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description | The invention relates to a method for the production of spherical fuel or breeder material particles from an oxide of the group of the heavy metals uranium, thorium, plutonium or mixtures thereof comprising the process steps of producing a starting solution of the nitrates of at least one of the heavy metals, adding a first reagent from the group of urea and/or ammonium carbonate and/or ammonium hydrogen carbonate and/or ammonium cyanate and/or biuret, adding at least one second reagent in the form of PVA and/or THFA in order to adjust the viscosity of the solution, transforming the solution into droplets to form microspheres, solidifying the microspheres, at least in the surface region, in an atmosphere containing ammonia, collecting the microspheres in a solution containing ammonia and subsequent rinsing, drying and thermal treatment. In high temperature reactors which are increasingly becoming of interest again because of their safety properties and the likelihood of using the high operating temperatures for generating process heat, normally graphitic fuel elements of various geometrical configurations are used. These have in common that the actual fuel or breeder material, the uranium, thorium or plutonium, is present therein in the form of so-called coated particles. These are spherical particles of the respective heavy metal oxides with diameters of between 0.1 and 1 mm, coated by layers of carbon and, for example, silicon carbide in order to render them suitable for use in the reactor. The pure oxide microspheres are referred to in nuclear technology as cores or, in the English speaking world, as kernels. Normally, for generating the kernels one proceeds from the appropriate nitric acid solutions: the low-viscosity nitrate solutions are transformed into high-viscosity solutions which are transformed as perfectly as possible into spherical droplets in order to subsequently convert them into solid gel microspheres by chemical reaction, hence also referred to as solution/gel-process. The reagent of choice for the reaction to form a solid body is ammonia: uranium reacts to form ADU (ammonium diuranate), thorium or plutonium to form hydroxide. To date two methods are being used to produce these kernels. The methods of “internal gelling” proceed from relatively highly-concentrated solutions, feeding solutions of the heavy metals in droplet form into heated organic oils, in which case the release of ammonia from the additives Urotropine, urea or the like, causes the solidification. A problem here is the use of the oils as a precipitation bath: that is to say, in further steps the fresh kernels need to be rinsed with water in order to remove reaction products. This inevitably creates water/oil mixtures which must be regenerated again in a complex manner. This causes considerable technical problems, in particular in view of the fact that radioactive liquids are involved. Methods for “external gelling” transform relatively low-concentrated solutions (approx. 100 g U/l) into droplets in an ammonia atmosphere, collect the microspheres generated in an ammonia solution, leaving them there to age (reacting to form ADU or the hydroxides), rinsing them first with ammonia-containing water, thereafter, however, with a water-miscible organic solvent, e.g. with isopropanol or another alcohol. The first rinsing, the one using water, removes the by-products of the reaction, such as ammonium nitrate as well as the added THFA (tetrahydrofurfuryl alcohol). The second rinsing, the one using isopropanol, removes the water from the kernels. Rinsing must even be performed with absolute isopropanol, which is particularly complex as the work-up of isopropanol for recycling needs to be performed beyond the azeotrope conditions. Only anhydrous kernels can subsequently be processed further without being damaged. The dry kernels are calcined in order to remove the organic components contained therein, reduced and finally sintered into the UO2 kernel. The disadvantage of both methods is the necessity of having to use organic liquids for the (post-) treatment of the newly formed fuel/breeder material droplets: The areas of production in which they are used must meet strict requirements regarding explosion protection. The use of certain apparatus such as continuous driers which are advantageous from a process-technical aspect is even impossible. Their emission from environmental points of view is restricted, they need to be removed from the exhaust air flows. Their disposal or recycling is complex, particularly since recycling requires conversion to the water-free state. All in all, using organic substances contributes significantly to the still considerable costs of producing fuels for high-temperature reactors. DE-B-20 37 232, DE-B-15 92 477, DE-B-18 17 092 are being cited as examples of the state of the art describing such methods. DE-B-24 59 445 describes that an aqueous suspension of uranyl nitrate, polyvinyl alcohol (PVA), urea and carbon black is transformed into droplets. DE-A-19 60 289 uses an aqueous solution of uranyl nitrate and urea to which hexamethylenetetramine is added within a temperature range of between 0° C. and 10° C. in order to obtain a stable solution. The stable solution is fed as droplets by means of a nozzle cooled to 5° C. into paraffin oil. From the reference “Journal of NUCLEAR SCIENCE and TECHNOLOGY”, Vol. 41, No. 9, p. 943-948 (September 2004), “Preparation of UO2 Kernel for HTR-10 Fuel Elements”, a method for producing combustible material particles is known according to which urea is added to a uranium solution prior to the addition of PVA and THFA. It is the object of the present invention to develop a method which retains the known favourable properties of fuel or breeder material kernels which are produced according to the solution/gel method, but which avoids the use of problematic organic substances. In addition, a concentrated solution of water-soluble, complex cations of the heavy metals is to be provided in order to allow simple further processing avoiding the drawbacks associated with the state of the art. In this context and in an unproblematic manner a stable solution is to be produced, which is to be transformed into droplets. The object is attained according to the invention substantially in that the first reagent is added to the starting solution at room temperature and the solution thus prepared is heated to a temperature T where 80°≦T<Ts where Ts=boiling temperature of the solution and is maintained at said temperature over a period of time t where 2 h≦t≦8 h, the solution is subsequently cooled to a temperature TA where TA≧room temperature and finally the second reagent is added. In particular, the second reagent is added to the solution at room temperature, in which case the said second reagent should be dissolved in solid form in order to prevent dilution of the solution. Surprisingly, it was found that if the starting solution containing the dissolved first reagent is heated at an elevated temperature, preferably in the range of between 80° C. and 100° C., in particular in the range of 90° C. and is maintained at this temperature for several hours, preferably 3 to 6 hours, the solution remains stable while at the same time the decomposition of the first reagent and the removal of excess water take place and at the same time a concentrated solution of water-soluble complex cations of the heavy metals is generated, which can then, after the second reagent has been added according to the gel-precipitation process, be solidified into microspheres in an ammonia-containing atmosphere, in which case the use of an alcohol such as isopropanol is not necessary for the subsequent post-treatment of the rinsed microspheres. The starting solution itself should be a 1 to 2.5 molar nitrate solution. In order to remove the water still present in the microspheres after rinsing, further processing is performed in a reduced pressure atmosphere. In this context it is the intention that further processing for the removal of water is performed at a pressure p where 0.07 MPa≦p≦0.09 MPa. According to the invention, urea or a first reagent acting in the same way is added to the starting solution at room temperature, more in particular, in the solid state in order to prevent dilution of the solution. The solution thus prepared is then heated to a temperature below boiling point, preferably in the range of between 80° C. and 100° C., in particular about 90° C. over a time period of between 3 and 6 hours, preferably about 4 hours, in which case the decomposition of the urea or the first reagent acting in the same way and the removal of the excess water results in a concentrated solution of water-soluble complex cations of the heavy metals. By adding PVA and/or THFA serving as the second reagent, microspheres are then produced according to the gel-precipitation method, which are subjected to subsequent treatment in a manner known per se but avoiding the use of alcohol. As a result, in accordance with the state of the art, the casting solution, that is to say the solution adjusted to a desired viscosity, is transformed into droplets in vibration nozzles to form microspheres, the latter being solidified in the surface region in an ammonia atmosphere, then collected in an aqueous ammonia solution in which they are left to age. The microspheres are subsequently rinsed, dried, calcined and finally reduced to the desired kernels and sintered. As far as that is concerned, reference is however made to process steps which are part of the state of the art. However, in contrast to these process steps post-treatment is performed without the use of alcohol. According to the invention, the solution is prepared without the use of hexamethylenetetramine. Cooling below room temperature is thus not necessary. According to the invention a casting solution is prepared as known per se from the known “external gelling” method, wherein the first reagent is however added at an elevated temperature for internal release of ammonia. At the same time, in comparison with known methods, the quantity of the second reagent such as PVA and/or THFA may be reduced substantially. The first reagent such as urea allows increasing the uranium concentration to values of e.g. up to 400 g/l (conventional methods with external gelling operate at concentrations of about 100 g/l). This solution can then be converted into relatively small droplets, the droplets then being gelled in an ammonia atmosphere, whereafter they are aged in an ammonia solution at an elevated temperature, rinsed with water, dried, calcined and sintered to form UO2-kernels conforming to specification. For the production of spherical fuel or breeder material particles from uranium-, thorium- or plutonium oxide or appropriate mixed oxides within a diameter range of preferably about 0.1 mm to 1 mm it is possible to mix a solution of the appropriate heavy metal nitrates with urea or a first reagent acting in the same way, the former or the latter releasing ammonia in a hot environment, thus reacting as a precipitation agent, as well as with additives for adjusting the viscosity, to transform this solution into droplets, to solidify the surface regions of the microspheres generated in an ammonia atmosphere, to further solidify the microspheres in an ammonia solution at an elevated temperature, to rinse them with water only and not with organic solvents, to dry, calcine and finally sinter them into the end product. In particular, the invention provides that to the solution PVA and THFA is added in a quantitative ratio of about 1:10, in particular about 50 g/kgU PVA and about 500 g/kgU THFA. The invention is elucidated in more detail below by way of examples, from which further details, advantages and characteristics of the invention are apparent. The quantities or ratios and parameters set out there are to be interpreted as being significant on their own, even independently of the other data stated. For a kernel batch, 20 kg of uranium in the form of U3O8 are dissolved in nitric acid, 8.8 kg urea being added to the resulting solution of uranyl nitrate after cooling and filtering, and maintained at about 90° C. for 4 h. After cooling, 1 kg PVA as well as 9.5 kg THFA are added and the solution is homogenized. This solution is now transformed into droplets of the required size via nozzles in vibrating plates, in the present example for a target diameter of the finished kernels of 500 μm, the droplets falling through an approximately 50 mm high ammonia gas path before they plunge into the precipitation bath of a 7-12 molar NH3-solution and gel there. The fresh kernels are transferred with the precipitation solution flow into the vessels for aging, rinsing, drying and are left to age here for several hours at about 60° C., subsequently they are rinsed repeatedly with water, likewise at about 60° C., and finally vacuum-dried at up to 80° C. The dried kernels are first calcined into UO3 in appropriate kilns in the presence of air according to a specific temperature program ranging between 100° C. and 500° C., then reduced and sintered into UO2 kernels under hydrogen at 600° C. to 700° C. and subsequently at 1650° C. According to conventional methods of quality control such as screening and sorting, UO2-kernels can be made available for further processing with the properties set out in the following table with a yield exceeding 90%: Properties of the UO2 Kernels Diameter/μm450 ≦ x ≦ 550)95/95Density/(g · cm−3)x ≧ 10.4Sphericity (Dmax/Dmin)(1)(x ≦ 1.2)95/95O/U ratio1.99 ≦ x ≦ 2.01 For a UO2-kernel batch having a diameter of 500 μm, 4 kg uranium in the form of U3O3-powder are dissolved in nitric acid. The solution is prepared by heating to 90° C. within 4 hours, bringing about a stoichiometric uranyl nitrate solution having the composition of UO2 (NO3)2. After cooling and filtering 8 l of solution are obtained with 500 g U/l. In this solution 0.44 kg urea/kgU, that is to say 1.76 kg urea in total are dissolved at room temperature. This solution is subsequently heated to about 90° C. and maintained at this temperature for 4 hours. Thereafter the hot solution is cooled to room temperature and used for preparing a casting solution. The volume is 8.1 l/4 kgU, corresponding to a U-content of 494 g/l and a density of about 1.6 g/ml. For preparing the casting solution, polyvinyl alcohol (PVA) is used, inter alia for increasing the viscosity. By dissolving the PVA in ultra pure water, a 10 wt-% PVA solution is prepared, the density thereof being 1.022 g/ml. For a batch of casting solution bath of 4 kgU, corresponding to 4.5 kg UO2-kernels having a diameter of 500 μm, the following components are mixed to form a homogenous casting solution: 8.1 l of the uranyl nitrate solution heated with urea to 90° C. for 4 h and cooled again to room temperature 1.92 k of the 10 wt-% PVA solution 2.0 l tetrahydrofurfuryl alcohol having a density of 1.05 g/ml (Kp 177° C.). The volume of this casting solution is 12.0 l and the weight 17.3 kg. The U-content of the solution is 231 g/kg and the viscosity is in the range of 55 to 80 mPa×s. The casting solution is divided into uniform drops in a manner known per se by means of 5-flow-meters and a 5-nozzle-vibrator-system at a frequency of 100 Hertz, the droplets after being formed into microspheres in ammonia gas being left to pre-cure and thereafter being collected in a 5 to 12 molar ammonia solution as spherical particles of ammonium diuranate. With a U-content per 500 μm-UO2-kernels of 0.622 mg, at f=100 Hertz and a U-content of the casting solution of 231 g/kg a throughput volume Q per nozzle ofQ=0.622·f·60/231=16.15 g/minresults. For a 5-nozzle-vibrator-system a throughput of 80.75 g of casting solution/min or of 4.845 kg/h, respectively, results. In an aging-, rinsing and drying vessel of criticality-proof geometry the kernels are aged in an ammonia solution at 60° C., rinsed subsequently three times with de-ionized water at 60° C., 20 minutes each time and then dried at low pressure of 0.07-0.09 MPa for 6 hours at 80 to 90° C. After calcination at 300° C. in the presence of air, subsequent reduction and sintering under H2/Ar-gas at up to 1600° C. the UO2-kernels with a diameter of 500±50 μm and a density of 10.8 g/cm3 met the requirements. |
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045171530 | summary | FIELD OF THE INVENTION The invention relates to a device for removing cooling fluid, making it possible to locate defective fuel arrays in a nuclear reactor in operation. BACKGROUND OF THE INVENTION Fast fission nuclear reactors, cooled by liquid metal, comprise a core consisting of fuel arrays arranged side-by-side, and in contact via their lateral faces, in a vessel containing the liquid metal for cooling the reactor, which is generally liquid sodium. The liquid sodium for cooling the arrays, or primary sodium, is circulated by means of pumps. The circulating sodium passes through the core from bottom to top, in the longitudinal direction of the arrays, with the result that the exit from the core is in the upper part. Each of the arrays constituting the core is itself formed of a set of long tubes or needles consisting of a canning material containing the fissile fuel materials or fertile materials. In this type of reactor, rapid detection of the cracks which can appear in the canning material of some of the arrays, during the operation of the reactor, is very important. These breaks in cans can be detected by demonstrating the presence of fission products in liquid metal constituting the reactor cooling fluid. In fact, in the case of a break in a can, the fission products are released by the fuel material into the cooling fluid in contact with the external surface of the can. The defective fuel arrays can be precisely located by removing samples of liquid metal coolant in the region of these arrays, near the exit from the core, i.e., in the upper part of the core, through which the heated liquid metal leaves the core. Thus, a set of sampling pipes is arranged above the core, each of the pipes in this set being associated with one fuel array, and the end of these pipes which is opposite the sampling end arranged above the array is connected to means for identifying and locating the defective arrays by detecting fission products in the cooling fluid. These identifying and locating means are grouped together to form one or more modules, referred to as can break location (CBL) modules, embedded in the slab covering the vessel above the reactor core. These modules generally comprise selectors and measuring means, such as neutron counters, which make it possible successively to analyze the samples removed from each of the arrays, and to determine those arrays for which the cooling fluid contains fission products representing a leak in the array in question. In the case of the fast fission nuclear reactors currently being constructed, the number of arrays in the core is generally of the order of 500, which requires the presence of the same number of sampling tubes connected to the selecting and measuring means. It has therefore seemed preferable to use several modules, and the sampling pipes corresponding to the arrays located in a given region of the core and connected to each of these modules. The locating modules comprise moving or fragile components, such as the sample selectors, the pumps for circulating the liquid metal, and the neutron detectors, which must remain functional throughout the operating period of the reactor. These modules can therefore be subject to breakdowns or shutdowns, with the result that the monitoring of a whole region of the core may be temporarily interrupted. This is incompatible with continuous operation of the reactor under very good safety conditions. SUMMARY OF THE INVENTION The object of the invention is thus to propose a device for removing cooling fluid and for locating defective fuel arrays in an nuclear reactor in operation, this reactor comprising a core consisting of fuel arrays arranged side-by-side, and in contact via their lateral faces, in a vessel containing the reactor cooling fluid circulated by a pumping means so as to pass through the core in the longitudinal direction of the arrays, the device comprising means for identifying and locating the defective arrays by detecting fission products in the cooling fluid, these means forming one or more locating modules, and pipes for removing cooling fluid, associated with each of the arrays, independently joining each of the zones located at the exit from each of the arrays to the locating modules, and conveying the cooling fluid from the exit from the core to the modules, thus sampling and locating device being intended to permit continuous monitoring of the whole of the reactor core, even if one of the locating modules experiences a temporary shutdown caused by a breakdown. For this purpose, the sampling device according to the invention comprises at least two totally independent locating modules, and, for each of the arrays of the core, there is at least one adjacent array, i.e., an array located in contact with the first array via one of its lateral faces, which is connected by its sampling pipe to a locating module different from the module to which the first array is connected. In order to provide a clear understanding of the invention, an embodiment of a sampling and locating device according to the invention, for the case where two modules are used to monitor the whole of the core and for the case where six independent modules are used for this monitoring, will now be described with reference to the attached drawings. |
048448389 | description | PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 is a flow chart showing the method of treatment of a radioactive liquid waste according to the present invention. First, a radioactive liquid waste containing fission products and a thermally decomposable sodium compound such as sodium nitrate is transferred to a heating step to be heated therein. In this heating step, the evaporation and denitration of the liquid waste are carried out and the nitrate and water contained therein are evaporated. By further heating, the thermal decomposition proceeds and a nitrogen oxide (NO.sub.x) gas is eliminated. For example, sodium nitrite is decomposed at 320.degree. C., while sodium nitrate is decomposed at 380.degree. C. Accordingly, the heating of the radioactive liquid waste may be carried out at a suitable temperature exceeding these temperatures. It is preferred to use microwave as a heat source in the heating step, because microwave heating gives a porous calcination product. By continuing the heating, there is formed a calcination product or denitrated product essentially comprising fission products, sodium oxide and sodium peroxide. Among initial fission products, volatile nuclides are evaporated by the above heating, so that the exhaust gas must be separately subjected to necessary treatment such as condensation, adsorption or absorption. Most of the nonvolatile nuclides are converted into oxides by the above heating. Then, the denitrated product (oxides) thus formed are transferred to a reaction step. In this reaction step, water vapor is sprayed directly to the denitrated product to convert the oxides into sodium hydroxide. In order to carry out the formation of sodium hydroxide more gently, the denitrated product may be reacted with carbon dioxide gas to convert the oxides of sodium into sodium carbonate, which is then converted to sodium hydroxide by reacting sodium carbonate with water vapor. The thus obtained sodium hydroxide containing fission products is transferred to a purification step. In this step, the sodium hydroxide is dissolved in a pure alcohol such as ethyl alcohol to be converted into its ethylate (sodium ethoxide), and the thus obtained sodium ethylate is separated by solid-liquid separation from an impurity residue. The impurity residue essentially comprises fission products. The separated sodium ethylate is then transferred to a decomposition step. In this step, the ethylate is decomposed with water into ethyl alcohol and sodium hydroxide. The sodium hydroxide is recovered and reused. The impurity residue separated in the purification step may be transferred to a solidification step. In this step, the residue is melted together with a glass forming agent to be vitrified. Alternatively, it is mixed with bitumen under heating to produce a product solidified by bitumen. Since the sodium content of the impurity residue is remarkably reduced, a vitrified product having excellent properties can be formed by the vitrification or the risk of fire and explosion can be reduced in the bitumen solidification. Thus, in either case, the volume of the radioactive liquid waste to be solidified can be greatly reduced. Some of the steps constituting the method of the present invention can be applied to the treatment of a metallic sodium waste accompanied with a radioactive corrosive product from a fast breeder reactor. Such a waste containing metallic sodium is generally washed with water vapor or the like and the condensed liquid waste is subjected to vaporization by heating and concentration, and the concentrated liquid waste is melted together with a small amount of a glass forming agent to be vitrified. However, the obtained vitrified product exhibits unfavorable properties including deliquescence. In order to solve this problem, the treatment of the metallic sodium waste from a fast breeder reactor may be carried out as follows: the metallic sodium waste is directly contacted with water vapor to convert the metallic sodium into sodium hydroxide. The obtained sodium hydroxide is then transferred to the purification step of the present invention, in which the sodium hydroxide is reacted with an alcohol to form a sodium alcoholate. Then, the sodium alcoholate is separated from an impurity residue, and the separated sodium alcoholate is decomposed into sodium hydroxide. This application of the latter two steps of the method according to the present invention to the metallic sodium waste from a fast breeder reactor allows the reuse of sodium and the vitrification of the impurity residue into an excellent vitrified product, similarly to the method according to the present invention. FIG. 2 shows a preferred embodiment of an apparatus to be used in the present invention. This apparatus comprises a heating apparatus 10 and a reaction apparatus 40. The heating apparatus 10 is provided with a feeder 12 of a radioactive liquid waste and a heating chamber 18 having a bottom tilted so as to form a sink 16 in the heating chamber 18. The feeder 12 and the sink 16 are connected by a pipe 14. The heating chamber 18 is provided with a heater 20 at the bottom and sides of its outer wall and with a plurality of microwave applying apertures 22 at the top thereof. A screw 24 for continuously transferring (discharging) the denitrated product is rotatably provided at the bottom in the heating chamber 18 and can be driven by a driving motor 26 disposed outside the heating chamber 18. Further, the interior of the heating chamber 18 is partitioned into three zones A, B and C by partition plates 28 and 30. The heating chamber 18 is simultaneously subjected to irradiation with microwave and heating by the heater 20, while the radioactive liquid waste containing fission products and sodium nitrate (NaNO.sub.3) is continuously fed to the sink 16 from the feeder 12 via the pipe 14. The screw 24 is rotated by the driving motor 26. In the zone A, the heating and concentration of the radioactive liquid waste are carried out, and in the zone B, the concentration and denitration (decomposition into NO.sub.x) of the liquid waste are carried out. The oxygen required in the reaction is fed via an air feed opening 32 provided at the upper part of the heating chamber 18 and the exhaust gas is discharged via an exhaust vent 34. In the zone C, the reaction is completed to form oxides of sodium, i.e., sodium oxide and sodium peroxide. The denitrated product thus obtained is discharged via a discharge opening 36 into the reaction apparatus 40 which will be described below. The reaction apparatus 40 is provided with a screw 46 at the lower part in a reaction chamber 42 and with a water vapor sprayer 48 at the top of the chamber 42. The screw 46 can be rotated by a driving motor 44. The denitrated product formed in the heating chamber 10 is fed to the reaction chamber 42 via a feed opening 50 provided at the top thereof and transferred by the screw 46, while being sprayed with water vapor from the sprayer 48 to thereby convert the oxides of sodium in the denitrated product into sodium hydroxide. The denitrated product containing sodium hydroxide and fission products is discharged via a discharge opening 52 to be collected in a collection vessel 54, while the gaseous product generated in the formation of sodium hydroxide is discharged via an exhaust vent 56. The sodium hydroxide containing fission products thus collected is transferred to the following purification step as shown in FIG. 1. As described hereinabove, according to the present invention, it becomes possible to reuse sodium contained in the radioactive liquid waste and to remarkably reduce the volume of the radioactive waste to be solidified. In addition, since the sodium content of the radioactive waste to be solidified is greatly reduced, the solidification thereof is significantly facilitated. Accordingly, the vitrification can be carried out with a reduced amount of a glass forming agent to give a vitrified product having excellent properties. In the bitumen solidification, on the other hand, the solidification treatment can be carried out safely with reduced risk of fire or explosion. Although the present invention has been described with reference to the preferred embodiments thereof, many modifications and alterations may be made within the scope of the appended claims. |
abstract | The present invention provides a method and device for observing a specimen in a field of view of an electron microscope. The method may include the steps of obtaining an image formed by irradiating an electron beam to a specimen; presetting an arbitrary search target pattern similar to a search target form; determining whether the field of view has a brightness inappropriate for observation or search; adjusting electro-optical conditions of an electron microscope when it is determined that a field of view is appropriate for observation or search; searching the field of view for a form having the same pattern as the search target pattern; and measuring a number of the forms obtained by the search. |
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062722026 | summary | FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure method and, more particularly, to a proximity exposure method using X-rays, for example. The exposure method of the present invention is suitably applicable to the manufacture of various microdevices such as a semiconductor chip (e.g., IC or LSI), a display device (e.g., a liquid crystal panel), a detecting device (e.g., a magnetic head), and an image pickup device (e.g., a CCD), for example. FIG. 1 shows an example of an X-ray proximity exposure apparatus of a known type (Japanese Laid-Open Patent Application No. 2-100311). Denoted in the drawing at 1 is an X-ray source (light emission point) such as synchrotron orbital radiation (SOR), and denoted at 2 is an SOR X-ray beam being expanded in an X direction into a slit-like shape. Denoted at 3 is a convex mirror, made of SiC, for example, for expanding the slit-like X-ray beam 2 in a Y direction. Denoted at 2a is the X-ray beam having been expanded by the convex mirror 3 into an area shape. Denoted at 7 is a workpiece to be exposed, such as a semiconductor wafer having been coated with a resist, for example. Denoted at 10 is a mask. Denoted at 4 is a beryllium film for isolating an ambience at the SOR side and an ambience at the mask (and workpiece) side from each other. Denoted at 5 is a focal plane type shutter being provided for exposure amount adjustment. In an exposure operation, the mask 10 and the workpiece 7 are placed with a spacing (gap) of about 10 microns maintained therebetween. As the shutter 5 is opened, a slit-like high-luminance X-ray beam 2 from the SOR, for example, and being expanded into an area shape (X-ray beam 2a) by the convex mirror 3, is projected to the mask 10 and then to the workpiece 7, by which a pattern image of the mask 10 is transferred to the workpiece 7 at a unit magnification. As regards the X-rays in this case, a wavelength of about 0.5-20 nm is used. Therefore, in connection with the wavelength only, theoretically, a very high resolution of 0.05 micron (50 nm) or less will be obtainable. Practically, however, such a high-resolution mask itself is difficult to manufacture. If a mask of a nominal smallest linewidth of 0.05 micron is manufactured by use of a technique for production of a conventional mask of a smallest linewidth of 0.1 micron (100 nm), any positional error or any error in the line-and-space (linewidth and spacing) of a pattern produced will be transferred to a workpiece as a mask defect. It will cause a void in the pattern to be formed, or a positional deviation of the pattern. Further, a produced mask pattern may not have a proper linewidth or a sufficient thickness. On these occasions, a sufficient contrast will not be attainable, and the pattern will not be resolved satisfactorily. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide an exposure method by which a pattern can be formed at a higher resolution and a higher precision, on the basis of a currently available X-ray exposure apparatus and a mask which can be produced in accordance with a current technique. It is another object of the present invention to provide an exposure method which enables accomplishment of resolution even in a strict condition under which the contrast is too low and the resolution is currently difficult to accomplish. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. |
description | The present invention relates to a method of making a fuel channel for a fuel assembly for a nuclear power boiling water reactor. The invention also concerns a fuel channel as such and a fuel assembly for a nuclear power boiling water reactor. In a fuel assembly for a nuclear power boiling water reactor (BWR), there are a number of fuel rods, which comprise a nuclear fuel material. The bundle of fuel rods are surrounded by a fuel channel, which forms a surrounding wall of the fuel assembly. When the fuel assembly is in operation in a nuclear reactor, a cooling medium, usually water, flows up through the fuel assembly. This water fulfils several functions. It functions as a cooling medium for cooling the fuel rods such that they will not be overheated. The water also serves as a neutron moderator, i.e. the water slows down the neutrons to a lower speed. Thereby, the reactivity of the reactor is increased. Since the water flows upwards through the fuel assembly, in the upper part of the fuel assembly, the water has been heated to a larger extent. This has as a consequence that the portion of steam is larger in the upper part of the fuel assembly than in the lower part. The internal pressure in the fuel channel during operation is higher in the lower part of the fuel channel than in the upper part of the fuel channel. It is known to produce a fuel channel which has a varying thickness. The thinner parts of the fuel channel are often obtained by some kind of working, where material is removed from the fuel channel wall, for example by milling. U.S. 2006/0144484 A1 describes a method of producing a fuel channel. FIGS. 4 and 5 in this document show that first two U-shaped profiles are produced, which profiles then are welded together such that the fuel channel is formed. U.S. Pat. No. 4,749,543 describes a fuel channel with a varying thickness. U.S. Pat. No. 4,970,047 describes a fuel channel with a varying thickness, obtained by stepwisely shaving the inner surface of the channel box (see abstract). DE 697 16 188 T2, JP 2-216087 and JP 53-43193 also show fuel channels with a varying thickness. An object of the present invention is to provide an improved method of making a fuel channel for a fuel assembly for a nuclear power boiling water reactor. An object thereby is to simplify the production of the fuel channel. A further object is to use less material when producing the fuel channel. A further object is to make it possible to optimize the performance of the fuel channel in a simple manner. Another object is to save costs for producing the fuel channel. The above objects are achieved by a fuel assembly as defined in a method of making a fuel channel for a fuel assembly for a nuclear power boiling water reactor, the fuel channel defining a length direction which in use corresponds substantially to the vertical direction, the method comprising: providing at least one first sheet of a Zr-based material, said at least one first sheet having a first thickness, providing at least one second sheet of a Zr-based material, said at least one second sheet having a second thickness, wherein said second thickness is less than said first thickness, assembling different elements which together are to form the fuel channel, which elements comprise said at least one first sheet and said at least one second sheet, such that a fuel channel is formed and such that said at least one first sheet forms a lower part of the fuel channel and such that said at least one second sheet forms a higher part of the fuel channel and such that said lower part is joined with said higher part in that said at least one first sheet is joined with said at least one second sheet, wherein the joint between said lower part and said higher part is located such that the lower part constitutes 20-75% of the length of the fuel channel. Since the fuel channel is made of at least a first sheet and a second sheet of different thickness, which are joined with each other, the fuel channel can be made in a simple manner. It is, for example, not necessary to remove material by milling, in order to vary the thickness of the fuel channel. Furthermore, since a thinner sheet is connected with a thicker sheet, material is saved, compared to the case when the fuel channel has a constant thickness or the case where material is removed by for example milling. Since a higher part of the fuel channel is made by the thinner sheet, it is possible to optimize the performance of the fuel channel. For example, the second, thinner, sheet can be arranged such that the inner cross sectional area of the fuel channel is larger in the upper part of the fuel channel. This will contribute to a decrease in the pressure drop in the upper part of the fuel channel. Moreover, since the fuel channel has a lower thicker part, which is relatively long, it is well adapted to the higher pressure which during operation is the case in the lower part. Furthermore, since the fuel channel according to the invention is produced in a simple manner, such that also material is saved, the cost for producing the fuel channel is reduced. It can be noted that a fuel channel can also be called for example a box or box wall or channel wall. The fuel channel is normally quite long (for example about 4 m) compared to its width (for example about 1.5 dm). It therefore has a length direction, which may be defined by a central longitudinal axis of the fuel channel. In use in a nuclear reactor, the fuel assembly, and the fuel channel, preferably extend mainly in the vertical direction. The length direction is thus, in use, the vertical direction. The concepts “lower” and “higher”, and similar expressions, are used in order to refer to different parts of the fuel channel, as seen when the fuel channel is positioned in the intended use position. The nuclear reactor is preferably a light water reactor. The concepts “first” and “second”, etcetera are used to distinguish the different parts from each other and should therefore not be seen to designate a certain number of parts. For example, it is possible that there are several “first sheets” that together form the lower part of the fuel assembly. Zr-based material means that the material to a large extent consists of Zr, the Zr content (in weight percent) may be at least 94%, preferably at least 97%. The Zr-based material can be an alloy, which is designed for use in a nuclear BWR, for example an alloy such as Zircaloy 2 or Zircaloy 4, or modifications of such alloys, or any other Zr-based alloy suitable for use in a nuclear BWR. Preferably, the at least one first sheet has a constant thickness, and the at least one second sheet has a constant thickness, and the assembled fuel channel has a constant first thickness where the at least one first sheet is located (except for possible small local deviations, for example caused by deformation when bending the sheets) and a constant second thickness where the at least one second sheet is located (except for possible small local deviations, for example caused by deformation when bending the sheets). According to one embodiment of the method according to the invention, said higher part constitutes 20-75% of the length of the fuel channel, preferably 30-50% of the length of the fuel channel. Such a length of the higher part has been found to be suitable, since such a higher part is suitable to be positioned where the internal pressure in the fuel channel, during operation, is lower than in the lower part of the fuel channel. It is therefore sufficient to use a thinner sheet for such higher part. Preferably, said lower part and said higher part together form at least 60% of the length of the fuel channel, preferably at least 90%, most preferred 100% of the length of the fuel channel (the fuel channel is the wall, which in use surrounds the (bundle(s) of) fuel rods of a fuel assembly). It is within the scope of the invention that the fuel channel comprises some further parts, in addition to said lower part and said higher part. For example, there may be a second higher part, which is made of at least one third sheet which has a third thickness which is less than said second thickness, wherein said at least one third sheet forms a second higher part of the fuel channel, located above said (first) higher part, and such that said (first) higher part is joined with said second higher part in that said at least one second sheet is joined with said at least one third sheet. Similarly, there may be a second lower part, which is located below the (first) lower part, and which is made of a sheet which is thicker than said first sheet. With such further parts, the thickness of the fuel channel can be adapted to the requirements in different parts of the fuel assembly. According to a further embodiment of the method according to the invention, said second thickness is 40-85% of said first thickness, preferably 55-80% of said first thickness. Such a thickness has been found to be suitable in order to provide sufficient strength and at the same time make the second sheet sufficiently thin in order to provide more space for water or steam (compared to the case if the second thickness were the same as the first thickness), and in order to reduce the amount of used material. According to a further embodiment of the method, said first thickness is 2.00-3.50 mm, preferably 2.00-3.00 mm, more preferred 2.20-2.80 mm. Such a thickness has been found to be appropriate in order to provide sufficient strength for the lower part where the first sheet is positioned, at the same time as it is avoided to use an unnecessarily thick sheet. According to a further embodiment of the method, the joint between said lower part and said higher part is formed by welding or soldering, preferably by welding. In particular by using welding, the fuel channel can be produced in a simple and efficient manner and such a joint also provides sufficient strength. The welding may for example be TIG welding, but also other welding methods may be used. The weld joint may for example be formed by butt welding. According to a further embodiment of the method, the assembling step is carried out such that the formed fuel channel has a cross sectional inner area in the higher part, which is larger than the cross sectional inner area in the lower part. By providing a larger inner area in the higher part, there is more space in the higher part. During operation, the higher part of the fuel assembly contains a large amount of steam. By providing more area in the higher part, the pressure drop in the water decreases. The water in the higher part can thereby flow in a more efficient manner through the fuel assembly. The inner area is thus the area inside the fuel channel, limited by the inside of the walls of the fuel channel, which walls are formed at least by said at least first and second sheets. The cross section is thus a horizontal section, if the fuel channel is seen in the intended use position, in which it extends vertically. The cross sectional inner area in the higher part may for example be 0.7-4.0%, preferably 1.0-4.0%, more preferred 1.5-3.0%, larger than the cross sectional inner area in the lower part. The fuel channel preferably has a rectangular cross sectional shape, more preferred a square cross sectional shape. The inner distance between two opposite sides in the higher part is preferably at least 0.50 mm larger, preferably at least 0.80 mm larger, more preferred at least 1.30 mm larger, than the inner distance between two opposite sides in the lower part. According to a further embodiment of the method, the assembling step is carried out such that the formed fuel channel has an outer cross sectional area in the higher part, which is the same, or at least substantially the same, as the outer cross sectional area in the lower part. In this manner, a smooth external surface is obtained at the same time as the internal cross sectional area in the higher part is made large. The outer cross sectional area is thus the area enclosed by the outside of the walls of the fuel channel, which walls are formed by said at least first and second sheets. By “substantially the same” is here meant that the outer cross sectional area in the higher part differs less than 0.50%, from the outer cross sectional area in the lower part. Preferably, this difference is less than 0.25%, more preferred the difference is 0. As mentioned above, the fuel channel preferably has a rectangular cross sectional shape, more preferred a square cross sectional shape. In this case, if the outer cross sectional area in the higher part is at least substantially the same, as the outer cross sectional area in the lower part, the difference between the distance between two opposite outer sides in the higher part and the distance between two opposite outer sides in the lower part is preferably less than 0.5 mm, more preferred less than 0.4 mm, most preferred 0.0 mm. According to an alternative embodiment, the assembling step is carried out such that the formed fuel channel has an outer cross sectional area in the higher part, which is less than the outer cross sectional area in the lower part. By having a smaller outer cross sectional area in the higher part, the water which, in operation, surrounds the fuel assembly will get closer to the fuel rods positioned in the fuel assembly. This leads to an improved moderation of the fuel rods. In this embodiment, the outer cross sectional area in the lower part may be for example 0.6-4.0%, preferably 1.0-4.0%, more preferred 1.5-3.0% larger than the outer cross sectional area in the upper part. If the fuel channel has a rectangular cross sectional shape, in particular a square cross sectional shape, the distance between two opposite outer sides in the lower part is preferably at least 0.60 mm larger, more preferred at least 0.80 mm larger, most preferred at least 1.30 mm larger, than the distance between two opposite outer sides in the upper part. According to this embodiment, the cross sectional inner area in the higher part may either be the same (or at least substantially the same) as, or larger than, the cross sectional inner area in the lower part. If the cross sectional inner area in the higher part is the same as the cross sectional inner area in the lower part, it is possible for example to use the same dimensions for the spacer grids that are positioned in the higher part and in the lower part. According to a further embodiment of the method, said at least one first sheet is joined with said at least one second sheet when the sheets are flat, after which the joined sheets are configured and arranged, possibly together with other elements, such that the fuel channel, which surrounds an inner space, is formed. It has been found that it is easy to join the sheets to each other when the sheets are flat. This embodiment therefore provides a simple manner of joining the sheets. According to an alternative manner, the at least one first sheet is formed into a lower part of the fuel assembly, which surrounds an inner space, and the at least one second sheet is formed into a higher part of the fuel assembly, which surrounds an inner space, after which the so formed lower and higher parts are joined with each other. The invention also concerns a fuel channel for a fuel assembly for a nuclear power boiling water reactor. The fuel channel defines a length direction which in use corresponds substantially to the vertical direction. The fuel channel comprises: at least one first sheet of a Zr-based material, said at least one first sheet having a first thickness, at least one second sheet of a Zr-based material, said at least one second sheet having a second thickness, wherein said second thickness is less than said first thickness, said at least one first sheet and said at least one second sheet being shaped and arranged, such that they, together with possible further elements, form said fuel channel, wherein said at least one first sheet forms a lower part of the fuel channel and said at least one second sheet forms a higher part of the fuel channel, said at least one first sheet having been joined with said at least one second sheet such that a formed joint is arranged where said at least one first sheet has been joined with said at least one second sheet, wherein said joint also forms a joint between said lower part and said higher part, wherein the joint between said lower part and said higher part is located such that the lower part constitutes 20-75% of the length of the fuel channel. Such a fuel channel has advantageous properties corresponding to those mentioned above, in connection with the method of making the fuel channel. Further embodiments of the fuel channel are defined in the dependent claims, and have advantages corresponding to those mentioned above in connection with the embodiments of the method according to the invention. The invention also concerns a fuel assembly for a nuclear power boiling water reactor. The fuel assembly comprises: a plurality of fuel rods arranged substantially parallel to each other, said fuel rods comprising nuclear fuel material, a plurality of spacer grids arranged to hold the fuel rods at predetermined positions relative to each other, a fuel channel as described above, arranged such it surrounds said fuel rods and said spacer grids. Such a fuel assembly has advantageous properties, as explained above in connection with the fuel channel and the method of making the fuel channel. An embodiment of a fuel assembly according to the invention will now be described, first with reference to FIGS. 1 and 2. FIG. 1 shows schematically a fuel assembly 8 for a nuclear power boiling water reactor (BWR). The fuel assembly 8 comprises a plurality of fuel rods 18. The fuel rods 18 are arranged substantially parallel to each other and they extend substantially in the length direction LD of the fuel assembly 8. The fuel rods 18 comprise nuclear fuel material 20 (just indicated as a few fuel pellets for one of the fuel rods 18). A plurality of spacer grids 22 are arranged to hold the fuel rods 18 at predetermined positions relative to each other. A fuel channel 10 is arranged such that it surrounds the fuel rods 18 and the spacer grids 22. The fuel assembly 8 also comprises a bottom plate 24 and a top plate 28, between which the fuel rods 18 are arranged. The fuel assembly 8 also comprises a lower transition piece 26, which forms an inlet for the cooling medium, i.e. the water, which in use flows through the fuel assembly 8. The fuel assembly also comprises one or more water channels 30, through which non-boiling water can flow. At the top of the fuel assembly 8 a handle 32 is arranged in order to facilitate the transportation of the fuel assembly 8. It should be noted that FIG. 1 only shows one possible embodiment of a fuel assembly according to the invention. Other designs of the fuel assembly are also possible. For example, the fuel assembly does not need to have a top plate and bottom plate of the kind shown in FIG. 1. For example, according to an alternative embodiment, the fuel assembly does not have any top plate 28 as shown in FIG. 1. Instead, the fuel rods 18 are held in position by the spacer grids 22, and the whole fuel assembly may be held together by for example one or more water channels (for non-boiling water) which extend to an upper lifting device, or by support elements (for example support rods) which, at one end, are attached to the water channel(s) and at the other end are attached to an upper lifting device. The fuel channel 10 shown in FIG. 1 (which fuel channel 10 illustrates an embodiment of a fuel channel according to the invention) comprises at least one first sheet 11 of a Zr-based material. The first sheet 11 has a first thickness T. One or more such first sheets 11 form a lower part LP of the fuel channel. The fuel channel 10 also comprises at least one second sheet 12 of a Zr-based material. The second sheet 12 has a second thickness t. The second thickness t is less than the first thickness T. One or more of said second sheets 12 form a higher part HP of the fuel channel 10. The one or more first sheets 11 and the one or more second sheets 12 are joined to each other by welding such that a weld joint 14 is formed. The weld joint 14 can for example be formed by TIG welding. The weld joint 14 is thus arranged where the at least one first sheet 11 has been joined with the at least one second sheet 12. The weld joint 14 therefore also forms a joint between the mentioned lower part LP and the higher part HP. The thickness T of the first sheet(s) 11 can be for example 2.50 mm. The thickness t of the second sheet(s) 12 can be for example 1.60 mm. According to the embodiment shown in FIG. 1, the whole fuel channel 10 is made of sheets of the two different thicknesses described. However, as explained above, it is within the scope of the present invention that there are further sections of the fuel channel, with further thicknesses of the sheets that make up the fuel channel. The fuel channel 10 has a length L, which may for example be 4.0 m. The lower part LP, which is made of the sheet(s) 11 of the first thickness T has a length l1. The higher part HP, which is made of the sheet(s) 12 of the second thickness t has a length l2. l1 may for example be 1.6 m and l2 may be for example 2.4 m. In the embodiment shown in FIG. 1 and FIG. 2, the fuel channel 10 has a cross sectional inner area in the higher part HP which is larger than the cross sectional inner area in the lower part LP. The outer cross sectional area in the higher part HP is the same as the outer cross sectional area in the lower part LP. The fuel channel 10 may have a square cross sectional shape. FIG. 2 shows schematically a sectional side view of such a fuel channel 10. The distance Dx between two opposite outer sides in the lower part LP may be for example 140 mm. The distance between two opposite outer sides in the higher part HP is indicated with dx in FIG. 2. According to this embodiment, Dx is thus equal to dx. According to this embodiment, the inner distance Di between two opposite sides in the lower part LP may be 135 mm. The inner distance di between two opposite sides in the higher part HP may, according to this embodiment, be 136.8 mm. FIG. 3 shows the same view as FIG. 2 of another embodiment of a fuel channel 10 according to the invention. According to this embodiment, the fuel channel 10 has a constant inner cross sectional area. The fuel channel 10 has, also according to this embodiment, a square cross sectional shape. The distance Dx between two opposite outer sides in the lower part LP may also in this embodiment be for example 140 mm. The inner distance Di between two opposite sides in the lower part LP may be 135 mm. According to this embodiment, the inner distance di between two opposite sides in the higher part HP is thus also 135 mm. The distance dx between two opposite outer sides in the higher part HP may according to this embodiment be 138.2 mm. According to a further embodiment (which is not shown in the figures), the design of the fuel channel 10 is intermediate between the embodiments shown in FIGS. 2 and 3. Also according to this embodiment, the fuel channel 10 may have a square cross sectional shape. The distance Dx between two opposite outer sides in the lower part LP may also in this embodiment be for example 140 mm. The inner distance Di between two opposite sides in the lower part LP may be 135 mm. According to this embodiment, the inner distance di between two opposite sides in the higher part HP may be 135.9 mm. The distance dx between two opposite outer sides in the higher part HP may according to this embodiment be 139.1 mm. An embodiment of a method according to the invention will now be described with reference to the flow chart in FIG. 6 and also to FIGS. 4 and 5. According to this embodiment, a first flat sheet 11 of a Zr-based material is provided. The first sheet 11 has a first thickness T. A second flat sheet 12 of the same Zr-based material is provided. The second sheet 12 has a second thickness t which is less than T. The sheets are joined to each other by welding. A first flat combined sheet 11, 12 is thus obtained. The above steps are repeated in order to form a second such combined sheet 11, 12. The first combined sheet is shaped into a U-profile as shown in the upper part of FIG. 4. The second combined sheet is also shaped into a U-profile as shown in the lower part of FIG. 4. These two U-profiles are then joined by welding as indicated in FIG. 5. Two weld joints 34 are thus produced, which extend in the length direction LD of the fuel channel 10 (and of the fuel assembly 8 when the fuel channel 10 is a part of a fuel assembly 8). The fuel channel 10 forms an inner space 16. The dimensions of the different parts are for example selected as indicated above in the embodiment of the fuel channel 10 and the fuel assembly 8. The formed fuel channel 10 may thus for example have a cross sectional inner area in the higher part HP which is larger than the cross sectional inner area in the lower part LP. The outer cross sectional area in the higher part HP may for example be the same as the outer cross sectional area in the lower part LP. As indicated above, there are other manners of making a fuel channel 10 according to the invention. It is thus for example possible to first form two U-profiles of first sheets 11 of a first thickness T and then join these two U-profiles together. After this, another two U-profiles are formed of second sheets 12 of a second thickness t and these U-profiles are joined together. In this manner one fuel channel section, which is to form a lower part LP, is formed and one fuel channel section, which is to form a higher part HP, is formed. After this, these two sections are joined to each other by welding, i.e. the joint 14 is formed. The present invention is not limited to the examples described herein, but can be varied and modified within the scope of the following claims. |
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claims | 1. Method for controlling an electrical energy storage device that is in service within a vehicle, comprising:providing a present state-of-life of the electrical energy storage device;establishing a target life objective for the electrical energy storage device as one of cumulative time and distance that the electrical energy storage device is in service within the vehicle at a predetermined state-of-life of the electrical energy storage device;determining a state-of-life gradient as a rate of change in the state-of-life of the electrical energy storage device with respect to the one of cumulative time and distance that the electrical energy storage device is in service within the vehicle which linearly converges the present state-of-life of the electrical energy storage device to the target life objective; and,controlling electrical energy storage device power to effect the state-of-life gradient. 2. The method of claim 1 wherein the predetermined state-of-life of the electrical energy storage device is indicative of the end of life of the electrical energy storage device. 3. The method of claim 1 wherein the life target is normalized with respect to the one of cumulative time and distance that the electrical energy storage device is in service within the vehicle upon which the target life objective is based. 4. Method for managing state-of-life of an electrical energy storage device that is in service within a vehicle, comprising:providing a state-of-life gradient based on a present state-of-life of the electrical energy storage device and a target life objective comprising at least one of cumulative time and distance that the electrical energy storage device is in service within the vehicle at a predetermined state-of-life of the electrical energy storage device; andcontrolling electrical energy storage device power such that electrical energy storage device state-of-life substantially tracks the state-of-life gradient comprising linearly converging the present state-of-life of the electrical energy storage device to the target life objective. 5. The method of claim 4 wherein controlling electrical energy storage device power such that electrical energy storage device state-of-life substantially tracks the state-of-life gradient comprises:providing a plurality of predicted effects upon electrical energy storage device state-of-life based on a plurality of potential electrical energy storage device currents; andcontrolling electrical energy storage device current based on the predicted effects and the state-of-life gradient. 6. Method for managing an operating state of an electrical energy storage device, comprising:establishing a target life objective for the electrical energy storage device comprising a predetermined service life for the electrical energy storage device, andcontrolling power transmitted through the electrical energy storage device such that the operating state of the electrical energy storage device is less than a predetermined value when the target life objective is attained comprising linearly converging a present operating state of the electrical energy storage device to the target life objective. 7. The method of claim 6, wherein the operating state of the electrical energy storage device comprises a state-of-life of the electrical energy storage device. 8. The method of claim 6, wherein controlling power transmitted through the electrical energy storage device such that an operating state of the electrical energy storage device is less than a predetermined value further comprises:determining the operating state of the electrical energy storage device, comprising:monitoring electrical current through the electrical energy storage device;monitoring a state-of-life of the electrical energy storage device;monitoring a temperature of the electrical energy storage device during active and quiescent periods of operation; and,determining a state-of-life of the electrical energy storage device, based upon the electrical energy storage device current, the state-of-life of the electrical energy storage device, and, the temperature of the electrical energy storage device during operation and during quiescent periods of operation. 9. The method of claim 7, wherein the electrical energy storage device is adapted for use in a hybrid vehicular powertrain and controlling power transmitted from the electrical energy storage device such that the state-of-life is less than a predetermined value when the target life objective is attained further comprises:calculating a life factor based upon an accumulated time and an accumulated distance of operation of the powertrain;determining a target state-of-life gradient based upon the life factor, the state-of-life, and the target life objective; and,controlling electrical power between the electrical energy storage device and the powertrain based upon the target state-of-life gradient. 10. The method of claim 9, wherein controlling electrical power between the electrical energy storage device and the powertrain based upon the target state-of-life gradient further comprises:determining potential changes in state-of-life for the electrical energy storage device based upon an array of potential electrical currents through the electrical energy storage device; and,selecting one of the array of potential electrical currents based upon the state-of-life gradient. 11. The method of claim 9, wherein controlling power transmitted through the electrical energy storage device comprises controlling electrical current between the electrical energy storage device and the powertrain. 12. The method of claim 10, wherein determining potential changes in state-of-life for the electrical energy storage device based upon an array of potential electrical currents through the electrical energy storage device further comprises:selecting the array of potential electrical currents through the electrical energy storage device; and,determining a corresponding array of changes in the state-of-life for the electrical energy storage device determined based upon the array of potential electrical currents through the electrical energy storage device;wherein changes in the state-of-life for the electrical energy storage device are determined based upon: time-based integration of the electrical currents through the electrical energy storage device, depth of discharge of the energy storage device, and, operating temperature of the electrical energy storage device. |
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040574636 | claims | 1. A method of operating a nuclear reactor having a reactive core including fissile material with an axial dimension and adjustable control means for controlling the reactivity within the core, comprising the steps of: monitoring a parameter representative of the power generated within the core at a first and second axial location; obtaining from the core power parameters measured at said first and second axial locations a representation of the axial power distribution within the core; and adjusting the control means to produce an axial power distribution to maintain a uniform and symmetric xenon distribution above and below substantially the center of the core over a substantial axial length of the core during normal reactor operation including load follow. 2. The method of claim 1 wherein the core is divided axially into upper and lower halves corresponding to said first and second monitored locations. 3. The method of claim 2 wherein the representation of the axial power distribution corresponds to the axial offset of the core. 4. The method of claim 3 wherein the adjusting step activates the control means to maintain the axial offset substantially equal to a predetermined target value throughout reactor operation including changes in reactor power. 5. The method of claim 4 wherein the control means includes control rods and the target value is obtained from the step of determining the axial offset at full power with equilibrium xenon and all control rods removed from the fuel region of the core. 6. The method of claim 4 wherein the target value is determined periodically. 7. The method of claim 6 wherein the interval between the determination of the target value is substantially equal to an equivalent full power month. 8. The method of claim 4 wherein the axial power distribution can vary during reactor operation to have a flux difference within a band of approximately plus or minus 5 percent of a predetermined value for the flux difference corresponding to the target value of the axial offset. 9. The method of claim 1 wherein the control means includes a plurality of elongated control rods comprising neutron absorbing material which are axially aligned with the core along the longitudinal control rod dimension and longitudinally movable into and out of the core with the longitudinal length of the rods at least substantially equal to the axis length of the core and a core cooling medium or moderator having a controlled variable concentration of a neutron absorbing element. 10. The method of claim 9 wherein the changes in reactor power are in part controlled to a desired level by variation of the concentration of the neutron absorbing element and wherein said adjusting step positions the control rods to maintain the substantially symmetric axial power distribution. 11. The method of claim 10 wherein the movement of the control rods within the core are approximately linearly proportional to changes in the power output of the core. 12. The method of claim 9 wherein the control means includes part length elongated control rods comprising neutron absorbing material which are axially aligned with the core along the longitudinal dimension and longitudinally movable within the core with the longitudinal length of the part length rods substantially less than the axial length of the core, wherein the control rods are adjusted for the reactivity control associated with changes in core power output and the adjusting step positions the part length rods to maintain the substantially symmetric axial power distribution. 13. The method of claim 12 wherein as a byproduct of the fission reaction of the fissile material the element xenon is created within the core having a neutron absorption property and wherein said adjusting step controls the concentration of the neutron absorbing element within the core to control the reactivity change due to xenon buildup or depletion corresponding to and associated with changes in core power output. 14. The method of claim 12 wherein the part length rod neutron absorbing capability is substantially equal to the control rod absorption capability of equivalent length. 15. The method of claim 12 wherein said adjusting step employs the part length rods for axial power distribution control for a power operating period approximately equal to less than 60 percent of every 30 equivalent full power days. 16. The method of claim 12 wherein the part length rods are inserted to a distance of approximately 30 percent from the bottom of the core at full power operation and the insertion linearly increases to approximately 10% from the bottom of the core at 50 percent core power. |
abstract | An x-ray computed tomography system (14) includes a gantry (15), a plurality of elements (18), and one or more processors (28). The gantry (15) moves to different orientations and generates x-ray data which includes image projection data at a plurality of the orientations. The plurality of elements (18) connect to the gantry and cause x-ray attenuation of the generated projection data. The one or more processors (28) are programmed to receive (60) the generated x-ray data and decompose (62) the received image projection data into indications of relative positions of the plurality of elements at different orientations of the gantry. |
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claims | 1. A method of suppressing deposition of a radioactive isotope on a structural member in contact with water coolant of a nuclear power plant, the method comprising the steps of:providing a chemical liquid conditioning device and locating the chemical liquid conditioning device in a non-radiation controlled area;providing a first chemical liquid tank in the chemical liquid conditioning device;adding an organic acid aqueous solution to the first chemical liquid tank;heating the organic acid aqueous solution in the first chemical liquid tank;circulating an inert gas through a gaseous phase section of the first chemical liquid tank;adding metal iron to the organic acid aqueous solution in the first chemical liquid tank;dissolving the metal iron in the organic acid aqueous solution in the first chemical liquid tank;ascertaining that the metal iron has been dissolved in the organic acid aqueous solution in the first chemical liquid tank;cooling the organic acid aqueous solution containing the dissolved metal iron;pressurizing the first chemical liquid tank with the inert gas;providing a transport container including a second chemical liquid tank;transferring the organic acid aqueous solution from the first chemical liquid tank to the second chemical liquid tank;pressurizing the second chemical liquid tank with the inert gas;storing the organic acid aqueous solution as a first chemical in the second chemical liquid tank;transporting the second chemical liquid tank filled with the first chemical which contains ferrous (II) ions from the non-radiation-controlled area into a radiation-controlled area in which a nuclear reactor of the nuclear power plant is installed;providing a film deposition apparatus in the radiation-controlled area;connecting the second chemical liquid tank as a first chemical container filled with the first chemical to the film deposition apparatus which further includes a second chemical container containing a second chemical for oxidizing the ferrous (II) ions into ferric (III) ions, and a third chemical container containing a third chemical for pH-adjusting and forming a processing liquid containing the first chemical, the second chemical and the third chemical;bringing the processing liquid that contains the first, second, and third chemicals in a mixed form, into contact with a surface of the structural member of the nuclear power plant with which surface the water coolant of the nuclear power plant comes into contact; andforming a ferrite film on the surface of the structural member contacted by the processing liquid. 2. The method of suppressing deposition of a radioactive isotope according to claim 1, further includingproviding the structural member as an inner surface of a pipeline of a system provided in the nuclear power plant, the system having the water coolant flowing inside; andsupplying the processing liquid to an interior of the pipeline. 3. The method of suppressing deposition of a radioactive isotope according to claim 1, further including pressurizing the second chemical liquid tank to be transported into the radiation-controlled area with an inert gas in a space in the second chemical liquid tank above a liquid level of the first chemical. 4. The method of suppressing deposition of a radioactive isotope according to claim 1, further including providing a carboxylic acid in the first chemical liquid tank and using the carboxylic acid for producing the ferrous (II) ions. 5. The method of suppressing deposition of a radioactive isotope according to claim 1, further including providing the organic acid aqueous solution as an aqueous solution of carboxylic acid. 6. The method of suppressing deposition of a radioactive isotope according to claim 5, further including providing the carboxylic acid as formic acid. 7. The method of suppressing deposition of a radioactive isotope according to claim 4, further including providing the carboxylic acid as formic acid. |
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051065720 | summary | FIELD OF THE INVENTION The present invention relates to a connection device for the centering and fixation of the upper core plate which closes the core cavity of a nuclear reactor, particularly of a PWR reactor, and a flange extending above said plate and on which are secured against movement the ends of guide tubes in which move cluster assemblies of neutron absorbing rods, adapted to be inserted in the core between the nuclear fuel elements, for ensuring the regulation of the fission reaction. More particularly, the invention relates to a device allowing relative positioning of two horizontal parallel plates by providing for perfect alignment of passages extending through them for the engagement or retraction in the core of the absorbing rod clusters, by eliminating any risk of jamming or blockage of said clusters during their movements, while allowing a slight relative axial displacement. BACKGROUND OF THE INVENTION In the prior art, the connection and accurate positioning of these two members is provided by means of spindles, one of the ends of which extends into an appropriate housing of the core plate by being axially slit in order to impart to it a relative resiliency in the transverse direction, the other end extending with a clearance through a bore of the flange of a cluster guide and being secured against movement with respect to the latter by screwing a nut coming in abutment against an inner shoulder of the bore so as to exert a reaction during the screwing on a threaded portion of the spindle. The nut is thereafter blocked on the flange, e.g., by soldering. By distributing over the flange periphery an appropriate number of such spindles and by providing for their coordinated tightening via the nuts associated thereto, accurate positioning of the flange with respect to the plate is achieved, notably so as to bring into alignment the vertical axes of these two members and to adjust to an accurately determined value the horizontal clearance between them. The axially slit end is formed of two flexible branches the outer diameter of which is slightly greater than the receiving bore, formed in the upper plate of the core, assuring sure that after mounting there is no remaining clearance subject to vibrations and wear, and providing an adaptation to the position tolerances of the two spindle axes respectively on the core upper plate and on the cluster guide lower flange. The two spindles are generally disposed in such manner that the slits are positioned perpendicularly with respect to one another. This state affords the best compromise between strength and flexibility. However, the centering of the two parallel members takes place against the resisting section of the spindles, which must provide not only for the orientation and coincidence of the cluster guides with respect to the network of fuel elements underneath the core plate, but also for the holding of the lower ends of these guides, while opposing the vibrations, which are sometimes significant, created by the hydromechanic stresses resulting from the axial flow of the cooling water flowing through the plate and flange and which is collected above said plate in the upper portion of the reactor vessel, and then is discharged through appropriate outlet nozzles. The prior art solutions only partly meet these requirements, and cannot provide assurance of reliability over time. SUMMARY OF THE INVENTION The object of the present invention is a device mitigating the disadvantages of the standard solutions by allowing dissociation of the two functions which consist respectively in centering the flange with respect to a common axial reference, and relative fixing of the two members by providing between them a spacing which is always unifrom whatever the operational speeds of the reactor and resulting stresses on the cluster guides and their connections with the plate. To this effect, the device includes at least two axial guiding spindles of the flange with respect to the core plate, diametrically opposite and rigidly fixed to the plate or to the flange in order to extend in a housing in alignment formed in the flange or in the plate respectively, and an assembly of self-locking shoes, adapted for sliding with a clearance in bores formed in the flange in order to apply against the plate surface, said shoes being each associated with a position control mechanism, carried by the flange and exerting on the shoes a force having a transverse component so as to provide by reaction the immobilization of the flange with respect to the plate. Thanks to these dispositions, the spindles ensure on the one hand the guiding in axial translation of the flange with respect to the upper core plate, save the mounting clearances of these spindles in their housings. Simultaneously, lateral self-locking shoes provide for the and axial retention of the flange with respect to the plate, the locking mechanism associated with each of said shoes allowing adjustment of their relative positioning in the bores of the flange, and therefore positioning of the latter, independently of the dimensional variations to which they may be subjected during the reactor operation, their structure being such that they readily absorb the effects of the vibrations created by the cooling water flow from the core through the plate and flange. According to a particular feature of the invention, the self-locking shoes have a general cylindrical shape and include a plane bearing face, applied against the core plate, and an opposite face slanting with respect to the horizontal. The control mechanism cooperating with each shoe is preferably made of a push-piece extending into a bore of the flange and including a convex face, bearing on the slanting face of the shoe, said push-piece being prolonged outside the flange bore at the end opposite to the plate by an elongated rod, located on the axis of a sleeve with an inner screw thread at its end for screwing a hollow calibration bushing, through which the rod extends freely and exerts a vertical force on the latter via a spring cartridge, bearing on the one hand against the bushing and on the other hand against a washer through which extends the rod, and in abutment on a shoulder of the latter. Advantageously, the spring cartridge includes a pack of conical washers mounted between the washer bearing against the rod shoulder and a complementary washer, sliding freely inside the sleeve, parallel to the rod axis, under the effect of the bushing being screwed on the sleeve inner thread. The spring cartridge thus permanently exerts on the shoe a force which is adjusted and develops a friction force between the plate and the shoe which opposes lateral displacement of the flange with respect to the plate in a selected direction. The arrangement of several shoes on the same flange cooperates for opposing any lateral displacement in any direction, while allowing the effects of any accidental vibrations to be absorbed, the flange resuming its its predetermined position with respect to the plate once these vibrations have disappeared or have been eliminated. According to another feature of the invention, the threaded sleeve includes, in its lower end, a hollow end-piece through which extends the stem and the end of which is in part inserted in the flange bore and then is secured against movement in position with respect to the flange, e.g. by soldering. According to still another feature, the elongated rod has, at its upper end extending beyond the calibration bushing, a transverse slit identifying its axial orientation and therefore that of the convex face of the push-piece with respect to the flange axis and allowing, by reaction on the shoe slanting face, relative adjustment of the push-piece and therefore of the flange connected thereto with respect to the core plate. Advantageously, each shoe has a configuration in the shape of a clevis, the two parallel sides of which are disposed on either side a plane central rib extending the push-piece downwardly, the clevis and the rib being connected by a transverse peg carried by the clevis sides and engaged with clearance in a hole of the rib so as to allow axial and radial movement of the push-piece with respect to the shoe when the flange bears on the plate. The mounting of the shoe and the push-piece thus formed allows making these two elements captive by connecting them to one another via a connection with a clearance which does not impede the relative displacement of these members for the flange centering and immobilization when the convex face of the push-piece bears against the shoe slanting face. The shoe can usefully carry a surface coating, such that the face of this shoe which is in contact with the core plate has a high coefficient of friction. On the contrary, the push-piece, the inner surface of the flange bore receiving the shoe, as well as the respective slanting and convex faces of the shoe and the push-piece, respectively carry a surface coating with a reduced coefficient of friction, facilitating the relative displacement of these parts. Advantageously, this coating can be made of chromium and "Stellite" or any similar material, conventional in the art and adapted to the operating conditions in the reactor vessel. |
053496140 | summary | FIELD OF THE INVENTION This invention generally relates to an apparatus for installing a plug in a line which communicates with a vessel. In particular, the invention is directed to an apparatus for installing a plug in the steam outlet nozzle of a boiling water reactor ("BWR"). BACKGROUND OF THE INVENTION During disassembly of a BWR, the steam outlet nozzles must be plugged to allow maintenance and testing of the main steam isolation valves in parallel with reactor refueling and servicing operations. The steam line plugs are used to seal the steam lines to prevent the flow of water from the reactor cavity during servicing of the safety valves, relief valves and main steam isolation valves. Historically, plug installation has been performed using an overhead crane and service poles manipulated by hand. This conventional operation is attended by problems. First, this current method of installing the plugs requires that personnel be located in the reactor cavity to position and maneuver the steam line plugs as they are being lowered by the overhead crane. Second, the current method of installing the plug requires that personnel push the plug into the steam outlet nozzle from the opposite side of the reactor vessel using a pole. Third, the steam line plug installation envelope should allow for unobstructed removal of the steam separator. Conventional installation tools interfere with or obstruct the removal of the separator and must be disengaged from the plug and removed after the plug has been installed. SUMMARY OF THE INVENTION The invention is a steam line plug installation tool which overcomes the foregoing disadvantages of the conventional apparatus. Using the installation tool of the invention, the steam line plug can be installed underwater by personnel standing on the refueling bridge. The tool inserts the steam line plug into the steam outlet nozzle using a scissors jack mechanism actuated by a lead screw operated using a grapple and a service pole. The installation tool is designed to position the plug at the proper elevation and azimuth using the reactor vessel flange and head closure stud as references. No personnel are required at the vessel flange to position the tool, thereby reducing the exposure of personnel to radiation. In addition, the plug installation tool envelope is such that the tool can remain in place after installation of the plug and still allow removal of the steam dryer and separator to their underwater storage pool. The steam line plug installation tool in accordance with the preferred embodiment of the invention comprises a strongback assembly on which the plug is securely mounted, a collapsible structure (e.g., a scissors jack assembly) which supports the strongback assembly and is movable between an extended state and a collapsed state, a hanging bracket assembly for hanging the collapsible structure inside the vessel, and a rotatable actuating screw coupled to the collapsible structure such that the latter moves between the extended and collapsed states in response to rotation of the actuating screw. During this operation, the plug is carried from a position outside and aligned with the vessel orifice to be plugged to a position inside the orifice. In accordance with the preferred embodiment, the plug installation tool further comprises a mechanism for adjusting the elevation of the collapsible structure relative to the hanging bracket assembly and a mechanism for adjusting the elevation of the strongback assembly to the collapsible structure. The latter mechanism is operated via a rotatable actuating screw. Both actuating screws are turned remotely using a conventional service pole. The plug installation tool also includes a guide plate which cooperates with the reactor head studs to place the tool at an azimuth corresponding to the azimuth of the orifice to be plugged. The tool is installed using a grapple which couples to a rotatable handling bracket assembly. The handling bracket is locked in a first angular position by a releasable pawl. After the plug has been installed in the orifice, the pawl is released remotely using a service pole. The handling bracket is then rotated to a position at which removal of the steam separator assembly from the reactor vessel will not be obstructed. |
abstract | Collimation device of the type intended to direct an energy beam in a given direction and at a given solid angle, the collimation device being capable of being installed on output of an energy beam generating arrangement and of being connected to a control unit. The collimation device includes the ability for testing operation of the assembly formed by the energy beam generating arrangement, the collimation device and the control unit. |
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06310931& | abstract | The present invention relates to a fuel assembly (1) and a method therefor. The fuel assembly is intended for a light-water cooled nuclear reactor and comprises a first and a second locking member (9a, 9b, 10), a plurality of elongated elements (3, 3a) wherein each of the lower ends of the elongated elements is provided with an end plug (3b). The end plug (3b) is arranged guided or locked in an end plate (6) which comprises at least two adjacently disposed plug holes (6b) for receiving one end plug (3b) each. The first locking member (9a, 9b) is made in an end plug (3b) and has a concave shape and the second locking member (10) is arranged slidable in a locking hole (6c) which is adapted to extend between the two adjacently disposed plug holes (6b) and opening out into these. The second locking member (10) is made with a length exceeding the length of the locking hole (6c) and has end surfaces with shapes intended for cooperation with the concave surface of the first locking member (9a, 9b). |
claims | 1. A container for producing radioisotopes by irradiation of a precursor material, the container comprising: a metal jacket of integral construction, the metal jacket having a symmetry of revolution about an axis, and having from top to bottom(i) an upper portion being open and having a conical shape, the opening of the cone being oriented upwards,(ii) a first cylindrical portion connected to the upper portion,(iii) a thin wall cylindrical section connected to the first cylindrical portion,(iv) a second cylindrical portion connected to the thin wall cylindrical section, and(v) a dome connected to the second cylindrical portion,the thin wall cylindrical section having a first thickness between 5 μm and 100 μm, the first and second cylindrical section and the dome having a second thickness larger than 100 μm. 2. The container as claimed in claim 1, wherein thin wall cylindrical section has an outside diameter between 4 mm and 100 mm. 3. The container as claimed in claim 1, wherein the container is at least partially made from at least one of nickel, titanium, niobium, tantalum, iron, chromium, cobalt or a stainless steel. 4. A method for obtaining a container as claimed in claim 1, the method comprising:providing a matrix;electrodepositing on the matrix a thickness of a metallic material, until a first thickness between 5 μm and 100 μm is obtained;masking a fraction of a surface of the matrix;electrodepositing on an unmasked section until a thickness larger than 100 μm is obtained;removing the matrix; andobtaining the container as claimed in claim 1. 5. The method as claimed in claim 4, wherein the matrix is removed by dissolution. 6. A target assembly for producing radioisotopes, including:a container as claimed in claim 1;a holding tube including at one end a threaded portion; anda ring including a suitable interior thread, the holding tube and the ring being configured to encase the container. 7. The target assembly as claimed in claim 6, wherein the container has an end having a conical shape, a base of the cone being oriented toward an exterior of the container, the holding tube has a conical end congruent with the end of the container, and the ring has a conical end congruent with the end of the container. 8. The target assembly as claimed in claim 6, wherein the holding tube and the container are mounted so as to be able to rotate about an axis, and the target assembly includes a motor arranged to make the holding tube and the container rotate. 9. The target assembly as claimed claim 6, further including a cooling tube placed inside the container and arranged to allow a cooling liquid to flow. 10. The target assembly as claimed in claim 9, wherein the cooling tube includes a cooling head that has a recess on a portion of a periphery of the cooling head, the recess to give incident beam a longer path in a precursor liquid. |
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047556862 | claims | 1. An electron beam irradiation apparatus for treating linear material with electron beams, said apparatus comprising: an electron beam accelerator means for emitting electron beams, the emitted electron beams collectively defining an irradiation zone; a plurality of pulley units, each of said pulley units comprising a pair of pulleys extending parallel to one another and around which the linear material is to be wound for supporting the linear material, and said pulley units being disposed end to end in the direction of the rotational axes of the pulleys; a plurality of drive means each of which is operatively connected to a respective one of said pulley units for rotating the pair of pulleys thereof to feed the linear material; and a position changing means operatively connected to said plurality of pulley units for positioning the pulleys of each of said pulley units with respect to the irradiation zone and for selectively moving said pulley units in a direction extending parallel to the rotational axes of the pulleys between a plurality of positions, each of said positions being one at which at least one of the pairs of pulleys of said plurality of pulley units assumes an irradiation position at which the linear material supported by said at least one of the pairs pulleys is in the irradiation zone and and at least another of said pairs of pulleys is in a non-irradiation position at which said at least another of said pairs of pulleys is out of the irradiation zone. wherein each of said positions to which said pulley units are selectively moved by said position changing means is a position at which at least two of said pairs of pulleys assume said irradiation position, and further comprising an electron beam interrupting means selectively movable over the irradiation zone between a first position at which the interrupting means blocks the electron beams to which one of said at least two of the pairs of pulley are exposed and a second position at which the interrupting means blocks the electron beams to which the other of said at least two of the pairs of pulleys are exposed. 2. An electron beam irradiation apparatus as claimed in claim 1, |
