as a result of corrosive processes. If the geometry of the neutron absorbing material 14 were to alter, for example, by dropping to a lower height, the neutron profile would reflect this circumstance. In the region of height from which the neutron absorber 14 has been removed, the detectors 30 would report locally higher neutron flux and .gamma.-ray flux, due to locally greater neutron multiplication, due to fission and the overall neutron flux would rise somewhat due to neutron leakage from this region. As another example, water incursion into the container 10 would produce a region of locally greater neutron flux and .gamma.-ray flux due to an increase in the fission reaction rate at the bottom of the spent fuel assembly region, which would lead to a skewing of the neutron and .gamma.-ray flux profiles toward the bottom and a slight overall increase in neutron flux due to neutron leakage from the bottom region. If water incursion is suspected, confirmation may be obtained by deploying a passive gamma spectrometer which would record the presence of the 2223 keV prompt gamma ray produced by the capture of thermal neutrons in hydrogen. This measurement would preferably be made in a configuration which isolates the spectrometer from 2223 keV gamma rays generated in other hydrogenous material, or in which there is sufficiently little other hydrogenous material that a foreground-background measurement approach can be taken. Alteration of the neutron absorbing material 14 or incursion of water into the container 10 may thus be detected in a timely fashion in accordance with the present invention. This allows the timely monitoring of other containers to determine the need for any possible fuel reloading. In one embodiment, if storage conditions allow retrieval of sensors, the monitoring of the fuel neutron field can be achieved by providing small wells in the inner wall of the surrounding cask, into which are placed passive, interrogable monitors such as a conventional Solid State Track Recorder (SSTR) neutron dosimeter. Alternatively, a string of such sensors can be deployed from the cask opening beneath the rain cover or other suitable penetation, using a flexible holder which can be fastened to the steel container outer wall or other suitable surface. Proper placement can be assured by aligning the holder with fiduciary marks. In this way, the neutron field sensors could be retrieved for readout and replaced as desired. In a preferred embodiment, the array of neutron and .gamma.-ray detectors 30 comprises a set of semiconductor detectors which have been specially configured to be both neutron and .gamma.-ray -sensitive. Such an array may be configured to provide a low volume probe suitable for deployment within the region between the container outer radius and the inner radius of a concrete storage cask, as shown in FIG. 3. The sensor strip 16 can be deployed by various means such as passing the strip through the ventilation opening 26 or other suitable penetration into the annular space between the container 10 and cask 20. Similar deployment is possible for storage in a horizontal orientation. In another embodiment, because the preferred semiconductor neutron and .gamma.-ray detectors 30 are radiation hard, can function in high temperature environments and could be configured to function without application of an external bias voltage, they may be loaded into the container 10 prior to sealing, without requiring external electrical connections. By using the detector 30 as a variable current source component of a low-frequency LRC circuit, the signal may be detected remotely using a pickup loop having a frequency varied to match the LRC output. In such a circuit containing the inductance L (henry), capacitance C (farad) and resistance R (ohm), the oscillation frequency .nu. is given by the formula: EQU .nu.=(1/2.pi.).times.[(1+L /LC)-(R/2+L L).sup.2 +L ]. The signal may then be picked up remotely using a pickup coil whose frequency is scanned to match the oscillation frequency. For frequencies less than or on the order of about 20 Hz, satisfactory transmission of the signal through a container wall of roughly one inch thickness of Type 304 or a similar stainless steel may be achieved. At 20.degree. C. the resistivity of copper is about 1.7 .mu..OMEGA.-cm and that of iron is about 9.7 .mu..OMEGA.-cm. Copper exhibits a skin depth for attenuation of electromagnetic signals of 0.85 cm for a signal of 60 Hz frequency. The skin depth (representing attenuation of an incident signal by the factor 1/e) varies according to the formula: EQU .delta.=c/(2+L .pi..mu..omega..sigma.); wherein .delta.=skin depth (cm); c=speed of light (3.0.times.10.sup.10 cm/sec); .mu.=magnetic permeability of the attenuating medium; .omega.=electromagnetic oscillation angular frequency (radian/sec); and .sigma.=electrical conductivity of the attenuating medium (.OMEGA.-cm).sup.-1. At 60 Hz iron is expected to exhibit a skin depth of about 2.1 cm (0.8 inch), while at 20 Hz this depth would be of the order of about 3.6 cm (1.4 inch). Thus, the skin depth in stainless steel for a 20 Hz signal is on the order of one inch or greater, and satisfactory transmission through the container wall can be achieved. Alternatively, the circuit may be coupled to a generator of acoustic signals in the Mhz frequency range to achieve satisfactory signal penetration through the container wall. The attenuation of a 2 Mhz acoustic signal in worked steel is less than 10 dB/meter. For a thickness of one inch, only a few percent of the intensity of a 2 Mhz acoustic signal would be expected to be lost during transmission, which is satisfactory. If electrical power is required to power the detectors within the container, it may be supplied by a thermoelectric generating device within the container which utilizes a small portion of the thermal heat output from the fuel. For example, 10-year cooled PWR fuel of typical burnup of 40,000 MWD/MTU has a heat output of roughly one kilowatt per assembly, whereas thermoelectric generators with a 50 watt heat source can produce 3 watts of electric power. Thus, in accordance with the present invention, neutron and .gamma.-ray field sensing may be achieved either through the application of passive or active sensors external to the surface of the container 10, or through the placement of sensors within the container. The preferred semiconductor neutron and .gamma.-ray detectors 30 of the present invention preferably comprise a neutron converter layer and a semiconductor active region which is designed to avoid radiation damage to the semiconductor material. Deterioration of prior art solid state radiation detectors caused by damage by energetic particles is a well known phenomenon. The accumulation of radiation damage in the semiconductor material leads to increased leakage current and decreased charge collection efficiency. This radiation damage is caused by the displacement of atoms in the semiconductor by the energetic charged particles. Over time, this damage causes substantial deterioration of detector performance. As a charged particle loses energy in a material, it creates both electron excitation events and displaced atoms. The energy loss can be described by the Bragg curve. The neutron detector of the present invention takes advantage of the change in the partitioning between electronic excitation and displacement events along the range of the charged particle. For high energy alpha particles (.sup.4 He ions), electron excitation is the predominant energy loss mechanism. As the particle loses energy, the importance of displacement damage increases. Most of the displacement damage therefore occurs near the end of the range of travel of the charged particles. In the preferred semiconductor neutron detectors 30, the type of neutron converter layer, the type of semiconductor material, and the thickness and placement of the semiconductor active region are preferably controlled to allow the charged particles to pass through the active semiconductor region without substantial displacement damage. The semiconductor active region is sufficiently thin to avoid displacement damage, but is thick enough to allow sufficient ionization or electron excitation to create a measurable electronic pulse. The relatively thin semiconductor detector is substantially less susceptible to radiation damage than conventional detectors. FIG. 4 schematically illustrates a neutron detector which may be used individually or in an array in accordance with the present invention. FIG. 4 is not drawn to scale for purposes of illustration. The neutron detector 30 preferably includes a substrate 32 made of a semiconductor material such as SiC, GaAs, CdTe, diamond, Ge, Si or other appropriate material. The substrate 32 preferably has a thickness of about 100 to 1000 microns. For high temperature operations, the substrate 32 is preferably made of temperature resistant materials such as SiC, diamond, silicon nitride, gallium nitride and indium nitride. Where SiC is used as the substrate 32 it may be doped with sufficient amounts of nitrogen or other appropriate impurities to provide sufficient conductivity. The substrate 32 may be formed by processes such as high-purity crystal growth or chemical vapor deposition. In the embodiment shown in FIG. 4, a semiconductor P-N junction is formed by an N-type semiconductor layer 34 and a P-type semiconductor layer 36. The N-type and P-type semiconductor layers 34 and 36 define the semiconductor active region of the neutron detector 30. Silicon and germanium are suitable semiconductor materials. However, for high temperature operations, the semiconductor active region 34, 36 is preferably made of materials capable of operating at elevated temperatures, such as SiC, diamond, GaAs, GaP, PbO and CdS. Where SiC is used as the N-type and P-type layers, such layers are preferably formed by chemical vapor deposition of layers containing an appropriate amount of impurity atoms to increase conductivity. For example, when nitrogen is the dopant, typical concentrations in the N- and P-type layers are about 10.sup.15 and greater than about 10.sup.19 atoms per cm.sup.3, respectively. While the active region shown in FIG. 4 comprises a P-N junction, other types of solid state active regions may be used such as Schottky diodes, diffused junction devices, ion implanted diodes or surface barrier detectors. For example, a Schottky diode may be placed adjacent to a neutron converter layer comprising boron, lithium, uranium or other suitable material. The neutron converter material may optionally serve as the metal rectifying Schottky contact. Alternatively, a Schottky diode may be used comprising a contact metal layer of Au, Ni or Pt, an n- layer of SiC, an n+ layer of SiC, and a conductive SiC substrate. In the embodiment of FIG. 4, electrical contacts are made to the semiconductor active region 34, 36 by means of the conductive substrate 32 and a thin conductive contact 38. Conventional electrical connections may be made to the substrate 32 and the contact 38 to receive electronic signals from the semiconductor active region 34, 36 during operation of the detector. The contact 38 preferably has a thickness of from about 0.075 to 1 micron, and is made of any suitable material such as gold, platinum, aluminum, titanium or nickel. An optional insulating material 40 may be provided around at least a portion of the semiconductor active region 34, 36 in order to protect the active region from mechanical stresses and/or chemical attack. The insulating material 40 may also be used to space the semiconductor active region 34, 36 a desired distance from a neutron converter layer 42, as more fully described below. The insulating material 40 may comprise any suitable material such as oxides, nitrides and phosphides. For high temperature operations, oxides such as SiO.sub.2 are particularly suitable. The SiO.sub.2 layer may be formed by methods such as chemical vapor deposition. The semiconductor detector 30 includes a neutron converter layer 42 which generates charged particles when the layer is impinged by neutrons. The neutron converter layer may comprise a relatively thin film or coating, or may comprise a doped region of the device. The composition of the neutron converter layer 42 is selected such that upon impingement by neutrons, charged particles such as .sup.1 H, .sup.3 H, .sup.7 Li and .sup.4 He ions are generated. Species capable of generating such charged particles include .sup.6 Li, .sup.10 B, H, and .sup.3 He. Alternatively, fissionable materials such as .sup.235 U, .sup.233 U or .sup.239 PU can be used to produced charged particles in the form of energetic fission fragments. In particular, .sup.238 U and .sup.237 Np, where fission cross sections exhibit threshold energies of 0.1 to 1.0 MeV, would be expected to provide the most faithful axial profile of the fuel neutron source, since they are insensitive to neutrons which have undergone downscattering in the surrounding materials. Although their fission cross sections are only on the order of 0.1 b to 1b, the long periods of data collection associated with the present application would be expected to render them suitable for this purpose. The size of the semiconductor active region 34, 36 and its placement in relation to the neutron converter layer 42 are preferably controlled in order to minimize radiation damage. As shown in FIG. 4, the neutron converter layer 42 is relatively thin, having a thickness A preferably ranging from about 0.1 to about 10 microns. The optional insulating material 40 has a thickness B which is selected in order to minimize displacement damage caused by charged particles, as more fully described below. The thickness B of the insulating material 40 typically ranges from 0 to 10 microns or more. The P-type semiconductor layer 36 has a thickness C, while the N-type semiconductor layer 34 has a thickness D. The thickness C preferably ranges from about 0.1 to about 5 microns, while the thickness D preferably ranges from about 1 to about 10 microns. The semiconductor active region, which is defined by the N-type and P-type layers 34 and 36, has a thickness E. The thickness E preferably ranges from about 1 to about 15 microns, and is selected such that dislocation damage caused by charged particles is minimized. As shown in FIG. 4, upon impingement by neutrons, some charged particles exit the neutron converter layer 42 in a normal direction N. As more fully described below, a charged particle traveling along direction N will cause electron excitation events as it travels, and will eventually come to rest a distance R.sub.N from the neutron converter layer 42. The semiconductor active region 34, 36 having the thickness E is positioned in relation to the neutron converter layer 42 such that the charged particles traveling in the direction N cause ionization within the thickness of the semiconductor active region E, and pass through the active region before they come to rest. In this manner, dislocation damage within the active region is minimized. As shown in FIG. 4, charged particles exiting the neutron converter layer 42 will also travel at non-normal angles, such as in the oblique direction O. Charged particles traveling along direction O pass through the semiconductor active region 34, 36 and come to rest a distance R.sub.o from the neutron converter layer 42. The charged particles thus pass through the semiconductor active region 34, 36 in many different directions ranging from normal angles N to relatively shallow oblique angles O. The range of the charged particles is defined by a band R which is located away from the neutron converter layer a minimum distance of R.sub.o and a maximum distance of R.sub.N. As schematically shown in FIG. 4, the range of the charged particles falls in a band R outside of the semiconductor active region 34, 36. Instead of causing dislocation damage within the active region, the charged particles come to rest in the substrate 32. FIG. 5 schematically illustrates a semiconductor detector 30 suitable for use in accordance with another embodiment of the present invention. The detector 30 of FIG. 5 likewise includes a substrate 32 having an N-type semiconductor layer 34 and P-type semiconductor layer 36 disposed thereon. An electrical contact 38 and optional insulating material 40 are also incorporated in the detector of FIG. 5. A collimator 44 is positioned between the active region 34, 36 and the neutron converter layer 42. The collimator 44 may be made of any suitable ion absorbing material such as SiO.sub.2, SiC or silicon nitride. The collimator 44 includes an inner passage 48 having a length F and a width G. The inner passage may comprise a gas such as air, nitrogen or helium. A cap 46 made of any suitable material such as aluminum or nickel provides support for the neutron converter layer 42. The collimator 44 is used to reduce the number of charged particles which enter the semiconductor active region 34, 36 at shallow angles. The height F of the inner passage 48 is preferably at least twice the width G of the passage. Charged particles exiting the neutron converter layer 42 at highly oblique angles are absorbed by the walls of the collimator 44 and do not pass into the active region 34, 36. As shown in FIG. 5, charged particles traveling in a normal direction N come to rest a distance R.sub.N from the neutron converter layer 42. Charged particles traveling in an oblique direction O come to rest a distance R.sub.o away from the neutron converter layer 42. The range of the charged particles is defined by a band R which is located a minimum distance R.sub.o from the neutron converter layer 42 and a maximum distance R.sub.N from the neutron converter layer. By increasing the ratio of the height F to width G of the inner passage 48, the maximum angle between the normal direction N and oblique direction O is decreased, thereby decreasing the width of the band R. Energy deposition curves for charged particles in the detector material may be used to determine the appropriate thickness of the semiconductor active region. Such energy deposition curves may be established from the TRIM computer code developed by Biersack and Ziegler, or other conventional rangeenergy calculation methods. The distribution curves for ionization and vacancy production by a normally incident beam of .sup.10 B reaction products in SiC is illustrated in FIG. 6. The reaction products comprise charged particles of Li and He ions. Due to its relatively high atomic number (Z), the range of the Li ion is relatively short, i.e., about 1.75 microns. The range of the He ion is nearly double the Li ion range. The displacement damage caused by each type of ion occurs near the end of the range. As shown in FIG. 6, in the first micron, the energy loss to ionization is relatively high and only minimal displacement damage occurs. At about 1.6 microns displacement damage caused by Li ions reaches a peak. After about 1.8 microns ionization energy loss again dominates displacement damage. However, at about 3.3 microns dislocation damage caused by He ions reaches a peak. In order to avoid dislocation damage, the semiconductor active region is positioned in a region where ionization energy loss is high and displacement damage is low. Thus, for a normally incident beam of reaction products, the SiC active region may be positioned at a distance of less than about 1.5 microns from the boron neutron converted layer and/or at a distance between about 1.8 and 3.1 microns from the neutron converter layer. FIG. 7 illustrates energy loss curves for a normally incident beam of .sup.6 Li reaction products in SiC. The reaction products comprise charged particles of .sup.4 He and .sup.3 H (tritium) ions. In comparison with the .sup.10 B reaction products shown in FIG. 6, the near surface low damage zone is larger for the lower Z, higher energy products of the .sup.6 Li reaction. As shown in FIG. 7, the He ions are the higher Z products with a shorter range of about 4.5 or 5 microns. The H ions have a longer range of about 27 microns. For the lithium reaction products, the low damage region extends over approximately the first 4 microns of the detector. At about 5 microns, dislocation damage caused by He ions reaches a peak, but quickly subsides thereafter. From about 5 microns to about 27 microns, ionization energy loss is again maximized. However, at about 27 microns dislocation damage caused by H ions reaches a peak. Thus, for a normally incident beam of reaction products, the SiC semiconductor active region should therefore be located at a distance of less than about 4 microns from the lithium neutron converter layer and/or at a distance between about 5 and 27 microns from the neutron converter layer. The semiconductor neutron detector is preferably provided with an active zone that corresponds to a region with a high ratio of ionization energy loss to displacement damage production. The spacing between the neutron convertor layer and the active region of the detector is preferably controlled depending on the incident radiation. For a normally incident beam, the neutron convertor layer may advantageously be placed adjacent to the semiconductor active region. However, the angular distribution of reaction product ions exiting the neutron convertor layer is usually random. This leads to a broadening of the energy dissipation curves as illustrated in FIG. 8 for the .sup.6 Li reaction. For this broadened curve, with SiC as the semiconductor active region, the maximum ionization to displacement ratio occurs between about 5 and 15 microns. Thus, the SiC active region is preferably about 5 to 10 microns thick and is spaced about 5 microns from the neutron converter layer. The semiconductor active region is thereby positioned away from the neutron converter layer in a location where the ratio of ionization energy loss to displacement damage is maximized. An energy dissipation curve for a collimated beam with Li as the neutron converter layer and SiC as the semiconductor active region is shown in FIG. 9. Although slight broadening of the damage peak is noted, the number of vacancies produced in the first 3.5 microns of the detector approximates the levels obtained from a normally incident beam, as shown in FIG. 7. While the use of a collimator may reduce the overall signal of the device by eliminating a proportion of the incident radiation, compensation for this signal loss may be provided by increasing the concentration of Li in the neutron convertor layer. Alternatively, microchannelling devices may be used to eliminate shallow incident angles. However, the increased collimation provided by such devices may not be sufficient to justify the resultant decrease in signal intensity. The preferred neutron detectors for use in accordance with the present invention possess several advantages over conventional designs. The use of a relatively thin semiconductor active region substantially reduces radiation damage. The use of a thin semiconductor active region also provides for gamma discrimination because the active thickness of the detector may be less than the range of most gamma radiation. This allows the detectors to measure neutron flux in the presence of large gamma fields. Furthermore, the use of high temperature resistant materials such as silicon carbide in the active region of the detector permits extended use in elevated temperature environments associated with spent nuclear fuel. The following examples are intended to illustrate various aspects of the present invention and are not intended to limit the scope thereof. Multiple detectors may be formed into an array or string for in-situ measurement of neutron flux and .gamma.-ray flux from spent nuclear fuel, as shown in FIGS. 1-3 and discussed previously. In a manner similar to that described above for the measurement of the spatial profile of neutron flux and .gamma.-ray flux, an axial array of thermocouples or other temperature sensors can be used to measure the axial profile of temperature within the container 10. The container 10 is typically sealed and back-filled with helium to a pressure of a few lbs/in.sup.2 gauge. If the helium backfill were to degrade, a significant loss of ability to dissipate heat to the outside could result. Further, the helium leak could also be indicative of significant canister leakage. Measurements taken at regular intervals such as weeks or months may indicate this degradation through a gradual, relatively uniform change in measured temperatures. On the other hand, if a significant alteration of fuel assembly 12 or absorbing material 14 geometry occurs within the container 10, a skewed temperature profile could result. This profile would correlate with skewed neutron flux and .gamma.-ray flux profiles to indicate a possible need for further attention. Conventional thermocouples may serve as temperature sensors in a flexible sensor holder applied externally to the container 10 within the concrete storage cask 20, as described above for neutron measurements. Thus, temperature sensors may be used in addition to the neutron detectors shown in FIG. 3. While thermocouples may require active interrogation, the thermal sensor may instead comprise a conventional passive Integrating Thermal Monitor (ITM). Like the SSTR for neutron dosimetry, these sensors could be retrieved for readout and replaced as desired. As described above for the neutron sensors, thermocouples may also be loaded into the container 10 prior to sealing. The voltage generated in the thermocouple junction (several mV) may be coded in an AC or acoustic signal for remote pickup, as described earlier for neutron detection using semiconductor detectors. It is also advantageous to detect any structural degradation in the container internals before failure actually occurs. This is especially true for a container which is to be transported to a new location. Transport may apply additional stresses to the container internals. Unanticipated failure of cracked components during transportation could lead to changes in the canister internal geometry that could lead to unsafe conditions if the canister were to be reflooded with water. Similarly, it is useful to verify that no damage occurred during transportation. In accordance with an embodiment of the present invention, schematic drawings of an incipient structural failure detection circuit are shown in FIGS. 10 and 11. A selected area or internal joint or component of the container 10 may be monitored for structural cracks or failures. For example, a critical joint 50 of the container 10 may be monitored by running a wire 52 and conductive tape 54 across the joint 50. The wire 52 and tape 54 are electrically connected by a wire 56 to an internal coil 58. An external coil 60 located outside the container 10 is inductively coupled to the internal coil 58. Wires 62 extend from the external coil 60 to an inductance meter 64 located outside of the cask 20. As shown in FIG. 10, when the critical joint 50 of the container 10 is intact, an uninterrupted circuit is provided through the internal coil 58. However, as shown in FIG. 11, when the critical joint 50 develops a crack or fails, the wire 52 is broken, thereby interrupting the inductive loop in the internal coil 58. This interruption is picked up by the external coil 60 and fed to the inductance meter 64. Detection of incipient structural failures can thus be accomplished in a manner similar to that described for internal neutron and .gamma.-ray detection. In this embodiment, the external coil 60 is coupled to the internal coil 58 which is part of a simple electrical network. This network preferably uses the continuity of the conductive wire 52 and tape 54 to confirm that critical components are in the correct location and are crack free. The tape preferably has a high conductivity, and is bonded to the monitored surface 10 using a ceramic adhesive with high dielectric strength, bond strength, radiation resistance and thermal stability. A magnesia based adhesive such as commercially available AREMCO Cermabond 571 and aluminum metal tape are a preferred embodiment. If a crack develops in a critical component, or if there is displacement across a critical joint 50, the wire 52 and tape 54 are severed and the continuity of the coil circuit is destroyed. This is observed as a drop is the low frequency inductance of the external probe coil. While certain embodiments of the present invention have been described, various changes, modifications, additions and adaptations may be made without departing from the scope of the invention, as set forth in the following claims. |