description | This application claims the benefit of priority of Japanese Patent Application Number 2016-216664 filed on Nov. 4, 2016, the entire content of which is hereby incorporated by reference. The present disclosure relates to a radioprotective unwoven fabric and a fiber product including the radioprotective unwoven fabric. Radioactive rays (e.g., Y rays and X rays) are emitted from radioactive materials and other materials in medical radiotherapy facilities, nuclear power plants, or the like. For this reason, to provide radioprotection, radioprotective items including a material shielding radioactive rays have been used in environments in which radioactive rays are emitted. Conventionally, lead has been used as a material shielding radioactive rays. A lead plate, a lead evaporation sheet on which lead is deposited by an evaporation method, or the like is known as a radioprotective item including lead. For example, Patent Literature (PTL) 1 (Japanese Unexamined Patent Application Publication No. 2015-206643) discloses a radiation shielding sheet including sheet-like lead. A radioprotective item including lead is heavy because the radioprotective item needs a sufficient thickness to achieve desired radioprotective effectiveness, or a radioprotective item including lead cannot be used in a place having a high temperature because the radioprotective item has a low melting point. In particular, a lead plate is difficult to cut or process or is damaged when bent because the lead plate is hard and unpliable. A lead evaporation sheet is damaged by a fold being exfoliated when bent. The present disclosure has an object to provide a radioprotective unwoven fabric and a fiber product which have superior radioprotective effectiveness and yet are not damaged when folded. In order to achieve the above object, a radioprotective unwoven fabric according to one aspect of the present disclosure is a sheet in which metal fibers are three-dimensionally and randomly stacked, the metal fibers each comprising a metal material having a specific gravity higher than a specific gravity of lead. Moreover, a fiber product according to one aspect of the present disclosure is obtained by sewing the radioprotective unwoven fabric. The present disclosure makes it possible to provide, for example, a radioprotective unwoven fabric and a fiber product which have superior radioprotective effectiveness and yet are not damaged when folded. Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. It should be noted that each of the subsequently described embodiments shows a specific example. Therefore, numerical values, shapes, materials, structural components, the arrangement and connection of the structural components, etc. shown in the following embodiments are mere examples, and are not intended to limit the scope of the present disclosure. Moreover, among the structural components in the following embodiments, structural components not recited in any one of the independent claims which indicate the broadest concepts of the present invention are described as optional structural components. Furthermore, the figures are schematic diagrams and are not necessarily precise illustrations. First, radioprotective unwoven fabric 1 according to Embodiment 1 will be described with reference to FIG. 1 and FIG. 2. FIG. 1 is a perspective view illustrating radioprotective unwoven fabric 1 according to Embodiment 1. FIG. 2 is a cross-sectional view illustrating radioprotective unwoven fabric 1 according to Embodiment 1. As illustrated in FIG. 1 and FIG. 2, radioprotective unwoven fabric 1 according to Embodiment 1 is a sheet having radioprotective effectiveness for shielding radioactive rays. In other words, radioprotective unwoven fabric 1 shields radioactive rays by blocking (completely shielding) or attenuating the radioactive rays. Radioprotective unwoven fabric 1 has a thickness of, for example, 5 to 20 mm, but is not limited to this thickness. Radioprotective unwoven fabric 1 according to Embodiment 1 is felt and a cloth-like sheet having flexibility. Accordingly, radioprotective unwoven fabric 1 can be folded like a cloth, and is not broken or chipped even when folded. Radioprotective unwoven fabric 1 has a structure in which metal fibers 2 are three-dimensionally and randomly stacked. Specifically, metal fibers 2 are interlaced and compacted. In Embodiment 1, metal fibers 2 are bonded by being interlaced without using an adhesive including resin. In consequence, even when folded, radioprotective unwoven fabric 1 is not folded by plastic deformation of each metal fiber 2, and radioprotective unwoven fabric 1 as a whole is allowed to easily return to a pre-folded shape like a fabric. Metal fibers 2 included in radioprotective unwoven fabric 1 each are a metal wire (metal wire material) including a metal material that is a shield material shielding radioactive rays and has a higher specific gravity than lead. Examples of the metal material having a higher specific gravity than lead include tungsten (W) and molybdenum (Mo). Such a metal material shields radioactive rays by absorbing the radioactive rays. In Embodiment 1, metal fibers 2 included in radioprotective unwoven fabric 1 include a tungsten wire (tungsten fiber). Each of metal fibers 2 may be a single strand of a tungsten filament (tungsten wire) or a composite strand of tungsten filaments made by twisting or paralleling two or more strands of tungsten filaments. In other words, each metal fiber 2 may be a monofilament fiber or multifilament fiber. Moreover, metal fibers 2 included in radioprotective unwoven fabric 1 may include a metal wire other than the tungsten wire, such as a molybdenum wire (molybdenum fiber). In this case, each of metal fibers 2 may be a composite strand made by twisting or paralleling a single strand of a tungsten filament and a metal wire of a different type, or may be a composite strand including a tungsten wire and a fiber other than a metal fiber (e.g., a chemical fiber). In Embodiment 1, metal fibers 2 included in radioprotective unwoven fabric 1 are only tungsten wires. A tungsten wire comprises, for example, pure tungsten (at a purity greater than 99.00%), but the purity of the tungsten wire is not limited to this. In Embodiment 1, tungsten wires comprising tungsten at a purity as great as almost 100% are used as metal fibers 2. Each metal fiber 2 is a ultrafine metal thin wire, and a diameter of metal fiber (metal wire) 2 is, for example, less than or equal to 1 mm. As an example, each metal fiber 2 has a diameter less than or equal to 150 μm, preferably less than or equal to 50 μm, still preferably less than or equal to 20 μm, or still further preferably less than or equal to 10 μm. In addition, each metal fiber 2 is a short fiber having a length of at least 10 mm and at most 100 mm. More preferably, metal fibers 2 having a length of at least 30 mm and at most 80 mm may be used. Next, a method for producing radioprotective unwoven fabric 1 will be described with reference to FIG. 3. FIG. 3 is a diagram illustrating the method for producing radioprotective unwoven fabric 1 according to Embodiment 1. First, metal fine particles 2a (metal powder) are prepared as illustrated in (a) of FIG. 3. Then, metal wire 2b is produced from metal fine particles 2a as illustrated in (b) of FIG. 3. Subsequently, metal wire 2b is cut to a predetermined length. Consequently, short metal fiber 2 can be produced as illustrated in (c) of FIG. 3. For example, when tungsten wires are produced as metal fibers 2, tungsten fine particles (tungsten powder) having a particle diameter of approximately 5 μm are prepared as metal fine particles 2a. Next, these tungsten fine particles are press-molded and sintered to be a tungsten ingot. Then, the sintered body of the tungsten ingot is swaged into a wire by being press-forged from its periphery and extended. After that, the wire is plastically deformed by being repeatedly drawn (wire drawn) using drawing dies having gradually reduced pore sizes, and is wound, thereby producing metal wire 2b (tungsten wire). Subsequently, metal wire 2b is sequentially cut to a length of at least 20 mm and at most 80 mm, thereby producing many tungsten wires as metal fibers 2. In Embodiment 1, metal fibers 2 are produced by cutting metal wire 2b to a length of approximately 20 to 30 mm. In this case, metal fibers 2 each may be produced by being cut as a monofilament or not as a monofilament. The tensile strength of the tungsten wires thus produced is increased as a result of work hardening by repeating drawing using dies in the process of making an ultrafine wire. In other words, the use of the tungsten wires makes it possible to obtain metal wires less likely to break even if the metal wires are made ultrafine. Moreover, although metal wires usually become more flexible with the increase in flexibility of the metal wires as a result of making the metal wires thinner, the tungsten wires become flexible when the diameter of the tungsten wires is approximately less than or equal to 100 μm. Next, metal fibers 2 resulting from the cutting are three-dimensionally and randomly stacked into a sheet. In Embodiment 1, an unwoven fabric that is sheet-like is produced by needle punching metal fibers 2. Hereinafter, a step of needle punching metal fibers 2 will be described in detail with reference to FIG. 4. FIG. 4 is a diagram illustrating the step of needle punching in the method for producing radioprotective unwoven fabric 1 according to Embodiment 1. As illustrated in FIG. 4, needle punching machine 100 is capable of processing metal fibers 2 into an unwoven fabric. Short metal fibers 2 are fed into feeder 110. Feeder 110 opens and stirs fed metal fibers 2 by flowing air, and supplies metal fibers 2 to a belt conveyor. Metal fibers 2 supplied to the belt conveyor are sent off in a certain amount by carding machine 120 etc. and supplied as web 2A to needle punching process machine 130. Needle punch 132 provided with needles 131 compacts metal fibers 2 (web 2A) supplied to needle punching process machine 130 while interlacing metal fibers 2. Specifically, by causing needle punch 132 to continuously move up and down at a high speed, needles 131 of needle punch 132 repeatedly pierce metal fibers 2 (web 2A). Here, tiny barbs provided to needles 131 interlace metal fibers 2. Accordingly, unwoven fabric 1A that is sheet-like and felted is formed. It should be noted that needle punching may be performed on stacked metal fibers 2 (webs 2A) according to the purpose or intended use. Elongated, sheet-like unwoven fabric 1A formed by needle punching process machine 130 is wound by wind-up roll 140. Subsequently, sheet-like radioprotective unwoven fabric 1 can be produced by drawing unwoven fabric 1A from wind-up roll 140 and cutting unwoven fabric 1A appropriately. It should be noted that needle 131 of needle punching process machine 130 breaks easily during processing, and needle 131 may get mixed in unwoven fabric 1A. In this case, although when, instead of metal fibers, chemical fibers are needle punched, a metal detector is capable of detecting and removing broken needle 131, the metal detector is incapable of detecting broken needle 131 in unwoven fabric 1A including metal fibers 2. For this reason, broken needle 131 mixed in unwoven fabric 1A can be detected and removed by determining a type of metal based on the magnetic field distribution of needle punched unwoven fabric 1A. Hereinafter, the advantageous effects of radioprotective unwoven fabric 1 according to Embodiment 1 will be described. A configuration in which metal fine particles are molded with resin is conceivable as a radioprotective sheet including metal fine particles such as tungsten fine particles. Such a radioprotective sheet can be produced as illustrated in, for example, FIG. 5. FIG. 5 is a diagram illustrating a method for producing a radioprotective sheet in which metal fine particles are molded with resin. Metal fine particles 2a such as tungsten fine particles are prepared as illustrated in (a) of FIG. 5. By molding metal fine particles 2a with resin and curing the resin, plate-like radioprotective sheet 1X can be produced as illustrated in (b) of FIG. 5. Radioprotective sheet 1X thus produced has radioprotective effectiveness corresponding to the amount of metal fine particles 2a contained. Radioprotecive sheet 1X, however, is broken or chipped when folded because radioprotective sheet 1X has a structure in which metal fine particles 2a are dispersed inside the cured resin. Moreover, it is difficult to use radioprotective sheet 1X produced by molding metal fine particles 2a with resin in a high-temperature environment because the resin melts at high temperature. In contrast, radioprotective unwoven fabric according to Embodiment 1 is a sheet in which metal fibers are three-dimensionally and randomly stacked, the metal fibers each comprising a metal material having a specific gravity higher than a specific gravity of lead. Radioprotective unwoven fabric 1 thus configured has superior radioprotective effectiveness and yet is not broken or chipped even when folded. Accordingly, radioprotective unwoven fabric 1 can be sewn in the same manner as a woven fabric and a knit fabric, thereby making it easy to produce a fiber product having superior radioprotective effectiveness. Examples of a fiber product made by sewing radioprotective unwoven fabric 1 include a garment, a hat, gloves, and a sheet. Examples of a garment include working clothes used in a working area and an ordinary garment such as a coat and pants, but the present disclosure is not limited to these examples. In particular, because radioprotective unwoven fabric 1 has the same texture as a cloth, radioprotective unwoven fabric 1 can be used for gloves, a product for around neck, etc. to give radioprotection to body parts of a person that are thin and require flexing. Furthermore, because radioprotective unwoven fabric 1 includes no resin, radioprotective unwoven fabric 1 does not melt even if radioprotective unwoven fabric 1 is used in a high-temperature environment. In addition, radioprotective unwoven fabric 1 has high strength and high resistance to cutting because radioprotective unwoven fabric 1 has a structure in which metal fibers 2 are three-dimensionally stacked and interlaced. For this reason, radioprotective unwoven fabric 1 is less likely to break even a knife is put to radioprotective unwoven fabric 1, and thus it is possible to use radioprotective unwoven fabric 1 as padding etc. for stopping the rotation of an electric chainsaw. Moreover, in radioprotective unwoven fabric 1 according to Embodiment 1, metal fibers 2 comprise a tungsten wire. With this, it is possible to easily achieve radioprotective unwoven fabric 1 that has superior radioprotective effectiveness and yet is not damaged even when folded. Moreover, in radioprotective unwoven fabric 1 according to Embodiment 1, each of metal fibers 2 has a diameter of at most 1 mm and a length of at least 20 mm and at most 80 mm. With this, it is possible to easily produce radioprotective unwoven fabric 1 that has superior radioprotective effectiveness and yet is not damaged even when folded. by, for example, needle punching metal fibers 2. Moreover, radioprotective unwoven fabric 1 according to Embodiment 1 is felt. With this, because radioprotective unwoven fabric 1 can be used as felt, a fiber product can be produced in the same manner as a felt cloth, by performing a conventional sewing process on radioprotective unwoven fabric 1. Hereinafter, radioprotective unwoven fabric 10 according to Embodiment 2 will be described with reference to FIG. 6 and FIG. 7. FIG. 6 is a plan view illustrating radioprotective unwoven fabric 10 according to Embodiment 2. FIG. 7 is a cross-sectional view illustrating radioprotective unwoven fabric 10 according to Embodiment 2. In radioprotective unwoven fabric 10 according to Embodiment 2, metal fibers 2 are made woolly and packed. For example, in radioprotective unwoven fabric 10, woolly metal fibers 2 are innumerably and randomly spread all over. Examples of a shape of woolly metal fibers 2 include an S shape, an O shape, a C shape, and a curved shape. As illustrated in FIG. 6 and FIG. 7, radioprotective unwoven fabric 10 according to Embodiment 2 is configured as a quilt including front cloth 11, back cloth 12, and padding 13, and metal fibers 2 bundled to be woolly are disposed as padding 13 between front cloth 11 and back cloth 12. In other words, woolly metal fibers 2 are packed between front cloth 11 and back cloth 12. Front cloth 11 and back cloth 12 are sewn with thread 14. In radioprotective unwoven fabric 10, metal fibers 2 are a shield material shielding radioactive rays, and like Embodiment 1, for example, tungsten wires can be used as metal fibers 2. In this case, woolly metal fibers 2 are cottony tungsten wool. As stated above, radioprotective unwoven fabric 10 according to Embodiment 2 is the quilt including front cloth 11, back cloth 12, and padding 13. In addition, metal fibers 2 are woolly and disposed as padding 13 of the quilt between front cloth 11 and back cloth 12. As described above, the use of woolly metal fibers 2 as the shield material for radioactive rays makes it possible to achieve radioprotective unwoven fabric 10 that has a high shield factor and yet can be easily folded. Moreover, woolly metal fibers 2 can be evenly spread all over by being packed. Furthermore, it is possible to reduce the degree of difficulty in downstream processing, by woolly metal fibers 2 being packed. It should be noted that woolly metal fibers 2 are packed by quilting in Embodiment 2, the present disclosure is not limited to this. Although the radioprotective unwoven fabrics according to the present disclosure have been described based on the aforementioned embodiments, the present disclosure is not limited to the aforementioned embodiments. For example, in the aforementioned embodiments, fiber products including the radioprotective unwoven fabrics are not limited to products wore by people, and may be products other than the products worn by the people, and the radioprotective unwoven fabrics is not limited for use in fiber products, and can be for use in products other than the fiber products. Moreover, the radioprotective unwoven fabrics are not limited to commercial products, and may be industrial products. For example, the radioprotective unwoven fabrics can be used as filters. In particular, the radioprotective unwoven fabrics according to the aforementioned embodiments have superior thermal resistance, and thus can be used as filters in a high-temperature environment. Moreover, since the radioprotective unwoven fabrics according to the aforementioned embodiments each include only the metal fibers and do not include an organic material such as a resin, the radioprotective unwoven fabrics according to the aforementioned embodiments can be used as chemical filters that transmit an acid solution, an alkaline solution, or the like. While the foregoing has described one or more embodiments and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings. |
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description | This application is a Continuation application of U.S. application Ser. No. 11/698,025 filed Jan. 26, 2007 now U.S. Pat. No. 7,566,871. Priority is claimed based on U.S. application Ser. No. 11/698,025 filed Jan. 26, 2007, which claims the priority of Japanese Patent Application No. 2006-027861 filed on Feb. 6, 2006, the content of which is hereby incorporated by reference into this application. The present invention relates to a method and an apparatus for inspecting an electrical defect of a microstructure circuit formed on a semiconductor wafer. As a method for detecting a defect of a circuit pattern formed on a wafer by comparing images in a manufacturing process of a semiconductor device, for example, a pattern comparing inspection method is disclosed in JP-A No. 258703/1993. The method uses an SEM in which, a point focused electron beam is scanned. The SEM type inspection apparatus is higher in resolution than optical inspection systems and it has a feature for enabling such an electrical defect as a connecting failure to be detected. However, because the SEM type inspection apparatus scans an electron beam on a specimen surface two-dimensionally to obtain an image, the scanning time is long. This disadvantage will become a substantial obstacle for reducing the inspection time. As an electron beam inspection method that has successfully reduced the inspection time, for example, the JP-A No. 249393/1995 discloses a projection type inspection apparatus, which illuminates a rectangular electron beam onto semiconductor wafer and forms an image of buck scattering and secondary electrons with use of electron lenses. The projection type inspection apparatus can illuminate an electron beam with a larger current than that of the SEM type at a time, thereby obtaining a plurality of images collectively. The projection type is thus expected to form images more quickly than those of the SEM type, that is, the scanning electron type. On the other hand, a secondary electron mapping type inspection apparatus cannot obtain a sufficient resolution due to the aberration of the objective lens, thereby it is difficult to obtain a required defect detection sensitivity. The JP-A No. 108864/1999 points out such disadvantages of the apparatus. The JP-A No. 108864/1999 discloses a mirror electron imaging type wafer inspection apparatus that uses electrons pulled back (hereunder, to be referred to as mirror electrons or mirror reflecting electrons) before colliding with a specimen due to a negative electric field formed just above the wafer as imaging electrons. Here, the mirror electron imaging type wafer inspection apparatus will be described. The mirror electron imaging type wafer inspection apparatus obtains an image to be used for inspection with use of a mirror electron microscope. An inspection image is obtained by illuminating an electron beam onto a specimen and forms an image of the reflecting electron beam. At this time, a negative potential is applied onto the surface of the specimen in advance so that the illuminated electron beam is reflected on a specific equipotential surface in the vicinity of the specimen surface without reaching the specimen surface. The electrons reflected on an equipotential surface in the vicinity of the specimen surface such way are referred to as “mirror electrons”. Because the equipotential surface of the specimen surface is influenced by the information of an unevenness and a potential change of the specimen surface itself, the image to be obtained is also influenced by the information of the unevenness and the potential change of the specimen surface when the mirror electrons are imaged. Consequently, shape and electrical defects of the specimen surface can be detected by comparing such a mirror electron image with a reference image, respectively. As described above, the mirror electron imaging type wafer inspection apparatus differs completely from any of the conventional SEM type inspection apparatuses. Consequently, to put the mirror electron imaging type wafer inspection apparatus for practical use, it is needed to think out a method for setting inspection conditions optimized for the apparatus. Under such circumstances, it is an object of the present invention to realize an inspection condition setting method optimized for the object mirror electron imaging type wafer inspection apparatus and make it easier to operate the apparatus. Upon thinking out a method for setting such inspection conditions optimized for the mirror electron imaging type wafer inspection apparatus, the present inventor has examined the following circumstances. A mirror electron imaging type wafer inspection apparatus employed in a semiconductor device manufacturing line is often used for defect inspection in all or some specific portions of every wafer flowing on the manufacturing line. Thus where an inspection process is to be inserted between semiconductor processes and how long time is to be spared for the inspection process should be determined carefully by giving consideration to the productivity of the semiconductor manufacturing line. In other words, if the inspection process is designed in detail to improve the yield, the productivity is lowered in proportion to an increase of the inspection time. Furthermore, when the inspection time is reduced, both the inspection accuracy and the productivity are lowered. Such way, in each of various manufacturing lines for improving the productivity, in which the defect generating rate, defect generating process, and productivity are different from each another, there is an optimized inspection time that should be employed for the object line specifically. Thus the inspection time comes to be varied among those manufacturing lines. This is why the inspection speed should be set flexibly for the mirror electron imaging type wafer inspection apparatus so as to make inspections most efficiently by giving consideration to the circumstances specific to each of such various semiconductor device manufacturing lines. The inspection speed of the mirror electron imaging type wafer inspection apparatus means an area of a wafer that can be inspected per unit time. FIG. 2 shows the arrangement of pixels for composing an inspection object image. In FIG. 2, each cell means a pixel 201. The call is usually a square of which the length of this side is represented by D. An inspection image of the mirror electron imaging type wafer inspection apparatus is obtained with use of a time delay integration data acquisition method (TDI method). In the TDI method, integration is made by sending image signals in the vertical direction of the image synchronously with the movement of the wafer (as shown with a white arrow in FIG. 2). The cycle in which one signals of pixel are sent in the vertical direction is defined as P. And the length in a direction (horizontal direction in FIG. 2) normal to the movement of the wafer in the image region is defined as L. The image data of length L×width D area (gray region shown in FIG. 2) is sent in a cycle P to an image processing apparatus. Consequently, the inspection speed S can be described by using D, P, and L in the following expression:S=D×L×P. To operate the apparatus at an optimized speed, therefore, the user is requested to satisfy the relationship among D, L, and P shown above and adjust the D, L, and P values so as not to degrade the inspection sensitivity. Particularly, in the case of the mirror electron imaging type wafer inspection apparatus, the pixel size optimized for inspection is changed depending on the magnification of the imaging optical system for mirror reflecting electrons. This change depends on the characteristics such as the material, structure, etc. of the specimen. And such characteristics are never generated in any of SEM and secondary electron projection type electron optical systems; the characteristics are specific to the mirror optical systems. The user of the apparatus, therefore, is requested to adjust the D, L, and P values by giving consideration to the magnification of the optical system. Conventionally, the apparatus manager and the apparatus developer have set such D, P, and L values with the method of trial and error by giving consideration to the characteristics of the mirror electron imaging type wafer inspection apparatus and the inspection object, which has leads very troublesome condition setting. Furthermore, usually the user's interest is just the inspection speed. The user would thus feel very troublesome when requested to set such conditions and will come to have a feeling of confusion when operating the apparatus. In order to solve the above described conventional problems, therefore, the present invention has enabled such S, D, L, and P values to be displayed on an operation screen so that the user can examine such conditions as inspection speed, inspection sensitivity, etc. intuitively. Furthermore, the present invention has provided a process newly for converting user determined conditions to conditions for operating an electron optical system, a time delay integration type imaging device, and a wafer moving stage respectively so that the user can make inspections in accordance with the circumstances of various semiconductor manufacturing lines without understanding the details of the inspection apparatus. According to the present invention, therefore, it is possible to set such conditions as optimized pixel size, illuminating area size, etc. to easily realize an inspection speed capable of preventing an semiconductor device manufacturing line from delay so that the user can inspect defects of each semiconductor pattern efficiently under optimized conditions. Because such inspection conditions can be set easily such way, the total inspection time from condition setting to end of inspection can be reduced. And because the apparatus can be operated easily, the apparatus will also have advantages in sales policy. Hereunder, a description will be made in detail for a configuration of a mirror electron imaging type wafer inspection apparatus in a preferred embodiment of the present invention with reference to the accompanying drawings. FIG. 1 shows an example of a hardware configuration of the mirror electron imaging type wafer inspection apparatus in the preferred embodiment of the present invention. In FIG. 1, vacuum pumps, their controller, pipes for evacuating systems, etc. are omitted. At first, main elements of the electron optical system of the apparatus will be described. An illuminating electron beam 100a emitted from an electron gun 101 is focused by a condenser lens 102 and deflected by an ExB deflector 103 to form a cross-over 100b, then illuminated onto a specimen wafer 104 as an approximate parallel flux. In FIG. 1, although only one condenser lens 102 is used, a plurality of lenses may be combined into a lens system to optimize the optical conditions. The electron gun 101 is usually a Zr/0/W type Schottky electron source. Such voltages and currents as an extracting voltage applied to the electron gun 101, an accelerating voltage to extracted electrons, a heating current of an electron source filament, etc. required for operating the apparatus are supplied and controlled by an electron gun controller 105. The ExB deflector 103 is disposed in the vicinity of an imaging plane 100d of an imaging electron beam 100c. At this time, an aberration occurs in the illuminating electron beam 100a due to the ExB deflector 103. If this aberration must be corrected, another ExB deflector 106 for correcting the aberration is disposed between an illuminating system condenser lens 102 and the ExB deflector 103. The illuminating electron beam 100a deflected by the ExB deflector 103 so as to go along an axis perpendicular to the wafer 104 is formed by an objective lens 107 as a planar electron beam entered in a direction perpendicular to the surface of the specimen wafer 104. On the focal plane of the objective lens 107 is formed a finer cross-over by the illuminating system condenser lens 102. Thus the electron beam can be illuminated onto the specimen wafer 104 just in parallel. A region of the specimen wafer 104, in which the illuminating electron beam 100a is illuminated, is an area as large as, for example, 2500 μm2, 10000 μm2, or the like. The specimen wafer 104 mounted on a wafer stage 108 receives a negative voltage almost equal to or slightly higher larger absolute value than the accelerating voltage of the electron beam. This negative potential works on the illuminating electron beam 100a so that it slows down just before reaching the wafer 104 and pulled back upward to become as reflecting mirror electrons, thereby it does not collide the wafer 104 in most cases. The voltage applied to the wafer 104 is supplied and controlled by a wafer voltage controller 109. In order to make the illuminating electrons reflected in the vicinity of the wafer 104, a difference from the accelerating voltage of the illuminating electron beam 100a is required to be adjusted accurately and the wafer voltage controller 109 and the electron gun controller 105 are controlled so that they are interlocked with each other. Mirror electrons flying from the wafer side includes information related to an electrical defect of an object circuit pattern formed on the wafer 104. Thus its image is formed with use of an electron imaging optical system to be fetched in the apparatus as an image for determining whether there is a defect in the pattern or not. The mirror electrons are focused by the objective lens 107. And the ExB deflector 103 is controlled so as not to deflect an electron beam advancing from below, so that the mirror electrons go up perpendicularly as are, then magnified and projected by an intermediate lens 110 and a projection lens 111 at an image detection part 112. In FIG. 1, only one projection lens 111 is used, but a plurality of lenses may be composed into a projection system to provide a higher magnification and correct distortions of images. The image detection part 112 converts an image to an electrical signal and sends a distribution of the local charging potential of the surface of the wafer 104, that is, a defect image to an image processing part 112. The electron optical system is controlled by an electron optical system controller 113. Next, the image detection part 112 will be described. A fluorescent plate 112a, an optical image detector 112b, and an optical image transmission system 112c are used for optical coupling to convert a mirror electron image to an optical image and detect the image. In this embodiment, an optical fiber bundle is used as the optical image transmission system 112c. The optical fiber bundle consists of the same number of thin optical fibers as the number of pixels and it can transmit optical images efficiently. In case where a fluorescent image is used with a sufficient light, the optical transmittance may be set lower. In such cases, instead of the optical fiber bundle, an optical lens is used and an optical image on the fluorescent plate 112a is formed by the optical lens on a light detecting surface of the optical image detector 112b. Furthermore, an amplifier is inserted in the optical image transmission system to transmit an optical image with a sufficient light. The optical image detector 112b converts an optical image formed on the light receiving plane to an electrical image signal and outputs the signal. As the optical image detector 112b, an TDI sensor is used. The TDI sensor uses a time delay integration (TDI) type CCD. The image processing part 116 is composed of an image memory 116a and a defect determination part 116b. The image memory 116a inputs electron optical condition, image data, and stage position data from the electron optical system controller 113, the image detection part 112, and the stage controller 115 respectively and stores the image data by relating it to the coordinate system used on the specimen wafer. The defect determination part 116b uses image data related to the coordinates on the wafer and compares it with a preset value or with an adjacent pattern image or an image of the same pattern position in an adjacent die, or the like with use of various defect determination methods so as to determine a defect. The defect coordinates and an intensity of its corresponding pixel signal are transferred to and stored in the inspection apparatus controller 117. The user sets any one of those defect determination methods or the inspection apparatus controller 117 selects a method corresponding to the object wafer type in advance. The inspection apparatus controller 117 inputs/outputs conditions for operating each part of the apparatus. The inspection apparatus controller 117 inputs beforehand various preset conditions such as electron beam accelerating voltage, current conditions for electron optical devices, wafer stage moving speed, timing for acquisition an image signal from an image detection element. The inspection apparatus controller 117 controls the controller of each element as an interface with the user. The inspection apparatus controller 117 may be composed of a plurality of computing devices connected to each another through a communication line and having a specific function. The apparatus further includes user interface device 118 with a monitor. In the mirror electron imaging type wafer inspection apparatus, the electron beam hardly collides with the object wafer. Thus the specimen wafer may not be charged sufficiently in some cases. To detect an electrical defect, however, the wafer must be charged sufficiently to cause a difference from that of normal parts. The present invention has solved this problem by mounting pre-charging devices 119a and 119b. Those devices are controlled by a pre-charging controller 120. A charging potential formed on the wafer by the pre-charging devices 119a and 119b is used not to disturb the status of the electron beam that is reflected in the vicinity of the wafer surface. Thus the pre-charging controller 120 is interlocked and controlled together with the wafer voltage controller 109 and the electron gun controller 105. FIG. 3 is a first embodiment of a screen on which the user operates the inspection apparatus. This screen 301 is an “inspection condition setting screen” on which the user select an inspection speed and an inspection sensitivity or part of the screen. The screen 301 belongs to the user interface device with a monitor 118. A graph 302 displayed on the screen 301 has a horizontal axis that indicates a pixel size D and a vertical axis that indicates an inspection speed S. In the graph 302, the inspection speed S means an area on a wafer surface to be inspected per unit time and it is represented by an inspection area (cm2/h) per hour. The user may select this unit to make it easier to understand. For example, the unit may be the number of wafers to be processed per hour or an inverse number to define a processing time of one wafer and a time required for a unit area inspection (e.g., h/cm2). In the graph 302, a range from 0 cm2/h to 600 cm2/h is shown. The pixel size D is represented by a value corresponding to an actual size on the object wafer. It is within a range from 0 nm to 250 nm. The graph 302 also has a plurality of characteristic straight lines 303. These straight lines are used for different cycle P values of the TDI sensor respectively. The graph 302 uses values of 100 to 700 kHz selected as P values. The width L of an inspection image is displayed on an inspection image width display part 304. In this example, it is set as 60 μm. A plurality of conditions are displayed as a pull-down menu for this value when the user clicks the selection arrow 305. The user can select and change any of the conditions. If the user selects another value, a newly calculated straight line is displayed as shown in FIG. 4. FIG. 4 shows an example in which 120 μm is selected as an L value. The L value has its upper limit, which depends on the aberration of the objective lens. If the value goes over 200 μm, the distortion and the resolution degradation in marginal area of the field of view advance significantly. Consequently, the upper limit of the field of view usable as an inspection image is about 200 μm×200 μm. The user can search an inspection speed and a pixel size by moving a white arrow pointer with a mouse on the graph 302. The values of the inspection speed, pixel size, TDI cycle calculated from the position of the pointer on the graph 302 are displayed in a display field 307 at the bottom of the screen. The user can select conditions with reference to such concrete values. In the graph 302, not only the values on straight lines, but also values between straight lines are calculated from the pointer position and displayed. When conditions are determined on the graph 302, the user clicks the mouse button (not shown) or press a specific key on the keyboard (not shown) to fix the conditions. Those conditions are sent to the controller of the inspection apparatus when the user clicks the [ENTER] button 308 on the screen, then those conditions are converted to detailed operation conditions of the apparatus. Each of those conditions has its upper limit, which depends on the specifications of the apparatus. For example, if P=700 kHz is the upper limit in the specifications of the TDI camera and a condition is set in a region over 700 kHz, the condition is ignored. The user can determine values of a set of the pixel size, inspection image width, and TDI sensor operation cycle with reference to the drawing. Using the condition setting method in this embodiment makes it possible for the user to set an inspection speed of the mirror electron imaging type wafer inspection apparatus without trial and error. In the first embodiment, the user determines conditions for operating the inspection apparatus with reference to mainly the values of inspection speed and pixel size and the relationship between the defect detection sensitivity and the pixel size is not clear. In this second embodiment, therefore, the horizontal axis of the graph displayed on the inspection speed S setting screen is used for defect detection sensitivity, thereby the user comes to know the relationship between the defect detection sensitivity and the pixel size intuitively. Instead of the horizontal axis, the vertical axis may also be used for the defect detection sensitivity. FIG. 5 shows a schematic diagram of the inspection speed S setting screen displayed on the user interface device with a monitor 118 of the mirror electron imaging type wafer inspection apparatus. The user operation screen shown in FIG. 5 is displayed on the monitor of the mirror electron imaging type wafer inspection apparatus or mirror electron imaging type specimen inspection apparatus. Unlike that shown in FIG. 3, the horizontal axis of the graph 501 is used for the defect detection sensitivity. Explanations of the same items such as the pointer, the characteristic curve, etc. as those shown in FIG. 3 will be omitted to simplify the description. The relationship between the pixel size and the defect detection sensitivity is based on the magnification function of defect images specific to the mirror electron imaging type wafer inspection apparatus. An inspection object image of the mirror electron imaging type wafer inspection apparatus is obtained by imaging a distortion of an equipotential surface caused by existence of a defect. FIG. 6 is a diagram for describing principles of such mirror electron imaging. FIG. 6A shows a view of an equipotential surface 603 and a view of a trajectory 604 of illuminating electrons reflected from the equipotential surface 603 when such a protruded defect 601 as a particle and such a recessed defect 602 as a scratch are detected on the object wafer surface. FIGS. 6B and 6C are diagrams for showing a distortion of the equipotential surface 606 and a trajectory 607 of illuminating electrons when connecting failure defects 605a and 605b exist in vias 605 used for connecting to the lower layer wiring embedded in an oxide film respectively. In FIG. 6B, the electrically open via 605a is negatively charged. In FIG. 6C, the open via 605b is positively charged. In any of the unevenness caused by the shape and the electrical difference of the wafer surface, the distortion of the equipotential surface appear more widely than the actual size of the defect. In addition, when the equipotential surface is positioned higher, the distortion spreads widely while the distortion level is low. Consequently, a larger image is obtained when compared with the actual defect size by adjusting the mirror electron imaging optical system. This means that defects can be detected even when defect images are obtained with pixels larger than the actual defect size. FIG. 7 is an example of an inspection image obtained with use of a mirror electron imaging method. FIG. 7A shows a schematic diagram of a circuit pattern. This pattern consists of 200 nm×200 nm square vias 702 embedded in an oxide film 701 and composed like a matrix patterns arranged in 5 rows×5 columns at pitches of 800 nm. Each normal via is continued to a wiring 703 in the lower layer. FIG. 7B is an inspection image, that is, a mirror electron image obtained with use of a mirror electron imaging method. The size of the via patterns in this mirror electron image, except for the center one, is as large as 600 nm, which is about 3 times the actual one. This magnification is made due to a distortion of the equipotential surface caused by a difference of voltage between the via voltage and the voltage of its peripheral insulation film. In the mirror electron image shown in FIG. 7B, the center via 704 has a disconnect defect and its voltage differs from that of other normal ones by about +1.5V. The size of the mirror electron image of this defect via 704 is about 1200 nm, which is about double that of a normal via and magnified up to 6 times that of the actual via pattern. It can thus be concluded from those data that the size of a mirror electron image is magnified to from 3 times to 6 times the actual size due to the via voltage. According to this result, in this embodiment, it is expected to be able to detect defects of patterns up to ⅓ of the pixel size and the horizontal axis of the graph 501 for the inspection speed is displayed for the detection sensitivity, which is ⅓ of the pixel. The value indicated by the horizontal axis of the graph 501 shown in FIG. 5 is converted from the value indicated by the horizontal axis of the graph 501 shown in FIG. 3 on the basis of the above detection sensitivity information. The calculation for converting a value of the horizontal axis or vertical axis such way is executed by a computing device built in the inspection apparatus controller 117 or user interface device with a monitor 118. In the same way, the relationship between the detection sensitivity and the pixel is stored in the memory means built in the inspection apparatus controller 117 or in the user interface device with a monitor 118. As the memory means, for example, any of a memory, a hard disk, etc. may be used. Next, a description will be made for how to transmit such conditions as user specified inspection speed, etc. to the electron optical system and the wafer stage. FIG. 8 shows a schematic diagram of a hardware configuration of a mirror electron imaging type wafer inspection apparatus in this embodiment. In FIG. 8, the same reference numbers will be used for the components of the same functions and operations as those shown in FIG. 1. In the mirror electron imaging type wafer inspection apparatus shown in FIG. 8, the inspection apparatus controller 117 is provided with a conversion part 801. Conditions for inspection operations inputted by the user through the user interface device 118 are sent to the inspection apparatus controller 117. In this embodiment, the inspection apparatus controller 117 is provided with a condition conversion part 801. Conditions inputted through the user interface device with a monitor 118 are values of the pixel size D, inspection speed S, TDI camera image acquisition cycle P, and size of the field of view L. The moving speed Vs of the wafer stage 108 is calculated on the basis of those values. The Vs is determined by the following relational expression according to the TDI camera image acquisition cycle P and the pixel size D.Vs=P×D This Vs value is sent to the stage controller 115. The stage controller 115 controls a stage driving mechanism by monitoring the stage position information received from the position detector 114 so as to keep the speed Vs while the stage is moving. The TDI camera image acquisition cycle P is sent to the condition conversion part 801 as is. The condition conversion part 801 controls the TDI camera image acquisition cycle so that the image acquisition is synchronized with the stage movement. The pixel size D, as well as a preset pixel size Dp on the TDI camera light detecting surface are used to calculate a magnification Dp/D of the imaging electron optical system. The magnification Dp/D of the imaging electron optical system is sent to the electron optical system controller 113 and used to control the voltage and the electromagnet current applied to the objective lens 107, the intermediate lens 110, and the projection lens 111 respectively. The voltage and current conditions of each electron optical element of the imaging optical system with respect to the magnification of the imaging optical system are stored as a numerical table beforehand in the electron optical system controller 113 or condition conversion part 801. The voltage and current conditions are determined with reference to those values in the table. If a magnification value that is not stored in the table is referred to, current and voltage values are determined by interpolating the values for the nearest magnification value. The condition conversion part 801 or electron optical system controller 113 stores a numerical table that records conditions of both the condenser lens 102 and the objective lens 107 with respect to the size of the field of view L. And upon a user's determination for the size of the field of view L, the voltage and current values of the illuminating electron optical system are referred to from the numerical table for controlling. With such a configuration, the user selected inspection conditions are reflected correctly in the inspection apparatus. As described above, therefore, in this embodiment, the user can set such inspection conditions as inspection speed and defect detection sensitivity as parameters. Consequently, the user can operate the apparatus more easily. In the second embodiment, a description is made for a user operation screen on which the defect magnification is set as 3 times. This third embodiment enables the user to change the defect magnification. FIG. 9 shows a user operation screen in this third embodiment. The user operation screen shown in FIG. 9 is displayed on the monitor of the mirror electron imaging type wafer inspection apparatus or mirror electron imaging type specimen inspection apparatus. In this third embodiment, the description for the same components as those shown in FIG. 5 will be omitted. In FIG. 9, there is only a difference from that shown in FIG. 5; a defect magnification selection field 901 is provided. The user can select a magnification from a plurality of defect magnification values by clicking the arrow in the defect magnification selection field 901. The value of the horizontal axis of the graph 902 is corrected by the selected defect magnification, thereby the displayed characteristic curve is also corrected. The user can change the defect magnification according to the objective lens focal condition, the height of the equipotential surface for reflecting mirror electrons, etc. in the mirror electron imaging. A mirror electron image is always formed due to a distortion of the equipotential surface even when the defect type is an uneven surface or a voltage variation caused by an electrical defect. Consequently, the user can estimate a defect image magnification in advance by using the height of the equipotential surface for causing mirror reflection of electrons and focal conditions of the objective lens as parameters. For such an estimate, the user is just requested to obtain a mirror electron image with respect to a different focal point of the objective lens and a different voltage potential value of the wafer and measure a magnification according to the actual defect size by using an Si wafer of which size is already known and having a protruded or recessed shape defect that is already processed. If the defect type is not such a shape defect, but it is a potential variation, a voltage that causes the equipotential surface to be distorted as much as a distortion generated by a protruded or recessed shape may be calculated by computer simulation and adjusted precisely with the relationship between the electron optical condition and the magnification in the shape defect. Because such calculation of a level of a distortion of an equipotential surface with respect to a voltage is simple calculation of an electrical field, it is so easy. Instead of using a standard specimen as described above, it is also possible to analyze a trajectory of electrons by computer simulation and change the condition of the objective lens, thereby calculating an image to be obtained, then obtaining a relationship with a magnification. In this embodiment, the inspection apparatus is provided with an inspection condition evaluation device 1001 for holding a table that stores a condition of the objective lens, a negative voltage value to be applied to each wafer to change its equipotential surface used for mirror reflection, and a defect magnification obtained as described above. FIG. 10 shows a schematic diagram of a system provided newly with the inspection condition evaluation device 1001. When an inspection is made with a defect magnification using this inspection apparatus, the equipotential surface for reflecting mirror electrons must be kept constant. Thus it is important to keep the wafer surface potential constant. This is why pre-charging devices 119a and 119b are used. Those charging devices are controlled by a pre-charging controller 120. For example, assume now that a wafer is passed under the pre-charging device, then just under the objective lens and moved just under the pre-charging device 119b. In such a case, the wafer surface potential is set to a prescribed potential by the pre-charging device 119a. This potential makes it possible to obtain a desired defect magnification. The potential is given from the numerical table of the inspection condition evaluation device 1001 and controlled by the pre-charging controller 120. As the pre-charging device, for example, such an electron beam illuminating device as a flood gun may be used. After the wafer passes just under the objective lens, the disturbance of the equipotential surface potential, caused by slight charging of the wafer when in observation of mirror electrons, must be eliminated so to as return the potential to a required level with use of the pre-charging device 119b again. According to this third embodiment, therefore, it is possible to optimize the such conditions as the inspection time including the user specified defect magnification, thereby the object semiconductor manufacturing line can be managed efficiently. Although a description has been made for the preferred embodiments of the present invention, the present invention also includes a combination of the first to the third embodiment described above. |
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abstract | A coating is applied to a work piece in a charged particle beam system without directing the beam to work piece. The coating is applied by sputtering, either within the charged particle beam vacuum chamber or outside the charged particle beam vacuum chamber. In one embodiment, the sputtering is performed by directing the charged particle beam to a sputter material source, such as a needle from a gas injection system. Material is sputtered from the sputter material source onto the work piece to form, for example, a protective or conductive coating, without requiring the beam to be directed to the work piece, thereby reducing or eliminating damage to the work piece. |
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041742540 | abstract | A hub for bucking horizontal forces of a fusion reactor is formed of a plurality of horizontal pancake elements. A coolant flow-path is formed between adjacent surfaces of the pancakes, and interconnection of these is by a limited number of vertical openings through the pancakes. |
047524340 | description | DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Referring to FIGS. 1-3, a coupling device is suitable for use in a nuclear reactor comprising a pressure vessel whose cover (not shown) is traversed by sleeves which each receive, externally to the vessel, means for controlling the movement and the position of a control bar. The fixed internal equipment of the reactor comprises, in alignment with each sleeve, a tubular guide 10, a fraction of which is shown in FIG. 1. Guide 10 is generally secured to the upper core plate which is placed above the nuclear fuel assemblies (not shown) during operation of the reactor. Referring to FIGS. 1-3, the coupling device of the invention is for connecting the upper part of a control bar 12, only the top end of which is shown, to a drive mechanism 14. The bar 12 comprises a "spider" not shown in the Figure, which has an upwardly projecting pommel 16 whose enlarged head has a downwardly turned frustoconical bearing surface 18. The extension of the spider is also formed with an upwardly directed frustoconical bearing face 20. Due to the use of conical surfaces, lateral contact reactions may be taken up and self centering of the sleeve and of the pommel is achieved, as will be seen later. The mechanism 14 comprises a sleeve 22 having a sliding fit in the tubular guide 10 and a drive shaft 24 which extends upwardly through the sleeve so as to co-operate with the means controlling the movement and position of the bar. As shown in FIG. 1, sleeve 22 and control rod 24 are fast with each other. Sleeve 22 bears on the tubular guide 10 through guide shoes 26 and 28 spaced apart from each other so as to withstand rocking torques. The coupling device further comprises a gripper body 30 movable longitudinally within and along sleeve 22. The gripper body is formed with a plurality of downwardly directed resilient gripping fingers 32. Each finger has a groove for locking on the pommel 16 and bearing on surface 18, as shown in FIG. 1. A core piece 33 placed in the body, between the fingers, limits the extent of flexure of the fingers. An annular recess 34 formed in sleeve 22 has dimensions such that the fingers may bend outwardly and release the pommel 16 whe the lower enlarged part of the fingers faces the recess. When, on the other hand, the enlarged part is located above the recess 34, as shown in FIG. 1, the fingers are held locked on pommel 16. Prestressing of the coupling device is provided by a spring 36 compressed between an internal flange 38 of the sleeve and an endmost plate 40 of a tube 42 coaxial with the drive shaft 24 and placed inside the latter. The compression force of spring 36 is transmitted from tube 42 to the gripper body 30 through an axial rod 44 having means for retaining it on the tube in the position shown in FIG. 1. In this position, tube 42 transmits the force exerted by spring 36 to the axial rod 44 and that force biases the resilient fingers 32 away from the endmost frustoconical surface 20 of sleeve 22. It will be appreciated that rod 44 pulls the gripper body 30 upwardly. The maximum inertial force exerted on the total mass gripped by the gripper may be readily balanced with an acceptable prestressing force. The fingers 32 of the gripper are firmly retained by their sliding abutment on the internal surface of the sleeve and they practically cannot bend, so that in practice they are subjected to a tractive force only. Alternate bending of the fingers is practically eliminated. The distance between surfaces 18 and 20 may be largely sufficient for absorbing the rocking torques under good conditions. Buckling of tube 42 is of no consequence since it is limited by the tubular drive shaft 24 which is subjected to tractive stresses by the load which it supports. The means for retaining rod 44 in abutment on tube 42 may have different constructions, for example that shown schematically in FIGS. 2 and 3 formed by keys 46 integral with rod 44 and slidably received in grooves 48 formed in the upper part of tube 42. The keys are retained by the upper surface of tube 42 when they are rotated after having been lifted above the level of the upper surface with a tool (not shown). When it is desired to avoid transmititng compression forces along the drive mechanism, the embodiment shown in FIGS. 4 to 8 rather than that of FIGS. 1 to 3 may be used. In FIGS. 4-8, the parts corresponding to those already shown in FIG. 1 are designated by the same reference number. The coupling device again comprises a gripper body 30 with a plurality of resilient fingers 32, generally four in number. When the coupling device is locked, endmost parts of the elastic fingers clamp the head of the pommel 16 and are retained by the wall of the bore in sleeve 22. As shown in FIG. 4, members for transmitting the force exerted by the prestressed spring are slightly more complex than in the first embodiment. (a) One of the ends of the prestressed spring 36 is in abutment against a slider 50. This slider is mounted with a sliding fit in an internal sleeve 52 of the gripper body 30, formed from several pieces assembled together. Radial slots in the slider contain three lockng cams 54 which are arranged so that a plunger 56 fixed to the end of the axial rod 44 may force them radially outwardly into a position where they retain the lower end face of sleeve 52. The plunger 56 is fixed to the base of the axial rod 44 while slider 50 is fixed tthe base of tube 42 which, contrary to the tube 42 in FIG. 1, does not have to transmit the forces exerted by the prestressed spring 36. (b) The other end of spring 36 has an abutting connection wit a slide 58 interlocked to sleeve 22 by a transverse pin 60. The tubular drive shaft 24, separated from sleeve 22, extends along a sleeve 61 which contains the means for controlling the movement and position of the bar. Such means will not be described, for they may have any conventional construction, such as that already described in the above-mentioned French Patent. Referring to FIG. 5, the three coils 62 which operate axially movable pole pieces and ratchets 64 co-operating with grooves 66 on shaft 24 for moving the shaft are partially illustrated. Referring to FIG. 5, rod 44 and tube 42 project upwardly beyond the tubular control rod 24. When the device is prestressed, the position of rod 44 with respect to tube 42 is determined by its abutment against a spring 68 of high stiffness so that its amount of deformation under stress will always remain small. Abutment is maintained by a return spring 70 which is of moderate (lower) stiffness. The two springs co-operate so as to absorb possible differential expansions between the central rod 44 and tube 42 due to heat. When the device is locked and under prestress, a fixed point of the central rod 44 is formed by the plunger 56 retained by abutment against the three locking cams 54. By way of example a possible construction of the upper part of cluster 12 has been shown in FIG. 4. Spider 72 carrying the rods of neutron absorbing (or spectral shift material) is provided with a damper 76. The upper core plate 77 which carries the tubular guides 10 can also be seen in FIG. 4. Since the operation of the device appears from its construction, only a very summary description thereof will now be given. Uncoupling a. The uncoupling sequence is as follows. First of all the control bar 12 is lowered until it is in the position shown in FIG. 4. Using a tool (not shown) which grips an endmost swelling 78 of rod 44, after opening the sleeve containing the electromagnetic means, the control rod 22 is slightly raised and tube 42 is pushed back so as to free the locking cams 54 which no longer receive the reaction of the abutment sleeve 52. The locking cams no longer exert a force on the plunger 56. The tool may the pull the central rod 44 upwards by overcoming only the force exerted by the return spring 70 of moderate stiffness. As soon as the small diameter part of plunger 56 is in front of the locking cams 54, these latter may rock inwardly to completely release the gripping body 30. if the tool continues to raise the central body 44, this latter takes tube 42 along with it. When the cams pass over the conical ramp of sleeve 52, they are pushed back inwardly of the slider 50 and retract before sliding along the bore of sleeve 52. During the lifting movement, slider 50 intercepts slide 58 and consequently drives sleeve 22 in its rising movement as far as a top end-of-travel position. Recess 34 in sleeve 22 is then opposite the enlarged portions of the resilient fingers 32 which may move apart for releasing pommel 16: the cluster slides downwards under the action of its own weight. b. When the tool continues to raise the central rod 44, tube 42 and the tubular control rod 24 accompany it in its movement. The sleeve is thus raised above the pommel. The tool may then lower sleeve 24 hitched to slider 50 to a low abutment position defined by an upper collar of slider 58 (FIG. 4). The prestress spring is relaxed and the locking cams are a little below sleeve 52. The central rod 44 may then be lowered by the tool. The tool may finally lock the control rod in the internal equipment in a low position, by means not shown which may be of a type known per se. It can be seen that once the separation is achieved, sleeve 22 is in a low position, with the gripping fingers 34 closed again. Coupling From the state thus reached, the coupling operations take place in the reverse order of the preceding ones. At the beginning of the operation, the resilient fingers 32 are facing recess 34 in sleeve 22 and may move freely apart. The operations (b) are carried out in a reverse order. The movable assembly comprising sleeve 22 and the rods moves down as shown by arrow F in Figure 8. If, in the initial state, pommel 16 is not correctly aligned, the bearing force of the conical end face of sleeve 22 recenters it during engagement of the sleeve. When the resilient fingers come into contact with the head of pommel 16, they are pushed back outwardly by the conical surface of this head, pass beyond the gripping projection, then close again in the groove which follows it. The top of the pommel then comes into contact with the core piece 33. At the end of lowering of the control rod 24, this rod rests on the pommel through the core piece 33. The operations (a) are then carried out also in a reversed order then the tool may be removed. The device which has just been described further comprises means for guiding the control bar in all its positions. When the bar is in a position in which the pommel is situated outside the tubular guide 10, the bar is guided by shoes 26 and 28 of the sleeve. The distance between the abutment surfaces is then relatively small. But this situation, which is not the most favorable from the point of view of absorption of the torques, only exists when the control bar is almost totally engaged in the core and when the abutment takes place at the low part of the tubular guide, which undergoes no appreciable wear. During normal operation of the reactor, the pommel is always entirely engaged in the channel. In this case, guiding is provided by the upper shoe 26 and by a shoe 80 placed at the bottom of the spider. So that shoe 28 does not disturb the guiding, it is given a diameter slightly smaller than that of shoe 80. In this case, the distance between abutments is considerable, which reduces correspondingly the abutment forces required for absorbing the torques applied. The invention is susceptible of numerous other embodiments. For example, instead of placing the spider 72 in the immediate vicinity of the core plate 74 increasing the flexibility of the part of the rods situated above the core, it is possible to provide a spider situated in the immediate vicinity of the core when the bar is completely engaged. Other locking and unlocking solutions than those which have been described by way of examples may be adopted and it should of course be understood that the scope of the present patent extends to such variations as well as more generally as to all others remaining within the scope of equivalences. |
description | The present invention involves all phases of catalytic processing including devices for performing catalytic processing, methods of making devices for catalytic processing, and methods for operating devices to perform catalytic processing. The present invention is described in terms of several specific examples but it is readily appreciated that the present invention can be modified in a predictable manner to meet the needs of a particular application. Except as otherwise noted herein, the specific examples shown herein are not limitations on the basic teachings of the present invention but are instead merely illustrative examples that aid understanding. Specific examples in this specification involve application of high surface area catalysts on porous structures such as, but not limiting to honeycomb structured substrates. This technique in accordance with the present invention reduces the thermal mass of the catalytic system comprising the catalyst and its supporting structure. It has been found that catalytic behavior is significantly enhanced by procedures and structures that reduce the system""s thermal mass while increasing surface area of the catalyst. The specification suggests reasons why the various examples behave in the manner observed, however, these explanations provided to improve understanding are not to be construed as limitations on the teachings of the present invention. The present invention is described using terms of defined below: xe2x80x9cCatalysis,xe2x80x9d as the term used herein, is the acceleration of any physical or chemical or biological reaction by a small quantity of a substance-herein referred to as xe2x80x9ccatalystxe2x80x9d-the amount and nature of which remain essentially unchanged during the reaction. Alternatively, the term, includes applications where the catalyst can be regenerated or its nature essentially restored after the reaction by any suitable means such as but not limiting to heating, pressure, oxidation, reduction, and microbial action. For teachings contained herein, a raw material is considered catalyzed by a substance into a product if the substance is a catalyst for one or more intermediate steps of associated physical or chemical or biological reaction. xe2x80x9cChemical transformation,xe2x80x9d as the term used herein, is the rearrangement, change, addition, or removal of chemical bonds in any substance or substances such as but not limiting to compounds, chemicals, materials, fuels, pollutants, biomaterials, biochemicals, and biologically active species. The terms also includes bonds that some in the art prefer to not call as chemical bonds such as but not limiting to Van der Waals bonds and hydrogen bonds. xe2x80x9cNanomaterials,xe2x80x9d as the term is used herein, are substances having a domain size of less than 250 nm, preferably less than 100 nm, or alternatively, having a domain size sufficiently small that a selected material property is substantially different (e.g., different in kind or magnitude) from that of a micron-scale material of the same composition due to size confinement effects. For example, a property may differ by about 20% or more from the same property for an analogous micron-scale material. In case the domain size is difficult to measure or difficult to define such as in porous networks, this term used herein refers to substances that have interface area greater than 1 square centimeter per gram of the substance. The ratio of the maximum domain dimension to minimum domain dimension in the catalyst for this invention is greater than or equal to 1. The term nanomaterials includes nanopowders, nanoparticles, nanofilms, nanofibers, quantum dots, and the nanomaterials may be coated, partially coated, fully coated, island, uncoated, hollow, porous, and dense domains. Furthermore, nanomaterials may be produced by any method to practice this invention. xe2x80x9cDomain size,xe2x80x9d as the term is used herein, is the minimum dimension of a particular material morphology. The domain size of a powder is the grain size. The domain size of a whisker or fiber is the diameter, and the domain size of a film or plate is the thickness. xe2x80x9cConfinement sizexe2x80x9d of a material, as the term is used herein in reference to a fundamental or derived property of interest, is the mean domain size below which the property becomes a function of the domain size in the material. xe2x80x9cActivityxe2x80x9d of a catalyst, as the term used herein, is a measure of the rate of conversion of the starting material by the catalyst. xe2x80x9cSelectivityxe2x80x9d of a catalyst, as the term used herein, is a measure of the relative rate of formation of each product from two or more competing reactions. Often, selectivity of a specific product is of interest, though multiple products may interest some applications. xe2x80x9cStabilityxe2x80x9d of a catalyst, as the term used herein, is a measure of the catalyst""s ability to retain useful life, activity and selectivity above predetermined levels in presence of factors that can cause chemical, thermal, or mechanical degradation or decomposition. Illustrative, but not limiting, factors include coking, poisoning, oxidation, reduction, thermal run away, expansion-contraction, flow, handling, and charging of catalyst. xe2x80x9cPorousxe2x80x9d as used herein means a structure with sufficient interstitial space to allow transport of reactant and product materials within the structure to expose the reactant materials to the constituent compositions making up the porous structure. xe2x80x9cElectrically activated catalysis,xe2x80x9d as the term is used herein, means providing a quantity of a catalyst, exposing a feed substance to the quantity of catalyst, inducing or providing a flow of charge inside the quantity of catalyst by applying an electromagnetic field across the catalyst during the exposure to a feed stream for a period sufficient to initiate a desired tranformation in the feed substance. xe2x80x9cElectrically activated catalyst,xe2x80x9d as the term is used herein, is the catalyst used in electrically activated catalysis. FIG. 1 illustrates an embodiment of the present invention in a basic form. Essentially, feed material or waste material is, if needed, pre-treated using a subsystem consisting of one or more unit operations such as those identified in 103. These include, for example, heat exchangers, distillation, extraction, condensation, crystallization, filtration, drying, membrane pumps, compressors, separation, expanders and turbines that function to modify the physical, chemical and/or electrical state of the raw materials using available processing techniques. The pretreated feed is then processed through one or more catalytic device(s) 101 within reactor network 104 where desirable transformations occur. The product from reactor network 104 is, if desired, post-treated using a subsystem consisting of one or more unit operations such as those identified in 105. In an alternative shown in FIG. 1B. catalytic device 101 is placed in contact with a gaseous, liquid, solid, or mixed phase feed 107 and the desirable transformation(s) occur. The catalytic device 101 is coupled across a source of electromagnetic energy such as, for example, power supply 106 by conductive electrodes 102. The feed composition is contained in an appropriate container, and the catalytic device is arranged within the container to contact the gaseous form of the feed 107 as shown in FIG. 1B, or may be submerged or enveloped in a solid or mixed-phase form or the feed 107 with straightforward modifications. FIG. 2 illustrates the catalytic device in an embodiment of the present invention in a basic form. Essentially, an active layer 201 is sandwiched between two electrodes 202. Active layer 201 comprises a material that either as applied or as later modified by postprocessing acts as a catalyst for to convert a particular feed composition into a desired product composition. The dimensions and geometry of active layer 201 are selected to provide both sufficient exposure to a feed composition (i.e., a composition that is to be catalyzed) and to allow an impeded current flow between electrodes 202 when an electromagnetic field is applied across electrodes 202. Although specific examples of materials suitable for active layer 201 are set out below, active layer 201 more generally comprises a material that is an active catalyst for a desired reaction when activated by an applied electric field. The properties of active layer 201 are selected to allow active layer 201 to both support an electric field and conduct current. It is not necessary that active layer 201 be active as a catalyst at ambient conditions (e.g., without applied electromagnetic field). However, in some embodiments, the active layer 201 may have catalytic activity in ambient or non-ambient conditions even when an electric field is not applied between electrodes 202. A method for preparing a chemical composition transformation device in accordance with the present invention involves selecting an active material comprising a surface that physically, chemically, or biologically interacts with the substance that is desired to be transformed or with one of the intermediates of such substance. The active material is preferably prepared in a high surface area form (i.e., a form that exhibits a surface area of preferably greater than 1 square centimeter per gram, more preferably 100 square centimeter per gram, and most preferably 1 square meter per gram). It is believed that the present invention is enhanced by the interaction between the surface area of particles making up the active layer 201 and the applied electromagnetic field. Accordingly, a higher surface area form tends to increase desirable catalytic behavior for a given quantity of material. By way of explanation, the inventors have noted that electromagnetic fields in the form of voltage and/or current gradients across a nanostructured material manifest markedly different effects as compared to fields of similar magnitude applied across materials with larger particle size. In conventional devices, materials exist either in an atomic state or in a bulk state. Larger particle sizes (e.g., particles larger than the critical domain size of the material) behave as bulk materials under exposure to electromagnetic fields. While an explanation of these unexpected effects is beyond the scope of this specification, it is contemplated that the interaction of particle sizes less than the critical domain sizes of a material result in surprisingly unusual interaction between particles and/or creation of an electronic state at a nanoscopic level that differs from either the materials in atomic form or the materials in bulk form. FIG. 3 illustrates basic steps in an exemplary process for manufacturing a catalytic device in accordance with the present invention. The active material, usually prepared as a powder or powder mixture in step 301 and then optionally blended with additional compositions to form a slurry, ink or paste for screen printing in step 303. In step 305 the active material is directly or alternatively formed into a film, pellet, or multilayer structure comprising the active material. The film, pellet, or multilayer structure may be prepared as free standing or on a substrate. In case of multilayer structure, dielectric or ferromagnetic layers may be utilized to modify or induce a field in the active layers. The active layer structure may be porous or the structure may be non-porous. It is preferred that the device be porous to reduce pressure drop and enhance contact of the active element with the chemical species of interest. Table 1 lists some catalysts and pore size ranges to illustrate but not limit the scope: In other embodiments, the structure may be smooth or wavy, flexible or rigid, homogeneous or heterogeneous, undoped or doped, flat or cylindrical or any other shape and form, nanostructured or non-nanostructured. In all cases, this invention prefers that the material compositions chosen be physically robust in presence of all species in its environment in particular and all environmental variables in general for a duration equal to or greater than the desired life for the device. In all cases, this invention requires that the material selected has a finite impedance in the presence of electromagnetic field. Once a suitable material composition has been selected for use in the chemical composition transformation device, in one embodiment, namely the formation of a chemical composition transformation device, a disc or body or single active layer laminated stack structure is formed, or in another embodiment a multilayer structure (as shown in FIG. 2) is formed in step 305 from the selected active material. The active material layer formed in step 305 or structure or device form can be formed by any method or combination of methods, including but not limited to spin coating, dip coating, surface coating a porous structure, powder pressing, casting, screen printing, tape forming, precipitation, sol-gel forming, curtain deposition, physical sputtering, reactive sputtering, physical vapor deposition, chemical vapor deposition, ion beam, e-beam deposition, molecular beam epitaxy, laser deposition, plasma deposition, electrophoretic deposition, magnetophoretic deposition, thermophoretic deposition, stamping, cold pressing, hot pressing, explosion, pressing with an additive and then removal of the additive by heat or solvents or supercritical fluids, physical or chemical routes, centrifugal casting, gel casting, investment casting, extrusion, electrochemical or electrolytic or electroless deposition, screen-stencil printing, stacking and laminating, brush painting, self-assembly, forming with biological processes, or a combination of one or more of the above-mentioned methods. The active material can be in film form or dispersed particle form or bulk form or wire form. The cross section area of the active material structure can be few microns square to thousands of meters square depending on the needs of the application. In a preferred embodiment, the active material can also be doped with available promoters and additives to further enhance the device""s performance. In another preferred embodiment, the active material can also be mixed with inert elements and compositions and insulating formulations to further reduce capital or operating costs such as those from raw materials and pressure drop. In a preferred embodiment, the catalyst is applied in a form and structure that minimizes the thermal mass of the system. In this regard, the catalyst and any supporting substrate(s) are considered components of the system. A given system""s effectiveness is related to the surface area of catalyst that participates in the reaction. Thin film or thick film catalyst layers provide large surface area compared to bulk or pellet forms using a smaller amount of catalyst. In a specific implementation illustrated in FIG. 10A and FIG. 10B, a substrate 1001 such as a ceramic honeycomb, for example, supports electrodes 102 and catalyst layer or layers 101. A variety of ceramic honeycomb support structures 1001 are available ranging in shape from screens and grids, to polygon-celled matrices, to coiled structures that resemble corrugated cardboard, to porous ceramic with multiple heterogeneously- or regularly-shaped cells. Each of these structures enable a catalyst 101 to be coated onto some or all surfaces of the support 1001 using deposition or thin film techniques to some or all surfaces while enabling a fluid stream to pass through the structure with high exposure to the catalyst as suggested by the arrows in FIG. 10A. The catalytic support may be ceramic or any other composition consisting of elements from the periodic table and composites thereof. The honeycomb may be of various pore sizes, pore size distributions, pore shapes, pore morphology, pore orientation, pore lattices, composition, size, and may be manufactured by any method. To illustrate, the honeycomb may have bee-like hexagonal pore shape and each layer of the pore may be aligned with the layer above it. Alternatively the honeycomb may have circular pore shape and each layer may center at the edge of the layer above it. Numerous other configurations may be applied to maximize the efficiency and effectiveness of the catalytic process. Electrodes 102 can be affixed to the catalyst coated honeycomb structure, for example, at the front and back of the structure (with respect to the pore opening) as suggested in FIG. 10B in a manner that enables an electromagnetic field (e.g. a voltage gradient or current flow) to be imposed substantially equally across the catalyst coating. Electrodes can be affixed to the catalyst 101 using thin or thick film techniques. Other electrode configurations may be equivalently substituted to meet the needs of a particular application so long as the electrodes when energized by a power supply 106 apply an electromagnetic field across the catalyst 101 itself. Care should be taken to ensure that the applied electromagnetic field is actually realized in the catalyst 101 and not dissipated by the support structure 1001. For this reason, relatively non-conductive materials are preferred for support structure 1001. In the case of magnetically induced electromagnetic fields, a non-permeable material may be preferred for support structure 1001. In contrast to bulk or pellet or film catalyst shapes, honeycomb catalyst layers maximize the potential contact of gases and active species such as radical while reducing the mass of catalyst needed which can reduce the capital cost of catalyst. Furthermore, it is preferred that the phonon pathways be minimized to reduce heat loss. One method of accomplishing this is to coat any and all surfaces of a honeycomb substrate. Another method is to produce a honeycomb structure from the catalytic material directly, with or without dopants; some, but not limiting, illustrations of such produce would be aerogels, hydrogels, imprint cast material. These techniques reduce the electrical energy needed to keep the catalyst at a given temperature and given operating condition. Less thermal mass and smaller area for conductive or convective or radiative thermal transport can decrease the cost of electrical energy needed for given yield or selectivity. The porosity of the honeycomb may be varied both in size and the density of pores and it is anticipated that the porosity characteristic may be different for different chemistries. These examples illustrate the utility of catalyst films in the practice of field assisted transformation of chemical and material compositions. Catalyst supported on honeycomb examples exhibit improved efficiency in converting chemical compositions from a feed product to an end product. It is contemplated that a wide variety of electrode patterns, substrate compositions, membrane compositions, and catalyst materials will benefit from the utility of these features of the present invention. In another preferred embodiment, the active layer comprises functional materials such as those that provide thermal, sensing, pressure, charge, field, photons, structural, regeneration or other needed functions. Secondary treatments of the active material through sintering, pressurization, doping, chemical reactions, solid state reaction, self-propagating combustion, reduction, oxidation, hydrogenation, and such treatments may enhance the performance of the active layer. Possible compositions of the active material include but are not limited to one or more of the following materials: dielectrics, ferrites, organics, inorganics, metals, semimetals, alloy, ceramic, conducting polymer, non-conducting polymer, ion conducting, non-metallic, ceramicxe2x80x94ceramic composite, ceramic-polymer composite, ceramic-metal composite, metal-polymer composite, polymerxe2x80x94polymer composite, metalxe2x80x94metal composite, processed materials including paper and fibers, and natural materials such as mica, percolated composites, powder composites, whisker composites, or a combination of one or more of these. Illustrative formulations include but are not limited to doped or undoped, stoichiometric or non-stoichiometric alloy or compound of s-, p-, d-, and f-group of periodic table. Illustrative compositions that can be utilized in this invention as is or on substrates include one-metal or multi-metal oxides, nitrides, carbides, borides, indium tin oxide, antimony tin oxide, rare earth oxides, silicon carbide, zirconium carbide, molybdenum carbide, bismuth telluride, gallium nitride, silicon, germanium, iron oxide, titanium boride, titanium nitride, molybdenum nitride, vanadium nitride, zirconium nitride, zirconium boride, lanthanum boride, iron boride, zirconates, aluminates, tungstates, carbides, silicides, borates, hydrides, oxynitrides, oxycarbides, carbonitrides, halides, silicates, zeolites, self-assembled materials, cage structured materials, fullerene materials, nanotube materials, phosphides, nitrides, chalcogenides, dielectrics, ferrites, precious metals and alloys, non-precious metals and alloys, bimetal and polymetal systems, ceramics, halogen doped ceramics (such as, but not limiting to fluorine doped tin oxide), stoichiometric or non-stoichiometric compositions, stable and metastable compositions, dispersed systems, dendrimers, polymers, enzymes, organometallics, bioactive molecules, and mixtures thereof. Some specific, but not limiting, examples are listed in Table 2A, 2B, and 2C. Additionally, the formed active layer 201 can be porous or non-porous, flat or tapered, uniform or non-uniform, planar or wavy, straight or curved, non-patterned or patterned, micron or sub-micron, micromachined or bulk machined, grain sized confined or not, homogeneous or heterogeneous, spherical or non-spherical, unimodal or polymodal, or a combination of one or more of these. In a preferred embodiment, the electrode structures may comprise any composition with a lower impedance than the active material composition. The composition of the electrode layer can include, but is not limited to, organic materials, inorganic materials, metallic, alloy, ceramic, polymer, non-metallic, ceramicxe2x80x94ceramic composite, ceramic-polymer composite, ceramic-metal composite, metal-polymer composite, polymerxe2x80x94polymer composite, metalxe2x80x94metal composite, or a combination of one is or more of these. Geometries may be porous or dense, flat or tapered, uniform or non-uniform, planar or wavy, straight or curved, non-patterned or patterned, micron or sub-micron, grain size confined or not, or a combination of one or more of these. In the exemplary implementation outlined in FIG. 3, electrodes 102 and 202 are formed by available press/coat/mask/print techniques in step 309 followed by formation of green electrode layer(s) using, for example, printing techniques. Alternative methods of forming the electrode layers 102 and 202 include any method including but not limited to spin coating, dip coating, surface coating a porous structure, powder pressing, casting, screen printing, tape forming, curtain deposition, physical sputtering, reactive sputtering, physical vapor deposition, chemical vapor deposition, ion beam, e-beam deposition, molecular beam epitaxy, laser deposition, plasma deposition, electrophoretic deposition, magnetophoretic deposition, thermophoretic deposition, stamping, cold pressing, hot pressing, pressing with an additive and then removal of the additive by heat or solvents or supercritical fluids, physical or chemical routes, placing metal plates or films on certain parts of the active material, inserting wire, chemically transforming section in the active layer, centrifugal casting, gel casting, investment casting, extrusion, electrochemical deposition, screen-stencil printing, stacking and laminating, brush painting, self-assembly, forming with biological processes, or a combination of one or more of the above-mentioned methods. After preparation of the stack, the stack may for some applications be cut cross sectionally into thin slices in step 313 to expose the layers of the active layer and the electrode. In another embodiment, one or more of step 307, step 309, and step 313 may be skipped. In such cases, it is necessary that the equipment containing the catalytic device provide external electrodes or equivalent means in some form to enable the flow of charge through the active material. Finally, given the catalytic properties of the active layer, some of the steps in FIG. 3 may be assisted or accomplished through the use of said catalytic properties. Each slice obtained from step 313 in FIG. 3 is a device that can be used in a circuit shown as FIG. 4 to transform one or more species in a gas, vapor, liquid, supercritical fluid, solid or a combination of these. In step 315 the stack is calcined or sintered to reach structural robustness, consistency, and performance in the active material and green electrode layers. In one embodiment, the device is terminated by forming an electrical coupling to electrodes 202, 302 in step 317 enabling application of an external electrical field. In a preferred embodiment, it is desirable that the active material and the electrode layers be isolated from external environmental damage such as that from thermal, mechanical, chemical, electrical, magnetic, or radiation effects, or a combination of one or more of these. This desired protection may be achieved in step 317 by providing a conformal covering (not shown) over the layers on the unexposed surfaces, such as an polymer conformal protective layer. In another preferred embodiment, the exposed surface may also be isolated from external thermal, mechanical, chemical, electrical, magnetic, or radiation damage by covering with a layer of ceramic or porous rigid material mesh. In yet another preferred embodiment, the exposed surface may be covered with a layer that enhances the selectivity of the feed species reaching the active surface. Such a layer can include, but is not limited to, polymers, metals, zeolites, self-assembled materials, or porous media, each of which has a higher permeability for the analyte of interest and a lower permeability for other species that are not of interest. In some preferred embodiments the exposed surface is covered with polymers such as but not limiting to polyethylene, polypropylene, teflon, polycarbonates, or polyaromatics. However, it is generally preferable that any covering on the exposed surface does not impede the interaction of the analyte or analytes to be transformed with the active layer by an amount greater than the species that are not of interest. Exceptions to this general rule may be made in certain cases, for example, when it is critical to protect the element from destructive effects of the environment. In another embodiment, steps 317 and 319 may be skipped. FIG. 4 shows an exemplary chemical transformation system or reactor 400 in using the chemical transformation processes and devices in accordance with the present invention. The reactor 400 shown in FIG. 4 is notable for its simplicity due to the fact that high pressures and high temperatures are not required because of the superior performance of transformation device 401 in accordance with the present invention. The electrodes of device 401 are coupled in a circuit with power supply 402 so as to supply an electromagnetic field between the opposing electrodes of device 401. The circuit shown in FIG. 4 is illustrative; it may be replaced with any suitable circuit that can provide a flow of charge, internally (such as but not limiting to ohmic or ion flow or hole flow based current) or externally (such as but not limiting to eddy current or induced current from applied electromagnetic field) or both, in a given application. Power supply 402 may supply direct current, alternating current, or any other form of electromagnetic waveform. The charge may be induced to flow in the device when the device is wired or through the use of wireless techniques. The device 401 may include a single device such as shown in FIG. 1B and FIG. 2 or an array of elements such as shown in FIG. 1B and FIG. 2. The electrodes of the device(s) 401 may alternatively provide means to connect the device to induce interaction with an externally induced field such as but not limited to radio frequency or microwave frequency waves, or the equivalent. Reactor 400 includes an inlet port 403 for receiving a feed stream and an outlet 404 producing a reactant stream. In operation, feed gas or liquid passes in contact with device 401 while power supply 402 is active and is transformed before passing from outlet 404. Device 401 shown in FIG. 4 may be placed in reactor 400 in various ways to manufacture and practice useful equipment such as, but not limiting to, obtrusive or non-obtrusive manner, as randomly or periodically arranged packed bed, with or without baffles to prevent short circuiting of feed, in open or closed reactors, inside pipes or separately designed unit, with accessories such as mixers, in a system that favors laminar or plug or turbulent or no flow, sealed or unsealed, isolated or non-isolated, heated or cooled, pressurized or evacuated, isothermal or non-isothermal, adiabatic or non-adiabatic, metal or plastic reactor, straight flow or recycle reactor, co-axial or counter-axial flow, and reactor or array of reactors that is/are available. Table 3 lists example reactor technologies that may be used in accordance with the present invention. To illustrate the scope without limiting it, some examples from the art are listed in Table 3 and some in Kirk-Othmer Encyclopedia of Chemical Technology, Reactor Technology, John Wiley and Sons, Vol 20, pp 1007-1059 (1993) which is hereby incorporated by reference. In another preferred embodiment, the catalyst is activated by passing current through the catalyst which results from applying an electrical voltage drop across the catalyst material. The catalyst is heated to a temperature greater than 500xc2x0 C., preferably greater than 1000xc2x0 C., most preferably greater than 1500xc2x0 C. The heating of the catalyst can be achieved by conducting an exothermic reaction as well in combination or without the electrical current passing through the material. A non-limiting illustration of exothermic reaction is combustion of hydrocarbons. The hot catalyst is then quenched rapidly by the removal of the applied current. The quenching can also be accomplished by contacting to the hot catalyst a cold gas such as that derived from liquid nitrogen, liquid argon or any other fluid. Rapid quenching reduces secondary reactions that may otherwise reduce yield or produce unwanted species. It is preferred that the quenching medium contains some or all of the species which would form the reactants after the activation of the catalyst. The activated catalyst so produced by in-situ thermal quench techniques may then be used in catalytic processes such as but not limiting to the various embodiments taught in this specification. The ohmic or exothermic reactions may lead to thermal runaway. Thermal runaway refers to an situation in which the processes supplying heat to the reaction sites of the catalyst produce heat at a faster rate than can dissipate from the site. While thermal runaway is normally considered to be a problem, for this embodiment thermal runaway offers a surprising opportunity to reach very high temperatures and large quenching. The thermal runaway may be controllably induced in accordance with the present invention by applied electromagnetic field with or without the presence of exothermic reactions during the activation process. So long as the heat generated by the exothermic reactions is by itself insufficient to cause a self-sustaining thermal runaway, the thermal runaway can be controlled by application of the electromagnetic field. Applications The method and techniques disclosed can be applied to prepare catalysts and devices in manufacturing of useful chemicals and drugs. The superior performance of the method and device proposed for chemical composition transformation may be used to produce intermediates or final products. Some illustrative, but not limiting reaction paths where this invention can be applied are listed in Table 4. Reactions that utilize one or more elementary reaction paths in Table 4 can also benefit from the teachings herein. The benefits of such applications of teachings are many. To illustrate but not limit, the near ambient condition operation can reduce the cost and ease the ability to control chemical synthesis; it can in some cases lesser levels of thermal shocks during start ups and shut downs can enhance the robustness of the catalysts. In general the invention can be applied to produce useful materials from less value added materials, readily available raw materials, or waste streams. One of the significant commercially important application of this invention is in providing candidates to and in improving the performance of catalysis science and technology. This is particularly desirable for existing precious-metal and non-precious metal based catalytic formulations, heterogeneous and homogeneous catalysis, and for catalytic applications such as but not limiting to those and as known in the art and which are herewith included by reference. To illustrate the scope without limiting it, some examples where this invention can be applied are listed in Tables 5A, 5B, 5C, 5D, 5E, 5F and some are listed in the art such as Kirk-Othmer Encyclopedia of Chemical Technology, Catalysis, John Wiley and Sons, Vol 5, pp 320-460 (1993) and references contained therein. The teachings of the present invention can be used to research and develop, to rapidly screen novel catalysts by techniques such as combinatorial methods, and to optimize catalysts through the use of arrays in electrical and microelectronic circuits. The application of electrical current in particular, and electromagnetic field in general, can enable the ability to extend the life of catalysts, or improve their activity, yields, light off temperatures, turn over rates, stability, and selectivity with or without simultaneous changes in the operating conditions such as temperature, pressure, and flow profile. The catalyst so operated with electromagnetic field is anticipated to enable reactor temperatures and pressures or conditions that are more desirable to customers and integrated to the operating conditions of a specific manufacturing scheme. Furthermore, this invention of applying electromagnetic effects on the catalyst can enable reaction schemes that are switched on or off at will by switching on or off of the electromagnetic field respectively. Such flexibilities can be highly valuable in controlling and enhancing of safety of reactions that may be explosive or that may yield dangerous and hazardous byproducts. The invention can also be applied to produce multiple useful products from same reactor through the variation on-demand of the applied electromagnetic field or feed or other operating conditions required to meet the needs of a particular application. The benefits of this invention can be practiced in lowering the light-off temperatures in combustion exhaust systems. As one illustration of many applications, it is known in the art that emission control catalysts such as the three-way catalysts placed in automobile exhausts operate efficiently at temperatures greater than about 350xc2x0 C. These non-ambient temperatures require a heat source and often the exhaust heat from the vehicle""s engine is the principal source of the needed heat. During initial start up phase of the engine, it takes about a minute to heat the catalyst to such temperatures. Consequently, the vehicle emission controls are least effective during the start. Methods to rapidly heat the catalyst to such temperatures or lower temperature catalysts are desired. Methods have been proposed to preheat the catalysts by various techniques, however, such techniques require high power to operate, add weight, and are not robust. The teachings contained herein can be used to prepare catalytic units or modify existing catalytic units to operate at lower temperatures (less than 350xc2x0 C., preferably less than 200xc2x0 C.) and quicker light-offs. These teachings apply to combustion in general and to emission control systems used in other mobile and stationary units. The teachings may also be practiced by coating the engine cylinder""s inside, operating the said coating with electrical current during part of or the complete combustion cycles. Such an approach can help modify the reaction paths inside the cylinder and thereby prevent or reduce pollution-at-source. The benefits of the teachings contained herein can be applied to the control of difficult-to-treat species such as NOx, SOx, CFCs, HFCs, and ozone. One method is to prevent these species from forming through the use of novel catalytic devices with electrical current in particular, and electromagnetic field in general. Alternatively, using such catalytic devices with electrical current, streams containing these species may be treated with or without secondary reactants such as CO, hydrocarbons, oxygen, ammonia, urea, or any other available raw material, or combinations thereof. The invention is particularly useful for applications that currently require high temperatures or heavy equipment due to inherently high pressures during reaction or excessive volumes, as the teachings of the presently claimed invention can offer a more economically desirable alternative. Illustrations of such applications, without limiting the scope of this invention, include pollutant treatment or synthesis of fuel and useful chemicals in space vehicles, submarines, fuel cells, miniature systems in weight sensitive units such as automobiles, airplanes, ships, ocean platforms, remote sites and habitats. This can help reduce the weight of the unit, reduce capital costs, reduce inventory costs, and reduce operating costs. Any applications that desire such benefits in general can utilize the teachings of this invention. The invention can offer a long sought alternative for catalyzing reactions on feeds that contain poisoning species, i.e. species that can cause reversible or irreversible poisoning of available catalysts (for example, but not limiting to, illustrations in Table 6A and 6B). To illustrate this feature of the present invention, it is well known in the art that precious metal catalysts are useful in numerous reactions. However, these and other catalysts tend to get poisoned when the feed stream contains sulfur or sulfur containing species. Extensive and often expensive pre-treatment of the feed streams is often required to ensure that the catalyst is not poisoned. The present invention describes materials and devices that can catalyze reactions with non-precious metal based formulations that are not known to be poisoned by sulfur. Thus, through appropriate variations in catalyst composition and electromagnetic field, chemical reactions may be realized even if poisoning species are present. This reduces or eliminate the need for expensive and complex pre-treatment of feed streams. This method is not limited to precious metal poisoning and can be applied to finding catalyst alternatives for presently used catalysts that are based on other materials (supported, unsupported, precipitated, impregnated, skeletal, zeolites, fused, molten, enzyme, metal coordination, ion exchange, bifunctional, basic, acidic, sulfide, salt, oxide, metal, alloys, and intermetallic catalysts). The method is also not limited to sulfur poisoning and the teachings can be used when poisoning or loss in stability is caused by species other than sulfur. The method can also be applied to cases where solutions need to be found for catalysts or systems that undergo coking, thermal run away, and chemical effects. The invention also offers a method of developing and practicing non-precious alternatives to expensive precious metal-based catalysts. This can reduce catalyst costs. Such uses of invention are desirable in automobile exhaust catalysts, emissions treatment catalysts, naphtha catalysts, petroleum cracking catalysts, and applications that utilize precious metals. Notwithstanding such use and uses discussed earlier, these teachings are not meant to limit to the teachings of presently claimed invention to non-precious metals and materials based thereof. Precious metals and materials based thereof may be used in the practice of this invention""s teachings. The benefits of this invention may be obtained where localized heating is desired because, at contact points between the catalytic particles, the grain boundaries may be hot because of the ohmic heating. These localized hot spots can offer active sites for chemical reactions. Given the nanostructured form of the catalysts, these microscopic hot spots are localized because of the low thermal conductivity of the porous ceramic substrate. Such localized heating would raise the reaction temperatures very locally, i.e. only of gas molecules that are in