abstract | An ion beam generator includes a discharge tank for generating plasma that includes ions. A lead-out electrode has an annular grid portion provided with openings for leading out the ions generated in the discharge tank, while accelerating the generated ions as an annular ion beam. A deflecting electrode deflects the annular ion beam, which is led out of the lead-out electrode, in an annular center direction. |
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051071258 | summary | FIELD OF THE INVENTION The invention is directed to an X-ray imaging screen and to a process for its preparation. BACKGROUND OF THE INVENTION Photographic elements relying on silver halide emulsions for image recording have been recognized to possess outstanding sensitivity to light for more than a century. Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913 the Eastman Kodak Company introduced its first product, a silver halide radiographic element, specifically intended to be exposed by X-radiation. The utility of X-ray imaging as a medical diagnostic tool was immediately recognized, and the desirability of limiting patient exposure to X-radiation was also quickly appreciated. This led to the first X-ray imaging screens, specifically X-ray intensifying screens. These screens are constructed by coating a fluorescent layer on a support, usually a film support. The fluorescent layer is comprised of a mixture of phosphor particles and a binder. In use, an assembly is formed by mounting an intensifying screen with its fluorescent layer adjacent the silver halide emulsion layer of a radiographic element. An imagewise pattern of X-radiation striking the assembly is directly absorbed to a small degree by the silver halide emulsion layer. A much larger portion of the X-radiation is absorbed by the phosphor particles of the fluorescent layer. The phosphor particles promptly fluoresce at longer wavelengths which the silver halide emulsion layer can more readily absorb. A latent image is produced in the silver halide emulsion layer primarily attributable to fluorescence from the X-ray imaging screen. A summary of X-ray intensifying screens is found in Research Disclosure, Vol. 184, August 1979, Item 18431. Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley Annex, 21a North Street, Emsworth, Hampshire P010 7DQ, England. Luckey U.S. Pat. No. 3,859,527 (reissued as U.S. Pat. No. Re. 31,847) proposed a second type of X-ray imaging screen, referred to as a storage phosphor screen to distinguish it from the X-ray intensifying screens described above. Storage phosphor screens can be essentially similar in construction to X-ray intensifying screens, differing primarily in the composition of the phosphor selected. Storage phosphor screens are imagewise exposed to X-radiation that is again absorbed by the phosphor particles. Although the phosphor may promptly fluoresce to some degree, most of the absorbed X-radiation energy is retained in the phosphor particles. When stimulated with longer wavelength radiation the screen emits in a third wavelength region of the spectrum. Typically X-ray imaging screens of the storage phosphor type are used alone for imaging--that is, these screens are not normally used to expose silver halide radiographic elements. Takahashi et al U.S. Pat. No. 4,926,047 is a recent example of the numerous patents that have sought to improve on Luckey. Because of their structural and functional similarities X-ray imaging screens of both the intensifying screen and storage phosphor screen types encounter similar difficulties. The cost of X-ray imaging screens dictates that they be used repeatedly. To maximize their durability the screens are most commonly constructed using dimensionally stable polymeric films. Since the sharpest possible images are achieved with the thinnest possible fluorescent layer construction, the fluorescent layers are constructed with the minimum proportion of binder compatible with structural integrity--i.e., with a high weight ratio of phosphor particles to binder. To further protect the phosphor particles it is also conventional practice to coat a thin transparent film (commonly referred to as an overcoat) over the fluorescent layer. In manufacturing scale construction a fluorescent layer containing phosphor particles and binder is coated on the planar coating surface of a continuous film as it is wound between storage rolls. To convert a wound roll of coated film into X-ray imaging screens the film is cut into convenient lengths. These cut lengths are then assembled into stacks, and the stacks are cut again to trim away edge areas, which are likely to contain coating irregularities. A third cutting step is usually undertaken to replace the corners with arcuate edges joining the perpendicular major edges. When cutting is undertaken by mechanical chopping, edge delamination (separation of the fluorescent layer form the film support) can occur. When the X-ray imaging screens have been cut to size, the phosphor particles along the edges of the fluorescent layer are exposed. To protect the phosphor from degradation by exposure to contaminants it is common practice to seal the edges after cutting. The edge sealant can also be relied upon to physically protect the edges during handling in use. Thus, a series of cutting and sealing steps are conventionally employed to create an X-ray imaging screen from a fluorescent layer coated film roll. A sectional detail of a conventional X-ray imaging screen 100 is shown in FIG. 1. A film support 101 is shown having a planar coating surface 103 bearing a fluorescent layer 105 which is in turn covered by a transparent protective overcoat 107. As shown the film support, fluorescent layer and overcoat have a common edge 109 produced by mechanical chopping. Flexing of the film support and fluorescent layer that occurs during mechanical chopping often results in areas of edge delamination, shown at 111. An edge sealant 113 applied in a post-chopping step is shown protecting the peripheral edge of the fluorescent layer that would otherwise be exposed. SUMMARY OF THE INVENTION In one aspect this invention is directed to an X-ray imaging screen comprised of a film support having a planar coating surface and, coated on the planar surface, a fluorescent layer comprised of a particulate phosphor capable of absorbing X-radiation and emitting longer wavelength electromagnetic radiation and a binder. The X-ray imaging screen is characterized in that the film support is comprised of a thermoplastic polymer and includes an integral lip at its outer boundary extending above the planar coating surface and along peripheral edge portions of the fluorescent layer to protect the fluorescent layer from wear and delamination from the film support. In another aspect this invention is directed to a process of preparing an X-ray imaging screen comprised of coating on a planar surface of a thermoplastic film support a fluorescent layer comprised of a particulate phosphor capable of absorbing X-radiation and emitting longer wavelength electromagnetic radiation and a binder, orienting the film support for sizing and cutting through the film support and fluorescent layer to define a peripheral edge of the imaging screen. The process is characterized in that cutting to define the peripheral edge is achieved by locally heating the film support above its softening point, directing a softened portion of the film support over the peripheral edge of the fluorescent layer to form a peripheral lip integral with the film support, and cooling the softened portion of the film support to immobilize the integral peripheral lip along the peripheral edge of the fluorescent layer, thereby providing a lateral protective buffer for the fluorescent layer along its peripheral edge. |
summary | ||
046559973 | claims | 1. In a nuclear reactor having a roof, depending hangers supported at upper ends thereof from said roof by hook and eye type connections to allow two dimensional movement of the hangers, and thermal insulation located under the roof and defining apertures through which the hangers extend to support said insulation, wherein the improvement comprises, each hanger comprising a rigid tie-rod having a said hook and eye type connection at its upper end, a support assembly at a lower end of each tie-rod, said assembly comprising a first element about the tie-rod and defining a first one dimensional ridge at the upper end of the first element, which first ridge engages the underside of the insulation to support the insulation and being pivotal on the insulation, a second element about the tie-rod and below the first element, a second one dimensional ridge at the upper end of the second element for allowing relative pivotal movement between the first element and the second element, means for aligning the first element and the second element such that the first ridge and the second ridge are aligned at substantially 90.degree. with respect to each other, and securing means for retaining the first element and the second element on the tie-rod. 2. An assembly as claimed in claim 1, wherein the aligning means comprises a first pair of pins protruding from the first ridge and locating in respective opposed holes in the insulation, and a second pair of pins protruding from the second ridge defined by the second element and locating in respective opposed holes in the first element. 3. An assembly as claimed in claim 1 wherein said first element includes a passage through which said tie-rod passes with clearance, and said securing means secures said second element to the tie-rod such that said first element is retained by engagement with the underside of the insulation by said first ridge and by engagement of said second ridge with the lower end of said first element. |
050930737 | summary | The invention relates to a process for the decontamination of surfaces, in particular on components of cooling circuits of nuclear reactors, by treatment of the radioactively contaminated surface layers with an aqueous, acid-containing decontamination solution. In the cooling circuits of nuclear reactors, layers in which radioactive contaminants such as, for example, activated corrosion products, and also fission products, are incorporated are formed on the surfaces of the cooling circuit components. With increasing age of the nuclear power stations, this leads to an increase in the activity, the proportion of longer-lived nucleides rising in particular. With increasing age of the nuclear power stations, however, maintenance work and repairs must also be carried out more frequently and modifications must be made, so that the radiation exposure of the personnel increases. In order to facilitate work on radioactively contaminated plants or even to make it possible, decontaminations are necessary. The contaminated surface layers must then be removed as completely as possible, but the base materials of the cooling circuit components must be protected. The composition of the surface layers does not have to be the same as that of the materials of the cooling circuit components. Physical conditions and water chemistry determine the corrosion of the materials and the transport and deposition of the resulting corrosion products and hence the composition and structure of the surface layers. For example under the conditions of a pressurized water reactor (PWR), oxide layers of high chromium content with spinel-type mixed oxides, which dissolve only extremely slowly in acids, form at a temperature of about 570 K in cooling water containing boric acid and lithium hydroxide. All known processes for the decontamination of the surfaces of components of pressurized water reactors therefore comprise two or more treatment steps, the insoluble Cr(III) oxide being converted in a first step in an oxidizing phase into soluble 6-valent chromium, and the entire oxide layer being loosened at the same time. In a second treatment step, in most cases after intermediate rinsing, the loosened oxide layer is then dissolved in an acidic, reducing and complex-forming solution and removed. For the first treatment step, that is to say the oxidative treatment step, a number of processes are usual, such as, for example, the so-called "AP" processes which consist of a treatment with alkaline permanganate solution, or the "NP" processes in which nitric acid solutions are used for the oxidation. Further known processes envisage the use of permanganic acid, hydrogen peroxide, cerium(IV) salts or other oxidizing agents. The current state of the art is extensively described, for example, in the following two publications: (1) "Decontamination of Nuclear Facilities to Permit Operation, Inspection, Maintenance, Modification or Plant Decommissioning", Technical Reports Series No. 249, International Atomic Energy Agency, Vienna 1985; PA1 (2) W. Morell, H. O. Bertold, H. Operschall and K. Frohlich: "Dekontamination - Stand der Technik und aktuelle Entwicklungsziele [Decontamination State of the Art and Current Development--Targets]", VGB Kraftwerkstechnik 66 (1986) 579-588. All the known processes have the common feature that they must be employed at relatively high temperatures, in most cases between 350 K. and 400 K. This involves various serious disadvantages, such as the necessity of relatively expensive and complicated auxiliary equipment, an increase in corrosivity, pressure build-up due to steam at treatment temperatures above 370 K., and others. Attempts have therefore already been made on various occasions to develop oxidation treatments which work satisfactorily at lower temperatures, preferably at usual room temperature. As an example, a Swedish process may be mentioned here, in which the oxidation is carried out by means of ozone-containing nitric acid. This process has, however, the disadvantage that control of a process with a gas-containing liquid as the reagent is difficult and that ozone is not easy to handle and, in addition, is toxic and moreover can lead to explosions. A further serious disadvantage of all the processes mentioned is the use of chemicals which contain elements which occur neither in the materials of the components which are to be decontaminated nor in the coolant. Since complicated components or entire cooling circuits of nuclear reactors can be completely flushed only with great difficulty and at considerable cost and thus be cleaned after the decontamination by removing all residues of the chemicals which have been introduced, it is unavoidable in practice that residues of such chemicals remain in the circuits and, under some circumstances, lastingly interfere with the further operation of the nuclear reactors, either as a result of depositions, local corrosion or of activation. It is therefore the object of the present invention to provide a decontamination process which avoids the abovementioned disadvantages of known processes and which is effective at lower temperatures, even at usual room temperature, and manages with relatively harmless chemicals, the elements of which are not "foreign to the reactor" but are also usually present in the coolant and in the materials of the cooling circuit components. This object is achieved by the process according to Patent Claim 1. In the process according to the invention, the decontamination solution employed in the first treatment step contains chromic acid (chromium(VI) oxide) and permanganic acid. Both chromium and manganese are present as accompanying elements or alloy elements in all steels normally used in reactor construction. These chemicals are not only inexpensive but also relatively non-toxic and easy to handle in the concentrations employed. The permanganic acid can preferably be prepared by passing an aqueous solution of an alkali metal permanganate or alkaline earth metal permanganate over a cation exchanger and thus forming the free acid which, after addition of chromic acid, is used as the decontaminating agent. Solutions of chromic acid and of salts of permanganic acid are also suitable as decontaminating agents; however, somewhat higher salt loads will then be obtained in the radioactive wastes due to the additionally introduced cation. The effectiveness of the decontaminating agent is characterized by the pH value and the redox potential of the solution. The first treatment step can therefore be monitored and controlled by means of these readily detectable measuring parameters. As a result of the reaction of permanganic acid with constituents of the contaminated oxide layers and of spontaneous decomposition of the permanganic acid, insoluble manganese dioxide ("brown oxide") is formed even at usual room temperatures and precipitates on the surfaces. The discoloration allows a visual check of the effectiveness of the decontamination solution. Because of the presence of chromic acid in the decontamination solution, no firmly adhering layers form, which would afterwards be difficult to remove. The surfaces of the cooling circuit components cannot yet be completely freed of radioactive substances by the oxidative first treatment step, so that a second treatment step is additionally necessary for removing the surface layers which have been modified by the oxidative treatment. The second treatment step can be of a chemical or physical nature. It has been found that the surface layers modified in the first treatment step, for example those of carbon steels, stainless chromium steels, nickel alloys and other materials usual in reactor construction, can be removed solely by mechanical and/or hydraulic action, for example by means of a high-pressure water jet, or chemically dissolved, in order to achieve complete decontamination. The chemical dissolution of the surface layers can be carried out with highly diluted solutions of organic acids, for example oxalic acid, citric acid or ascorbic acid, at usual room temperature, it also being possible in addition to add complexing agents and corrosion inhibitors to the solutions. In order to minimize the volumes of the spent decontaminating agents, which are to be regarded as liquid radioactive wastes, it can be advantageous subsequently to add to the decontamination solution, employed in the first treatment step, further substances which make the solution suitable for use in the second treatment step. Possible such further substances are reducing agents, such as oxalic acid, ascorbic acid, formic acid and the like. The reducing agents have the effect that the chromic acid as well as the permanganic acid and its decomposition products, i.e. also the brown oxide, are converted into soluble chromium(III) salts and manganese(II) salts. The success of the second treatment step can also be checked visually, since the brownish-red violet colored surface layers disappear from the decontaminated surfaces. The efficiency of the decontamination solution employed in the first treatment step can be considerably enhanced by circulation, stirring or application of ultrasonics. The chemical removal of the modified surface layers in the second treatment step can also be accelerated by the same measures. To enable the quantity of the particular solution required to be minimized, it is expedient to squirt or to spray it during the first treatment step and, if appropriate, also during the second treatment step onto the surface layers which are to be treated. It is also possible to apply the solution as a foam or thixotropic phase to the surfaces which are to be treated. Finally, a thickener can also be added to the solution which can then be applied as a coating directly to the surface layers which are to be treated. It is clear that the chemical solutions consumed in the first and, if appropriate, in the second treatment step contain radioactive constituents and therefore require safe disposal. Disposal of solutions which contain chromic acid and permanganic acid or the decomposition products thereof is possible in various ways, the choice of the best approach in a particular case depending, on the one hand, on the potential further treatments of the decontaminated components and, on the other hand, also on the equipment present in the nuclear power station for the treatment of radioactive wastes. If the decontamination solution containing chromic acid and permanganic acid was used only for the oxidative first treatment step, it is advantageous for disposal to reduce the higher oxidation stages of the chromium and manganese by the addition of oxalic acid to chromium(III) salts and manganese(II) salts respectively. If the solution used in the oxidative first treatment step is subsequently to be used also for the second treatment step, the oxalic acid is directly added to the treatment solution, whereupon further chemicals, for example organic acids, complexing agents, corrosion inhibitors and the like, are then added for concluding the decontamination treatment. The chromium(III) salts and manganese(II) salts can be separated from the solutions thus reduced by chemical precipitations or solidified by evaporation and subsequent cementing to give products suitable for ultimate waste disposal. The effectiveness of the process described, according to the invention, was tested on extensive sample material from the primary part of Swiss and foreign pressurized water reactors. Above all, radioactively contaminated samples consisting of the following materials were available: a) plates of ferritic chromium steel (material no. 1.4001 according to DIN) from the seal of the manhole cover of steam generators; b) plates and pipes of austenitic stainless steels; c) steam generator tubes of iron/nickel/chromium alloys of the trade name INCOLOY 800 and of nickel/chromium/ iron alloys of the trade name INCONEL 600. (INCOLOY and INCONEL are registered trademarks of International Nickel Company). These samples a), b) and c) were contaminated mainly by the cobalt isotope Co.sup.60. |
051981858 | summary | Discussion of Background In a nuclear reactor, coolant, usually water, is used to remove heat from the fissioning fuel. Depending upon the reactor design, water may also serve to increase the rate of fission by moderating the speed of neutrons so that they are more likely to cause fission in the nuclei of fuel material. In the event of an abnormal occurrence during reactor operations or a reactor accident, the control system of the reactor can be activated to shut down the fission process. Although the rate of fission can be reduced very quickly, the fuel continues to generate considerable heat as a result of the radioactive decay of the fission products that resulted from nuclear fission of fuel material prior to shutdown. A particularly severe type of accident is a loss-of-coolant accident, wherein the flow of coolant to the reactor core is abruptly reduced. Although the core is shut down by activating the control system, the decay heat can be sufficient to cause melting of the fuel material. Good reactor design anticipates this accident scenario and seeks to minimize the effects of decay heat following a LOCA. In normal power operation the distribution of heat produced by the reactor core, that is, the collection and arrangement of nuclear fuel elements, is not uniform. Fuel elements toward the center of the core tend to produce more power than those toward the periphery of the core. If the distribution of power varies too much, several reactor performance-related problems can occur. Therefore, in many reactors, design features are incorporated to reduce power variation across the core and, indeed, to "shape" the power distribution. To permit an increase in total reactor power, the coolant distribution should be shaped to correspond to the power distribution. In certain reactors, coolant flows into a plenum above the core and then down into the core through various orifices. Briefly, and referring to FIG. 1 which illustrates an example of this type of reactor, the coolant flows from the plenum through slots in a first sleeve surrounding each fuel element position, then through an array of holes in a universal sleeve housing into the region directly above the fuel element. An orifice plate is positioned in the sleeve housing, below the holes, to reduce the flow to the element. Each position in the core may have a different orifice plate. The different plates have different numbers and arrangements of holes so that the flow in each position may vary. Reducing the flow in the outer positions and increasing the flow to the more centrally-located elements improves flow distribution generally to the higher powered fuel elements. Unfortunately, this design, although working well during normal operation, does not provide optimum flow distribution during the very low flow conditions that occur in the event of a LOCA and result in an unnecessarily restrictive operating power limit. Various other designs exist to improve reactor flow. In U.S. Pat. No. 4,947,485, Oosterkamp discloses a design for better flow during "load follow" (the adjusting or reactor power level to accommodate changes in electrical demand during the day). His improved flow results from better mixing and by establishing flow between the downcomer region and the chimney. Veronesi provides holes of different sizes and patterns in an upper-core, plenum shroud, as described in U.S. Pat. No. 4,793,966. The use of vanes is described by Dotson, et al. in U.S. Pat. No. 3,623,948 to improve flow distribution at the entrance of the fuel region. Zmola, et al., use a variety of structural elements to force more flow to the hotter, higher power density regions of the core from the cooler, lower-power density regions, as described in U.S. Pat. No. 3,623,999. In particular, Zmola, et al. use entrance reduction elements and holes in the sides of tubular members to achieve the improved flow. There remains, however, a need for improved flow of coolant in reactors under both nominal and accident conditions. SUMMARY OF THE INVENTION According to its major aspects and broadly stated, the present invention is a coolant flow distribution that results in improved flow during accident conditions without degrading flow during nominal conditions. The modification comprises imposing a variation in the number and size of holes in the sleeve housings from one sleeve to another to increase amount of coolant flowing to the fuel in the center of the core and decrease, relatively, flow to the peripheral fuel. Preferably, the holes are arranged in rows and columns from the bottom of the upper portion of the sleeves to the top, where the plenum ends, with all holes having the same diameter and some sleeves having more rows than others to create the different flows. Those sleeves with the greatest number of rows are placed in the center of the core; those with the least are placed in the core periphery. An important feature of the present invention is the use of the variations in the number and possibly the size of holes in the sides of the sleeve to change the flow distribution in the core to a more favorable one. This feature eliminates the orifice plate and improves distribution of coolant flow during both accident and nominal conditions. Moreover, considerable flexibility is available to a designer in varying the number of holes and size of holes to meet a particular power shape across the core. Another feature of the present invention is the variation of the number of rows of holes by eliminating rows of holes from the top of the upper portion of the sleeve. Preferably the core is divided into zones that correspond roughly to rings. Beginning with the next-to-central ring, one row of holes is eliminated with each ring until the peripheral ring is reached. Eliminating a few rows of holes in the outer rings substantially increases flow during LOCA without impacting the flow during nominal conditions. Other features and advantages of the present invention will be apparent to those skilled in the art from a careful reading of the Detailed Description of a Preferred Embodiment presented below and accompanied by the drawings. |