immediate vicinity or in direct contact with the catalyst. Once the products leave the hot spot, the product compositions are expected to quench from thermal collisions and low bulk temperatures. Hence, the present invention enables thermally activated reactions to be confined to the vicinity of the catalyst. Such a localized heating phenomena may dramatically limit the secondary series reactions. In conventional catalysts that are heated by external furnace, both the active site temperatures and the bulk gas temperatures are high. Therefore, in conventional catalysis, the products can participate in secondary series reactions leading to complex reaction pathway and possibly poor selectivity. When raw materials are preheated, for example, reactions may occur before contact with the catalyst. When the reaction environment itself is heated, secondary reactions may continue after contact with the catalyst. These secondary reactions are independent the desired catalytic reactions and so may produce undesirable effects and/or products. In electrically activated catalysis in accordance with the present invention, an unusual flexibility exists as it can provide localized hot spots suitable for selective chemistry that is dependent on (i.e., assisted by) the catalyst, and then low bulk temperatures before and after catalyst contact suitable for limiting the kinetics of secondary reactions. These benefits are anticipated when the grain surface is similarly or more or less conductive than the grain bulk. In other words, one of the unique inventions disclosed here is the method of conducting useful chemical reactions and transformations from any raw material when the active site on the catalyst surface is heated by the flow of current while the bulk of the reactor environment is maintained at a different temperature (difference is preferably greater than 10xc2x0 C.). It is important to note that for the described benefit, the substrate on which the catalyst is deposited should offer higher impedance to current than the catalyst itself, and preferably the impedance of the substrate should be 50% or more than the impedance of the catalyst. Most and preferably substantially all the current flows in the catalyst rather than the catalytic support. It is known to use current flowing in the catalytic support to create ohmic heating that modifies the catalytic performance and/or regenerates the catalyst affixed to the support. However, the present invention operates to cause current in the catalyst, and is not concerned primarily with heating or current flow in the catalytic support structure. Preferably, current flowing in the catalyst exceeds the current flowing through the catalytic support. More specifically, for example, current flowing in the catalyst represents more than 75%, more preferably more than 90%, and still more preferably greater than 95% of the total available current. This can be implemented, for example, by using insulating, semi-insulating, and/or highly resistive materials and structures to support the catalyst. The benefits of this invention may also be applied in the design of novel catalysts and other performance materials. Catalytic activity has its origin in the electronic state of a substance (i.e. amongst other things the number of electrons and the orbitals associated with these electrons). It is known that precious metals (Pt, Pd, Ir, Ru, etc.) show superior catalytic activity for a wide range of chemical reactions. However, these elements are expensive. There has been a need for a technology that can help design substance that are more affordable than precious metals and yet that show performance comparable with the precious metals. An embodiment of the present invention involves modification of the electronic state of a substance through the application of an electromagnetic field applied to the substance. The application of an electromagnetic field may be used to modify the performance of such materials (e.g. catalytic, structural, thermal, electromagnetic, optical, photonic, physical, chemical, biological performance). This may be achieved by the application of an electrical field (such as passage of current or application of a voltage gradient) or through induced field. While the former method is explained in detail elsewhere in this disclosure, the later method is illustrated hereinafter. It is known to those in the art that dissimilar substances in contact induce an electromagnetic potential. This effect is in part the basis of Seebeck and Peltier Effects. This induced voltage offers another opportunity to modify the electronic state of a substance and consequently modify the materials performance. For example, a combination of disparate nanostructured particles can be formed by any available mixing technique such that particles with different compositions are sufficiently adjacent that the share domain boundaries. In other words, their domain boundaries overlap. Because their domain boundaries overlap, it is believed that an electromagnetic field is induced about the domain boundary. This induced electromagnetic field, either alone or in combination with an externally applied electromagnetic field, modifies the catalytic performance of the combined nanostructured materials. This effect is believed to be more pronounced in dissimilar materials when these materials are in nanostructured form. This is believed to be because of the fact that nanostructured materials have high interface area. This provides more interaction of the surface atoms of the contacting substances. With particle sizes smaller than the critical domain sizes of the materials involved, these effects are believe to be more pronounced. With very small clusters, this effect is expected to be most pronounced. In this embodiment, two or more dissimilar nanomaterials are formed into a structure where the dissimilar nanomaterials share grain boundaries. At the grain boundaries, the dissimilarity induces an electromagnetic potential in the grains, i.e. one grain is somewhat positively induced and the other is negatively induced. The charge so induced affects the Fermi level electrons in the respective material. Given the fact that the useful performance and properties of a material are in part dependent on the nature and state of the Fermi electrons in a material, induced charge in a material is anticipated to modify the performance of the material by 5% or more. These effects can be used to generalize a method of making useful catalytic materials from nanomaterials. This embodiment involves a method of manufacturing catalysts with nanomaterials where two or more dissimilar materials are formed into a structure such that at least at some of the grain boundaries there is interaction between the dissimilar materials. Furthermore at these grain boundaries there is an induced charge in the nanostructured grains because of the dissimilar material compositions. This induced charge modifies the performance of the material in contrast to the state where the material has no induced charge. Such dissimilar nanomaterial catalysts may be used to conduct useful chemical reactions and transformations from any raw material. Furthermore, nanomaterial structures of these types may be used to modify other performance of the material as well in other applications, e.g. structural, thermal, electromagnetic, optical, photonic, physical, chemical, biological. Finally, one may use a dielectric, ferromagnetic, or other materials to allow one to combine external electromagnetic field and the induced charges for beneficial modification of the materials"" performance. It should be noted that these embodiments are akin to, yet distinct from, alloy catalysts. For example, this embodiment of the invention requires the use of materials in a form that has high interfacial area per unit volume. Furthermore, it is necessary in this embodiment that electromagnetic interactions occur between the different materials at these interfacial grain boundaries. In contrast, in alloyed mixtures there are no grain boundaries and there is no electromagnetic interaction between the different constituent of an alloy. Also, there are a limited set of materials that will form alloys, and the materials structures of the present invention include a much wider range of materials including materials that normally cannot be alloyed together. Similarly, it should be noted that this embodiment is akin to, yet distinct from, catalysts that are produced by mixing different materials (metals, oxides, alloys, etc.). As stated above, this embodiment of the invention requires the use of materials in a form that has high specific interfacial area. Furthermore, it is necessary in this embodiment that electromagnetic interactions occur between the different materials at these interfacial grain boundaries. In contrast, in catalyst produced by mixing materials, other than grain contact leading to point junctions, there is no intimate contact between the mixed materials. Furthermore, the mixed materials are essentially equipotential with no electromagnetic interaction between the different constituent of the mixture. The embodiment explained here requires that there be an interaction and that the nanomaterials interfaces be not at the same electromagnetic potential. As specific example of implementing an embodiment of induced voltage, when cobalt nanomaterial and gold nanomaterial are mixed, it is anticipated that cobalt will perform with a nickel-like behavior while gold will perform with a platinum-like behavior (because platinum is next to gold in the periodic table and gold Fermi electrons under induced charge are expected to behave like platinum Fermi electrons; similarly nickel is next to cobalt in the periodic table and cobalt Fermi electrons under induced charge are expected to behave like nickel Fermi electrons) . As another example, when iron and silver nanoparticles are mixed, it is anticipated that cobalt-like and palladium-like behavior will be observed. As yet another example, when tungsten and gold nanoparticles or nanofilms are brought into proximity, rhenium and platinum-like performance is anticipated to be observed at the interface and interface influenced sites. Also, a mixture of tantalum and copper nanoscale clusters is expected to yield a tungsten and nickel-like performance. This behavior is expected to be observed even in non-stoichiometric substances, e.g. non-stoichiometric reduced mixtures of metal oxides, nitrides, carbides, borides, oxonitrides, carbonitrides, and other substances. While the above illustrates the embodiment with two metals, these teachings can be applied to more than two metals and to substances that are not metals. While this disclosure specifically teaches methods and processes for engineering catalytic performance of substances through the use of applied or induced charge, the teachings can be applied in general to engineer the structural, thermal, electrical, magnetic, electronic, optical, photonic, electrochemical, physical, chemical, biological performance of substances as well, through the application of applied or induced charge. Such engineering using induced or applied charge is expected to yield performance enhancements greater than 5% over the case where no charge is induced or applied. Both applied and induced electromagnetic potential may be utilized for engineering the performance of a substance or mixture of substances. The benefits of this invention may also be applied where the charge flow through the catalyst affects the surface potential of active sites. It may also participate in the surface diffusion of any radicals or charged species adsorbed on the catalyst""s surface. In such a case, the charge flow can be responsible in modifying the adsorption and desorption kinetics of the species involved in the chemical reaction. The surface charge potential can also have some steric influences. These effects can be pronounced if the rate limiting step in a specific chemistry is either surface diffusion or the adsorption/desorption of specific radicals on the surface of the catalyst. Furthermore, this effect can be pronounced when the charge flow is primarily over the grain boundaries and surface of the catalyst. Electrical current, in such circumstances, can offer an additional independent process variable. This variable can help control a chemical pathway through variations in the applied and/or induced electromagnetic potential. The benefits of the teachings contained in this invention can be utilized in research and development and manufacture of inorganic, organic, and pharmaceutical substances from various precursors, such as but not limiting to illustrations in Table 7A, 7B, 7C, 7D, 7E, 7F, and 7G(these and others can be found in literature). Application of the Present Invention These benefits of the present invention can also be utilized in the manufacture of fuels, propellants, chemicals, biochemicals, petrochemicals and polymer. Furthermore, the use of electromagnetic energy and active materials in high surface area form can provide benefits in microbe-based, cell-based, tissue-based, and artificial implant-based devices and reaction paths. Finally, the benefits of this invention can be applied to gaseous, liquid, solid, superfluid, plasma or mixed phase reactions. These devices can be enabling to the production of improved and novel products. To illustrate, the catalyst with optimization techniques available in the art can enable devices to produce hydrogen from low cost chemicals, which in turn can be used to prepare hydrogen based engines, alternative fuel vehicles, hybrid vehicles, captive power generation and other applications. To illustrate, the teachings contained herein, preferably combined with optimization techniques available in the art, can enable affordable devices to produce hydrogen from low-cost chemicals (such as but not limiting to methanol, agriculturally derived ethanol, gasoline, natural gas, gasohol), which in turn can be used to prepare hydrogen based engines, alternative fuel vehicles, hybrid vehicles, captive power generation and other applications. The teachings can assist in reducing the costs of implementing novel engine-based vehicles and power generation equipment since the distribution infrastructure of said low-cost chemicals to homes, buildings, and roads already exists. The novel chemical composition transformation method and devices as described can be utilized to degrade undesirable species from a feed into more preferred form. Illustration include degradation of species such as toluene, methylethyl ketone, ethylene oxide, methylene chloride, formaldehyde, ammonia, methanol, formic acid, volatile organic vapors, odors, toxic agents, biomedical compounds into intermediates or final products such as carbon dioxide and water vapor. In another application, organics in liquid streams may be treated using these devices. Alternatively, novel chemical composition transformation devices as described can be utilized to remove and recover precious and strategic metals from liquid waste streams; or to remove hazardous metal ions from waste streams (waste water). The device can also be used to purify fluid streams by removing low concentrations of contaminants such as in preparing extremely pure water or extremely pure gases needed in semiconductor device manufacturing. The invention can be applied to automatically and on-demand clean contaminants and stained surfaces such as windows in skyscrapers and hotels, and window shields of automobiles and aircraft. Stains are often organic in nature or comprises of substances that change the refractive index of a surface. A thin nanostructured coating of transparent ceramic or film (such as but not limiting to indium tin oxide, doped glasses, metals, and ceramics) can be deposited with electrodes printed connecting said film. The film can be part of an electrical circuit that is triggered on-demand to catalyze the substance in any stain on surface of interest. The invention may also be integrated in air conditioners, heating, and ventilation systems to clean air, or at-source and conveyors of emissions such as carpets, combustion chambers, and ducts. The teachings can also be utilized to build low-cost odor control systems inside microwaves, refrigerators, and portable or plug-in type odor removal devices at homes and offices. Odors are organic chemicals and preferred method of treating odors is to transform the chemicals responsible for odor into carbon oxide and moisture. The teachings contained herein can be applied to produced catalytic units that transform the chemicals responsible for odors into more desired products. Similarly, the teachings can yield devices to address the problems inside printers and photocopiers and other such office and industrial equipment that emit gases such as ozone and volatile chemicals. The invention can enable the use of multifunctional equipment. An illustration of this, without limiting the scope, would be to coat the surface of a pipe with conducting formulation and then conduct the reaction while the raw material is been transported from source to some desired destination. The pipe in this case performs more than one function-it helps transport the feed and it also enables the reaction to occur during such transport. The invention can be applied in membrane reactors, ion exchange units, catalytic distillation, catalytic separation, analytical instruments, and other applications that combine the benefits of catalysts with chemical unit operations known in the art. This invention can also be utilized to develop and produce products that are based on catalytic or high surface area-based properties of materials used in the product. An illustrative, but not limiting, product of this type would be one that sense, react, trigger, or adapt to changes in environment in general, and in the chemical composition of a fluid in particular such as the teachings in commonly assigned U.S. patent application Ser. No. 09/074,534 and which is incorporated herewith. The invention can be generically applied to develop and produce products that sense, react, trigger, or adapt to changes in the environment such as changes in the thermal state, mechanical state, magnetic state, electromagnetic state, ionic state, optical state, photonic state, chromatic state, electronic state, biological state, or nuclear state, or a combination of two or more of these. In all cases, when the teachings contained herein are applied to a device in conjunction with electrical field, the benefit obtained is the modification of surface state of the active material and/or the modification in the property of the active material and/or the modification in the environment, as the said surface interacts with the environment. As a non-limiting example, if the active layers are prepared from thermally sensitive material compositions, rapid response thermal sensors can be produced. In another example, if piezoelectric compositions are used in the active layer in a multilaminate stack, vibration and acceleration sensors can be produced. In yet another example, magnetic compositions can yield rapid response magnetic sensors and magnetoresistive sensors. If the active layer instead is prepared from compositions that interact with photons, novel chromatic, luminescent, photodetectors and photoelectric devices may be produced. With compositions interacting with nuclear radiation, sensors for detecting nuclear radiation may be produced. In another example, with biologically active layers, biomedical sensors may be produced. With insulating interlayers, these device may be thermally isolated or made safe and reliable. The active layers can be mixed, as discussed before, to provide multifunctional devices and products. The sensing layers may be cut or left intact for specific applications. The sensing layer may be just one layer or a multitude of as many layers as cost-effectively desirable for the application. The electrode may also be one layer or a multitude of as many layers as cost-effective and necessary for the application. These sensors have performance characteristics desired in chemical, metallurgical, environmental, geological, petroleum, glass, ceramic, materials, semiconductor, telecommunications, electronics, electrical, automobile, aerospace and biomedical applications. Such sensors can be combined with metrology techniques and transducers to produce smart products and products that adapt and learn from their environments. A mixture of 75% ITO (15.7 m2/g BET surface area) and 25% Al2O3 (61.7 m2/g surface area) nanoparticles is formed by milling the two powders together. A slurry is prepared from this high surface area mixture in iso-propanol. An electroded porous (0.2-0.3 mm pores) honeycomb Al2O3 structures (3.8 cmxc3x971.3 cmxc3x970.6 cm) is dipped into the mixture. The electrodes are made of silver, although other conductive electrodes are expected to work as well. The sample is dried at room temperature. The catalyst is reduced in a flow through quartz tube reduction system in 5% H2 in Nitrogen at 350xc2x0 C. After 30 minutes its resistance drops to about 1000 ohms, with a visible change of color to green-blue to light blue. The reduced or activated thin film is transferred to the reactor and is exposed to 100 ml/min of Methanol/Air vapor under a small electric field. The results of this experiment are tabulated in the following table. Interestingly, the reaction produced less than 2% carbon monoxide. This example suggests that electrically activated catalysis can produce greater than 10% hydrogen from methanol and air at average substrate temperatures below 300xc2x0 C. Alternatively, this example suggests that hydrogen can be produced from alcohols such as methanol with low concentrations of carbon monoxide. The feed is preheated in this example by, for example, unit processes 103 shown in FIG. 1. The catalyst of Example 1 is treated to 60% oxygen/40% nitrogen that is saturated with methanol heated to 40xc2x0 C. To prevent condensation of methanol, the feed line connecting the methanol tank and the reactor 104 is heated as well. The reaction is initiated with electrical current and then the current is switched off. Table 9 presents the results observed. This example suggests that electrically activated catalysts in some reactions remain active even without the current. Hence, this invention may be used to activate catalysts in conditions that would not otherwise result in similarly activated catalyst. Alternatively, this example suggests that hydrogen can be produced from alcohols such as methanol with negligible input of power. This example differs from Example 1 in that the feed is methane and water vapor. Methane (16% CH4, 84% Nitrogen) is bubbled through warmed water in unit operations network 103 and this mix is fed into the reactor. The results are presented in Table 10. This example suggests that electrically activated catalysts is not limited to methanol oxidation. It has broad impact application. Specially, this example shows that the technology may be used for hydrocarbon reforming. A honeycomb surface was coated with indium tin oxide using sputtering process. Palladium acetate was applied to the surface such that it yield a continuous layer of palladium. The honeycomb catalyst was placed in a circuit and a voltage drop applied across the catalyst. This passage of current so resulting activated the catalyst. This activated catalyst was externally heated with a heating plate. Methane was passed over the catalyst along with water vapor and oxygen (as air) in the reactor system of example 1. The products from the reactor were primarily hydrogen and carbon dioxide. The observed carbon monoxide as measured by gas chromatograph was less than 2%, even though the hydrogen concentration was greater than 10%. This high hydrogen to carbon monoxide ratio (greater than 5) is highly unusual as conventional methane reforming produces greater than 10% carbon monoxide and the hydrogen to carbon monoxide ratio is less than 5. This examples suggests that electrically activated catalysis is useful in hydrocarbon reactions and that it may be used to produce hydrogen from hydrocarbons, water vapor and oxygen in a single step with low concentrations of carbon monoxide. The hydrogen so produced could be used, after suitable post-processing, as feed for fuel cells, merchant hydrogen, chemical and biochemical reactions, pharmaceutical synthesis, fuels for rockets, and for instrumentation applications. Gas storage and discharge is often a physisorption or chemisorption process. Gas storage applications exist in many situationsxe2x80x94e.g. hydrogen, methane, gas purification, refrigeration cycles, batteries etc. While the teachings of the present invention can be applied to all gases, the particular example illustrates an embodiment for hydrogen storage applications. Surface adsorbed and/or chemical hydrides are formed during hydrogen storage process. This process often requires thermal cycles. This can be provided by applying electromagnetic field and passing electrical current through the material of interest. This can be accomplished because most alloys and hydrides offer reasonable electrically conductivity. The resistance of these materials changes with extent of hydrogen storage. With a circuit that determines the resistance of the storage bed, the hydrogen loading of a bed can be estimated. Thus this feature can also be used to systematically monitor and control the adsorption or desorption process. The flow of current, can through ohmic heating, change the temperature of the bed and this in turn can affect the discharge rates and extent. Application of electromagnetic field in general and the flow of current in particular is simpler, smaller, and more rapid than achieving temperature profile through the use of an external furnace. Such a technique can be useful for the storage of any gas. It is also anticipated that this process can be used to separate isotopes and processes that benefit from adsorption and/or desorption phenomena over surfaces. Some specific illustrations of hydrogen storage materials include Mg 80%+LaNi5 20% amorphous/nanostructured composite materials, Mgxe2x80x94Nixe2x80x94Ce, ZrNixe2x80x94Mg2Ni, TiMn1.5, TiMn2 based amorphous and amorphous/nanostructured composite materials, fullerenes, and La2Mg17 (66.6 wt %)+LaNi5 (33.3 wt. %) . Pd, Pt, Ni, and V are potential additives for this application. Reactor Variations The reactor network 104 may be implemented using a continuous stirred-tank reactor (CSTR), plug-flow reactor (PFR), batch or any other form of reactor design. Process control and automation may be added to improve the process. The process control may be proportional (P), proportional-integral (PI), proportional integral derivative (PID), proportional-derivative (PD) or any other type. The reactor may comprise solid walls formed of a non-reactive material including ceramics, metals, polymers and the like selected to meet the chemical, mechanical and electrical needs of a particular application. Alternatively, a membrane 501 replaces some or all of the reactor walls of the reactor 104 containing the electrically activated catalyst as shown schematically in FIG. 5A and FIG. 5B. The membrane can be functionally gradient type integrated into the reactor wall as shown in FIG. 5B, or simple layer type shown in FIG. 5A. Some of the products (e.g., Products 1 in FIG. 5A and FIG. 5B) that are formed in the vicinity of electrically activated catalyst 101 diffuse through membrane 501. The passage through membrane 501 enriches certain desired components within in the reactor 502 outside of the membrane 501. FIG. 6A and FIG. 6B show an optional embodiment in which an electrically activated catalyst 601 is incorporated into a plug-in type device. As shown in FIG. 6A, catalyst 601 is on affixed to a supporting substrate 603 by lamination, adhesives, surface tension or other means. Catalyst 601 may be provided as a decal applied to substrate 603, or may be applied to substrate 603 by screen printing, evaporation, sputtering, or other thin or thick film techniques. The device of FIG. 6A and FIG. 6B can be plugged into any electrical outlet such as conventional 110 or 220 volt AC mains power, or 12 volt DC power available in vehicles. Electromagnetic field is coupled to catalyst 601 by electrodes 602. In the specific embodiment, electrodes 602 pass through holes or plated vias through substrate 603. However, it is contemplated that printed conductors using printed circuit board and or ceramic module techniques may be readily applied to provide other electrical conduction configurations. Alternatively, electronic and electrical circuit is incorporated to convert the electrical outlet voltage and current into more desirable magnitude or frequency of voltage and current for the device. Further, an electromagnetic field may be induced in catalyst 601 using, for example, radiating coils or antenna structures formed on one side of substrate 603 that produce electromagnetic field that penetrate to catalyst 601. Such a configuration, not shown, isolates exposed surfaces from electrical potentials to improve safety and convenience. Preferably, a ventilated cover 604 is provided to mechanically protect the catalyst 601 while allowing environmental atmosphere to reach the surface of catalyst 601. Sensor(s) or timers or both may be added to improve functionality of the device. A sensor, for example, may be used to indicate the need to replace the device. In operation, a polluted gas stream (e.g. air) diffuses into the cover, is catalytically remediated, and the benign products diffuse away from catalyst and through the cover. This device can destroy harmful gases, odor, biospecies, pathogens, etc. FIG. 7A and FIG. 7B illustrate an example configuration illustrating a manner in which the process components may be integrated. The process integration requires less equipment, has lower capital and operating costs, and is therefore preferable in some cases. However, sometimes, integrated process require better process monitoring and controls. FIG. 7A is largely analogous to the process configuration shown in FIG. 1 where heat exchanges 703 and 705 are specific instances of unit operation networks 103 and 105 in FIG. 1. Functionally, heat exchangers 703 and 705 serve to add/remove heat from the feed stream and product stream, respectively. Heat exchanges are preferably implemented in a manner that provides acceptable flow without otherwise interfering with or impeding the feed stream and/or product stream. Heat exchanges 703 may comprise electrical or fuel powered heating elements, or obtain heat energy by other available heat source. FIG. 7B shows an integrated configuration in which heat removed from the product stream is exchanged into the feed stream to provide energy efficient operation. A feed composition is preheated by heat exchanger 705 and passed to an electrically activated reactor 704 in accordance with the present invention. Electrically activated reactor 704 includes the catalyst 101 that while electrically activated, transforms the feed composition into the product composition. The heated product composition is passed to heat exchanger 705 for heat removal. Heat exchanger 705 in FIG. 7B is configured to isolate the feed stream from the product stream. FIG. 8 presents an example in which the electrically activated reactor 804 is part of a reactor network 801. The first reactor 803 comprises a combustion reactor whose products enter the electrically activated catalyst reactor 804. The products from the catalyst reactor 804 then enter into another reactor 805 where the products are further reacted. The specificity of electrically activated catalyst reactor 804 enables a high degree of functional control over the products produced at each stage. For example, as described above the reaction environment of electrically activated reactor 804 can be carefully controlled to avoid secondary reactions that may produce uncontrolled or undesired reactions in downstream reactor 805. While the example of FIG. 8 illustrates only three reactors in series, a smaller or larger number of reactors can be used in series or parallel to produce desired substances. FIG. 9 illustrates one of the many embodiments of processes that can be designed around electrically activated catalysis. The reactor network of FIG. 9 is useful for the production of hydrogen from a feed stream comprising a hydrogen containing compound or compounds. Hydrogenation unit 903 receives the feed stream and preferably receives a portion of the hydrogen product. Hydrogenation unit 903 functions to combine free hydrogen with the feed composition to pre-treat unsaturated hydrocarbon compounds in the feed composition. The zinc oxide bed 913 provides a catalyst bed to promote the hydrogenation process. The products of the hydrogenation process are passed directly or after thermal repositioning by heat exchanger 923 to electrically activated catalyst (EC) reforming unit 904. Reforming unit 904 performs a reaction such as described in example 3 and example 4 set out above to convert a hydrogen containing compound, such as methane, into hydrogen and byproducts such as carbon dioxide. Steam regenerator 906 supplies water vapor, which may be a byproduct of hydrogen enricher 905. The converted product is passed, optionally through heat exchanger 915 to post-processing unit 905 that performs hydrogen enriching by removing water vapor and or other components of the converted product stream. Heat exchanger 915 operates to remove heat from the hydrogen stream generated by hydrogen enricher 905. The enriched hydrogen from the enricher can be sent into components such as fuel cell stack subsystem. The fuel processing subsystem in combination with fuel cell stack subsystem and power conditioning subsystem can be utilized for electricity generation applications. While the examples herein do not show process control, process control mechanisms and techniques are widely known and applicable to the mechanisms shown in FIG. 9 to meet the needs of a particular application. For example temperature, pressure, flow rate, composition, voltage, current indicators or controllers may be added before, with, and after the electrically activated catalysis. This process begins with natural gas to produce hydrogen for fuel cells. Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims. |
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048521337 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, the present invention will be described in detail in conjunction with an illustrative embodiment by referring to FIGS. 1 and 2. The X-ray lithography apparatus according to the invention includes a soft X-ray generating unit 1, a gas chamber 2, a wafer stage 5 and others which can be of same structures as those of the prior art lithography apparatus such as the one disclosed in the aforementioned JP-A-57-16924 (corresponding to U.S. Pat. No. 4,403,336). As will be readily seen from the description of the prior art, if the heat generating components such as imaging unit and others can be installed outside of the gas chamber 2, cooling effect due to natural convection can be expected. However, mark detection optics 6 for allowing alignment marks of the mask and wafer to be picked up by the imaging unit 9 must be movable for adjusting its position in accordance with the sizes of masks as used by means of a positioning mechanism 10 including an X-Y stage which has a stroke greater than about 5 mm in at least one of the X- and Y-directions. Further, in view of the fact that the mask and the wafer must be positionally aligned with each other in the X-direction, Y-direction and in the angular direction 8, there are required at least three sets of the detection optics 6 and the imaging units 9, only one set of which is shown in FIG. 1 for simplification of the illustration. Additionally, a mirror 27 and an illuminating lens 28 constituting parts of illuminating optics are required to be mounted in the manner as shown in FIG. 1. Accordingly, the detection optics 6 and the imaging unit 9 are preferred to be disposed within the atmospheric gas chamber 2 in view of the hermetically sealed structure of the X-ray lithography apparatus as a whole. On the other hand, the imaging unit 9 such as television camera constitutes a major heat generating source. Accordingly, when the imaging unit 9 is disposed within the gas chamber 2, eat generated by the imaging unit is transmitted to the gas such as helium gas or the like filling the gas chamber 2, which in turn results in a temperature rise of the gas atmosphere and hence the detection optics disposed within the gas chamber 2, bringing about the problem of drift described hereinbefore. Under the circumstance, according to an aspect of the invention, a duct 13 is provided which opens in the gas chamber 2 at a position near the main heat generating source constituted by the imaging unit 9 realized in the form of a television camera, solid state imaging device such as charge-coupled device (CCD) or the like to be used for withdrawing under suction the helium gas from the gas chamber 2. The duct 13 is connected to a recharging duct 17 also opening in the gas chamber 2 through a flexible duct 14, a blower 15, a heat exchanger 16 and a flexible duct 14' so that the helium gas withdrawn through the discharge duct 13 is returned into the gas chamber 2 through the charging port 17. The temperature of the gas leaving the heat exchanger 16 is detected by a sensor 18 for controlling the heat transfer function of the heat exchanger 16 so that the temperature of the gas leaving the heat exchanger 16 remains constant. FIG. 2 shows a mounting structure of the imaging unit 9. As will be seen, the imaging unit 9 is composed of a solid state imaging device 19 and a control circuit substrate 20 and is disposed above the detecting optics 6. More specifically, the imaging unit 9 is fixedly secured to a supporting member 30 of the detecting optics 6 through an interposed heat insulation member 21. The optical axis of the detecting optics 6 is deflected upwardly by a mirror 22 so that the positioning mark image is projected onto the solid state imaging device 19. A reference numeral 25 denotes a light source for illumination which is disposed externally of the gas chamber 2. A glass fiber 26 serving for conduction of light emitted by the light source 25 has a light exit end portion which is secured on the detecting optics 9. A reference numeral 27 denotes a mirror which is so disposed that the light beam emitted from the exit end of the glass fiber 26 and reflected by the mirror 27 illuminates the alignment patterns on the mask 3 and wafer 4 in the direction inclined thereto. The control circuit substrate 20 which is a main heat generating source is enclosed by a casing 23 having an open top connected to the discharging duct 13, whereby the ambient gas surrounding the substrate 20 is withdrawn under suction into the discharging duct 13, as is indicated by arrows 24. The charging duct 17 (FIG. 1) is preferably disposed at such a position that a uniform flow of the helium gas can take place within the gas chamber 2 in the direction toward the discharging duct 13. More preferably, a flow rectifying plate member (not shown) is provided within the gas chamber 2 for ensuring more uniform gas flow taking place within the gas chamber 2. The heat generating part of the imaging unit 9 such a television camera or the like is supported by the heat insulation material 21 to thereby prevent heat from being transmitted directly to the parts constituting the detecting optics 6. Upon operation of the X-ray lithography apparatus of the structure described above, heat generated by the heat generating source within the gas chamber causes the temperature of the ambient helium gas to rise. However, the heated gas is immediately withdrawn through the discharging duct 13 and cooled down to a predetermined temperature level by means of the heat exchanger 16. Thus, accumulation of heat within the gas chamber 2 as well as the accompanying drift phenomenon of the alignment mark position detected by the optics 6 can be positively reduced to a minimum. Further, since the flexible ducts 14 and 14' are employed for incorporating the blower 15 in the gas recirculation path, vibration of the blower 15 is positively prevented from being transmitted to the detecting optics 6 and the mask 3, which would otherwise bring about fluctuation in the detected mark position and hence positional deviations of the mask 3 relative to the wafer 4. In the case of the illustrative embodiment, the heat exchanger 16 is disposed adjacent to the blower 15. However, since the heat exchanger 16 scarcely produces vibration of any significant magnitude, it can be disposed at a position adjacent to the gas chamber 2 if allowable in view of the available space, wherein the heat exchanger 16 may be connected to the blower 15 by another flexible duct 14. In a further modification, the blower 15 and the heat exchanger 16 may be disposed within the gas chamber 2, wherein the blower 15 may be supported by an appropriate anti-vibration mechanism (not shown) for preventing any vibration which would otherwise be transmitted to the detecting optics. It has been described that the amount of heat exchange is controlled or regulated in dependence on the exit temperature of the heat exchanger. However, when the heat exchanger as employed has a sufficiently large capacity, the exit temperature can be maintained constant simply by supplying a cooling water of a constant temperature to the heat exchanger. In a further version, a heater (not shown) may be additionally provided between the heat exchanger 16 and the temperature sensor 18, wherein the amount of heat generated by the heater is controlled as a function of the output signal of the sensor 18 to thereby maintain constant the temperature of the recirculated gas. For particulars of the structures of the detecting optics 6, the imaging unit 9 and others, reference may be made to U.S. patent application No. 789,778 filed on Oct. 21, 1985. As will now be appreciated from the foregoing description, it is possible according to the present invention to suppress drift of the alignment mark position detected by the detecting optics within a short time, whereby continuous operation of the X-ray lithography apparatus over day and night is rendered unnecessary. Further, the operating state of the X-ray lithography apparatus is stabilized rapidly upon alteration of the operating conditions. Thus, an enhanced working ratio of the apparatus can be accomplished. |
description | The present application is a Divisional patent application which claims priority from all the following applications: U.S. patent application Ser. No. 13/161,563 filed on Jun. 16, 2011, which is a Continuation-In-Part application of U.S. patent application Ser. No. 12/697,322, filed on Feb. 1, 2010, which is a Divisional application of U.S. patent application Ser. No. 11/087,844, filed on Mar. 23, 2005, which claims priority from U.S. Provisional Application Ser. No. 60/555,600, filed on Mar. 23, 2004, and Provisional Application Nos. 60/564,416, 60/564,417 and 60/564,469, each filed on Apr. 22, 2004, the disclosures of all of which are incorporated herein by reference. 1. Field of the Invention The present invention generally relates to a zirconium based alloy usable for the formation of strips and tubing for use in nuclear fuel reactor assemblies. Specifically, the invention relates to new technology that improves the in-reactor corrosion and/or the in-reactor creep of Zr—Nb based alloys by an essential and critical final heat treatment. The invention was applied to Zr—Nb based alloys that were developed by alloying element additions and exhibit improved corrosion resistance in water based reactors under elevated temperatures. 2. Description of the Prior Art In the development of nuclear reactors, such as pressurized water reactors and boiling water reactors, fuel designs impose significantly increased demands on all of the fuel components, such as cladding, grids, guide tubes, and the like. Such components are conventionally fabricated from zirconium-based alloys commercially titled ZIRLO, corrosion resistant alloys that contain about 0.5-2.0 wt. % Nb; 0.9-1.5 wt. % Sn; and 0.09-0.11 wt. % of a third alloying element selected from Mo, V, Fe, Cr, Cu, Ni, or W, with the rest Zr, as taught in U.S. Pat. No. 4,649,023 (Sabol et al.). That patent also taught compositions containing up to about 0.25 wt. % of the third alloying element, but preferably about 0.1 wt. %. Sabol et al., in “Development of a Cladding Alloy for High Burnup” Zirconium in the Nuclear Industry: Eighth International Symposium, L. F. Van Swan and C. M. Eucken, Eds., American Society for Testing and Materials, ASTM STP 1023, Philadelphia, 1989. pp. 227-244, reported improved properties of corrosion resistance for ZIRLO (0.99 wt. % Nb, 0.96 wt. % Sn, 0.10 wt. % Fe, remainder primarily zirconium) relative to Zircaloy-4. There have been increased demands on such nuclear core components, in the form of longer required residence times and higher coolant temperatures, both of which cause increase alloy corrosion. These increased demands have prompted the development of alloys that have improved corrosion and hydriding resistance, as well as adequate fabricability and mechanical properties. Further publications in this area include U.S. Pat. Nos. 5,940,464; 6,514,360 (Mardon et al. and Jeong et al.) and Reexamination Certificate U.S. Pat. No. 5,940,464 C1 (both Mardon et al.), and the paper “Advanced Cladding Material for PWR Application: AXIOM™”, Pan et al., Proceedings of 2010 LWR Fuel Performance/Top Fuel/WRFPM, Orlando, Fla. September 26-29, 2010 (“technical paper”). Mardon et al. taught zirconium alloy tubes for forming the whole or outer portion of a nuclear fuel cladding or assembly guide tube having a low tin composition: 0.8-1.8 wt. % Nb; 0.2-0.6 wt. % Sn, 0.02-0.4 wt. % Fe, with a carbon content of 30-180 ppm, a silicon content of 10-120 ppm and an oxygen content of 600-1800 ppm, with the rest Zr. Jeong et al. taught a niobium containing zirconium alloy for high burn-up nuclear fuel application containing Nb, Sn, Fe, Cr, Zr with possible addition of Cu. The Pan et al. “technical paper” lists Alloys listed as X1, X4, X5, X5A, but deliberately only very generally describes the actual composition weight percentages, being very vague in this regard. Pan et al. reports tensile strength, elongation and creep test data, and shows micrographs and in-reactor corrosion and oxide thickness data. Aqueous corrosion in zirconium alloys is a complex, multi-step process. Corrosion of the alloys in reactors is further complicated by the presence of an intense radiation field which may affect each step in the corrosion process. In the early stages of oxidation, a thin compact black oxide film develops that is protective and retards further oxidation. This dense layer of zirconia exhibits a tetragonal crystal structure which is normally stable at high pressure and temperature. As the oxidation proceeds, the compressive stresses in the oxide layer cannot be counterbalanced by the tensile stresses in the metallic substrate and the oxide undergoes a transition. Once this transition has occurred, only a portion of the oxide layer remains protective. The dense oxide layer is then renewed below the transformed oxide. A new dense oxide layer grows underneath the porous oxide. Corrosion in zirconium alloys is characterized by this repetitive process of growth and transition. Eventually, the process results in a relatively thick outer layer of non-protective, porous oxide. There have been a wide variety of studies on corrosion processes in zirconium alloys. These studies range from field measurements of oxide thickness on irradiated fuel rod cladding to detailed micro-characterization of oxides formed on zirconium alloys under well-controlled laboratory conditions. However, the in-reactor corrosion of zirconium alloys is an extremely complicated, multi-parameter process. No single theory has yet been able to completely define it. Corrosion is accelerated in the presence of lithium hydroxide. As pressurized water reactor (PWR) coolant contains lithium, acceleration of corrosion due to concentration of lithium in the oxide layer must be avoided. Several disclosures in U.S. Pat. Nos. 5,112,573 and 5,230,758 (both Foster et al.) taught an improved ZIRLO composition that was more economically produced and provided a more easily controlled composition while maintaining corrosion resistance similar to previous ZIRLO compositions. It contained 0.5-2.0 wt. % Nb; 0.7-1.5 wt. % Sn; 0.07-0.14 wt. % Fe and 0.03-0.14 wt. % of at least one of Ni and Cr, with the rest Zr. This alloy had a 520° C. high temperature steam weight gain at 15 days of no more than 633 mg/dm2. U.S. Pat. No. 4,938,920 to Garzarolli teaches a composition having 0-1 wt. % Nb; 0-0.8 wt. % Sn, and at least two metals selected from iron, chromium and vanadium. However, Garzarolli does not disclose an alloy that had both niobium and tin, only one or the other. Sabol et al. in “In-Reactor Corrosion Performance of ZIRLO and Zircaloy-4,” Zirconium in the Nuclear Industry: Tenth International Symposium, A. M. Garde and E. R. Bradley Eds., American Society for Testing and Materials, ASTM STP 1245, Philadelphia 1994, pp. 724-744, demonstrated that, in addition to improved corrosion performance, ZIRLO material also has greater dimensional stability (specifically, irradiation creep and irradiation growth) than Zircaloy-4. More recently, U.S. Pat. No. 5,560,790 (Nikulina et al.) taught zirconium-based materials having high tin contents where the microstructure contained Zr—Fe—Nb particles. The alloy composition contained: 0.5-1.5 wt. % Nb; 0.9-1.5 wt. % Sn; 0.3-0.6 wt. % Fe, with minor amounts of Cr, C, O and Si, with the rest Zr. While these modified zirconium based compositions are claimed to provide improved corrosion resistance as well as improved fabrication properties, economics have driven the operation of nuclear power plants to higher coolant temperatures, higher burn-ups, higher concentrations of lithium in the coolant, longer cycles, and longer in-core residence times that have resulted in increased corrosion duty for the cladding. Continuation of this trend as burn-ups approach and exceed 70,000 MWd/MTU will require further improvement in the corrosion properties of zirconium based alloys. The alloys of this invention provide such corrosion resistance. Another potential way to increase corrosion resistance is through the method of forming of the alloy itself. To form alloy elements into a tubing or strip, ingots are conventionally vacuum melted and beta quenched, and thereafter formed into an alloy through a gauntlet of reductions, intermediate anneals, and final anneals, wherein the intermediate anneal temperature is typically above 1105° F. for at least one of the intermediate anneals. In U.S. Pat. No. 4,649,023 to Sabol et al., the ingots are extruded into a tube after the beta quench, beta annealed, and thereafter alternatively cold worked in a pilger mill and intermediately annealed at least three times. While a broad range of intermediate anneal temperatures are disclosed, the first intermediate anneal temperature is preferably 1112° F., followed by a later intermediate anneal temperature of 1076° F. The beta annealing step preferably uses temperatures of about 1750° F. Foster et al., in U.S. Pat. No. 5,230,758, determined the formability and steam corrosion for intermediate anneal temperatures of 1100° F., 1250° F., and 1350° F. An increase in intermediate anneal temperature is associated with an increase in both formability and corrosion resistance. U.S. Pat. No. 5,887,045 to Mardon et al. discloses an alloy forming method having at least two intermediate annealing steps carried out between 1184° to 1400° F. Note that the prior art for corrosion improvement summarized above involves alloying element additions and different intermediate anneal temperatures, but, notably, not the final anneal heat treatment temperature. Rudling et al., in, “Corrosion Performance of Zircaloy-2 and Zircaloy-4 PWR Fuel Cladding,” Zirconium in the Nuclear Industry: Eight International Symposium, ASTM STP 1023, L. F. Van Swam and C. M. Eucken, eds. American Society for Testing and Materials, Philadelphia, 1989, pp. 213-226, reported that Zr-4 fuel rod cladding fabricated from the same ingot with final heat treatments of stress-relieved (SRA) and fully recrystallized (RXA) exhibited similar oxide thickness corrosion (see Table 1). TABLE 1Post irradiation oxide thickness of Zr-4 cladding after 1-cycle of irradiation.Final Heat4 Rod Average of the Maximum OxideTreatmentThickness (μm)SRA12 +/− 1RXA10 +/− 1 Foster et al., in U.S. Pat. No. 5,125,985, presents a straightforward method of controlling the creep by use of the final area reduction and intermediate anneal temperature. A decrease in final area reduction decreases creep, and an increase in intermediate anneal temperature decreases creep. In different applications, the in-reactor creep can be more important than in-reactor corrosion. One such example is fuel rods containing fuel pellets coated with ZrB2. ZrB2 is a neutron absorber. When neutrons are absorbed, He gas is released which increases the rod internal pressure. In this case, creep resistant cladding is necessary so that the fuel/cladding gap remains closed. A closed fuel/cladding gap ensures that the fuel temperatures do not increase due to the formation of a He gas gap between the fuel and cladding. The new technology presented below in the Summary of the Invention will show that either the cladding corrosion or the cladding in-reactor creep may be improved by the final heat treatment. A further issue in nuclear reactors is corrosion of welds utilized in a nuclear fuel assembly. In a typical fuel rod, nuclear fuel pellets are placed within the cladding, which is enclosed by end caps on either end of the cladding, such that the end caps are welded to the cladding. The weld connecting the end caps to the cladding, however, generally exhibits corrosion to an even greater extent than the cladding itself, usually by a factor of two over non-welded metal. Rapid corrosion of the weld creates an even greater safety risk than the corrosion of non-welded material, and its protection has previously been ignored. In addition, grids have many welds and the structural integrity depends on adequate weld corrosion resistance. Thus, there continually remains a vital need, even in this late stage of nuclear power development, for novel zirconium cladding alloys that exhibit improved corrosion resistance and improved in-reactor irradiation creep resistance over known alloys in the field, and improved welds for holding end caps on claddings and for joining grid straps that likewise exhibit increased corrosion resistance. And, as can be seen, these cladding art patents and papers provide an extremely compact art area, where only very minor changes have shown, after extended testing, major and dramatic improvements. Thus, minor improvements can easily establish patentability in this specific area. Accordingly, an object of the present invention is to provide Zr—Nb alloys with improved corrosion resistance and/or improved in-reactor irradiation creep resistance through the selection of a specific type combination of final heat treatment. New technology presented below in the Summary of the Invention, and elsewhere in the specification following, will show that the in-reactor corrosion is, in part, unexpectedly dependent on the specific type of final heat treatment. The Zr—Nb alloys of this invention have improved alloy chemistry, improved weld corrosion resistance, and improved method of formation of alloys having reduced intermediate anneal temperatures during formation of the alloys. The new technology showing the effect of an essential and critical final heat treatment (and the final microstructure) on the in-reactor corrosion of Zr—Nb—Sn—Fe type alloys is presented in FIGS. 1 and 2. FIG. 1 shows the in-reactor oxide thickness corrosion data for 0.77 weight % Sn ZIRLO irradiated for 1, 2 and 3 cycles in the Vogtle Unit 2 PWR. All of the cladding was fabricated from the same ingot and received identical processing except for the final heat treatment. The cladding was given 3 different final anneal heat treatments of stress relief annealed (“SRA”), partially recrystallized (“PRXA”) and fully recrystallized (“RXA”). The amount of recrystallization in the PRXA heat treatment was about 15-20%. A generic composition useful in this invention, to provide unexpected results in corrosion resistance and/or in-reactor irradiation creep resistance, is an alloy comprising: 0.2 to 1.5 weight percent niobium, 0.01 to 0.6 weight percent iron, and additional alloying elements selected from the group consisting of: 0.0 to 0.8 weight percent tin 0.0 to 0.5 weight percent chromium 0.0 to 0.3 weight percent copper 0.0 to 0.3 weight percent vanadium 0.0 to 0.1 weight percent nickel, with the balance at least 97 weight percent zirconium, including impurities, wherein said alloy is characterized in that it has improved corrosion resistance properties due to a final heat treatment selected from one of i) SRA or PRXA (15-20% RXA) providing low corrosion; or ii) RXA or PRXA (80-95% RXA) providing low creep rate. Impurities mean less than 60 ppm or 0.006 wt. %. Other more specific compositions are set forth in the specification and claims. Referring now to the drawings; FIG. 1 very importantly shows that the oxide thickness depends on the final heat treatment. FIG. 1 presents the corrosion of 0.77 Sn ZIRLO. All of the cladding was fabricated from the same ingot and received identical processing except for the final heat treatment. The cladding was given three final heat treatments of SRA, PRXA and RXA. The highest corrosion (highest oxide thickness) was exhibited by cladding with the RXA—fully recrystallized—final heat treatment. Significantly lower corrosion was exhibited by cladding with both SRA and PRXA (15% to 20%) final heat treatments. FIG. 2 very importantly shows the in-reactor oxide thickness corrosion data for Standard ZIRLO (1.02 weight % Sn) irradiated for 1, 2 and 3 cycles in the Vogtle Unit 2 PWR. All of the cladding was fabricated from the same ingot and received identical processing except for the final heat treatment. The cladding was given 2 different final anneal heat treatments of SRA and RXA. FIG. 2, very importantly, shows that the oxide thickness depends on the final heat treatment as exhibited by the 0.77 weight % Sn ZIRLO data in FIG. 1. The highest corrosion (highest oxide thickness) was exhibited by cladding with the RXA final heat treatment. Significantly lower corrosion was exhibited by cladding with the SRA final heat treatment. As discussed above, depending on the application, improved in-reactor creep resistance can be as important as improved corrosion resistance. The in-reactor creep is also dependent on the final heat treatment. FIG. 3, very importantly, presents the in-reactor steady state creep rate for 0.77 weight % Sn ZIRLO irradiated for 1, 2 and 3 cycles in the Vogtle Unit 2 PWR. FIG. 3 shows that the highest in-reactor creep resistance (that is, the lowest in-reactor creep rate) is exhibited by cladding with a RXA final heat treatment. The lowest in-reactor creep resistance (that is, the highest in-reactor creep rate) is exhibited by cladding with a SRA final heat treatment. Intermediate in-reactor creep resistance is exhibited by the PRXA final heat treatment. Thus, both SRA and PRXA are effective in this regard with RXA the best. Hence, the effect of final heat treatment on in-reactor creep is opposite that of in-reactor corrosion. As a result, the cladding may be optimized for either maximum improved in-reactor corrosion resistance with a SRA or PRXA (15-20% RXA) final heat treatment, or maximum improved in-reactor creep resistance with a final PRXA (80-95% RXA) or RXA heat treatment. In more substantial detail, each of these “terms,” RXA, PRXA, SRA, etc. is defined as: SRA means—heat treatment where the microstructure is stress-relief annealed. RXA means—heat treatment where the microstructure is fully recrystallized. PRXA (15-20% RXA) means—heat treatment where 15-20% of the microstructure is recrystallized and 80-85% of the microstructure is stress relief annealed. PRXA (80-95% RXA) means—heat treatment where 80-95% of the microstructure is recrystallized and 5-20% of the microstructure is stress relief annealed. Note that the above SRA, PRXA and RXA designations represent more detailed descriptions of the final heat treatment process methods. It should be clear that this art area is not an area in patent filing where broad conclusions are suggestive of improved alloys within broad ranges; where, for example, 0.4 to 1.5 weight percent niobium and 0.1 to 0.8 weight percent tin, should be considered taught or obvious in view of a teaching of 0.0 to 3.0 weight percent niobium and 0.1 to 3.5 weight percent tin. As shown in FIG. 4, standard Zirlo compared to compositions X4 and X5 shows the dramatic difference a few tenths of weight percent elements make in this area: Standard Zirlo:0.5-2 wt % Nb;0.9-1.5 wt. % SnX4:1 wt. % Nb;0 wt. % Sn, etc. orX5:0.7 wt. % Nb;0.3 wt. % Sn, etc.; where these seemingly reduced and very important minor changes in component elements provide extraordinarily improved oxide thickness. Specifically, at a burnup of 70 GWd/MTU, the oxide thickness is reduced at least by a factor of 3.5. FIG. 4, very dramatically, illustrates at 75 GWd/MTU a range of oxide thickness of about 35-40 micrometer for alloy X1, and a range of about 16 to 26 micrometers for alloys X4 and X5, all showing critical improvements relative to standard ZIRLO. A further object of the present invention is to provide a zirconium based alloy for use in an elevated temperature environment of a nuclear reactor, the alloy having 0.2 to 1.5 weight percent niobium, 0.01 to 0.6 weight percent iron, and additional alloy elements selected from 0.0 to 0.8 weight percent tin, 0.0 to 0.5 weight percent chromium, 0.0 to 0.3 weight percent copper, 0.0 to 0.3 weight percent vanadium, 0.0 to 0.1 weight percent nickel, the remainder at least 97 weight percent zirconium, including impurities. Further descriptions of vastly improved alloys X1, X4 and X5 follow. Alloy X4: A further object of the present invention is to provide a zirconium based alloy (denoted as Alloy X4) for use in an elevated temperature environment of a nuclear reactor, the alloy having 0.6 to 1.5 weight percent niobium, 0.02 to 0.3 weight percent Cu, 0.01 to 0.1 weight percent iron, 0.15 to 0.35 weight percent chromium, the balance at least 97 weight percent zirconium, including impurities. Alloy X5: A further object of the present invention is to provide a zirconium based alloy (denoted as Alloy X5), the alloy having 0.2 to 1.5 weight percent niobium, 0.25 to 0.45 weight percent iron, 0.05 to 0.4 weight percent tin, 0.15 to 0.35 weight percent chromium, 0.01 to 0.1 weight percent nickel, the balance at least 97 weight percent zirconium, including impurities. Alloy X1: A further object of the invention is to provide a zirconium based alloy (denoted as Alloy X1), the alloy having 0.4 to 1.5 weight percent niobium, 0.05 to 0.4 weight percent tin, 0.01 to 0.1 weight percent iron, 0.02 to 0.3 weight percent copper, 0.12 to 0.3 weight percent vanadium, 0.0 to 0.5 weight percent chromium, the balance at least 97 weight percent zirconium, including impurities. Alloy X6: A further specific object of the invention is to provide a zirconium based alloy (denoted as Alloy X6 and referred to as “Optimized” ZIRLO), shown in FIG. 4, the alloy having 0.4 to 1.5 weight percent niobium, 0.1 to 0.8 weight percent tin, 0.01 to 0.6 weight percent iron, 0.0 to 0.5 weight percent chromium, the balance at least 97 weight percent zirconium, including impurities. This alloy is still vastly superior to standard ZIRLO. The final heat treatment of Alloy X1 is PRXA (˜80% RXA), which is associated with maximum, improved (low) in-reactor creep resistance. In addition, note that the corrosion resistance of Alloy X1 is significantly increased relative to Standard ZIRLO, by a factor of 2.2 at a burn-up of 70 GWd/MTU (see FIG. 4), because of decreased Sn and the addition of Cu. Further, if the amount of RXA in the PRXA final heat treatment of Alloy X1 is decreased to about 15-20%, the corrosion resistance of Alloy X1 would be further improved. The final heat treatment of Alloy X4 is PRXA (˜80% RXA) which is associated with maximum improved in-reactor creep resistance. At a burn-up of 70 GWd/MTU, the corrosion resistance of Alloy X4 is increased be a factor of about 3.5 (see FIG. 4) relative to Standard ZIRLO. Note that the corrosion resistance of Alloy X4 is significantly increased relative to Standard ZIRLO because of decreased Sn and the additions of Cu and Cr. In addition, if the amount of RXA in the PRXA final heat treatment of Alloy X4 is decreased to about 15-20% PRXA (15-20% RXA), the corrosion resistance of Alloy X4 would by further improved. The final heat treatment of Alloy X5 is PRXA (˜50% RXA), which is considered to be intermediate between maximum improved in-reactor creep resistance and maximum improved in-reactor corrosion resistance. FIG. 4 shows that at a burn-up of 70 GWd/MTU, the corrosion resistance of Alloy X5 is increased be a factor of about 3.0 relative to Standard ZIRLO. Note that the corrosion resistance of Alloy X5 is significantly increased relative to Standard ZIRLO because of decreased Sn, increased Fe and the addition of Cr. A sequence of steps for forming a cladding, strip, tube or like object known in the art from an alloy of the present invention is shown in FIGS. 5A and 5B. To create tubing for cladding, as shown in FIG. 5A, compositional zirconium based alloys were fabricated from vacuum melted ingots or other like material known in the art. The ingots were preferably vacuum arc-melted from sponge zirconium with a specified amount of alloying elements. The ingots were then forged into a material and thereafter β-quenched. β-quenching is typically done by heating the material (also known as a billet) up to its β-temperature, between around 1273 to 1343K. The quenching generally consists of quickly cooling the material by water. The β-quench is followed by extrusion. Thereafter, the processing includes cold working the tube-shell by a plurality of cold reduction steps, alternating with a series of intermediate anneals at a set temperature. The cold reduction steps are preferably done on a pilger mill. The intermediate anneals are conducted at a temperature in the range of 960-1125° F. The material may be optionally re-β-quenched prior to the final and formed into an article there-from. The final heat treatment discussed previously is also shown. For tubing, a more preferred sequence of events after extrusion includes initially cold reducing the material in a pilger mill, an intermediate anneal with a temperature of about 1030 to 1125° F., a second cold reducing step, a second intermediate anneal within a temperature range of about 1030° to 1070° F., a third cold reducing step, and a third intermediate anneal within a temperature range of about 1030° to 1070° F. The reducing step prior to the first intermediate anneal is a tube reduced extrusion (TREX), preferably reducing the tubing about 55%. Subsequent reductions preferably reduce the tube about 70-80%. Each reduction pass on the pilger mill is preferred to reduce the material being formed by at least 51%. The material then preferably goes through a final cold reduction. The material is then processed with a final anneal at temperatures from about 800-1300° F. To create strip, compositional zirconium based alloys were fabricated from vacuum melted ingots or other like material known in the art. The ingots were preferably arc-melted from sponge zirconium with a specified amount of alloying elements. The ingots were then forged into a material of rectangular cross-section and thereafter β-quenched. Thereafter, the processing as shown in FIG. 5B, includes a hot rolling step after the beta quench, cold working by one or a plurality of cold rolling and intermediate anneal steps, wherein the intermediate anneal temperature is conducted at a temperature from about 960-1105° F. The material then preferably goes through a final pass and anneal, wherein the final anneal temperature is in the range of about 800-1300° F. The final heat treatment discussed previously is also shown. A more preferred sequence to create the alloy strip includes an intermediate anneal temperature within a range of about 1030 to 1070° F. Further, the pass on the mill preferably reduces the material being formed by at least 40%. The corrosion resistance was found to improve with intermediate anneals also that were consistently in the range of 960-1105° F., most preferably around 1030-1070° F., as opposed to typical prior anneal temperatures that are above the 1105° F. for at least one of the temperature anneals. As shown in FIGS. 6-10, a series of preferred alloy embodiments of the present invention were tested for corrosion in a 680° F. water autoclave and measured for weight gain. Tubing material was fabricated from the preferred embodiments of alloys of the present invention, referenced as Alloys X1, X4, X5 and X6, and placed in the 680° F. water autoclave. Data were available for a period of 100 days. Corrosion resistance measured in 680° F. water autoclaves for long term exposure have previously been found to correlate to corrosion resistance data of like alloys placed in-reactor. The preferred composition of these embodiments, further discussed below, are shown in Table 2. The preferred ranges of the compositions are presented in Table 3. TABLE 2AlloyPreferred Composition, by weight percentageX1Zr-0.7Nb-0.3Sn-0.12Cu-0.18V-0.05FeX1Zr-1.0Nb-0.3Sn-0.12Cu-0.18V-0.05FeX1 + CrZr-0.7Nb-0.3Sn-0.12Cu-0.18V-0.05Fe-0.2CrX1 + CrZr-1.0Nb-0.3Sn- 0.12Cu-0.18V-0.05Fe-0.2CrX4Zr-1.0Nb-0.05Fe-0.25Cr-0.08CuX5Zr-0.7Nb-0.3Sn-0.3Fe-0.25Cr-0.05NiX6Zr-1.0Nb-0.65Sn-0.1FeX6 + CrZr-1.0Nb-0.65Sn-0.1Fe-0.2Cr TABLE 3AlloyPreferred Composition Ranges, by weight percentageX1Zr; 0.4-1.5Nb; 0.05-0.4Sn; 0.01-0.1Fe; 0.02-0.3Cu; 0.12-0.3VX1 − CrZr; 0.4-1.5Nb; 0.05-0.4Sn; 0.01-0.1Fe; 0.02-0.3Cu; 0.12-0.3V; 0.05-0.5CrX4Zr; 0.6-1.5Nb; 0.01-0.1Fe; 0.02-0.3Cu; 0.15-0.35CrX5Zr; 0.2-1.5Nb; 0.05- 0.4Sn; 0.25-0.45Fe; 0.15-0.35Cr;0.01-0.1NiX6Zr; 0.4-1.5Nb; 0.14-0.8Sn; 0.01-0.6FeX6 + CrZr; 0.4-1.5Nb; 0.1-0.8Sn; 0.01-0.6Fe; 0.05-0.5Cr In order to evaluate the effect of intermediate anneal temperature on corrosion/oxidation, tubing of Standard ZIRLO and Alloys X1, X4 and X5 were processed with intermediate anneal temperatures of 1030° and 1085° F. The alloys of the invention were tested for corrosion resistance by measuring the weight gain over a period of time, wherein the weight gain is mainly attributable to an increase of oxygen (the hydrogen pickup contribution to the weight gain is relatively small and may be neglected) that occurs during the corrosion process. In general, corrosion related weight gain starts quickly and then the rate decreases with increasing time. This initial corrosion/oxidation process is termed as pre-transition corrosion. After a period of time, the corrosion rate increases, approximately linearly with time. This corrosion/oxidation phase is termed post-transition or rapid corrosion. As would be expected, alloys with greater corrosion resistance have lower corrosion rates in the pre- and post-transition phases. FIGS. 6-10 present 680° F. water corrosion test data. As can be seen in FIGS. 6-10, the weight gain associated with tubing processed with 1030° F. intermediate anneal temperatures was less than for higher intermediate anneal temperatures. Further, the weight gains for Alloys X1, X4, X5 and X6 in FIGS. 7-10 were less than that of Standard ZIRLO in FIG. 6. Thus, as the modified alloy compositions and the lower intermediate anneal temperatures exhibit reduced weight gain, and reduced weight gain is correlated with increased corrosion resistance, increased corrosion resistance is directly correlated with the modified alloy compositions and the lower intermediate anneal temperature of the invention. The chemistry formulation of the alloys is correlated with increased corrosion resistance. All of the weight gains from the 680° F. water autoclave testing presented in FIGS. 6-10 are in the pre-transition phase. Although the improvement in the 680° F. water autoclave corrosion weight gain due to lowering of the intermediate anneal temperature appears to be small in view of FIGS. 6-10, the improvement of in-reactor corrosion resistance is expected to be higher than shown by the 680° F. water autoclave data because of in-reactor precipitation of second phase particles in these Zr—Nb alloys and a thermal feedback from a lower oxide conductivity due to lower oxide thickness. Such second phase particle precipitation only occurs in-reactor and not in autoclave testing. In order to evaluate the effect of intermediate anneal temperature in post-transition corrosion, an 800° F. steam autoclave test was performed, as shown in FIGS. 11-15. The test was performed for sufficient time to achieve post-transition corrosion. Post transition corrosion rates generally began after a weight gain of about 80 mg/dm2. Alloys X1, X4, X5 and Standard ZIRLO were processed using intermediate anneal temperatures of 1030° and 1085° F. Alloy X6 (Optimized Zirlo) tubing was processed using intermediate anneal temperatures of 1030° and 1105° F. The tubing was placed in an 800° F. steam autoclave for a period of about 110 days. FIGS. 11-15 show that the post-transition weight gains of the alloys processed at the intermediate anneal temperature of 1030° F. are less than for alloy materials processed at the higher temperatures of 1085° or 1105° F. Further, the weight gain for Alloys X1, X4, X5 and X6 (Optimized Zirlo) of FIGS. 12-15 are less than those of the prior disclosed Standard ZIRLO presented in FIG. 11. Thus, the low intermediate anneal temperatures provide substantial improvements over the prior art as it provides a significant advantage in safety, by protecting cladding or the grids from corrosion, in cost, as replacement of the fuel assemblies can be done less often, and through efficiency, as the less corroded cladding better transmits the energy of the fuel rod to the coolant. Standard ZIRLO strip was processed with intermediate anneal temperatures of 968° and 1112° F. The material was tested for corrosion resistance by measuring the weight gain over a period of time, wherein the weight gain is mainly attributable to an increase of oxygen (the hydrogen pickup contribution to the weight gain is relatively small and may be neglected) that occurs during the corrosion process. The low temperature strip was processed with an intermediate anneal temperature of 968° F. and a final anneal temperature of 1112° F. The standard strip was processed with an intermediate anneal temperature of 1112° F. and a final anneal temperature of 1157° F. FIG. 16 shows that the low temperature processed material exhibits significantly lower corrosion/oxidation than the higher temperature processed material. The zirconium alloys of the present invention provide improved corrosion resistance through the chemistry of new alloy combinations. The alloys are generally formed into cladding (to enclose fuel pellets) and strip (for spacing fuel rods) for use in a water based nuclear reactor. The alloys generally include 0.2 to 1.5 weight percent niobium, 0.01 to 0.6 weight percent iron, and additional alloying elements selected from the group consisting of: 0.0 to 0.8 weight percent tin, 0.0 to 0.5 weight percent chromium, 0.0 to 0.3 weight percent copper, 0.0 to 0.3 weight percent vanadium and 0.01 to 0.1 weight percent nickel. The balances of the alloys are at least 97 weight percent zirconium, including impurities. Impurities may include about 900 to 1500 ppm of oxygen. A first embodiment of the present invention is a zirconium alloy having, by weight percent, about 0.4-1.5% Nb; 0.05-0.4% Sn, 0.01-0.1% Fe, 0.02-0.3% Cu, 0.12-0.3% V, 0.0-0.5% Cr and at least 97% Zr including impurities, hereinafter designated as Alloy X1. This embodiment, and all subsequent embodiments, should have no more than 0.50 wt. % additional other component elements, preferably no more than 0.30 wt. % additional other component elements, such as nickel, chromium, carbon, silicon, oxygen and the like, and with the remainder Zr. Chromium is an optional addition to Alloy X1. Wherein chromium is added to Alloy X1, the alloy is hereinafter designated as Alloy X1+Cr. Alloy X1 was fabricated into tubing and its corrosion rate was compared to that of a series of alloys likewise fabricated into tubing, including ZIRLO-type alloys and Zr—Nb compositions. The results are shown in FIG. 4. FIG. 4 shows that the in-reactor corrosion resistance of Alloy X1 is increased by a factor of 2.2 relative to Standard ZIRLO. The chemistry formulations of Alloy X1 provide substantial improvement over the prior art as it relates to corrosion resistance in a nuclear reactor. A second embodiment of the present invention is a zirconium alloy having, by weight percent, about, about 0.6-1.5% Nb; 0.01-0.1% Fe, 0.02-0.3% Cu, 0.15-0.35% Cr and at least 97% Zr, hereinafter designated as Alloy X4. FIG. 4 shows that the in-reactor corrosion resistance of Alloy X4 is increased by a factor of 3.5 relative to Standard ZIRLO. A preferred composition of Alloy X4 has weight percent ranges for the alloy with about 1.0% Nb, about 0.05% Fe, about 0.25% Cr, about 0.08% Cu, and at least 97% Zr. The preferred Alloy X4 was fabricated into tubing and its corrosion rate was compared with the corrosion rate of Standard ZIRLO. The chemistry formulations of Alloy X4, like Alloy X1, provides substantial improvements over the prior art as it relates to corrosion resistance in a nuclear reactor. A third embodiment of the present invention is a zirconium alloy having, by weight percent, about 0.2-1.5% Nb; 0.05-0.4% Sn, 0.25-0.45% Fe, 0.15-0.35% Cr, 0.01-0.1% Ni, and at least 97% Zr, hereinafter designated as Alloy X5. This composition should have no more than 0.5 wt. % additional other component elements, preferably no more than 0.3 wt. % additional other component elements, such as carbon, silicon, oxygen and the like, and with the remainder Zr. A preferred composition of Alloy X5 has weight percent values for the alloy with about 0.7% Nb; about 0.3% Sn, about 0.35% Fe, about 0.25% Cr, about 0.05% Ni, and at least 97% Zr. The preferred embodiment of Alloy X5 was fabricated into tubing and its corrosion rate was compared to that of a series of alloys likewise fabricated into tubing. FIG. 4 shows that the in-reactor corrosion resistance of Alloy X5 is increased by a factor of 3.0 relative to Standard ZIRLO. The chemistry formulations of Alloy X5 provide substantial improvement over the prior art as it relates to corrosion resistance in a nuclear reactor. Another embodiment of the invention is a low-tin ZIRLO alloy designated as Alloy X6 (“Optimized Zirlo”). FIG. 4 shows that the corrosion in-reactor resistance of Alloy X6 is increased by a factor of 1.5 relative to Standard ZIRLO. The reduction of tin increases the corrosion resistance. Tin, however, increases the in-reactor creep strength, and too small an amount of tin makes it difficult to maintain the desired creep strength of the alloy. Thus, the optimum tin of this alloy must balance these two factors. As a result, this embodiment is a low-tin alloy essentially containing, by weight percent, 0.4-1.5% Nb; 0.1-0.8% Sn, 0.01-0.6% Fe, and the balance at least 97% Zr, including impurities, hereinafter designated as Alloy X6. A preferred composition of Alloy X6 has weight percent ranges of about 1.0% Nb, about 0.65% Sn, about 0.1% Fe, and at least 97% Zr, including impurities. Tin may be decreased if other alloy elements are included to replace the strengthening effect of tin. A second preferred embodiment of Alloy X6 (“Optimized Zirlo”) has generally the same weight percentages plus 0.05-0.5% Cr, hereinafter designated as Alloy X6+Cr. A preferred embodiment of Alloy X6+Cr has about 1.0% Nb, about 0.65% Sn, about 0.1% Fe and about 0.2% Cr. Alloy X6 provides substantial improvements in comparison to Standard ZIRLO over the prior art as it relates to corrosion resistance in a nuclear reactor. Weld-Corrosion Resistance In a typical nuclear fuel assembly large numbers of fuel rods are included. In each fuel rod nuclear fuel pellets are placed within cladding tubes that are sealed by end caps such that the end caps are welded to the cladding. The end cap-cladding weld, however, is susceptible to corrosion to an even greater extent than the non-welded cladding itself, usually by a factor of two. Zirconium alloys that include chromium show increased weld corrosion resistance. Thus, the addition of chromium in a zirconium alloy includes substantial advancement over prior zirconium alloys that do not include chromium. Multiplicities of alloys were tested for their effect on weld corrosion, as shown in Table 4. Several alloys were tested for their effect on laser strip welds in a 680° F. water autoclave test for an 84 day period. Some of these alloys had chromium, while the other alloys did not include chromium except in unintentional trace amounts. Still other alloy tube welds were tested in the form of magnetic force welds in an 879-day 680° F. water autoclave test. Each weld specimen placed in the two autoclave tests contained the weld and about 0.25 inches of an end plug and tube on either side of the weld. Separate same length tube specimens without the weld were also included in the test. The weight gain data were collected on the weld and tube specimens. The ratio of the weld corrosion to the non-weld corrosion was determined either from the weight gain data or the metallographic oxide thickness measurements at different locations on the specimen. TABLE 4Weld/Base Alloy NameComposition by weight %Corrosion RatioLASER STRIPWELDSStandard ZIRLOZr-0.95Nb-1.08Sn-0.11Fe2.07Zr-NbZr-1.03Nb2.307Low-Sn ZIRLOZr-1.06Nb-0.73Sn-0.27Fe1.71StandardZr-0.97Nb-0.99Sn-0.10Fe2.094ZIRLO/590° C.RXAAlloy AZr-0.31Nb-0.51Sn-0.35Fe- 1.3330.23CrMAGNETICFORCE TUBEWELDSOptin Zr − 4Zr-1.35Sn-0.22Fe-0.10Cr0.805Zr − 4 + FeZr-1.28Sn-0.33Fe-0.09Cr0.944Zr − 2PZr-1.29Sn-0.18Fe-0.071.008Ni-0.10CrAlloy CZr-0.4Sn-0.5Fe-0.24Cr0.955Alloy EZr-0.4Nb-0.7Sn-0.45 1.168Fe-0.03Ni-0.24Cr As shown in Table 4, the ratios of the zirconium alloys not having chromium had a weld to base metal corrosion ratio of 1.71 or greater. In contrast, the zirconium alloys containing chromium had a maximum ratio of 1.333 or lower. The chromium additions reduce the ratio of weld corrosion relative to that of the base metal. Thus, the addition of chromium significantly reduces weld corrosion, thereby increasing the safety, cost and efficiency of the nuclear fuel assembly. The differences in weld versus base metal corrosion may be explained by differences in vacancy concentration. The weld region is heated to high temperature during welding, and cools at a faster rate than the base material. In a typical increase of temperature, the vacancies in the metal increase exponentially with the temperature. A fraction of the atomic vacancies introduced during the temperature increase are quenched during the cooling of the weld and, as a result, the vacancy concentration is higher in the weld region. Thus, the vacancy concentration is higher in the weld than the heat affected regions of the non-weld region. Since waterside corrosion of zirconium alloys is postulated to occur by vacancy exchange with oxygen ions, increased vacancy concentration in the weld region can increase vacancy/oxygen exchange and thereby increase corrosion in the weld region if the vacancies are not pinned by an alloying element. This exchange will be reduced resulting in improvement of corrosion resistance of the weld. Due to a high solubility of chromium in beta zirconium (about 47% weight percent), chromium is an effective solid solution element to pin the vacancies in the beta phase and thereby decrease the corrosion enhancement due to oxygen ion exchange with supersaturated vacancies in the quenched weld region. While a full and complete description of the invention has been set forth in accordance with the dictates of the patent statutes, it should be understood that modifications can be resorted to without departing from the spirit hereof or the scope of the appended claims. For example, the time for the intermediate anneals can vary widely while still maintaining the spirit of the invention. |
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claims | 1. An arrangement for generating intensive radiation based on a plasma, comprising:a target generator with a nozzle for metering and orientation of a target flow for plasma generation;a vacuum chamber; anda high-energy excitation radiation being directed to the target flow in the vacuum chamber and the target flow being completely converted piece by piece by a defined pulse energy of the excitation radiation into a plasma having a high conversion efficiency for the intensive radiation in a desired wavelength region;said nozzle of the target generator being a multiple-channel nozzle with a plurality of separate orifices, the orifices generating a plurality of target jets, the excitation radiation for generating plasma being directed simultaneously portion by portion to the target jets within a spot of radiation;said separate orifices of the nozzle being arranged in such a way that the target jets fill the radiation spot of the excitation radiation without gaps and without overlapping, wherein the orifices are arranged offset although the target jets appear closed to one another in the radiation spot. 2. The arrangement according to claim 1, wherein said separate orifices of the nozzle are arranged in a plurality of rows so as to be offset to one another. 3. The arrangement according to claim 2, wherein said separate orifices of the nozzle are provided as parallel rows with an equal spacing between the orifices, wherein the rows are arranged one behind the other with respect to the incident direction of the excitation radiation and are arranged so as to be offset relative to one another by a fraction of the spacing between the orifices depending upon the quantity of rows arranged one behind the other. 4. The arrangement according to claim 3, wherein said separate orifices of the nozzle are arranged in two parallel rows which are oriented orthogonal to the direction of the excitation radiation and are offset relative to one another by one half of the orifice spacing. 5. The arrangement according to claim 2, wherein the rows of orifices intersect, and intersecting rows share their first or last orifice as a common intersection and are oriented in a mirror-symmetric manner relative to the incident direction of the excitation radiation at the same angle of intersection. 6. The arrangement according to claim 5, wherein two intersecting rows of orifices are oriented in a V-shaped manner relative to the incident direction of the excitation radiation. 7. The arrangement according to claim 6, wherein the V-shape is oriented with the tip in the incident direction of the excitation radiation. 8. The arrangement according to claim 6, wherein the V-shape is oriented with the opening opposite to the incident direction of the excitation radiation. 9. The arrangement according to claim 1, wherein said separate orifices of the nozzle are arranged in one row wherein said one row of orifices is oriented oblique to the direction of excitation at an acute angle as to have each separate orifice of the row in different parallel planes being arranged one behind the other and perpendicular to the incident direction of the excitation radiation. 10. The arrangement according to claim 1, wherein a pulsed energy beam is provided as excitation radiation, wherein the energy beam has a focus whose cross-sectional area covers the width of all adjacent target jets simultaneously. 11. The arrangement according to claim 10, wherein the energy beam is generated by a pulsed laser. 12. The arrangement according to claim 10, wherein the energy beam is a particle beam, particularly an electron beam. 13. The arrangement according to claim 10, wherein the energy beam is a particle beam, particularly an ion beam. 14. The arrangement according to claim 10, wherein the energy beam is focused through suitable optics onto the target jets as a focus line which is oriented orthogonal to the direction of the target jets. 15. The arrangement according to claim 10, wherein the energy beam is composed of a plurality of individual energy beams, the plurality of energy beams being arranged in a row orthogonal to the direction of the target jets to form a quasi-continuous focus line by suitable optical elements and strike all target jets simultaneously. 16. The arrangement according to claim 10, wherein the energy beam is composed of a plurality of individual energy beams, each of the individual energy beams being focused on one target jet and all target jets are irradiated simultaneously. 17. The arrangement according to claim 15, wherein a laser with beam-splitting optical elements is provided for generating a row of individual energy beams. 18. The arrangement according to claim 15, wherein a plurality of synchronously operated lasers is provided for generating a row of individual energy beams. 19. The arrangement according to claim 10, wherein the energy beam is optimized with respect to the efficiency of energy conversion into plasma through the use of multiple pulses, particularly double pulses comprising pre-pulse and main pulse. 20. The arrangement according to claim 1, wherein the target jets proceeding from said separate orifices of the multiple-channel nozzle are continuous jets in the area of interaction with the excitation radiation. 21. The arrangement according to claim 1, wherein the target jets proceeding from said separate orifices of the multiple-channel nozzle fall in droplets at the latest in the area of interaction with the excitation radiation. 22. The arrangement according to claim 1, wherein the target jets are liquid jets. 23. The arrangement according to claim 1, wherein the target jets are frozen solid jets when exiting from the orifices into the vacuum chamber. 24. The arrangement according to claim 22, wherein the target jets are generated from condensed xenon. 25. The arrangement according to claim 22, wherein the target jets are generated from aqueous solution of metallic salts. 26. The arrangement according to claim 1, further comprising the step of generating plasma-emitted radiation in a wavelength range between soft x-ray and infrared spectral range. 27. The arrangement according to claim 1, comprising the step of generating EUV radiation in the wavelength range between 1 nm and 20 nm for devices used in semiconductor lithography, particularly for EUV lithography in the wavelength band about 13.5 nm. 28. The arrangement according to claim 1, wherein the separate orifices of the nozzle are arranged in such a way that a radiation spot focused by the excitation radiation on all of the target jets exiting the nozzle is covered spatially essentially uniformly by parallel target jets, all of the target jets being completely irradiated over their diameter. |