044850689 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The handling and storage of irradiated assemblies removed from a fast neutron reactor involves certain precautions to prevent the rods containing the fuel from exceeding the maximum thermal conditions imposed and which are generally a few hundred .degree. C. on the sheath. Account must also be taken of the fact that the residual power of an assembly decreases exponentially in time after it has been removed from the reactor. As is diagrammatically shown in FIG. 1 and in accordance with a known process for the extraction of irradiated assemblies, initially said assemblies are extracted from the core of reactor 10 by means of a not shown raking means and they are then transported by means of a hod 14 into a cylinder 16 containing liquid sodium like the vessel of reactor 10. It is pointed out that sodium is an excellent heat transfer agent, whose low steam pressure and melting temperature make it possible to provide unpressurized reservoirs, which are still insulated from the atmosphere by inert covering gases 5. When the cylinder 16 is filled with irradiated assemblies, it must be emptied to enable the loading of the reactor with new assemblies and which are transferred into the same to replace the irradiated assemblies which have been removed. According to a preferred procedure shown in FIG. 1, the irradiated assemblies are removed by means of a handling shoot 17 to a conditioning room 18 in which they are placed in sheaths, said room being cooled by a nitrogen flow. A transfer shoot 20 is in part positioned below the conditioning room 18 and in part below the handling room 22. This transfer shoot 20 contains a transfer hod 24, which receives the sheets containing the fuel assemblies. This transfer shoot is coded by an air or nitrogen flow. The transfer hod 24 makes it possible to transport the irradiated assemblies in their sheaths to the handling room 22, which is also cooled by a nitrogen flow and in which the fuel assemblies are conditioned in caskets permitting the transfer thereof to the site of the reprocessing plant. The different elements of the installation described hereinbefore, as well as the operations which they perform are well known to those skilled in the art and will not be described in detail. According to the present invention, the handling room 22 is used only for transferring the irradiated assemblies in their sheaths from transfer shoot 20 to a storage installation 26 constructed according to the invention. Before describing the storage installation 26, it is pointed out that on the one hand this installation is not necessarily located on the site of the reactor as has been stated hereinbefore and on the other that the location of said storage installation on the site of the reactor could also take place in some other way, in particular by positioning the said installation directly below the conditioning room 18. Thus, transfer shoot 20 and handling room 22 are in principle intended for the conditioning of irradiated assemblies in caskets permitting their transportation to the site of the reprocessing plant. The arrangement of FIG. 1 is merely intended to permit the adaptation of the storage installation 26 to an existing irradiated fuel removal installation. As can be gathered more particularly from FIGS. 2 and 3, storage installation 26 comprises a concrete confinement enclosure 28 ensuring the biological protection of the environment. Confinement enclosure 28 is in the form of a rectangular parallelepiped defining in cross-sectional manner and in the way shown in FIG. 2 a certain number of stations P.sub.s and P.sub.c with a square cross-section. In a first direction, they are arranged in two rows 30a and 30b of four stations and in a second direction, which is perpendicular to the first, in four rows 32a, 32b, 32c and 32d of two stations. It is pointed out that the number of stations in the storage installation can differ from that shown in the drawings and in particular that the number of rows of type 30 and 32 can be the same (e.g. 4 or 5) or the number of rows of two stations of type 32 can be higher or lower than 4. In addition, the square cross-section of each of the stations is not limitative and can in particular be rectangular or in the shape of a lozenge or parallelogram, the cross-section of enclosure 28 also then being in the shape of a parallelogram. Station P.sub.c, defined at the intersection of rows 30a and 32d in the represented variant, is located below a trapdoor 25 formed in the ceiling or top of the enclosure and communicating with the handling room 22. Thus, station P.sub.c permits the loading and unloading of storage installation 26. According to a not shown constructional variant, the loading and unloading of the storage installation can take place with two different stations both located in the manner of station P.sub.c below a trapdoor formed in the top of enclosure 28 and communicating with an appropriate handling room like room 22. All the other stations defined within enclosure 28 constitutes storage stations P.sub.s. According to the invention, if the total number of stations P.sub.c and P.sub.s defined within enclosure 28 is n (8 in the represented embodiment) n-1 modules 34 are placed within confinement enclosure 28. The modules 34, which will be described in greater detail hereinafter, are all identical and each of them normally occupies one of the stations P.sub.s, station P.sub.c being left free for loading and unloading. Obviously, the number of modules 34 could be less than n-1 and then certain of the storage stations P.sub.s would be empty. However, it is pointed out that the capacity of storage installation 26 relative thereto would be reduced, which is obviously not desirable. As will be shown hereinafter, each of the modules 34 is able to receive a number of sheaths containing irradiated fuel assemblies. Each empty or full module 34 can also be removed from enclosure 28 by the trapdoor made in the top or ceiling above station P.sub.c. In order to permit the loading and unloading of the modules in sheaths, as well as the extraction and installation of the modules if this proves necessary, a per se known, not shown handling raking means is placed in handling room 22 above the trapdoor ceiling station P.sub.c. According to the invention and due to the fact that at least one of the stations defined within enclosure 28 is empty, it is possible to move modules 34 within the enclosure so as to bring them in turn level with the loading and unloading station P.sub.c, so that they can receive the sheets containing the irradiated assemblies or, conversely, to enable said assemblies to be removed to permit their conditioning in a per se known casket when their transportation to the reprocessing plant can be envisaged. This movement of modules 34 is made possible by the presence of lifting means diagrammatically indicated at 36 in FIG. 3 level with the base of enclosure 28 and by the presence of means for moving the modules between the different stations, such as jacks 38, able to move modules 34 when the latter are raised by light means 36. Obviously, the jacks 38 can be replaced by any equivalent means making it possible to move the modules between the different stations, although the use of jacks offers the advantage of enabling work to be carried out thereon from the outside. However, solutions based on a thrust chain or a drive by cables or chains and pins are also possible. The lifting means 36 comprise a not shown piping system, which can be embedded in the concrete constituting the floor or base of enclosure 28 or can be positioned on the latter when modules 34 do not rest directly thereon and instead rest on horizontal beams. This piping system is constituted by a plurality of assemblies or parallel pipes arranged on the one hand below each of the rows 30a and 30b and on the other below two rows 32a and 32d arranged on the periphery of enclosure 28. These pipes are supplied by a pressurized fluid issuing into the enclosure 28 by means of a large number of vertically axed lifting nozzles or jets 40 (FIG. 4). The nozzles 40 are positioned as close together as possible to permit a correct lift of modules 34. Thus, if they are cylindrical, hexagonal or triangular they are arranged with a triangular pitch, whereas if they are square, they are arranged with a square pitch. The arrangement of the nozzles 40 over part of the bearing surface of modules 34 which is as large as possible makes it possible to ensure a correct lifting thereof, no matter what their load. Preferably, when the fluid used is a gas, the nozzles or jets 40 are in the form of sonic necks. In per se known manner, the sonic necks have the essential feature of ensuring a constant gas flow when the upstream pressure is constant and independently of the downstream pressure. In the present case, it is obvious that this feature is particularly interesting because it makes it possible to ensure a correct lift of modules 34, in spite of the fact that certain of the nozzles 40 are not covered by any other module. Preferably, the groups of parallel pipes of the piping system 36 ensuring the lifting of the modules located in each of the rows 30a, 30b, 32a and 32d are supplied independently of one another. As shown in FIG. 3, this feature makes it possible to raise the module or modules 34 arranged in the corresponding row in order to permit the displacement thereof by means of the corresponding jack 38, whilst maintaining the other modules 34 in the stations P.sub.s or P.sub.c which they occupy, said other modules then resting by gravity on the floor of enclosure 28. Through the use of this gravity action, the reciprocal friction ensures a good lateral hold of the modules in the case of earthquakes. As can particularly be seen from FIG. 2, there are preferably four jacks or four groups of jacks 38-1, 38-2, 38-3 and 38-4 positioned externally of the confinement enclosure 28 so as to act across said enclosure by their push rods 38a on the module or modules 34 located in each of the peripheral rows 30a, 30b, 32a and 32d. More specifically, one jack or groups of jacks 38 is located at one of the ends of each of these peripheral rows, said end being selected in such a way that the consecutive putting into operation of jacks of adjacent peripheral rows makes it possible to move the group of modules in a predetermined rotation direction within the peripheral rows. In addition, the push rods 38a of each of the jacks exert a pressure action on the closest module 34 of the corresponding row, the movement of said module being imparted to the other modules of the row, if other modules are provided. In the variant shown in FIG. 2, the successive operation of jacks 38-1 to 38-4 makes it possible to move all modules 34 in a counterclockwise direction within enclosure 28. Thus, the operation of jack 38-1 makes it possible to move module 34 arranged in row 32d in the direction of the arrow up to the loading and unloading stage P.sub.c. This movement obviously takes place following the operation of that part of the pressurized fluid circuit 36 corresponding to row 32d, which is then depressurized and the rotation of modules 34 between the different stations defined within enclosure 28 continues by means of jack 38-4. The operation of this jack is accompanied by a pressurization of that part of the circuit 36 corresponding to row 30b. It is then jack 38-3 which is operated, following the pressurization of that part of the lifting circuit 36 corresponding to row 32a. Finally, the rotation of modules 34 is completed by the operation of jack 38-2 accompanied by a pressurization of that part of lifting circuit 36 corresponding to row 30a. The complete cycle described hereinbefore corresponds to the movement of each of the modules 34 contained in enclosure 28 between two adjacent stations in a counterclockwise direction. The repetition of this cycle makes it possible to successively move all the modules 34 into station P.sub.c, where they can be loaded and unloaded at random. Thus, it is possible by displacing the modules, to check by any known means (visual, eddy currents, etc.) the state of the modules stored in the single fixed station constituted by station P.sub.c. Obviously, the arrangement of jacks 38 could be reversed, whereby each of the jacks would then be positioned at the opposite end of the corresponding row in such a way that the rotation of the modules 34 within enclosure 28 would take place in a clockwise direction. Moreover, the course of the modules is not limited to that described, although it gives the best filling coefficient, Thus, it may also vary with the configuration of enclosure 28 and the internal partition thereof. As all the modules 34 are identical, one of them will be described with reference to FIGS. 4 and 5. Each module 34 essentially comprises three superimposed parts enabling them to vertically support a certain number of sheaths 41 containing the irradiated fuel assemblies. Thus, each storage module 34 comprises, when starting from the top, a ribbed horizontal supporting plate 42 supporting sheaths 41, an intermediate member 44 making it possible to channel the flow of a cooling gas such as nitrogen, in the manner to be described hereinafter and prevent rocking or swinging of sheaths particularly in the case of earthquakes, and a horizontal lower plate 46 having a level lower face 48 enabling the lifting of module 34 by means of nozzles 40. The three parts 42, 44 and 46 are spaced from one another and rendered integral by means of six feet 50 fixed e.g. by welding to the centre of each of the faces of the intermediate member 44. The latter defines a ferrule or funnel having a hexagonal shape as shown in FIG. 5. The opposite ends of feet 50 are fixed respectively to plate 42 and plate 46, e.g. by welding. In plan view, supporting plate 42 also has a hexagonal shape and its sides are located in the extension of the corresponding faces of intermediate member 44. Plate 42 has holes 52 regularly distributed in directions parallel to each of the sides of the hexagon and permitting the passage of sheets 41. Only the centre of plate 42 is not perforated, because it has a recess 54 able to receive an appropriate gripping system manipulated by a raking means, which enables the modules to be introduced into enclosure 28 by the trapdoor made in the top thereof or to remove them therefrom in the manner indicated hereinbefore. For information, in the embodiment shown in FIG. 5, the supporting plate 42 has 18 holes 52 which make it possible to receive 18 sheaths 41. Moreover, the supporting plate 42 is provided above each of the holes 52 with a drop or fall absorber 56 having on its upper end a support 58 on which is suspended the corresponding sheath 41. The absorber 56, constituted e.g. by a perforated tube, makes it possible to limit the slowing down force of sheath 41 by limiting the deceleration to 10 g in the case of an accidental jettisoning of a loaded sheath. The funnel or ferrule-shaped intermediate member 44 is surrounded in its upper part by a square frame 60, whose sides substantially correspond to the maximum overall dimension of the module, i.e. to the dimensions of stations P.sub.s and P.sub.c defined within enclosure 28. Frame 60 is fixed by welding to two feet 50 and to two opposite apices of the hexagon formed by ferrule 44. At two different levels, ferrule 44 also supports intersecting bars 62 arranged parallel to certain of the faces of the ferrules. The function of the bars 62 is to prevent rocking or swinging of sheaths 41 in the case of an earthquake. Lower plate 46 has peripheral edges 64 which, in plan view, define a square, whose sides are aligned with those of frame 60. Thus, lower plate 46 defines a tightly sealed reservoir able to receive sodium which may have escaped from one or more sheaths 41. As shown in FIGS. 3 and 4, in the embodiment described plate 46 is provided with four rollers 66 at each of its angles. More specifically, rollers 66 located at the ends of two opposite sides of the square defined by plate 46 are positioned at two different levels in such a way that hereinafter they will be called lower rollers 66a and upper rollers 66b. The modules 34 are placed within enclosure 28 in such a way that the sides of the modules carrying the rollers of the same level are parallel to the small sides of the rectangle defined by the enclosure and that the facing rollers of two adjacent modules of each of the rows 30 are at two different levels. As a result of this arrangement and as illustrated more particularly in FIG. 3 in which the scale has been deliberately increased in the heightwise direction in order to facilitate understanding, the modules 34 of the same row are in contact with one another by means of lower rollers 66a, which bear against the edges 64 of the lower plate 46 of the adjacent module. This structure enables the lower rollers 66a of module 34 displaced by jack 38-1 to roll on edges 64 of the modules arranged in row 32c and for edge 64 of module 34 displaced by jack 38-3 to roll on the lower rollers 66a of modules 34 arranged in row 32b without the upper rollers 66b impairing this movement, even when modules 34 are raised by the pressurization of the corresponding part of lifting circuit 36. Running rails 68 are also provided within enclosure 28 to cooperate with rollers 66 in order to guide modules 34 in their displacement. These rails 68 are arranged on the one hand along the vertical walls of enclosure 28 level with rollers 66 and on the other hand in the centre of enclosure 28 between rows 30, except at the level of the two end rows 32a, 32d in order to permit the displacement of modules 34 in these two rows. It is clear that these rails 68 on which roll rollers 66 make it possible to guide modules 34 when they are moved between two stations P.sub.s and P.sub.c under the action of jacks 38. Obviously, the lateral guidance of the modules can be obtained by any other means. Thus, it is possible to use guide blocks in place of rollers 66 or to create a fluid cushion comparable to that ensuring the lift of the modules. As has been stated, the fuel assemblies to be stored reach the storage installation 26 in a relatively short time when the latter is directly installed on the site of the reactor. It is appropriate in this case to provide a cooling circuit making it possible to remove the calories which continue to be dissipated by the irradiated assemblies. According to another feature of the invention, this cooling circuit is a cooled gas and preferably nitrogen circuit. For the installation of this cooling circuit, the storage installation room preferably occupies a central position between two gallery bays separated from the storage room by concrete walls, whose thickness ensures the biological protection. These gallery bays make it possible on the one hand for personnel to move about and on the other the installation of the cooling gas circulation sheaths. This not shown nitrogen circuit operates in two closed loops. The first of these loops is defined between the actual storage installation and a group of exchangers of a freon refrigerating unit. This refrigerating unit is itself enclosed in a circuit with its condenser and thus defines the second loop. The condenser exchanges its calories with the atmospheric air or with a heat recovery device. Preferably, the cold nitrogen enters from the bottom of the room and particularly by means of openings made in the vertical walls of enclosure 28 level with spaces defined between the lower plates 46 and the ferrules 44 of modules 34. The cold nitrogen rises within the funnels or ferrules 44 in order to cool the fuel assemblies contained in sheaths 41 and leaves by spaces defined between ferrules 44 and the support plates 42 of the modules. The hot nitrogen escapes by other openings made, for example, in the top or ceiling of the enclosure in order to reach the exchangers of the refrigerating unit. Preferably, extra cooling circuit machines are provided, so that in the case of a mechanical or electrical fault, compensation thereof is brought about by putting into operation standby machines or by starting up electricity generating machines. The valves then assure the connection of the storage installation to the operating machines and isolate effective machines. By means of the storage installation 26, whereof an embodiment has been described with reference to the drawings, it is possible to store on the actual reactor site the irradiated assemblies extracted from the reactor core by successively passing an adequate number of empty modules 34 level with the loading station P.sub.c. The modules are displaced by means of jacks 38 after raising the modules 34 to be moved by pressurizing the corresponding part of the lifting means 36. Each of the modules 34 arriving at the loading station P.sub.c in the represented embodiment receives 18 sheaths 41 before being replaced by a new empty module. When the fuel assemblies in their sheaths have to be removed to the reprocessing plant, the loaded modules 34 are brought to the unloading station P.sub.c in order to remove the sheaths containing the assemblies, e.g. by means of a racking means equipped with a drag hook. Obviously, the number of modules 34 and storage stations P.sub.s can differ significantly from the example shown in FIG. 2. The numbers will mainly be chosen as a function of needs, i.e. taking account both of the storage duration prior to transferring the assemblies to the reprocessing plant, the gap between two reactor loading operations, the number of assemblies extracted from the reactor core during each of these operations and the number of assemblies received in each of the modules. The dimensions of the storage installation 26 still remain limited as a function of the maximum thrust which can be exerted by the jacks or groups of jacks 38. If the storage capacity of enclosure 28 is inadequate to meet these requirements, it is possible to juxtapose a plurality of such enclosures having a common wall and optionally a single loading station. According to the second embodiment of the invention (not shown), the installation ensuring the storage and/or transfer of the irradiated fuel assemblies can be constituted by a pool filled with a liquid such as water or sodium. The installation is then very similar to that described hereinbefore with reference to the attached drawings, as will be apparent from the following brief description. As in the previous embodiment the assemblies extracted from the reactor core are transferred into a cylinder under sodium. Following a partial decrease in their residual power, the assemblies are taken up again in the cylinder by handling means placed in a handling chute like chute 17 in FIG. 1. They are then fed into a washing station where traces of sodium deposited on their structure are removed, this being followed by a rinsing process. An advantageous solution consists of using the washing installation as a "sieve" between the sodium-polluted handling chute and the part of the installation which is under water. The assemblies are removed from the washing installation by the lower end thereof. They are then either placed in a machine which transfers them to the pool or are placed directly in the latter if it can be located at this point. Contrary to the first embodiment, the assemblies are then introduced into modules without sheaths. This leads to a slight modification to the modules permitting them to support the assemblies, no longer by the top, but instead by the lower shoulder constituting the base on a support grid with the interpositioning of a drop absorber. Earthquake-resisting gratings are then positioned towards the top of the modules in order to guide the assemblies during their removal. Otherwise, the operation of the modules and their arrangement within the storage installation are identical to the aforementioned function and arrangement of the storage modules in the gaseous medium. Obviously, the arrangement of the modules in a liquid such as water or liquid sodium does not permit the use of lifting means creating a gas cushion below the modules. This gas cushion is replaced by a liquid cushion created by means of injectors (e.g. using water) placed on the bottom of the pool and connected to a supply pipe, which can particularly take up water from the upper part of the pool. Pressurization is brought about by a pump located outside the pool or embedded. As in the first embodiment, the handling means can be constituted by jacks arranged so that they can be repaired or replaced outside the pool. In order to bring about uniformity, these jacks are preferably water-controlled. The removal of the heat given off by the assemblies in the water of the pool takes place in conventional manner to a secondary circuit via a water - water exchanger. This heat can be discharged into the atmosphere by an atmospheric coolant or can be recovered for heating an external installation, e.g. a greenhouse or the like. Although the two embodiments described hereinbefore relate to an irradiated fuel element storage installation, it is clear that the invention is not limited thereto. Thus, the invention can also be applied to a transfer installation. In the same way, the invention can also be applied to products other than irradiated fuel assemblies, such as products constituting an irradiation hazard (radioactive waste, feed materials, sources), chemical contamination products (plutonium, liquid effluents), explosive products, etc. |
060375973 | abstract | Described are preferred devices and systems useful in the non-destructive detection of predetermined substances, such as plastique explosives, in objects under interrogation. The devices and systems are readily constructed and can be manufactured as self-contained, portable detection devices. |