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description | The present invention relates to fuel assemblies for nuclear reactors and power plants and, more particularly, to fuel assemblies in which at least one fuel rod has been replaced with a structural support replacement rod. Nuclear power plants typically utilize water to remove the heat created by the fission of an element such as uranium within the nuclear reactor. In a pressurized water reactor (PWR), heat is removed from the reactor by water flowing in a closed pressurized loop. The heat is transferred to a second water loop through a heat exchanger. The second loop is kept at a lower pressure, allowing the water to boil and create steam. The steam is used to turn a turbine-generator and produce electricity. Afterward, the steam is condensed into water and returned to the heat exchanger. The Voda-Vodyanoi Energetichesky Reaktor (VVER) is the Russian version of a PWR. FIG. 1a presents an elevational view of a standard fuel assembly 2 for use with a VVER. The fuel assembly 2 contains a plurality of fuel rods 3, a plurality of grids 4, a top nozzle 6, and a bottom nozzle 8. FIG. 1b presents a close-up view of Area A shown in FIG. 1a, depicting the top nozzle 6 and top grid 5. FIG. 1c presents a close-up view of Area B shown in FIG. 1a, depicting two mid-grids 7, 9 and a portion of the fuel rods 3. FIG. 1d presents a close-up view of Area C shown in FIG. 1a, depicting the bottom nozzle 8 and bottom grid 10. Each fuel rod 3 contains uranium oxide pellets that are stacked in cladding. A spring is positioned at the top of the stack to compress the pellets. The fuel rod is closed at both ends by end plugs that are welded to the cladding. Grid springs provide lateral support for the fuel rods 3 and accommodate for growth that occurs during irradiation. Control rods are interspersed among the fuel rods to regulate the nuclear reaction. The control rods slidably move within guide thimbles that are anchored to the grids 4 and/or nozzles 6, 8 by welding. The grids 4 are positioned one on top of the other in a tandem array, usually at regularly spaced intervals. An instrumentation tube may be positioned in the center of the fuel rods and control rods. FIG. 2 presents a cross-sectional view of section D-D′ shown in FIG. 1a. FIG. 2 illustrates the geometric array 11 or shape in which the fuel assembly 2 is contained in a VVER. As shown, the fuel rods 3 are contained within a geometric array 11 that is shaped like a hexagon with six corners 13 (a “hexagonal array”). Control rods 14 and their associated guide thimbles (indicated by the outer circle (i.e., perimeter) surrounding each of the control rods 14 in FIG. 2) are interspersed among the fuel rods 3, and an instrumentation tube 16 is located in the center. Typically, a VVER fuel assembly with a hexagonal array will include 312 fuel rods, 18 control rods and associated guide thimbles, and 1 instrumentation tube. The structural support for the fuel assembly is provided by the grids, the top nozzle, and the bottom nozzle, which are anchored to the guide thimbles. Structural support is also provided by the grid springs which offer some lateral stability to the fuel rods. In addition to hexagonal arrays, VVER fuel assemblies may have square or circular arrays. Square fuel assemblies will typically have a 14×14, 15×15, 16×16, or 17×17 array. A 16×16 array may include 237 fuel rods, 18 control rods and associated guide thimbles, and 1 instrumentation tube. Unfortunately, standard VVER fuel assemblies may not provide adequate geometric and dimensional stability during irradiation, or sufficient resistance to fuel assembly distortion. Fuel assembly bow and twist measurements, handling incidents, and incomplete rod insertion (IRI) events indicate that standard VVER fuel assembly designs may not adequately support current fuel management schemes with four annual cycles (i.e., four year long fuel cycles, during which time a region of fuel assemblies may remain within the reactor core). Moreover, standard fuel assembly designs may not adequately support proposed fuel management schemes with 6 annual cycles (i.e., six year long fuel cycles, during which time a region of fuel assemblies may remain within the reactor core) and maximum fuel rod burn-up of 75,000 MWD/MTU. Some fuel assemblies have been designed to include structural support straps that wrap around the assembly perimeter. These structural support straps provide an increased resistance to fuel assembly distortion. However, their design has some disadvantages associated with manufacturing problems (e.g., a significant number of weld joints) and thermal-hydraulic limitations (increased fuel assembly pressure drop; decrease in the DNB performance for fuel rods at corner locations). Thus, there exists a need for a new fuel assembly design that provides adequate structural stability or skeletal rigidity and resistance to distortion to support current and proposed fuel management schemes without degradation of thermal hydraulic performance and without manufacturing problems. The goal is to sustain the fuel supply for as long as possible while at the same time maintaining the power rating of the nuclear reactor. The present invention provides novel fuel assemblies for use with PWR nuclear reactors and power plants, and in particular, VVER nuclear reactors. The fuel assemblies offer enhanced structural stability, skeletal rigidity, and distortion resistance to support high burn-up fuel management. Each fuel assembly may include a plurality of fuel rods, a plurality of control rods and guide thimbles, at least one instrumentation tube, and a plurality of grids. At least one fuel rod is replaced with a structural support replacement rod made from zirconium (Zr) alloy, stainless steel, or any other suitable material. Zirconium alloy is preferred because it provides a low neutron capture cross-section, which makes the nuclear reaction more efficient, while maintaining adequate corrosion resistance. The structural support replacement rods may be placed at or about the periphery of the geometric array in which the fuel assembly is contained. In a preferred embodiment, the structural support replacement rods may be placed at or about the corners of the geometric array, which is preferably a hexagon or square. It is an aspect of the present invention to provide a fuel assembly for a nuclear reactor. The fuel assembly forms a geometric array having a periphery. The fuel assembly comprises: a plurality of fuel rods; a plurality of control rods; a plurality of guide thimbles, wherein the control rods are slidably movable within the guide thimbles; at least one instrumentation tube; at least one structural support replacement rod; and a plurality of grids that are structured and arranged in a tandem array to support the fuel rods, the guide thimbles, the at least one instrumentation tube, and the at least one structural support replacement rod in a spatial relationship in the geometric array, wherein the guide thimbles are anchored to the grids, and wherein at least one of the at least one structural support replacement rod is disposed at or about the periphery of the geometric array in order to provide enhanced structural stability to the fuel assembly. It is another aspect of the present invention to provide a nuclear reactor including a pressure vessel and a plurality of fuel assemblies housed by the pressure vessel. Each fuel assembly forms a geometric array having a periphery, and comprises: a plurality of fuel rods; a plurality of control rods; a plurality of guide thimbles, wherein the control rods are slidably movable within the guide thimbles; at least one instrumentation tube; at least one structural support replacement rod; and a plurality of grids that are structured and arranged in a tandem array to support the fuel rods, guide thimbles, at least one instrumentation tube, and at least one structural support replacement rod in a spatial relationship in the geometric array, wherein the guide thimbles are anchored to the grids, and wherein at least one of the at least one structural support replacement rod is disposed at or about the periphery of the geometric array in order to provide enhanced structural stability to the fuel assembly. It is an object of the present invention to provide a novel fuel assembly for use with VVERs. It is another object of the present invention to provide a fuel assembly with enhanced structural stability, skeletal rigidity, and resistance to distortion (e.g., without limitation, bow and twist). It is a further object of the present invention to provide a fuel assembly that can support increased fuel burn-up management requirements. It is another object of the present invention to enhance the structural stability of fuel assemblies having hexagonal or square arrays. It is a further object of the present invention to utilize structural support replacement rods to enhance the structural stability of a fuel assembly. These and other objects of the present invention will become more readily apparent from the following detailed description and appended claims. Table 1, which is incorporated hereinbelow in the section Detailed Description of the Preferred Embodiments, presents the results of a skeleton stiffness assessment for fuel assemblies with structural support replacement rods located in various positions. Table 2, which is incorporated hereinbelow in the section Detailed Description of the Preferred Embodiments, present the results of nuclear assessment calculations for fuel assemblies with structural support replacement rods located in various positions. The present invention provides novel fuel assemblies for use with PWR nuclear reactors and power plants, and in particular, VVER nuclear reactors. The invention contemplates the novel fuel assemblies themselves, as well as nuclear reactors that comprise a fuel assembly surrounded by a pressure vessel 100 (shown in simplified form in FIG. 9) and nuclear power plants that contain one or more fuel assemblies. The fuel assemblies offer enhanced structural stability, skeletal rigidity, and distortion resistance to support high burn-up fuel management. Each fuel assembly may include a plurality of fuel rods, a plurality of control rods and guide thimbles, at least one instrumentation tube, and a plurality of grids. At least one fuel rod is replaced with a structural support replacement rod made from zirconium (Zr) alloy, stainless steel, or any other suitable material. The replacement rod may be hollow or solid. Zirconium alloy is the preferred material because it provides a low neutron capture cross-section, which makes the nuclear reaction more efficient, while maintaining adequate corrosion resistance. The grids are positioned one on top of the other in a tandem array. The purpose of the grids is to support the fuel rods, guide thimbles, instrumentation tube, and replacement rods in a spatial relationship with respect to each other. The spatial relationship is defined by the fuel assembly's geometric array. As used herein, the term “geometric array” refers to the cross-sectional shape or design in which the fuel assembly is contained, and expressly includes, for example and without limitation, a hexagon, a square, or a circle. In other words, the periphery of the fuel assembly, when viewed in plan view, forms a hexagon, square, or circle. The guide thimbles may be anchored, welded, or coupled to the grids. To provide additional support, the guide thimbles may also be anchored to the top and bottom nozzles of the fuel assembly. Grid springs provide lateral support to the fuel rods and accommodate for growth that occurs during irradiation. As will be illustrated and discussed herein, the structural support replacement rods are disposed at or about the periphery of the geometric array in which the fuel assembly is contained. In a preferred embodiment, the structural support replacement rods are disposed at or about the corners of the geometric array, which is preferably a hexagon or square. As employed herein, the term “corner” refers to the point on the periphery of the geometric array where two sides of the fuel assembly intersect. Thus, for example, a hexagonal geometric array in accordance with the invention has six corners. For a hexagonal array (FIGS. 2-6, and FIG. 8), the fuel assembly may include between about 1 to about 12 replacement rods, and preferably includes between about 3 to about 6 replacement rods, wherein each replacement rod is placed at or about a corner of the hexagon. However, the present invention is not limited to any particular number of replacement rods or positioning of replacement rods. FIG. 3 presents a cross-sectional view of a fuel assembly 28 in accordance with a preferred embodiment of the present invention. The fuel assembly 28 includes fuel rods 30, control rods 32 that are slidably movable within guide thimbles (indicated by the outer circle (i.e., perimeter) surrounding each of the control rods 32 in FIG. 3, and an instrumentation tube 34. The fuel assembly 28 is contained within a geometric array 36 that comprises a hexagon with six corners 37. While the present invention primarily focuses on the use of hexagonal (FIGS. 2-6 and FIG. 8) and square arrays (FIG. 7), it is understood that numerous other shapes or designs (not shown) may be utilized, including regular and irregular shapes (not shown), although the geometric array is preferably non-circular in shape. Thus, in accordance with a preferred embodiment, the geometric array has at least one corner (e.g., corner 37 of FIG. 3). In the example of FIG. 3, the fuel rods adjacent to each corner 37 of the hexagonal array 36 have been replaced with structural support replacement rods 38. In this manner, additional structural stability and skeletal rigidity is provided for the entire fuel assembly 28. Although the structural support replacement rods 38 are preferably made from solid zirconium alloy, it will be appreciated that they could be hollow or solid, and made from any known or suitable material other than zirconium alloy. FIGS. 4, 5, 6, and 8 show cross-sectional views of exemplary structural support replacement rod configurations within fuel assemblies having hexagonal geometric arrays, in accordance with the present invention. The components of the fuel assemblies in each case are essentially identical with the only difference being the number, location, and/or type (i.e., solid or hollow) of the structural support replacement rods. More specifically, in the fuel assembly 128 of FIG. 4, six structural support replacement rods 138 have been positioned one fuel rod away from the corners 37 of the hexagonal array 36 to replace six fuel rods 30. In another embodiment of the invention, shown in FIG. 5, six structural support replacement rods 238 have been positioned proximate the corners 37 of the hexagonal array 36 to replace six fuel rods 30 of the fuel assembly 228. More specifically, each of the structural support replacement rods 238 is disposed two fuel rods 30 away from the corners 37, as shown. In the fuel assembly 328 of the example of FIG. 6, six structural support replacement rods 338 replace six fuel rods 30 at a location between the corners 37 of the hexagonal array 36. More specifically, the replacement rods 338 are generally disposed midway between a pair of corners 37 at the periphery of the array 36. In the embodiments shown in FIGS. 3-6, each fuel assembly includes 306 fuel rods 30, six structural support replacement rods 28,138,238,338, 18 control rods and guide thimbles 32, and one instrumentation tube 34. It will be appreciated, however, that a hexagonal array in accordance with the invention may include as few as about three or less structural support replacement rods to about six or more structural support replacement rods. However, it will also be appreciated that the present invention is not limited to any particular number of fuel rods, replacement rods, control rods, guide thimbles, instrumentation tubes, grids, or nozzles. Generally, the number of structural support replacement rods corresponds to the number that is required to achieve the desired structural stability while balancing the effects of fuel rod replacement on the nuclear reactor's performance. It will still further be appreciated that the present invention is not limited to any particular positioning of the structural support replacement rods. Each replacement rod may be positioned at any spatial location within the geometric array. This is evidenced by the aforementioned examples of FIGS. 3-6. Specifically, as previously discussed, the replacement rods (e.g., 38,138,238,338) may be positioned at or about the corners 37 of the geometric array (e.g., hexagonal geometric array 36), or the replacement rods may be positioned generally between the corners 37 at or about the periphery of the array 36. Positioning of the structural support replacement rods may be determined so as to: 1) maximize the lateral stiffness of the fuel assembly, and 2) minimize the radial flux peaking near the periphery of the fuel assembly. The latter is important in order to minimize the overall flux peaking within the core to levels deemed acceptable by the plant safety analysis. FIG. 7 presents a cross-sectional view of a fuel assembly 50 with a square array 58 in accordance with an embodiment of the present invention. The square array 58 is preferably 14×14, 15×15, 16×16, or 17×17. In the example of FIG. 7 the fuel assembly 50 has a 17×17 square array 58 with two hundred sixty-four fuel rods 60, twenty control rods 62 and associated guide thimbles 63, one instrumentation tube 64, and four structural support replacement rods 66. The structural support replacement rods 66 are placed at the corners 70 of the square array 58. It will, however, be appreciated that the invention is not limited to any particular size of square array, number of components, or positioning of components. As previously noted, the substitution of fuel rods with one or more structural support replacement rods in accordance with the invention will improve the structural stability and skeletal rigidity of the entire fuel assembly. This will make the fuel assembly more resistant to distortion/bow and twist during irradiation, and more capable of maintaining rigidity under increased fuel burn-up management. Thus, the structural support replacement rods serve as skeletal structural elements of the fuel assembly. To provide additional rigidity to the skeletal structure, the replacement rods may be anchored, crimped, welded, or otherwise suitably secured to the grids and/or the nozzles of the fuel assembly. In other words, several different structural support replacement rod embodiments are disclosed. For example, and without limitation, in one embodiment the structural support replacement rods could be anchored to the grids of the fuel assembly and to the top and bottom nozzles of the fuel assembly. In another embodiment, the structural support replacement rods may not be anchored or fixedly secured to the grids but could be connected to the nozzles. Alternatively, the structural support replacement rods may not be anchored to the grids and are also not connected to the top and bottom nozzles. Finally, as shown for example in FIG. 9, which is a vertical elevation view of the fuel assembly 28 of FIG. 3, the structural support replacement rods 38 of the fuel assembly 28 may be anchored only to the grids 5, 7, 9, 10. Thus, in the embodiment of FIGS. 3 and 9, like the fuel rods 30 (see also fuel rods 3 of FIGS. 1b, 1c and 1d) that they replace, the exemplary structural support replacement rods 38 are not connected to either of the top end (e.g., top nozzle 6) of the fuel assembly 28 or the bottom end (e.g., bottom nozzle 8) of the fuel assembly 28, together or individually. When fuel rods are replaced, there is a subsequent reduction of fuel material loading in the nuclear reactor which must be addressed. For example, when six fuel rods are replaced, fuel material loading may decrease by approximately two percent. To compensate for the loss in fuel, the pellet stack length or fuel density may be increased for each remaining fuel rod. By way of example, in which six fuel rods are replaced with six replacement rods, the pellet stack length of each remaining fuel rod may be increased by two pellets resulting in a total increase in fuel density of up to about 96.5% theoretical density (TD). The present invention, however, is not limited to any particular fuel density. It will, therefore, be appreciated that the fuel density may be increased higher than 96.5%. The invention will be more fully understood with reference to the following example which is intended to illustrate the invention and should not be construed as limiting the scope of the invention in any way. FIG. 8 presents four different structural support replacement rod configurations or patterns in accordance with the invention. The patterns are denoted in the legend of FIG. 8 as Pattern A, Pattern B, Pattern C, and Pattern D. For each pattern, six structural support replacement rods made from zirconium were positioned in the fuel assembly 36 having hexagonal geometric array 36. For Pattern A, it was assumed that the structural support replacement rods were positioned adjacent to the corners 37 of the hexagonal array 36. For Pattern B, it was assumed that the structural support replacement rods were positioned one fuel rod 30 away from the corners 37 of the hexagonal array 36. For Pattern C, it was assumed that the structural support replacement rods were positioned two fuel rods 30 away from the corners 37 of the hexagonal array 36. For Pattern D, it was assumed that the structural support replacement rods were positioned approximately halfway in between the corners 37 of the hexagonal array 36. Modeling calculations were conducted to provide a skeleton stiffness assessment and nuclear assessment for Patterns A-D. The assessments were also conducted for a reference fuel assembly that contained no replacement rods. Patterns A-D were tested twice for two different types of replacement rods. The first type of replacement rod was solid zirconium, and the second type of replacement rod was hollow zirconium with an inside and outside diameter. Table 1 presents the results of the skeleton stiffness assessment, including skeleton moment of inertia in inches and bending stiffness benefit. TABLE 1Skeleton Stiffness AssessmentGuideFuel RodSkeletonThimblesReplacementMomentBending(19 Places)(6 places)of Inertia,StiffnessPatternIDODIDODinch4BenefitReference0.433″0.496″——2.071.0A0.360″2.07 +4.77.70 =9.77B2.07 +4.06.24 =8.31C2.07 +3.44.93 =7.00D2.07 +3.85.78 =7.85A0.433″0.496″2.07 +2.73.48 =5.55B2.07 +2.42.82 =4.89C2.07 +2.12.23 =4.30D2.07 +2.32.61 =4.68 As shown, all of the fuel assemblies employing replacement rods displayed a higher bending stiffness benefit than the reference fuel assembly that contained no replacement rods. Additionally, the solid replacement rods displayed a higher bending stiffness benefit than the hollow replacement rods. Pattern A, with solid zirconium replacement rods, displayed the maximum skeleton stiffness benefit of 4.7. Pattern B, with solid zirconium replacement rods, displayed the next highest bending stiffness benefit (4.0), followed by Pattern D (3.8) and Pattern C (3.4) with solid zirconium rods. Table 2 presents the results of nuclear assessment calculations. TABLE 2Nuclear AssessmentPeakingPeakingReactivityFactorFactorChangePatternFuel DensityminmaxDifference(BOL), pcmReference95% TD0.9081.0560.148—A97% TD0.9521.0450.093−60B0.9331.0850.152−40C0.9281.0590.131+102D0.9041.0450.141+94BOL = Beginning of lifepcm = percent-mille = 0.00001 change in k/k in core reactivity More specifically, among the assessed parameters were the peaking factor and the reactivity change. Peaking factor represents the ratio of heat generation versus average heat generation. The difference between the minimum and maximum peaking factor is preferably a low number. Reactivity change represents the change in nuclear reactivity that occurs when fuel rods are replaced by one or more replacement rods, and it is preferable for this change to be negligible, regardless of whether it is positive or negative. For the EXAMPLE, the reference fuel assembly was assumed to contain a fuel density of 95% TD, and the fuel assemblies of Patterns A-D were assumed to contain a fuel density of 97% TD each. For Patterns A-D, it was assumed that solid zirconium bars (outside diameter=0.360 inches) were used as replacement rods. As shown in Table 2, Pattern A displayed the narrowest distribution range between the maximum and minimum peaking factor (a difference of 0.093), and a small reactivity change (−60), followed by Pattern C with a peaking factor difference of 0.131 and Pattern D with a peaking factor difference of 0.141. Pattern B displayed a higher peaking factor difference (0.152) than the reference fuel assembly (0.148). Thus, it was determined that zirconium replacement rods (outside diameter=0.360 inches) in six locations as specified in Patterns A and C, where the pellet TD (nominal) is equal to or greater than 96.5%, are the most appropriate design solutions to support the proposed fuel management (high burn-up up to 75,000 MWD/MTU and extended resident time up to 6 years). Furthermore, it was determined that the positioning and number of the replacement rods for any geometric array can be determined by balancing three important factors: reactivity, lateral stiffness, and peaking factors. Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims. |
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050646044 | summary | BACKGROUND OF THE INVENTION The present invention relates to a fluid line status sensor system which can be used to determine whether fluid is flowing, contained, or absent in a pipe or vessel. In a typical power plant, there are hundreds of fluid pipelines for conveying fluid (e.g., hot steam) through heat exchangers and to and from a turbine. Fluid which passes through these lines is, in many cases, at a temperature well above the ambient temperature of the environment in which the pipes are located. Fluid pipe systems, such as those used in a typical power plant, may include flow status monitoring systems. Power plant monitoring and on-line diagnostic systems often require electronic verification of the flow status in various pipelines, such as drain lines or process fluid lines. As these lines can be valved in and out of the overall flow circuit, the flow in these lines may be intermittent. It is beneficial to verify by independent signals whether contact closures associated with flow control devices, such as isolation valves or dump valves, have produced the state of flow expected. Generally, it is of interest to verify whether a large flow exists (e.g., a relatively large volume of fluid is flowing through the pipe), no flow exists, or a significant leakage flow exists (e.g., a relatively small volume of fluid is flowing from a leaky valve). Diagnostic systems may employ sensors located at hundreds of locations about the fluid pipe systems. Such diagnostic systems can be extremely expensive. The total installed cost of sensors in such systems can be a significant portion of the overall system cost. Accordingly, it is beneficial to employ an inexpensive sensor at each of the sensing locations. Such inexpensive sensors may include thermocouples. Some conventional systems employ several one-of-a-kind installations of thermocouple junction devices (hereafter referred to as thermocouples). Each installation having an arrangement of thermocouples mounted axially (with respect to the pipe) on a pipe surface across a valve or over a span where a significant thermal difference is developed during operation. However, this axial arrangement of thermocouples gives rise to several disadvantages. For example, several long lengths of wires are required to connect the axially arranged thermocouples with evaluation electronics. Additionally, engineering costs in determining locations for placing the thermocouples are relatively high in such conventional systems. Moreover, engineering costs for interpreting signals provided by several one-of-a-kind installations are relatively high. Furthermore, with the axially arranged thermocouples located to produce differential signals from two axial locations (e.g., on either side of an isolation valve), flow blockage occurring elsewhere (e.g., at the mouth of a drain line) in the fluid line cannot be detected. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide an improved fluid line status sensor system for determining the flow status of a pipe or vessel. It is further an object of the present invention to provide such a fluid line status sensor system which includes a relatively inexpensive sensor device. It is further an object of the present invention to provide such a fluid line status sensor system which is relatively easy and inexpensive to install in conjunction with a fluid pipe system. These and other objects are accomplished according to an embodiment of the present invention by employing a relatively inexpensive sensor assembly comprising a rod-shaped thermally conductive element oriented radially with respect to a flow pipe and two or more thermocouples installed on the thermally conductive element. A first end of the thermally conductive element is arranged in contact with or in thermal communication with the outer periphery of the pipe, while a second end of the thermally conductive element is spaced from the pipe. As a result of heat conduction between the pipe and the first end, a temperature gradient is created along the thermally conductive element since the temperature at the end of the element adjacent the pipe is influenced by the temperature within the pipe to a greater extent than is the temperature at the end of the element remote from the pipe. For example, a relatively high temperature may exist near the first end and a relatively low temperature near the second end. The thermocouples are installed along the length of the thermally conductive element. One thermocouple is arranged nearer to the pipe than the other thermocouple. Temperature dependent signals obtained from the thermocouples are transmitted to suitable evaluation electronics. The evaluation electronics determine a temperature difference between the two thermocouples based on the thermocouple signals. The temperature difference is then compared with known or predetermined values to determine the flow status of the pipe. |
abstract | Provided are magnetohydrodynamic stirrers comprising a conduit or cavity having at least two electrodes disposed in such an orientation that, upon the application of a potential or current across the electrode pair within a magnetic field, secondary flows such as chaotic advection is generated. |
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description | This application claims the benefit of Korean Patent Application No. 10-2005-101531, filed on Oct. 26, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entity by reference. 1. Field of the Invention The present invention relates to a separation and receiving apparatus for a spent nuclear fuel rod, and more particularly, to a separation and receiving apparatus for separating a hull and a pellet from a spent nuclear fuel rod, capable of effectively and automatically separating and receiving a hull and a pellet made of uranium oxide (UO2), while security and automation being guaranteed. 2. Description of the Related Art Nuclear fuel is a material capable of producing energy by entering a nuclear reactor and causing a chain reaction of nuclear fission. Spent nuclear fuel is the material left after the nuclear fission. Generally, uranium 235 235U•uranium 233 233U•plutonium 239 239Pu and the like is a representative as material used for nuclear fuel. Uranium 235 235U is contained in only 0.7% of natural uranium. Accordingly, in the case of using natural uranium, the amount needed for reaching critical mass increases. Also, light water strongly absorbing neutrons may not be used as a moderator. Accordingly, the capacity of a nuclear reactor becomes large. Consequently, a lot of nuclear reactors use enriched uranium which artificially increases the ratio of uranium 235 235U as fuel material. In particular, a reactor for ship propulsion needing minimization or an electricity generating reactor limited by building cost per a certain output usually uses enriched uranium. Nuclear generation is to slowly react the nuclear fuel in a reactor, generate thermal energy, and generate electricity by using the generated thermal energy. Nuclear generation uses nuclear fuel such as natural uranium that is enriched to between about 3 and 5%. When new fuel is added into a reactor, the fuel is burnt for about three periods to generate thermal energy. When one period is terminated, the reactor is stopped and a third of fuel is replaced. In this case, one period is about 18 months for which nuclear fuel is put in a reactor and generates energy through nuclear fission. When one period is over, equipment comprising a power plant such as a turbine or a steam turbine, a generator, all types of valves, a pump, etc. receive maintenance. When the maintenance is completed, the power plant is restarted and generates electricity for the next period, 18 months. In this instance, nuclear fuel undergoes fission in a reactor in the form of being contained in a nuclear fuel rod. In this instance, the nuclear fuel rod is about 10 mm in diameter and about 4 m in length. A stable, corrosion-resistant zirconium alloy, for example Zircaloy, that is about 1 mm in width. Hull caps are provided on both sides of the hull to be capable of being sealed by resistance welding or the like. Fuel manufactured in the form of a pellet is loaded into the hull of each nuclear fuel rod and tens to millions of nuclear fuel rods manufactured as above are used in a bundle for nuclear fuel used for nuclear power generation. According to a conventional method, spent nuclear fuel burnt in a nuclear power plant is stored in a tank without being processed. However, the longer the period of nuclear power generation, the more an amount of spent nuclear fuel accumulates. Consequently, a huge storage space is needed. Also, the necessity and dangerousness of disposing the accumulated nuclear wastes remains. In some countries, spent nuclear fuel rods are transferred to a permanent disposal area to be stored for the long term. On the other hand, nuclear fuel may be separated from the hull for recycling the spent nuclear fuel. To recycle or to dispose of nuclear fuel, a nuclear fuel rod is dismembered to separate the nuclear fuel and the hull after the nuclear fuel is completely used in a reactor. However, in the case of separating nuclear fuel from a hull by using a current technology, nuclear fuel materials such as solid uranium, plutonium, or the like, nuclear fission products, and hull materials remain in the hull. The hull is classified as high-level radioactive waste. In particular, in the case of separating nuclear fuel from a hull by using wet processing, high-level radioactive waste such as a nuclear fuel a liquid cleaning solution and the like are spread on the inner surface and the outer surface of the hull. Accordingly, more special processing is needed. Two methods are generally used for the management of spent nuclear fuel. One is a method of putting spent nuclear fuel in a rock bed in the ground to a depth of more than 500 meters and thoroughly isolating the spent nuclear fuel from the human ecosystem. This is known as permanent disposal. The other is a method of separating recyclable materials from spent nuclear fuel (this is referred to as ‘reprocessing’), reusing the separated nuclear fuel materials, and permanently disposing of high-level radioactive waste. In particular, a spent nuclear fuel rod is cut to about 25 cm in length. The cut spent nuclear fuel rod is transferred to a disposal area such as a hot cell by a robot and a slitting operation for separating a pellet and a hull is performed. In this instance, a heating device is provided to supply the high heat of reaction to the inside of a vertical reactor in order to separate a hull and a fuel rod in the form of a pellet in the conventional method. In this instance, the heating device is in the shape of a cylinder wrapping the outside of the vertical reactor. Also, a vertical screw is provided in the vertical reactor and splits the hull through a complicated mechanical mechanism. Accordingly, it takes a long time to complete the operation. Also, the complicated structure makes manufacturing difficult and increases manufacturing cost. Also, the manipulation of the complicated structure prolongs the operation time. Namely, since the introduction of automation processing becomes difficult and a handle or the like has to be manually manipulated, the operation efficiency decreases. Also, it is difficult to secure the safety of the process because of a complicated driving method and complicated processing. Also, it is very inconvenient to separate a hull and a pellet contained in the same vessel. To solve the aforementioned problems, the present invention provides a separation and receiving apparatus of a spent nuclear fuel rod, which can be easily manufactured because of its simple structure, and effectively separate a hull and a pellet. The present invention also provides a separation and receiving apparatus of a spent nuclear fuel rod, which can be easily automated, improve operation efficiency because of the shortened operation time, and have enhanced reliability for operation. The present invention also provides a separation and receiving apparatus of a spent nuclear fuel rod, which can safely separate a hull and a pellet that is spent nuclear fuel and automatically receive the separated pellet and hull in respectively different vessels without another process for separating. To achieve the above objectives, according to the present invention, there is a separation and receiving apparatus of a spent nuclear fuel rod, in which a pin moving by a driving unit downwardly presses the spent nuclear fuel rod, a plurality of blades provided below the pin peels the hull of the nuclear fuel rod in the lengthwise direction, and a separator provided below the blade separates the hull and a pellet positioned therein, and the separated hull and pellet are received in each vessel. The blade includes blade modules provided with the plurality of blades located according to the transfer direction of the nuclear fuel rod, the blade modules provided in plurality around the blade body. In this instance, it is preferable that there are 3 blade modules and are provided to the blade body at intervals of 120 degrees and the said each blade module is provided with four blades. The separator is in the shape of a cone and provided with a pellet passing hole in its center to pass the pellet, and a hull guide guiding the hull cut within the blade module and the hull guide is inwardly caved in from the outside of the separator. The vessels include a hull vessel provided below the separator and capable of receiving the hull; and a pellet vessel provided in a center of the hull vessel and receiving the pellet passing through a pellet passing hole formed in the center of the separator. In this instance, a hull passing hole is formed on a side of the pellet vessel to pass and receive the hull in the hull vessel. As described above, the separation and receiving apparatus of the present invention may be easily manufactured because of its simple structure. Also, a pellet and a hull may be automatically separated. Namely, the present invention may contribute to shortening of operation time and effective and stable management of spent nuclear fuel. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments or restricted thereby. FIG. 1 is a perspective view illustrating a separation and receiving apparatus of a spent nuclear fuel rod according to the present invention, and FIG. 2 is an exploded perspective view illustrating a separation and receiving apparatus of a spent nuclear fuel rod according to the present invention. As illustrated in the figures, a separation and receiving apparatus 10 of a spent nuclear fuel rod includes a driving unit 100, a slitting unit 200 and a receiving unit 300. The present invention will first describe the configuration of the driving unit 100, the slitting unit 200 and the receiving unit 300, and subsequently describe in detail operations thereof. The driving unit 100 includes a motor 110, a driving power transfer unit 120 and a pin 130. The driving power transfer unit 120 is connected to the motor 110 to transfer the driving power. The pin 130 is connected to the driving power transfer unit 120 to be capable of pressing a spent nuclear fuel rod. A spent nuclear fuel rod is used in the form of a fuel rod. The present invention accepts fuel rods cut in certain lengths. The motor 110 is placed on a motor support 111. The motor support 111 is attached to a vertical pole 11 of the separation and receiving apparatus 10. The motor 110 is supplied with power and converts electric energy into rotational motion/movement. Besides direct current and alternating current motors, the motor 110 may also include a motor activated by hydraulic pressure. The driving power transfer unit 120 includes a plurality of gears 121 connected to the motor 110, and a ball screw 122 connected to the gear 121 to transfer the driving power to the pin 130. The gears 121 are provided on both sides of the pin 130 and connected to the pin 130. In this instance, the gears 121 function to transfer driving power to the ball screw 122 transferring the driving power to the pin 130. The gear 121 includes a bevel gear and the like. The driving unit 100 functions to push down the pin 130 to press a cut spent nuclear fuel rod. The operation thereof will be described in detail later. A limit switch 131 is provided on one side of the vertical pole 11 to be capable of instantaneously stopping the driving unit 100. Accordingly, when the limit switch 131 is pressed, the driving unit 100 is immediately stopped. The slitting unit 200 will be described. The slitting unit 200 includes a blade portion 220 provided with a nuclear fuel rod guide 211 passing a cut spent nuclear fuel rod in its center and having a plurality of blades around the nuclear fuel rod guide 211 to peel the hull formed of the surface of the nuclear fuel rod; a nuclear fuel rod support 230 supporting the nuclear fuel rod placed in the nuclear fuel rod guide 211; and a separator 240 connected to the blade portion 220 and separating the peeled hull and the pellet positioned therein. First, the blade portion 220 will be described with reference to FIG. 3. FIG. 3 is an exploded perspective view illustrating a blade portion and a separator according to the present invention. As illustrated in the figure, the blade portion 220 includes a blade body 213 and a supporting plate 214 fixing the blade body 213 to a table 12. The blade body 213 is provided with the nuclear fuel rod guide 211 in its center and an insertion hole 212 where the blades 250 are inserted in its side. The blade body 213 is nearly in the shape of a cylinder. The nuclear fuel rod guide 211 is formed to pass through the inside of the blade body 213 and in the shape of a cylinder that is the same as the shape of a cut spent nuclear fuel rod. The supporting plate 214 may be connected to the table 12 by using various methods such as bolts, rivets, welding, and the like. The blades 250 are inserted in an insertion hole 212. Also, the blades 250 are constructed to be exposed within the nuclear fuel rod guide 211 to be capable of cutting the hull of a spent nuclear fuel rod passing through the nuclear fuel rod guide 211. The blades 250 are provided in plurality. In the present embodiment, the blades 250 are four. Namely, the blades 250 include a first blade 251, a second blade 252, a third blade 253, and a fourth blade 254. This is the order of which they are positioned in, from the most upper portion and first contacting a nuclear fuel rod. While contacting the fuel rod in the determined order, the first, second, third, and fourth blades 251, 252, 253, and 254 sequentially scratch and cut the hull. The first, second, third, and fourth blades 251, 252, 253, and 254 form one blade module. The blade module is attached to the blade body 213 at intervals of 120 degrees and cuts the hull in the lengthwise direction. The blades are provided in plurality. A blade first contacting the hull of the nuclear fuel rod forms regularly spaced guide grooves on the external surface of the hull and subsequent blades peel according to the guide grooves. Each of the first, second, third, and fourth blades 251, 252, 253, and 254 is rotatably attached to each of blade mounting plates 261, 262, 263, and 264. In this instance, the blade mounting plates 261, 262, 263, and 264 may be provided with a blade knob 270 protruded on their outside. The blade knob 270 includes a combination portion 271 attachable to the blade body 213 and a knob portion 272 connected to the combination portion 271 of the blades 251, 252, 253, 254. The blade knob 270 is used for separating the first, second, third, and fourth blades 251, 252, 253, and 254 when replacing or repairing the same by using a robot or a manipulator. The separator 240 functions to separate a hull and a pellet from a nuclear fuel rod. A hull cut at intervals of 120 degrees by a blade module provided at intervals of 120 degrees is outwardly split apart and discharged from a hull guide 241. Namely, the separator 240 is in the shape of a cone and provided with a pellet passing hole 242 in its center to pass the pellet, and a hull guide 241 capable of guiding the cut hull may be inwardly caved in the outside of the separator 240 or outwardly protruded. Accordingly, the hull guide 241 guides a hull to a hull passing hole 311. A hull cut in the blade portion 220 is outwardly separated from the separator 240 via the hull guide 241 and received in a receiving unit. Also, a pellet is separated via the pellet passing hole 242 formed in the center of the separator 240 and received in a receiving unit 300. The receiving unit 300 will be described with reference to FIG. 4. FIG. 4 is a cross-sectional perspective view illustrating a portion of a receiving unit. As illustrated in the figure, a hull vessel 320 is provided below the separator 240 to be capable of receiving the hull, and a pellet vessel 310 is provided in the center of the hull vessel 320 to receive the pellet. In this instance, the pellet vessel 310 is hung over a hole for the pellet vessel 321 of an upper cover 323. The upper cover 323 is provided on the top of the hull vessel 320. A disk-shaped ring member 324 is interposed between the pellet vessel 310 and the upper cover 323. Three hull passing holes 311 are formed on the side of the pellet vessel 310 at intervals of 120 degrees. Also, a knob 312 is provided on one side of the pellet vessel 310 to ease separation and transfer by using a robot or a manipulator. Also, for the same reason, a knob 322 is provided below the hull vessel 320. A hull peeled in the blade portion 220 passes through the hull passing hole 311 via the hull guide 241 and is received in the hull vessel 320. A pellet separated in the blade portion 220 passes through the pellet passing hole 242 of the separator 240 and is received in the pellet vessel 310. Hereinafter, operations and effects of a separation and receiving apparatus of a spent nuclear fuel rod will be described. FIG. 5 is a perspective view illustrating a mounted spent nuclear fuel rod and FIG. 6 is a perspective view illustrating a pin pressing a spent nuclear fuel rod. As illustrated in the figures, one spent nuclear fuel rod 20 cut to about 25 cm is mounted in the nuclear fuel rod guide 211. The spent nuclear fuel rod 20 may be transferred and attached by using a robot or a manipulator. Also, the spent nuclear fuel rod 20 may be configured to be automatically attached via some other device. When the motor 110 is driven, driving power is transferred to the pin 130 via the driving power transfer unit 120 including the gear 121 and the ball screw 122. The pin 130 presses the spent nuclear fuel rod 20 while slowly descending because of the driving power. In this instance, the spent nuclear fuel rod 20 is cut to about 25 cm and slowly descends by the pressing of the pin 120. The nuclear fuel rod support 230 is separated from the spent nuclear fuel rod 20 while slowly moving apart therefrom. While the dropped spent nuclear fuel rod 20 is passing through the nuclear fuel rod guide 211 formed in the blade portion 220, a hull positioned on the outside is peeled by the first, second, third, and fourth blades 251, 252, 253 and 254. The first blade 251 functions only to help the second blade 252 to easily cut through. Also, while the spent nuclear fuel rod 20 is passing through the third and fourth blades 253 and 254 in succession, the hull is peeled. As described above, the first, second, third, and fourth blades 251, 252, 253 and 254 form one blade module, which is provided to the blade body 213. Since three of the blades modules are provided to the blade body 213 at intervals of 120 degrees, the hull is peeled at an interval of 120 degrees by the blade modules. The peeled hull and a pellet positioned in the hull are transferred to the separator 240. FIG. 7 is a perspective view illustrating a hull and a pellet separated from a spent nuclear fuel rod. As illustrated in the figure, in the case of a hull 22 and a pellet 21 transferred to the separator 240, while the hull 22 peeled by the hull guide 241 is outwardly cracked apart, the hull 22 passes through the hull passing hole 311 refer to FIG. 4 or add to FIG. 7 and is received in the hull vessel 320. Also, the pellet 21 passes through the pellet passing hole 242 provided in the center of the separator 240 and is received in the pellet vessel 310. When the above separating operation is completed, the received pellet 21 is stored or transferred for subsequent processing by using the knob 312 via a robot or a manipulator. Also, the hull 22 is stored in another vessel or transferred for subsequent processing by using the knob 322 of the hull vessel 320. Namely, a hull and a pellet are automatically received in respectively different vessels. Accordingly, it is not only safe but also separates precisely. This may improve the reliability of operations. Also, since operation time is shortened, operation efficiency is improved. Accordingly, the present invention may simplify manufacturing operation because of its simple structure and automatically separates a pellet and a hull. Also, since the separation and receiving is automatically performed, the present invention does not need separate operation processes for the separation and receiving. Also, since a hull and a pellet are each received in separate vessels, the safety and reliability of operation may be improved. Also, the present invention adopts an automation method instead of a conventional manual method. Accordingly, the present invention may contribute to shortening of operation time and safe and efficient management of spent nuclear fuel. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, 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 present invention as defined by the following claims. |
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summary | ||
claims | 1. A method of storing high level radioactive waste comprising:(a) providing a body portion comprising a floor, an open top end, an inner shell extending upward from the floor and forming a cavity, an outer shell extending upward from the floor and surrounding the inner shell so as to form a space therebetween, and at least one opening in the inner shell that forms a passageway from a bottom of the space into a bottom of the cavity;(b) placing a canister containing high level radioactive waste into the cavity, the canister passing through the open top end from a location external to the body portion; and(c) positioning a lid having at least one outlet vent atop the inner and outer shells so as to enclose the open top end of the body portion and the at least one outlet vent forms a passageway from a top of the cavity to the ambient atmosphere; andwherein at least one inlet vent forms a passageway from an ambient atmosphere to a top of the space to facilitate natural convective cooling of the canister containing high level radioactive waste. 2. The method of claim 1 wherein the space is an annular space that circumferentially surrounds the inner shell. 3. The method of claim 1 wherein the canister is a hermetically sealed multi-purpose canister. 4. The method of claim 1 wherein the cavity has a horizontal cross-section that accommodates no more than one canister. 5. The method of claim 1 wherein step (a) comprises positioning the body portion so that at least a major portion of a height of the inner and outer shells are below grade, and wherein step (b) comprises lowering the canister containing high level waste into the cavity until the entire canister is below grade. 6. The method of claim 5 wherein step b) comprises positioning a transfer cask containing the canister above the cavity, and lowering the canister from the transfer cask into the cavity. 7. The method of claim 5 wherein step a) further comprises providing a concrete pad around a portion of the outer shell that protrudes above grade. 8. The method of claim 1 wherein the lid comprises the at least one inlet vent. |
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041490878 | summary | The present invention relates to equipment for recharging of nuclear reactors and, more particularly, to a drum for storing fuel assemblies of a nuclear reactor. The proposed drum for storing fuel assemblies can be used for short-term storage of both new and spent fuel assemblies in the course of recharging a nuclear reactor, which process consists in replacing used fuel assemblies by new ones and transporting the spent assemblies to washing means with the aid of recharging mechanisms arranged in recharging and washing boxes. There is known a drum for storing fuel assemblies, comprising a holder which is rotatable around its axis. The holder is provided with tubular sockets to receive fuel assemblies. The sockets are arranged in a number of rows which are concentric with the circumference of the holder. The drum's inner space communicates with that of the recharging box through a recharging channel which comprises a plurality of pipes whose axes coincide with those of the sockets. The number of pipes is equal to that of the sockets provided in the holder. Fuel assemblies are transported from the drum to the recharging box with the aid of a recharging mechanism arranged in the recharging box. The holder is turned about its axis so that the axis of a socket is matched with that of the recharging channel's pipe. The recharging mechanism is adjusted in advance for the recharging channel's pipe of one row, and the gripping means of this mechanism withdraws the fuel assemblies from the sockets. In order to extract a fuel assembly from its socket and insert a new one, the drum's holder must be turned through a certain angle until the axis of the socket is matched with that of the recharging channel's pipe through which the inside of the drum communicates with the box, whereto fuel assemblies are transported. After the fuel assemblies of one row have been removed from the drum, the recharging mechanism is adjusted for another pipe of the recharging channel, which also applies to the drum charging process. When all the sockets of a row have been filled, the recharging mechanism is adjusted for another pipe of the recharging channel. The drum under review is constructed so that in the course of recharging, each socket of the drum must be brought to the recharging channel's pipe, which necessitates multiple turns of the drum's holder and complicates the recharging process. Besides, every now and then, the recharging mechanism must be set in motion or adjusted for a certain pipe of the recharging channel, whereas the joint between the recharging mechanism and the recharging channel's pipe must be hermetically sealed. All these factors account for a prolonged recharging process. It is an object of the present invention to simplify the process of recharging the nuclear reactor drum. It is another object of the invention to speed up the recharging process. It is still another object of the invention to raise the operational reliability of the drum. The foregoing objects are attained by providing a drum for storing fuel assemblies of a nuclear reactor, comprising a holder which is rotatable around its axis and provided with tubular sockets arranged in a number of rows concentrically with the circumference of the holder, said sockets being intended to receive fuel assemblies to be installed there with the aid of a recharging mechanism through pipes of a recharging channel, which are arranged coaxially with the sockets, opposite one socket in each row, in which drum the rows of sockets are so arranged in the holder, in accordance with the invention, that the axis of at least one socket in each row intersects with the trajectory described by a grip of the recharging mechanism in the course of its movement, whereas the pipes of the recharging mechanism are arranged opposite the intersection points. The foregoing arrangement of sockets in the drum's holder makes it possible to simplify and speed up the recharging process and raise the operational reliability of the drum. |
051436906 | summary | BACKGROUND OF THE INVENTION This invention relates to nuclear reactors and, more particularly, to fuel arrangements in a reactor core. A major objective of the present invention is to provide for more thorough fuel burnups to enhance fuel utilization and minimize active waste products. Fission reactors rely on fissioning of fissile atoms such as uranium isotopes (U233, U235) and plutonium isotopes (Pu239, Pu241). Upon absorption of a neutron, a fissile atom can disintegrate, yielding atoms of lower atomic weight and high kinetic energy along with several high-energy neutrons. The kinetic energy of the fission products is quickly dissipated as heat, which is the primary energy product of nuclear reactors. Some of the neutrons released during disintegration can be absorbed by other fissile atoms, causing a chain reaction of disintegration and heat generation. The fissile atoms in nuclear reactors are arranged so that the chain reaction can be self-sustaining. To facilitate handling, fissile fuel is typically maintained in modular units. These units can be assemblies of vertically extending fuel rods. Each rod has a cladding which encloses a stack of fissile fuel pellets. Generally, each rod includes a space or "plenum" for accumulating gaseous byproducts of fission reactions which might otherwise unacceptably pressurize the rod and lead to its rupture. The assemblies are arranged in a two-dimensional array in the reactor. Neutron-absorbing control rods are inserted between or within fuel bundles to control the reactivity of the core. The reactivity of the core can be adjusted by incremental insertions and withdrawals of the control rods. Both economic and safety considerations favor improved fuel utilization, which can mean less frequent refuelings and less exposure to radiation from a reactor interior. In addition, improved fuel utilization generally implies more complete fuel "burnups". Variations in neutron flux density, which occur along the length of a bundle, make it difficult to achieve complete burnups. For example, fuel near the top or bottom of a fuel bundle is subjected to less neutron flux than is fuel located midway up a fuel bundle. These axial variations are not effectively addressed by radial redistribution of fuel elements. In addition to the variations in neutron flux density, variations in spectral distribution affect burnup. Initially, neutrons released during fissioning move too quickly and have too high an energy to readily induce the further fissioning required to sustain a chain reaction. These high energy neutrons are known as "fast" neutrons. Slower neutrons, referred to as "thermal neutrons", most readily induce fission. Dual-phase reactors store heat generated by the core primarily in the form a phase conversion of a heat transfer medium from a liquid phase to a vapor phase. The vapor phase can used to physically transfer stored heat to a turbine and generator, which are driven to produce electricity. Condensate from the turbine can be returned to the reactor, merging with recirculating liquid for further heat transfer and cooling. The primary example of a dual-phase reactor is a boiling-water reactor (BWR). Dual-phase reactors are contrasted with single-phase reactors, which store energy primarily in the form of elevated temperatures of a liquid heat-transfer medium, such as liquid metal. The following discussion relating to BWRs is readily generalizable to other forms of dual-phase reactors. In BWRs, thermal neutrons are formerly fast neutrons that have been slowed primarily through collisions with hydrogen atoms in the water used as the heat transfer medium. Between the energy levels of thermal and fast neutrons are "epi-thermal" neutrons. Epithermal neutrons exceed the desired energy for inducing fission but promote resonance absorption by many actinide series isotopes, converting some "fertile" isotopes to "fissile" (fissionable) isotopes. For example, epithermal neutrons are effective at converting fertile U238 to fissile Pu239. Within a core, the percentages of thermal, epithermal, and fast neutrons vary over the axial extent of the core. Axial variations in neutron spectra are caused in part by variations in the density or void fraction of the water flowing up the core. In a boiling-water reactor (BWR), water entering the bottom of a core is essentially completely in the liquid phase. Water flowing up through the core boils so most of the volume of water exiting the top of the core is in the vapor phase, i.e., steam. Steam is less effective than liquid water as a neutron moderator due to the lower density of the vapor phase. Therefore, from the point of view of neutron moderation, core volumes occupied by steam are considered "voids"; the amount of steam at any spatial region in the core can be characterized by a "void fraction". Within a fuel bundle, the void fraction can vary from about zero at the base to about 0.7 near the top. Continuing the example for the BWR, near the bottom of a fuel bundle, neutron generation and density are relatively low, but the percentage of thermal neutrons is high because of the moderation provided by the low void fraction water at that level. Higher up, neutron density reaches its maximum, while void fraction continues to climb. Thus, the density of thermal neutrons peaks somewhere near the lower-middle level of the bundle. Above this level, neutron density remains roughly stable while the percentages of epithermal and fast neutrons increase. Near the top of the bundle, neutron density decreases across the spectrum since there are no neutrons being generated just above the top of the bundle. The inhomogeneities induced by this spectral distribution can cause a variety of related problems. Focusing on the upper-middle section, problems of inadequate burnup and increased production of high-level waste are of concern. Since the upper-middle section has a relatively low percentage of thermal neutrons, a higher concentration of fissile fuel is sometimes used to support a chain reaction. If the fuel bundle has a uniform fuel distribution, this section could fall below criticality (the level required to sustain a chain reaction) before the other bundle sections. The fuel bundle would have to be replaced long before the fissile fuel in all sections of the bundle were depleted, wasting fuel. While it is possible to disassemble a spent fuel bundle to recover unspent fuel, this is much more expensive and complicated than using fuel while it is in the bundle. The problem with waste disposal is further aggravated at this upper-middle section since the relatively high level of epithermal neutrons results in increased production of actinide-series elements such as neptunium, plutonium, americium, and curium, which end up as relatively long half life, high-level waste. For example, about 1% of the U238 in a fuel bundle is converted to plutonium, mainly Pu239, along with Pu240, Pu241 and Pu242. Pu239 and Pu240 have long halflives so that considerable expense is incurred if these isotopes remain unburned and long term protection and storage are required. One method of dealing with axial spectral variations is using a control rod. For the BWR, control rods typically extend into the core from below and contain neutron-absorbing material which robs the adjacent fuel of thermal neutrons which would otherwise be available for fissioning. Thus, control rods can be used to modify the distribution of thermal neutrons over axial position to achieve more complete burnups. However, control rods provide only a gross level of control over spectral density. More precise compensation for spectral variations can be implemented using enrichment variation and burnable poisons. Enrichment variation using, for example, U235 enriched uranium, can be used near the top of a fuel bundle to partially compensate for a localized lack of thermal neutrons. Similarly, burnable poisons such as gadolinium oxide (Gd.sub.2 O.sub.3), can balance the exposure of bundle sections receiving a high thermal neutron flux. Over time, the burnable poisons are converted to isotopes which are not poisons so that more thermal neutrons become available for fissioning as the amount of fissile material decreases. In this way, fissioning can remain more constant over time in a section of the fuel bundle. By varying the amount of enrichment and burnable poisons by axial position along a bundle, longer and more complete burnups can be achieved. In addition, the enrichment and poison profiles can be varied by radial position to compensate for radial variations in thermal neutron density. Fuel management using control rods, selective enrichment and burnable poisons can be used to control the void fraction within the core as a function of time. Controlling the void fraction over time, in turn, results in control over the neutron flux profile. Thus, early in the life cycle of a fuel element, a large void fraction can be implemented, resulting in high heat generation at the bottom of a fuel bundle, while conversion of fertile fuel is facilitated over most of the fuel bundle length. Over time, the void fraction can be reduced, so that the portion of the fuel bundle subjected to thermal neutrons is increased, promoting further burnup at successively higher levels within the bundle that have been enriched by the earlier conversion. Imposing a progressively diminishing void fraction permits more complete burnups. However, it requires non-uniform power distributions. Non-uniform power distributions require lower reactor outputs, since peak temperatures must remain within limits to prevent excessive outgassing of fission products within fuel rods. Furthermore, non-uniform power distributions can induce additional thermal stresses along fuel rods; these stresses must be managed by limiting reactor output power. Moreover, void fractions can be controllably varied by adjusting pumping rates and thus coolant flow. The ability to control void fractions by increasing coolant flow is much more limited in some types of reactors. For example, natural-circulation boiling-water reactors rely on convection rather than pumps to promote circulation. Taken together, the use of control rods, control of void fraction over time, radial positional exchange of fuel assemblies, selective enrichment and distribution of burnable poisons still leave problems with axial variations in burn rates and neutron spectra. Furthermore, none of these employed methods effectively addresses the problem of the high level of fissile material produced and left in the upper-middle sections of the bundle due to the high level of epithermal neutrons and the low level of thermal neutrons. What is needed is a system that deals more effectively with axial spectral variations in neutron flux so that higher fuel burnups are provided and so that high-level waste is minimized. SUMMARY OF THE INVENTION In accordance with the present invention, fuel assemblies in a dual-phase nuclear reactor are inverted between operational cycles to provide for more uniform heat distribution in the core and more complete burnup during the lifetime of a fuel assembly. A fuel assembly can be inverted once to allow more complete burnup of fissile fuel created by conversion of fertile fuel near what was the top of a fuel assembly. In one realization of the present invention, a fuel assembly is inverted exactly once before retirement, while in another, exactly two inversions are implemented to allow more complete burnup of conversion products generated during the second cycle. Greater number of inversions are also provided for. Fuel assemblies can be sufficiently symmetric to permit installation in the core in both the intial and the inverted position. Means for supporting the bundle in the core and for manipulating the bundle in and out of the core are adapted to this symmetric fuel assembly. This symmetry is 180.degree. rotational symmetry about a line perpendicular to the major axis of the fuel assembly. In either the initial or inverted position, the major axis of the fuel assembly is generally codirectional with the direction of flow of the heat transfer fluid. The symmetry need not be complete. Asymmetric fuel distributions are provided for within fuel rods of a fuel assembly. In addition, mechanical asymmetries within a fuel rod are provided for. For example, while outgas plenums can be arranged at both ends of a fuel rod, only one of these ends needs a spring to provide the required level of fuel compression. Preparatory steps include assembly of fuel rods and a fuel assembly. During a first operational cycle, a "heads up" fuel bundle is exposed to more thermal neutrons near its foot and more fast neutrons near its head. Thus, more heat tends to be generated at the foot and more fissile fuel tends to be generated near the head. Upon inversion of the fuel assembly, the fissile actinide series fuel is subject to the greater thermal neutron flux, and thus burns more completely. In the meantime, further conversion of fertile fuel occurs at the bundle foot, which is in the upper, fast-neutron, region of the core. A second inversion allows this newer fertile fuel to be burned. While further inversions are provided for, two inversions insures that substantial quantities of conversion products are burned at both ends of each fuel bundle. By appropriate distributions of fuel fertile material, and burnable poisons in the fuel rods, fuel assemblies can be designed for either one or two inversions. The optimal number of inversions can depend also on the radial position of a fuel assembly. Different fuel rod compositions and different numbers of inversions can be applied across a core. Furthermore, an inverted fuel assembly can be installed in a position other than its original position. Thus, the present invention provides considerable flexibility in fuel management. The present invention provides a more uniform time-averaged neutron flux distribution over the length of a fuel bundle. Accordingly, more complete burnup is possible. In particular, inverting fuel assemblies promotes more complete burnup of actinide conversion products that would otherwise remain out of the high thermal flux regions toward the bottom of the core. Thus, greater efficiency and less problematic waste disposal are advantages provided by the present invention. Both of these advantages result in considerable cost savings. Increased efficiency results in greater amortization of the costs of a fuel assembly; more thorough burnup, especially of the actinide series isotopes, reduces the extent and term required for waste disposal. The more uniform power distribution permits a greater total power for a given constraint on spatial power peaks. Such constraints are required to prevent fuel rods from being damaged by excessive local temperatures. In addition, lower thermal peaks can be maintained, reducing stress on fuel rod claddings, enhancing their reliability. In addition, limiting thermal peaks minimizes outgassing of fission products, allowing smaller plenums to be used. Smaller plenums result in shorter fuel rods, shorter fuel assemblies; and a smaller reactor overall. Since the present invention is compatible with more uniform spatial distributions there is less need to manipulate factors such as void fraction, fertile fuel distribution, and burnable poison distribution to control burnup. Thus, the present invention removes the need to compromise other design goals in order to achieve longer fuel burnups. The invention is particularly useful in the context of natural-circulation reactors, that have limited flexibility in terms of neutron spectrum engineering. For example, instead of implementing a variable void fraction to improve time-averaged neutron flux distribution, void fraction can be optimized for core stability. Stable thermal hydraulic operation, that is, the propensity to damp stochastic disturbances in flow and void fraction, is promoted more effectively where there is a liquid water phase adjacent to the fuel rod plenums than where there is a combination of liquid and vapor phases. Relative to one-level cores in which all plenums are near the top, the present invention provides greater stability since at least part of the plenum volume is at the core entrance where there are no steam voids and the overall two-phase flow pressure drop is reduced. While time-averaged uniformity is advantageous, the present invention also provides a greater range of neutron flux for a given vertical location in a fuel bundle. This greater range provides for greater conversion of fertile fuel to fissile fuel in one cycle and then greater burn up of the converted fuel in a later cycle. These and other features and advantages of the present invention are apparent in the following description with references to the drawings below. |
description | In the following, modes for carrying out the present invention will be explained. FIG. 1 is a cross section of an essential structure of one embodiment of first and second intensifying screens of the present invention. In the figure, reference numeral 1 denotes a support consisting of plastic film or nonwoven fabric, on one surface of the support 1 a phosphor layer 2 being disposed. On the phosphor layer 2, there is disposed a protective film 3 consisting of plastic film or covering film. Of these respective elements, an intensifying screen 4 to be used for radiography is constituted. A phosphor layer 2 comprises a first phosphor layer 2a formed on the support 1 side and a second phosphor layer 2b formed on the protective film 3 side. Here, when an average particle diameter of a first phosphor particles constituting a first phosphor layer 2a is D1 and an average particle diameter of a second phosphor particles constituting a second phosphor layer 2b is D2, D1 less than D2 is satisfied. That is, on the support 1 side, a first phosphor layer 2a containing phosphor particles of smaller particle diameter is disposed, and on the protective film 3 side, a second phosphor layer 2b containing phosphor particles of larger particle diameter is disposed. A phosphor layer 2 of two-layer structure consisting of phosphor particles of different average particle diameters may be formed of CaWO4 phosphor or the like, it is, however, preferable to constitute particularly of rare earth phosphors such as Gd2O2S:Tb, LaOBr:Tb, BaFCl:Eu or the like of high emission efficiency. The first and second phosphor layers 2a and 2b are phosphor layers containing such particles of phosphors as described above, respectively. The intensifying screens 4 involving rare earth phosphors of high emission efficiency are particularly preferable. Even when the rare earth phosphors of high emission efficiency are employed, since the phosphor layer 2 is constituted of two phosphor layers 2a and 2b of different average particle diameters, while preventing deterioration of speed and sharpness from occurring, granularity can be improved. In addition, the phosphor layers 2 of two-layer structure can be produced similarly with the ordinary phosphor layers, resulting in satisfying mass-productivity. A first phosphor layer 2a disposed on a support 1 side is preferable to be constituted of phosphor particles of smaller particle diameter of an average particle diameter D1 in the range of 1 to 5 xcexcm. In FIG. 2, one example of sharpness performance when average particle diameter D1 of the first phosphor particles constituting the first phosphor layer 2a is varied is shown. By the way, in FIG. 2, Gd2O2S:Tb phosphor particles are employed, average particle diameter D2 of phosphor particles constituting the second phosphor layer 2b being 9 xcexcm, and range coefficient k thereof being 1.6. The ratio (CW1:CW2) of coating weight per unit area CW1 of phosphor particles of smaller particle diameter in the first phosphor layer 2a and coating weight per unit area CW2 of phosphor particles of larger particle diameter in the second phosphor layer 2b is set at 7:3. In FIG. 2, such intensifying screens 4 are employed as back intensifying screen. Phosphor particles of smaller particle diameter that are employed here has range coefficient k of 1.5 to 1.8. As obvious from FIG. 2, the smaller the average particle diameter D1 of phosphor particles of smaller particle diameter is, the sharper the sharpness becomes. However, when average particle diameter D1 is less than 1 xcexcm, manufacture of phosphor particles itself becomes difficult, and the brightness and formability of the phosphor layer may be deteriorated. The average particle diameter D1 of phosphor particles of smaller particle diameter constituting the first phosphor layer 2a is preferable to be 1 xcexcm or more, accordingly. Further, upon suppressing lowering of the sharpness, the average particle diameter D1 is preferable to be set at 5 xcexcm or less, particularly preferable being 3 xcexcm or less. By the way, when the intensifying screen 4 is employed as front screen, similar tendency arises. The second phosphor layer 2b disposed on the protective film 3 side, in addition to satisfying D2 greater than D1, is preferable to be constituted of larger phosphor particles of average particle diameter D2 in the range of 5 to 20 xcexcm. When the average particle diameter D2 of phosphor particles is less than 5 xcexcm, even if D2 greater than D1 is satisfied, an effect of the second phosphor layer 2b employing phosphor particles of larger particle size can not be fully obtained. FIG. 3 shows one example of sharpness performance when average particle diameter D2 of phosphor particles constituting the second phosphor layer 2b is varied. In FIG. 3, Gd2O2S:Tb phosphor particles are employed. Average particle diameter D1 of phosphor particles constituting the first phosphor layer 2a is 2 xcexcm, range coefficient k is 1.5, and the ratio of phosphor coating weights of the first phosphor layer 2a and the second phosphor layer 2b (CW1:CW2) is set at 7:3. In FIG. 3, such intensifying screens 4 are employed as the back screen. Employed phosphor particles of larger particle diameter has range coefficient k in the range of 1.6 to 1.8. As obvious from FIG. 3, when the average particle diameter D2 of larger phosphor particles is too large, the sharpness deteriorates largely. Accordingly, the average particle diameter D2 is preferable to be 20 xcexcm or less, further being preferable to be 10 xcexcm or less. Since the sharpness also deteriorates when the larger phosphor particles has too small average particle diameter D2, the average particle diameter D2 is preferable to be 7 xcexcm or more. When the intensifying screen 4 is employed as the front screen either, similar tendency exists. Particles of each phosphor constituting the first and second phosphor layers 2a and 2b such as described above have such particle size distribution as shown in the following, respectively. That is, the phosphor particles of smaller particle size being employed in the first phosphor layer 2a have range coefficient k (k1), which shows particle size distribution thereof, in the range of 1.3 to 1.8. By contrast, the phosphor particles of larger particle size being employed in the second phosphor layer 2b have range coefficient k (k2), which shows particle size distribution thereof, in the range of 1.5 to 2.0. In particular, the range coefficient k1 of the phosphor particles of smaller particle size and the range coefficient k2 of the phosphor particles of larger particle size are preferable to satisfy k1 less than k2. Thus, by making narrow the particle size distribution of the phosphor particles of smaller particle size one side and by making relatively broad the particle size distribution of the phosphor particles of larger particle size the other side, sharpness and granularity of the phosphor layer 2 of two-layer structure can be improved with reproducibility. When phosphor particles (both of smaller size phosphor particles and larger size phosphor particles) of which range coefficient k deviates from the aforementioned range are employed, improvement effect of sharpness and granularity due to two-layer structure of the phosphor layer 2 decreases. That is, when the range coefficient k1 of smaller size phosphor particles constituting the first phosphor layer 2a is less than 1.3, sharpness and speed are deteriorated largely, and when exceeding 1.8, the sharpness deteriorates. On the other hand, when the range coefficient k2 of larger size phosphor particles constituting the second phosphor layer 2b is less than 1.5, the sharpness becomes remarkably low, and when exceeding 2.0, the sensitivity deteriorates largely. In addition, when k2 is equal with k1 or smaller than that, the sharpness decreases largely. The range coefficient k1 of smaller size phosphor particles constituting the first phosphor layer 2a is further preferable to be in the range of 1.5 to 1.7. The range coefficient k2 of larger size phosphor particles constituting the second phosphor layer 2b is further preferable to be in the range of 1.6 to 1.8. By employing the smaller size phosphor particles and larger size phosphor particles having such range coefficients k1 and k2, the sharpness and granularity of the phosphor layer 2 of two-layer structure can be further improved. Furthermore, the first phosphor layer 2a and the second phosphor layer 2b, by controlling the ratio of coating weights thereof (CW1:CW2) within an appropriate range, can further improve the sharpness and granularity. In concrete, when the coating weight per unit area of phosphor particles in the first phosphor layer 2a is CW1 and the coating weight per unit area of phosphor particles in the second phosphor layer 2b is CW2, the ratio (CW1:CW2) of these CW1 and CW2 is preferable to be in the range of 8:2 to 6:4. FIG. 4 shows one example of sharpness performance when the ratio of coating weights of the first phosphor layer 2a and the second phosphor layer 2b is varied. In FIG. 4, the ratio of coating weights of phosphor is shown with the ratio (%) of the coating weight of the second phosphor layer 2b to the total coating weight of phosphor of the phosphor layer 2. In FIG. 4, Gd2O2S:Tb phosphor particles are employed. Average particle diameter D1 of phosphor particles constituting the first phosphor layer 2a is 2 xcexcm, average particle diameter D2 of phosphor particles constituting the second phosphor layer 2b is 9 xcexcm, and the total coating weight per unit area of phosphor particles of the phosphor layer 2 is 0.60 kg/m2. In FIG. 4, such intensifying screen 4 is employed as the front screen. As obvious from FIG. 4, when the ratio of coating weights of phosphor of the first phosphor layer 2a and the second phosphor layer 2b (CW1:CW2) is in the range of 8:2 to 6:4, excellent sharpness can be obtained. The same is with the granularity. When the intensifying screen 4 is employed for the back screen, similar tendency can be observed. Thus, by forming a phosphor layer 2 in two-layer structure (D1 less than D2) consisting of the first phosphor layer 2a and the second phosphor layer 2b of phosphor particles of different average particle sizes, and by further setting average particle diameters D1 and D2, particle size distribution, the ratio of coating weights (CW1:CW2) of the first phosphor layer 2a and the second phosphor layer 2b, or the like in appropriate ranges, excellent sensitivity and sharpness can be obtained, and in addition granularity can be improved. The phosphor layers 2 of two-layer structure can be manufactured in the identical manner with the ordinary phosphor layers. Accordingly, mass-productivity of the intensifying screens 4 can be fully satisfied. In addition, intended performance can be obtained with reproducibility. The intensifying screens of the aforementioned mode can be produced in the following manner. That is, smaller size phosphor of which average particle diameter is D1 and range coefficient k1 is in the range of from 1.3 to 1.8 is mixed with an appropriate amount of binder. Organic solvent is added thereto to prepare a coating liquid of smaller particle size phosphor of appropriate viscosity. This coating liquid is used for preparation of the first phosphor layer 2a. On the other hand, larger size phosphor of which average particle diameter is D2 ( greater than D1) and range coefficient k2 is in the range of 1.5 to 2.0 is mixed with an appropriate amount of binder. Organic solvent is added thereto to prepare a coating liquid of larger particle size phosphor of appropriate viscosity. This coating liquid is used to prepare the second phosphor layer 2b. The coating liquid of smaller particle size phosphor being used for preparation of the first phosphor layer 2a is coated on a support 1 by the use of knife coating or roller coating, followed by drying, to form a first phosphor layer 2a. Next, on the first phosphor layer 2a, the coating liquid of larger size phosphor being used for preparation of the second phosphor layer 2b is coated by the use of knife coating or roller coating, followed by drying, to form a second phosphor layer 2b. Incidentally, in some cases, there are intensifying screens of a structure in which light reflection layer, light absorption layer, layer of metallic foil or the like is disposed between a support 1 and a phosphor layer 2. In that case, the light reflection layer, light absorption layer, layer of metallic foil or the like can be formed in advance on the support 1, and thereon the phosphor layer 2 needs only be formed. As binders being employed for preparation of phosphor coating liquid, existing ones such as nitrocellulose, cellulose acetate, ethyl cellulose, polyvinyl butyral, flocculate polyester, polyvinyl acetate, vinylidene chloride-vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, polyalkyl (metha) acrylate, polycarbonate, polyurethane, cellulose acetate butyrate, polyvinyl alcohol or the like can be cited. As organic solvents, for instance, ethanol, methyl ethyl ether, butyl acetate, ethyl acetate, ethyl ether, xylene or the like can be cited. By the way, to the phosphor coating liquid, dispersion agents such as phthalic acid, stearic acid or the like and plasticizers such as triphenyl phosphate, diethyl phthalate or the like can be added. For the support 1, for instance, such resins as cellulose acetate, cellulose propionate, cellulose acetate butyrate, polyesters such as polyethylene terephthalate, polystyrene, polymethyl methacrylate, polyamide, polyimide, vinyl chloride-vinyl acetate copolymer, polycarbonate or the like can be formed in film to use. A protective film consisting of transparent resinous film of such as polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide or the like is laminated on the aforementioned phosphor layer 2 of two layer structure to form an intended intensifying screen 4. The protective film 3 may be formed by dissolving resins such as cellulose derivatives such as cellulose acetate, nitrocellulose, cellulose acetate butyrate or the like, polyvinyl chloride, polyvinyl acetate, polycarbonate, polyvinyl butyral, polymethyl methacrylate, polyvinyl formal, polyurethane or the like in solvent to form protective film coating liquid of appropriate viscosity, followed by coating and drying thereof. The intensifying screen 4 such as described above is used as radiation receptor 5 such as shown in FIG. 5 in radiography such as X-ray photography. In the radiation receptor 5 shown in FIG. 5, radiation film 6 such as X-ray film is interposed between two sheets of intensifying screen 4 (the intensifying screen 4 having the phosphor layer 2 of two-layer structure due to the aforementioned mode) and is accommodated in a cassette 7 in this state. Among the aforementioned two sheets of intensifying screen 4, one 4 that is disposed at subject side is so-called front-screen F, and the other one 4 is so-called back-screen B. The intensifying screens 4 to be used for the front intensifying screen F and back intensifying screen B have a basically identical structure as described in the aforementioned embodiment. When the total coating weight per unit area of phosphor particles in the phosphor layer 2 of two layer structure of the front intensifying screen F (summation of coating weights of phosphor particles of the first and second phosphor layers 2a and 2b) is TCWf and the total coating weight per unit area of phosphor particles in the phosphor layer 2 of two layer structure of the back screen B is TCWb, the ratio of TCWf and TCWb (TCWf:TCWb) is preferable to be in the range of 3:7 to 4:6. FIG. 6 shows one example of sharpness performance when the ratio of total coating weight per unit area (TCWf ratio) of phosphor particles of the front screen F and that of the back screen B is varied. By the way, in FIG. 6, Gd2O2S:Tb phosphor is employed. The summation of the total coating weight per unit area of phosphor particles of the front screen F and that of the back screen B is 1.5 kg/m2. As obvious from FIG. 6, when the ratio of the total coating weight per unit area of phosphor particles of the front screen F and that of the back screen B (TCWf:TCWb) is in the range of 3:7 to 4:6, excellent sharpness can be obtained. The radiation receptor 5 such as described above is used in a radiation inspection device 8 such as shown in FIG. 7. The radiation inspection device 8 shown in FIG. 7 comprises radiation source 9 and table 11 disposed opposite to the radiation source through subject 10 to be inspected such as a patient. The radiation receptor 5 is inserted into the table 11 from the side of the table 11 to use. At this time, the radiation receptor 5 is inserted so that the front screen F is disposed at the subject 10 side. The radiation receptor 5 constituted of the intensifying screen 4 of the aforementioned embodiment and the radiation inspection device 8 to be used therewith, even when X-ray exposure to an subject is reduced through improvement of system speed, can give excellent recognizability. That is, when used for medical X-ray radiography, for instance, amount of X-ray exposure to a subject can be reduced and excellent diagnosis can be carried out. When used in industrial nondestructive inspection or the like, in addition to reduction of an amount of X-rays, inspection accuracy can be improved. Next, concrete embodiments of intensifying screens of the aforementioned modes and evaluation results thereof will be explained. First, 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 3 xcexcm and range coefficient k of particle size distribution is 1.62 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of smaller particle size phosphor. Similarly, 10 parts by weight of Gd2O2S:Tb phosphor particles of which average particle diameter is 9 xcexcm and range coefficient k of particle size distribution is 1.70 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of larger size phosphor. Then, first, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.40 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller particle size phosphor. The support consists of polyethylene terephthalate film in which carbon black is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.20 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, first, a front intensifying screen is prepared. On the other hand, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.55 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which carbon black is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating method to be a phosphor coating weight of 0.30 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a back intensifying screen is prepared. In the intensifying screens for the front and back intensifying screens, the ratio of coating weights CW1:CW2 of the front intensifying screen is 6.7:3.3 and for the back intensifying screen, CW1:CW2 is 6.5:3.5. In addition, the ratio of the total phosphor coating weights of the front screen and back screen TCWf:TCWb is 4.1:5.9. Such front and back intensifying screens are provided for performance evaluation. 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 6.5 xcexcm and range coefficient k of particle size distribution is 1.55 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of phosphor. The aforementioned coating liquid of phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.45 kg/m2 after drying, followed by drying to form a phosphor layer. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a front intensifying screen is prepared. On the other hand, on a support consisting of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm, the aforementioned phosphor coating liquid is coated uniformly by the use of knife coating to be phosphor coating weight of 0.55 kg/m2 after drying, followed by drying to form a phosphor layer. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a back intensifying screen is prepared. These front and back intensifying screens are provided for the performance evaluation that will be described later. In the aforementioned embodiment 1, for the smaller size phosphor, Gd2O2S:Tb phosphor powder of which average particle diameter is 3 xcexcm and range coefficient k of particle size distribution is 1.13 is employed, and for the larger size phosphor, Gd2O2S:Tb phosphor powder of which average particle diameter is 9 xcexcm and range coefficient k of particle size distribution is 1.40 is employed. Except for the above, in the identical way with the embodiment 1, the front and back intensifying screens are prepared. Such front and back intensifying screens are provided for the performance evaluation that will be described later. First, 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 3 xcexcm and range coefficient k of particle size distribution is 1.62 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of smaller size phosphor. Similarly, 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 9 xcexcm and range coefficient k of particle size distribution is 1.70 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of larger size phosphor. Then, first, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.40 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.20 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, first, a front intensifying screen is prepared. On the other hand, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.70 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.35 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a back intensifying screen is prepared. In the front and back intensifying screens, the ratio of coating weights CW1:CW2 of the front intensifying screen is 6.7:3.3 and of the back intensifying screen, CW1:CW2 is 6.7:3.3. In addition, the ratio of the total phosphor coating weights of the front screen and back screen TCWf:TCWb is 3.6:6.4. Such front and back intensifying screens are provided for performance evaluation that will be described later. 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 10.8 xcexcm and range coefficient k of particle size distribution is 1.60 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of phosphor. The aforementioned coating liquid of phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.55 kg/m2 after drying, followed by drying to form a phosphor layer. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a front intensifying screen is prepared. On the other hand, on a support consisting of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm, the aforementioned coating liquid of phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 1.15 kg/m2 after drying, followed by drying to form a phosphor layer. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a front intensifying screen is prepared. These front and back intensifying screens are provided for the performance evaluation that will be described later. In the aforementioned embodiment 2, for the smaller particle size phosphor, Gd2O2S:Tb phosphor powder of which average particle diameter is 3 xcexcm and range coefficient k of particle size distribution is 1.95 is employed, and for the larger size phosphor, Gd2O2S:Tb phosphor powder of which average particle diameter is 9 xcexcm and range coefficient k of particle size distribution is 2.10 is employed. Except for the above, in the identical way with the embodiment 2, front and back intensifying screens are prepared. Such intensifying screens for the uses of front and back screens are provided for the performance evaluation that will be described later. First, 10 parts by weight of CaWO4 phosphor powder of which average particle diameter is 3.5 xcexcm and range coefficient k of particle size distribution is 1.53 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of smaller size phosphor. Similarly, 10 parts by weight of CaWO4 phosphor powder of which average particle diameter is 15.7 xcexcm and range coefficient k of particle size distribution is 1.65 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of larger size phosphor. Then, first, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.30 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which carbon black is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.20 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, first, a front intensifying screen is prepared. On the other hand, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.50 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which carbon black is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.30 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a back intensifying is prepared. In the front and back intensifying screens, the ratio of phosphor coating weights CW1:CW2 of the front intensifying screen is 6:4 and of the back intensifying screen, CW1:CW2 is 6.3:3.7. In addition, the ratio of the total phosphor coating weights of the front screen and back screen TCWf:TCWb is 3.8:6.2. Such front and back intensifying screens are provided for performance evaluation that will be described later. 10 parts by weight of CaWO4 phosphor powder of which average particle diameter is 10.0 xcexcm and range coefficient k of particle size distribution is 1.40 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of phosphor. The aforementioned coating liquid of phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.60 kg/m2 after drying, followed by drying to form a phosphor layer. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a front intensifying is prepared. On the other hand, on a support consisting of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm, the aforementioned coating liquid of phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.90 kg/m2 after drying, followed by drying to form a phosphor layer. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, a front intensifying screen is prepared. These front and back intensifying screens are provided for the performance evaluation that will be described later. In the aforementioned embodiment 3, for the smaller size phosphor, CaWO4 phosphor powder of which average particle diameter is 3.5 xcexcm and range coefficient k of particle size distribution is 1.20 is employed, and for the larger size phosphor, CaWO4 phosphor powder of which average particle diameter is 15.7 xcexcm and range coefficient k of particle size distribution is 1.45 is employed. Except for the above, in the identical way with the embodiment 3, front and back intensifying screens are prepared. Such front and back intensifying screens are provided for the performance evaluation that will be described later. First, 10 parts by weight of BaFCl:Eu phosphor powder of which average particle diameter is 3.8 xcexcm and range coefficient k of particle size distribution is 1.58 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of smaller size phosphor. Similarly, 10 parts by weight of BaFCl:Eu phosphor powder of which average particle diameter is 8.5 xcexcm and range coefficient k of particle size distribution is 1.65 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of larger size phosphor. Then, first, the aforementioned coating liquid of smaller size phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.30 kg/m2 after drying, followed by drying to form a first phosphor layer consisting of smaller size phosphor. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Then, on the first phosphor layer, the coating liquid of larger size phosphor is coated uniformly by the use of knife coating to be a phosphor coating weight of 0.20 kg/m2 after drying, followed by drying to form a second phosphor layer consisting of larger size phosphor. Thereafter, on the aforementioned phosphor layer of two layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, front and back intensifying screens are prepared. In the front and back intensifying screens, the ratio of coating weights CW1:CW2 of the front intensifying screen and back intensifying screen is 6:4. In addition, the ratio of the total phosphor coating weights of the front screen and back screen TCWf:TCWb is 5:5. Such front and back intensifying screens are provided for performance evaluation that will be described later. 10 parts by weight of BaFCl:Eu phosphor powder of which average particle diameter is 4.5 xcexcm and range coefficient k of particle size distribution is 1.50 is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a coating liquid of phosphor. The coating liquid of phosphor is coated uniformly on a support by the use of knife coating to be a phosphor coating weight of 0.50 kg/m2 after drying, followed by drying to form a phosphor layer. The support consists of polyethylene terephthalate film in which titanium white is kneaded and of which thickness is 250 xcexcm. Thereafter, on the phosphor layer of one layer structure, a protective film of a thickness of 9 xcexcm is laminated. Thus, front and back intensifying screens are prepared. These front and back intensifying screens are provided for performance evaluation that will be described later. In the aforementioned embodiment 4, for the smaller size phosphor, BaFCl:Eu phosphor powder of which average particle diameter is 3.8 xcexcm and range coefficient k of particle size distribution is 1.85 is employed, and for the larger size phosphor, BaFCl:Eu phosphor powder of which average particle diameter is 8.5 xcexcm and range coefficient k of particle size distribution is 1.40 is employed. Except for the above, in the identical way with the embodiment 4, front and back intensifying screens are prepared. Such front and back intensifying screens are provided for the performance evaluation that will be described later. The respective intensifying screen pairs (pair of a front intensifying screen and a back intensifying screen) due to the aforementioned Embodiments 1 and 2, and Comparative Examples 1, 2, 3 and 4 are evaluated of their sensitivity, sharpness and granularity with ortho-type X-ray film (product name of Konica: SR-G). The respective intensifying screen pairs due to the aforementioned Embodiments 3 and 4, and Comparative Examples 5, 6, 7 and 8 are evaluated of their sensitivity, sharpness and granularity with regular-type X-ray film (product name of Konica: New-A). The results thereof are shown in Table 1. By the way, photographic performance of the aforementioned intensifying screen pairs is evaluated of sensitivity, sharpness and granularity with X-rays of tube-voltage of 120 kV after transmission of a water phantom of a thickness of 100 mm. The sensitivity is expressed in terms of relative value with each value of comparative example 1, 3, 5 and 7 as 100, respectively. The sharpness, after evaluating the respective MTFs at a spatial frequency of 2 lines/mm, is expressed in terms of relative values with each value of comparative examples 1, 3, 5 and 7 as 100, respectively. The granularity is expressed as relative RMS value at a spatial frequency of 3.12 line/mm under photographic density of 1.0. As obvious from Tables 1 and 2, all of the respective intensifying screen pairs (pair of a front intensifying screen and a back intensifying screen) due to Embodiments 1 through 4, compared with intensifying screen pairs of single layer structure, are improved in their granularity. In addition to this improvement, lowering of sensitivity or sharpness is small or improved. Next, another embodiments for implementing intensifying screens of the present invention will be described. FIG. 8 is a cross section showing a structure of one embodiment of a third intensifying screen of the present invention. In the same figure, reference numeral 21 denotes a support consisting of plastic film or nonwoven fabric. On one surface the support 21, there is disposed a powder layer 22. The powder layer consists of at least one kind of particles selected from particles of simple metal, particles of alloy consisting mainly of metal and particles of compound consisting mainly of metal and has a thickness of 2 to 40 kg/m2 in terms of weight per unit area. The powder layer 22, as will be explained in detail later, is disposed so as to absorb X-rays of high energy to be the intensity of the X-rays of high energy appropriate for the sensitivity of X-ray film. Further, the powder layer 22, due to an elimination effect of scattered X-rays and a sensitizing effect of phosphor due to secondary electrons based on Compton scattering, improves sensitivity, sharpness and granularity. Upon obtaining such effects, as the metal constituting the powder layer 22, at least one kind of heavy metal selected from W, Mo, Nb and Ta is preferable. On the powder layer 22, there is disposed a phosphor layer 23. For the phosphors constituting the phosphor layer 23, generally used CaWO4 may be employed and also rare earth phosphors of high emission efficiency such as BaFCl:Eu, Gd2O2S:Tb, LaOBr:Tb or the like may be used. The phosphor layer 23 contains particles of such phosphors. On the phosphor layer 23, a protective film 24 consisting of plastic film or plastic cover film is disposed. With these elements, an X-ray intensifying screen 25 being used in high energy X-ray radiography of 1 MV or more is constituted. The X-ray intensifying screen 25 of this embodiment is suitable for one that is used to confirm an irradiation area prior to treatment with X-rays of high energy for treatment such as approximately 4 MV that is obtained by a linear accelerator called as linac. For particles constituting the aforementioned powder layer 22, at least one kind of particles selected from simple particles of heavy metals, in particular of W, Mo, Nb, Ta or the like, alloy particles consisting mainly of these metals, and compound particles consisting mainly of these metals can be employed. In concrete, simple particles of metals such as W particles, Mo particles, Nb particles and Ta particles, alloy particles consisting mainly of heavy metals such as Wxe2x80x94Re alloy particles, Wxe2x80x94Mo alloy particles, Wxe2x80x94Nb alloy particles, Wxe2x80x94Ta alloy particles, Moxe2x80x94Nb alloy particles, Moxe2x80x94Ta alloy particles and Nbxe2x80x94Ta alloy particles, and compound particles consisting mainly of heavy metals such as particles of tungsten carbide (WC), particles of tungsten oxides (such as WO3 or the like), particles of molybdenum oxides (such as MoO3 or the like), particles of tungsten carbide (MoC), particles of niobium carbide (Nbxe2x80x94C) and particles of tantalum carbide (Taxe2x80x94C) can be employed. Compounds consisting mainly of refractory metals, without restricting to oxides and carbides, can be various kinds of compounds such as intermetallic compounds or the like, and are not limited to particular types of compounds. However, when particles of alloys or compounds consisting mainly of heavy metals are employed, alloys or compounds of which amount of heavy metal is 60% or more by weight in these particles are preferable. When the heavy metal is contained less than 60% by weight in the particles, there is a danger that an absorption effect of X-rays of high energy can not be obtained fully. In other words, alloys or compounds of which heavy metal is 60% or more by weight can give an effect similar to that obtained by simple particles of heavy metals. Heavy metals such as W, Mo, Nb and Ta that are main constituents of the powder layer 22 can largely absorb X-rays of high energy such as described above. Accordingly, when the X-ray intensifying screen 25 of this embodiment is employed for radiography as a preparatory inspection means of X-ray treatment with X-rays of high energy, the high energy X-rays irradiated from the support 21 side, before reaching the phosphor layer 23, is absorbed to the value appropriate for exposure sensitivity of such as X-ray film. In addition, even if the X-rays converted to an appropriate energy state by going through the powder layer 22 are scattered by the phosphor layer 23 or the protective film 24, the scattered X-rays can be effectively absorbed by the powder layer 22. Thus, by effectively absorbing the scattered X-rays by the powder layer 22, the scattered X-rays can be made less probable in reentering into the phosphor layer 23, the granularity and sharpness can be improved accordingly. Furthermore, since the powder layer 22 consisting mainly of heavy metals such as W or the like has a sensitizing effect of phosphor due to secondary electrons based on Compton scattering, the sensitivity and sharpness can be further improved. The thickness of the powder layer 22 constituted mainly of heavy metals is in the range of 2 to 40 kg/m2 in terms of weight per unit area. When the thickness of the powder layer 22 is less than 2 kg/m2 in terms of weight per unit area, the X-rays of high energy can not be effectively absorbed, resulting in exposure of less contrast of X-ray film. On the other hand, when the thickness of the powder layer 22 exceeds 40 kg/m2 in terms of weight per unit area, absorption of the X-rays becomes too large, resulting in lowering of sensitivity. The thickness of the powder layer 22 is preferable to be in the range of 5 to 30 kg/m2 in terms of weight per unit area. The powder layer 22 can be formed in the similar manner with the phosphor layer 23. That is, particles selected from for instance simple particles of W, alloy particles consisting mainly of W or compound particles consisting mainly of W are mixed with adequate amount of binder and organic solvent is added thereto to prepare a powder coating liquid of appropriate viscosity. This powder coating liquid is coated on a support 21 by the use of knife coating or roller coating and dried to result in a desired powder layer 22. According to such coating methods, the powder layer 22 having the aforementioned thickness can be obtained easily and less expensively. Thus, in the intensifying screen 25, X-rays of high energy are absorbed by the powder layer 22 consisting mainly of heavy metals to be a state adequate for radiography and, further an absorption effect of scattered X-rays and a sensitizing effect of phosphor due to secondary electrons based on Compton scattering can be obtained. Accordingly, in radiography employing high energy X-rays, in addition to excellent contrast and sensitivity, granularity and sharpness can be improved. Improvement effects of sensitivity, granularity and sharpness can be obtained with a simple structure in which powder layer 22 is disposed between support 21 and phosphor layer 23. As a result of this, intensifying screens 25 that can cope with the X-rays of high energy such as 1 MV or more and can improve the granularity and sharpness can be produced with ease and less expensively. In addition, there is no handling problem as existing fluorometallic screens cause and they are advantageous from the viewpoint of cost. According to the intensifying screens 25 of this embodiment, even when radiographs are taken with X-rays of high energy for treatment such as approximately 4 MV, due to existence of the powder layer 22, the excellent contrast can be obtained. In addition, since excellent sensitivity, granularity and sharpness can be obtained, when the intensifying screen is employed for radiography (medical radiography) as preparatory inspection means of X-ray treatment employing X-rays of high energy, reproducibility of an irradiation field set by a treatment program can be clearly confirmed. That is, excellent recognizability of portions to be treated can be obtained. Intensifying screens 25 of the aforementioned embodiment can be produced by the following way, for instance. That is, at least one kind of particles selected from simple particles of metals, alloy particles having heavy metals as main constituent and compound particles having heavy metals as main constituent are mixed with an appropriate amount of binder, followed by addition of organic solvent to result in a powder coating liquid of appropriate viscosity. This powder coating liquid is coated on a support 21 by the use of knife coating or roller coating and is dried to result in a powder layer 22 consisting mainly of heavy metals. As binders being employed for preparation of powder coating liquid, nitrocellulose, cellulose acetate, ethyl cellulose, polyvinyl butyral, flocculate polyester, polyvinyl acetate, vinylidene chloride-vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, polyalkyl (metha) acrylate, polycarbonate, polyurethane, cellulose acetate butyrate, polyvinyl alcohol or the like can be employed. As organic solvents, for instance, ethanol, methyl ethyl ether, butyl acetate, ethyl acetate, ethyl ether, xylene or the like can be cited. By the way, to the powder coating liquid, dispersion agent such as phthalic acid, stearic acid or the like and plasticizer such as triphenyl phosphate, diethyl phthalate or the like can be added. For the support 21, for instance, such resins as cellulose acetate, cellulose propionate, cellulose acetate butyrate, polyesters such as polyethylene terephthalate, polystyrene, polymethyl methacrylate, polyamide, polyimide, vinyl chloride-vinyl acetate copolymer, polycarbonate or the like can be formed in film to use. On the other hand, phosphor is mixed with an appropriate amount of binder, followed by addition of organic solvent to prepare a phosphor coating liquid of appropriate viscosity. This phosphor coating liquid is coated on a protective layer 24 by the use of knife coating or roller coating and dried to form a phosphor layer 23. Binders or organic solvents being used for preparation of the phosphor coating liquid can be similar ones employed for preparation of the powder coating liquid. For protective film 24, such transparent resinous films as polyethylene terephthalate, polyethylene, polyvinylidene chloride and polyamide can be employed. As demands arise, dispersion agents such as phthalic acid, stearic acid or the like or plasticizer such as triphenyl phosphate, diethyl phthalate or the like can be added to phosphor coating liquid. By laminating a support 21 thereon the powder layer 22 containing the aforementioned heavy metals such as W or Mo is formed and a protective film thereon a phosphor layer 23 is formed, an intended X-ray intensifying screen (radiation intensifying screen) 25 can be obtained. By the way, by coating the phosphor coating liquid directly on the powder layer 22 and drying, followed by laminating thereon a filmy protective film 4 or by coating thereon a protective film coating liquid that is adjusted to an appropriate viscosity by dissolving various kinds of resins in solvent, followed by drying, an X-ray intensifying screen 25 can be produced. The X-ray intensifying screens 25 can be produced with other method than that described above. That is, a protective film 24 is formed in advance on a flat plate and thereon a phosphor layer 23 and a powder layer 22 are formed sequentially. Thereafter, together with the protective film they are peeled off the plate and on the powder layer 22 thereof a support 21 is laminated. Next, concrete embodiments of the radiation intensifying screens (X-ray intensifying screen 25) of the aforementioned implementing modes and evaluation results thereof will be described. First, 10 parts by weight of Gd2O2S:Tb phosphor powder of which average particle diameter is 6.0 xcexcm is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a phosphor coating liquid. The phosphor coating liquid is coated uniformly on a protective film consisting of polyethylene terephthalate film of a thickness of 9 xcexcm by the use of knife coating to be a phosphor coating weight of 1.20 kg/m2 after drying, followed by drying to form a phosphor layer. On the other hand, 1 part by weight of particles of W metal of an average particle diameter of 3.0 xcexcm is combined with 1 part by weight of vinyl chloride-vinyl acetate copolymer as binder and an appropriate amount of ethyl acetate as organic solvent to prepare a W particle coating liquid. The W particle coating liquid is coated uniformly on a support by the use of knife coating to be a coating weight of W particles of 10 kg/m21 followed by drying to form a W powder layer (powder layer). The support consists of polyethylene terephthalate film of which thickness is 250 xcexcm and in which carbon black is kneaded. Thereafter, the protective film thereon the phosphor layer is formed and the support thereon the W powder layer is formed are laminated so that the phosphor layer face the W powder layer, resulting in an intended X-ray intensifying screen. This X-ray intensifying screen is provided for performance evaluation to be described later. As constituent particles of powder layer, WC (tungsten carbide) particles of an average particle diameter of 3.5 xcexcm (Embodiment 6) and Wxe2x80x94Re alloy particles (Embodiment 7) of an average particle diameter of 4.0 xcexcm are coated to be coating weights of 15 kg/m2 (Embodiment 6) and 16 kg/m2 (Embodiment 7), respectively. Except for the above, as identical with Embodiment 5, X-ray intensifying screens are produced, respectively. These X-ray intensifying screens are provided for performance evaluation to be described later. As constituent particles of powder layer, Mo particles (Embodiment 8) of an average particle diameter of 5 xcexcm, Nb particles (Embodiment 9) of an average particle diameter of 8 xcexcm and Ta particles (Embodiment 10) of an average particle diameter of 7 xcexcm are coated to be coating weights of 19 kg/m2 (Embodiment 8), 18 kg/m2 (Embodiment 9), and 11 kg/m2 (Embodiment 10), respectively. Except for the above, as identical with Embodiment 5, X-ray intensifying screens are produced, respectively. These X-ray intensifying screens are provided for performance evaluation to be described later. In the place of the powder layer in Embodiment 5, a lead foil of a thickness of 0.5 mm is employed. In the identical manner with embodiment 1 except for the above, X-ray intensifying screens are prepared. These X-ray intensifying screens are supplied for performance evaluation to be described later. The respective X-ray intensifying screens of the aforementioned Embodiments 5 through 10 and Comparative Example 9 are evaluated of sensitivity and sharpness with ortho-type X-ray film (Fuji Photo-Film Co: Super HR-S) when X-rays of energy of 4 MV are irradiated. The results are shown in Table 3. By the way, each of photographic sensitivity of intensifying screens is shown as relative value with the value of comparative example as 100. The sharpness, by evaluating MTFs at spatial frequency of 2 lines/mm, is shown as relative values with that of intensifying screen of comparative example 9 as 100. As obvious from Table 3, each X-ray intensifying screen due to Embodiments 5 through 10 shows the sensitivity comparative with those of existing fluorometallic screens (Comparative Example 9) that employ lead foil. That is, these intensifying screens due to the above embodiments are obvious to have performance enough to be applied practically. In addition, each sharpness thereof is remarkably improved compared with that of Comparative Example 9. First and second intensifying screens of the present invention, while preventing the lowering of sensitivity and sharpness from occurring, are improved in granularity due to the phosphor layer of two-layer structure that is easy in produce and less of restricting factors. Radiation receptors and radiation inspection devices that employ such radiation intensifying screens of the present invention are particularly effective when high sensitivity of radiography system is aimed. Even in such systems, excellent recognizability can be obtained. Third intensifying screens of the present invention, while having the absorption of high energy X-rays comparable with that of existing fluorometallic intensifying screens that employ lead foil, are improved further in sensitivity, sharpness and granularity. Such intensifying screens can be employed effectively in X-ray radiography using high energy X-rays and such radiation intensifying screens that can cope with high energy X-rays can be provided easily and less expensively. |