049888838 | claims | 1. A fingernail light system for curing photo-polymerizable plastics on fingernails, having a housing (1) with a bottom plate (7) in which housing there is provided a support body (4), having indentations (18) on its outer contour, for positioning fingers (20-24) of a hand to be irradiated, and having at least one irradiation lamp (14), which at least partially surrounds the support body in a spaced-apart manner in an irradiation position, the support body being accessible in the irradiation position via an opening (10) formed in the housing (1), and wherein, the support body (4) has a generally convex outer contour, defining a central palm-support surface with said indentations radiating therefrom, said indentations defining channels (18) that extend substantially in the direction of a longitudinal axis (3) of the support body (4), and positively position fingers placed therein, and the axis (3) of the support body (4) forms an angle (30) in the range from 0.degree. to 90.degree. with the direction (31) orthogonal to the bottom plate (7). wherein the channels (18) of the support body (4) are located symmetrically with respect to a first plane (19) extending through the axis (3) of the support body (4) and in the direction of the arm (16) of a hand (5) to be placed on the support body (4). wherein the channel (18) associated with the middle finger (20) extends in the vicinity of the first plane (19). wherein the support body (4) has one channel (18) each for the little finger (23) of the left and right hand, which channels extends approximately along a second plane extending through the axis (3) of the support body (4) and vertically to the first plane (19). wherein the channels (18) for the little fingers (23) are on a raised portion of the support body, in such a way that the finger nails (15) of the little fingers (23) are positioned outside the shadow of the ring finger. wherein that two channels (18) are provided for the thumbs (24), two channels (18) are provided for the ring fingers (21) and two channels (18) are provided for the index fingers (22). wherein the channels (18) are distributed about the circumference of the support body (4) over an angular range extending approximately 300.degree. to 320.degree. about said circumference. wherein the support body (4) is located movable in the direction of its axis (3) into and out of the housing (1). wherein the support body (4) is located such that it is displaceable counter to the force of at least one spring (8). wherein the rim of the housing opening (10) merges with a support (17), which is located on the housing (1) opposite the channel (18) for the index finger (22) of the support body (4). wherein the housing opening (10) is at least partly closeable by means of a hinged glare protection hood (33). wherein the support body (4), at least in the region of the channels (18), has positioning means in the form of stops (34) against which the fingertips of the hand (5) to be irradiated rest. wherein the stops (34) are located at the lower rim, oriented toward the bottom plate (7), of the support body (4). wherein an end switch (26) is provided, which is actuated for operation of the system upon introduction of the support body (4) into the housing (1). wherein the at least one irradiation lamp (12) approximately describes a circle or a circular segment. wherein the circle or the circular segment is approximated by means of a plurality of elongated irradiation lamps (12) having a straight lamp axis (14). 2. A fingernail light system according to claim 1, wherein the axis (3) of the support body (4) forms an angle (30) in the range from 0.degree. to 60.degree. with the direction (31) orthogonal to the bottom plate (7). 3. A fingernail light system according to claim 1, 4. A fingernail light system according to claim 3, 5. A fingernail light system according to claim 3, 6. A fingernail light system according to claim 1, 7. A fingernail light system according to claim 1, 8. A fingernail light system according to claim 7, 9. A fingernail light system according to claim 1, 10. A fingernail light system according to claim 9, 11. A fingernail light system according to claim 9, 12. A fingernail light system according to claim 1, 13. A fingernail light system according to claim 1, 14. A fingernail light system according to claim 13, 15. A fingernail light system according to claim 9, 16. A fingernail light system according to claim 1, 17. A fingernail light system according to claim 16, |
043671845 | abstract | Nuclear fuel microspheres are made by sintering microspheres containing uranium dioxide and uncombined carbon in a 1 mole percent carbon monoxide/99 mole percent argon atmosphere at 1550.degree. C. and then sintering the microspheres in a 3 mole percent carbon monoxide/97 mole percent argon atmosphere at the same temperature. |
description | This application claims the benefit of Korean Patent Application No. 10-2019-0121738, filed on Oct. 1, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. The present disclosure relates to a sliding type transfer cask for spent nuclear fuel which is easy to install and move, and particularly, to a sliding type transfer cask for spent nuclear fuel, the sliding type transfer cask having reduced weight and volume, being easy to install and move by coupling an opening/closing portion to a lower portion of a transfer container, and simplifying a transfer procedure of spent nuclear fuel. FIG. 1 schematically illustrates a work procedure for moving spent nuclear fuel by using a transfer cask. FIG. 1A illustrates an initial situation before the spent nuclear fuel is transferred. A canister 2 in which the spent nuclear fuel is stored is located with an upper lid opened at a lower portion of a work table 1. The spent nuclear fuel remains sealed in the canister 2. Subsequently, a temporary shielding body 3, a transfer collar 4, a lid opening/closing apparatus 5, and a lower lid assembly 6 are installed as illustrated in FIGS. 1B to 1E. An actuator 7 opens lower lids 9 of the lower lid assembly 6, which are formed of two square plates, by moving the lower lids 9 in opposite directions to each other. Subsequently, a lifting apparatus connected to a crane is connected to a lifting adapter 2a installed on an upper portion of the canister 2 to take out the canister 2 into the transfer cask 8, and then, the actuator 7 operates to close the lower lids 9. Through a series of the processes, moving the canister 2 into the transfer cask 8 is completed. Subsequently, a process of moving the transfer cask 8 to a position of a storage cask used only for storing spent nuclear fuel is performed. However, in the process of transferring the canister 2 as described above, the transfer collar 4, the lid opening/closing apparatus 5, the lower lids 9, and so on have to be designed and installed separately, and thus, the work requires too much time and a procedure becomes complicated. In addition, if much work time is spent because of a complicated procedure, a possibility that a worker is exposed to radiation increases. The present disclosure provides a sliding type transfer cask for spent nuclear fuel, the sliding type transfer cask having reduced weight and volume, being easy to install and move by coupling an opening/closing portion to a lower portion of a transfer container, and simplifying a transfer procedure of spent nuclear fuel. Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. According to an embodiment of the present disclosure, a sliding type transfer cask for spent nuclear fuel that transfers a canister for storing the spent nuclear fuel, includes a transfer container having a space for accommodating the canister; a neutron shielding body disposed around an outer circumference of the transfer container to shield neutrons; and an opening/closing portion coupled to a lower portion of the transfer container to open and close the lower portion of the transfer container, wherein the opening/closing portion includes a support portion that has a first through-hole communicating with the transfer container and supports the transfer container, wherein a lower portion of the transfer container is placed on the support portion; a base plate that is arranged below the support portion at a certain interval and has a second through-hole through which the canister to be taken out passes; and a lid assembly that includes a first lid portion sliding between the support portion and the base plate to open and close part of the first through-hole, and a second lid portion sliding between the support portion and the base plate to open and close a remaining portion of the first through-hole, and wherein the first lid portion includes a first lid and a first motor for sliding the first lid, and the second lid portion includes a second lid and a second motor for sliding the second lid. In addition, it is preferable that the transfer cask includes a first support frame coupled to the outside of the first lid and a second support frame coupled to the outside of the second lid. In addition, it is preferable that the first and second motors are coupled to the support portion, and a first motor shaft of the first motor and a second motor shaft of the second motor protrude downward through the support portion, and the outside of the first support frame is engaged with the first motor shaft, and the outside of the second support frame is engaged with the second motor shaft, and when the first and second motors rotate, the first and second support frames slide to open and close the first through-hole. In addition, it is preferable that a protrusion portion is formed at an end of the first lid, a placement portion on which the protrusion portion is placed is formed in the second lid, and the protrusion portion is placed on the placement portion of a step shape to close the first through-hole. In addition, it is preferable that a guide rail for guiding the first and second support frames when the first and second support frames are slid is coupled to the base plate. In addition, it is preferable that the first and second lids are formed in a semicircular shape, respectively, and the first support frame includes a pair of first side frames arranged to face each other in a sliding direction of the first lid and a first connection frame connecting the pair of first side frames to each other, and when the pair of first side frames and the first connection frame are arranged outside the first lid, an arc portion of the first lid, the pair of first side frames, and the first connection frame are spaced apart from each other to form an empty space, and the second support frame includes a pair of second side frames arranged to face each other in a sliding direction of the second lid and a second connection frame connecting the pair of second side frames to each other, and when the second side frame and the second connection frame are arranged outside the second lid, an arc portion of the second lid, the pair of second side frames, and the second connection frame are spaced apart from each other to form an empty space. In addition, it is preferable that a lower side of the base plate is coupled to a fitting plate that includes an insertion portion protruding downward and is fitted to an upper side of the canister. In addition, it is preferable that a first guide groove extending in one direction is formed in a lower surface of the first lid, a second guide groove extending in one direction is formed in a lower surface of the second lid, and the base plate includes a first stopper that is inserted into the first guide groove and caught on an end of the first guide groove when the first lid is opened, and a second stopper that is inserted into the second guide groove and is caught on an end of the second guide groove when the second lid is opened. Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Hereinafter, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. FIG. 2 is a perspective view of a transfer cask for spent nuclear fuel according to an embodiment of the present disclosure, and FIG. 3 is a perspective view of a main portion of FIG. 2; FIG. 4 is a cross-sectional view of first and second lids in a closed state, and FIG. 5 is a bottom perspective view of FIG. 2. FIG. 6 is an enlarged view of a main portion of FIG. 3, and FIG. 7 is a view illustrating first and second stoppers and first and second guide grooves. The present disclosure relates to a transfer cask used for transferring a canister for storing spent nuclear fuel. A sliding type transfer cask for spent nuclear fuel that is easy to install and move according to an embodiment of the present disclosure includes a transfer container 10, a neutron shielding body 20, and an opening/closing portion 30. As illustrated in FIG. 2, the transfer container 10 has a space for accommodating the canister. According to the present embodiment, the transfer container 10 are formed in a shape of a cylinder and upper and lower portions of the transfer container 10 are in an open state. According to the present embodiment, the transfer container 10 is made of a steel material. The opening/closing portion 30 to be described below may be coupled to the lower portion of the transfer container 10, and an upper lid (not illustrated) may be coupled to the upper portion of the transfer container 10. Two trunnions 60 are coupled to each of upper and lower sides of the transfer container 10. The trunnions 60 are provided to be coupled to a lifting apparatus. The lower trunnion 60 is required for horizontal lifting and may be omitted when the horizontal lifting is not required in a work process. The neutron shielding body 20 is provided to prevent neutrons emitted from spent nuclear fuel stored in the canister from being emitted to the outside. According to the present embodiment, the neutron shielding body 20 is arranged around an outer periphery of the transfer container 10 to shield neutrons. The neutron shielding body 20 may be configured such that a water jacket containing water wraps the transfer container 10 or may be implemented in a form in which a separate outer wall is prepared to be spaced apart from an outer peripheral surface of the transfer container 10 at a certain interval to form an inner space therebetween and an epoxy resin (NS-4-FR) is included in the inner space. Of course, the neutron shielding body 20 is not limited to the shape described above. The opening/closing portion 30 is coupled to the lower portion of the transfer container 10 and opens and closes the lower portion of the transfer container 10. According to the present embodiment, the opening/closing portion 30 includes a support portion 31, a base plate 32, and a lid assembly 33. The support portion 31 supports the transfer container 10. The lower portion of the transfer container 10 is placed on the support portion 31, and a first through-hole 311 communicating with the transfer container 10 is formed in the support portion 31. According to the present embodiment, the support portion 31 is coupled to the transfer container 10 by using a method such as bolting or welding. The support portion 31 may be moved to an installation space together with the transfer container 10. The base plate 32 is arranged below the support portion 31 to be spaced apart from the support portion 31 at a certain interval. A second through-hole 321 through which the canister to be taken out passes is formed in the base plate 32. A size of the second through-hole 321 is substantially the same as a size of the first through-hole 311. The base plate 32 is formed to have a size corresponding to the support portion 31. According to the present embodiment, the support portion 31 is formed in a square shape, and the base plate 32 is also formed in a square shape. Of course, the shapes of the support portion 31 and the base plate 32 are not limited thereto. An interval formed between the base plate 32 and the support portion 31 is provided as a space in which the lid assembly 33, which will be described below, may be moved. Referring to FIG. 3, the lid assembly 33 is provided to open and close the lower portion of the transfer container 10 and includes a first lid portion 331 and a second lid portion 332. The first lid portion 331 opens and closes part of the first through-hole 311. According to the present embodiment, the first lid portion 331 is provided to be slidable between the support portion 31 and the base plate 32. According to the present embodiment, the first lid portion 331 includes a first lid 41 and first motors 42. The first lid 41 has a semicircular shape. The first lid 41 approaches the center of the first through-hole 311 or slides while moving back from the center of the first through-hole 311 in a radial direction. A protrusion portion 411 is formed to protrude from an end of the first lid 41. When the first lid 41 is completely slid toward the center of the first through-hole 311, the protrusion portion 411 is located outside a diameter of the first through-hole 311. The first motors 42 are provided to slide the first lid 41. According to the present embodiment, the first motors 42 are coupled to the support portion 31. Specifically, bodies of the first motors 42 are coupled to an upper surface of the support portion 31, and first motor shafts 421 of the first motors 42 pass through the support portion 31 to protrude downward. As illustrated in FIG. 3, according to the present embodiment, the first motors 42 are respectively installed at both corners of one side of the support portion 31. According to the present embodiment, the second lid portion 332 includes a second lid 43 and second motors 44. The second lid 43 is formed in a semicircular shape and forms a circular plate together with the first lid 41. The second lid 43 approaches the center of the first through-hole 311 or slides while moving back from the center of the first through-hole 311 in a radial direction, like the first lid 41. The second lid 43 and the first lid 41 slide in a direction close to or spaced apart from each other. A placement portion 431 on which the protrusion portion 411 is placed is formed on the second lid 43. The placement portion 431 is formed to face the protrusion portion 411. As illustrated in FIG. 4, when the first and second lids 41 and 43 slide in a direction close to each other to cover the first through-hole 311, the protrusion portion 411 is placed on the placement portion 431 having a step shape to close the first through-hole 311. The second motors 44 are provided to slide the second lid 43. According to the present embodiment, the second motors 44 are coupled to the support portion 31. Specifically, bodies of the second motors 44 are coupled to the upper surface of the support portion 31, and second motor shafts 441 of the second motors 44 pass through the support portion 31 to protrude downward. As illustrated in FIG. 3, according to the present embodiment, the second motors 44 are respectively installed at both corners of another side facing the one side of the support portion 31 on which the first motors 42 are installed. An embodiment of the present disclosure includes a first support frame 34 and a second support frame 35. The first support frame 34 is coupled to the outside of the first lid 41 and stably slide the first lid 41 while supporting the first lid 41. The first support frame 34 includes first side frames 341 and a first connection frame 342. The first side frames 341 are arranged to face each other in a direction in which the first lid 41 slides. A pair of the first side frames 341 face each other in contact with the first lid 41. The first connection frame 342 connects the pair of first side frames 341 to each other. Accordingly, the pair of first side frames 341 and the first connection frame 342 are coupled in a “⊏” shape, and the first lid 41 is coupled thereto in an inner space thereof. According to the present embodiment, when the pair of first side frames 341 and the first connection frame 342 are arranged outside the first lid 41, an arc portion of the first lid 41, the pair of first side frames 341, and the first connection frame 342 are spaced apart from each other to form an empty space. A weight is reduced due to the empty space, and thus, the pair of first side frames 341 and the first connection frame 342 may slide smoothly together with the first lid 41. As illustrated in FIG. 3, the outside of the first support frames 34 is engaged with the first motor shafts 421. Specifically, racks are formed on outer surfaces of the first side frames 341 of the first support frame 34, the first motor shafts 421 are coupled to the racks in a serrated manner, and when the first motors 42 rotate, the first support frame 34 slides to open and close the first through-hole 311. The second support frame 35 is coupled to the outside of the second lid 43 and stably slides the second lid 43 while supporting the second lid 43. The second support frame 35 includes second side frames 351 and a second connection frame 352. The second side frames 351 are arranged to face each other in a direction in which the second lid 43 slides. A pair of the second side frames 351 face each other in contact with the second lid 43. The second connection frame 352 connects the pair of second side frames 351 to each other. A structure in which the second lid 43 is coupled to the pair of second side frames 351 and the second connection frame 352 is the same as a structure in which the first lid 41 is coupled to the pair of first side frames 341 and the first connection frame 342, that is, the pair of second side frames 351 and the second connection frame 352 are coupled to each other in a “⊏” shape and the second lid 43 is coupled thereto in an inner space thereof. According to the present embodiment, when the pair of second side frames 351 and the second connection frame 352 are arranged outside the second lid 43, an arc portion of the second lid 43, the pair of second side frames 351, and the second connection frame 352 are spaced apart from each other to form an empty space. A weight is reduced due to the empty space, and thus, the pair of second side frames 351 and the second connection frame 352 may slide smoothly together with the second lid 43. As illustrated in FIG. 3, the outside of the second support frame 35 is engaged with the second motor shafts 441. Specifically, racks are formed on outer surfaces of the second side frames 351 of the second support frame 35, the second motor shafts 441 are coupled to the racks in a serrated manner, and when the second motors 44 rotate, the second support frame 35 slides to open and close the first through-hole 311. An embodiment of the present disclosure may further include a guide rail 40 and a fitting plate 50. The guide rail 40 is provided on the base plate 32 to guide the first and second support frames 34 and 35 when the first and second support frames 34 and 35 slide. As illustrated in FIG. 6, according to the present embodiment, the guide rail 40 is provided under the pair of first and second side frames 341 and 351 and protrudes from the base plate 32 to the outside, and thus, when the first and second support frames 34 and 35 move back to open the first through-hole 311, the first and second support frames 34 and 35 may be prevented from falling down due to gravity. As illustrated in FIG. 5, the fitting plate 50 is provided under the base plate 32, and the fitting plate 50 has an insertion portion 51 that protrudes downward to be fitted to an upper side of the canister. An inclined surface 511 is provided on an outer surface of the insertion portion 51. When the transfer cask according to the present disclosure is installed in a transport cask in which the canister is temporarily accommodated, the insertion portion 51 may be easily inserted into an upper side of the transport cask due to the inclined surface 511, and the insertion portion 51 is formed to have a certain height, and thus, the insertion portion 51 serves as a transfer collar required when a transfer cask of the related art is installed. An embodiment of the present disclosure may further include first and second stoppers 322 and 323 and first and second guide grooves 412 and 432. The first stopper 322 is formed to protrude upward from one side of the base plate 32. The second stopper 323 is formed to protrude upward from the other side of the base plate 32. The first guide groove 412 is formed so that the first stopper 322 may be inserted thereinto. According to an embodiment of the present disclosure, the first guide groove 412 is formed to extend in one direction on a lower surface of the first lid 41. When the first lid 41 is opened and closed, the first stopper 322 is moved in a state inserted into the first guide groove 412, and when the first lid 41 is completely opened, the first stopper 322 is caught on an end of the first guide groove 412 to regulate movement of the first lid 41. The second guide groove 432 is provided so that the second stopper 323 may be inserted thereinto. According to an embodiment of the present disclosure, the second guide groove 432 is formed to extend in one direction on a lower surface of the second lid 43. When the second lid 43 is opened and closed, the second stopper 323 is moved in a state inserted into the second guide groove 432, and when the second lid 43 is completely opened, the second stopper 323 is caught on an end of the second guide groove 432 to regulate movement of the second lid 43. Of course, according to an embodiment of the present disclosure, the first and second stoppers 322 and 323 are formed on the base plate 32, and the first and second guide grooves 412 and 432 are respectively formed in the first and second lids 41 and 43, and the stoppers and the guide grooves may change in position. For example, the first and second stoppers 322 and 323 may be respectively formed in the first and second support frames 34 and 35, and the first and second guide grooves 412 and 432 may be formed in the guide rail 40. Hereinafter, an operation and an effect of a sliding type transfer cask for spent nuclear fuel which is easy to install and move according to the above-described configuration will be described in detail. According to an embodiment of the present disclosure, a transfer collar, a lid opening/closing apparatus, and a lower lid of the related art (see FIG. 1) are integrated with the above-described opening/closing portion 30 and coupled to the lower portion of the transfer container 10. The transfer cask according to the present disclosure is moved to an upper side of the canister by using a lifting apparatus, and the opening/closing portion 30 is inserted into the transport cask. In this case, the insertion portion 51 of the fitting plate 50 coupled to a lower side of the base plate 32 is inserted into an upper portion of the transport cask. Subsequently, when the first and second motors 42 and 44 operate, the first and second support frames 34 and 35, which are gear-coupled with the first and second motor shafts 421 and 441, move back and the first and second lids 41 and 43 open. The canister is pulled up into the transfer container 10 by connecting the lifting apparatus to a lifting adapter 2a provided in the canister. When the canister is accommodated inside the transfer container 10, the first and second motors 42 and 44 are reversely rotated again to slide the first and second support frames 34 and 35 toward the center of the first through-hole 311 and close the first and second lids 51 and 53. After an upper lid (not illustrated) of the transfer container 10 is covered to close an upper portion, the transfer cask is moved to a desirable storage place. As such, the sliding type of transfer cask for spent nuclear fuel, which is easy to install and move according to the present disclosure, may transfer the transfer container 10 in a state in which the opening/closing portion 30 is coupled to a lower portion of the transfer container 10, and thus, there is an effect of simplifying transfer of the canister. In addition, when a cylinder is used to open and close a lid of the related art, a length of a body and a rod of the cylinder have to be considered, and thus, there is a problem that a size of an installation plate on which the cylinder is installed is increased to cause a significant increase in weight and volume, and according to an embodiment of the present disclosure, the first and second motors 42 and 44 for sliding the first and second lids 41 and 43 are installed on the support portion 41, and thus, there is no need to add a separate installation plate to install the first and second motors 42 and 44, and when the first and second lids 41 and 43 move back, the first and second support frames 34 and 35 slide along the guide rail 40, and thus, the weight and volume are significantly reduced to provide an effect in which transfer is convenient. In addition, by reducing weight and volume of a transfer cask, the transfer container 10 coupled to the opening/closing portion 30 may be moved to a lifting apparatus at one time, thus, there is an effect that a work time is reduced when moving a canister and the amount of radiation exposure of an operator is reduced. A sliding type transfer cask for spent nuclear fuel which is easy to install and move, according to an embodiment of the present disclosure, provides an effect of simplifying installation and movement by reducing weight and volume and of simplifying a transfer procedure for spent nuclear fuel. In addition, an opening/closing portion that opens and closes a lower portion of a transfer container is integrally manufactured with the transfer container to simplify a work procedure at the time of moving a canister, and thus, it is possible to obtain an effect of reducing an operation time and reducing the amount of exposure of an operator. It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the following claims. |
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