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description | This is a Continuation of International Application PCT/EP2019/060523, which has an international filing date of Apr. 24, 2019, and the disclosure of which is incorporated in its entirety into the present Continuation by reference. This Continuation also claims foreign priority under 35 U.S.C. § 119(a)-(d) to and also incorporates by reference, in its entirety, German Patent Application DE 10 2018 207 146.2 filed on May 8, 2018. The invention relates to a mirror, in particular for a microlithographic projection exposure apparatus. Microlithography is used for producing microstructured components such as, for example, integrated circuits or LCDs. The microlithography process is conducted in a so-called projection exposure apparatus, which comprises an illumination device and a projection lens. The image of a mask (=reticle) illuminated with the illumination device is projected with the projection lens onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (=photoresist) and disposed in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate. In projection lenses designed for the extreme ultraviolet (EUV) range, i.e., at wavelengths of, e.g., approximately 13 nm or approximately 7 nm, mirrors are used as optical components for the imaging process owing to the lack of availability of suitable light-transmissive refractive materials. In this case, it is also known to configure one or more mirrors in an EUV system as an adaptive mirror with an actuator layer composed of a piezoelectric material, wherein an electric field having a locally varying strength is generated across this piezoelectric layer by an electrical voltage being applied to electrodes arranged on both sides with respect to the piezoelectric layer. In the case of a local deformation of the piezoelectric layer, the reflection layer stack of the adaptive mirror also deforms, with the result that, for example, imaging aberrations (possibly also temporally variable imaging aberrations) can be at least partly compensated for by suitably driving the electrodes. FIG. 5 shows a representative, feasible construction of a conventional adaptive mirror 50, in a merely schematic illustration. The mirror 50 comprises in particular a mirror substrate 52 and also a reflection layer stack 61 and has a piezoelectric layer 56, which is produced from lead zirconate titanate (Pb(Zr,Ti)O3, PZT) in the example. Electrode arrangements are respectively situated above and below the piezoelectric layer 56, by way of which electrode arrangements an electric field for producing a locally variable deformation is able to be applied to the mirror 50. Of said electrode arrangements, the second electrode arrangement facing the substrate 52 is configured as a continuous, planar electrode 54 of constant thickness, whereas the first electrode arrangement has a plurality of electrodes 60, to each of which an electrical voltage relative to the electrode 54 is able to be applied by way of a lead 59. The electrodes 60 are embedded into a common smoothing layer 58, which is produced e.g. from quartz (SiO2) and serves for levelling the electrode arrangement formed from the electrodes 60. Furthermore, the mirror 50 has, between the mirror substrate 52 and the bottom electrode 54 facing the mirror substrate 52, an adhesion layer 53 (e.g. composed of titanium, Ti) and a buffer layer 55 (e.g. composed of LaNiO3), which is arranged between the electrode arrangement 54 facing the substrate 52 and the piezoelectric layer 56 and which further supports the growth of PZT in an optimum, crystalline structure and ensures consistent polarization properties of the piezoelectric layer over the service life. During operation of the mirror 50 or of an optical system comprising said mirror 50, applying an electrical voltage to the electrodes 54 and 60, by way of the electric field that forms, results in a deflection of the piezoelectric layer 56. In this way, it is possible—for instance for the compensation of optical aberrations e.g. owing to thermal deformations in the case of EUV radiation incident on the optical effective surface 51—to achieve an actuation of the mirror 50. In accordance with FIG. 5, the mirror 50 furthermore has a mediator layer 57. Said mediator layer 57 is in direct electrical contact with the electrodes 60 (which are illustrated in plan view in FIG. 5 only for elucidation purposes). Said mediator layer 57 serves to “mediate” between the electrodes 60 in terms of potential, wherein it has only low electrical conductivity (preferably less than 200 siemens/meter (S/m)), with the consequence that a potential difference existing between adjacent electrodes 60 is dropped substantially across the mediator layer 57. An advantage achieved owing to the presence of the mediator layer 57 is evident from the diagram in FIG. 6, in which diagram the stray light proportion is plotted as a function of the number of electrodes 60. As illustrated in FIG. 6, in order to fall below an upper threshold (i.e., an exemplary, predefined “Specification”) for the stray light proportion, in the example chosen, a number of sixty electrodes is required in each of two mutually perpendicular spatial directions if no mediator layer 57 is present. In other words, a total number of 60*60=3600 electrodes is required without the presence of the mediator layer 57. If, on the other hand, the mediator layer 57 is present, said number can be reduced to fewer than ten electrodes in one of the two mutually perpendicular spatial directions, with the consequence that the realizability of the electrode arrangement formed from the electrodes 60 is significantly simplified. The above-described application of electrical voltage to the electrode arrangements in the adaptive mirror results in an electric current in the mediator layer 57 and thus, by way of the electrical power generated thereby, in an undesired development of heat. It is therefore desirable, in principle, to limit said electrical power by setting a sufficiently high electrical resistance of the mediator layer (of e.g. 100 kΩ). Even though such a configuration may be suitable for specific scenarios of use of the adaptive mirror, such as e.g. for correcting the influence of deformations of the optical elements, such as mirrors or lens elements that are induced thermally by absorption of radiation, in practice scenarios also exist in which the setting of the desired surface shape of the adaptive mirror has to be effected on a significantly shorter timescale, e.g. within milliseconds (ms). Such scenarios, in which the electrical potential would propagate too slowly in a mediator layer having the abovementioned high resistances for limiting the electrical power, include e.g. accounting for thermally induced mask deformations in the lithography process. In such event, owing to the absorption of, in terms of magnitude, more than 30% of the EUV light, the mask forms an irregular “mountainous region”, which ultimately results in a focus variation in the lithographic imaging process. In order to take into account the above-described variation in surface shape of the mask by setting the adaptive mirror accordingly has to take place in the lithography process during the scanning operation itself, which lasts on the order of 100 ms, and thus must take place on a comparatively small time scale of milliseconds (ms). Even though it is readily possible to drive the electrodes in the adaptive mirror sufficiently fast, the practical implementation of the abovementioned small time constants proves to be problematic with regard to the mediator layer, since reducing the electrical resistance of the mediator layer in turn results in thermal problems, owing to the above-described reciprocal dependence involving the electrical power. Regarding the prior art, reference is made merely by way of example to DE 10 2013 219 583 A1 and DE 10 2015 213 273 A1. It is an object of the present invention to provide a mirror, in particular for a microlithographic projection exposure apparatus, which, based on the principle of the locally varying deformation of a piezoelectric layer, enables aberrations of various types to be corrected better than was heretofore possible while at the same time generating as little heat as possible in the optical system. This and related objects are achieved in accordance with the novel structures and innovations described hereinbelow. A mirror according to one aspect of the invention comprises: an optical effective surface, a mirror substrate; a reflection layer stack for reflecting electromagnetic radiation that is incident on the optical effective surface, and at least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and to which an electric field for producing a locally variable deformation is able to be applied by way of a first electrode arrangement situated on the side of the piezoelectric layer facing the reflection layer stack, and by way of a second electrode arrangement situated on the side of the piezoelectric layer facing the mirror substrate; wherein both the first electrode arrangement and the second electrode arrangement have a plurality of electrodes, to each of which an electrical voltage relative to the respective other electrode arrangement is able to be applied by way of a lead; wherein each of said electrode arrangements is respectively assigned a separate mediator layer for setting a continuous profile of the electrical potential along the respective electrode arrangement; and where said mediator layers differ from one another in their average electrical resistance by a factor of at least 1.5. The present invention makes use of the concept, in particular, in the case of an adaptive mirror comprising a piezoelectric layer, to which an electric field for producing a locally variable deformation is able to be applied via electrode arrangements, for the purpose of mediation in potential between the respective electrodes of an electrode arrangement, of not using just a single mediator layer having a comparatively low electrical conductivity, but rather of using two separate mediator layers from the outset. This permits—through a division of tasks as described below—the different requirements or scenarios of use that occur during practical operation to be taken into account in each case in a targeted manner and without undesired acceptance of compromises (for instance with regard to thermal problems). In particular, this aspect of the invention here includes the concept of designing one of two separate and different mediator layers for realizing a comparatively fast potential propagation within the mediator layer with a comparatively low electrical resistance (e.g. with an electrical resistance of 1 kilohm (kΩ) for realizing a switching time with regard to the electrical potential of 100 ms) and the second separate mediator layer with a significantly higher electrical resistance (e.g. 100 kΩ), in order in this respect to limit the generation of electrical power as far as possible and here to accept comparatively longer switching times with regard to the electrical potential established in each case in the mediator layer (e.g. switching times on the order of 10 s or more). The above-described concept according to the invention is based on the further consideration that in the typical application scenarios for the mediator layer mentioned first, which has a comparatively low electrical resistance and thus enables fast switching with regard to the electrical potential or with regard to the effect of the adaptive mirror, such as e.g. in the application for taking into account thermally induced mask deformations in the lithography process, the (deformation) amplitudes typically required are comparatively small and, merely by way of example, may be on the order of magnitude of 1 nm. By contrast, the (deformation) amplitudes typically required in the use scenario—likewise described above—of correcting the influence of deformation of optical elements, such as mirrors or lens elements, that is induced thermally by absorption of radiation are comparatively larger and may be e.g. on the order of magnitude of 10 nm. The differences thus present with regard to the order of magnitude of the deformation amplitudes to be set in each case in the different use scenarios can now be used in the context of the invention to the effect that for correcting the influence of thermally induced deformations e.g. of mirrors, although comparatively large gradients of the electrical voltage are required on the part of the relevant mediator layer (having a comparatively higher resistance), a significantly higher electrical resistance can also be accepted since comparatively more time is available for switching between the respective electrical potentials. By contrast, for the application scenario of taking into account thermally induced mask deformations in the lithography process, the mediator layer having a comparatively low resistance (e.g. having an electrical resistance of 1 kΩ) can be used since, in this respect, only comparatively small deformation amplitudes and thus also small gradients of the electrical voltage are required and the development of heat accompanying electric current flow is thus significantly limited from the outset. In summary, in accordance with one aspect of the invention, a functional division between two mutually separate mediator layers is effected, of which one mediator layer is designed for “fast operation” (i.e. switching between different electrical potentials on a comparatively short timescale of e.g. on the order of 1 ms) with a small amplitude (e.g. on the order of 1 nm) and the other mediator layer is designed for comparatively “slow operation” (e.g. switching between different electrical potentials on a longer timescale on the order of 10 s) with a comparatively large amplitude (e.g. 10 nm). Both mediator layers are drivable independently of one another with regard to the electrical voltage, wherein the potential difference between the electrical potentials set by way of the two mediator layers is once again crucial for the locally varying deformation set in the piezoelectric layer. In other words, during operation of the adaptive mirror according to this aspect of the invention, depending on what effect is intended to be corrected precisely with the set locally variable deformation of the adaptive mirror, one mediator layer or the other (optionally also a suitable combination) is used for producing the corresponding deformation. In this case, owing to the circumstance that in each case structured electrode arrangements are required for both mediator layers used according to the invention, this aspect of the invention deliberately accepts a higher outlay from the standpoint of production engineering for instance in comparison with a conventional construction that manages with only one mediator layer e.g. in accordance with FIG. 5 (in which one electrode arrangement can be embodied as a planar electrode and thus only one structured electrode arrangement is required). This aspect of invention accepts this disadvantage in order in return, through the above-described division of tasks with regard to the two mediator layers according to the invention, to be able to satisfy in a targeted manner the requirements that exist in each case in different application scenarios, and to realize here as a result correction of aberrations as optimally as possible with at the same time as little heat as possible being generated in the optical system. In accordance with one embodiment, the mediator layers differ from one another in their average electrical resistance by a factor of at least 3, in particular by a factor of at least 5. In accordance with one embodiment, the mediator layers differ from one another in their average thickness (wherein the different electrical resistance can be provided via different thicknesses in particular in the case where identical materials are used for the mediator layer). In accordance with one embodiment, the mediator layers differ from one another with regard to their stoichiometry (wherein, with identical thicknesses, in particular, the different electrical resistance can be provided by the use of different materials for the mediator layer). In this case, in particular, a difference in the stoichiometry can be produced even in the case of identical material and identical thickness, by varying the background pressure during deposition, by varying the oxygen partial pressure or by adapting the deposition temperature. In accordance with one embodiment, the material of at least one of the mediator layers comprises titanium dioxide (TiO2), LaCoO3, LaMnO3, LaCaMnO3 or LaNiO3. In accordance with a further aspect, the invention also relates to a mirror, in particular for a microlithographic projection exposure apparatus, wherein the mirror has an optical effective surface, comprising a mirror substrate, a reflection layer stack for reflecting electromagnetic radiation that is incident on the optical effective surface, at least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and to which an electric field for producing a locally variable deformation is able to be applied by way of a first electrode arrangement situated on the side of the piezoelectric layer facing the reflection layer stack, and by way of a second electrode arrangement situated on the side of the piezoelectric layer facing the mirror substrate, wherein at least one of said electrode arrangements is assigned a mediator layer having a controllable electrical conductivity for the temporally variable setting of a continuous profile of the electrical potential along the respective electrode arrangement. In accordance with one embodiment, the mirror has at least one control electrode, in particular a plurality of mutually independently operable control electrodes, for controlling the electrical conductivity of the mediator layer. With this configuration, the electrical voltage of the mediator layer can be set in a temporally variable manner. In this case, a comparatively higher electrical conductivity or a lower average electrical resistance can serve for setting comparatively smaller deformation amplitudes on a smaller time scale, whereas the electrical conductivity can then be correspondingly decreased for the purpose of setting comparatively higher deformation amplitudes on a longer time scale. The mirror can be in particular a mirror for a microlithographic projection exposure apparatus. However, the invention is not limited thereto. In other applications, a mirror according to the invention can also be employed or utilized for example in an apparatus for mask metrology. In accordance with one embodiment, the mirror is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm. However, the invention is not limited thereto, and the invention can therefore also be realized advantageously in further applications in an optical system having an operating wavelength in the VUV range (for example of less than 200 nm). The concept according to the invention of using two separate mediator layers in order to achieve the division of tasks described above is not limited to realization in one and the same adaptive mirror. Rather, the two mediator layers used according to the invention can also be present on two separate adaptive mirrors, wherein then in this respect, analogously to FIG. 5, each of these mediator layers can be assigned a structured electrode arrangement and an electrode arrangement designed as a planar electrode. In this case, preferably that adaptive mirror with the mediator layer having a comparatively low resistance (for the fast setting of comparatively small deformation amplitudes e.g. for correcting a thermally induced mask deformation) is positioned in a near-field plane of the optical system, whereas the other adaptive mirror with the mediator layer having a comparatively higher resistance (for the comparatively slow setting of larger deformation amplitudes e.g. for correcting thermally induced mirror deformations) is positioned in a near-pupil position. In accordance with a further aspect, the invention therefore also relates to an optical system, in particular an illumination device or a projection lens of a microlithographic projection exposure apparatus, comprising at least two mirrors, wherein each of said mirrors has an optical effective surface, a mirror substrate and a reflection layer stack for reflecting electromagnetic radiation that is incident on the optical effective surface, wherein each of said mirrors has a piezoelectric layer, which is arranged in each case between the mirror substrate and the reflection layer stack and to which an electric field for producing a locally variable deformation is able to be applied by way of a first electrode arrangement situated on the side of the piezoelectric layer facing the reflection layer stack, and by way of a second electrode arrangement situated on the side of the piezoelectric layer facing the mirror substrate, wherein each of said mirrors has in each case a mediator layer for setting a continuous profile of the electrical potential, and where said mediator layers differ from one another in their average electrical resistance by a factor of at least 1.5. The invention furthermore relates to an optical system of a microlithographic projection exposure apparatus, in particular an illumination device or a projection lens, comprising at least one mirror having the above-described features, and also to a microlithographic projection exposure apparatus. Further configurations of the invention can be gathered from the description and the dependent claims. The invention is explained in greater detail below on the basis of exemplary embodiments illustrated in the accompanying figures. FIG. 1 shows a schematic illustration for elucidating the construction of a mirror according to the invention in one exemplary embodiment of the invention. The mirror 10 comprises in particular a mirror substrate 12, which is produced from any desired suitable mirror substrate material. Suitable mirror substrate materials are e.g. quartz glass doped with titanium dioxide (TiO2), with materials that are usable being, merely by way of example (and without the invention being restricted thereto), those sold under the trade names ULE® (from Corning Inc.) or Zerodur® (from Schott AG). Furthermore, the mirror 10 has, in a manner known per se in principle, a reflection layer stack 21, which, in the embodiment illustrated, comprises merely by way of example a molybdenum-silicon (Mo—Si) layer stack. Without the invention being restricted to specific configurations of this layer stack, one suitable construction that is merely by way of example can comprise approximately 50 plies or layer packets of a layer system comprising molybdenum (Mo) layers having a layer thickness of in each case 2.4 nm and silicon (Si) layers having a layer thickness of in each case 3.3 nm. The mirror 10 can be in particular an EUV mirror of an optical system, in particular of the projection lens or of the illumination device of a microlithographic projection exposure apparatus. The impingement of electromagnetic EUV radiation (indicated by an arrow in FIG. 1) on the optical effective surface 11 of the mirror 10 during operation of the optical system can have the consequence of an inhomogeneous volume change of the mirror substrate 12 due to the temperature distribution which results from the absorption of the radiation that is incident inhomogeneously on the optical effective surface 11. In order to correct such an undesired volume change or else in order to correct other aberrations that occur during operation of the microlithographic projection exposure apparatus, the mirror 10 is of adaptive design, as is explained in greater detail below. In this respect, the mirror 10 according to the invention has a piezoelectric layer 16, which is produced from lead zirconate titanate (Pb(Zr,Ti)O3, PZT) in the exemplary embodiment. In further embodiments, the piezoelectric layer 16 can also be produced from some other suitable material (e.g. aluminum nitride (AlN), aluminum scandium nitride (AlScN), lead magnesium niobate (PbMgNb) or vanadium-doped zinc oxide (ZnO)). The piezoelectric layer 16 can have for example a thickness of less than 5 μm, more particularly a thickness in the range of 1 μm to 4 μm. In embodiments, the performance of the piezoelectric layer 16 can be increased by a calcium niobate layer (CaNbO3 layer) being introduced at a suitable location of the layer stack. The increase in performance is achieved here by the piezoelectric layer 16 preferably growing in the [001] crystal direction. An electric field for producing a locally variable deformation is able to be applied to the piezoelectric layer 16 by way of a first electrode arrangement having electrodes 20b (which are connected to leads 19b), said first electrode arrangement being situated on the side of the piezoelectric layer 16 facing the reflection layer stack 21, and by way of a second electrode arrangement having electrodes 20a (which are connected to leads 19a), said second electrode arrangement being situated on the side of the piezoelectric layer 16 facing the mirror substrate 12. The electrodes 20a and 20b are respectively embedded into a smoothing layer 18a and 18b, which is produced from quartz (SiO2) in the exemplary embodiment and serves for levelling the electrode arrangement formed from the electrodes 20a and 20b, respectively. Furthermore, the electrodes 20a and 20b respectively have—without the invention being restricted thereto—a hexagonal geometry, wherein in particular they can also be arranged substantially over a wide area and in a manner isolated from one another only by way of comparatively narrow trenches. The invention is generally not restricted to specific geometries of the electrodes or distances therebetween (wherein the distance between the electrodes can also be e.g. a number of millimeters (mm) or a number of centimeters (cm)). In accordance with FIG. 1, the leads 19a and 19b respectively each have a first section, which runs perpendicular to the stacking direction of the reflection layer stack 21, and a second section (also referred to as “via” or “plated-through hole”), which runs in the stacking direction of the reflection layer stack 21. Other types of contacting are also possible, wherein e.g. the leads in further embodiments can also be realized with just one section running perpendicular to the stacking direction (in a two-dimensional design and without “vias”). Furthermore, the mirror 10 in accordance with FIG. 1 has an optional adhesion layer 13 (in the example composed of titanium, Ti) between the mirror substrate 12 and the bottom electrode arrangement formed from the electrodes 20a and facing the mirror substrate 12. Furthermore, buffer layers present on both sides of the piezoelectric layer 16 are designated by “15a” and “15b”, respectively. Same buffer layers 15a, 15b serve to further support the growth of PZT in an optimum, crystalline structure and to ensure consistent polarization properties of the piezoelectric layer 16 over the service life, and can be produced e.g. from LaNiO3. During operation of the mirror 10 or of an optical system comprising said mirror 10, applying an electrical voltage to the electrode arrangements formed from the electrodes 20a and 20b, respectively, by way of the electric field that forms in the region of the piezoelectric layer 16, results in a deflection of said piezoelectric layer 16. In this way, it is possible to achieve an actuation of the mirror 10 for compensating optical aberrations. In contrast to the conventional construction of an adaptive mirror described in the introduction with reference to FIG. 5, in the case of the mirror 10 according to the invention as described here with reference to FIG. 1, the electrode arrangements situated on mutually opposite sides of the piezoelectric layer 16 are assigned in each case separate mediator layers 17a and 17b, respectively, for setting a continuous profile of the electrical potential along the respective electrode arrangement. In this arrangement, both mediator layers 17a and 17b respectively—if they are produced from LaNiO3—can then also serve as buffer layers for the PZT of the piezoelectric layer 16, in which case separate buffer layers 15a, 15b can then be dispensed with. By contrast, if the mediator layer is produced from a different material than LaNiO3, buffer layers 15a, 15b are provided, as illustrated, on both sides of the PZT of the piezoelectric layer 16. Furthermore, in contrast to the conventional arrangement depicted in FIG. 5, rather than for instance one of the two electrode arrangements being embodied as a planar continuous electrode, both electrode arrangements situated on mutually opposite sides of the piezoelectric layer 16 comprise electrodes 20a, 20b, to which electrical voltage is able to be applied by way of separate leads in each case. The mediator layers 17a and 17b are not embodied identically to one another, but rather differ from one another with regard to their average electrical resistance by a factor of at least 1.5 (in further embodiments by a factor of at least 3, in particular by a factor of at least 5). For this purpose, the mediator layers 17a, 17b have mutually different stoichiometries and/or mutually different average thicknesses. Different stoichiometries can be achieved e.g. by way of different partial pressures, different background pressures or different temperatures during deposition. The use of different materials for the mediator layer is likewise possible. The different configuration of the mediator layers 17a, 17b with regard to their respective electrical resistance has the consequence that the mediator layer having a comparatively low resistance enables the respective electrical potential to be “switched” comparatively faster or on a shorter time scale during operation of the mirror 10 or of the associated optical system, whereas on account of the reciprocal dependence of the generated electrical power on the electrical resistance, the mediator layer having a comparatively higher resistance results in comparatively low thermal loads during operation of the mirror 10 or of the relevant optical system. These different characteristic properties can, in turn, be used, as already described above, in order to utilize the particular electrode arrangement which is assigned to the mediator layer that has the relatively lower average electrical resistance in order to apply particular voltages for the purpose of producing locally variable deformations of the piezoelectric layer 16. This is desirable especially in scenarios in which comparatively small deformation amplitudes are to be set on a comparatively short time scale. One such exemplary embodiment is, in particular, the compensation of thermally induced mask deformations during a given lithography operation. By contrast, the electrode arrangement assigned to the mediator layer having the relatively higher electrical resistance is used for setting comparatively larger deformation amplitudes on a longer time scale. One exemplary scenario for this is the compensation of thermally induced mirror deformations or aberrations caused thereby in the optical system. In one specific exemplary embodiment, for instance, the mediator layer 17b can have an average electrical resistance of 100 kΩ and can be driven with electrical voltages in the range of 100 V, in order to make it possible to switch between deformation amplitudes on the scale of 10 nm on a time scale of 10 s. The deformations of the adaptive mirror provided as a result are suitable for compensating the above-described thermally induced mirror deformations in the optical system. By contrast, merely by way of example, the mediator layer 17a can have an average electrical resistance of 1 kΩ and can be driven with electrical voltages having an amplitude of approximately 10 V, in order to switch between deformation amplitudes on the scale of 1 nm in approximately 100 ms. The deformations of the adaptive mirror 10 brought about thereby are suitable for compensating the thermally induced mask deformations—likewise described above—during lithography operation. In a further embodiment (not illustrated by one specific figure), the separate mediator layers described above, which differ from one another with regard to their average electrical resistance, can also be realized in different separate mirrors in order to take account of the abovementioned use scenarios in each case in a targeted manner or to realize the above-described division of tasks with regard to the compensation of different aberrations during operation of the optical system. For this purpose, preferably, the adaptive mirror having the mediator layer with a comparatively low resistance and serving for the compensation of thermally induced mask deformations is positioned in a near-field plane and the other adaptive mirror, having the mediator layer with a comparatively higher resistance and serving for the compensation of thermally induced mirror deformations is positioned in a near-pupil plane. In further embodiments described below with reference to FIG. 2 and FIG. 3, the mediator layer in an adaptive mirror according to the invention can also be designed such that the electrical conductivity of the mediator layer is controllable or can be set in a temporally variable manner during operation. In one exemplary embodiment, merely illustrated schematically in FIG. 2, “27” denotes a mediator layer with FET structure, which can be produced e.g. from doped semiconductor material and the electrical conductivity of which is controlled by way of a control electrode 30 configured in a continuous fashion (to which control electrode an electric field is able to be applied by way of a lead 33). In FIG. 2, “32” denotes the electrodes serving for controlling the deflection of the piezoelectric layer (not illustrated in FIG. 2), wherein these electrodes 32 are electrically insulated from the control electrode 30 with insulators 31. In accordance with the configuration illustrated in FIG. 2, the electrical voltage of the mediator layer 27 can be set in a temporally variable manner. In this case, a comparatively higher electrical conductivity or a lower average electrical resistance, analogously to the embodiment described above with reference to FIG. 1, can serve for setting comparatively smaller deformation amplitudes on a smaller time scale, whereas the electrical conductivity can then be correspondingly decreased for the purpose of setting comparatively higher deformation amplitudes on a longer time scale. During exemplary operation of the arrangement in FIG. 2, a maximum permissible evolution of heat can be predefined in a first step, wherein proceeding from the deformation profile that is desired or to be aimed at in each case, the FET control voltage is then chosen in a second step such that precisely that maximum conductivity of the mediator layer arises which leads to said maximum evolution of heat. In this way, at any point in time it is possible to achieve a maximum speed with regard to setting the electrical potential that is desired in each case. The maximum evolution of heat can be characterized here by way of either a global value or a local peak value. If the setting speed attained is lower than desired with regard to the deformation pattern or electrical potential striven for, the deformation amplitude can alternatively be “scaled down” in such a way that both the desired setting speed and the maximum evolution of heat are attained. Alternatively or additionally, feedback to an external closed-loop control loop can also be effected, which ensures a suitable compromise for ensuring the best possible correction taking into account the requirements with regard to the setting speed and evolution of heat. FIG. 3 shows a further embodiment, wherein components analogous or substantially functionally identical to those in FIG. 2 are designated by reference numerals increased by “10”. In contrast to FIG. 2, in the case of the embodiment in FIG. 3, separate control electrodes 30a, 30b, 30c . . . (to which an electric field is able to be applied by way of leads 43) for controlling the conductivity of the mediator layer 37 are provided in a manner electrically insulated from one another, wherein electrodes 42 present once again analogously to FIG. 2 for controlling the deflection of the piezoelectric layer are situated within these electrode sections 30a, 30b, 30c . . . in a manner insulated independently by way of insulators 41. The setting of locally different values for the FET control voltage that is able to be realized in accordance with FIG. 3 enables the flexibility of the arrangement to be increased further. In this way, for example, at a predefined point in time, a desired fast setting of a specific deformation pattern can be restricted to a central region of the adaptive mirror, whereas e.g. in a radially outer region of the mirror it is possible to realize relatively larger deformation amplitudes on a longer time scale or with a lower setting speed. For this purpose, e.g. control electrodes 30a, 30b, 30c . . . arranged radially further inward can set a comparatively higher electrical conductivity of the mediator layer 37, while a comparatively lower electrical conductivity can be predefined by way of control electrodes arranged radially further outward. FIG. 4 shows a schematic illustration of an exemplary projection exposure apparatus which is designed for operation in the EUV and in which the present invention can be realized. According to FIG. 4, an illumination device in a projection exposure apparatus 400 designed for EUV comprises a field facet mirror 403 and a pupil facet mirror 404. The light from a light source unit comprising a plasma light source 401 and a collector mirror 402 is directed onto the field facet mirror 403. A first telescope mirror 405 and a second telescope mirror 406 are arranged in the light path downstream of the pupil facet mirror 404. A deflection mirror 407 is arranged downstream in the light path, said deflection mirror directing the radiation that is incident thereon onto an object field in the object plane of a projection lens comprising six mirrors 451-456. At the location of the object field, a reflective structure-bearing mask 421 is arranged on a mask stage 420, said mask being imaged with the aid of the projection lens into an image plane in which a substrate 461 coated with a light-sensitive layer (photoresist) is situated on a wafer stage 460. Of the mirrors 451-456 of the projection lens, the mirrors 451 and 452, which are arranged in the initial area of the projection lens with respect to the optical beam path, are good candidates to be configured in a manner according to the invention. This is so because the described effect of compensating for thermal deformations is particularly noticeable at these mirrors 451, 452 as a result of the still comparatively low summed reflection losses and the associated relatively high light intensities that prevail at these mirrors. However, the specific mirrors 451 and 452 are noted simply by way of example, since any of the other mirrors 453-456 can be configured in a manner according to the invention either in lieu of or in addition to the mirrors 451, 452. Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments will be apparent to the person skilled in the art, for example through combination and/or exchange of features of individual embodiments. Accordingly, such variations and alternative embodiments are also encompassed by the present invention, and the scope of the invention is restricted only within the meaning of the appended patent claims and equivalents thereof. |
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abstract | A vibration mitigation clamp apparatus is provided, which is designed to stiffen a riser brace assembly in a nuclear reactor so as to increase the natural vibration frequency of the riser brace assembly. In an embodiment, the vibration mitigation clamp apparatus may include a first plate, a second plate and a wedge assembly. The vibration mitigation clamp apparatus is attached to upper and lower riser brace leaves of the riser brace assembly, at a location near a weld that attaches the leaves to a riser brace block of the riser brace assembly that is affixed to an RPV sidewall. The wedge assembly is expandable to apply forces on inside surfaces of the riser brace leaves, countering clamping forces applied to the first and second plate to fixedly secure the vibration mitigation clamp apparatus on the riser brace assembly. |
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060027363 | summary | FIELD OF THE INVENTION The invention relates to a dismountable fuel assembly of a nuclear reactor cooled by light water, and in particular to a dismountable fuel assembly of a reactor cooled by pressurized water. BACKGROUND OF THE INVENTION Nuclear reactors cooled by water, and particularly pressurized-water nuclear reactors, include assemblies consisting of a bundle of very long fuel rods arranged parallel to one another and held in a framework formed by guide thimbles, spacers, and two end nozzles. The guide thimbles are arranged in the longitudinal direction of the assembly and are connected to transverse spacers spaced evenly along the length of the assembly. The guide thimbles are also connected at each of their ends to one of two nozzles, constituting components for stiffening and closing the assembly. The fuel rods of the assembly constitute a bundle in which the rods are parallel to each other and arranged in the transverse sections of the assembly, in a uniform pattern defined by the spacers. Some positions of the bundle are occupied by guide thimbles which are generally connected rigidly to the spacers. The guide thimbles are longer than the fuel rods and are placed in the bundle so as to include a part which projects relative to the bundle of fuel rods at each of their ends. The nozzles are fixed to these projecting end parts of the guide thimbles so as to close the assembly at each of its ends. The fuel rods consist of sintered pellets of nuclear fuel substance stacked up inside metal cladding isolating the pellets from the fluid surrounding the fuel assembly. In the event of the cladding of a rod of a fuel assembly breaking, it is necessary to replace this rod very rapidly in order to avoid leaks of radioactive product into the fluid for cooling the reactor. In order to gain access to the fuel rods and replace them, it is necessary to dismount one of the nozzles of the assembly, which involves eliminating the links between the end parts of the guide thimbles and the nozzle. The nozzles include a transverse plate, termed adaptor plate, including through-holes reproducing the pattern of the guide thimbles in each of which a guide thimble is engaged and fixed. To replace the defective rods in fuel assemblies, novel fuel assemblies including guide thimbles have been designed and developed in which the link with at least one of the end nozzles is dismountable. In order to replace the defective fuel rods, the assembly is placed under water in a vertical position, in a pit such as a storage pit, such that the assembly rests on the bottom of the pit via one of its nozzles, or bottom nozzle. The other nozzle, or top nozzle, is accessible under a certain depth of water from the top of the pit. In one type of known dismountable fuel asembly, those parts of the guide thimbles which are engaged in the top nozzle of the assembly include a radially expansible part, which may, for example, be a split bush connected to the end of the guide thimble. An immobilizing sleeve inserted inside the guide thimble radially expands the split bush and fastens the guide thimble, a radially projecting part of which becomes accommodated inside a cavity machined in the nozzle. Such a device requires special forming of the end of the guide thimble which is to be engaged inside the adaptor plate of the nozzle. Furthermore, the fitting and extraction of the sleeves for immobilizing the guide thimbles when assembling or dismounting the fuel assembly require special tools allowing tension or thrust to be exerted on the immobilizing sleeve and allowing the immobilizing sleeves to be dismounted and removed, leading to the formation of radioactive waste. Fuel assemblies have also been proposed which include linking means which can be maneuvered quickly by turning an immobilizing element through a fraction of a turn, in order to lock or unlock the link between a tie for holding the assembly and the dismountable nozzle. Such devices are described, for example, in U.S. Pat. No. 4,064,004 and U.S. Pat. No. 5,268,948, and have a complicated structure and many components. Furthermore, these devices require the guide thimble to project above the adaptor plate of the nozzle and include parts projecting above the adaptor plate which are fixed to the end of the guide thimble and have an appreciable height which is incompatible with the use of consumable poison clusters. These parts include a bearing plate coming into a superposed arrangement relative to the adaptor plate of the fuel assembly, when the consumable poison rods are inserted into the guide thimbles of the fuel assembly. The device according to U.S. Pat. No. 5,268,948 may include a sleeve fixed to the guide thimble and coming to bear under the adaptor plate of the nozzle, and two components which are also mounted on the end of the guide thimble so that they can move in rotation relative to one another about the axis of the guide thimble. One of these components is a ring rotatably mounted on the guide thimble and including two radially projecting parts. The adaptor plate of the nozzle is traversed by an opening of constant cross-section, the shape of the opening corresponding to the shape of the transverse section of the ring. The ring is mounted on the end of the guide thimble projecting out of the opening of the plate, and a second component fixed to the end of the guide thimble is provided in order to immobilize the ring in the position in which the guide thimble is locked or in the position in which it is unlocked. The device for fixing the guide thimble is therefore, in the main, situated outside the nozzle above the adaptor plate. SUMMARY OF THE INVENTION The object of the invention is to provide a fuel assembly of a nuclear reactor cooled by light water and including a bundle of parallel fuel rods held in a framework formed by guide thimbles or solid ties, spacers and end nozzles fixed onto the ends of the guide thimbles or ties, at least one of the nozzles being fixed onto one of the ends of each of the guide thimbles or ties in a dismountable manner, via an end part of the guide thimble which is engaged in an opening passing through a transverse plate of the nozzle, associated with quick dismountable means for fixing the guide thimble including a bearing sleeve integral with the end of the guide thimble comprising at least one bearing rim intended to come into contact with a face of the adaptor plate on the periphery of the opening and a ring mounted coaxially around the sleeve for rotation about the sleeve and including at least two bearing stops projecting radially and separated by at least two axial passages and at least one part with elastic radial deformation, these fixing means being placed inside the adaptor plate, so that the end of the guide thimble can be flush with the external face of the nozzle. To this end, the opening in the nozzle has at least two bearing stops projecting inwards, separated by at least two axial passages and including a bearing surface for the stops of the ring perpendicular to the axis of the opening, inside the opening, at least one of the two elements: opening of the nozzle and bearing sleeve including radial openings for receiving the part with elastic deformation of the ring, for immobilizing the ring in a position in which the bearing sleeve is locked inside the opening of the adaptor plate or in an unlocked position, PA1 the bearing sleeve, when it does not have a receiving opening for immobilizing the ring, comprising at least two bearing stops separated by at least two passages of axial direction. |
052271285 | claims | 1. A fuel assembly removably positionable in a reactor core inside a pressure vessel of a nuclear reactor comprising: an upper tie plate; a lower tie plate spaced from said upper tie plate, and including a lower manifold therein; a plurality of laterally spaced apart fuel rods extending longitudinally between said upper and lower tie plates and joined thereto; a plurality of laterally spaced apart hollow control rods extending longitudinally between said upper and lower tie plates and joined in flow communication with said lower manifold; a reservoir containing a neutron absorbing control liquid joined to said lower tie plate in flow communication with said lower manifold, and being removable together with said fuel assembly when said fuel assembly is removed from said reactor core; and means for pumping said control liquid from said reservoir through said lower manifold and into said control rods for selectively varying the level of said control liquid in said control rods. a lower housing fixedly joined to said lower tie plate and surrounding said reservoir, and including a lower nosepiece for channeling a liquid coolant into said lower housing and around said reservoir; and wherein said lower tie plate includes a plurality of inlets extending therethrough at respective ones of said fuel rods, and disposed in flow communication with said lower housing for channeling said coolant through said lower tie plate and along said fuel rods. a lower bellows disposed inside said reservoir in flow communication with said lower manifold, said lower bellows containing said control liquid; and wherein said pumping means include a piston disposed inside said reservoir and adjacent to said lower bellows, said piston being selectively translatable inside said reservoir for selectively compressing said lower bellows to pump said control liquid into said lower manifold and said control rods for varying said control liquid level. said reservoir is spaced longitudinally from said lower tie plate to define an access channel for allowing said coolant to flow from said metering orifice around said reservoir and into said lower tie plate inlets; and further comprising a transfer tube extending between said lower tie plate and said reservoir and disposed in flow communication between said lower manifold and said lower bellows for channeling said control liquid therebetween. an actuator having a selectively extendable plunger positionable through said lower nosepiece and into said reservoir for translating said piston to selectively compress said lower bellows to pump said control liquid into said control rods to raise said level thereof. 2. A fuel assembly according to claim 1 further comprising: 3. A fuel assembly according to claim 2 further comprising: 4. A fuel assembly according to claim 3 wherein said reservoir is spaced radially inwardly from said lower housing to define an annular orifice for metering flow of said coolant through said lower tie plate inlets. 5. A fuel assembly according to claim 4 wherein: 6. A fuel assembly according to claim 5 being top-and-bottom symmetrical for being reversible in said reactor core and including an upper manifold in said upper tie plate in flow communication with said control rods, and an upper bellows in flow communication with said upper manifold. 7. A fuel assembly according to claim 6 wherein said control rods include a non-neutron absorbing fluid being displacable from said control rods as said control liquid is pumped therein. 8. A fuel assembly according to claim 7 wherein said displacable fluid is a liquid being immiscible with said control liquid and effective for moderating neutrons emitted from said fuel rods, said upper bellows being effective for storing said liquid moderator upon displacement thereof from said control rods by said control liquid pumped therein. 9. A fuel assembly according to claim 6 wherein said pumping means further include: 10. A fuel assembly according to claim 9 wherein said actuator is disposed inside said reactor pressure vessel below said reactor core. |
061817597 | claims | 1. A method for determining the closeness to criticality of a nuclear reactor during start-up, comprising the steps of: completing a control rod withdrawal step, thereby generating a change in an output signal of a neutron detector; measuring the output signal after the completion of the control rod withdrawal step and during a transient portion of the output signal; calculating the effective neutron multiplication factor (K.sub.eff) based upon the measured output signal and elapsed time between the output signal measurements; and determining the closeness to criticality of the nuclear reactor based upon the calculated value of the effective neutron multiplication factor K.sub.eff, wherein the step of calculating the effective neutron multiplication factor (K.sub.eff) based upon the recorded output signals and elapsed time between at least two of the recorded signals, comprises the step of: .beta.=effective 1-group delayed neutron fraction, .lambda..sub.eff =effective 1-group neutron precursor decay constant, ##EQU6## t=a time after completion of the control rod withdrawal step, n(t.sub.s)=the value of the output signal measured at a time t.sub.s following completion of the control rod withdrawal step, n(t)=the value of the output signal measured at a time t following completion of the control rod withdrawal step, and n(.infin.)=the value of the output signal measured after neutron flux stops increasing. determining the time required for the output signal to achieve a specific fraction of an equilibrium signal level at the calculated value of the effective neutron multiplication factor (K.sub.eff). measuring the relative change in the output signal occurring in a predetermined time after the control rod withdrawal step. 2. The method of claim 1, wherein the step of determining the closeness to criticality of the nuclear reactor based upon the calculated value of the effective neutron multiplication factor (K.sub.eff), comprises the step of: 3. The method of claim 1, wherein the step of determining the closeness to criticality of the nuclear reactor based upon the calculated value of the effective neutron multiplication factor (K.sub.eff), comprises the step of: |
claims | 1. An apparatus for altering the radiation intensity delivered from a radiation source to a patient for medical treatment of the patient comprising, in combination: a plate member for holding a plurality of radiation modulating devices used for radiation treatment of the patient; and a frame member coupled to the radiation source for holding and locking the plate member, the frame member allowing the plate member to be positioned between the radiation source and a target area of the patient wherein the frame member allows the plate member to rotate within the frame member so different radiation modulating devices may be positioned between the radiation source and the target area of the patient to alter the radiation intensity delivered to the patient for medical treatment. 2. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 1 wherein the plate member comprises a plurality of openings formed around the periphery of the plate member for holding the plurality of radiation modulating devices. claim 1 3. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 1 wherein the plate member comprises at least one handle formed on the plate member. claim 1 4. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 1 wherein in the frame member comprises: claim 1 a housing which is positioned around a section of the plate member when the plate member is placed within the frame member; a channeling which runs along a length of the housing; a cross bar member coupled between a first end and a second end of the housing; and a pair of support arms coupled to the housing for coupling the frame member to the radiation source. 5. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 4 wherein the frame member further comprises a rotatable arm member rotatably coupled to the cross bar for securing the plate member within the frame member. claim 4 6. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 5 wherein the rotatable arm member has a raised member coupled to an end of the rotatable arm. claim 5 7. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 4 wherein the frame member further comprises a plurality of rollers located within the channeling for rotating the plate member within the channeling. claim 4 8. An apparatus for altering the radiation intensity delivered from a radiation source comprising, in combination: a plate member having a plurality of openings formed around the periphery of the plate member for holding a plurality of radiation modulating devices; and a frame member coupled to the radiation source for holding the plate member between the radiation source and a target area wherein the frame member allows the plate member to rotate within the frame member so different radiation modulating devices may be positioned between the radiation source and the target area to alter the radiation intensity delivered wherein the frame member comprises: a housing which is positioned around a section of the plate member when the plate member is placed within the frame member; a channeling which runs along a length of the housing; a cross bar member coupled between a first end and a second end of the housing; a pair of support arms coupled to the housing for coupling the frame member to the radiation source; and a rotatable arm member rotatable coupled to the cross bar for securing the plate member within the frame member. 9. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 8 wherein the plate member further comprises at least one handle formed on the plate member. claim 8 10. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 8 wherein the rotatable arm member has a raised member coupled to an end of the rotatable arm. claim 8 11. An apparatus for altering the radiation intensity delivered from a radiation source in accordance with claim 8 wherein the frame member further comprises a plurality of rollers located within the channeling for rotating the plate member within the channeling. claim 8 |
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abstract | The present invention relates to a system and method for automatic measurements and calibration of computerized magnifying instruments. More particularly, the method includes an automatic calibration aspect, which includes obtaining an optimized digital image of a reference object including at least one standardized landmark feature, and establishing calibration parameters based on one or more measured attributes of the landmark feature. The method further describes a calibration aspect, which includes providing calibration parameters, obtaining a digital image including at least one known attribute, measuring the at least one known attribute and comparing the measured value with the known value. The method further includes an aspect of automatic measurement of an attribute of one or more object, which includes retrieving calibration parameters, acquiring a digital image and measuring the attribute. The system includes an object support, a reference object including one or more standardized landmark features, and an automatically readable identification means. |
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claims | 1. A forged nozzle shell course for a pressure vessel, said shell course comprising at least one reinforcement portion extending radially outward from an outer surface of said shell course, each said reinforcing portion comprising a nozzle having a radius, said nozzle comprising: a bore extending from an outside surface of said reinforcing portion to an inside surface of said shell course; and at least one extension attachment surface located adjacent to and coaxial to said bore, said at least one extension attachment surface set back from said outside surface of said reinforcing portion, said reinforcing portion comprising a longitudinal dimension equal to about 2.0 times said radius of said nozzle, and a circumferential dimension equal to about 1.5 times the radius of said nozzle, measured from the centerline of said nozzle bore, said shell course, said at least one reinforcing portion, and said nozzle machined from one forging forming one unitary shell course. 2. A forged nozzle shell course according to claim 1 further comprising an integral groove extending into an outer end of said nozzle, said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 1 3. A forged nozzle shell course according to claim 1 further comprising an integral groove extending into said inner surface of said shell course said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 1 4. A forged nozzle shell course according to claim 2 further comprising an integral groove extending into said inner surface of said shell course said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 2 5. A forged nozzle shell course according to claim 1 further comprising an integral stub projecting radially outward from said outer surface of said shell course for attaching a bracket. claim 1 6. A forged nozzle shell course according to claim 1 further comprising an integral bracket projecting radially outward from said outer surface of said shell course. claim 1 7. A forged nozzle shell course according to claim 1 further comprising an integral track stub projecting radially outward from said outer surface of said shell course for attaching an inspection apparatus to said shell course. claim 1 8. A forged nozzle shell course according to claim 1 , further comprising an extension sleeve welded to an extension attachment surface. claim 1 9. A forged nozzle shell course according to claim 1 , further comprising at least one of a safe end and a pipe welded to the forged nozzle. claim 1 10. A pressure vessel comprising: a plurality of forged shell courses wherein at least one forged shell course comprises at least one reinforcement portion extending radially outward from an outer surface of said shell course, each said reinforcing portion comprising a nozzle having a radius, said nozzle comprising: a bore extending from an outside surface of said reinforcing portion to an inside surface of said shell course; and at least one extension attachment surface located adjacent to and coaxial to said bore, said at least one extension attachment surface set back from said outside surface of said reinforcing portion, said reinforcing portion comprising a longitudinal dimension equal to about 2.0 times the radius of said nozzle, and a circumferential dimension equal to about 1.5 times the radius of said nozzle, measured from the centerline of said nozzle bore, said at least one shell course, said at least one reinforcing portion, and said nozzle machined from one forging forming one unitary shell course; a top head coupled to a first forged shell course; and a bottom head assembly coupled to a last shell course. 11. A pressure vessel according to claim 10 wherein said at least one forged shell course further comprises an integral groove extending into an outer end of said nozzle, said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 10 12. A pressure vessel according to claim 11 wherein said at least one forged shell course further comprises an integral groove extending into said inner surface of said at least one forged shell course said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 11 13. A pressure vessel according to claim 10 wherein said at least one forged shell course further comprises an integral groove extending into said inner surface of said at least one forged shell course said groove coaxial with said nozzle bore and located adjacent an extension attachment surface. claim 10 14. A pressure vessel according to claim 10 wherein said at least one forged shell course further comprises an integral track projecting radially outward from an outer portion of a shell wall of said shell course for attaching an inspection apparatus to said shell course. claim 10 15. A pressure vessel according to claim 10 wherein said at least one forged shell course further comprises an integral bracket projecting radially outward from an outer portion of a shell wall of said shell course. claim 10 16. A pressure vessel according to claim 10 wherein said at least one forged shell course further comprises at least one of a safe end and a pipe welded to said forged nozzle. claim 10 |
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042773059 | claims | 1. A device for generating a hot plasma comprising: a cylindrically shaped fuel element concentrically aligned with a predetermined axis; a linear theta pinch device concentrically aligned with said predetermined axis; a working gas contained within said linear theta pinch device; cylindrical plasma sheath means generated by said linear theta pinch device from said working gas for producing a theta pinch compression wave in said fuel element; a concentric fuel element plasma layer formed by vaporization and ionization of an outer portion of said fuel element by the application of said cylindrical plasma sheath to said fuel element; annular beam means concentrically aligned with said concentric fuel element plasma layer to dispose energy in said concentric fuel element plasma layer sufficient to ablatively drive said fuel element to produce a beam generated compression wave in said fuel element; whereby said theta pinch compression wave and said beam generated compression wave arrive at the center of said fuel element nearly simultaneously to enhance generation of said hot plasma. 2. The device of claim 1 wherein said annular beam means comprises an annular photon beam. 3. The device of claim 1 wherein said annular means comprises an annular electron beam. 4. The device of claim 1 wherein said annular beam means comprises an annular ion beam. 5. The device of claim 1 wherein said cylindrical plasma sheath comprises a cylindrical sheath of DT plasma. |
043483399 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing oxidic nuclear fuel bodies with an oxygen-to-metal ratio of 2.0.+-.0.02 at sintering temperatures between 1000.degree. and 1400.degree. C. 2. Description of the Prior Art In the manufacture of nuclear fuel bodies, it is the general practice today to sinter them in a reducing atmosphere at 1700.degree. C. Hydrogen or cracked ammonia is used as the reducing atmosphere. Sintered bodies of nuclear fuel materials must attain high operating reliability during the irradiation in the nuclear reactor; they must therefore meet special requirements. These requirements are in substance: The sintered density of the molded bodies is to be higher than 93% of theoretical density; the microstructures should be stable against densification; and the fission gas liberation should be limited; for reasons of corrosion, the fluorine contents should be less than 10 ppm; and an oxygen-to-metal ratio of 2.0.+-.0.02 should be maintained. Since the present furnace temperatures of 1700.degree. C. represent an extraordinarily high stress for the furnace insulation and the furnace lining as well as for the heating elements, which limits the service life seriously, it would be highly desirable if sintering temperatures were sufficient which are substantially lower. Therefore, various proposals in this respect have been made. According to a proposal of U.S. Pat. No. 3,375,306, the pressed nuclear fuel powder is sintered in gas mixtures of CO.sub.2 and CO up to 95% of its theoretical density at a temperature of 1300.degree. to 1600.degree. C. The reduction of the overstoichiometrically sintered molding is accomplished during the cooling in hydrogen or in mixtures of CO.sub.2 and CO. A method described in U.S. Pat. No. 3,927,154 works likewise with CO.sub.2 /CO mixtures and sintering temperatures in the range of 1000.degree. to 1400.degree. C. This method represents in substance sintering operation with continuously changing oxygen-to-metal ratio in the sintered body. The oxygen potential present in the sintering atmosphere is low, so that from the moment of reaching the sintering temperature on, the oxygen-to-metal ratio of the sintered body decreases slowly and finally should reach the specified value .ltoreq.2.02. Thus, this method depends heavily on the oxygen-to-metal ratio of the starting powder. Unfortunately, these sintering methods have not found acceptance in practice. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for effectively sintering nuclear fuels in temperature ranges of 1000.degree.-1400.degree. C., which produce reliably, leads to uniform end products, the grain structure of which can also be adjusted, independently of the oxygen-to-metal ratio of the starting powder of the nuclear fuel to be sintered. With the foregoing and other objects in view, there is provided in accordance with the invention a method for manufacturing oxidic nuclear fuel bodies with an oxygen-to-metal ratio of 2.0.+-.0.02 at sintering temperatures between 1000.degree. and 1400.degree. C., which comprises adding a grain-growth-promoting sintering additive to a nuclear fuel powder with an arbitrary oxygen-to-metal ratio, mixing the additive and fuel powder and pressing the mixture into blanks, passing the blanks into a sintering zone of a furnace and sintering the blanks therein in an oxidizing atmosphere at a temperature within the range of 1000.degree.-1400.degree. C., and subsequently passing the sintered blanks into a reducing zone and treating the blanks therein in a reducing atmosphere at a temperature within the range of 1000.degree.-1400.degree. C. In accordance with the invention, there is provided an apparatus for manufacturing oxidic nuclear fuel bodies with an oxygen-to-metal-ratio of 2.0.+-.0.02 at sintering temperatures between 1000.degree. and 1400.degree. C., which comprises a high-temperature furnace with a continuous passageway through which nuclear bodies are moved, said passageway having an oxidation zone followed by a reduction zone with the two zones separated by a gas lock, transport means for moving the nuclear bodies into and through the oxidation zone, then the gas lock, and then through and out of the reduction zone, an inlet near the entrance of the oxidation zone for the introduction of CO.sub.2 -gas and an outlet at the gas lock for the discharge of CO.sub.2 -gas with the CO.sub.2 -gas passing through the oxidation zone in the same direction as the nuclear bodies, conduit means in the gas lock for removing the discharged CO.sub.2 -gas, a second inlet near the exit of the reduction zone for the introduction of a reducing gas and an outlet at the gas lock for the discharge of reducing gas with the reducing gas passing through the reduction zone in a direction opposite to the direction of the nuclear bodies, an inlet and an outlet to the gas-lock for continuously flushing the gas-lock with an inert gas, and electrical heating means for heating the oxidizing zone and the reduction zone at temperatures between 1000.degree. and 1400.degree. C. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for manufacturing oxidic nuclear fuel bodies, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. |
040653528 | summary | BACKGROUND OF THE INVENTION This invention relates to a hydrogen getter capable of preventing a cladding tube from becoming brittle and being destroyed by hydrogen gas and also to a nuclear fuel element provided with said hydrogen getter. A nuclear fuel element used with various types of nuclear reactor generally consists of fuel material sealed in a container or cladding tube made of corrosion-resistant, nonreactive and heat-conducting material. The cladding tube is customarily formed of stainless steel, aluminium or alloys thereof, or zirconium or alloys thereof. However, a cladding tube constructed of, for example, zirconium or alloys thereof sometimes tends to get locally hydrogenated and brittle by hydrogen gas evolving from various sources in the cladding tube during the run of a nuclear reactor and be destroyed by the resultant increase in a pressure difference originally occuring inside and outside of the cladding tube. A nuclear fuel element used with, for example, a light-water type power reactor is constructed by packing a zircalloy cladding tube with pellets of uranium dioxide as fuel material and sealing helium gas in said cladding tube. The uranium dioxide pellets generally contain hydrogen and remnants of hydrogen atom-carrying organic compounds, for example, metal salts of stearic acid used as a binder. All these contaminants are generally liable to be brought into said pellets while they are prepared. Further, water particles tend to be adsorbed to the surface of the uranium dioxide pellets or the inner wall of the cladding tube. Consequently, hydrogen gas, water vapor and hydrocarbon gas are generated in the tightly closed nuclear fuel element while a nuclear reactor is operated. Water vapor and hydrocarbon gas often release hydrogen by reaction with the cladding tube and uranium dioxide pellets. No serious problems arise, as long as atmosphere in the nuclear fuel element containing the above-mentioned gasseous mixture is of the oxidizing type. Where, however, said atmosphere is turned into the reducing type due to increased amounts of released hydrogen, then the zircalloy cladding tube is rapidly hydrogenated and becomes brittle. FIG. 1 sets forth the measured hydrogen-absorbing property of zircalloy in an atmosphere (1 atmospheric pressure) consisting of a water vapor-hydrogen mixture with the proportions of both gases varied during experiments. In FIG. 1, a ratio of the partial pressure of hydrogen to that of water vapor is plotted on the abscissa, and an amount of hydrogen absorbed in 6 hours after the start of the experiment is plotted on the ordinate, both plottings being given in terms of log graduations. As apparent from FIG. 1, the more prominent the reducing tendency of the atomsphere, and the higher the atmosphere temperature, the larger the amount of hydrogen absorbed by zircalloy, resulting in the more accelerated brittleness thereof. It will therefore be easily understood that a nuclear fuel element is quickly hydrogenated in a high temperature reducing atmosphere easily produced in the cladding tube during the run of a nuclear reactor. As already known, a hydrogen getter alloy for absorbing hydrogen gas and water vapor has been used to prevent the cladding tube from being hydrogenated and becoming brittle by hydrogen gas. A hydrogen getter alloy known to-date is, for example, a nickel-titanium-zirconium hydrogen getter alloy (hereinafter referred to as a "Ni-Ti-Zr getter alloy") marketed by General Electric Company, U.S.A. This Ni-Ti-Zr getter alloy is formed of about 3 to 12 wt% of nickel, about 3 to 30 wt% of titanium and zirconium as the remainder. However, this type of hydrogen getter alloy has the drawback that the alloy material reacts with water vapor in the hydrogen-water vapor atmosphere to have the surface coated with a protective film, resulting in a decline in the hydrogen-absorbing capacity of said getter alloy. Generally, vapors are actually evolved from the water adsorbed to the surface of uranium dioxide pellets and the inner wall of a cladding tube ahead of hydrogen gas, causing a getter alloy to absorb water and have the surface coated with a protective film due to reaction between both materials. As the result, the getter alloy not only decreases in the hydrogen-absorbing capacity, but also renders the atmosphere of the cladding tube more of the reducing type, thereby giving rise to the danger of the cladding tube itself being hydrogenated. Another hydrogen-removing process already applied is to weld an end plug to a cladding tube, seal helium gas in the cladding tube after evacuating it and dry off absorbed water by applying high temperature during the evacuation. However, this process still has the drawbacks that the cladding tube has to be quickly sealed after drying; the sealed atmosphere of the cladding tube is rendered more of the reducing type due to the subsequent generation of various gases in the cladding tube, failing to minimize the danger of said cladding tube being again hydrogenated; and in consequence said prior art process is unadapted for permanent applicability. SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a hydrogen getter adapted to absorb hydrogen alone in the atmosphere of a cladding tube containing both hydrogen and water vapor and a nuclear fuel element equipped with said hydrogen getter. A hydrogen getter according to this invention used with a nuclear fuel element is prepared by enclosing metal material capable of absorbing hydrogen in a metal member permeable to hydrogen and baking the metal assembly at high temperature. |
041566580 | summary | BACKGROUND OF THE INVENTION This invention relates to a method for fixing ions in porous media and is particularly directed towards the fixation of radioactive ions in soil. Although every precaution is taken to avoid release of radioactivity to the environment, it is not inconceivable that soil could be contaminated with radioactive material as a result of a leak, spill, or other accidental release. In such an event, it will be necessary to localize the contamination as much as possible and to prevent any spreading of the radioactive contamination. Radioactive contamination of soil is of grave concern as radioactive ions could be leached and migrate through the soil, eventually entering water supplies for surrounding areas. Strontium and cesium are of particular concern because of the very long half-lives of their radioactive isotopes and because of the manner in which they concentrate in certain body tissues. It is therefore essential to find techniques which ensure that the radioactive ions will remain isolated from the environment for long periods of time. While radioactive contamination can be removed for safe storage elsewhere by excavating the soil around the spill, the excavating operation itself could cause a further spreading of the contamination. Therefore, fixation of the radioactive contamination of the soil in situ is preferable to excavation. Techniques are available for immobilizing radioactive contamination of soil in situ such as by scavenging the contaminated soil by spraying the surface with a polyurethane foam which picks up contamination, soil, and rocks and forms a protective coating over the contaminated area, thereby preventing further spreading of the contamination from weathering. Another technique, disclosed by one of the present applicants in U.S. Pat. No. 3,723,338, provides for injecting into the contaminated soil a polymerizable monomer which polymerizes around the particles of the soil, immobilizing the radioactive material by physical entrapment. Unfortunately, these prior art techniques do not prove completely satisfactory in preventing the spread of leachable radioactive ions, strontium-90 and cesium-137 in particular. These ions can be leached and gradually migrate from the polymerized mass into the surrounding free soil. The present invention is an improved method for fixing such radioactive ions in the soil. SUMMARY OF THE INVENTION In accordance with the present invention, a method is provided for fixing radioactive ions in porous media such as soil by means of ion exchange gels. The interstices of the porous media are filled with a liquid chemical grout which subsequently forms a gel with ion exchange properties, thereby both immobilizing the ions in the structure of the gel and limiting their diffusion rate through the gel. The chemical grout contains water-soluble organic monomers which are polymerized in the presence of a catalyst to gel structures with ion exchange sites, such as carboxyl groups, which chemically fix the ions in addition to the physical retention of the materials within the gel structure. |
description | 1. Field of the Invention The present invention relates to a radiographic image detector on which a radiographic image is recorded by being irradiated with radiation carrying the radiographic image, and from which a signal corresponding to that radiographic image is read out by being scanned with image-reading light. 2. Description of the Related Art In the medical field, a variety of radiographic image detectors have been proposed and put to practical use, in which electric charges are produced by being irradiated with radiation transmitted through a radiographer object, and a radiographic image relating to the radiographer object is recorded by storing the produced electric charges. Such a radiographic image detector has been proposed, for example, in U.S. Pat. No. 6,770,901. This radiographic image detector includes a first electrode layer for transmitting radiation, a photoconductive recording layer for producing electric charges by being irradiated with radiation, an electric-charge transporting layer that operates as an insulator with respect to latent-image electric charges and operates as a conductor with respect to transport electric charges having polarities opposite from the latent-image electric charges, a photoconductive read-out layer for producing electric charges by being irradiated with image-reading light, and a second electrode layer in which first line electrodes for transmitting the image-reading light and second line electrodes for intercepting the image-reading light are alternately arranged in parallel. These layers are stacked in the recited order. When recording a radiographic image onto the radiographic image detector constructed as described above, radiation is first irradiated onto the detector 20 with a negative high voltage applied to the first electrode layer 1 of the detector 20 by a high-voltage source 30 connected to the first electrode layer 1, as shown in FIG. 8A. Then, the radiation is transmitted through the first electrode layer 1 and irradiated onto a photoconductive recording layer 2. At a portion of the photoconductive recording layer 2 irradiated with radiation, electric charge pairs are produced. The positive electric charges of the electric charge pairs move toward the negative-charged first electrode layer 1, combine with the negative electric charges in the first electrode layer 1 and are neutralized. On the other hand, the negative charges of the electric charge pairs move toward a positive-charged second electrode layer 5, but since an electric-charge transporting layer 3 operates as an insulator with respect to negative charges, the above-described negative charges are stored at an charge accumulating portion 6, which is the interface between the photoconductive recording layer 2 and the electric-charge transporting layer 3. A radiographic image is recorded by the storage of the negative charges on the charge accumulating portion 6. And when reading out from the radiographic image detector 20 the radiographic image recorded as described above, image-reading light is first irradiated onto the second electrode layer 5, as shown in FIG. 9. The image-reading light is transmitted through the first line electrode 5a of the second electrode layer 5 and is irradiated onto a photoconductive read-out layer 4, in which electric charge pairs are produced. The positive charges of the produced electric charge pairs combine with the negative charges stored at the charge accumulating portion 6, while the negative charges of the electric charge pairs combine with positive charges at the first line electrode 5a and with positive charges flowing to the first line electrode 5a through ground from a second line electrode 5b. As a result, a current I is detected by a current-detecting amplifier 8 connected to the first line electrode 5a. The current I is converted into a voltage, which is output as an image signal. However, when image-reading light is irradiated near the edge of the second line electrode 5b, as shown in FIG. 9, there are cases where electric discharge occurs near the edge of the second line electrode 5b. Positive charges produced by this edge discharge combine with the negative charges stored at the charge accumulating portion, so the amount of negative charges to combine with the positive charges at the first line electrode 5a is reduced. For this reason, the current I detected by the current-detecting amplifier is reduced and the image read-out efficiency is reduced. This results in the degradation of the picture quality of a read out radiographic image. The present invention has been made in view of the circumstances described above. Accordingly, it is the primary object of the present invention to provide a radiographic image detector that is capable of enhancing picture quality by preventing electric discharge from occurring near the edge of the second line electrode. To achieve this end, there is provided a radiographic image detector in accordance with the present invention. The radiographic image detector includes a first electrode layer for transmitting electromagnetic waves carrying a radiographic image, a photoconductive recording layer for producing electric charges by being irradiated with the electromagnetic waves, and a charge accumulating portion for storing the electric charges produced in the photoconductive recording layer. The radiographic image detector also includes a photoconductive read-out layer for producing electric charges by being irradiated with image-reading light, and a second electrode layer. The second electrode layer has a first stripe electrode, in which a plurality of first line electrodes for transmitting the image-reading light are arranged in parallel at predetermined intervals, and a second stripe electrode, in which a plurality of second line electrodes are arranged in parallel between the first line electrodes. The radiographic image detector further includes an insulating member, which is mounted on at least one of the side surfaces extending in a longitudinal direction of the second line electrode and on a part or whole of the top surface of the second line electrode continuous with the side surfaces. The first electrode layer, the photoconductive recording layer, the photoconductive read-out layer, and the second electrode layer are stacked in this order. It is preferable that the aforementioned “part of the top surface” be an edge portion of the top surface extending from one end to another end of the line electrode along the side surface of the line electrode. In the radiographic image detector of the present invention, the insulating member may be formed from a material that absorbs the image-reading light. In the radiographic image detector of the present invention, the image-reading light may be blue light. In this case, the insulating member is formed from a material in which diaminoanthranilic red is dispersed in acrylic resin. The image-reading light may also be red light. In this case, the insulating member is formed from a material in which copper phthalocyanine is dispersed in acrylic resin. According to the radiographic image detector of the present invention, an insulating member for intercepting image-reading light is mounted on at least one of the side surfaces extending in a longitudinal direction of the second line electrode and on a part or whole of the top surface of the second line electrode continuous to the side surfaces. Therefore, electric discharge from the edge of the second line electrode can be prevented. Since a reduction in the image read-out efficiency due to the electric discharge from the electrode edge can be prevented, the picture quality of a radiographic image read out can be enhanced. Referring now in greater detail to the drawings and initially to FIG. 1, there is shown a radiographic image detector 10 constructed in accordance with a first embodiment of the present invention. The radiographic image detector 10 includes a first electrode layer 1 for transmitting radiation (electromagnetic waves, etc.) carrying a radiographic image, a photoconductive recording layer 2 for producing electric charges by being irradiated with the radiation transmitted through the first electrode layer 1, and an electric-charge transporting layer 3 that operates as an insulator with respect to the electric charges produced in the photoconductive recording layer 2 and also operates as a conductor with respect to transport electric charges having polarities opposite from the electric charge produced in the photoconductive recording layer 2. The radiographic image detector 10 further includes a photoconductive read-out layer 4 for producing electric charges by being irradiated with image-reading light, and a second electrode layer 5 that has a first stripe electrode consisting of first line electrodes 5a for transmitting the image-reading light and a second stripe electrode consisting of second line electrodes 5b for intercepting the image-reading light. These layers 1 through 5 are stacked in the recited order. Also, between the photoconductive recording layer 2 and electric-charge transporting layer 3, there is formed a charge accumulating portion 6 for storing the electric charges produced in the photoconductive recording layer 2. The above-described layers 1 to 5 are formed on a glass substrate in the order listed from the second electrode 5, but for clarity, the glass substrate is not shown in FIGS. 1 to 3. The first electrode layer 1 can employ a film of 50 to 200 nm in thickness, which transmits radiation, such as a SnO2 film, an indium tin oxide (ITO) film, an IDEMITSU indium X-metal oxide (IDIXO) film (which is an amorphous light-transmitting metal oxide film), etc. It can also employ a 100-nm-thick film of Al or Au. The second electrode 15 has a first stripe electrode and a second stripe electrode, as described above, and the first line electrodes 5a of the first stripe electrode and the second line electrodes 5b of the second stripe electrode are alternately arranged in parallel at predetermined intervals, as shown in FIG. 1. The material of the first line electrode 5a may be any conductive material for transmitting image-reading light. For example, it is able to employ ITO or IDIXO, as with the first electrode layer 1. It may also employ a metal film (Al, Cr, etc.) formed to a thickness (e.g., about 10 nm) such that it can transmit image-reading light. The material of the second line electrode 5b may be any conductive material that intercepts image-reading light. For instance, it can employ a metal film (Al, Cr, etc.) formed to a thickness (e.g., about 100 nm) such that it can intercept image-reading light. The material of the photoconductive recording layer 2 may be a material that produces electric charges by being irradiated with radiation. One example is a material that has a-Se, which is relatively high in quantum efficiency with respect to radiation and also high in dark resistance, as a main component. A suitable thickness is about 500 μm. The charge-transferring layer 3 employs a material in which the difference between the mobility of an electric charge on the first electrode layer 1 and the mobility of an electric charge of opposite polarity is great (e.g., 102 or greater, preferably 103 or greater). Suitable materials are an organic compound (such as, poly-N-vinylcarbazole (PVK), N,N′-diphenyl-N,N′-bis(3-methylphenyle)-[1,1′-biphenuyl]-4,4′-diamine (TPD), discotic liquid crystal, etc.), a polymer (polycarbonate, polystyrene, PVK) dispersion substance of TPD, and a semiconductor substance such as a-Se doped with 10 to 200 ppm of Cl. The photoconductive read-out layer 4 employs a material that exhibits photoconductivity by being irradiated with image-reading light. For example, a preferable material is a photoconductive material that has at least one of a-Se, Se-Te, Se-As-Te, organic phthalocyanine, metal phthalocyanine, MgPc (magnesium phthalocyanine), VoPc (phase II of vanadyl phthalocyanine), or CuPc (copper phthalocyanine), as its main component. A suitable thickness is about 0.1 to 1 μm. In the radiographic image detector 10 of the first embodiment, an insulatingmember 7 ismountedon the side surfaces 5c and top surface 5d extending in the longitudinal direction of the second line electrode 5b, as shown in FIGS. 1 and 2. The insulating member 7 can prevent electric discharge from occurring near the edge of the second line electrode 5b and is also used to intercept image-reading light. The insulating member 7 can utilize a material that absorbs image-reading light. For instance, in the case where image-reading light is blue light, the insulating member 7 can utilize a red insulating material that absorbs blue light. An example is an insulating material in which diaminoanthranilic red is dispersed in acrylic resin. In the case where image-reading light is red light, the insulating member 7 can utilize a blue insulating material that absorbs red light. An example is an insulating material in which copper phthalocyanine is dispersed in acrylic resin. That is, the insulating material 7 is not limited to the aforementioned materials, but may utilize an insulating material having a color complementary to the wavelength of image-reading light. When reading out a radiographic image by employing the radiographic image detector 10 constructed as described above, the insulating material 7 can absorb image-reading light. Therefore, electric discharge is prevented from occurring at the edge of the second line electrode 5b, as is done in the conventional radiographic image detector 20. As a result, a reduction in the image read-out efficiency due to the edge discharge is prevented. In recording a radiographic image by employing the radiographic image detector 10 constructed as described above, in the case of a massive dose of radiation, negative charges produced in the photoconductive read-out layer 2 sometime pass through the charge accumulating portion 6 and electric-charge transporting layer 3, as shown in FIG. 4A. The negative charges remain near the insulating member 7 mounted on the second line electrode 5b, as shown in FIG. 4B. If the radiographic image recorded as described above is read out from the radiographic image detector 10, the positive charges produced in the photoconductive read-out layer 4 combine with the negative charges near the insulating member 7. As a result, not only the negative charges on the charge accumulating portion 6 but also the negative charges near the insulating layer 7 are detected as an image signal. Particularly, the negative charges remaining near the insulating layer 7 combine with the positive charges produced in the photoconductive read-out layer 4 with a very great time constant, so an afterimage develops in a radiographic image based on the detected image signal. Hence, as shown in FIG. 6, it is desirable to mount insulating members 7 on the side surfaces 5c of the second line electrode 5b and on the edge portions 5d, which is a part of the top surface, continuous with the side surfaces 5c. No insulating member is mounted on the top surface 5e other than the edge portions 5d. If the insulating members 7 are mounted as described above, the above-described negative charges flow out from the second line electrode 5b, and the negative charges are prevented from being stored near the insulating member 7 mounted on the second line electrode 5b, as is done in the radiographic image detector 10 shown in FIG. 5. As a result, the occurrence of an afterimage due to the above-described negative charge can be prevented. In addition, the insulating members 7 do not necessarily need to be mounted on both side surfaces 5c of the second line electrode 5b, as is done in the second embodiment shown in FIG. 6. For example, as shown in FIG. 7, an insulating member 7 may be mounted on one of the side surfaces 5c extending in the longitudinal direction of the second line electrode 5b and on a part or whole of the top surface of the second line electrode 5b continuous with the one side surface. While the present invention has been described with reference to the preferred embodiments thereof, the invention is not to be limited to the details given herein, but may be modified within the scope of the invention hereinafter claimed. For example, the radiographic image detector may contain additional layers. |
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048287601 | description | DESCRIPTION OF A PREFERRED EMBODIMENT The present invention provides a method of removing sodium from fuel assemblies which is uniquely suited for fuel assemblies removed from a breeder reactor. In a breeder reactor, a coolant, typically sodium, potassium or a mixture thereof, is circulated through a reactor core wherein it is heated and subsequently the heat is extracted from the coolant. The reactor core comprises an array of fuel assemblies provided with passageways for the circulation of the coolant therethrough. Each fuel assembly 14 is comprised of a plurality of elongated pressurized metallic fuel pins. The fuel pin typically is a stainless steel cylinder or tube which is sealed at each end and contains, throughout a substantialy portion of its length, fuel pellets. The outer metal portion of the pin generally is referred to as the cladding. Generally, the fuel pellet is formed from an oxide or carbide of uranium and/or plutonium, some of the uranium may be converted to plutonium during service as a result of exposure to fast neutrons. As a result of the exposure to neutrons a high pressure fission gas is generated in each fuel pin of the fuel assembly. Because of the high pressure fission gas, the heating and cooling parameters, explained in more detail herein below, must be carefully controlled to preclude rupturing of the fuel pins during the decontamination or cleaning process. During service, it is not uncommon for an individual fuel pin to crack or rupture such that the alkali metal coolant seeps within the metal tube. This, of cource, complicates cleaning. To reprocess the fuel from a breeder reactor, it is essential that all of the alkali metal be removed as it will have a detrimental effect on the subsequent chemical reprocessing. In addition, during service, the alkali metal becomes radioactive, which is not removed could complicate the handling and shipment of the fuel assemblies. Generally, breeder reactor facilities include an adjacent fuel handling building or facility (also called a "cell") which is maintained under an inert atmosphere, typically argon gas. New fuel assemblies for loading into the reactor was well as spent fuel assemblies removed from the reactor, are temporarily stored in such a facility. It is an advantage of the present invention that it is particularly suited for use in such an enviroment. FIG. 1 shows in part a fuel storage building housing a fuel handling system for a sodium cooled breeder reactor. The spent fuel assembly is removed from the reactor into a remotely operated, inert gas filled, fuel handling cell or facility. In the cell, the fuel assembly is moved to the spent fuel cleaning device wherein the adhering alkali metal is removed from the fuel assembly outer surface. The cleaned spent fuel assembly is then transferred, via a gas lock or under floor transporter, to another remotely operated fuel handling cell or facility. The second cell may have an inert atmosphere or be air-filled, The spent fuel assembly may be stored under water to cool the fuel assembly or may be loaded into a spent fuel shipping cask for transportation to a reprocessor. Referring now to FIG. 2, therein is depicted apparatus 10 for use in practicing the method of the present invention. The apparatus includes a sealed chamber 12 for containing a spent fuel assembly 14. Fuel assembly 14 rests on a baffle member 16 and extends therethrough. Baffle member 16 engages the outer periphery of fuel assembly 14 to insure that those gases entering an upper portion 18 of chamber 12 must flow through fuel assembly 14 and into a lower portion 20 of chamber 12. Lower portion 20 of chamber 12 is provided with a recirculation outlet conduit 24 which is in fluid communication with a blower 26 which discharges into a recirculation inlet conduit 28 through a three-way valve 55 which conduit 28 is located above baffle member 16. and communicates into chamber 12 as shown in FIG. 2. Advantageously, conduit 28 also is provided with an electrical heater 30. Blower 26 is driven by a motor 32 which is interconnected to blower 26 via a magnetic coupling 34. Typically there also will be provided some means for preventing the transfer of heat from blower 26 back to magnetic coupling 34. As depicted, this would be accomplished by a cooling jacket 36 provided with an inlet and outlet for the flow of a cooling fluid therethrough. Chamber 12 also includes a conduit 38 and valve 40 for the introduction of an inert gas into chamber 12 in upper portion 18. Any inert gas may be used, typically the inert gas will be argon, particularly when the method of the present invention is practiced within a fuel storage or handling cell is maintained under an inert atmosphere of argon. An upper end of chamber 12 is provided with a discharge conduit 42 for conducting gas exiting upper portion 18 of chamber 12 to a condenser 44. Condenser 44 includes means for passing a coolant through an internal cooling coil 46 to condense any sodium vapors contained in the gas passing therethrough. Generally the coolant will be an organic fluid which is inert with respect to the alkali metal to prevent any reaction in the event of a leak. Condenser 44 further includes a sump portion 48 for the collection of condensed alkali metal coolant. A conduit 50 provides fluid communication between condenser 48 and a cryogenic trap 52 and also a bypass conduit 54 which connects to the three-way valve 55. Downstream of cryogenic trap 52 are two vaccum pumps 56 and 58. Pumps 56 and 58 are in fluid communication with cryogenic trap 52 via conduits and valves 60,61 and 62. Pump 58 is also provided with a discharge conduit 64. In accordance with the practice of the method of the present invention, a fuel assembly 14 is placed within chamber 12 which is then sealed. An inert gas, typically argon, is introduced into chamber 12 through conduit 38 and valve 40. Generally, spent fuel assembly 14 will have an initial temperature of about 400.degree. F. (204.degree. C.). Power is supplied to motor 32 which drives blower 26 via magnetic coupling 34 to cause circulation of the argon from lower portion 20 of chamber 12 through conduit 24 and valve 55 and back to upper portion 18 of chamber 12 via conduit 28. Power also is supplied to electric heater 30 until the temperature of the fuel assembly is increased to about 800.degree. F. After the fuel assembly has been heated to a desired temperature, power to the electric heater is turned off, valve 61 is opened and vacuum pump 58 started. Typically, vacuum pump 58 will be a dry, reciprocating vacuum pump which is operated for a sufficient time to decrease the chamber pressure from atmospheric to approximately 10 mm of mercury, during which time blower 26 is maintained in operation. Thereafter, secondary vacuum pump 56 (typically an oil-sealed rotary pump) is started. Valves 60 and 62 are opened and 61 closed. The chamber pressure is then further decreased from 10 mm of mercury to at least 0.05 mm of mercury. Preferably the secondary vacuum pump 56 is operated until the pressure within chamber 12 is reduced to 0.005 mm of mercury of less. During this time, blower 26 is inoperative. During the vacuum drying time, the gas and entrained sodium vapor is withdrawn via conduit 42 and cooled in condenser 44. Any residual sodium vapor leaving through conduit 50 is removed in cryogenic trap 52. The condensed sodium may be recovered at a later point in time. Typically, this would be accomplished in condenser 44, for example, by increasing the coolant temperature to melt the sodium and then draining it from sump 48. During the vacuum drying time, the fuel assembly temperature will continue to increase as a result of the decay heat. When the temperature reaches the maximum safe temperature for the cladding of the individual fuel pins, generally about 1000.degree. F., the vacuum treatment is stopped. Valves 60, 61 and 62 are closed and pumps 56 and 58 turned off. Valve 40 is open and chamber 12 is filled with argon gas to one atmosphere via conduit 38. After chamber 12 is filled with gas, valve 40 is closed and valve 55 repositioned to close conduit 28 and open conduit 54. Power is supplied to motor 32 to drive blower 26 and the argon gas is circulated through valve 55 and conduit 54 in a reverse direction through condenser 44 and back to chamber 12 via conduit 42. Typically, heater 30 would not be required for the remainder of the cleaning cycle backpressure created by the presence of heater 30 in conduit 28. The gas is circulated through chamber 12 and fuel assembly 14 until the temperature of the fuel assembly is reduced back to a desired level, typically below 800.degree. F. The vacuum treatment and cooling are repeated as required to insure substantially complete removal of the radioactive alkali metal contaminant. The number of cycles required is readily determinable through experimentation. It will be appreciated that various other valves and instrumentation such as pressure sensors, temperature sensors, also would normally be incorporated as well as additional redundant gas cleaning techniques. However, those matters are well within the skill of those versed in the art. The foregoing description and example illustrate a specific embodiment of the invention and what is now considered to be the best mode of practicing it. Those skilled in the art, however, will understand that changes may be made in the form of the invention without departing from its generally broad scope. Accordingly, it should be understood that within the scope of the appended claims the invention may be practiced otherwise than as is specifically illustrated and described. |
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056420145 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 is a perspective view of an embodiment of a self-powered device 10 comprising a p-substrate 24, an n.sup.+ layer 22 formed over the bottom surface of the p-substrate 24 and a tritium containing layer formed over the n.sup.+ layer 22. For this embodiment, a metal tritide layer 20 is the tritium containing layer. Alternative materials also could be used such as organic compounds or aerogels as described in U.S. Pat. No. 5,240,647. The p-substrate 24 and the n.sup.+ layer 22 form a pn junction having a depletion region 28. The metal in the metal tritide layer is selected from metals which form stable tritides with tritium such as titanium, palladium, lithium, and vanadium. Tritium is a hydrogen atom having two neutrons. During decay, the tritium atoms become helium atoms and emit beta particles. The emitted beta particles have a mean beta energy of about 5.68 KeV, a maximum energy of about 18.6 KeV, and a range of about 2 microns in silicon. When the tritium atoms of the metal tritide layer 20 decay, the helium atoms either diffuse into the atmosphere or remain trapped in the metal. The beta particles that penetrate the depletion region 28 generate electron-hole pairs. The electrons of the electron-hole pairs are swept by the pn junction electric field producing an electric current at a voltage of about 0.7 V for a silicon device. The amount of energy that is recovered from the beta particles 26 depends on the number of electron-hole pairs that is generated and the amount of electron-hole recombination that occurs. An accurate estimate of the maximum energy available from surfaces of a metal tritide film is a function of an areal density of tritium. For titanium or lithium tritides, the maximum energy flux is between about 1.3-2.8 .mu.W/cm.sup.2 for each surface of the metal tritide film. At this power level, beta voltaic power sources provide a practical long term energy source for applications such as watches. A typical watch chip consumes about 0.5 .mu.w of power. Thus, at 1.3 .mu.w/cm.sup.2, about 0.4 cm.sup.2 of surface is required for a titanium or a lithium tritide beta voltaic power source. While the voltage level generated by a silicon beta voltaic power source is about 0.7 V, conventional circuit voltage requirement is usually about 3.3 V. However, devices such as Dynamic threshold voltage MOSFETs (DTMOS) that function at ultra low voltages may be used. See Assaderaghi et al., IEEE 1994, IEOM 94-809, 33.1.1-33.1.4. Alternatively, multiple beta voltaic power sources can be interconnected in series and/or in parallel to generate a power source of a variety of voltage and current capabilities. In addition, DC--DC conversion techniques such as charge pumping can be used to increase voltage levels. FIG. 2 shows a second embodiment of the self-powered device 100. An n layer 103 is formed over a surface of a p-substrate 102, and a p.sup.+ layer 104 is formed over the n layer 103. The n layer 103 and the p.sup.+ 104 form a pn junction having a depletion layer that converts the beta particles into electrical current. A metal tritide layer 106 is formed over the p.sup.+ layer 104. An electrode 107 is formed over the p.sup.+ layer 104 to provide an electrical contact for connection to an integrated circuit 110 as a V.sub.dd power supply. Ann.sup.+ layer 105 is formed over the n layer 103. An electrode 108 provides a V.sub.ss power supply for the integrated circuit 110. FIG. 3 is a cross-sectional view of the self-powered device 100 across a line III--III. The pn junction 109 is formed by the p.sup.+ layer 104 and the n layer 103. The metal tritide layer 106 emits beta particles 112 into the pn junction 109 and produce an electrical current which is supplied to the integrated circuit 110 through the electrodes 107 and 108. Since the beta voltaic power source is formed on the same p-substrate 102 as the integrated circuit 110, the beta voltaic power source structures are formed using the same process used to form the integrated circuit 110. The metal tritide layer 106 is formed by first forming a metal layer over the p.sup.+ layer 104. The metal layer is formed by standard sputtering or physical vapor deposition techniques. For metals, such as palladium, that do not form a passivating layer of oxide on the metal layer surface, the tritium could be incorporated into the metal layer after the metal layer is deposited. For metals that do form the passivating layer of oxide such as titanium, the tritium could be incorporated during or immediately after the deposition of the metal layer. Incorporating tritium into metals is described in "Tritium and Helium-3 in Metals", R. Lasser, Springer-Verlag, 1989. For this embodiment, a metal that does not form the passivating layer is used. The surface of the p-substrate 102, except for the metal layer, is passivated. Then, the metal layer is exposed to tritium allowing the tritium atoms to diffuse into the metal layer to form the required metal tritide layer 106. This procedure permits the formation of the complete self-powered device without unnecessarily exposing the manufacturing environment with beta radiation. FIG. 4A is another embodiment of a self-powered device 170 comprising an integrated circuit portion 180 and a radioactive cap portion 150. The integrated circuit portion 180 is substantially similar to the self-powered device 100 shown in FIG. 3. However, the metal tritide layer 106 is not formed over the p.sup.+ layer. The electrode 108 is connected to the V.sub.ss power supply of the integrated circuit 110 (not shown). The electrode 107, which contacts the p.sup.+ layer 104, is not connected to the V.sub.dd power supply of the integrated circuit 110 but contacts the electrode 162 of the radioactive cap portion 150. The radioactive cap portion 150 comprises a p-substrate 152 and an n.sup.+ layer 154 formed over the bottom surface of the p-substrate 152. The n.sup.+ layer 154 and the p-substrate 152 form pn junction 163. The electrode 162 is formed over the surface of the n.sup.+ layer 154. A metal tritide layer 158 is formed over the surface of the n.sup.+ layer 154 providing the beta particles. A p.sup.+ layer 156 is formed on the top surface of the p-substrate 152. The p.sup.+ layer 156 provides an electrical contact region for the V.sub.dd power supply connection required for the integrated circuit 110. An electrode 160 is formed over the p.sup.+ layer 156 for connecting the V.sub.dd power supply to the integrated circuit 110. The structural dimensions of the integrated circuit portion 180 and the radioactive cap portion 150 are coordinated so that the electrodes 107 and 162 contact each other when the radioactive cap portion 150 is placed directly above the integrated circuit portion 180. The metal tritide layer 158 is also placed so that the beta particles emitted by the tritium contained in the metal tritide layer 158 is enclosed by both the pn junction 109 of the integrated circuit portion 180 and the pn junction 162 of the radioactive cap portion 150. Since there are two pn junctions 109 and 162 and the pn junctions are connected in series by connecting the electrodes 107 and 162 to each other, the total voltage generated by the two beta voltaic power sources are added together generating about a 1.4 V power source. Thus, this embodiment provides twice the voltage available from only one beta voltaic power source. FIG. 4B shows a self-powered device 190 substantially similar to the self-powered device 170 with the exception that the metal tritide layer 159 is not formed directly over the surface of the n.sup.+ layer 154 of a cap portion 151. The metal tritide layer 159 is placed between the integrated circuit portion 180 and the cap portion 151. The metal tritide layer 159 may be a film that is manufactured separately from the integrated circuit portion 180 and the cap portion 151. By using a separate metal tritide layer 159, this embodiment further controls the radioactive exposure of the manufacturing environment and permits the integrated circuit processing to be accomplished without any exposure to radioactivity. After the required processing for the integrated circuit portion 180 and the cap portion 151, the metal tritide layer 159 is put in place during final assembly by placing the cap portion 151 over the integrated circuit portion 180 and enclosing the metal tritide layer 159 in-between. The n layer 103, the p.sup.+ layer 104, the n.sup.+ layer 105, and electrodes 107 and 108 form a power supply portion 182. A plurality of power supply portions 182 can be formed over the p-substrate 102. When a corresponding plurality of cap portions 151 are placed above the plurality of power supply portions 182 and a metal tritide layer 159 is placed between each corresponding pair of power supply portion 182 and cap portion 151, a plurality of beta voltaic power supplies are formed. The plurality of beta voltaic power supplies can be interconnected in series and/or in parallel to obtain voltage levels in increments of about 1.4 V and current levels limited only by the amount of surface area available on the p-substrate 102. FIGS. 5A-E is a process for manufacturing the self-powered device 100 shown in FIG. 3 using silicon. In FIG. 5A a thin oxide layer 204 is formed on a surface of a p-substrate 202. A silicon nitride layer 206 is formed over the thin oxide layer 204 and patterned so that field oxide portions 210 are formed on the surface of the p-substrate 202. After the field oxide portions 210 are formed, the silicon nitride and thin oxide layers 206 and 204, respectively, are removed and the p-substrate 202 is blanket implanted with phosphorous 211 to form lightly doped n layer 208 on the surface of the p-substrate 202. The surface of the p-substrate 202 is then patterned with photoresist 214 and implanted with boron 213 to form a p-tub region 212 as shown in FIG. 5C. After forming the p-tub region 212, the photoresist layer 214 is removed and similar photoresist and implant steps are applied to form the n.sup.+ region 216 as shown in FIG. 5D. After the ion implant steps, the surface of the p-substrate 202 contain the lightly doped n region 208, the p-tub region 212 and the n.sup.+ region 216. Then, a thin oxide layer 218 is formed over the substrate and a polysilicon layer 220 is formed over the thin oxide layer 218. A phosphorous implant 215 is applied to dope the polysilicon layer 220. After the phosphorous implant step, the polysilicon layer 220 and the thin oxide layer 218 is patterned and etched to form transistor gates 224 and 222 for transistors 225 and 227, respectively. After the formation of the transistor gates 222 and 224, the surface of the p-substrate 202 is patterned with photoresist and ion-implanted with n-type dopant to form n-channel transistor source and drain regions 232 and 230, respectively, and also ion-implanted with p-type dopant to form p-channel transistor source and drain regions 226 and 228. Further, n.sup.+ region 234 is implanted for the beta voltaic power source contact and the p.sup.+ region 236 is implanted to form the beta voltaic power source pn junction 237. In FIG. 6A, a silicon dioxide passivation layer 240 is formed over the surface of the p-substrate 202. The passivation layer 240 is patterned to form via holes 242, 244, 246, 248 and 250. Electrodes 252, 254, 256 and 258 are formed over the respective via holes. Electrode 256 connects the drain of the n-channel transistor 225 together with the drain of the p-channel transistor 227 to form a basic CMOS configuration. Electrode 258 is shown as a typical connection to the source of the p-channel transistor 227 and is connected to the V.sub.dd power supply (not shown). Electrode 252 contacts the p.sup.+ region 236 and is the V.sub.dd power supply terminal. The electrode 254 contacts the n.sup.+ region 234 and is the V.sub.ss power supply terminal. In FIG. 6C, after the electrodes 252, 254, 256 and 258 are formed, another silicon dioxide passivation layer 259 is formed over the p-substrate 202. The passivation layer 259 is patterned and etched to expose the electrodes 252 and 254 as well as the p.sup.+ region 236. Electrodes 260 and 262 are formed to contact the electrodes 252 and 254, respectively, and supplies the V.sub.dd and V.sub.ss to the integrated circuits, such as transistors 225 and 227. A metal tritide layer 264 is formed above the p.sup.+ layer region 236 to supply the radio-active beta particles, as shown in FIG. 6D. FIG. 7 shows an integrated circuit portion 295 and a radioactive cap portion 297. The integrated circuit portion 295 has a structure substantially similar to the structure shown in FIG. 6D but without the metal tritide layer 264. The radioactive cap portion 297 comprises a p-substrate 270 having n.sup.+ portion 268 and p.sup.+ portion 272. An electrode 266 is formed over a passivation layer 278 to contact the n.sup.+ portion 268. An electrode 274 is formed over the passivation layer 276 to contact the p.sup.+ portion 272. When the radioactive cap portion 297 is placed immediately above the integrated circuit portion 295, the electrodes 260 and 266 contact each other so that the integrated circuit portion 295 and the radioactive cap portion 297 form one beta voltaic power source supplying about 1.4 V to the integrated circuit 110 (not shown) which is also formed on the p-substrate 202. The electrode 262 is the V.sub.ss power supply terminal and the electrode 274 is the V.sub.dd power supply terminal for the integrated circuit 110. A metal tritide layer 280 is formed over the n.sup.+ surface of the radioactive cap portion 297. When the radioactive cap portion 297 is placed above the integrated circuit portion 295, the beta particles from the metal tritide layer 280 penetrates the pn junctions 237 and 282 of the integrated circuit portion 295 and radioactive cap portion 297. In FIG. 1, beta particles 27 do not penetrate the depletion region 28 and thus the energy of the beta particles 27 is lost. Thus, the energy conversion efficiency from the energy contained in a total amount of emitted beta particles 26 and 27 to electrical energy is reduced. In FIG. 8, the energy conversion efficiency is improved by embedding metal tritides in substrate trenches 364. An integrated circuit 352 is formed on a top surface 354 of a substrate 344. An n region 368 is formed over the bottom surface 356 of the substrate 344. Trenches 364 are etched into the n region 368. The depth 360 of the trenches 364 is about 10 microns and the width 362 of the trenches 364 is about 1 micron. The space 366 between the trenches 364 is about 2 microns. An p.sup.+ layer 342 is formed over the surface of the trenches 364. Metal tritides 340 are formed in the trenches 364 over the surface of the p.sup.+ layer 342 to complete the beta voltaic power supply. The trench dimensions are selected to increase trench density. Of course, other dimensions are possible without affecting the invention. All the p.sup.+ layers 342 are electrically connected together forming a V.sub.dd power supply terminal 350 connected to the integrated circuit 352. An n.sup.+ layer 367 is formed over the n region 368 to provide the V.sub.ss contact. The n.sup.+ layer is connected externally to the integrated circuit 352 through a V.sub.ss power supply terminal 369 for the V.sub.ss power supply. Accordingly, the beta voltaic cells provide continuous power to the integrated circuit 352. Placing the metal tritides 340 in the trenches 364 surrounds the metal tritides 340 with a depletion layer. The beta particle penetration of the depletion region is increased by about a factor of 10 over the embodiment shown in FIG. 1. The trench structure can also be used in embodiments shown in FIG. 3 and FIG. 4A. Instead of forming a planar pn junctions 109 and 162, a trench structure is formed to increase the energy conversion efficiency. For the embodiment shown in FIG. 4A, the metal tritide layer is formed in both the radioactive cap portion 150 and the integrated circuit portion 180. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modification and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims. |
summary | ||
042235758 | claims | 1. Apparatus for manipulating reactor vessel studs comprising: a carriage; engagement means associated with said carriage for firmly contacting said studs; rotation means mounted on said carriage and connected to said engagement means for rotating said engagement means when said engagement means is in contact with said studs thereby manipulating said stubs; drive means mounted on said carriage and connected to said rotation means for rotating said rotation means; a vertical mounting member; a load equalizing device attached to said vertical mounting member for establishing a uniform vertical force; and a swivel connecting rod attached at one end to said load equalizing device and removably attachable to said studs at the other end for transmitting a uniform vertical force from said load equalizing device to said studs for maintaining a uniform vertical force on said studs. inserts mounted on said rotation means having sides complimentary to the sides of said studs for firmly contacting said studs; and a bar mounted on said inserts and extending across the top of said studs and near said swivel connecting rod for preventing rotation of said swivel connecting rod with respect to said studs while said studs are being rotated. a motor having a drive shaft and mounted on said carriage; and a first gear mounted on said drive shaft for rotating said rotation means under the influence of said motor. bearings mounted on said carriage; a gear segment mounted on said bearings for supporting said engagement means; and a second gear mounted around said gear segment and engaged with said first gear for rotating said gear segment and said engagement means about said bearings under the influence of said first gear. struts mounted on said carriage; and a ring attached to said struts with said swivel connecting rod disposed in said ring for supporting said carriage by contact of said swivel connecting rod and said ring. handles mounted on said carriage having controls mounted thereon for controlling said carriage and said motor. 2. The apparatus according to claim 1 wherein said vertical mounting member is an overhead crane. 3. The apparatus according to claim 2 wherein said engagement means comprises: 4. The apparatus according to claim 3 wherein said drive means comprises: 5. The apparatus according to claim 4 wherein said rotation means comprises: 6. The apparatus according to claim 5 wherein said apparatus further comprises: 7. The apparatus according to claim 6 wherein said engagement means further comprises spacers mounted on said second gear and extending along the inside of said gear segment for contacting said studs. 8. The apparatus according to claim 7 wherein said apparatus further comprises: 9. The apparatus according to claim 8 wherein said apparatus further comprises bumpers mounted on said carriage for protecting said carriage. |
041561465 | description | DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS In FIG. 8, a fixed port 37 has a through-hole at its central portion, which communicates with the outside. The inner wall 39 of the through-hole is threaded. Similarly as in the conventional fixed port, the fixed port 37 of the invention is fixed to the wall 2 of the box 1 through a ring-shaped packing 7, "U"-shaped in section, by a ring-shaped retainer 40 and bolts 41. The glove replacement port 42 screwed into the threaded portion 39 of the fixed port 37 is composed of metal, hard plastics, or the like and comprises cylindrical parts 43 and 44 different in diameter. The base 9 of the glove 3 is, in a manner similar to the conventional one, fixedly mounted over the outer wall of the cylindrical part 44 having a smaller diameter by means of a sealing tightening band 46 and an "O" ring 47. A screw member 48 made of elastic material such as rubber is solidly mounted over the outer wall of the cylindrical part 43, and, has a larger diameter than the replacement port 42. In this case, the base 9 of the glove 3 may be directly fixed onto the surface of the cylindrical portion 44 without using the sealing band 46 and the O-ring 47. By means of this elastic screw member 48, the glove replacement port 42 can be screwed into the threaded portion 39 of the fixed port, and elastic deformation of the elastic screw member 48 serves to seal between the fixed port 37 and the glove replacement port 42. It goes without saying that the out-side diameter of the elastic screw member 48 is larger than the inside diameter of the fixed port 37. The outside diameter of the cylindrical part 43 should be designed so that the thickness of the elastic screw member 48 is a predetermined value. Preferably, the inside diameter of the cylindrical port 43 is larger than that of the cylindrical part 44 to which the glove 3 is secured, while the length of the former is close to that of the latter 44. The elastic screw member 48 can be manufactured in accordance with the well-known method in which the space between the cylindrical member 42 and a metallic mold is filled with rubber compound. The elastic screw member 48 is strongly adhered to the cylindrical member 42 by a conventional method so that the former is not caused to slide on the latter. One end surface of the larger diameter cylindrical part 43 of the cylindrical member 42 is provided with at least one pin 50, while a corresponding hole whose diameter is slightly larger than the outside diameter of the pin 50 is provided on the other end surface of the cylindrical part 43. The pin and the hole may be of the other configuration if they can be engaged with each other. The elastic screw member may be adhered to the inner wall of the fixed port 37 instead of adhering to the cylindrical member 42, or may be adhered to both between the outer wall of the cylindrical part 43 and the inner wall of the fixed port 37. However, it is preferable that the elastic member is provided on the side of the replacement port 42, judging from the service life of the elastic member. In view of the frictional coefficient between the elastic screw member 48 and the fixed port 37, it is possible to provide a thin film of polytetrafluoroethylene, known as "Teflon", on the surface of the elastic screw member, or to coat the surface of the elastic screw member with lubricant such as grease. In replacing the glove 3 with a new one, the new glove 12, as shown in FIG. 9, is secured to the end face of the glove replacement port 42 screwed into the fixed port 37, and the front end of another new glove replacement port 49 having the same construction as the glove replacement port 42 is brought into contact with the latter port 42. In this case, by aligning the pin 50 of the replacement port 42 with the hole 51 of the new replacement port 49, the new replacement port 49 is screwed in the fixed port in such a manner that the old and new replacement ports 42 and 49 are simultaneously advanced as one unit. Accordingly, when the new replacement port 49 reaches a predetermined position, the old replacement port 42 is automatically removed from the fixed port 37, or readily removed if the old glove 3 is pulled through the new glove 12. Thus, the replacement of the glove can be achieved. During this replacement operation, the sealing between the fixed port 37 and the replacement ports 42 and 49 are maintained perfect by the elastic deformation of the elastic screw member 48. Therefore, the shielded material will never leak out. FIG. 10 shows another embodiment of this invention where essential elements of the glove port section are applied to the bag port section. Similarly as in the case of the gloves 3 and 12, a bag 52 for insertion or removal of a material or article is fixedly mounted on a cylindrical member 45 by means of a sealing tightening band 46 and an "O" ring 47. In the case when the bag 52 becomes unserviceable by frequently inserting an article into or removing it from the shielding box, the bag must be replaced with a new one. This replacement can be readily achieved in a manner similar to that in the embodiment of FIGS. 8 and 9. By the use of this bag 52, an article dropped into the shielding box 1, such as glove replacement ports 42, and 49, bag replacement port 53, or the like can be taken out of the shielding box 1. FIG. 11 illustrates a modified sealing replacement port where a sealing member 58 is employed instead of the glove. The sealing replacement port 54 comprises a cylindrical member with a cylindrical part 55 larger in diameter and a cylindrical part 56 smaller in diameter. The smaller diameter cylindrical part 56 has the sealing member 58 in such a manner that the part 56 and the sealing member 58 form one unit. The sealing replacement port 54 can be applied to any glove replacement section which becomes unnecessary to use. The sealing replacement port 54 shown in FIG. 11 is disposed, for example, at the end face of the glove replacement port 42 (as shown in FIG. 8 also) screwed into the fixed port 37 in such a manner that the pin 50 is in alignment with the pin hole 60. Thereafter, the same procedure as described before is carried out to install the sealing replacement port 54. The same procedure can be applied to the bag replacement port section. If, as was described above, the sealing replacement ports 54 are employed at the port sections where normally the gloves 3 and 12 are scarcely used, wasting of gloves which are abandoned without being used during their serviceable periods of time can be eliminated. Accordingly, the replacement of such gloves and the inspection of such gloves can be eliminated also. In the case when during the operation it is required to urgently provide the glove 12 or the bag 52 at the sealing replacement port section, the replacement can be quickly achieved by conducting the screwing operation in a manner similar to that in the replacement of the glove or the bag. FIG. 12 illustrates a modified sealing replacement port. In this case, a replacement port 63 can be obtained by removing a part of the sealing member 58 of the cylindrical part 56 in the replacement port 54 thereby to provide a recessed section 62 with a bottom 61. Thus, the use of the sealing replacement port thus constructed can maintain the box sealed. In addition, an article or a material 65 can be readily put in to the shielding box 1 by the use of the sealing replacement port. More specifically, the article 65 is placed in the recessed section 62, and another sealing replacement port 64 having the same construction or the sealing replacement port 54 as shown in FIG. 11 is connected to the end face of the firstly-mentioned sealing replacement port. Then, the above-described screwing operation is carried out with the two replacement ports, the article 65 can be readily put into the shielding box 1. FIG. 13 illustrates still another embodiment of this invention where a filter replacement port 69 with a filter 68 is mounted on the wall 2 of the shielding box 1. The filter is obtained by forming a cylindrical filter with glass fiber cloth. However, the filter may be fabricated with other material if it is suitable for sufficiently filtering the atmosphere in the shielding box. In this embodiment, the cylindrical replacement port is made of the same material as that of the filter 68. An elastic screw member 48, a pin 70 and a pin hole 71 are provided directly in the outer wall of the filter 68. In the case where the filtering capacity is lowered and it is necessary to replace the filter replacement port with a new one all that is necessary is to screw a new filter replacement port having the same construction into the fixed port, as a result of which, the old filter replacement port 69 is allowed to drop into the shielding box 1. A modified filter replacement port is shown in FIG. 14. In this example, similarly as in the case of the glove replacement port 42 or the bag replacement port 53, the filter replacement is of a rigid cylindrical member 73. Therefore, the inward compression force of the elastic screw member 48 screwed into the fixed port 37 is suppressed by the cylindrical member 73, as a result of which deformation of the filter 68 itself is prevented. Accordingly, this method is most applicable to the filter 68 which is of soft material. FIG. 15 illustrates another example of the filter replacement port section. In this example, there is provided a through-hole 38 in the part of the fixed port, which extends outside the shielding box 1. In the filter replacement port 75, a filter 68 is provided on the side of the free end 77 of a cylindrical member 76 having a central small diameter section 74 and a sealing member 58 as its bottom 79, and there are provided a number of through-holes in a part corresponding to the small diameter section 74 and between the filter 68 and the bottom 79. If when the filter replacement port 75 is mounted on the box, the small diameter section 74 is in alignment with the through-hole 38, the atmosphere cleaned by the filter 68 is delivered through the through-holes 81 of the filter replacement port 75, the central small diameter section 38, and the through-hole 74 of the fixed port 37 to the exhaust pipe 82 connected to the hole 74. In this connection, it goes without saying that similarly as in the above-described case, there is provided an elastic screw member 48 over the outer wall of the cylindrical member 78. FIG. 16 illustrates another example of the shielding box 1. Shielding boxes 1 are connected through a branched exhaust duct 87 to a filter room 86. Polluted air from each shielding box 1 is discharged from a stack 26 through the filter room 86. The filter room 86, as shown in FIG. 17, is divided into a polluted air room 84 and a clean air room 85 by an intermediate partition 83 provided with a number of filters 69. The port section shown in FIG. 13 or FIG. 14 can be employed to the respective filter sections of the intermediate partitition 83 in the filter room 86. As a worker can enter the clean air room 85 the replacement of the filters can be readily achieved. It goes without saying that the replacement is conducted by directing the new replacement port 69 or 72 toward the polluted air room 84. The replacement of each filter can be achieved by a remote-controlled robot placed in the filter room 86. In this connection, the filter replacement port 69 dropped into the polluted air room 84 can be taken out by providing the above-described glove port section or the bag port section on the wall of the polluted air room 84. The elastic member may be of a viscous elastic material, so that the fixed port can be in close contact with the replacement port. The fixed port 37 in FIGS. 8, 10, 11, 12, 13, 14 or 15 is fixedly mounted on the wall 2 of the shielding box 1 through the ring shaped packing 7. However, the wall 2 and the fixed port may be integrally formed. Further, although the elastic material having the threaded portion on its outer surface is provided on the outer peripheral surface of the replacement port, a plurality of annular projections may be used as a substitution for the thread. As is apparent from the above-described various embodiments, according to this invention, when the glove, the bag, the filter, and the sealing member of the shielding box are replaced with new ones, the shielded material will scarcely leak out of the shielding box, and the replacement can be accomplished with high efficiency within an extremely short period of time. |
043371671 | description | DETAILED DESCRIPTION During the metamorphic alteration of ultramafic rocks to form serpentine, native nickel-iron alloys are often produced under thermodyanmically stable conditions. These alloys constitute the mineral awaruite and are composed mainly of nickel (60 to 90 percent) and iron (10 to 40 percent), together with small amounts of cobalt and copper (less than 5 percent each). The most common composition corresponds to the formula Ni.sub.3 Fe, which is that of an ordered stoichiometric phase. Awaruite has been produced at elevated temperatures, probably exceeding 300.degree. C., during serpentinization of periodotite. In some examples, serpentinization has been caused by circulating sea water. In both cases, it can be demonstrated that occurrences of awaruite have survived for periods exceeding tens of millions of years. Another natural alloy which is found in serpentinized periodotite in large lumps is josephinite, which has a chemical composition similar to awaruite. The origin of josephinite is unclear, but it can be demonstrated that this alloy has also survived in association with serpentine and periodotite for periods exceeding tens of millions of years. Both awaruite and josephinite are thermodynamically stable over wide ranges of Eh, pH, temperature, pressure, and in the presence of ground waters containing substantial amounts of chloride ions and other solutes in the natural geochemical environment. Moreover, these alloys have a high melting point, high mechanical strength, and can be cast, fabricated, and machined. Because of these properties, it has become apparent to us that these alloys make ideal containers for solid nuclear waste materials which are to be buried underground in the natural geochemical environment. This is the essence of our invention. Both minerals are known per se, and we of course do not claim to have discovered or invented the minerals as such. Similarly, our invention is not a new structural design for nuclear waste containers, nor is it limited to any particular waste container structure. |
description | 1. Field This invention pertains in general to chemical mixing systems and in particular a system for dissolving uranium compounds and uranic residues on a production line basis. 2. Related Art In the processing of nuclear fuel, uranium compounds are often dissolved in an acid. At known uranium enrichments it is possible to guarantee the criticality safety of the material by restricting the geometry in which it is held. This concept is known as Safe Geometry and is the preferred method of criticality control due to its passive nature. However, the restricted dimensions employed to achieve a Safe Geometry can prove problematic when dissolving uranium compounds and uranic residues due to the high potential for blockages and difficulty in providing adequate agitation within the system in which the uranium compounds and uranic residues are dissolved. Accordingly, a loop dissolution system is desired that can safely dissolve uranium compounds and uranic residues on a high thru put, production line basis with a substantially reduced potential for blockages with enhanced agitation. Further, such a system is desired that accomplishes those objectives with a Safe Geometry. These and other objects are achieved by a loop dissolution system having an upper material feed dissolution plate into which a material to be dissolved is fed. The dissolution system also includes a lower mixing and dissolution ring with a drop pipe system connecting and establishing fluid communication between the upper material feed dissolution plate and the lower mixing and dissolution ring. A pump has an intake from the lower mixing and dissolution ring and an outlet that directs a first portion of the fluid employed to dissolve the material, to the upper material feed dissolution plate and a second portion of the fluid back into the lower mixing and dissolution ring to circulate the material suspended in the fluid within the lower mixing and dissolution ring to promote turbulence to facilitate dissolution. Preferably, the second portion of the fluid is directed back into the lower mixing and dissolution ring through an acceleration jet and, more preferably, the second portion of the fluid is directed back into the lower mixing and dissolution ring through a plurality of spaced inlets around the mixing and dissolution ring. In one embodiment, the pump has a first inlet from an underside of the lower mixing and dissolution ring and a second inlet from an upper side of the lower mixing and dissolution ring with each of the first and second inlets respectively having a cutoff valve so the pump can draw the fluid alternately from the first inlet or the second inlet. Preferably, the first inlet has a vortex separation chamber in series with the pump for separating undissolved solids before the liquid enters the pump. In another embodiment, the drop pipe system comprises a plurality of pipes respectively spaced around the upper material feed dissolution plate and respectively connected to spaced inlets around the lower mixing and dissolution ring. Preferably, the first portion of the fluid is directed to the upper material feed dissolution plate through a valved manifold compatible with different fluid distribution arrangements. In one preferred arrangement, an active level trip system is provided for determining the level of fluid in the upper material feed dissolution plate and shutting off the first portion of the fluid from entering the upper material feed dissolution plate if the level exceeds a preselected value. Desirably, shutting off the first portion of the fluid from entering the upper material feed dissolution plate permits the fluid in the upper material feed dissolution plate to drain into the drop pipe system. In some applications, the upper material feed dissolution plate is enclosed within a fume extraction chamber with an air inlet and vacuum extraction outlet. Preferably, a flow meter is provided in the air inlet that is responsive to a preselected decrease in flow to cease the dissolution operation. The drop pipe system may also be fitted with a compressed air inlet to aid mixing and transfer of the solids into the lower mixing and dissolution ring. Preferably, the compressed air inlet is positioned adjacent a juncture of the drop pipe system and the lower mixing and dissolution ring. The system may also have a temperature controller for maintaining the temperature of the fluid within a selected range before the fluid is fed into the material feed dissolution plate. At known uranium enrichments it is possible to guarantee the criticality safety of such a material by restricting the geometry in which it is held. This concept is known as Safe Geometry and is the preferred method of criticality control due to its passive nature. However, the restrictive dimensions can prove problematic when dissolving uranium compounds and uranic residues due to the high potential for blockages and difficulty in providing adequate agitation within the system. Configuring a dissolver system as a high velocity loop dissolver overcomes these problems while allowing the Safe Geometry principles to be maintained. One embodiment of a dissolver constructed in accordance with the principles claimed hereafter, that employs Safe Geometry dimensions for criticality safety is illustrated in FIGS. 1-5. The dissolver system 10 has two main elements, an upper dissolution plate 12 and a lower mixing and dissolution ring 14. These two main elements are configured to allow continuous circulation of an acidic solution by pumping the solution from the mixing and dissolution ring 14 through the pump 18 and conduit 16 to the upper dissolution plate 12 while a second portion is fed into acceleration jets 20 through conduit 22 and inlets 24 on the mixing and dissolution ring. This arrangement provides the necessary mixing and agitation to effectively dissolve the uranics at an increased rate while avoiding the blockage issues seen in conventional uranic feed and dissolution systems. The upper dissolution plate 12 acts as a simple safe geometry slab into which can be installed a range of acid distribution arrangements to suit the particular characteristics of the material to be dissolved. These arrangements include, but are not limited to, fluidized beds, single and multi-chamber weirs and acid flow tubes with containment baskets. The main acid feed to the dissolution plate 12 is fed into a valve manifold 26 that allows the connection of the different acid distribution arrangements. Overflow weirs 28 (figuratively shown in FIG. 1) may be incorporated into the dissolution plate 12 to provide a passive method to prevent the Safe Geometry dimensions from being exceeded and may be supplemented with an active level trip system 30 for additional safety. The overflow weir preferably drains to a further Safe Geometry containment vessel or bund. Should an unexpected event or reaction occur on the dissolution plate 12, it can be quickly controlled by stopping the acid feed to the plate and allowing the existing acid to drain away, thereby halting the reaction. Preferably, the upper dissolution plate 12 is enclosed within a glazed fume extraction chamber 32 (figuratively shown in FIG. 3), with fixed atmospheric inlets and vacuum extraction points to ensure all generated gases are safely extracted while simultaneously providing an air “wash” over the glazed sections to prevent chemical attack of the windows. A flow meter 34 is preferably installed in the air inlet pipe-work to inhibit dissolution operations if the fume extract is not functional. Placing the flow meter in the air inlet ensures that the instrument is not subject to damage or coating by the process gases while still effectively indicating that the extraction chamber is under negative pressure due to the extraction system being active. The extraction chamber provides a large gas buffer capable of accepting any gases released by the process without causing the system to pressurized or lose containment. The chamber 32 may be provided with glove port access, material feed routes and wash down facilities. Access to the chamber to load problematic/unusual material, change acid distribution arrangements, remove non-dissolvable solids or perform maintenance activities is through an interlocked door arrangement 52 (figuratively shown in FIG. 3) that provides direct access to the dissolution plate 12. The lower dissolution ring 14 consists of a ring of pipe-work into which are inserted acceleration nozzles 20 that introduce jets of acid to induce motion and agitation of the material within the ring 14. Drop pipes 36 extending from the upper dissolution plate 12 enable the transfer of liquids and potentially solids into the lower mixing ring 14. The multiple large diameter drop pipes negate the potential for blockages of the liquor route from the upper dissolution plate to the lower dissolution ring. These drop legs 36 also increase the system volume permitting larger quantities of material to be dissolved prior to reaching concentrations that will likely crystallize and can optionally be fed with compressed air (figurative shown by reference character 38 in FIG. 1) to the base of the drop pipes 36 to aid mixing and the transfer of solids into the lower ring 14. The ring 14 has both a top and bottom off take 40, 42 to the circulation pump 18, with the top off take 40 being used during dissolution to minimize solid carryover to the pump and the bottom off take 42 being used to empty the system via an in-line vortex separation chamber 44. The pump outlet acid flow is split between conduit 22 which communicates a first portion of the fluid flow to the lower ring acceleration jets 20 and conduit 16 which communicates the acid to the upper dissolution plate 12 during normal operations and can be diverted to recirculate the system contents via a filter system to remove solids prior to final filtration and transfer for onward processing. A temperature control system 46 can be used to heat or cool the acid feed to the dissolution plate 12, and hence the overall system. Temperature control is achieved via an in-line heater/cooler arrangement on the main acid feed line 16 to the upper manifold 26. The heater is controllable and capable of achieving upwards of 80° centigrade acid temperature for effective dissolution of the uranic metals. In order to improve safety of the onward filtration process, following the dissolution period the acid temperature would be reduced to less than 30° centigrade before enabling the transfer valve 48 to the filtration system 50. The Safe Geometry principles employed by this system are common to most enriched uranium dissolution processes, however, applying these principles in a loop dissolver configuration where acid is continually recirculated through/over the material to be dissolved is novel. In addition, the use of acid propulsion jets, vortex separation of solids, interchangeable and distribution arrangements, an ability to view the dissolution process within the extracted chamber and stop the process at any time by removing the acid from the dissolution plate are novel implementations. While this embodiment is described in connection with the dissolution of uranium compounds in an acidic fluid, it should be appreciated that it can be employed for the dissolution of any material capable of being dissolved in a fluid. This embodiment provides a high capacity enriched uranium dissolution facility capable of dealing with a wide range of feed materials from conventional powders and contaminated residues to recovered fuel pins for defabrication. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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052746836 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is generally related to nuclear system pressure vessels and in particular to the replacement of nozzle penetrations in the pressure vessels. 2. General Background The pressurizer in a nuclear reactor coolant system establishes and maintains the reactor coolant system pressure within the prescribed limits of the system. It provides a steam surge chamber and a water reserve to accommodate reactor coolant density changes during operation. A typical pressurizer is a vertical, cylindrical vessel with replaceable electric heaters in its lower section. The heater elements extend into the vessel through nozzle or sleeve penetrations in the vessel. The pressurizer also contains a plurality of nozzle penetrations at various locations for purposes such as sensing the liquid level or temperature in the pressurizer. Due to the operating environment, it is a common requirement that sleeve or nozzles be replaced. In some instances the entire nozzle is removed and replaced while in others only a portion of a nozzle is removed and replaced. In either case, it is necessary during the replacement process to provide a seal that prevents water seepage between the replacement nozzle and the vessel wall. The pressure vessels are normally made from a low carbon steel and water seepage would cause corrosion of the vessel wall. Since pressurizer components in nuclear power plants become radioactive after they have been in operation, it is desirable to minimize the time and amount of work required inside the pressurizer. Applicants are aware of the following patents directed to the replacement of nozzles or sleeves. U.S. Pat. Nos. 5,094,801 and 5,091,140 disclose an apparatus and method for replacing a heater sleeve. The original sleeve is removed and the original bore in the pressurizer is enlarged. An outer sleeve is installed in the bore with its upper end being seal welded to the cladding on the interior of the pressurizer. An inner sleeve is installed in the outer sleeve to extend into the pressurizer and is welded to the lower end of the pressurizer. U.S. Pat. No. 5,149,490 discloses a method and apparatus for replacing a nozzle where the entire nozzle has been removed. The nozzle bore is partially tapped and a replacement nozzle is threaded therein. The end of the replacement nozzle inside the vessel is seal welded to the inside of the pressurizer. A flange on the opposite end of the replacement nozzle bears against the exterior of the pressurizer. The known art does not address the problems associated with the need for a seal weld at the junction of the replacement nozzle and the interior of the pressure vessel. SUMMARY OF THE INVENTION The present invention addresses the above problems in a straightforward manner. What is provided is a method for replacing a nozzle that eliminates the need for a seal weld at the junction of the replacement nozzle and the interior of the pressure vessel. The original nozzle is cut adjacent the interior wall of the pressure vessel. The portion of the original nozzle that extends beyond the exterior of the pressurizer is removed. A weld pad is deposited on the pressure vessel. The remainder of the original nozzle is removed from the nozzle bore. A corrosion resistant thermal spray coating is applied to the nozzle bore. A replacement nozzle is inserted in the bore and welded in place on the exterior of the pressurizer. |
abstract | A method of processing objects by a FIB (Focused Ion Beam) system and a carrier used therewith are provided. The carrier includes a carrying member and a processing portion having an object disposed thereon. Before the carrier is disposed into the FIB system, the carrying member is set to be flush in height with the processing portion having the object disposed thereon. After an eucentric height adjustment inside the FIB system, both the carrying member and the processing portion are in a same plane with the eucentric point of the system. Therefore, after the object on the processing portion is processed, a processed object or a processed block of the object can be moved to the carrying member without performing further eucentric height adjustment with respect to the carrying member. |
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048246336 | summary | BACKGROUND OF THE INVENTION This invention relates to a method and an apparatus for controlling fuel exchange and more particularly to refuelling control method and apparatus suitable for manipulating a plurality of fuel grippers. In a prior art atomic power plant, upon exchange of atomic fuel, the atomic fuel is transferred between a reactor core and a fuel storage pool by a single fuel gripper, as disclosed in JP-A-58-34392. To speed up the fuel transfer, the fuel gripper must therefore be operated at an increased speed but the speed of the fuel gripper is permitted to be increased within only a limited range because the highest safety is required of the power plant. With the view of reducing the time required for transfer, JP-A-61-65192 and JP-A-61-149897 also propose a method which uses a refuelling machine having a plurality of grippers for gripping a plurality of fuel elements, whereby a plurality of fuel elements are gripped simultaneously and then transferred between a reactor core, hereinafter called a core, and a fuel storage pool (hereinafter called a pool). In JP-A-61-65192, however, the simultaneity is only valid for the horizontal transfer between the pool and the core as well as for the horizontal motion in two directions namely, the X and Y directions, and, as a result, the effect of the paralleling (simultaneity) of operation is limited in part. However, JP-A-61149897, neither clearly describes the paralleling of operation nor discloses a specific means for realizing the parallel operation. Thus, under the circumstances, it is desired that as many operations as possible be performed in parallel in order to efficiently effect fuel exchange. Actually, however, a space for mounting the refuelling machine is so limited that mounting of a plurality of, even only two, grippers is almost impossible if the grippers are perfectly mutual non-interfering. Accordingly, a technical task is to provide the manner of performing as many operations as possible by using a plurality of grippers which mutually impose constraint. SUMMARY OF THE INVENTION An object of this invention is to solve the above task and effect fuel exchange with high efficiency. According to the invention, a refuelling machine of reactor comprises a plurality of grippers. Each gripper is comprised of a plurality of telescopic bars which are telescopically actuatable independently of each other and at least one gripping member (grapple) mounted to each telescopic bar. A method for controlling the reactor refuelling machine comprises deciding whether the movement of a particular gripper in the Z direction is constrained by a status of the movement of a different gripper, and performing the parallel operation when the movement of the particular gripper in the Z direction is not constrained and placing the particular gripper in condition for waiting when constrained. An apparatus for controlling the reactor refuelling machine comprises gripper manipulation procedure memory means for storing operations to be carried out by respective grippers in sequence of steps, allowed motion direction deciding means for determining a gripper which is manipulated preferentially hereinafter referred to as the preferential gripper during a step presently under course of execution, hereinafter referred to as an execution step, and determining every moment allowable directions of the movement (directions of allowed motion) of individual grippers inclusive of the preferential one, gripper controlling means for causing the individual grippers to perform the operations to be carried out thereby in accordance with the determined directions of allowed motion during the execution step and the succeeding step, and execution step managing means for deciding the end of the execution step and permitting the procedure to proceed to a subsequent execution step. In the case of manual operation, however, the gripper manipulation procedure memory means and the execution step managing means may be eliminated. The allowed motion direction deciding means determines a preferential gripper during an execution step and decides as to which directions, two horizontal directions, namely upward and downward directions namely, the individual grippers inclusive of the preferential gripper are allowed to freely move in, that is, decides directions of allowed motion of the individual grippers inclusive of the preferential gripper on the basis of a horizontal position and a vertical position or height of each gripper, whether each gripper suspends a fuel element, whether the suspended fuel element is shaking and whether a gripper in question is the preferential gripper. The gripper controlling means causes the preferential gripper to preferentially perform an operation during an execution step in accordance with its allowed motion direction while permitting a non-preferential gripper to perform an operation in parallel with the operation of the preferential gripper during the execution step and the succeeding step in accordance with its allowed motion direction as far as the operation of the non-preferential gripper does not interfere with the operation of the preferential gripper. In this manner, the paralleling of operation of the individual grippers can proceed efficiently while the individual grippers are prevented from interfering with each other and with various parts of facilities of the reactor. |
abstract | There is provided an optical apparatus for radiation with a wavelength xe2x89xa6160 nm. The apparatus comprises a mirror with a mirror surface, and a first device for generating elastic oscillations with different acoustic wavelengths on the mirror surface due to surface deformations. Radiation impinging on the mirror surface is diffracted in a predetermined range of angles (xcex1). |
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062657232 | abstract | A magnetic shield apparatus includes a magnetic shield room, a tubular member, and a flange portion. The magnetic shield room has an opening to shield external magnetism. The tubular member is made of a magnetic shield material and attached to the opening to project from the magnetic shield room by a first predetermined length. The flange portion is made of a magnetic shield material and formed around a distal end portion of the tubular member to be spaced apart from it by a second predetermined length. |
claims | 1. A plant operation data monitoring apparatus comprising:plant-data inputting means for inputting plant data from a plant facility;a plant-data most-recent-value table for temporarily storing a most recent value of said plant data;plant-data recording means for retrieving said most recent value from said plant-data most-recent-value table and recording long-term time-series plant data in a plant data history table;monitoring point editing means for editing to register data regarding one or more monitoring points for monitoring an error of said plant facility in response to an operator request;a monitoring-point registering table for storing a result registered by said monitoring-point editing means;data-correlation determining means for selecting one or more main variable points having a strong correlation to the corresponding monitoring point from said plant-data history table using said monitoring point as a key;a main-variable-point registering table for registering a main variable point selected by said data-correlation determining means;limit calculating means for calculating to define a statistical upper/lower limit value function for said plant-data history table on the basis of time-series plant data of said monitoring point and said main variable point;a limit-value function table for storing a limit-value function defined by said limit-value calculating means;limit-value determining means for referring to table information in said limit-value function table and for periodically matching content of said plant-data most-recent-value table with the table information, and if the most recent value is outside the limit value range, deviation information due to a plant error is determined and stored in a determination result table;plant-error monitoring/outputting means for monitoring and outputting an error signal and content of said determination result table if a new plant error occurs; anda display device for displaying an output from said plant-error monitoring/outputting means. 2. The plant operation data monitoring apparatus according to claim 1, further comprising:a data-count/weighting-factor conversion function, whereinwhen statistical upper/lower limit values are calculated with monitoring points and main variable points by said limit-value calculating means, an optimum upper/lower limit range is obtained by performing a limit calculation considering a data distribution density in units of divided clusters. 3. The plant operation data monitoring apparatus according to claim 1, wherein:a condition indicating the plant is stable is provided from outside; when statistical upper/lower limit values are calculated with monitoring points and main variable points, history data is extracted on the basis of said condition to calculate a less varying limit value; andthe limit value is used to perform monitoring checking. 4. The plant operation data monitoring apparatus according to claim 1, wherein as a result of statistical processing, if a distribution in a correlation between said monitoring points and said main variable points is divided into two or more groups, a condition for distinguishing these groups is provided from outside. 5. The plant operation data monitoring apparatus according to claim 4, wherein as a condition for distinguishing a plurality of groups, a data mining method is applied to history data to automatically extract the most appropriate plant condition for distinguishing groups. 6. The plant operation data monitoring apparatus according to claim 1, wherein:a plurality of plant states are defined;one or more main variable points having a strong correlation to said monitoring point in each plant state are automatically calculated;the statistical upper/lower limit values of said monitoring point are provided as a plurality of functions of said main variable points for monitoring whether the function is in a defined plant state; andthe upper/lower limit values of the matched function are used for monitoring. 7. The plant operation data monitoring apparatus according to claim 6, wherein a priority statistical process is performed so that said main variable points may be reduced to a same point even in a plurality of plant states. 8. The plant operation data monitoring apparatus according to claim 6, wherein said main variable point is provided from outside to calculate the statistical upper/lower limit values in a plurality of plant states. 9. The plant operation data monitoring apparatus according to claim 6, wherein the statistical upper/lower limit values of a plurality of said monitoring points in each of the plurality of plant states are calculated. 10. The plant operation data monitoring apparatus according to claim 9, wherein:when a common plant state is defined for a plurality of said monitoring points to perform monitoring, an independent plant condition is provided for each of the said monitoring points; andthe statistical upper/lower limit values are calculated to perform monitoring. 11. The plant operation data monitoring apparatus according to claim 10, wherein:the calculated statistical upper/lower limit values of said monitoring points and said plant data used for calculation are displayed on a same graph;at the same time, upper/lower limit matched data count and outlier count are displayed; andvalidation is performed on the calculated values. 12. The plant operation data monitoring apparatus according to claim 11, wherein:a functional expression indicating a statistical upper/lower limit value or a factor thereof is displayed;the factor is manually modified; andthe modified factor can be confirmed on a graph display. 13. The plant operation data monitoring apparatus according to claim 12, wherein the statistical upper/lower limit values and said plant data used for calculation in a plurality of common plant states and independent plant conditions can be displayed on a same graph by changing colors and marker shapes. 14. The plant operation data monitoring apparatus according to claim 13, further comprising:means for not displaying information in a certain state as needed when a plurality of states are overlay-displayed. |
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description | The present application is a Continuation of International Application No. PCT/EP2011/065873, filed on Sep. 13, 2011, which claims priority of German Patent Application No. 10 2010 041 397.6, filed on Sep. 27, 2010, U.S. Provisional Application No. 61/386,634, filed on Sep. 27, 2010, German Patent Application No. 10 2010 041 502.2, filed on Sep. 28, 2010, and U.S. Provisional Application No. 61/387,214, filed on Sep. 28, 2010. The disclosures of these five applications are hereby incorporated by reference in their respective entireties. The invention relates to a mirror. Furthermore, the invention relates to a projection objective comprising such a mirror. Moreover, the invention relates to a projection exposure apparatus for microlithography comprising such a projection objective. Projection exposure apparatuses for microlithography for the EUV wavelength range have to rely on the assumption that the mirrors used for the imaging of a mask into an image plane have a high reflectivity since, firstly, the product of the reflectivity values of the individual mirrors determines the total transmission of the projection exposure apparatus and since, secondly, the light power of EUV light sources is limited. Mirrors for the EUV wavelength range around 13 nm having high reflectivity values are known from DE 101 55 711 A1, for example. The mirrors described therein consist of a layer arrangement which is applied on a substrate and which has a sequence of individual layers, wherein the layer arrangement comprises a plurality of surface layer systems each having a periodic sequence of at least two individual layers of different materials that form a period, wherein the number of periods and the thickness of the periods of the individual layer systems decrease from the substrate toward the surface. Such mirrors have a reflectivity of greater than 30% in the case of an angle of incidence interval of between 0° and 20°. In this case, the angle of incidence is defined as the angle between the direction of incidence of a light ray and the normal to the surface of the mirror at the point where the light ray impinges on the mirror. In this case, the angle of incidence interval results from the angle interval between the largest and the smallest angle of incidence respectively considered for a mirror. What is disadvantageous about the abovementioned layers, however, is that their reflectivity in the angle of incidence interval specified is not constant, but rather varies. A variation of the reflectivity of a mirror over the angles of incidence is disadvantageous, however, for the use of such a mirror at locations with high angles of incidence and with high angle of incidence changes in a projection objective for microlithography since such a variation leads for example to an excessively large variation of the pupil apodization of such a projection objective. In this case, the pupil apodization is a measure of the intensity fluctuation over the exit pupil of a projection objective. What is furthermore disadvantageous about the abovementioned layers is that the latter transmit too much EUV radiation to the substrate, as a result of which the substrate is exposed to high doses of EUV radiation over a long period of time. However, under high doses of EUV radiation, substrates for EUV mirrors composed of materials such as for example Zerodur® from Schott AG or ULE® from Corning Inc. tend toward densification of the order of magnitude of a few percent by volume. In the case of generally non-uniform irradiation of the mirrors, said densification leads to a non-uniform change in their surface form, as a result of which the optical imaging properties of the mirrors are changed in an undesirable manner during the operating period. In order to obtain a high reflectivity of mirrors for the EUV wavelength range it is also necessary to avoid losses on account of stray light, which leads to stringent requirements made of the surface roughness of such mirrors in the so-called HSFR range, see U. Dinger et al. “Mirror substrates for EUV-lithography: progress in metrology and optical fabrication technology” in Proc. SPIE Vol. 4146, 2000, in particular for the definition of the surface roughness in the HSFR range with spatial wavelengths of the roughness of 10 nm to 1 μm (HSFR=high spatial frequency roughness) and in the MSFR range with spatial wavelengths of the roughness of 1 μm to 1 mm (MSFR=mid spatial frequency roughness). Furthermore, such mirrors have to ensure the high reflectivity values and the desired optical imaging quality even over a period of several years under continuous irradiation with high-intensity EUV radiation. Other mirrors, too, which are used within projection exposure apparatuses for microlithography at wavelengths of less than 250 nm have to have low values for the surface roughness in the HSFR range in order to avoid stray light losses. Therefore, it is an object of the invention to provide a mirror which minimizes the losses as a result of stray light. Furthermore, the object of the invention is to provide a mirror for the EUV wavelength range which, even at high doses of EUV radiation, has a high long-time stability of its optical properties during the operating period of from a few months to a few years and simultaneously minimizes the losses as a result of stray light. According to one formulation of the invention, this object is achieved by a mirror comprising a substrate and a layer arrangement, wherein the layer arrangement is designed in such a way that light having a wavelength of less than 250 nm that is incident on the mirror at at least an angle of incidence of between 0° and 30° is reflected with more than 20% of its intensity, and the layer arrangement comprises at least one surface layer system consisting of a periodic sequence of at least two periods of individual layers, wherein the periods comprise two individual layers composed of different materials for a high refractive index layer and a low refractive index layer and wherein the layer arrangement comprises at least one layer composed of graphene. In the context of this application, a layer comprised of graphene is understood to mean a layer which consists at least of a monolayer of carbon atoms, wherein the carbon atoms have an sp2 hybridization. The terms high refractive index and low refractive index are in this case relative terms with regard to the respective partner layer in a period of a surface layer system. Surface layer systems generally function only if a layer that acts with optically high refractive index is combined with an optically lower refractive index layer relative thereto as main constituent of a period of the surface layer system. This applies in particular to the EUV wavelength range. According to the invention, it has been recognized that a low surface roughness of the at least one layer composed of graphene is sufficient to reduce the stray light losses of surfaces of optical elements. This applies in particular to mirrors since the latter, by their nature, are more susceptible to stray light losses than lenses. In particular mirrors for the EUV wavelength range, as mentioned in the introduction, have to have very low values for stray light. This applies in particular to mirrors for the EUV wavelength range which are equipped with a substrate protecting layer (SPL) or a substrate protecting layer system (SPLS), since said substrate protecting layer (SPL) or the layers of the substrate protecting layer system (SPLS) are generally constructed from metals having high surface roughnesses. In this respect, it is possible to compensate for the roughness of other layers, in particular of substrate protecting layers, utilizing the surface roughness of graphene, such that at least one reflective surface layer system can be applied on the smooth graphene layer as support, which system can thereby grow in a manner undisturbed by the roughness of the support. Otherwise, the roughness of the substrate protecting layers is transferred directly to the reflective surface layer system. Consequently, it is possible to reduce the stray light losses of a mirror with a layer composed of graphene. Furthermore, it is possible to protect the substrate of a mirror for the EUV wavelength range against long-term degradation to a sufficient extent with the help of a substrate protecting layer or a substrate protecting layer system and simultaneously to avoid stray light losses as a result of said substrate protecting layer or the substrate protecting layer system. In one embodiment, the at least one layer composed of graphene has a surface roughness of less than 0.1 nm rms HSFR, in particular less than 0.04 nm rms HSFR. Stray light losses are avoided as a result of such low roughness values in the HSFR range. Furthermore, the object of the present invention is achieved with a mirror comprising a substrate and a layer arrangement, wherein the layer arrangement is designed in such a way that light having a wavelength of less than 250 nm that is incident on the mirror at at least an angle of incidence of between 0° and 30° is reflected with more than 20% of its intensity, and the layer arrangement comprises at least one surface layer system consisting of a periodic sequence of at least two periods of individual layers, wherein the periods comprise two individual layers composed of different materials for a high refractive index layer and a low refractive index layer. Furthermore, the layer arrangement comprises at least one layer having a surface roughness of less than 0.1 nm rms HSFR, in particular less than 0.04 nm rms HSFR. According to the invention, it has been recognized that a low surface roughness in the HSFR range of at least one layer of the layer arrangement is sufficient to avoid stray light losses of a mirror. In particular, the surface roughness of a substrate protecting layer (SPL) or of a substrate protecting layer system (SPLS) can be compensated for by a low surface roughness in the HSFR range of at least one layer of the layer arrangement. As a result, it is possible to protect the substrate against long-term degradation to a sufficient extent with a substrate protecting layer or a substrate protecting layer system and simultaneously to avoid stray light losses as a result of said substrate protecting layer or the substrate protecting layer system. In one embodiment, the at least one layer has a surface roughness of less than 0.1 nm rms, in particular less than 0.07 nm for spatial frequencies above the HSFR range. Such layers, which are designated as “atomically smooth”, reduce the roughness of other layers applied to the “atomically smooth” layer by virtue of the fact that from the outset no defects are present which could be intensified by the growth of the other layers and could thus contribute to the surface roughness of said layers. In another embodiment, the mirror is a mirror for the EUV wavelength range which reflects EUV radiation incident on the mirror at at least an angle of incidence of between 0° and 30° with more than 20% of its intensity. Particularly in the case of mirrors for the EUV wavelength range which are used at locations of high angle of incidence intervals, it is necessary to minimize the stray light losses since said mirrors generally do not have overly high reflectivity values in the entire angle of incidence interval in comparison with so-called “normal incidence” mirrors, which cover only small angle of incidence intervals. Consequently, stray light losses in the case of these mirrors lead to greater relative light losses than in the case of pure “normal incidence” mirrors. These relative light losses lead directly to an undesirable high pupil apodization, as mentioned in the introduction. In a further embodiment, the layer arrangement is chosen in such a way that the transmission of EUV radiation through the layer arrangement amounts to less than 10%, in particular less than 2%. In this case, it has been recognized according to the invention that, in order to protect the substrate from excessively high doses of EUV radiation, it suffices to design the layer arrangement on the substrate of the mirror such that only a small fraction of the EUV radiation reaches the substrate. For this purpose, either the layer arrangement or the surface layer systems of the layer arrangement can be provided with a corresponding number of periods of layers or a surface protecting layer (SPL) or a surface protecting layer system (SPLS) is used, such that at all events the transmission of EUV radiation through the layer arrangement to the substrate amounts to less than 10%, in particular less than 2%. In another embodiment, the layer arrangement comprises at least one surface protecting layer SPL or at least one surface protecting layer system SPLS having a thickness of greater than 20 nm, in particular 50 nm, wherein the surface protecting layer SPL or the surface protecting layer system SPLS experience an irreversible change in volume of less than 1%, in particular less than 0.2%, under EUV radiation. In this case, an irreversible change in volume under EUV radiation is understood to mean not the reversible change in volume on account of thermal expansion, but rather the long-term irreversible change in volume on account of structural changes in the material under consideration caused by high doses of EUV radiation. In this case, it has been recognized according to the invention that, besides protection of the substrate, for which a 20 nm thick surface protecting layer SPL or a 20 nm thick surface protecting layer system SPLS may already suffice depending on choice of material, it must also be taken into consideration that the surface protecting layer SPL or the surface protecting layer system SPLS must remain stable even under EUV radiation at high doses that are accumulated over the lifetime of a lithography apparatus. Otherwise, the problem of the irreversible change in volume is merely shifted from the substrate to the surface protecting layer or the surface protecting layer system, respectively. In a further embodiment, the layer arrangement comprises at least one surface protecting layer or at least one surface protecting layer system having a thickness of greater than 20 nm, in particular of greater than 50 nm, wherein the surface protecting layer or the surface protecting layer system is provided for preventing an irreversible alteration of the surface of the substrate under EUV radiation of more than 0.1 nm measured in the normal direction. In this case, this irreversible alteration along the normal direction is compared at a location within the irradiated region of the substrate with a location outside the irradiated region. At the same time the surface protecting layer or the surface protecting layer system is provided for exerting a tensile stress for compensation of layer stresses in the layer arrangement. In this case it has been recognized according to the invention that, besides protection of the substrate, for which a 20 nm thick surface protecting layer SPL or a 20 nm thick surface protecting layer system SPLS may already suffice depending on choice of material, it must also be taken into consideration that the surface protecting layer SPL or the surface protecting layer system SPLS is at the same time adapted for compensation of the layer stresses in the layer arrangement since otherwise the substrate bends impermissibly on account of the layer stresses. Consequently, particularly in the design of a surface protecting layer system, the resultant layer stress has to be concomitantly taken into account in the optimization. Furthermore, through the choice of material in the case of the surface protecting layer SPL and in the case of the surface protecting layer system SPLS, care must be taken to ensure that these are not altered in the case of EUV radiation at high doses since this inevitably entails an alteration of the layer stress and thus of the surface form. In one embodiment, the layer arrangement of the mirror comprises at least one layer which is formed from or as a compound is composed of a material from the group: nickel, carbon, graphene, boron carbide, cobalt, beryllium, silicon, silicon oxides. These materials are suitable individually or in combination with one another for a surface protecting layer SPL or a surface protecting layer system SPLS. In particular relatively thick layers composed of graphene are able, given appropriate design of the other surface layer systems of the layer arrangement, to absorb the remaining EUV radiation that passes through the surface layer system, such that rough surface protecting layers SPL or surface protecting layer systems SPLS can be dispensed with in this case. In a further embodiment, the layer arrangement of a mirror according to the invention comprises at least three surface layer systems, wherein the number of periods of the surface layer system that is situated closest to the substrate is greater than for the surface layer system that is most distant from the substrate and/or is greater than for the surface layer system that is second most distant from the substrate. This use of a large number of periods fosters a decoupling of the reflection properties of the mirror from layers lying below the layer arrangement or from those of the substrate, such that it is possible to use other layers with other functional properties or other substrate materials below the layer arrangement of the mirror. Firstly, it is thus possible to avoid perturbing effects of the layers lying below the layer arrangement or of the substrate on the optical properties of the mirror, and in this case in particular on the reflectivity, and, secondly, it is thereby possible for layers lying below the layer arrangement or the substrate to be protected from the EUV radiation in addition to the measures already mentioned above. In this case, it should be taken into consideration that the properties of reflectivity, transmission and absorption of a layer arrangement behave nonlinearly with respect to the number of periods of the layer arrangement; the reflectivity, in particular, exhibits a saturation behavior toward a limit value with regard to the number of periods of a layer arrangement. The abovementioned surface protecting layer SPL or the abovementioned surface protecting layer system SPLS can also thus be used to the effect that the required number of periods of a layer arrangement is limited to the required number of periods for achieving the reflectivity properties. Otherwise, a very large number of periods would have to be used in order, besides the reflectivity, also simultaneously to provide corresponding protection by the surface layer systems. In another embodiment, the layer arrangement comprises a quartz layer having a thickness of greater than 2 μm, in particular of greater than 5 μm, which was deposited by a CVD method, in particular a PICVD, PACVD or PECVD method. Such layers exhibit long-term stability under EUV radiation and at the same time protect the underlying substrate by virtue of their absorption. In one embodiment, the layer arrangement comprises a quartz layer, wherein the quartz layer has a surface roughness of less than 0.5 nm rms HSFR, in particular less than 0.2 nm rms HSFR. Such quartz layers firstly lead, as mentioned in the introduction, to low stray light losses of the mirror and, secondly, can be used to provide the substrate material, which is generally difficult to polish, with a surface layer that can be polished well. As an alternative thereto, a graphene layer is suitable for compensating for the roughness of the substrate material. In a further embodiment, the layer arrangement comprises at least one surface protecting layer system SPLS consisting of a periodic sequence of at least two periods of individual layers, where the periods comprise two individual layers composed of different materials for a high refractive index layer and a low refractive index layer, wherein the materials of the two individual layers forming the periods are either nickel and silicon or cobalt and beryllium. What is advantageous about such surface protecting layer systems SPLS by comparison with an individual surface protecting layer SPL is that although the total thickness of the absorbent layers of the surface protecting layer system SPLS corresponds to the thickness of the individual surface protecting layer SPL for the absorption effect, said absorbent layers, by comparison with said surface protecting layer, are interrupted by other layers composed of other material, as a result of which the crystal growth in the layers of the surface protecting layer system SPLS is interrupted by comparison with the crystal growth in the surface protecting layer SPL. This makes it possible to provide very smooth surfaces without high stray light losses or to produce said surfaces during the coating process using, for example, an assisting ion bombardment. In another embodiment, the individual layers of the surface protecting layer system SPLS are separated by at least one barrier layer and the barrier layer consists of a material which is selected from or as a compound is composed of the group of materials: B4C, C, graphene, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride. These materials mentioned prevent the interdiffusion of the individual layers of the SPLS. In this case, in particular the roughness of graphene as a barrier layer has a compensating effect according to the invention with respect to the surface protecting layer SPL or the surface protecting layer system SPLS. As a result, even the reduced surface roughnesses of the layers interrupted in their crystal growth by intermediate layers can be decreased further. Furthermore, the graphene itself as intermediate layer can provide for the interruption of the crystal growth. In a further embodiment, the layer arrangement comprises at least one surface protecting layer system SPLS consisting of a periodic sequence of at least two periods of individual layers, wherein the periods comprise two individual layers composed of different materials for a low refractive index layer and a barrier layer. Such surface protecting layer systems SPLS are extremely simple in their construction since the high refractive index layer or the spacer has been dispensed with. In another embodiment, the layer arrangement comprises at least one surface protecting layer system SPLS consisting of a periodic sequence of at least two periods of individual layers, wherein the periods comprise two individual layers composed of different materials for a low refractive index layer and a barrier layer, and wherein the material for the low refractive index layer consists of nickel and the material for the barrier layer is selected from or as a compound is composed of the group of materials: B4C, C, graphene, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride. Such surface protecting layer systems SPLS constitute a preferred material combination of a simple surface protecting layer system SPLS. In a further embodiment, the at least one surface protecting layer system SPLS has low refractive index layers having a surface roughness of less than 0.5 nm rms HSFR, in particular of less than 0.2 nm rms HSFR. Such layers lead, as mentioned in the introduction, to low stray light losses and can be produced during the coating process for example via assisting ion bombardment. In one embodiment, the mirror for the EUV wavelength range comprises a substrate and a layer arrangement, wherein the layer arrangement comprises a plurality of surface layer systems. In this case, the surface layer systems each consist of a periodic sequence of at least two periods of individual layers. In this case, the periods comprise two individual layers composed of different materials for a high refractive index layer and a low refractive index layer and have within each surface layer system a constant thickness that deviates from a thickness of the periods of an adjacent surface layer system. In this case, the surface layer system that is second most distant from the substrate has a sequence of the periods such that the first high refractive index layer of the surface layer system that is most distant from the substrate directly succeeds the last high refractive index layer of the surface layer system that is second most distant from the substrate and/or the surface layer system that is most distant from the substrate has a number of periods that is greater than the number of periods for the surface layer system that is second most distant from the substrate. In this case, the surface layer systems of the layer arrangement of the mirror according to the invention succeed one another directly and are not separated by a further layer system. Furthermore, in the context of the present invention, a surface layer system is distinguished from an adjacent surface layer system, even given otherwise identical division of the periods between high and low refractive index layers, if a deviation by more than 0.1 nm is present as deviation in the thickness of the periods of the adjacent surface layer systems since, starting from a difference of 0.1 nm, it is possible to assume a different optical effect of the surface layer systems with otherwise identical division of the periods between high and low refractive index layers. It has been recognized that in order to achieve a high and uniform reflectivity across a large angle of incidence interval, the number of periods for the surface layer system that is most distant from the substrate must be greater than that for the surface layer system that is second most distant from the substrate. Furthermore it has been recognized that, in order to achieve a high and uniform reflectivity across a large angle of incidence interval, as an alternative or in addition to the measure mentioned above, the first high refractive index layer of the surface layer system that is most distant from the substrate should directly succeed the last high refractive index layer of the surface layer system that is second most distant from the substrate. In a further embodiment the mirror for the EUV wavelength range comprises a substrate and a layer arrangement, wherein the layer arrangement comprises a plurality of surface layer systems. In this case, the surface layer systems each consist of a periodic sequence of at least two periods of individual layers. In this case, the periods comprise two individual layers composed of different materials for a high refractive index layer and a low refractive index layer and have within each surface layer system a constant thickness that deviates from a thickness of the periods of an adjacent surface layer system. In this case, the surface layer system that is second most distant from the substrate has a sequence of the periods such that the first high refractive index layer of the surface layer system that is most distant from the substrate directly succeeds the last high refractive index layer of the surface layer system that is second most distant from the substrate. Furthermore, the transmission of EUV radiation through the surface layer systems amounts to less than 10%, in particular less than 2%. It has been recognized that, in order to achieve a high and uniform reflectivity across a large angle of incidence interval, the influence of layers situated below the layer arrangement or of the substrate must be reduced. This is necessary primarily for a layer arrangement in which the surface layer system that is second most distant from the substrate has a sequence of the periods such that the first high refractive index layer of the surface layer system that is most distant from the substrate directly succeeds the last high refractive index layer of the surface layer system that is second most distant from the substrate. One simple possibility for reducing the influence of layers lying below the layer arrangement or of the substrate consists in designing the layer arrangement such that the latter transmits as little EUV radiation as possible to the layers lying below the layer arrangement. This affords the possibility for said layers lying below the layer arrangement or the substrate to make a significant contribution to the reflectivity properties of the mirror. In one embodiment, the surface layer systems are in this case all constructed from the same materials for the high and low refractive index layers since this simplifies the production of mirrors. A mirror for the EUV wavelength range in which the number of periods of the surface layer system that is most distant from the substrate corresponds to a value of between 9 and 16, and a mirror for the EUV wavelength range in which the number of periods of the surface layer system that is second most distant from the substrate corresponds to a value of between 2 and 12, lead to a limitation of the layers required in total for the reflective effect of the mirror and thus to a reduction of the complexity and the risk during the production of the mirror. Furthermore, it has been recognized that it is possible to achieve particularly high reflectivity values for a layer arrangement in the case of a small number of surface layer systems if, in this case, the period for the surface layer system that is most distant from the substrate has a thickness of the high refractive index layer which amounts to more than 120% of the thickness, in particular more than double the thickness, of the high refractive index layer of the period for the surface layer system that is second most distant from the substrate. It is likewise possible to achieve particularly high reflectivity values for a layer arrangement in the case of a small number of surface layer systems in a further embodiment if the period for the surface layer system that is most distant from the substrate has a thickness of the low refractive index layer which is less than 80%, in particular less than two thirds of the thickness of the low refractive index layer of the period for the surface layer system that is second most distant from the substrate. In a further embodiment, a mirror for the EUV wavelength range has, for the surface layer system that is second most distant from the substrate, a thickness of the low refractive index layer of the period which is greater than 4 nm, in particular greater than 5 nm. As a result of this it is possible that the layer design can be adapted not only with regard to the reflectivity per se, but also with regard to the reflectivity of s-polarized light with respect to the reflectivity of p-polarized light over the angle of incidence interval striven for. Primarily for layer arrangements which consist of only two surface layer systems, the possibility is thus afforded of performing a polarization adaptation despite limited degrees of freedom as a result of the limited number of surface layer systems. In another embodiment, a mirror for the EUV wavelength range has a thickness of the periods for the surface layer system that is most distant from the substrate of between 7.2 nm and 7.7 nm. It is thereby possible to realize particularly high uniform reflectivity values for large angle of incidence intervals. Furthermore, a further embodiment has an additional intermediate layer or an additional intermediate layer arrangement between the layer arrangement of the mirror and the substrate, which serves for the stress compensation of the layer arrangement. With such stress compensation, it is possible to avoid deformation of the mirror during the application of the layers. In another embodiment of a mirror according to the invention, the two individual layers forming a period consist either of the materials molybdenum (Mo) and silicon (Si) or of the materials ruthenium (Ru) and silicon (Si). It is thereby possible to achieve particularly high reflectivity values and at the same time to realize production engineering advantages since only two different materials are used for producing the surface layer systems of the layer arrangement of the mirror. In this case, in a further embodiment, said individual layers are separated by at least one barrier layer, wherein the barrier layer consists of a material which is selected from or as a compound is composed of the group of materials: B4C, C, graphene, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride. Such a barrier layer suppresses the interdiffusion between the two individual layers of a period, thereby increasing the optical contrast in the transition of the two individual layers. With the use of the materials molybdenum and silicon for the two individual layers of a period, one barrier layer above the Si layer, as viewed from the substrate, suffices in order to provide for a sufficient contrast. The second barrier layer above the Mo layer can be dispensed with in this case. In this respect, at least one barrier layer for separating the two individual layers of a period should be provided, wherein the at least one barrier layer may perfectly well be constructed from various ones of the above-indicated materials or the compounds thereof and may in this case also exhibit a layered construction of different materials or compounds. Barrier layers which comprise the material B4C and have a thickness of between 0.35 nm and 0.8 nm, preferably between 0.4 nm and 0.6 nm, lead in practice to high reflectivity values of the layer arrangement. Particularly in the case of surface layer systems composed of ruthenium and silicon, barrier layers composed of B4C exhibit a maximum of reflectivity in the case of values of between 0.4 nm and 0.6 nm for the thickness of the barrier layer. In a further embodiment, a mirror according to the invention comprises a covering layer system comprising at least one layer composed of a chemically inert material, which terminates the layer arrangement of the mirror. The mirror is thereby protected against ambient influences. In another embodiment, the mirror according to the invention has a thickness factor of the layer arrangement along the mirror surface having values of between 0.9 and 1.05, in particular having values of between 0.933 and 1.018. It is thereby possible for different locations of the mirror surface to be adapted in a more targeted fashion to different angles of incidence that occur there. In this case, the thickness factor can also comprise the surface protecting layer SPL or the surface protecting layer system SPLS, and the abovementioned additional intermediate layer or the abovementioned additional intermediate layer arrangement for stress compensation. In this case, the thickness factor is the factor with which all the thicknesses of the layers of a given layer design, in multiplied fashion, are realized at a location on the substrate. A thickness factor of 1 thus corresponds to the nominal layer design. The thickness factor as a further degree of freedom makes it possible for different locations of the mirror to be adapted in a more targeted fashion to different angle of incidence intervals that occur there, without the layer design of the mirror per se having to be changed, with the result that the mirror ultimately yields, for higher angle of incidence intervals across different locations on the mirror, higher reflectivity values than are permitted by the associated layer design per se given a fixed thickness factor of 1. By adapting the thickness factor, it is thus also possible, over and above ensuring high angles of incidence, to achieve a further reduction of the variation of the reflectivity of the mirror according to the invention over the angles of incidence. In a further embodiment, the thickness factor of the layer arrangement at locations of the mirror surface correlates with the maximum angle of incidence that occurs there, since, for a higher maximum angle of incidence, a higher thickness factor is useful for the adaptation. In another embodiment, the substrate of the mirror consists of a metal or a metal alloy, in particular Si, Glidcop® or Elmedur®. Glidcop® is a registered trade name of SCM Metal Products, Inc. for dispersion-hardened Si alloys comprising different admixtures of aluminium oxide ceramic particles. Elmedur® is a registered trade name of DURO METALL GmbH for copper alloys comprising proportions of approximately 1% Co, 1% Ni and 0.5% Be. Such materials are used in particular for the production of so-called facet mirrors for the EUV wavelength range. In the case of said facet mirrors, which are generally used in the illumination system of projection exposure apparatuses for microlithography, it is particularly important to reduce the stray light losses, since said mirrors are used very close to the light source and, therefore, the light losses thereof have a greater effect on the total transmission of the projection exposure apparatus. Furthermore, the object is achieved through another formulation of the invention with a projection objective comprising at least one mirror according to the invention. Moreover, the object of the invention is achieved with a projection exposure apparatus according to the invention for microlithography comprising such a projection objective. Furthermore the object of the invention is achieved by the use of graphene on optical elements for reducing the surface roughness to less than 0.1 nm rms HSFR and/or by the use of graphene for protecting the optical element in the EUV wavelength range against a radiation-induced irreversible change in volume of more than 1% and/or by the use of graphene as a barrier layer for preventing interdiffusion between layers of so-called multilayer layer mirrors in the EUV wavelength range. Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention with reference to the figures, which show details essential to the invention, and from the claims. The individual features can be realized in each case individually by themselves or as a plurality in any desired combination in a variant of the invention. A respective mirror 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention is described below with reference to FIGS. 1, 1a, 2, 2a, 3 and 3a, the corresponding features of the mirrors having the same reference signs in the figures. Furthermore, the corresponding features or properties of these mirrors according to the invention are explained in summary for FIGS. 1 to 3a below following the description concerning FIG. 3a. FIG. 1 shows a schematic illustration of a mirror 1a according to the invention for the EUV wavelength range comprising a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of surface layer systems P′, P″ and P′″ each consisting of a periodic sequence of at least two periods P1, P2 and P3 of individual layers, wherein the periods P1, P2 and P3 comprise two individual layers composed of different materials for a high refractive index layer H′, H″ and H′″ and a low refractive index layer L′, L″ and L′″ and have within each surface layer system P′, P″ and P′″ a constant thickness d1, d2 and d3 that deviates from a thickness of the periods of an adjacent surface layer system. In this case, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate. In addition, the surface layer system P″ that is second most distant from the substrate has a sequence of the periods P2 such that the first high refractive index layer H′″ of the surface layer system P′″ that is most distant from the substrate directly succeeds the last high refractive index layer H″ of the surface layer system P″ that is second most distant from the substrate. Consequently, in FIG. 1, the order of the high H″ and low refractive index L″ layers within the periods P2 in the surface layer system P″ that is second most distant from the substrate is reversed relative to the order of the high H′, H′″ and low refractive index L′, L″ layers within the other periods P1, P3 of the other surface layer systems P′, P′″, such that the first low refractive index layer L″ of the surface layer system P″ that is second most distant from the substrate also optically actively succeeds the last low refractive index layer L′ of the surface layer system P′ that is situated closest to the substrate. Therefore, the surface layer system P″ that is second most distant from the substrate in FIG. 1 also differs in the order of the layers from all the other surface layer systems in FIGS. 2 and 3 that are described below. FIG. 1a shows the mirror 1a′ according to the invention, said mirror substantially corresponding to the mirror 1a according to the invention in FIG. 1. The difference between these mirrors is merely that, in the case of the mirror 1a′, a surface protecting layer SPL having the thickness dp and a layer G composed of graphene is situated between the upper three surface layer systems P′, P″ and P′″ and the substrate S. Such a surface protecting layer SPL serves to protect the substrate from excessively high doses of EUV radiation since mirror substrates composed of e.g. Zerodur® or ULE® exhibit an irreversible densification of the order of magnitude of a few percent by volume at high doses of EUV radiation. The layer composed of graphene G provides for compensation of the surface roughness of the surface protecting layer SPL, such that stray light losses are avoided. In this case, a mirror surface protecting layer SPL composed of a metal such as e.g. nickel (Ni) having a thickness of approximately 50 to 100 nm has enough absorption, such that only very little EUV radiation penetrates as far as the underlying substrate S. The substrate is thereby sufficiently protected even at high doses of EUV radiation which occur during operation of a microlithography apparatus over many years. It is thus possible to prevent the situation where the optical imaging properties of a mirror no longer suffice for the operation of the microlithography apparatus after just a few months or years on account of the irreversible change in the surface of the substrate. A 2 to 5 μm thick quartz layer as a surface protecting layer SPL likewise has enough absorption to sufficiently protect the substrate. Such a quartz layer should be applied on the substrate using a CVD method, in particular a PICVD, PACVD or PECVD method, since these coating methods mentioned lead to very compact layers which, even under EUV radiation, are stable and do not exhibit irreversible densification. The metal layers mentioned, such as e.g. nickel, are likewise stable under EUV radiation and do not exhibit irreversible densification. The explanation as to why quartz layers, in contrast to the substrate material, are stable under high doses of EUV radiation even though the substrate materials are likewise based on the basic material quartz presumably resides in the process for producing the substrate materials, which takes place at high temperatures. As a result, presumably an intermediate thermodynamic state is frozen in the substrate material, this state undergoing transition to a thermodynamic ground state under high doses of EUV radiation, as a result of which the substrate material becomes more compact. Conversely, the quartz layers are applied at low temperatures with the methods mentioned, as a result of which presumably a thermodynamic ground state of the material is realized from the outset, and said state cannot be converted into a further ground state at a thermodynamically lower level as a result of high doses of EUV radiation. As an alternative to a single surface protecting layer SPL, it is also possible to design a surface layer system P′ of the mirror 1a from FIG. 1 in such a way that it affords sufficient protection for the underlying substrate on account of its absorption. For this purpose, the surface layer system should have a corresponding number of layers. In particular, a surface layer system P′ having a number of periods that exceeds the number of periods of the surface layer systems P″ and P′″ of a layer arrangement for an EUV mirror is suitable for this purpose. In this case, the reflectivity properties, the transmission properties and the stress properties of all the layers simultaneously have to be taken into account during each overall optimization of a layer arrangement. Specific surface protecting layer systems SPLS as discussed below with reference to FIGS. 2a and 3a are likewise suitable for sufficiently protecting the substrate of the mirror 1a in FIG. 1 from EUV radiation. In this case, at least one layer composed of graphene G, B is used for smoothing the surface. Furthermore, it is possible to use layers composed of graphene G, B both in the surface protecting layer system SPLS in FIGS. 2a and 3a and in the surface layer systems in FIGS. 1 to 3a as so-called barrier layers that prevent the interdiffusion of adjacent layers. In this case, a layer composed of graphene G, B consists at least of a monolayer composed of graphene. In this case, monolayers or bilayers composed of graphene can be disregarded in the implementation of the layer design with regard to their refractive index. By contrast, the layers G, B should be taken into account in the layer design starting from a thickness of approximately four monolayers of graphene. Since no values are known for the refractive index of a few layers composed of graphene at 13.5 nm, the values of graphite such as are reproduced in Table 2a should be used for the implementation of layer designs. Layers composed of graphene can be deposited on areas, or transferred thereto, in any desired size in accordance with the method specified in WO 2009/129194. In the case of quartz or nickel layers as SPL or SPLS according to the present invention, direct CVD deposition from WO 2009/129194 is appropriate. This gives rise to layers composed of graphene which comprise both monolayers and multilayers composed of graphene. It is thereby possible to compensate for the unevennesses of the layer situated directly below the graphene. Furthermore, such layers are “atomically smooth”, see the discussion of the roughness of a layer composed of graphene G, B with reference to FIGS. 16 to 23. Alternatively, multilayers composed of graphene can be deposited directly onto mirror substrates composed of Si, Cu or alloys thereof in accordance with WO 2009/129194 and can act as an SPL. For this purpose, however, the further surface layer systems of the layer arrangement have to be designed accordingly with regard to transmission, since graphene is not absorbent to the same extent as nickel, for example, see Table 2a. Alternatively, multilayers composed of graphene can also be deposited on a quartz layer in accordance with WO 2009/129194 and can act together with the latter as an SPL. FIG. 2 shows a schematic illustration of a mirror 1b according to the invention for the EUV wavelength range comprising a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of surface layer systems P′, P″ and P′″ each consisting of a periodic sequence of at least two periods P1, P2 and P3 of individual layers, wherein the periods P1, P2 and P3 comprise two individual layers composed of different materials for a high refractive index layer H′, H″ and H′″ and a low refractive index layer L′, L″ and L′″ and have within each surface layer system P′, P″ and P′″ a constant thickness d1, d2 and d3 that deviates from a thickness of the periods of an adjacent surface layer system. In this case, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate. In this case, unlike in the case of the exemplary embodiment concerning FIG. 1, the surface layer system P″ that is second most distant from the substrate has a sequence of the periods P2 which corresponds to the sequence of the periods P1 and P3 of the other surface layer systems P′ and P′″, such that the first high refractive index layer H′″ of the surface layer system P′″ that is most distant from the substrate optically actively succeeds the last low refractive index layer L″ of the surface layer system P″ that is second most distant from the substrate. FIG. 2a shows a mirror 1b′ according to the invention corresponding to the mirror 1b according to the invention in FIG. 2, the third surface layer system P′ of which is designed as a surface protecting layer system SPLS. In this case, the surface protecting layer system SPLS comprises a plurality of periods of a high refractive index layer Hp, a low refractive index layer Lp and two barrier layers B. In this case, the low refractive index layer consists of a metal, such as e.g. nickel or cobalt, and accordingly has a high absorption for EUV radiation, see Table 2a. In this case, the total thickness of the layers Lp of the surface protecting layer system SPLS corresponds approximately to the thickness of the surface protecting layer SPL in accordance with the mirror 1a′ according to the invention from FIG. 1a. A surface protecting layer SPL in accordance with the exemplary embodiment 1a′ in FIG. 1a can be used between the layer arrangement of the mirror 1b and the substrate or as a replacement of the surface protecting layer system SPLS of the mirror 1b′ in FIG. 2a. The advantage of a surface protecting layer system SPLS over an individual surface protecting layer SPL is that possible crystal growth of the metal layers is prevented by the high refractive index layers. Such crystal growth leads to rough surfaces of the metal layers and this in turn leads to undesired stray light losses, as already mentioned in the introduction. Silicon as material of a high refractive index layer of a period is suitable for the metal nickel, whereas beryllium as high refractive index layer is suitable for the metal cobalt. In order to prevent interdiffusion of these layers mentioned, it is possible to use barrier layers B such as are discussed in further association with other high and low refractive index layers in the context of this application. In particular layers composed of graphene as barrier layers B firstly prevent interdiffusion and secondly lead to “atomically smooth” surfaces, see the discussion concerning FIGS. 16 to 23. FIG. 3 shows a schematic illustration of a further mirror 1c according to the invention for the EUV wavelength range comprising a substrate S and a layer arrangement. In this case, the layer arrangement comprises a plurality of surface layer systems P″ and P′″ each consisting of a periodic sequence of at least two periods P2 and P3 of individual layers, wherein the periods P2 and P3 comprise two individual layers composed of different materials for a high refractive index layer H″ and H′″ and a low refractive index layer L″ and L′″ and have within each surface layer system P″ and P′″ a constant thickness d2 and d3 that deviates from a thickness of the periods of an adjacent surface layer system. In this case, in a fourth exemplary embodiment in accordance with the description concerning FIGS. 14 and 15, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate. This fourth exemplary embodiment also comprises, as a variant with respect to the illustration of the mirror 1c in FIG. 3 corresponding to mirror 1a, the reversed order of the layers in the surface layer system P″ that is second most distant from the substrate S, such that this fourth exemplary embodiment also has the feature that the first high refractive index layer H′″ of the surface layer system P′″ that is most distant from the substrate optically actively succeeds the last low refractive index layer L″ of the surface layer system P″ that is second most distant from the substrate. Particularly in the case of a small number of surface layer systems of, for example, just two surface layer systems, it is found that high reflectivity values are obtained if the period P3 for the surface layer system P′″ that is most distant from the substrate has a thickness of the high refractive index layer H′″ which amounts to more than 120% of the thickness, in particular more than double the thickness, of the high refractive index layer H″ of the period P2 for the surface layer system P″ that is second most distant from the substrate. FIG. 3a shows a schematic illustration of a further mirror 1c′ according to the invention, said mirror differing from the mirror 1c in FIG. 3 in that the surface layer system P″ that is situated closest to the substrate is embodied as a surface protecting layer system SPLS. In FIG. 3a, said surface protecting layer system SPLS merely consists of layers Lp interrupted by barrier layers B. The barrier layers B serve, as already discussed above concerning FIG. 2a, to interrupt the crystal growth of the layers Lp. The surface protecting layer system SPLS illustrated in FIG. 3a can be replaced by other surface protecting layers SPL or other surface protecting layer systems SPLS as discussed in association with FIG. 1a and FIG. 2a. In this case, the surface protecting layer system SPLS illustrated in FIG. 3a merely represents a simplified surface protecting layer system SPLS by comparison with the surface protecting layer system illustrated in FIG. 2a, in which the high refractive index layers Hp have been dispensed with. Consequently, the surface protecting layer system SPLS in FIG. 3a corresponding to the surface protecting layer SPL in FIG. 1a is restricted purely to the protection function for the substrate (S) by absorption and therefore has only little interaction with regard to the optical properties of the other surface layer systems. By contrast, the surface protecting layer system in FIG. 2a has a double function by virtue of the fact that, owing to its absorption properties, it provides for the protection of the substrate and by virtue of the fact that, owing to its reflection properties, it contributes to the reflection and thus to the optical performance of the mirror. The transition in the designation of a layer system from a surface protecting layer system SPLS to a surface layer system P′, P″ or P′″ of the layer arrangement is fluid here since, as already discussed above in association with FIG. 1a, a surface layer system P′ of the mirror 1a, given a corresponding design with a multiplicity of periods, also both contributes to the reflectivity effect of the mirror and undertakes a protective effect with respect to the substrate on account of the increased absorption of the multiplicity of periods. In contrast to the reflectivity, all of the layers of a layer arrangement have to be taken into account when considering the layer stresses of a layer design. The surface layer systems of the layer arrangement of the mirrors according to the invention with respect to FIGS. 1, 2 and 3 succeed one another directly and are not separated by a further layer system. However, separation of the surface layer systems by an individual intermediate layer is conceivable for adapting the surface layer systems to one another or for optimizing the optical properties of the layer arrangement. This last does not apply, however, to the two surface layer systems P″ and P′″ of the first exemplary embodiment with respect to FIG. 1 and the fourth exemplary embodiment as a variant with respect to FIG. 3 since the desired optical effect would thereby be prevented by the reversal of the sequence of the layers in P″. The layers designated by H, Hp, H′, H″ and H′″ in FIGS. 1 to 3a are layers composed of materials which, in the EUV wavelength range, can be designated as high refractive index layers in comparison with the layers of the same surface layer system which are designated as L, Lp, L′, L″ and L′″, see the complex refractive indices of the materials in Table 2 and Table 2a. Conversely, the layers designated by L, Lp, L′, L″ and L′″ in FIGS. 1 to 3a are layers composed of materials which, in the EUV wavelength range, can be designated as low refractive index layers in comparison with the layers of the same surface layer system which are designated as H, Hp, H′, H″ and H′″. Consequently, the terms high refractive index and low refractive index are relative terms with regard to the respective partner layer in a period of a surface layer system. Surface layer systems function generally only if a layer that acts optically with a high refractive index is combined with a layer that optically has a lower refractive index relative thereto, as main constituent of a period of the surface layer system. The material silicon is generally used for high refractive index layers. In combination with silicon, the materials molybdenum and ruthenium should be designated as low refractive index layers, see the complex refractive indices of the materials in Table 2. In FIGS. 1 to 3a, a barrier layer B is in each case situated between the individual layers of a period, said barrier layer consisting of a material which is selected from or as a compound is composed of the group of materials: B4C, C, graphene, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride. Such a barrier layer suppresses the interdiffusion between the two individual layers of a period, thereby increasing the optical contrast in the transition of the two individual layers. With the use of the materials molybdenum and silicon for the two individual layers of a period, one barrier layer above the silicon layer, as viewed from the substrate, suffices in order to provide for a sufficient contrast. The second barrier layer above the molybdenum layer can be dispensed with in this case. In this respect, at least one barrier layer for separating the two individual layers of a period should be provided, wherein the at least one barrier layer may perfectly well be constructed from various ones of the above-indicated materials or the compounds thereof and may in this case also exhibit a layered construction of different materials or compounds. Barrier layers which comprise the material B4C and have a thickness of between 0.35 nm and 0.8 nm, preferably between 0.4 nm and 0.6 nm, lead in practice to high reflectivity values of the layer arrangement. Particularly in the case of surface layer systems composed of ruthenium and silicon, barrier layers composed of B4C exhibit a maximum of reflectivity in the case of values of between 0.4 nm and 0.6 nm for the thickness of the barrier layer. Barrier layers composed of graphene lead to very smooth surfaces and thus reduce stray light losses. In the case of the mirrors 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention, the number Np, N1, N2 and N3 of periods Pp, P1, P2 and P3 of the surface layer systems SPLS, P′, P″ and P′″ can comprise in each case up to 100 periods of the individual periods Pp, P1, P2 and P3 illustrated in FIGS. 1 to 3a. Furthermore, between the layer arrangements illustrated in FIGS. 1 to 3a and the substrate S, an additional intermediate layer or an additional intermediate layer arrangement can be provided, which serves for the stress compensation of the layer arrangement with respect to the substrate. The same materials in the same sequence as for the layer arrangement itself can be used as materials for the additional intermediate layer or the additional intermediate layer arrangement for stress compensation. In the case of the intermediate layer arrangement, however, it is possible to dispense with the barrier layer between the individual layers since the intermediate layer or the intermediate layer arrangement generally makes a negligible contribution to the reflectivity of the mirror and so the issue of an increase in contrast by the barrier layer is unimportant in this case. Multilayer arrangements composed of alternating chromium and scandium layers or amorphous molybdenum or ruthenium layers would likewise be conceivable as the additional intermediate layer or intermediate layer arrangement for stress compensation. The latter can likewise be chosen in terms of their thickness, e.g. greater than 20 nm, such that an underlying substrate is sufficiently protected from EUV radiation. In this case, the additional intermediate layer or the additional intermediate layer arrangement would likewise act as a surface protecting layer SPL or as a surface protecting layer system SPLS, respectively, and protect the substrate from EUV radiation. The layer arrangements of the mirrors 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention are terminated in FIGS. 1 to 3a by a covering layer system C comprising at least one layer composed of a chemically inert material such as e.g. Rh, Pt, Ru, Pd, Au, SiO2 etc. as a terminating layer M. Said terminating layer M thus prevents the chemical alteration of the mirror surface on account of ambient influences. The covering layer system C in FIGS. 1 to 3a consists, besides the terminating layer M, of a high refractive index layer H, a low refractive index layer L and a barrier layer B. The thickness of one of the periods Pp, P1, P2 and P3 results from FIGS. 1 to 3a as the sum of the thicknesses of the individual layers of the corresponding period, that is to say from the thickness of the high refractive index layer, the thickness of the low refractive index layer and the thickness of two barrier layers. Consequently, the surface layer systems SPLS, P′, P″ and P′″ in FIGS. 1 to 3a, given the same choice of material, can be distinguished from one another by virtue of the fact that their periods Pp, P1, P2 and P3 have a different thickness d1, d2 and d3. Consequently, in the context of the present invention, different surface layer systems SPLS, P′, P″ and P′″ given the same choice of material are understood to be surface layer systems whose produced periods Pp, P1, P2 and P3 differ by more than 0.1 nm in their thicknesses d1, d2 and d3, since a different optical effect of the surface layer systems can no longer be assumed below a difference of 0.1 nm given otherwise identical division of the periods between high and low refractive index layers. Furthermore, inherently identical surface layer systems can fluctuate by this absolute value in their period thicknesses during their production on different production apparatuses. For the case of a surface layer system SPLS, P′, P″ and P′″ having a period composed of molybdenum and silicon, it is also possible, as already described above, to dispense with the second barrier layer within the period Pp, P1, P2 and P3, such that in this case the thickness of the periods Pp, P1, P2 and P3 results from the thickness of the high refractive index layer, the thickness of the low refractive index layer and the thickness of a barrier layer. FIG. 4 shows a schematic illustration of a projection objective 2 according to the invention for a projection exposure apparatus for microlithography having six mirrors 1, 11, including at least one mirror 1 configured on the basis of the mirrors 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention in accordance with the exemplary embodiments with respect to FIGS. 8 to 15. The task of a projection exposure apparatus for microlithography is to image the structures of a mask, which is also referred to as a reticle, lithographically onto a so-called wafer in an image plane. For this purpose, a projection objective 2 according to the invention in FIG. 4 images an object field 3, which is arranged in the object plane 5, into an image field in the image plane 7. The structure-bearing mask, which is not illustrated in the drawing for the sake of clarity, can be arranged at the location of the object field 3 in the object plane 5. For orientation purposes, FIG. 4 illustrates a system of Cartesian coordinates, the x-axis of which points into the plane of the figure. In this case, the x-y coordinate plane coincides with the object plane 5, the z-axis being perpendicular to the object plane 5 and pointing downward. The projection objective has an optical axis 9, which does not run through the object field 3. The mirrors 1, 11 of the projection objective 2 have a design surface that is rotationally symmetrical with respect to the optical axis. In this case, said design surface must not be confused with the physical surface of a finished mirror, since the latter surface is trimmed relative to the design surface in order to ensure passages of light past the mirror. In this exemplary embodiment, the aperture stop 13 is arranged on the second mirror 11 in the light path from the object plane 5 to the image plane 7. The effect of the projection objective 2 is illustrated with the aid of three rays, the principal ray 15 and the two aperture marginal rays 17 and 19, all of which originate in the center of the object field 3. The principal ray 15, which runs at an angle of 6° with respect to the perpendicular to the object plane, intersects the optical axis 9 in the plane of the aperture stop 13. As viewed from the object plane 5, the principal ray 15 appears to intersect the optical axis in the entrance pupil plane 21. This is indicated in FIG. 4 by the dashed extension of the principal ray 15 through the first mirror 11. Consequently, the virtual image of the aperture stop 13, the entrance pupil, lies in the entrance pupil plane 21. The exit pupil of the projection objective could likewise be found with the same construction in the backward extension of the principal ray 15 proceeding from the image plane 7. However, in the image plane 7 the principal ray 15 is parallel to the optical axis 9, and from this it follows that the backward projection of these two rays produces a point of intersection at infinity in front of the projection objective 2 and the exit pupil of the projection objective 2 is thus at infinity. Therefore, this projection objective 2 is a so-called objective that is telecentric on the image side. The center of the object field 3 is at a distance R from the optical axis 9 and the center of the image field 7 is at a distance r from the optical axis 9, in order that no undesirable vignetting of the radiation emerging from the object field occurs in the case of the reflective configuration of the projection objective. FIG. 5 shows a plan view of an arcuate image field 7a such as occurs in the projection objective 2 illustrated in FIG. 4, and a system of Cartesian coordinates, the axes of which correspond to those from FIG. 4. The image field 7a is a sector from an annulus, the center of which is given by the point of intersection of the optical axis 9 with the object plane. The average radius r is 34 mm in the case illustrated. The width of the field in the y-direction d is 2 mm here. The central field point of the image field 7a is marked as a small circle within the image field 7a. As an alternative, a curved image field can also be delimited by two circle arcs which have the same radius and are displaced relative to one another in the y-direction. If the projection exposure apparatus is operated as a scanner, then the scanning direction runs in the direction of the shorter extent of the object field, that is to say in the direction of the y-direction. FIG. 6 shows an exemplary illustration of the maximum angles of incidence (rectangles) and of the interval lengths of the angle of incidence intervals (circles) in the unit degrees [°] against different radii or distances between the locations of the mirror surface and the optical axis, indicated in the unit [mm], of the penultimate mirror 1 in the light path from the object plane 5 to the image plane 7 of the projection objective 2 from FIG. 4. Said mirror 1, in the case of a projection objective 2 for microlithography which has six mirrors 1, 11 for the EUV wavelength range, is generally that mirror which has to ensure the largest angles of incidence and the largest angle of incidence intervals or the greatest variation of angles of incidence. In the context of this application, the interval length of an angle of incidence interval as a measure of the variation of angles of incidence is understood to be the number of angular degrees of that angular range in degrees between the maximum and minimum angles of incidence which the coating of the mirror has to ensure for a given distance from the optical axis on account of the requirements of the optical design. The angle of incidence interval will also be abbreviated to AOI interval. The optical data of the projection objective in accordance with Table 1 are applicable in the case of the mirror 1 on which FIG. 6 is based. In this case, the aspheres of the mirrors 1, 11 of the optical design are specified as rotationally symmetrical surfaces utilizing the perpendicular distance Z(h) of an asphere point relative to the tangential plane in the asphere vertex as a function of the perpendicular distance h of the asphere point with respect to the normal in the asphere vertex in accordance with the following asphere equation:Z(h)=(rho*h2)/(1+[1−(1+ky)*(rho*h)2]0.5)++c1*h4+c2*h6+c3*h8+c4*h10+c5*h12+c6*h14 with the radius R=1/rho of the mirror and the parameters ky, c1, c2, c3, c4, c5, and c6 in the unit [mm]. In this case, said parameters are normalized with regard to the unit [mm] in accordance with [1/mm2n+2] in such a way as to result in the asphere Z(h) as a function of the distance h also in the unit [mm]. TABLE 1Data of the optical design regarding the angles of incidence of the mirror 1 in FIG.6 in accordance with the schematic illustration of the design on the basis of FIG. 4.Designation ofthe surface inDistance from theaccordance withnearest surface inAsphere parameters with theFIG. 2Radius R in [mm][mm]unit [1/mm2n+2] for cnObject plane 5infinity697.6578210796431st mirror 11−3060.189398512395494.429629463009ky = 0.00000000000000E+00c1 = 8.46747658600840E−10c2 = −6.38829035308911E−15c3 = 2.99297298249148E−20c4 = 4.89923345704506E−25c5 = −2.62811636654902E−29c6 = 4.29534493103729E−342nd mirror 11−1237.831140064837716.403660000000ky = 3.05349335818189E+00-- diaphragm --c1 = 3.01069673080653E−10c2 = 3.09241275151742E−16c3 = 2.71009214786939E−20c4 = −5.04344434347305E−24c5 = 4.22176379615477E−28c6 = −1.41314914233702E−323rd mirror 11318.277985359899218.770165786534ky = −7.80082610035452E−01c1 = 3.12944645776932E−10c2 = −1.32434614339199E−14c3 = 9.56932396033676E−19c4 = −3.13223523243916E−23c5 = 4.73030659773901E−28c6 = −2.70237216494288E−334th mirror 11−513.327287349838892.674538915941ky = −1.05007411819774E−01c1 = −1.33355977877878E−12c2 = −1.71866358951357E−16c3 = 6.69985430179187E−22c4 = 5.40777151247246E−27c5 = −1.16662974927332E−31c6 = 4.19572235940121E−37Mirror 1378.800274177878285.840721874570ky = 0.00000000000000E+00c1 = 9.27754883183223E−09c2 = 5.96362556484499E−13c3 = 1.56339572303953E−17c4 = −1.41168321383233E−21c5 = 5.98677250336455E−25c6 = −6.30124060830317E−295th mirror 11−367.938526548613325.746354374172ky = 1.07407597789597E−01c1 = 3.87917960004046E−11c2 = −3.43420257078373E−17c3 = 2.26996395088275E−21c4 = −2.71360350994977E−25c5 = 9.23791176750829E−30c6 = −1.37746833100643E−34Image plane 7infinity It can be discerned from FIG. 6 that maximum angles of incidence of 24° and interval lengths of 11° occur at different locations of the mirror 1. Consequently, the layer arrangement of the mirror 1 has to yield high and uniform reflectivity values at these different locations for different angles of incidence and different angle of incidence intervals, since otherwise a high total transmission and an acceptable pupil apodization of the projection objective 2 cannot be ensured. The so-called PV value is used as a measure of the variation of the reflectivity of a mirror over the angles of incidence. In this case, the PV value is defined as the difference between the maximum reflectivity Rmax and the minimum reflectivity Rmin the angle of incidence interval under consideration divided by the average reflectivity Raverage in the angle of incidence interval under consideration. Consequently, PV=(Rmax−Rmin)/Raverage holds true. In this case, it should be taken into consideration that high PV values for a mirror 1 of the projection objective 2 as penultimate mirror before the image plane 7 in accordance with FIG. 4 and the design in Table 1 lead to high values for the pupil apodization. In this case, there is a correlation between the PV value of the mirror 1 and the imaging aberration of the pupil apodization of the projection objective 2 for high PV values of greater than 0.25 since, starting from this value, the PV value dominates the pupil apodization relative to other causes of aberration. In FIG. 6, a bar 23 is used to mark by way of example a specific radius or a specific distance of the locations of the mirror 1 having the associated maximum angle of incidence of approximately 21° and the associated interval length of 11° with respect to the optical axis. Said marked radius corresponds in FIG. 7, described below, to the locations on the circle 23a—illustrated in dashed fashion—within the hatched region 20, which represents the optically used region 20 of the mirror 1. FIG. 7 shows the substrate S of the penultimate mirror 1 in the light path from the object plane 5 to the image plane 7 of the projection objective 2 from FIG. 4 as a circle centered with respect to the optical axis 9 in plan view. In this case, the optical axis 9 of the projection objective 2 corresponds to the axis 9 of symmetry of the substrate. Furthermore, in FIG. 7, the optically used region 20 of the mirror 1, said region being offset with respect to the optical axis, is depicted in hatched fashion and a circle 23a is depicted in dashed fashion. In this case, the part of the dashed circle 23a within the optically used region corresponds to the locations of the mirror 1 which are identified by the depicted bar 23 in FIG. 6. Consequently, the layer arrangement of the mirror 1 along the partial region of the dashed circle 23a within the optically used region 20, in accordance with the data from FIG. 6, has to ensure high reflectivity values both for a maximum angle of incidence of 21° and for a minimum angle of incidence of approximately 10°. In this case, the minimum angle of incidence of approximately 10° results from the maximum angle of incidence of 21° from FIG. 6 on account of the interval length of 11°. The locations on the dashed circle at which the two abovementioned extreme values of the angles of incidence occur are emphasized in FIG. 7 by the tip of the arrow 26 for the angle of incidence of 10° and by the tip of the arrow 25 for the angle of incidence of 21°. Since a layer arrangement cannot be varied locally over the locations of a substrate S without high technological outlay and layer arrangements are generally applied rotationally symmetrically with respect to the axis 9 of symmetry of the substrate, the layer arrangement along the locations of the dashed circle 23a in FIG. 7 comprises one and the same layer arrangement such as is shown in its basic construction in FIGS. 1 to 3a and is explained in the form of specific exemplary embodiments with reference to FIGS. 8 to 15. In this case, it should be taken into consideration that a rotationally symmetrical coating of the substrate S with respect to the axis 9 of symmetry of the substrate S with the layer arrangement has the effect that the periodic sequence of the surface layer systems SPLS, P′, P″ and P′″ of the layer arrangement is maintained at all locations of the mirror and only the thickness of the periods of the layer arrangement depending on the distance from the axis 9 of symmetry acquires a rotationally symmetrical profile over the substrate S, the layer arrangement being thinner at the edge of the substrate S than in the center of the substrate S at the axis 9 of symmetry. It should be taken into consideration that it is possible, through a suitable coating technology, for example through use of distribution diaphragms, to adapt the rotationally symmetrical radial profile of the thickness of a coating over the substrate. Consequently, in addition to the design of the coating per se, with the radial profile of the so-called thickness factor of the coating design over the substrate, a further degree of freedom is available for optimizing the coating design. The reflectivity values illustrated in FIGS. 8 to 15 were calculated using the complex refractive indices ñ=n−i*k indicated in Table 2 for the used materials at the wavelength of 13.5 nm. In this case, it should be taken into consideration that reflectivity values of real mirrors can turn out to be lower than the theoretical reflectivity values illustrated in FIGS. 8 to 15, since in particular the refractive indices of real thin layers can deviate from the literature values mentioned in Table 2. The refractive indices employed for the materials of the surface protecting layer SPL, Lp and the surface protecting layer system SPLS and for graphene G, SPL, B are indicated in Table 2a. TABLE 2Employed refractive indices ñ = n − i*k for 13.5 nmChemicalLayer designMaterialsymbolsymbolnkSubstrate0.9737130.0129764SiliconSiH, H′, H″, H″′0.9993620.00171609Boron carbideB4CB0.9637730.0051462MolybdenumMoL, L′, L″, L″′0.9212520.0064143RutheniumRuM, L, L′, L″, L″′0.8890340.0171107Vacuum10 TABLE 2aEmployed refractive indices ñ = n −i*k for 13.5 nm for materials for the surface protectinglayer SPL and the surface protecting layer system SPLSChemicalLayer designMaterialsymbolsymbolnkQuartzSiO2SPL, Lp0.97840.0107NickelNiSPL, Lp0.94830.0727CobaltCoSPL, Lp0.93350.0660SiliconSiHp0.99940.0017BerylliumBeHp0.98880.0018Boron carbideB4CB0.96380.0051CarbonCB0.96170.0069GraphiteCG, SPL, B0.96170.0069 Moreover, the following short notation in accordance with the layer sequence with respect to FIGS. 1, 2 and 3 is declared for the layer designs associated with FIGS. 8 to 15: Substrate/ . . . /(P1)*N1/(P2)*N2/(P3)*N3/covering layer system C where P1=H′ B L′ B; P2=H″ B L″ B; P3=H′″ B L′″ B; C=H B L M; for FIGS. 2 and 3 and where P1=B H′B L′; P2=B L″B H″; P3=H′″B L′″B; C=H B L M; for FIG. 1 and for the fourth exemplary embodiment as a variant with respect to FIG. 3. In this case, the letters H symbolically represent the thickness of high refractive index layers, the letters L represent the thickness of low refractive index layers, the letter B represents the thickness of the barrier layer and the letter M represents the thickness of the chemically inert terminating layer in accordance with Table 2 and the description concerning FIGS. 1, 2 and 3. In this case, the unit [nm] applies to the thicknesses of the individual layers that are specified between the parentheses. The layer design used with respect to FIGS. 8 and 9 can thus be specified as follows in the short notation: Substrate/ . . . /(0.4B4C2.921Si0.4B4C4.931Mo)*8/(0.4B4C4.145Mo0.4B4C2.911Si)*5/(3.509Si0.4B4C3.216Mo0.4B4C)*16/2.975Si0.4B4C2Mo1.5Ru Since the barrier layer B4C in this example is always 0.4 nm thick, it can also be omitted for illustrating the basic construction of the layer arrangement, such that the layer design with respect to FIGS. 8 and 9 can be specified in a manner shortened as follows: Substrate/ . . . /(2.921Si4.931Mo)*8/(4.145Mo2.911Si)*5/(3.509Si3.216Mo)*16/2.975Si2Mo1.5Ru It should be recognized from this first exemplary embodiment according to FIG. 1 that the order of the high refractive index layer Si and the low refractive index layer Mo in the second surface layer system, comprising five periods, has been reversed relative to the other surface layer systems, such that the first high refractive index layer of the surface layer system that is most distant from the substrate, with a thickness of 3.509 nm, directly succeeds the last high refractive index layer of the surface layer system that is second most distant from the substrate, with a thickness of 2.911 nm. Correspondingly, it is possible to specify the layer design used with respect to FIGS. 10 and 11 as second exemplary embodiment in accordance with FIG. 2 in the short notation as: Substrate/ . . . /(4.737Si0.4B4C2.342Mo0.4B4C)*28/(3.443Si0.4B4C2.153Mo0.4B4C)*5/(3.523Si0.4B4C3.193Mo0.4B4C)*15/2.918Si0.4B4C2Mo1.5Ru Since the barrier layer B4C in this example is in turn always 0.4 nm thick, it can also be omitted for illustrating this layer arrangement, such that the layer design with respect to FIGS. 10 and 11 can be specified in a manner shortened as follows: Substrate/ . . . /(4.737Si2.342Mo)*28/(3.443Si2.153Mo)*5/(3.523Si3.193Mo)*15/2.918Si2Mo1.5Ru Accordingly, it is possible to specify the layer design used with respect to FIGS. 12 and 13 as third exemplary embodiment in accordance with FIG. 3 in the short notation as: Substrate/ . . . /(1.678Si0.4B4C5.665Mo0.4B4C)*27/(3.798Si0.4B4C2.855Mo0.4B4C)*14/1.499Si0.4B4C2Mo1.5Ru and, disregarding the barrier layer B4C for illustration purposes, as: Substrate/ . . . /(1.678Si5.665Mo)*27/(3.798Si2.855Mo)*14/1.499Si2Mo1.5Ru Likewise, it is possible to specify the layer design used with respect to FIGS. 14 and 15 as fourth exemplary embodiment in accordance with a variant with respect to FIG. 3 in the short notation as: Substrate/ . . . /(0.4B4C4.132Mo0.4B4C2.78Si)*6/(3.608Si0.4B4C3.142Mo0.4B4C)*16/2.027Si0.4B4C2Mo1.5Ru and, disregarding the barrier layer B4C for illustration purposes, as: Substrate/ . . . /(4.132Mo2.78Si)*6/(3.609Si3.142Mo)*16/2.027Si2Mo1.5Ru It should be recognized from this fourth exemplary embodiment that the order of the high refractive index layer Si and the low refractive index layer Mo in the surface layer system P″, comprising six periods, has been reversed relative to the other surface layer system P′″ having 16 periods, such that the first high refractive index layer of the surface layer system P′″ that is most distant from the substrate, with a thickness of 3.609 nm, directly succeeds the last high refractive index layer of the surface layer system P″ that is second most distant from the substrate, with a thickness of 2.78 nm. This fourth exemplary embodiment is therefore a variant of the third exemplary embodiment in which the order of the high and low refractive index layers in the surface layer system P″ that is second most distant from the substrate has been reversed according to the first exemplary embodiment with respect to FIG. 1. The layer designs specified above can also be provided with a surface protecting layer SPL or a surface protecting layer system SPLS, such that it is possible e.g. to specify the first layer design with respect to FIGS. 8 to 9 with a 2 μm thick quartz layer and a layer composed of graphene G in accordance with FIG. 1a as: Substrate/2000SiO2/G(0.4B4C2.921Si0.4B4C4.931Mo)*8/(0.4B4C4.145Mo0.4B4C2.911Si)*5/(3.509Si0.4B4C3.216Mo0.4B4C)*16/2.975Si0.4B4C2Mo1.5Ru Correspondingly, it is possible to specify this layer design with a 100 nm thick nickel layer as surface protecting layer SPL and a layer composed of graphene G in accordance with FIG. 1a as: Substrate/100Ni/G(0.4B4C2.921Si0.4B4C4.931Mo)*8/(0.4B4C4.145Mo0.4B4C2.911Si)*5/(3.509Si0.4B4C3.216Mo0.4B4C)*16/2.975Si0.4B4C2Mo1.5Ru As an alternative, it is possible to specify this layer design with a surface protecting layer system SPLS consisting of 20 periods of 5 nm thick nickel layers which are separated by layers composed of graphene G, B, in accordance with FIG. 3a as: Substrate/(5NiG)*20/(0.4B4C2.921Si0.4B4C4.931Mo)*8/(0.4B4C4.145Mo0.4B4C2.911Si)*5/(3.509Si0.4B4C3.216Mo0.4B4C)*16/2.975Si0.4B4C2Mo1.5Ru In this case, it should be taken into consideration that individual surface protecting layers SPL composed of quartz or nickel have only a small influence on the reflectivity curves of the layer designs with respect to FIGS. 8 to 15. The alteration of the reflectivity values is approximately 1% in this case. Layers composed of graphene which consist only of a few monolayers can in this case be disregarded in terms of their influence on the reflectivity curves. However, layers composed of graphene should be taken into account in the layer design starting from a thickness corresponding to 4 monolayers of graphene with the optical constants of thin graphite layers. A surface protecting layer system SPLS composed of 20 periods of 5 nm thick nickel layers which are separated by layers composed of graphene has the effect that the reflectivity curves of the layer designs with respect to FIGS. 8 to 15 shift by approximately an angle of incidence of 2°, such that a subsequent optimization of the layer design becomes necessary in this case given a fixedly predetermined angle of incidence interval. After such an optimization has been carried out, the alteration of the reflectivity values of these layer designs with the surface protecting layer system SPLS by comparison with the layer designs with respect to FIGS. 8 to 15 is approximately 2%. In this case, too, relatively thick layers composed of graphene can no longer be disregarded in the optimization. FIG. 8 shows reflectivity values for unpolarized radiation in the unit [%] of the first exemplary embodiment of a mirror 1a according to the invention in accordance with FIG. 1 plotted against the angle of incidence in the unit [°]. In this case, the first surface layer system P′ of the layer arrangement of the mirror 1a consists of N1=8 periods P1, wherein the period P1 consists of 2.921 nm Si as high refractive index layer and 4.931 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P1 consequently has a thickness d1 of 8.652 nm. The second surface layer system P″ of the layer arrangement of the mirror 1a having the reversed order of the layers Mo and Si consists of N2=5 periods P2, wherein the period P2 consists of 2.911 nm Si as high refractive index layer and 4.145 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P2 consequently has a thickness d2 of 7.856 nm. The third surface layer system P′″ of the layer arrangement of the mirror 1a consists of N3=16 periods P3, wherein the period P3 consists of 3.509 nm Si as high refractive index layer and 3.216 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P3 consequently has a thickness d3 of 7.525 nm. The layer arrangement of the mirror 1a is terminated by a covering layer system C consisting of 2.975 nm Si, 0.4 nm B4C, 2 nm Mo and 1.5 nm Ru in the order specified. Consequently, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate and the first high refractive index layer H′″ of the surface layer system P′″ that is most distant from the substrate directly succeeds the last high refractive index layer H″ of the surface layer system P″ that is second most distant from the substrate. The reflectivity values of this nominal layer design with the thickness factor 1 in the unit [%] at a wavelength of 13.5 nm are illustrated as a solid line against the angle of incidence in the unit [°] in FIG. 8. Moreover, the average reflectivity of this nominal layer design for the angle of incidence interval of 14.1° to 25.7° is depicted as a solid horizontal bar. Furthermore, FIG. 8 correspondingly specifies, at a wavelength of 13.5 nm and given a thickness factor of 0.933, as a dashed line the reflectivity values against the angles of incidence and as a dashed bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 2.5° to 7.3°. Consequently, the thicknesses of the periods of the layer arrangement with respect to the reflectivity values illustrated as a dashed line in FIG. 8 amount to only 93.3% of the corresponding thicknesses of the periods of the nominal layer design. In other words, the layer arrangement is thinner than the nominal layer design by 6.7% at the mirror surface of the mirror 1a at the locations at which angles of incidence of between 2.5° and 7.3° have to be ensured. FIG. 9 shows, at a wavelength of 13.5 nm and given a thickness factor of 1.018, in a manner corresponding to FIG. 8, as a thin line the reflectivity values against the angles of incidence and as a thin bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 17.8° to 27.2°, and also, given a thickness factor of 0.972, in a corresponding manner, as a thick line the reflectivity values against the angles of incidence and as a thick bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 8.7° to 21.4°. Consequently, the layer arrangement is thicker than the nominal layer design by 1.8% at the mirror surface of the mirror 1a at the locations at which angles of incidence of between 17.8° and 27.2° have to be ensured and is correspondingly thinner than the nominal layer design by 2.8% at the locations at which angles of incidence of between 8.7° and 21.4° have to be ensured. The average reflectivity and PV values which can be achieved by the layer arrangement with respect to FIG. 8 and FIG. 9 are compiled relative to the angle of incidence intervals and the thickness factors in Table 3. It can be discerned that the mirror 1a comprising the layer arrangement specified above, at a wavelength of 13.5 nm for angles of incidence of between 2.5° and 27.2°, has an average reflectivity of more than 43% and a variation of the reflectivity as PV value of less than or equal to 0.21. TABLE 3Average reflectivity and PV values of the layer design withrespect to FIG. 8 and FIG. 9 relative to the angle of incidenceinterval in degrees and the thickness factor chosen.AOI IntervalThicknessR_average[°]factor[%]PV17.8-27.21.01843.90.1414.1-25.7144.30.21 8.7-21.40.97246.40.072.5-7.30.93346.50.01 FIG. 10 shows reflectivity values for unpolarized radiation in the unit [%] of the second exemplary embodiment of a mirror 1b according to the invention in accordance with FIG. 2 plotted against the angle of incidence in the unit [°]. In this case, the first surface layer system P′ of the layer arrangement of the mirror 1b consists of N1=28 periods P1, wherein the period P1 consists of 4.737 nm Si as high refractive index layer and 2.342 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P1 consequently has a thickness d1 of 7.879 nm. The second surface layer system P″ of the layer arrangement of the mirror 1b consists of N2=5 periods P2, wherein the period P2 consists of 3.443 nm Si as high refractive index layer and 2.153 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P2 consequently has a thickness d2 of 6.396 nm. The third surface layer system P′″ of the layer arrangement of the mirror 1b consists of N3=15 periods P3, wherein the period P3 consists of 3.523 nm Si as high refractive index layer and 3.193 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P3 consequently has a thickness d3 of 7.516 nm. The layer arrangement of the mirror 1b is terminated by a covering layer system C consisting of 2.918 nm Si, 0.4 nm B4C, 2 nm Mo and 1.5 nm Ru in the order specified. Consequently, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate. The reflectivity values of this nominal layer design with the thickness factor 1 in the unit [%] at a wavelength of 13.5 nm are illustrated as a solid line against the angle of incidence in the unit [°] in FIG. 10. Moreover, the average reflectivity of this nominal layer design for the angle of incidence interval of 14.1° to 25.7° is depicted as a solid horizontal bar. Furthermore, FIG. 10 correspondingly specifies, at a wavelength of 13.5 nm and given a thickness factor of 0.933, as a dashed line the reflectivity values against the angles of incidence and as a dashed bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 2.5° to 7.3°. Consequently, the thicknesses of the periods of the layer arrangement with respect to the reflectivity values illustrated as a dashed line in FIG. 10 amount to only 93.3% of the corresponding thicknesses of the periods of the nominal layer design. In other words, the layer arrangement is thinner than the nominal layer design by 6.7% at the mirror surface of the mirror 1b at the locations at which angles of incidence of between 2.5° and 7.3° have to be ensured. FIG. 11 shows, at a wavelength of 13.5 nm and given a thickness factor of 1.018, in a manner corresponding to FIG. 10, as a thin line the reflectivity values against the angles of incidence and as a thin bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 17.8° to 27.2°, and also, given a thickness factor of 0.972, in a corresponding manner, as a thick line the reflectivity values against the angles of incidence and as a thick bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 8.7° to 21.4°. Consequently, the layer arrangement is thicker than the nominal layer design by 1.8% at the mirror surface of the mirror 1b at the locations at which angles of incidence of between 17.8° and 27.2° have to be ensured and is correspondingly thinner than the nominal layer design by 2.8% at the locations at which angles of incidence of between 8.7° and 21.4° have to be ensured. The average reflectivity and PV values which can be achieved by the layer arrangement with respect to FIG. 10 and FIG. 11 are compiled relative to the angle of incidence intervals and the thickness factors in Table 4. It can be discerned that the mirror 1b comprising the layer arrangement specified above, at a wavelength of 13.5 nm for angles of incidence of between 2.5° and 27.2°, has an average reflectivity of more than 45% and a variation of the reflectivity as PV value of less than or equal to 0.23. TABLE 4Average reflectivity and PV values of the layer design withrespect to FIG. 10 and FIG. 11 relative to the angle of incidenceinterval in degrees and the thickness factor chosen.AOI IntervalThicknessR_average[°]factor[%]PV17.8-27.21.01845.20.1714.1-25.7145.70.23 8.7-21.40.97247.80.182.5-7.30.93345.50.11 FIG. 12 shows reflectivity values for unpolarized radiation in the unit [%] of the third exemplary embodiment of a mirror 1c according to the invention in accordance with FIG. 3 plotted against the angle of incidence in the unit [°]. In this case, the surface layer system P″ of the layer arrangement of the mirror 1c consists of N2=27 periods P2, wherein the period P2 consists of 1.678 nm Si as high refractive index layer and 5.665 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P2 consequently has a thickness d2 of 8.143 nm. The surface layer system P′″ of the layer arrangement of the mirror 1c consists of N3=14 periods P3, wherein the period P3 consists of 3.798 nm Si as high refractive index layer and 2.855 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. Consequently, the period P3 has a thickness d3 of 7.453 nm. The layer arrangement of the mirror 1c is terminated by a covering layer system C consisting of 1.499 nm Si, 0.4 nm B4C, 2 nm Mo and 1.5 nm Ru in the order specified. Consequently, the surface layer system P′″ that is most distant from the substrate has a thickness of the high refractive index layer H′″ that amounts to more than double the thickness of the high refractive index layer H″ of the surface layer system P″ that is second most distant from the substrate. The reflectivity values of this nominal layer design with the thickness factor 1 in the unit [%] at a wavelength of 13.5 nm are illustrated as a solid line against the angle of incidence in the unit [°] in FIG. 12. Moreover, the average reflectivity of this nominal layer design for the angle of incidence interval of 14.1° to 25.7° is depicted as a solid horizontal bar. Furthermore, FIG. 12 correspondingly specifies, at a wavelength of 13.5 nm and given a thickness factor of 0.933, as a dashed line the reflectivity values against the angles of incidence and as a dashed bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 2.5° to 7.3°. Consequently, the thicknesses of the periods of the layer arrangement with respect to the reflectivity values illustrated as a dashed line in FIG. 12 amount to only 93.3% of the corresponding thicknesses of the periods of the nominal layer design. In other words, the layer arrangement is thinner than the nominal layer design by 6.7% at the mirror surface of the mirror 1c at the locations at which angles of incidence of between 2.5° and 7.3° have to be ensured. FIG. 13 shows in a manner corresponding to FIG. 12, at a wavelength of 13.5 nm and given a thickness factor of 1.018, as a thin line the reflectivity values against the angles of incidence and as a thin bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 17.8° to 27.2°, and also, given a thickness factor of 0.972, in a corresponding manner, as a thick line the reflectivity values against the angles of incidence and as a thick bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 8.7° to 21.4°. Consequently, the layer arrangement is thicker than the nominal layer design by 1.8% at the mirror surface of the mirror 1c at the locations at which angles of incidence of between 17.8° and 27.2° have to be ensured and is correspondingly thinner than the nominal layer design by 2.8% at the locations at which angles of incidence of between 8.7° and 21.4° have to be ensured. The average reflectivity and PV values which can be achieved by the layer arrangement with respect to FIG. 12 and FIG. 13 are compiled relative to the angle of incidence intervals and the thickness factors in Table 5. It can be discerned that the mirror 1c comprising the layer arrangement specified above, at a wavelength of 13.5 nm for angles of incidence of between 2.5° and 27.2°, has an average reflectivity of more than 39% and a variation of the reflectivity as PV value of less than or equal to 0.22. TABLE 5Average reflectivity and PV values of the layer design withrespect to FIG. 12 and FIG. 13 relative to the angle of incidenceinterval in degrees and the thickness factor chosen.AOI IntervalThicknessR_average[°]factor[%]PV17.8-27.21.01839.20.1914.1-25.7139.50.22 8.7-21.40.97241.40.172.5-7.30.93343.90.04 FIG. 14 shows reflectivity values for unpolarized radiation in the unit [%] of the fourth exemplary embodiment of a mirror according to the invention as a variant of the mirror 1c in which the order of the layers in the surface layer system P″ has been reversed, plotted against the angle of incidence in the unit [°]. In this case, the surface layer system P″ of the layer arrangement of the mirror consists of N2=6 periods P2, wherein the period P2 consists of 2.78 nm Si as high refractive index layer and 4.132 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P2 consequently has a thickness d2 of 7.712 nm. The surface layer system P′″ of the layer arrangement of the mirror consists of N3=16 periods P3, wherein the period P2 consists of 3.608 nm Si as high refractive index layer and 3.142 nm Mo as low refractive index layer, and also of two barrier layers each comprising 0.4 nm B4C. The period P3 consequently has a thickness d3 of 7.55 nm. The layer arrangement of the mirror is terminated by a covering layer system C consisting of 2.027 nm Si, 0.4 nm B4C, 2 nm Mo and 1.5 nm Ru in the order specified. Consequently, the surface layer system P′ that is most distant from the substrate has a thickness of the high refractive index layer H′″ which amounts to more than 120% of the thickness of the high refractive index layer H″ of the surface layer system P″ that is second most distant from the substrate. Furthermore, the surface layer system P′″ that is most distant from the substrate has a number N3 of periods P3 that is greater than the number N2 of periods P2 for the surface layer system P″ that is second most distant from the substrate, and the first high refractive index layer H′″ of the surface layer system P′ that is most distant from the substrate directly succeeds the last high refractive index layer H″ of the surface layer system P″ that is second most distant from the substrate. The reflectivity values of this nominal layer design with the thickness factor 1 in the unit [%] at a wavelength of 13.5 nm are illustrated as a solid line against the angle of incidence in the unit [°] in FIG. 14. Moreover, the average reflectivity of this nominal layer design for the angle of incidence interval of 14.1° to 25.7° is depicted as a solid horizontal bar. Furthermore, FIG. 14 correspondingly specifies, at a wavelength of 13.5 nm and given a thickness factor of 0.933, as a dashed line the reflectivity values against the angles of incidence and as a dashed bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 2.5° to 7.3°. Consequently, the thicknesses of the periods of the layer arrangement with respect to the reflectivity values illustrated as a dashed line in FIG. 14 amount to only 93.3% of the corresponding thicknesses of the periods of the nominal layer design. In other words, the layer arrangement is thinner than the nominal layer design by 6.7% at the mirror surface of the mirror according to the invention at the locations at which angles of incidence of between 2.5° and 7.3° have to be ensured. FIG. 15 shows, at a wavelength of 13.5 nm and given a thickness factor of 1.018, in a manner corresponding to FIG. 14, as a thin line the reflectivity values against the angles of incidence and as a thin bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 17.8° to 27.2°, and also, given a thickness factor of 0.972, in a corresponding manner, as a thick line the reflectivity values against the angles of incidence and as a thick bar the average reflectivity of the above-specified layer design for the angle of incidence interval of 8.7° to 21.4°. Consequently, the layer arrangement is thicker than the nominal layer design by 1.8% at the mirror surface of this mirror according to the invention at the locations at which angles of incidence of between 17.8° and 27.2° have to be ensured and is correspondingly thinner than the nominal layer design by 2.8% at the locations at which angles of incidence of between 8.7° and 21.4° have to be ensured. The average reflectivity and PV values which can be achieved by the layer arrangement with respect to FIG. 14 and FIG. 15 are compiled relative to the angle of incidence intervals and the thickness factors in Table 6. It can be discerned that the mirror according to the invention comprising the layer arrangement specified above, at a wavelength of 13.5 nm for angles of incidence of between 2.5° and 27.2°, has an average reflectivity of more than 42% and a variation of the reflectivity as PV value of less than or equal to 0.24. TABLE 6Average reflectivity and PV values of the layer design withrespect to FIG. 14 and FIG. 15 relative to the angle of incidenceinterval in degrees and the thickness factor chosen.AOI IntervalThicknessR_average[°]factor[%]PV17.8-27.21.01842.40.1814.1-25.7142.80.24 8.7-21.40.97244.90.152.5-7.30.93342.30.04 In all four exemplary embodiments shown, the number of periods of the surface layer system that is respectively situated closest to the substrate can be increased in such a way that the transmission of EUV radiation through the surface layer systems is less than 10%, in particular less than 2%, particularly preferably less than 0.2%. Firstly, it is thus possible, as already mentioned in the introduction, to avoid perturbing effects of the layers lying below the layer arrangement or of the substrate on the optical properties of the mirror, and in this case in particular on the reflectivity, and, secondly, it is thereby possible for layers lying below the layer arrangement or the substrate to be sufficiently protected from the EUV radiation. FIG. 16 shows a schematic illustration of the surface profile z(x,y) of a unit cell of a monolayer composed of graphene. In this case, an ideal flat plane was assumed as a model of said monolayer, on which plane the carbon atoms of the graphene are situated as solid spheres in a hexagonal arrangement. The diameter of a sphere is 0.192 nm in this case, and the sphere centres of two adjacent spheres are respectively situated at a distance of 0.334 nm from one another. The surface profile of graphene which results from this model is illustrated in FIG. 16 as a grey scale over an area of approximately 0.6 nm2. On account of this surface profile, this results in a theoretical surface roughness of Rq=0.065 nm rms and of Ra=0.052 nm with the height deviation z, of a point of the surface profile relative to the ideal flat plane in accordance with: R q = 1 N ∑ l = 1 N z i 2 and R a = 1 N ∑ l = 1 N | z i | . However, such a theoretical roughness of graphene can be determined experimentally only with a measuring device with a spatial resolution in the subnanometers range. By contrast, the present-day AFM microscopes used for determining the roughness in the HSFR frequency range average over an area having a diameter of approximately 20 nm. Therefore, in the case of measurements using such an AFM microscope, the roughness of a monolayer of graphene is exactly 0 nm HSFR or an HSFR value within the measurement accuracy of the AFM microscope, since the microscope perceives only an averaged smooth area of the graphene and cannot detect the frequency range above the HSFR range on account of the lack of spatial resolution. Therefore, a monolayer composed of graphene has a roughness measured by AFM of 0 nm rms HSFR and a theoretical roughness of 0.065 nm rms above the HSFR range. The statements made with reference to FIG. 16 concerning the surface roughness of a monolayer composed of graphene are correspondingly applicable to the topmost layer of a graphene layer consisting of multilayers. For the subdivision of surface roughnesses according to spatial frequency ranges with the high spatial frequency range (HSFR range) having spatial wavelengths of the roughness of 10 nm to 1 μm, the medium spatial frequency range (MSFR range) having spatial wavelengths of the roughness of 1 μm to 1 mm, and the figure range (surface form defect or alternatively called figure) having spatial wavelengths of 1 mm to the free optical diameter, reference is made to U. Dinger et al. “Mirror substrates for EUV-lithography: progress in metrology and optical fabrication technology” in Proc. SPIE Vol. 4146, 2000. Furthermore, for clarification purposes, FIG. 17 illustrates the spatial frequency ranges figure, MSFR, HSFR and very HSFR (VHSFR) on the basis of the associated spatial wavelengths X and on the basis of the associated spatial frequencies f=1/λ. By comparison with the above-cited publication by U. Dinger et al., the HSFR range in the meantime is subdivided into the HSFR range having spatial wavelengths of 50 nm to 1 μm or spatial frequencies of 1 μm−1 to 0.02 nm−1 and the very HSFR range (VHSFR) having spatial wavelengths of 10 nm to 50 nm or spatial frequencies of from 0.02 nm−1 to 0.1 nm−1. The deviation of a real area from the ideal design area of an optical element, in the spatial wavelength range of 1 mm to the diameter of the optical element, is designated as surface form defect or as figure defect. These deviations are produced during the form processing of the optical element by form processing machines and lead to imaging aberrations of the optical system such as astigmatism, coma, distortion and the like. Such deviations of a real optical element from the ideal surface form can be measured using an interferometer over the entire surface of the optical element and can be reduced by form correction processes such as ion beam processing, for example. In this case, the specifications for EUV mirrors are approximately 0.1 nm rms surface form defect. The deviation of a real area from the ideal design area of an optical element in the MSFR range leads to a point pattern widening. In customary usage this is referred to as flare. Through an optical system comprising optical elements having high roughness values in the MSFR range, specified in the unit nm rms MSFR, a halo arises around the point pattern of a bright point to be imaged, which halo widens the point pattern and thus reduces the contrast of the imaging. References in the MSFR range usually arise as a result of damage to the surface during form processing by diamond cutting, for example. These roughnesses are measured using microscope interferometers on an area of 0.25 mm×0.25 mm of the optical element and can be reduced by polishing the surface or through ion beam processing. In this case, the specifications for EUV mirrors are approximately 0.1 nm rms MSFR. The deviation of a real area from the ideal design area of an optical element in the HSFR range, by contrast, leads to stray light losses since light is diffracted by the high-frequency HSFR structures. These roughnesses in the HSFR range are measured using AFM microscopes on an area of 10 μm×10 μm with a spatial resolution of 0.3-3 μm or on an area of 1 μm×1 μm with a spatial resolution of 10-300 nm of the optical element and can be reduced by so-called superpolishing methods. In this case, the specifications for EUV mirrors are approximately 0.1 nm rms HSFR. A monolayer composed of graphene which extends at least over an area of approximately 0.5 μm×0.5 μm of an optical element has, as already discussed with reference to FIG. 16, a surface roughness of 0 nm rms HSFR in the HSFR range and also in the VHSFR range. It is only in the spatial frequency range above VHSFR with spatial wavelengths of below 1 nm that a monolayer composed of graphene actually has a roughness. This spatial frequency range is identified in FIG. 17 with the aid of the solid arrow for graphene and will be discussed in greater detail with reference to FIGS. 21 and 23. Such a monolayer composed of graphene thus avoids stray light losses since the structural distances of graphene are too small to diffract light having the EUV wavelength. The deposition of graphene layers onto polished nickel, silicon or silicon oxide is known from WO 2009/129194 A2, which in the entire scope becomes part of the present disclosure by reference (incorporation by reference). In WO 2009/129194 A2, the graphene is deposited in mono-, bi- or multilayers over a large area region, wherein the monocrystalline states, i.e. states with pure mono-, bi- or multilayers, extend over areas of approximately 0.5 μm×0.5 μm, see for example the discussion concerning FIG. 15 and FIG. 31 in WO 2009/129194. Such homogeneous layers composed of graphene make it possible to reduce the roughness in the HSFR range to 0 nm rms HSFR and to minimize the stray light losses at mirrors comprising such graphene layers. In this case, the graphene layers can indeed have regions having a different number of graphene layers along the mirror surface. Although the transitions of these regions contribute to the roughness in the MSFR range, as is illustrated in FIG. 17 with the aid of the interrupted double-headed arrow for graphene, it is possible to correct MSFR roughnesses, particularly in the case of a layer deposited on the graphene layer, using polishing methods, such as ion beam processing, for example. In this respect, the use of graphene layers for the mirrors 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention makes it possible to reduce the roughness of at least said graphene layers to less than 0.1 nm rms HSFR, in particular less than 0.04 nm rms HSFR. Furthermore, the theoretical roughness of graphene layers of Rq=0.065 nm rms above HSFR contributes to the fact that other layers growing on the graphene layers grow, on account of a lack of imperfections, in such a way that their surface likewise has lower roughness values in the HSFR range. FIG. 18 shows, in the left-hand illustration, a mirror from the prior art comprising a substrate S and a layer arrangement, wherein the layer arrangement is designed in such a way that light 32 having a wavelength of less than 250 nm which is incident on the mirror at at least an angle of incidence of between 0° and 30° is reflected with more than 20% of its intensity, illustrated as reflected arrow 34, and the layer arrangement comprises at least one surface layer system P′″ which consists of a periodic sequence of at least two periods P3 of individual layers, and wherein the periods P3 comprise two individual layers composed of different materials for a high refractive index layer H′″ and a low refractive index layer L′″. The surface roughness of the substrate or of the layers of such a mirror from the prior art leads to stray light, which is illustrated with the aid of the arrow 36 in FIG. 18. By contrast, the at least one graphene layer of a mirror 1a, 1a′, 1b, 1b′, 1c and 1c′, according to the invention, such as is illustrated schematically in a simplified manner in the right-hand illustration in FIG. 18, leads to a reduction of the stray light proportion on account of the “frequency hole” in the HSFR range of the at least one graphene layer, as is illustrated in FIG. 17. In this case, the use of the graphene layer for reducing stray light in mirrors is not restricted to the EUV wavelength range. Such a graphene layer is also suitable for other mirrors such as are used in projection exposure apparatuses for microlithography at wavelengths of less than 250 nm. The graphene layer G, SPL and B, in the case of the mirror 1a, 1a′, 1b, 1b′, 1c and 1c′ according to the invention in FIG. 18, can be formed as a graphene layer G, as a surface protecting layer SPL or as a barrier layer B within the surface protecting layer system SPLS or within the other surface layer systems of the layer arrangement. FIG. 19 shows a schematic illustration of the surface profile of a plurality of unit cells—illustrated in FIG. 16—of a monolayer composed of graphene. In this case, in a manner corresponding to FIG. 16, the same amplitude scale in the unit nm for the amplitude of the innovation relative to the ideal plane applies to FIG. 19. The square of the absolute value of the Fourier spectrum of the surface profile of FIG. 19, which is obtained through discrete Fourier transformation, is illustrated in FIG. 20. FIG. 20 shows a schematic illustration of the area-normalized two-dimensional power spectral density (PSD) of a monolayer composed of graphene against the spatial frequencies in the X and Y directions. In this case, the area-normalized PSD corresponds to the square of the absolute value of the Fourier transform of the surface profile and deviates, on account of this area normalization, from the classic PSD, as used in text books: PSD area - normalized = 1 L x L y * PSD classic = lim L x L y → ∞ 1 ( L x L y ) 2 | ∫ - L x / 2 L x / 2 ∫ - L y / 2 L y / 2 z ( x , y ) ⅇ - i 2 π ( f x x + f y y ) ⅆ x ⅆ y | 2 In this case, Lx and Ly denote the extent of the surface region considered in the X and Y directions, fx and fy denote the spatial frequencies and z(x,y) denotes the amplitude of the surface profile in the surface region considered. The discrete spatial frequency spectrum of the honeycomb-like structure of graphene from FIG. 19 is clearly discernible in FIG. 20. A corresponding discrete spectrum can be determined experimentally for example using electron diffraction on graphene, see FIG. 17 in WO 2009/129194. In FIG. 20, the spatial frequencies shown white at approximately 3.3 l/nm are dominant, which corresponds to the spatial wavelength of 0.334 nm in accordance with the first interatomic distance in the graphene. As a result of the discrete structure of graphene, therefore, the discrete PSD of graphene in FIG. 20 differs from a continuous PSD of other surfaces, which is based on statistical surface defects. FIG. 21 shows a schematic illustration of the area-normalized radial PSD function in logarithmic representation to base 10 for the amplitude of the PSD function of a monolayer composed of graphene against the spatial frequency in a radial direction as a thick line, and also ten times the area-normalized radial PSD function as a thin line for comparison. This area-normalized radial PSD is produced from the two-dimensional PSD shown in FIG. 20 by integration over the azimuth: PSD area - normalized , radial = 1 2 π ∫ 0 2 π PSD area - normalized ( f , φ ) ⅆ φ The dominance of the spatial frequencies—identified as white in FIG. 20—at low spatial frequencies of less than 10 l/nm is clearly discernible in FIG. 21. It can likewise be discerned that graphene has harmonics up to spatial frequencies of 150 l/nm. None of the spatial frequencies illustrated in FIG. 21 can be resolved by an AFM microscope, since the latter can resolve only up to a frequency of approximately 0.1 l/nm and, consequently, can measure only the HSFR range. FIG. 22 shows a schematic illustration—reduced in size by comparison with FIG. 19—of the surface profile of a plurality of unit cells of a monolayer composed of graphene, which corresponds in terms of lateral extent approximately to the area over which the measuring tip of an AFM performs averaging. That means that an AFM determines, for the area illustrated in FIG. 22, only an average value of the surface profile, which does not deviate relative to an adjacent area within a region of a monolayer or multilayer composed of graphene of approximately 0.5 μm×0.5 μm. Consequently, a roughness determined using an AFM of 0 nm rms HSFR results for a graphene layer, since the AFM cannot laterally resolve the structure of the graphene and, consequently, cannot detect the frequency range above HSFR. FIG. 23 shows a schematic illustration of the area-normalized radial PSD function of a monolayer composed of graphene against the spatial frequency in a radial direction, this illustration being enlarged relative to FIG. 21, wherein, for determining the area-normalized radial PSD function in FIG. 23, the frequency axis in FIG. 20, for numerical integration, was graduated more finely than for the determination of the area-normalized radial PSD function in FIG. 21. It is clearly discernible that, for spatial frequencies between 0 and approximately 1.6 l/nm, this concerns the range of figure, MSFR, HSFR to VHSFR, no amplitude of the PSD is present and, consequently, no roughness is present for the frequency range considered. Above the spatial frequency of 1.6 l/nm as well there are frequency ranges in which no PSD and, consequently, no roughness are present. This is owing to the crystalline hexagonal structure of graphene, which has the effect that discrete frequencies or frequency bands appear in the Fourier spectrum of the surface profile and, consequently, in the case of graphene, a Fourier spectrum does not contain a uniform distribution as in the case of an amorphous or statistical surface structure. The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof. |
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042345553 | summary | This invention was developed in response to a need for a simple but effective method for decreasing the uranium content of a large volume of by-product aqueous hydrofluoric acid contaning uranium in the parts-per-million range. The acid solution comprised about 20 wt-% HF and 76 ppm uranium (uranium species in solution not known). Sale of the solution on the open market required that its uranium concentration be decreased below 10 ppm by some technique which would not introduce additional impurities into the product solution. An attempt was made to decrease the uranium content of the solution by passing it over amorphous carbon maintained at 350.degree.-450.degree. C. This decreased the uranium content by only 64%. In another approach, the solution was passed through an anion exchange column of the hydroxide type. This decreased the uranium concentration by only 32%. Various other removal techniques were considered but rejected as impractical. Various publications describe the adsorption of uranium from solutions by selective adsorption. The following is an example of such a publication: Minhai Dai and Shaw-Chii Wu, "Adsorption of Uranium from Dilute Aqueous Solution on Inorganic Adsorbents," Separation Science, 10(5), pp. 633-638 (1975). That paper described recommends adsorbing uranium with a mixture of aluminum hydroxide, ferric hydroxide, and activated carbon. It also describes experiments conducted with various alkaline earth oxides, hydroxides, and sulfates as adsorbents. OBJECTS OF THE INVENTION Accordingly, it is an object of this invention to provide a novel method for decreasing the uranium content of aqueous hydrofluoric acid containing trace amounts of uranium in solution. It is another object to provide a simple and effective method for decreasing the uranium content of a uranium-bearing aqueous HF solution without introducing a contaminant into the product solution. Other objects will be made evident hereinafter. SUMMARY OF THE INVENTION This invention may be summarized as being a method of decreasing the uranium content of an aqueous HF solution containing uranium, said method comprising mixing particulate calcium fluoride with said solution to form uranium-bearing particulates; permitting said particulates to sediment from said solution; and separating the resulting solution from the sedimented particulates. BACKGROUND OF THE INVENTION This invention is generally applicable to the recovery of uranium from aqueous HF solutions containing the same. It is based on our finding that intimately contacting such solutions with particulate CaF.sub.2 and then sedimenting the particulates effects removal of much of the uranium. That is, uranium is carried down out of solution by the sedimented CaF.sub.2 particles. The resulting solution then is separated from the sedimented, uranium-bearing particulates by any suitable technique. The mechanism by which the uranium is carried down is not yet well understood. So far as is known, this process has not been reported previously. It is clear from the very low solutility of CaF.sub.2 in aqueous solutions that the well-known common-ion effect is not involved here. If the uranium is in solution as UF.sub.4 and no ionization has occurred, then the solubility-product principle would not be governing the carry-down of uranium. If the uranium is present as UO.sub.2 F.sub.2, the solubility of this species is too high to account for the carry-down of uranium when present in trace quantities. |
051620960 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, an explosive detection system 10 includes a loading station 12 and an unloading station 14. The loading station 12 leads to an input conveyer belt 16 having a motion as shown by the arrow 18. Adjacent the input conveyer belt 16 is a first cavity structure module 20. A second cavity structure module 22 is located adjacent to the first cavity structure module 20 and adjacent to the second cavity structure module 22 is an output conveyer belt 24 having a motion as shown by the arrow 26. The output conveyer belt 24 extends to the unloading station 14. Internal to the cavity structure modules 20 and 22 are conveyer means which interconnect the conveyer belts 16 and 24. The internal conveyer means is shown in FIGS. 2 and 3. Extending from the cavity structure modules 20 and 22 are shield members 27 and 28 which shield members enclose the conveyer belts 16 and 24 and prevent access to the interior of the cavity structure modules 20 and 22. FIGS. 2 and 3 illustrate in more detail cross sectional views of the cavity structure module 20, but is to be appreciated that FIGS. 2 and 3 are also illustrative of the cavity structure module 22 but with the following exception. As shown in FIG. 1 in the broken away portion, cavity structure 20 includes a source of neutrons 30 located at a top position, detector structures 32 and 34 located at side positions and a further detector structure 36, as shown in FIG. 2, located at a bottom position. Cavity structure module 22 includes an opposite structure having side detector structures 38 and 40 and with a top detector structure 42 and with a bottom source of neutrons (not shown). The groups of detector structures provide for a C-ring configuration, the C-ring of detectors in the cavity modules 20 and 22 having their open ends facing each other so as to essentially form a complete ring if the output signals from the two C-rings of detectors are combined electronically. As indicated above, although the invention is described with reference to a particular configuration for the detectors as shown in the drawings, it is to be appreciated that other types of detector arrays may be used and that the invention is not to be limited to the particular C-ring configuration for the detectors. The signals from the detectors in the cavity structures 20 and 22 are introduced to a computer system 43 (FIG. 5) for processing the signals to provide a profile of the three-dimensional concentration of the element such as nitrogen at different positions of the object to be detected. The computer system 43 is shown in some detail in FIG. 8 of application Ser. No. 321,511 and is disclosed in detail in that pending application. Turning now to FIGS. 2 and 3, a more detailed view of the cavity structure is shown. Extending through the cavity structure is a conveyer belt 44. The conveyer belt 44 is located adjacent to the input conveyer belt 16 at an input end an adjacent the output conveyer belt 24 at an output end. This allows the various portions of the entire detector structure to be built in modular form so that the system may be easily transported for set up at a desired location. A plate member, such as plate member 46, may be used to bridge the space between the input and conveyer belt 16 and the conveyer belt 44 extending through the cavity structure. A similar plate member would be used the bridge the space between the conveyer belt 44 and the output conveyer belt 24. As shown in FIG. 3 a piece of luggage, such as luggage 48, is shown entering the cavity structure for inspection. The piece of luggage 48 or any other luggage, baggage or parcels to be inspected is passed through an opening 50 defined by thin walls 52 through 58 of hydrogenous material such as a rigid nonclorinated hydrocarbon material. A preferred material is polyethylene but other material such as acrylic resin may be used. The thin polyethylene walls help contain low energy neutrons. Specifically, the cavity 50 will tend to retain a cloud of thermal neutrons within the cavity for interaction with an object under inspection such as the piece of luggage 48. The upper surface of the conveyer 44, which supports the objects for inspection, is supported by the bottom thin plastic wall 58. Additionally, the lower portion of the conveyer 44 is supported for return by a pair of spaced bearing layers 60 and 62. This above described structure provides for a smooth movement of the conveyer belt 44 through the cavity opening 50 to thereby smoothly and continuously move objects under observation through the cavity 50. In order to produce the desired cloud of thermal neutrons within the cavity 50, a source of neutrons is used such as either a radioactive or electronic neutron source. As shown in FIGS. 2 and 3, a radioactive source 64 is supported at the end of a rod 66 so that the source 64 of neutrons may be inserted into the cavity structure at a position adjacent to the cavity opening 50. The source of neutrons 64 may produce a variety of neutrons that would typically have a flux pattern as shown in FIG. 4(a). As can be seen in FIG. 4(a) the maximum production of neutrons is at approximately 2.5 MeV, the majority of the neutrons in the flux pattern ranging between 2 to 4 MeV. Also as can be seen in FIG. 4(a), the desired thermal neutrons are at a point outside the normal flux pattern and it is, therefore, necessary to slow down most of the neutrons in the flux pattern to the thermal neutrons area which is at the position designated in FIG. 4(a). In order to accomplish slowing down of the neutrons, it is desirable to use a variety of moderators to affect different portions of the flux pattern shown in FIG. 4(a). These different portions of the flux pattern are marked on FIG. 4(a) and with these different portions affected by specific portions of the cavity structure shown in FIGS. 2 and 3. Specifically, surrounding the radioactive source 64 for producing the neutrons is a sleeve of nonclorinated hydrocarbon material 68 (FIG. 3) such as polyethylene material. This sleeve of polyethylene material acts as a premoderator and affects a portion of the flux shown in FIG. 4(a) and moderates this portion to a lower energy, as shown by the arrow 70. Surrounding the polyethylene premoderator 68 is heavy water 72. The heavy water 72 is disposed in a container formed by the upper wall 54 of the cavity 50, plus a cylindrical member 74 and end plate 76. The heavy water 72 serves to slow down neutrons within the portion shown in FIG. 4(a) and to convert these neutrons to neutrons in the thermal energy range as shown by arrow 78. The heavy water 72 is positioned immediately adjacent the source 64 so as to maximize the effectiveness of the heavy water while at the same time minimizing the amount of heavy water that has to be used. Surrounding the cavity 50 at a position adjacent to the cavity and the radiation source 64 are large portions of carbonaceous material such as graphite material. All of the graphite material is marked with reference numeral 80. The graphite material 80 affects the portion of the flux field as shown in FIG. 4(a) and slows down neutrons in this portion of the flux field as shown by the arrow 82. As a substitute for the graphite material, other carbonaceous material such as polyethylene may be used. This will affect the flux pattern as will be described at a later portion of this specification. It can, therefore, be seen that all of the various types of moderator material slow down the neutrons to the desired thermal energy range, each moderator acting on different portions of the spectrum to progressively reduce the energy to build and enhance the cloud of thermal neutrons within the cavity 50. This can be seen initially in FIG. 4(b) which illustrates the effect of the cavity structure, but not including the moderating effect of the polyethylene thin wall liner formed by the walls 52 to 58. As can be seen in FIG. 4(b), a thermal portion of the neutron spectrum is shown in dotted lines 84. In addition, the graphite material 80 has greatly reduced the energy for the vast bulk of the neutrons in the spectrum. FIG. 4(c) shows the effect of the structure including the polyethylene thin walls 52 to 58 forming the polyethylene liner for the cavity 50. As shown in FIG. 4(c), a large percentage of the neutrons are now in the desired thermal energy range and a much smaller percentage are at higher energies. However, the composite preferred embodiment of the cavity of the present invention does not completely moderate all of the neutrons to the thermal neutron range, but leaves a small portion of the neutron spectrom at higher energys, such as in the area 86 in FIG. 4(c). The neutrons at this higher energy are useful to help provide a detection of particular types of explosives. Specifically, neutrons at this higher energy can easily penetrate luggage and thermalize in the explosive. This has the effect of making it harder to shield the explosive. These higher energy neutrons are particularly useful for detecting explosives that have a high hydrogen content. Many low nitrogen explosives typically include a relatively high content of hydrogen and the neutrons at the higher energies react with the hydrogen content in the explosive so that the explosive itself acts as a moderator to thermalize the neutrons. Since the explosive itself acts as a moderator, this produces a high level of thermal neutrons within the explosive to thereby increase the reaction with the smaller amount of nitrogen. This tends to increase the number of gamma rays from the smaller nitrogen content. This in turn produces a relatively larger amount of detectable gamma rays than would normally be produced with this low nitrogen content explosive. It is thereby preferable to produce a neutron spectrum as shown in FIG. 4(c) which includes some high energy neutrons in addition to the high level of thermal neutrons so as to detect not only explosives with a high nitrogen content, but also explosives with a high hydrogen content. In addition, as indicated above, the higher energy neutrons can more easily penetrate any shielding material so that the preferred cavity structure can more efficiently detect explosives even when there has been a deliberate attempt to shield the explosive material. Surrounding the various layers of moderator material described above are layers of hydrogenous material generally marked with reference numeral 88. This hydrogenous material may be, for example, borated paraffin. As a substitute for the borated paraffin, other hydrogenous material, such as polyethylene, plexiglas, water etc. mixed with lithium compound may be used. These additional layers 88 of hydrogenous material provide for the final shielding of personnel operating the equipment. This mixed hydrogenous material absorbs any stray neutrons which escape the other layers of moderator material. The layers 88 of hydrogenous material may also tend to reflect some high energy neutrons back into the cavity structure, but primarily this material is used to provide for personnel shielding. FIG. 4(d) illustrates an alternative cavity structure wherein a hydrocarbon material such as polyethylene or other plastic material is substituted for the graphite. While this type of cavity structure tends to even further slow down the high energy neutrons, as shown in FIG. 4(d), it does not produce a greater amount of thermal neutrons. As indicated above, a neutron spectrum, such as shown in FIG. 4(c) is preferable, but a composite cavity structure using polyethylene instead of the graphite to produce a spectrum as shown in FIG. 4(d) may also be useful in some situations. In addition to the various moderator materials described above, the present invention may also include a shield member 90, which shield member surrounds the premoderator 68 and is located within the heavy water 72. The shield member 90 may be constructed of a heavy metal such as bismith and is specifically used to shield the detectors located around the cavity 50 from unwanted gamma rays produced by the radiation source 64. These unwanted gamma rays are harmful to the detectors when they are in line with any of the detectors. In order to absorb these unwanted gamma rays, the shield member 90 has a configuration to lie within substantially the same plane as the detectors. In this way, the shield members 90 will absorb these unwanted gamma rays which are in line and would be directly received by a detector. As a substitute for the bismuth, other heavy metals such as lead or tungsten can be used. The detector structures are arranged in a C-ring around the cavity 50, the detectors and the source 64 of neutrons being disposed in a common plane. Specifically, the detector structures 32 and 34 are located along the sides of the cavity 50 and the detector structure 36 is located below the cavity structure 50. As can be seen in FIG. 2, the detector structures 32 and 34 include a plurality of detectors arranged in a column and the detector structure 36 includes a plurality of detectors arranged in a row. Actually, two adjacent columns and two adjacent rows are provided so that detector structure 32 includes two adjacent columns of four detectors each and with a similar structure for detector structure 36 and with bottom detector structure 36 including two adjacent rows each with seven detectors. In a preferred form of the detection system as described in the co-pending application, the individual detectors are formed by inorganic scintillators, such as sodium iodide scintillators. Each detector structure is shielded by heavy metal material such as lead shields, all of which are generally designated by reference character 92. In this way, all sides of the detector structures are shielded from the reception of unwanted gamma rays with the exception of a front window which allows for the reception of the desired gamma rays. The shields 92 are formed of a heavy metal, such as lead, tungsten, bismuth, etc. so as to insure that no gamma rays can enter the detector structures 32, 34 and 36 except through the front window. Detector structure 32 includes a window member 94 positioned in front of the detector structure so that any gamma rays representative of nitrogen will pass through the window 94 to impinge on the plurality of detectors forming the detector structure while preventing the passage of neutrons. Similarly, detector structure 34 includes a window 96 and detector structure 36 includes a window 98. The windows 94, 96 and 98 may be composed of an hydrocarbon mixture such as an hardened epoxy resin mixed with boron carbide. This type of material provides for the passage of the gamma rays representative of nitrogen which would be the gamma rays at approximately 10.8 MeV. In order to properly shield the detector structures from neutrons, a similar epoxy boron carbide mixture is used to surround and support the detector structures. This may be seen, for example, by the use of the epoxy material 100 and 102 adjacent to the detector structure 32, the epoxy material 104 and 106 adjacent to the detector structure 34 and epoxy material 108 and 110 adjacent to detector structure 36. These materials represent the epoxy material along two sides of the detector structures, but similar epoxy material such as epoxy material 112 and 114 shown in FIG. 3 would also be along the other two sides. The present invention, therefore, provides for a composite cavity structure including a cavity opening for receiving and supporting a conveyer belt to move objects under inspection through the cavity opening. The cavity opening is subjected to cloud of neutrons having a flux spectrum including mostly thermal neutrons and some neutrons at higher energy so as to produce an enhanced detection of nitrogen contained in explosives having both a high and low content of nitrogen. Initially, neutrons are produced from a source, the initial spectrum of neutrons predominantly containing neutrons that are at high energy. A composite cavity includes a plurality of moderator means including a premoderator located adjacent the radiation source to slow down a portion of the flux spectrum and a heavy water moderator to further moderate neutrons to the desired thermal energies. In addition, the composite cavity includes a relatively large quantity of graphite which tends to flatten out the flux spectrum and to in general produce a large quantity of the neutrons to a lower energy. The graphite moderator, therefore, not only reduces the energy of the neutrons, but also makes the flux pattern more uniform. The cavity opening is defined by a thin polyethylene wall liner which serves as a moderator to confine the thermal neutrons and to provide a low friction surface in case the luggage rubs it. Higher energy neutrons can escape and be moderated by the graphite so that the total combination produces the desired spectrum for the detection of nitrogen. The preferred flux spectrum includes a small fraction of neutrons at higher energies and this is desirable since some of the higher energy neutrons are thermalized in the explosive since the explosive itself can act as a moderator. This is particularly useful for explosives which do not have a high nitrogen content. The higher energy neutrons react with the hydrogen in this low nitrogen type of explosive and are moderated by the hydrogen to lower energy thermal neutrons. This increases the number of thermal neutrons that can react with the available nitrogen to increase the production of gamma rays. Because of the close proximity between these newly created thermal neutrons and the smaller amount of nitrogen, this enhances the output to the detector even from explosives having a relatively low concentration of nitrogen. The composite cavity also includes the use of a mixed hydrogenous material such as borated paraffin to provide for a final shield structure for any personnel operating the equipment. The composite cavity is also constructed in a modular form to provide ease of construction and also ease of access to the various detector structures. Although the invention has been described with reference to a particular embodiment, it is to be appreciated that various adaptations and modifications may be made and the invention is only to be limited by the appended claims. |
description | This application is a U.S. nationalization of PCT application No. PCT/FR2013/053167, filed Dec. 18, 2013 and published as PCT publication No. WO2014/096705 on Jun. 26, 2014, the disclosure of which is incorporated by reference herein. The invention concerns a scanning illuminating device, called a radiation modulator, an imaging device using such a modulator and a method of implementing such a modulator. Imaging consists in illuminating an object using a source of radiation, often of high energy, and of forming an image on the basis of the radiation that is back-scattered (especially in the case of objects opaque to the radiation) or transmitted. The radiation considered here is for example radiation that penetrates the material, typically X-rays, or even “gamma” rays, but may also be what is referred to as THz radiation, that is to say radiation of which the frequency, of the order of the terahertz, situates it between the infrared and the microwave domain. These concepts of illumination or imaging do not in any way imply that the radiation is in the visible domain (generally it is the opposite case); the term irradiation is sometimes used, in the case of certain penetrating radiation. There are two broad families of imaging devices according to the illumination configuration used: Imaging devices with “imager”, in which the source fully and uniformly illuminates the object; the detection of the back-scattered radiation is carried out by a pixelated imager of large format associated with an image forming system of greater or lesser complexity, “Scanning” devices in which the source illuminates part (in practice a small zone) of the object at a given time and performs scanning in order to cover the whole of that object during a scanning cycle. Collimation is generally placed in front of the source in order to reduce the angular amplitude of the illumination beam at each instant and thus the illuminated zone. The back-scattered radiation (and/or the transmitted radiation) is collected by one or more one-dimensional detectors synchronized with the scanning by the source. There are a wide variety of imaging devices with imager. There are thus imaging devices with a virtual imager (reconstitution by scanning of the field of view of a detector, in practice one-dimensional, which is strongly collimated, and of which movement is provided using Cartesian or polar coordinates), and imaging devices with a matrix imager (this matrix imager is formed from a matrix of strongly collimated one-dimensional detectors). Developed before the appearance of large detection matrices, they are still used in in vitro scintigraphy and for the examination of small laboratory animals. These devices lack spatial resolution given the size of the unit detector and the collimation used to form the image. Imaging devices with imager were then developed thanks to the appearance of pixelated imagers; a particularly simple version is the pinhole imager, that is to say it employs a hole of small size formed in a screen interposed between the illuminated object and the detector. The spatial resolution increases when the size of the hole reduces such that the main drawback of this type of imager is that an increase in spatial resolution implies a reduction in the quantity of radiation transmitted by the pinhole; this leads either to very long exposure times, or to images of poor signal-to-noise ratio. To improve the signal-to-noise ratio, it is possible to use the technique of penumbra imaging, in which the pinhole is replaced by an aperture of greater size (in the shape of a disk, or in a ring, for example). The quantity of radiation received by the detector is higher but the image is blurred and must be deconvoluted by mathematical processing using the knowledge of the aperture shape and of the detection geometry to determine the deconvolution kernel. A second way to get around the limitations of the pinhole principle is the coded aperture technique, consisting of having multiple pinholes within the same screen, also called a mask; the quantity of radiation reaching the detector increases with the number of apertures. A reconstruction operation must then be carried out to reconstitute the image of the object. The distribution of the pinholes within a given mask must satisfy a certain number of rules to facilitate that reconstruction of the image and minimize the contribution of the noise. The principle of the method has been described by: E. Fenimore and T. M. Cannon “Coded aperture imaging with uniformly redundant arrays”, Applied Optics, Vol. 17, No. 3, p. 337-347, Jan. 2, 1978; several patents disclose devices implementing this coded aperture technique: U.S. Pat. No. 4,389,633 (Fenimore et al) published in 1983, PCT Pub. No. WO 97/45755 published in 1997, PCT Pub. No. WO 02/13517 published in 2002, PCT Pub. No. WO 02/056055 published in 2002, U.S. Pat. Pub. No. 2004/218714 published in 2004 and PCT Pub. No. WO 2007/091038 published in 2007, The main limitations of the coded aperture devices are their high cost since the large-size masks are costly to produce while the associated imagers must have dimensions at least equal to those of the mask. Their spatial resolution is not adjustable since it is linked, in particular, to the size of the holes in the mask and to the detection geometry. An original device, described in PCT Pub. No. WO 2007/015784, consists of using X-ray focusing optics of very particular form enabling the radiation scattered by the object to be focused onto an imager of small size; however, the X-focusing optics do not operate for all radiation energies and its efficiency is rather low. The other category of imagers, referred to as “scanning” imagers, also comprises several variants. Thus, the simplest version consists of illuminating the object with a radiation beam (typically X-rays) of very small diameter (the term “pencil beam” is sometimes used) and of scanning the entire object by virtue of a mechanical system; the dimension of the radiation beam and the scanning step size determine the spatial resolution; such scanning is typically carried out by means of an annular ring movable around its center, pierced with collimation passages, the source of radiation being fixed, situated at the center of this annular wall; this ring may be of greater or lesser thickness depending on whether it is a wall pierced with holes or a disc holed in its center, in which radial channels are formed; this ring is sometimes called a chopper wheel. The rotation of this ring causes scanning of the beam perpendicularly to the rotational axis of the ring; the other movement ensuring the scanning of the object is conventionally provided by a movement of the object parallel to the rotational axis of the ring. A detector is placed beside the source; it records a series of signals which are then provided in matrix form to constitute the back-scattered image of the object. Such a configuration, and examples of application are in particular described in U.S. Pat. No. 5,764,683, and PCT pub. Nos. WO 00/33060, WO 01/94984, WO 2004/043740 or WO 2006/102274. According to a variant, the pencil beam results from the interception of a fan beam which is intercepted by a wheel of which the axis is parallel to the plane of the beam and which comprises radial slits; such a configuration and examples of application are in particular described in U.S. patents Re 28 544, U.S. Pat. No. 4,031,545, U.S. Pat. No. 4,799,247, U.S. Pat. No. 5,179,581, U.S. Pat. No. 5,181,234 or U.S. Pat. No. 6,094,472. Instead of providing scanning by movement of a pencil beam in two transverse directions, it is also possible to generate a fan beam which is passed through by the object to observe, as is for example described in PCT pub. No. WO 98/20366. It is to be noted that the reconstruction of an image based on such scanning may involve coding similar to that indicated above in connection with the imaging devices with imager. Variants implement both types of aforementioned scanning devices (by a pencil beam and by a fan beam), as is proposed by the PCT pub. Nos. WO 99/39189 and WO 2008/021807. The devices described above serve in practice for the inspection of parcels, baggage, even freight trucks or people. The drawback of this scanning configuration is in practice to use only a very small part of the radiation emitted by the source since the spatial resolution improves the finer the illumination beam; the source must therefore be of high intensity and the detection surface of large size if acquisition times of reasonable length are desired. An increase in the quantity of radiation used may be obtained by increasing the number of beams; this may be provided by the coding of a localized source with absorbent masks comprising holes; it is then necessary to reconstruct the image by matrix inversion techniques. A simple version (with a plurality of pencil beams simultaneously formed by means of a chopper wheel, combined with movement of the object) is described in PCT pub. No. WO 01/94894. To obtain a good result, in particular when the scanning is provided in two transverse directions, the collimation holes forming the beams must satisfy disposition rules; the best-known principle consists of projecting masks and their opposites constituting the elements of a Hadamard matrix; this imaging method requires little computation power (it is a simple matrix multiplication) but its practical implementation is very complex. Typically, for an image of size N×N, it is necessary to project 2·N2 masks. The resolution of the final image depends on the size of the smallest projected pattern; the more it is sought to have details in that image, the higher the number of masks to project has to be; mechanically these masks must be produced and positioned with high precision; such a system is extremely complex and costly (see PCT pub. No. WO 2008/127385 published in 2008). Another approach consists of performing coding in relation to an area source, with a pinhole to project the pattern onto the object. In the same way as previously, it is necessary to have a succession of different patterns to acquire the data then reconstruct the back-scattered image (cf. U.S. Pat. No. 6,950,495 published in 2005). These coding devices are extremely complex since a source of large area must be produced with zones (pixel) that can be modulated individually for emission; furthermore, the emitted intensity must be sufficiently high to enable the projection of the patterns via a pinhole, which considerably attenuates the signal; as previously, the resolution depends on the size of the smallest projected pattern. Thus, the known solutions implement scanning illuminating devices which are generally voluminous and complex from the mechanical point of view, particularly as the scanning in two perpendicular directions in practice requires movement of the object relative to the radiation source. Furthermore, these scanning illuminating devices in practice enable a high spatial resolution to be obtained only provided a beam of small dimensions only is applied to the object. The invention aims to mitigate the drawbacks of the known solutions and to provide, in a compact volume, illumination by scanning in two directions, while enabling the formation of images with a resolution which is not dictated by the scanning beam. Preferably, it is directed to enabling the scanning to be made by absorbing the radiation emitted by the source in a manner that is variable over time and in space; thus, preferably, it is directed to enabling the illumination to be made according to first provisions, for example for the purpose of taking a crude image, then according to other provisions enabling an image of better quality to be taken, possibly limited to part only of the first image. Thus the invention provides to implement two cylinders or ring portions rotatable around two axes crossing at a center from which center radiation is generated forming a non-zero angle between them (preferably equal to 90°), those rotatable elements being formed from open parts and from portions opaque to the radiation such that the crossing of parts of those elements of the same nature define either a non-illuminating zone within a large illuminated zone, or an illuminated zone within a large non-illuminated zone, those elements being actuated in rotation by stepper motors of which the elementary steps have angular amplitudes which are sub-multiples of the amplitude of the parts which cross. In the context of the invention, a step of a motor is referred to herein as an “elementary step” when that step is the smallest, taken with any reduction gearing, that such motor is configured to operate according to its supply mode; thus when that supply is made pole by pole, the elementary step is equal to one step of the motor, whereas, if the supply is made two poles by two poles, the elementary step is a half-step of the motor; when, in a measurement cycle, it is provided always to apply several pulses to such a motor, the elementary step may then be understood as being the step to which such a number of pulses corresponds. The angular step through which an element actuated by such a motor turns when the latter turns by such an elementary step is called “elementary angular step” or “scanning elementary step”. Preferably, one of the ring portions forms part of a complete ring of which the actuation is provided by a stepper motor designed to be able to rotate that ring in the same rotational direction; by way of variant, each of the portions may turn in one direction, then the other to return to a configuration of start of scanning. There are thus two cases, depending on whether the elements that cross are open parts or parts opaque to radiation, with an “illumination beam” which is, either a locally increased illumination beam, or a locally neutralized illumination beam. Thus, according to a first definition of the invention, the latter provides a scanning illuminating device comprising an illumination source defining an emission center, a collimation element delimiting a sector of illumination from the center in which the emitted radiation is substantially homogenous, at least one cylindrical ring portion centered on the source and rotatable about a first axis passing through the emission center, that cylindrical ring portion comprising a slit having an angular amplitude α surrounded by two portions transparent to radiation each having an angular amplitude at minimum equal to that of the illumination sector delimited by the collimation element, a cylinder portion centered on the source and rotatable, within a given travel, around a second axis passing through the emission center and forming a non-zero angle relative to the first axis, that cylinder portion comprising a slit parallel to the second rotational axis having an angular amplitude β surrounded by two portions transparent to the radiation each having an angular amplitude at minimum equal to that of the illumination sector delimited by the collimation element, a first device for stepwise actuation of the rotation of the cylindrical ring portion defining an elementary angular step αα which is a sub-multiple of the angular amplitude α of said slit of that cylindrical ring portion such that there is an integer N1 different from 1 meeting the condition α=N1·αα, and a device for stepwise actuation of the rotation of the cylindrical ring portion defining an elementary angular step ββ which is a sub-multiple of the amplitude β of the slit of that cylinder portion such that there is an integer N2 different from 1 meeting the condition β=N2·ββ. Particularly advantageously, the cylindrical ring portion is a cylindrical ring comprising a plurality of slits having said angular amplitude α and which are regularly distributed around its rotational axis and the first stepwise actuation device is designed to be able to actuate that ring in the same rotational direction. According to the other definition referred to above (which inverses the role of the open parts and the slits of the aforementioned device, the “illumination beam” being a beam in which the lighting amplitude is locally reduced), the invention also provides a scanning illuminating device comprising an illumination source defining an emission center, a collimation element delimiting a sector of illumination from the center in which the emitted radiation is substantially homogenous, at least one cylindrical ring portion centered on the source and rotatable about a first axis passing through the emission center, that cylindrical ring portion comprising a portion opaque to the radiation and having an angular amplitude α surrounded by two portions transparent to the radiation each having an angular amplitude at minimum equal to that of the illumination sector delimited by the collimation element, a cylinder portion centered on the source and rotatable, within a given travel, around a second axis passing through the emission center and forming a non-zero angle relative to the first axis, that cylinder portion comprising a portion opaque to the radiation which is parallel to the second rotational axis and has an angular amplitude β surrounded by two portions transparent to the radiation each having an angular amplitude at minimum equal to that of the illumination sector delimited by the collimation element, a first device for stepwise actuation of the rotation of the cylindrical ring portion defining an elementary angular step αα which is a sub-multiple of the angular amplitude α such that there is an integer N1 different from 1 meeting the condition α=N1·αα, and a device for stepwise actuation of the rotation of the cylindrical ring portion defining an elementary angular step ββ which is a sub-multiple of the amplitude β such that there is an integer N2 different from 1 meeting the condition β=N2·ββ. Particularly advantageously, the cylindrical ring portion is a cylindrical ring comprising a plurality of slits regularly distributed around its rotational axis and separated by opaque portions having said angular amplitude α and the first stepwise actuation device is designed to be able to actuate that cylindrical ring in the same rotational direction. It can be appreciated that such a scanning illuminating device, called modulator below, is compact in that the movements of the beam are made in two transverse scanning directions in a volume scarcely greater than that of a known chopper wheel. Furthermore, the fact that the movements are actuated by stepper motors enables the taking of images of an object so illuminated to be made at a very specific frequency, to which corresponds a very specific angular measurement step (which is the angular step of rotation of one or other of the rotary elements between two instances of image taking). The taking of images may be carried out outside the movements of those motors if those movements are sufficiently slow; as a variant, if the motors do not completely stop between two successive measurement steps, the images so captured between those two measurement steps may be subjected to blur correction processing, as is known, in particular, in the field of tomography. The fact that the elementary steps of these stepper motors are such that the beams emitted for two positions neighboring by an elementary step have parts in common advantageously makes it possible to vary the illumination in several ways depending on whether the motors are actuated elementary step by elementary step (a measurement step then corresponds to an elementary step), or multiple steps by multiple steps (a measurement step then having the value of several elementary steps), while enabling the scanning to be applied to the whole of the object, whatever the ways chosen. It can be understood that the elementary scanning steps contribute to determining the maximum spatial resolution which can be attained by an imaging device comprising such a modulator, without that resolution being imposed by the dimensions of the illumination beam, which makes it possible to increase the use of the stream generated by the radiation source, or on the contrary to reduce the power of that radiation source. Such a modulator may be considered as being dynamic in that the spatial resolution may be chosen and modified according to need for the same structural configuration. According to preferred features of the invention: The angular amplitudes α and β are equal and the integers N1 and N2 are equal; this simplifies the geometry of the illumination beam as well as the later processing, within an imaging device. the integers N1 and N2 are both odd, which has the advantage of enabling the illumination beam to be centered on an elementary beam of which the angular amplitude would be that of a single elementary step; this arises from the mathematical formulae which are symmetrical, but even numbers are just as usable. the number of slits is comprised between 5 and 10 (this applying when the illumination beam is delimited by the slits and also when the opaque parts locally obscure the illumination beam); this corresponds to a reasonable number from a practical point of view. The device contained in a casing of dimensions less than 50×50×50 cm3; this results in a good level of compactness, which enables the device to be portable by an operator without great difficulty. The invention is furthermore directed to providing a scanning imaging device, using X-rays for example, in back-scatter or transmission, of which the spatial resolution of the back-scattered or transmitted image is not determined by the dimensions of the scanning beam and may, preferably, be adjusted according to the needs of the analysis without having to modify the structure of that device. It is also directed to enabling use of a significant part of the radiation emitted by the radiation source, therefore enabling the utilization of sources that are less powerful than the known solutions. More particularly the invention further provides a scanning imaging device comprising an illuminating device of the aforementioned type, further comprising a reception zone of which the volume is configured to receive an object to image, and at least one unitary detector positioned relative to that reception zone such that its field of view can detect radiation back-scattered or transmitted by such an object subjected in that zone to scanning by a scanning beam emitted by the illuminating device, while being synchronized with the stepwise actuation devices of the illuminating device so as to perform detection operations between successive measurement steps of those actuation devices and provide a measurement of radiation received in its field of view for each measurement position of the scanning beam actuated by those stepwise actuation devices, those measurement steps having the value of one or more elementary steps. It is to be noted that, according to need, the actuation devices may actuate scanning according to the aforesaid elementary steps, or according to larger measurement steps. Preferably: the unitary detector is designed to be able to supply radiation measurements for positions of cylinder portions in which the zones of those portions which have said amplitude α or β intercept at most only part of the illumination sector of the illuminating device. The device comprises at least one detector of scattered radiation and at least one detector of transmitted radiation. As is known, two different quantities may be distinguished with regard to the dimensions of such a unitary detector: the thickness which is in practice configured for the radiation to detect (the thicker it is, the more the radiation interacts with the sensitive material of the detector, and the more effective the detection) and the area presented to the radiation stream to measure. This area solely depends on the quantity of radiation to intercept, which quantity is linked to the temporal response of the scintillator in the case of photon counting (pile-ups should be avoided) and the counting capacity of the card (it must be possible to individually count two pulses separated by a very short time). In the case of integrator operation, the size of the detector will depend on the dynamics of the integrator that follows the detector. The invention also provides a method of forming an image of an object situated in a reception zone, wherein: a. the object is subjected to scanning by an illumination beam emitted by an illuminating device as defined above, measurement step by measurement step in each scanning direction, each measurement step of one of the actuation devices of that illuminating device having the value of one or more elementary steps of that actuation device. b. after each measurement step of one of the actuation devices of that illuminating device, a measurement is acquired of the quantity of radiation scattered (and/or transmitted) by the object subjected to the illumination beam at that time and that measurement is stored in a matrix of which the rows and the columns correspond to the respective positions of the actuation devices of the illuminating device, c. next the image of the object is reconstructed by deconvolution of said matrix containing said measurements by a matrix representing the illumination beam at that time. Advantageously, the object is first subjected to scanning by an illumination beam emitted by the illuminating device with a measurement step equal to a number of elementary steps greater than 1, part of the object to analyze is selected within the reception zone and steps a to c are applied to that part only with a measurement step equal to said elementary step. It can be understood that, to apply the aforesaid steps to part only of the object, it is possible to take radiation measurements only for some of the positions of the cylinder portion (which amounts to not taking measurements over the full amplitude possible, transversely to the second rotational axis; as regards the scanning actuated by the first stepwise actuation device, it may be chosen to take measurements only for some possible positions of a slit, or to choose back-and-forth actuation of such a stepwise device. Selective scanning of part only of an object is particularly easy when each stepwise actuation device actuates, in back-and-forth actuation, a single portion cylinder, in particular when the cylindrical ring 3 or 103 is reduced to a cylinder portion. FIG. 1 represents a scanning illuminating device, called radiation modulator, according to first embodiment of the invention. This modulator, denoted M overall, comprises a radiation source 1 assumed to be localized and thus situated at a point, which is designated by the reference 1. This radiation source may be a continuous source emitting a constant stream of photons or else a pulsed source emitting a succession of identical pulses at a determined frequency; in this second case, the time between two successive pulses is sufficiently small relative to the changes in configuration of the modulator (see below) for the average stream of radiation to be considered as practically constant. It is around this point 1, called emission center, or just center, below, that the other elements constituting the modulator are disposed. In a general manner, this modulator is operative to move, in front of the source, alternations of materials that are absorbent and non-absorbent of the radiation from the source in order to successively illuminate determined zones of space so as to form a beam providing scanning in two directions that are transverse to each other and transverse to the direction of the scanning beam. This modulator comprises a static primary collimator suitable for giving the beam emitted by the source 1 a given form and amplitude; the beam so collimated is designated by reference 2 which thus indirectly designates that primary collimator; the extension of this beam to the outside of the modulator is designated by reference 2′. It can be understood that this collimator delimits the zone of space (it is an angular sector starting at the source 1) in which the radiation from the primary source may, by virtue of the other elements of the modulator, be projected outside the modulator, and in which must be situated an object to image. In the represented example, this angular sector is pyramidal but may, as a variant, be conical, or even have a more complex form, for example hexagonal, or even a form with several lobes. This angular sector defines the angular field in which the modulator can provide illumination by scanning. Around the source and the collimator there is disposed a cylindrical ring designated by the reference 3. This ring is centered on an axis 4 around which it is rotatable; this axis, here vertical, passes via the source 1, that is to say the center of the modulator. This ring comprises a plurality of slits 5, in practice parallel to its axis; these slits, 8 in number here, are all identical and their angular spacing is regular (that is to say that the angular spaces, or intervals, between two successive slits are identical, whatever the slits considered). The function of these slits is to allow to pass a fraction of the radiation 2 transmitted by the collimator when they are positioned in front of it; on the other hand, the closed zones 6 situated between those slits are dimensioned such that the radiation transmitted by the collimator can be fully blocked, and thus stopped, by each of those closed zones. These full zones, which are opaque to the radiation, have an angular amplitude at minimum equal to the angular amplitude, around the axis 4, of the illumination sector delimited by the collimation element. These slits have angular amplitudes, measured relative to the center 1, which are the same, denoted α. The modulator further comprises a portion 7 of a second cylinder, of axis 8 passing by the source 1, making a non-zero angle, preferably equal to 90°, with the axis of the cylindrical ring 3. This portion 7 is also rotatable around its axis 8. I comprises a single slit 9, in practice parallel to that axis 8; its angular amplitude from the center 1 is denoted β. This slit, conjointly with the slits 5, is also operative to allow passage of a fraction of the radiation 2 transmitted by the collimator when it is positioned in front of the latter; it can be understood in fact that each of the slits 5 may delimit, with the slit 9 an aperture delimiting, according to each of the axes, a fraction of the collimated beam that is permitted, at a given instant, to illuminate a fraction of the external space. As for the closed portions 6 of the cylindrical ring 3, the closed portions 10 situated on respective opposite sides of the slit 9, which are opaque to the radiation, have a sufficient angular amplitude to enable the entirety of the collimated beam 2 to be blocked, and thus have an angular amplitude at least equal to the angular amplitude, around the axis 8, of the illumination sector delimited by the collimation element. In the configuration represented in FIG. 1, one of the slits 5 delimits with the slit 9 an illumination beam designated by reference 11. For reasons of legibility, the dimensions of the latter have been exaggerated in FIG. 1 relative to the angular dimensions of the aperture formed conjointly by the slit 9 and one of the slits 5; as a matter of fact, its amplitude in width (perpendicular to the slits 5) has the value α while its amplitude in height (perpendicular to the slit 9) has the value β. By way of example, the beam represents 1/16th of the zone covered by the collimator (9°/36°)2. Advantageously these angular amplitudes α and β are equal to each other. The cylinder portion 7 is here situated within the volume of the cylindrical ring, but may as a variant be situated outside it. The modulator further comprises stepper motors enabling the ring 3 and the portion 7 to be moved in their respective movements. The fact that these motors are of stepper type means that they are configured to incrementally move the ring and respectively the cylinder. The concept of stepper motors here includes the reduction gearing with which they are usually provided. The arrow situated above the cylindrical ring 3 of FIG. 1 designates a constant direction of movement (here clockwise), while the arrow associated with the portion 7 is double, which means that portion can move in either direction around its axis 8, within a given angular travel. The stepper motor associated with the movement of the ring is shown diagrammatically under the reference 12, while that associated with the movement of the cylinder portion is shown diagrammatically under the reference 13. The constancy of the direction of scanning by the cylindrical ring 3 is rendered possible by the regular distribution of the slits 5 and of the closed zones 6; is will be understood below that, as a variant, it suffices for the cylindrical ring to comprise a single slit 5 (or be reduced to one cylindrical ring portion) if the associated stepper motor 12 can act in both directions (one direction for the scanning and the opposite direction to return to starting configuration); however, as will be apparent below, it is much simpler for the cylindrical ring to be only moved in one direction, and this enables faster scanning. Of course, both types of actuation (single direction, and back and forth, according to need). The stepper motors 12 and 13 are actuated so as to be able to act in synchronized manner on the cylindrical ring 3 and the cylinder portion 7. In particular, the stepper motor 13 actuating the cylinder portion 7 makes that cylinder portion advance by one measurement step (angular separation between two configurations in which an image is taken—as will be detailed later, this measurement step may have the value of one elementary step or several of those elementary steps) when the stepper motor 12 actuating the cylindrical ring 3 turns through an angle corresponding to the angular amplitude combined with a closed portion 6 and a slit 5 (the ring is formed from a plurality of patterns, each pattern comprising a slit and a closed part). In other words, the rotation of the motor 12 necessary to bring a slit into the same angular position as the preceding slit corresponds to a whole number of its elementary steps. Similarly, the angular amplitude of the slits 5 corresponds to a whole number of elementary steps of the motor 12. Similarly, the angular amplitude of the single slit 9 advantageously corresponds to a whole number of elementary steps of the motor 13. To be precise, for a given position of the cylinder portion, scanning parallel to the axis thereof is provided by moving a slit, measurement step by measurement step, from on to the other of the sides of the collimated beam; next, the scanning continues in the same manner, by virtue of an adjacent slit, for another position of the motor after the movement of a new measurement step. It is important to note that, according to the invention, stepper motors have elementary steps which correspond to angular amplitudes which are sub-multiples of the angular amplitudes of the slits 5 or 9. Thus, if αα is the elementary angular amplitude of an elementary step of the motor 12, there is an integer N1 different from 1 such that α=N1·αα. Similarly, if ββ is the elementary angular amplitude of an elementary step of the motor 13, there is an integer N2 different from 1 such that β=N2·ββ. The elementary steps of angular rotation of the ring 3 and of the cylinder portion 7 are advantageously equal (αα=ββ), which makes it possible to ensure scanning of the same fineness in both scanning directions. On a subsidiary basis, this facilitates the implementation of identical motors for both scanning directions. Similarly, it is advantageous to give equal angular amplitudes, α=β, to the slits (hence a square shape of the sections of the apertures thus conjointly delimited). When αα=ββ, this amounts to saying that N1=N2. It may be noted that the illumination beam leaving the modulator, that is to say passing through slits of the ring and of the cylinder portion, maintain a shape and dimensions that are identical when it moves angularly: this outgoing radiation beam is named pencil in the following portion of text. FIG. 2 represents an example of use of the modulator of FIG. 1 to produce a device for back-scattered and/or transmitted imaging. The modulator M is illustrated diagrammatically therein in the form of a small cylinder much smaller than in FIG. 1, for reasons of legibility. An object 20 to image (or the part which it is wished to image within an object) is placed inside the field 2′ in which the modulator is capable of providing illumination by scanning. It may be understood that this object to image, that is to say to analyze by means of the chosen radiation, is often a container the single or multiple content of which it is desired to identify; it is represented diagrammatically here by a cube in which several items are hidden. The cube here occupies practically the whole of the volume of a reception zone within which an object must be located to be able to be analyzed; the shape of this reception zone is defined by the shape of the primary collimator. Below, reference 20 will designate in the same way that reception zone and the object to image which is situated therein. As was explained with regard to FIG. 1, the modulator makes it possible to scan the object 20 to analyze with a radiation pencil 11 delimited by the crossing of one of the slits 5 of the ring and the slit 9 of the second cylinder. It is to be recalled that the radiation pencil is represented exaggeratedly large; it is designated by reference 14 when it is in central position. The projection of that radiation pencil into a plane 15 situated behind the object is referenced 16. According to an aspect of the invention, in projection into a transverse plane passing through the object, the radiation pencil of greater dimension than the spatial resolution sought in the back-scattered (or transmitted) image since the spatial resolution does not depend on the size of the radiation pencil but it depends on the step of movement thereof between two measurements, that is to say between two instances of image taking (hence the concept of measurement step). It is thus possible, according to the invention, to use a quite large radiation pencil to pass sufficient radiation and improve the signal-to-noise ratio at the detector. Reference 17 designates a unitary detector which detects the radiation back-scattered by the object for each illumination position of the radiation pencil coming from the source and selected by the modulator. The transmitted image (the same reasoning applies to the back-scattered image) is reconstituted from the set of successive recordings as described below. The unitary detector 17 serving to detect the image back-scattered by the object 20 is advantageously complemented by a unitary detector of large size in order to detect the radiation transmitted through the object for each position of the pencil radiation beam and use that information, following the same principle as for a back-scattered image, to reconstruct an image from the radiation transmitted by the object as a complement to the back-scattered image. As a variant, it may be chosen to form only a transmitted radiation image. This unitary detector for transmitted image detection may be constituted by the plane 15 represented in FIG. 2. The starting position for a scanning cycle corresponds to positions of the ring and of the cylinder portion such that the trace on the plane 15 of the angular sector delimited by a slit 5 and a slit 9 (the term “pattern” is used subsequently) is located outside the analysis zone; this starting position is designated by the reference 19. That is to say that, a minima, the outer limit of the pattern 19 is tangential to the outer limit of the trace on the plane 15 of the analysis zone 2′. The scanning is terminated when the pattern has traversed stepwise the whole analysis zone and has arrived at the opposite outer limit of that zone. It is to be noted that, in the case represented in which the starting position 19 is tangential to the analysis zone, there is no pencil radiation beam since the aperture delimited by one of the slits 5 and the slit 9 is outside the collimated beam 2′. The same will apply at the time of the first scan in a direction X or Y (see the arrows in FIG. 2), for the extreme positions of the following scans and at the time of the last scan. This is why it may be preferable for the starting position to correspond to a position in which the trace 19 is superposed on the trace of the analysis zone over an amplitude corresponding to one motor step in each of the directions. At the limit it is possible to start with a motor step in the zone 2′ knowing that the preceding row will be at zero. In reality that first row will not be zero but will contain background noise above all. By shifting several steps, the size of the reconstructed image will be the same number of steps smaller. Thus by starting at the edge, the entirety of the zone delimited by the primary collimator is taken advantage of. The scattered radiation measurement (the reasoning is the same for the transmitted radiation) received by the unitary detector 17 is synchronized with the stepper motors. After each movement of one of the two cylinders (that is to say after each measurement step) a measurement of scattered radiation arriving on the detector is started and that measurement is stopped at the next movement of one of the two cylinders. The detector measures the quantity of radiation it receives, over the entirety of its field of view, either by counting the photons (weak radiation stream), or by integration of the radiation (high radiation stream). The choice of the detection mode depends on the activity of the source, on the characteristics of the modulator and on the geometry of the device. The measurements are stored row by row in correspondence with the X-Y scanning of the zone illuminated by the radiation pencil beam. The measurements end when the entire zone delimited by the primary collimator has been scanned. The set of measurements constitutes a matrix corresponding to the convolution product of the back-scattered image of the object with the intensity and the shape of the projection of the radiation pencil beam in the plane of the object. An operation of deconvolution of that matrix enables the back-scattered image to be reconstructed. The matrix corresponding to the shape and the intensity of the projected pencil beam may be computed based on the knowledge of the width of the slits of the modulator and of the acquisition geometry. It may also be identified experimentally in a laboratory using an imager. The scanning step, between two measurements, defines the pixel size of the image. The spatial resolution of that image is thus fixed by the size of the movement step of the radiation pencil beam in movements by the motors. This imaging device thus makes it possible to choose, and thus to modify, the spatial resolution with which the object is analyzed without modification either of the device itself, or of its installation in relation to the object. It is thus possible to rapidly make a first image with low resolution (with a coarse scanning step, with a measurement step equal to several elementary steps) to determine a zone of interest which will then be inspected with a finer resolution (reduced scanning step, that is to say with a measurement step equal to a smaller number of elementary steps, possibly equal to 1) for example. The principle of the construction of a measurement acquisition matrix is illustrated diagrammatically in FIG. 3. This diagram serves to illustrate the fact that the scanning zone may be cut up virtually into pixels which correspond to a movement step, here an elementary step. However, since each detector is of unitary type, it provides a single measurement at a time. As a matter of fact all the information coming from the detector is used; its measurement constitutes an element of the measurement matrix, for a position of the beam. Since, as explained above, the angular amplitudes of the radiation pencil beam are multiples of those elementary steps, the trace of such a pencil beam on a zone of the object is delimited by a rectangle, or even by a square in the case considered here in which the angular amplitudes are the same in both directions; the number of elementary steps contained in one side of that trace is denoted h. In other words, h is the number of positions of the beam, in each scanning direction, for which the same elementary zone of the object interacts with the scanning beam. In the case defined above in which the scanning is carried out with extreme positions where the aperture defined by the slits is tangential, without overlap, to the trace of the analysis zone, the total zone of scrutiny represented on that FIG. 3 is of width m+2 h and of height n+2 h if m and n are the numbers of elementary steps in width and in height to explore the analysis zone and thus the size of the reconstructed image. After a first scan in the X direction (without illumination), the second scan, after an elementary step p downward, makes the beam 11 circulate in such a way as to intercept the collimated beam, such that it provides an illumination of the object, even though this is with dimensions different from those which that beam would have when the apertures delimited by the slits 5 and 9 are fully contained in the collimated beam. The total number of measurement steps (or scrutinizing steps) in this case is (m+h)·(n+h). Let X (i,j) denote the matrix representing the back-scattered image which it is sought to reconstruct. At each elementary step, if the numbers of elementary steps made by the actuation devices are denoted by k and i, the quantity Mkl measured by the detector is proportional to the sum (on the rows and columns) of the product (multiplication term by term) of the matrix X by the matrix H representing the shape and the intensity of the radiation pencil beam projected into the plane of the object. Written otherwise, for a pencil beam H of size h×h with h=2N+1 M kl = ∑ j = - N N ∑ i = - N N X ( k - i , l - j ) . H ( i , j ) Which, in the context of the distributions, corresponds to the convolution product of X by H.Mkl=(X*H)(k,l) where * is the convolution product Mathematical definition of the convolution according to the functions:(f*g)(x,y)=∫−∞∞∫−∞∞f(x−t,y−u)·g(t,u)·dt·du=∫−∞∞∫−∞∞f(t,u)·g(x−t,y−u)·dt·du=(g*f)(x,y)Which for the entirety of the scanning, gives the convolution product between the object X and the pencil beam H. ( x 11 x 12 x 13 x 14 · · · · x 1 j · · · · · x 1 n x 21 · x 31 · · · · · · · · · x i 1 · · · · · · · x ij · · · · · x in · · · · · · · · x m 1 · · · · · · · · · · · · · x mn ) Dimensions m × n Object X * ( a b c d e f g h i j k l m n ) h × h pencil beam H = ( M 11 M 12 M 13 M 14 · · · · · · M 11 · · · · · · · M 1 q M 21 · M 31 · · · · · · · · · M k 1 · · · · · · · M k 1 · · · · · · M kq · · · · · · · · · · · · · · M p 1 · · · · · · · · · · · · · · · · · M pq ) measurements M ( m + h ) × ( n + h ) Nota bene: it is not mandatory for the matrices to be square. The pencil beam may have any suitable dimensions. A pencil beam of dimension 1 will be equivalent to scanning by a very fine beam and the matrix of the measurements will directly be the image of the object. It may thus be understood that, on the same object, first coarse scanning may be carried out, with an enlarged measurement step, for example equal to h elementary steps in at least one direction (with a processing operation indicated at the preceding paragraph for the pencil beam of size equal to the elementary step), then fine scanning scrutinizing the object with the minimum step, that is to say the elementary step. The object X may be reconstructed by several mathematical methods based on the measurement matrix M and the pencil beam matrix H. This reconstruction may be carried out by the use of an algorithm, a matrix inversion method or for instance by taking advantage of the properties of Fourier transforms. f * g = F - 1 [ F ( f ) . F ( g ) ] F Fourier transformation , F - 1 inverse Fourier transformation To retrieve the object X based on the measurement M and the pencil beam H using the Fourier transformations:X=F−1[F(M)/F(H)] division term by term It should be noted that the method of reconstructing the image does not make use of any source/object/detector size. The image is sharp everywhere. Corrections may be made to the reconstructed image (they are within the capability of the person skilled in the art): in principle, the source must emit a constant quantity of radiation per unit time for the duration of the scanning. If this is not the case, correction of the measurements may be made based on monitoring of the source, it is possible for the spatial distribution of the intensity of the radiation emitted by the source inside the analysis zone not to be uniform. For example, the source may present an emission lobe. It will be possible for this non-uniformity to be the subject of correction of the reconstructed image provided measurement thereof has been made in advance, the geometry of the mechanical system is such that the projection of the radiation pencil beam is regular over a spherical dome. As the image of the object is reconstructed in a plane, it is possible to perform geometric corrections at the time of the reconstruction of the image in order to take into account that distortion. Possible blur of the images taken between two measurement steps, if there is no full stoppage of the motor considered, may be corrected by means of processing which is known per se in the field of tomography. In order to improve the signal-to-noise ratio of the reconstructed image, it is possible to add other unitary detectors (positioned outside the emission zone of the modulator) which will simultaneously collect the scattered radiation reaching each of them during scanning. The position of these detectors is not involved in the reconstruction of the image, their putting in place is thus very fast and does not require painstaking adjustment. The advantage of using several detectors and their judicious disposition is also to limit the zones of shadow due to the masking by each other of the different parts of the object inspected. Lastly this disposition, by reconstruction of the individual images coming from each detector and by combination between them, gives access to the depth of the object inspected by using the principles implemented in photogrammetry. FIG. 4 represents a complete device for back-scattered and transmitted imaging with a modulator M (including a radiation source) which generates a radiation pencil beam configured to be moved in two directions, several unitary detectors 17A, 17B, 17C and 17D measuring the radiation scattered by the object 20, a unitary detector 15 measuring the radiation transmitted through the object, electronics 30 for acquiring signals from the aforesaid detectors, and a system 31 for actuation and control which governs the stepper motors 12 and 13 of the modulator, synchronizes the detectors with the motors, and processes the signals to reconstruct the back-scattered and transmitted images. An advantage of choosing values N1 and N2 equal to odd integers is that, when each measurement is made, the pencil beam is centered on a given pixel. Such a case is envisioned above, which has the advantage of a certain symmetry of the matrices; but the case of even values is just as possible, by modifying the matrices above. When it is wished to be able to perform scanning with several different measurement steps, it has been indicated that there is at least the possibility of carrying out coarse scanning with a measurement step equal to the angular amplitude of the pencil beam in the direction considered (that is to say equal to N1 or N2 times the elementary step). When it is wished to be able to perform, furthermore, scanning with an intermediate measurement step, it is recommended that this intermediate measurement step also be a sub-multiple of the angular amplitude of the pencil beam, which means that the integers N1 and N2 are advantageously numbers which are not prime, but products of smaller integers. It can be understood that if N1 and N2 (for which it has been stated that there is an advantage for them to be equal) are products of different integers, each of these integers then enables scanning at intermediate measurement step while following calculations easily deduced from those indicated above; by way of example, values N1=N2=5 enable scanning operations at measurement steps of 5 (coarse scanning) and of 1 (fine scanning), and values N1=N2=15 enable scanning operations at measurement steps of 15 (very coarse scanning), of 5 and of 3 (intermediate scanning operations) and of 1 (fine scanning). FIG. 5 represents a variant embodiment for a modulator in accordance with the invention, distinguished from the configuration of FIG. 1 by the fact that the width of the slits made in the cylinders at the point of inverting the closed and open parts of the ring and of the cylinder portion of the modulator M is very significantly increased. The parts similar to those of FIG. 1 are designated by reference signs which may be derived from those of FIG. 1 by increasing by the number 100; thus the center is denoted 101, the rotational axes 104 and 108; however, the cylinder portion is limited to a single closed part 107, of width similar to that of the closed parts 106 alternating with spaces 105 within the cylindrical ring 103. Through analogy with the above, the ring portion 106, which is opaque to the radiation, is delimited by two portions 105 transparent to the radiation, each having an angular amplitude at minimum equal to the illumination sector 102 delimited by the collimation element around the first axis; similarly the portion 107 opaque to the radiation is delimited by two portions transparent to the radiation each having an annular amplitude at minimum equal to the illumination sector 102 delimited by the collimation element around the second axis. The radiation pencil beam occupies any space 102′ delimited by the primary collimator with a cross-shaped shadow 111 moving during the scanning. Such a modulator may be integrated into a device for back-scattered and/or transmitted imaging (of which the other elements are similar to those described above), the construction of the images being carried out on the basis of radiation induced by the scanning of the shadow caused by the crossing of the closed parts. This disposition uses a greater portion of the radiation emitted by the source and thus makes it possible to improve the signal-to-noise ratio and/or to shorten the acquisition times. FIGS. 6 and 7 show a radiation modulator produced for a commercially available portable X-ray source of 120 kV, 1 mA DC (CP120 from the company ICM). This source 1 is in practice contained in a cylindrical body; the latter is advantageously removable in relation to the rest of the modulator. The primary collimation is of lead. It delimits a cone of 36° of which the vertex is the emission point of the generator (illuminated field of 65 cm diameter at 1 m from the center of the source). The collimator is not represented here per se. The ring and the cylinder portion are provided with shutters 6 and 10 of tantalum of 3 mm thickness. The closed parts of the first cylinder cover an angle of 36°, the slits 5 and 9 each cover 9°. This disposition leads to eight slits on the cylindrical ring. The radiation pencil beam so formed by the crossing of the vertical and horizontal slits covers a square of 9°×9°, that is to say a sixteenth (9°/36°)2 of the illuminated zone. Two identical stepper motors (NEMA17, 0.9°) with integrated electronics of 200 steps per revolution actuate the two rotatable parts via reduction gearing with a 1/50 ratio. This configuration leads to movement of the slits of 0.036° per motor step. The scrutinized zone thus corresponds to 1000+250 motor steps (36°/0.036 and 9°/0.036). This makes it possible to reconstruct an image of 1000×1000 pixels. For a source/object distance of 1 m, the size of a pixel is 0.65×0.65 mm. The motors are configurable in elementary steps of value ½ step, ¼, ⅛ steps, etc., which enables the acquisition of images of larger size thus of smaller resolution (0.018° in ½ step mode). For images of lower resolution, for example 500×500 (0.072°), two successive pulses are applied to the motors to make the slits advance between each measurement acquisition (the measurement step then having the value of two elementary steps). These motors are actuated by programmable electronic cards which supply the signals for synchronization of the acquisitions and also count the pulses delivered by the detectors between two successive positions of the slits. As in FIG. 1, the cylinder portion 7 is situated inside the volume of the cylindrical ring. It can however be understood that, as a variant, this cylinder portion may be situated outside that cylindrical ring. The assembly is integrated within a casing comprising a support 60, a lateral wall 61 and covering elements 62. By way of example, the diameter of the ring is 320 mm for a height of 270, which corresponds to a particularly compact device for scanning in two directions. FIG. 8 is a timing diagram of the operation of such a modulator integrated into an imaging device comprising 4 detectors. Based on a clock signal, here of 80 MHz, pulses of the vertical motor (that is to say of the motor which causes the rotation of the ring about the vertical axis) trigger rotational steps of the ring; however, one pulse is applied to the horizontal motor (that is to say to the motor which causes the rotation of the cylinder around the horizontal axis) after a number of pulses of the vertical motor corresponding to full scanning along a row (here over 1250 steps). A synchronization signal alternates from one acquisition step to another: the measurements made after each movement of the vertical motor correspond to the values indicated above with regard to the matrix calculation enabling the image of the analyzed object to be reconstructed. The acquisition of an image of 1000×1000 pixels of an object situated at 1 m from the source is carried out in 15 min. This corresponds to counting intervals of 576 μs and to a rotational speed of the ring of 10.4 revolutions per minute. An image of 200×200 pixels with the same signal-to-noise ratio is produced in 1 min. These acquisition times may be further reduced by increasing the number of detectors, the size of the scintillators and by using faster counter cards. To be precise, the more photons there are per pixel, the faster it is necessary to be able to count them. FIG. 9 represents an example of a counter chain for the acquisition of the measurements; this counter chain comprises a fast plastic scintillator (the typical dimensions are a diameter of 50 millimeters for a height of 50 millimeters) coupled to a photomultiplier (PMT): the output signal is put into TTL format and is applied to a card for controlling synchronization and counting generating actuation signals for the motors. It is to be noted that if, for a given analysis operation, it is chosen to use the actuation devices only with minimum steps which are multiples of the elementary steps, the comments made above regarding the elementary steps apply to the minimum steps; in other words, the concept of elementary step used above may be modified according to need, with the same structural configuration. The system is in particular adapted to inspect objects of everyday life (suitcase, bag, cardboard package, etc.) upon the size of which depends the aperture of the primary collimator of the radiation source. An illuminated zone of the order of 50 cm seems to be a minimum. By placing the generator at 1 m from the object, this leads to a minimum angular aperture of the collimator of the order of 30°. A reasonable maximum aperture is ≦90°, which leads to an illuminated field of 2 at a distance of 1 m; beyond, the illumination on the edges is less than 40% relative to the center (lobe of the radiation generator having a localized source). The imaging principle used (in FIG. 1) means that at a time of the cycle the object is not illuminated. The closed parts of the modulator must therefore cover the aperture of the collimator. This advantageously gives a domain comprised between approximately 30 and 90° for the closed parts. The slits between the closed parts must enable the passage of a significant part of the radiation. A minimum aperture of the order of 10° (field of 17 cm at 1 m) is desirable. The maximum aperture will be at most equal to the aperture of the collimation. Indeed, a greater aperture leads to acquiring more information than necessary to reconstruct the image. A large width of slit means a greater quantity of measurements to acquire and thus a longer time of scrutiny (to reconstruct an image m×n, the number of measurements required is (m+h)×(n+h) with h being the width of the beam. If the slits have the same width as the closed parts, it is necessary to acquire 4 times as many pixels of the image as it is desired to reconstruct. In a practical manner, the aperture of the slits may advantageously be limited to half the aperture of the closed parts to reduce the number of acquisitions (2.25 times the size of the image). This leads preferably to choosing a domain comprised between approximately 10 and 45° for the slits. The first choice to make is the size of the field to scrutinize. This requires the opening of the closed parts. The opening of the slits is a result of what has just been described (i.e. an aperture>10° and <½ the closed part). The regular distribution of those closed parts and slits, in the limit of the predefined apertures, on a cylinder, will set the possible values for those same apertures. The implementation of a cylinder portion leaves a greater choice of possible apertures. Examples of values of pairs of apertures for a distribution over a cylinder: all the pairs for which 360/(Slit+Closed)=integer operate with ≈30°≦closed≦90° et≈10° slit≦½ closed. SlitClosed partN patternsField illuminated at(°)(°)over a cylinder1 m (m)927100.48103090.549.330.790.55153080.54154560.83306041.15187241.45309032.00 |
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summary | ||
abstract | The dental fluoroscopic imaging system includes a flat panel detector comprised by a gamma-rays or x-rays converter, a plate, a collector, a processing unit and a transmitter suitable for 2D intraoral/extraoral and 3D extraoral dental fluoroscopy. The x-ray converter contains a material capable of transforming the low dose gamma rays or x-rays beam received from an emitter after going through the dental examination area into electrical signals or a light image consequent with the radiographed image. The plate transmits the electric signals or light image to a collector which amplifies it and sends it to a processing unit and then to transmitter designed to transfer digital images sequentially to a host computer and software which can acquire, process, transform, record, freeze and enhance 2D and 3D images of video frame rates. Two dimensional images are obtained while using a C-arm/U-arm configuration while 3D images are obtained while using the O-arm configuration. |
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abstract | The object of this invention is to provide a device and method for the dry intermediate storage of irradiated fuel elements. The apparatus includes a casing which includes tiered superposed modules made of thermally conductive material and having compartments for accommodating fuel elements with a heat sink arranged on a perforated support plate. The system includes a retaining system which includes a clearance space left between a top module of a tier and a support plate of a tier above the superposed module. |
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claims | 1. A method for removing a thermal sleeve from a cold leg of a reactor coolant system, the thermal sleeve being installed to minimize the effect of thermal shock at a junction between a coolant pipe of a reactor and a safety injection pipe connected to a midway position of the coolant pipe, the method comprising:installing an extension pipe operation for connecting the extension pipe having a predetermined length to the safety injection pipe so as to set a secondary working zone at a predetermined height corresponding to a height of a primary working zone, wherein the extension pipe has a bent lower end portion located inside the safety injection pipe and configured to obliquely extend toward the coolant pipe by a predetermined guidance angle;inserting a cable into the safety injection pipe, a wire rope connection operation inserting a cable into the safety injection pipe after disassembling a check valve of the safety injection pipe so as to allow the cable to be moved into the reactor through the coolant pipe and thereafter, connecting a plurality of wire ropes to one end of the cable at the primary working zone provided at an upper end of the reactor and pulling the other end of the cable from the secondary working zone above the safety injection pipe so as to allow the wire ropes to be moved to the secondary working zone;descending a vertical movement carrier in which a sleeve removal tool and a horizontal movement carrier are seated, the vertical movement carrier descent operation connecting one ends of the respective wire ropes to one side of the vertical movement carrier, the sleeve removal tool and the horizontal movement carrier respectively while connecting additional pulling wire ropes to the other side of the vertical movement carrier, the sleeve removal tool and the horizontal movement carrier, and slowly descending the vertical movement carrier, in which the sleeve removal tool and the horizontal movement carrier are seated, to a height of the coolant pipe inside the reactor;moving the sleeve removal tool and the horizontal movement carrier from the descended vertical movement carrier along the coolant pipe, the horizontal movement carrier sliding operation pulling the wire rope connected to the horizontal movement carrier from the secondary working zone, so that the sleeve removal tool and the horizontal movement carrier are moved from the descended vertical movement carrier along the coolant pipe and are positioned at the junction of the safety injection pipe and the coolant pipe, the junction being an installation location of the thermal sleeve;lifting and inserting the sleeve removal tool into the safety injection pipe, the sleeve removal tool insertion operation pulling the wire rope connected to the sleeve removal tool from the secondary working zone, so that the sleeve removal tool accommodated in the horizontal movement carrier is lifted and is inserted into the safety injection pipe after passing through the thermal sleeve;sealing an upper end of the extension pipe preventing fluid leakage prior to the generation of a high hydraulic pressure inside the safety injection pipe;removing the thermal sleeve, a thermal sleeve removal operation generating high flow rate hydraulic pressure inside the safety injection pipe by driving a high pressure pump that is previously installed at a front end of the safety injection pipe so that the generated hydraulic pressure is applied to a corn head and an upper end of a pressure plate included in the sleeve removal tool to produce a force pushing the thermal sleeve downward, thereby allowing the sleeve removal tool to be separated from the safety injection pipe along with the thermal sleeve; andtransporting the thermal sleeve, a thermal sleeve transportation operation transporting the horizontal movement carrier, in which the separated thermal sleeve and the sleeve removal tool are seated, toward the reactor, in which the vertical movement carrier is on standby, along the coolant pipe by pulling the pulling wire rope of the horizontal movement carrier from the primary working zone. 2. The method according to claim 1, wherein the thermal sleeve removal operation includes a sleeve removal tool removing operation for manually pulling a wire rope additionally connected to the sleeve removal tool from the primary working zone so that the sleeve removal tool is folded and drops into the horizontal movement carrier when separation of the thermal sleeve ends in failure and the sleeve removal tool is caught in the safety injection pipe. 3. The method according to claim 1, wherein the sleeve removal tool includes:the corn head formed at a front end of a shaft having a predetermined length;the pressure plate provided below the corn head and divided into a plurality of sections so as to be folded or unfolded;a spring connected to an upper surface of the pressure plate to keep the pressure plate in an unfolded state;a guide wheel provided at a midway position of the shaft to guide the sleeve removal tool into the safety injection pipe;a slider ring movably installed to the shaft and having a wire connection loop for connection of a wire rope required to forcibly release a tensile force applied to the pressure plate; anda tension release link to connect the pressure plate and the slider ring to each other. 4. The method according to claim 1, wherein the vertical movement carrier descent operation includes manually pulling a connection wire rope connected to an anti-separation bar, which is provided at the vertical movement carrier to prevent unintentional separation of the horizontal movement carrier, from the primary working zone after completion of the descent of the vertical movement carrier, so that the anti-separation bar is pivotally rotated and raised about a hinge to allow the horizontal movement carrier to be movable from the vertical movement carrier toward the coolant pipe. 5. The method according to claim 2, wherein the sleeve removal tool includes:the corn head formed at a front end of a shaft having a predetermined length;the pressure plate provided below the corn head and divided into a plurality of sections so as to be folded or unfolded;a spring connected to an upper surface of the pressure plate to keep the pressure plate in an unfolded state;a guide wheel provided at a midway position of the shaft to guide the sleeve removal tool into the safety injection pipe;a slider ring movably installed to the shaft and having a wire connection loop for connection of a wire rope required to forcibly release a tensile force applied to the pressure plate; anda tension release link to connect the pressure plate and the slider ring to each other. |
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description | The instant application is a national phase of PCT International Application No. PCT/RU2014/000169 filed Mar. 19, 2014, and claims priority to Russian Patent Application Serial No. 2013135672, filed Jul. 31, 2013, the entire specifications of both of which are expressly incorporated herein by reference. The invention relates to a field of nuclear technology, and more particularly to a method for long-term safe storage of waste nuclear fuel of nuclear reactors. Long-term (for decades) safe storage of waste nuclear fuel (WNF), particularly waste fuel assemblies (WFA) of nuclear reactors poses a complex technical challenge. This is due to the fact that there is a high radiation potential associated with radioactivity of fuel materials' nuclear fission products contained in WNF, and also with radioactivity of secondary nuclear fuel (Plutonium) and minor actinides (Neptunium, Americium, Curium) formed during operation of nuclear reactor (NR) when exposed to neutrons of primary nuclear fuel. Damage of the principal safety barrier, the casing of fuel element (FE), resulting from corrosion, thermal and mechanical impact, will lead to escape of radioactivity and will cause serious radioecological consequences. The problem is further complicated by the fact that WNF is an irremovable source of afterpower, emission of which gradually decreases over time, but even after many years it requires an organized heat removal, the failure of which will cause an increase in WNF temperature and loss of hermetically sealed state of FEs casing. Currently, the customary method for long-term storage of WNF consists in arranging WFA in cooling ponds (CPs) filled with water which removes afterpower of WFA. Since water in the CPs may be radioactive, it is cooled using a heat exchanger connected to an external source of cooling water. The prior art discloses methods for storage of waste nuclear fuel in cooling ponds. For example, there is a method known in the art for storage of waste nuclear fuel by placing cases perforated at their top and filled with desalinated water in ponds with desalinated water. The level of water in the cases and the pond is kept below the edge of the holes by intermittently feeding desalinated water from a stand-alone reservoir to the cases and the pond. In addition, it has been proposed to feed water to the cases intermittently, upon reaching maximum allowable level in test cases with a maximum value of afterpower (RU patent 2403633, G21C19/06, G21F9/36, 2010). The prior art also discloses a method for storage of radioactive materials, including a) submersion of a container having a top part, a bottom part and a cavity inside the container housing for filling of water, b) installation of a radioactive material inside the cavity of the container placed for water filling, c) lifting of the submerged contained until its top part is disposed above water reservoir surface level with the main part of the container remaining below water reservoir surface level, and d) removal of water from the cavity of the container with the top part of the container remaining above water reservoir surface level, and the remaining part of the container being submerged (US patent application US2009069621, G21F5/005, 2009). There is known a method used in waste nuclear fuel storage facilities, at NPPs and waste nuclear fuel reprocessing plants. For long-term storage of waste nuclear fuel in cases filled with water, placed in a water pond under a beam floor using suspension rods, the supporting parts of the cases are installed on the bottom of the pond, and the upper end of the cases is placed under the beam floor with a clearance of 100+150 mm and case density based on 30+50 cases per square meter of the pond bottom area (RU patent 2407083, G21C19/22, 2010). The practice of using such method for WNF storage has shown that over time under the action of corrosive processes there occurs a loss of tightness of the container or case with waste nuclear fuel in cooling ponds as well as radioactive contamination of water. In order to prevent this phenomenon, lately a “dry” storage of WFA has been used, wherein the WFA, after being stored in cooling ponds for some time (approximately three years) and after reduction of afterpower, is removed from the cooling ponds and placed into hermetically sealed cases, which are placed in an air-cooled “dry” storage facility. It is known that as a result of the accident at the Fukushima-1, due to failure of water cooling system power supply, there occurred evaporation of water in the cooling ponds, overheating of FEs, destruction of their bodies accompanied by the formation of a large quantity of oxygen formed during zirconium-steam reaction, and emission of radioactivity to the environment. In view of such a situation, it seems quite reasonable to switch to the “dry” WNF storage, omitting the stage of “wet” storage inside the cooling ponds. There are known methods for storage, which utilize a “dry” storage technique, described in U.S. Pat. No. 6,802,671, DE 3816195, U.S. Pat. No. 5,887,042, U.S. Pat. No. 8,098,790. The prior art describes a method for transportation and/or storage of nuclear materials, wherein the nuclear materials are arranged inside a container with radiation shielding made of cast lead arranged over metal framing (US application US2010183110, G21F5/008, 2010) This invention provides for presence of at least one level of radiation shielding which consists of at least one metal framing which is aligned along the longitudinal axis and enveloped with a block of lead or one of lead alloys, cast over the metal framing, with metal framing being equipped with at least one element for preventing cast lead (or one of its alloys) block from moving longitudinally. In addition, the said metal framing is embedded in the block cast from lead (or one of its alloys) at least by a portion of its length along the longitudinal axis, and in the preferred embodiment—along the whole length of the block. Thus, a solid mechanical connection of a metal framing and the lead (or one of its alloys) block is created, and a relative longitudinal movement of these two elements relative to each other in case of a free falling of a package, is precluded. The prior art also describes a method for storage of waste nuclear fuel in a convection-cooled container, wherein a bag with waste fuel is arranged inside a metal tank with hermetically sealed covers, with the tank having heat-removing side and end ribs, which at the same time act as distancing and damping elements. The tank is mounted inside the housing of the container while creating a clearance for air passage, with the ribs of the tank being in contact with the bottom and the side surface of the container's interior. The housing of the container is formed of outer and inner metal casings, space between which is filled with a radiation protection material, for example, with a heat-resistant concrete and/or neutron-absorbing composition. Between the casings, there are reinforcing heat-removing elements made in the form of perforated metal plates welded onto the inner casing and tightly contacting with the outer casing, mounted along the tangent to the inner casing. In the bottom part of the housing, the inlet cooling ducts are made, and in the cover, the outlet cooling ducts are made. In case of depressurization of the tank, the cooling ducts are closed with blind covers (RU patent 2231837, G21F5/008, 2004). The disadvantage of this technical solution is that there is a possibility of radioactivity emissions to the environment in case of depressurization of metal tank, inside which the bag with the waste nuclear fuel is placed. The closest analog of the claimed invention is the method for “dry” storage of WNF from reactors of nuclear submarines (NSs), wherein the unloaded waste removable part (WRP) along with the active core with WNF being a part of it, is, immediately after unloading, placed into one of the boxes of the preliminary cooldown storage facility in a steel hermetically sealed tank, inside of which a liquid melt of Pb—Bi, preliminarily heated above its melting temperature, was contained. A hermetically sealed cap is mounted atop of the tank. After disconnection of the heating system, reduction of the afterheat and solidifying of the eutectics, the tank with the WRP is moved to the box of the long-term cooldown storage facility for its further storing for 3-5 years or more (Zrodnikov A. V, et al.). Problems and approaches to handling of waste nuclear fuel of liquid-metal reactors of nuclear submarines. Higher education institutions bulletin Nuclear power industry—Ministry of Education and Science of the Russian Federation, Obninsk: No 1, 2007, p. 16). The disadvantage of the closest analog lies in the extremely limited field of use—only the active cores of the reactors of NSs, unloaded in whole as a part of WRP, having a very low level of afterpower at the time of unloading. This is caused by two factors: 1) reactors of NSs are mainly operated at low power levels; and 2) refueling is timed to confine with the yard repairs of the NSs, that's why the unloading is performed after a sufficiently long period upon shutdown of the reactor. For reactors of civil-use nuclear power plants, such method of unloading and storage of WNF is inapplicable due to high level of afterpower, caused by operation of the reactor, mainly, at nominal power level, and a short period of cooldown prior to unloading of the WNF. For the same reason, it is inapplicable to use eutectic Pb—Bi alloy having a low melting temperature (123.5° C.) as a heat-transfer medium, because this heat-transfer medium will be in a liquid state for a long time and will not function as an additional safety barrier. Moreover, such storage method does not allow transportation of WNF to a reprocessing plant in accordance with the applicable regulatory documents. A labor-consuming disassembly of the active core, being a source of a high nuclear and radiation hazard, is required. The object of the invention lies in increasing the safety of long-term storage of waste nuclear fuel when storing the waste fuel assemblies of the nuclear reactor in storage facilities with cooling using atmospheric air, preferably with natural circulation of atmospheric air. The set object is achieved by forming a multi-barrier protection on the way of emission of radioactivity to the environment. The multi-barrier protection is formed by heating a steel case for WFA, filled with material which has a sufficiently high melting temperature, chemically inert in relation to the material of the casing of the FEs of the WFA, to the material of the body of the case, to air and to water, until it is melted, placing the WFA inside a hermetically sealed heated steel case, wherein the above material is contained in a liquid state. After removing the case from the heating device, it is placed inside a “dry” WNF-storage facility with atmospheric air cooling. After solidifying the material, which is chemically inert in relation to the material of the casing of the FEs of the WFA, to the material of the body of the case, to air and to water, inside the steel case, a multi-barrier protection on the way of emission of radioactivity to the environment is formed, ensuring a long-term reliable and safe storage of the WFA. The case may be further arranged in a box of a “dry” storage facility cooled with naturally circulated atmospheric air, or in a convection-cooled container, made, for example, according to a closest analog RU patent 2231837, inside which the WFA may be transported to the reprocessing plant. By choosing a case filling material having a sufficiently high heat conductivity, the allowable temperature of casings of the ELs of the WFA is not exceeded even with natural circulation of atmospheric air, which ensures a passive heat-removal for an indefinite period of time. The method for long-term safe storage of WNF consists of the following. Prior to unloading the WFA from the nuclear reactor, a steel ribbed case, which is preliminarily filled with a necessary amount of material, which is chemically inert in relation to the materials of the casing of the FEs, to the material of the body of the case, to air and to water, having an acceptable melting temperature and heat conductivity, e.g. lead, is mounted in the heating device. Under the effect of heat emitted by the heating device, lead is converted into liquid state (melting temperature 327° C.). Using proper accessories, the WFA is removed from the nuclear reactor and placed inside the case so that the fuel portion of the FEs remains below the level of liquid lead in the case and is fixed in this position by mechanical devices installed in the case and/or in the grill of the WFA. After that, the case is hermetically sealed with cover. The hermetically sealed case is further extracted from the heating device and mounted in the appropriate box of the “dry” storage which is cooled using naturally circulated atmospheric air. Material, with which the WFAs are filled, solidifies, creating a multi-barrier protection—each FE of the WFA is individually enveloped with a layer of lead, and the whole WFA is also wrapped all around by a layer of lead, disposed between the WFA and the inner wall of the steel case housing. Thereafter, a protector plug is mounted inside the hole of the box of the storage facility, whereupon the described cycle is repeated. |
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052001172 | description | DETAILED DESCRIPTION According to the present invention, alkaline earth metal sulfate scales, especially barium sulfate scale, are removed by the use of a combination of chemical scale-removing agents. The method is particularly useful for the removal of such scale from oilfield equipment used to bring oil and/or water from subterranean formations to the surface. The method may, however, also be used to remove scale from the formations themselves, especially in the regions surrounding production and injection wells, as mentioned above. The method may also be used to remove scale from above- ground equipment both in the oilfield and elsewhere, for example, from boilers and heat exchangers and other equipment exposed to scale-forming conditions. The scale itself is usually in the form of an adherent deposit of the scale-forming mineral on metal surfaces which have been exposed to the water containing the scale-forming components. These components comprise alkaline earth metals including calcium, strontium and barium, together with variable amounts of radium, depending upon the origin of the waters. As noted above barium sulfate scale is particularly difficult to remove by existing chemical methods in view of its very low solubility. The present scale removal is effected with an aqueous solvent which comprises a polyaminopolycarboxylic acid such as EDTA or DTPA as a chelant or chelating agent which is intended to form a stable complex with the cation of the alkaline earth scale-forming material. Of these chelants, DTPA is the preferred species since it forms the most soluble complexes at greatest reaction rate. EDTA may be used but is somewhat less favorable and, as noted below, may be less responsive to the addition of the catalyst or synergist. The chelant may be added to the solvent in the acid form or, alternatively, as a salt of the acid, preferably the potassium salt. In any event the alkaline conditions used in the scale removal process will convert the free acid to the salt. The concentration of the chelant in the solvent should normally be at least 0.1M in order to achieve acceptable degree of scale removal. Chelant concentrations in excess of 1.0M are usually not necessary and concentrations from about 0.3M up to about 0.6M will normally give good results; although higher concentrations of chelant may be used, there is generally no advantage to doing so because the efficiency of the chelant utilisation will be lower at excess chelant concentrations. This economic penalty is particularly notable in oilfield operations where large volumes of solvent may be used, especially in formation scale removal treatment. In addition to the chelant, the present scale removal compositions contain a catalyst or synergist for the dissolution of the scale. This catalyst is an anion or anions of at least one monocarboxylic acid. The acid may be substituted with various functional groups, especially electronegative groups such as hydroxyl, amino, halo or mercapto or may be unsubstituted. The lower substituted fatty acids such as the C.sub.1 -C.sub.3 substituted fatty acids where the substituent is an electronegative group such as hydroxy, mercapto, or amino are suitable since they have good solubility in oilfield waters, are readily available and are relatively inexpensive. Suitable acids of this type include mercaptoacetic acid, aminoacetic acid and hydoxyacetic acid. The unsubstituted fatty acids such as acetic acid and formic acid have not be found to provide any major improvement in scale removal with DTPA as a chelant and are therefore not preferred. The aromatic carboxylic acids may also be used when they have an adequately high solubility in water. The acid may have substituents other than the carboxyl group on the aromatic nucleus, for example, hydroxyl as in salicylic acid which is a preferred acid of this type. Other aromatic carboxylic acids with carboxyl groups attached directly to the aromatic nucleus may also be used. The preferred acids have been found to enhance the rate of barium sulfate scale dissolution using polyaminopolycarboxylic chelants, especially DTPA, to a significant and useful degree, so that dissolution of oilfield scales is usefully accelerated by the use of these compositions. It has been found that the action of the synergist may be selective for the chelant. For example, salicylate produces a significant increase in scale removal with the chelant DTPA but only a slight improvement with EDTA. The use of DTPA is therefore favored not only because it generally shows an improved propensity in itself to remove the alkaline earth metal sulfate scales but also because it exhibits better response to a number of these synergists. The concentration of the catalyst or synergist in the aqueous solvent will be of a similar order: thus, the amount of the carboxylate anion in the solvent should normally be at least 0.1M in order to achieve a perceptible increase in the efficiency of the scale removal, and concentrations from about 0.3M up to about 0.6M will give good results. Although higher concentrations of the synergist e.g. above 1.0M may be used, there is generally no advantage to doing so because the efficiency of the process will be lower at excess catalyst concentrations. Again, this economic penalty is particularly notable in oilfield operations. As with the chelant, the carboxylate synergist may be added as the free acid or the salt, preferably the potassium salt. If the free acid is used addition of the potassium base to provide the requisite solution pH will convert the acid to the salt form under the conditions of use. The scale removal is effected under alkaline conditions preferably at pH values of from about 8.0 to about 14.0, with optimum values being from about 11 to 13, preferably about 12. The prefered solvents comprise about 0.1 to about 1.0M ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA), or salts of these acids, as a chelant. In addition, the carboxylate catalyst is added to the aqueous solution in about 0.01 to about 1.0 preferably about up to 0.5M. The pH of the solvent is then adjusted by the addition of a base to the desired value, preferably to about pH 12. We have found that it is important to avoid the use of sodium cations when operating at high pH values, above pH 8, and instead, to use potassium or alternatively, cesium as the cation of the scale-removing agent. Potassium is preferred for economy as well as availability. Thus, the normal course of making up the solvent will be to dissolve the chelant and the acid synergist (or its potassium salt) in the water to the desired concentration, after which a potassium base , usually potassium hydroxide is added to bring the pH to the desired value of about 12. This aqueous composition can be used to remove scale from the equipment, or alternatively, pumped into the subterranean formation when it is the formation which is to be subjected to descaling. The mode of operation of the synergist or catalyst is not presently understood. While not desiring to be bound to a particular theory concerning the actual mechanism of its activity in converting or dissolving the scale, it is believed that adsorption of the synergist or catalyst on the barium sulfate surface may modify the surface crystal structure in such a way that the barium in the modified crystal is easily removed by the chelating agent. The aqueous solution containing the composition can be directed down a wellbore to remove barium sulfate scale which has fouled the tubular equipment e.g. piping, casing etc., and passage ways. Prior to being directed into the wellbore, the composition may be heated to a temperature between about 25.degree. C. to about 100.degree. C., although the temperatures prevailing downhole may make pre-heating unnecessary. Once within the tubular goods and the passageways requiring treatment, the composition is allowed to remain there for about ten minutes to about 7 hours. After remaining in contact with the equipment for the desired time, the composition containing the dissolved scale is produced to the surface and may be disposed of as required, possibly by re-injection into the subsurface formation. This procedure can be repeated as often as required to remove scale from the equipment. In one procedure for circulating the solvent through the tubular goods the well the solvent is pumped down through the production tube and returned to the surface through the annular space between the production tubes and the casing (or vice versa). Also the cleaning solution may be pumped down through the production tubing and into the formation, thereby cleaning the well, including the well casing, and the formation pore space by dissolving barium sulfate present as it flows over and along the surfaces that need cleaning. The spent composition containing the dissolved, complexed barium together with any other alkaline earth metal cations which may have been present in the scale, especially radium, can be subsequently returned to the surface, for example, by displacement or entrainment with the fluids that are produced through the well after the cleaning operation. In an alterative manner, the cleaning solution may be applied batchwise fashion, for example, by flowing the solution into the well and optionally into the pore spaces of the adjacent earth formation and there keeping the solution in contact in non-flowing condition with the surfaces that are covered with barium sulfate scale, for a period of time sufficient to dissolve the scale. The present scale removal technique is very effective for lowering residual radioactivity of pipe contaminated with radium-containing barium sulfate scale. As noted above, radium is frequently precipitated with barium in scale with the result that scaled pipe is often radioactive to the point that it cannot safely be used. Using the present scale removal compositions, activity can be reduced to an acceptable levels comparatively short times without further treatment. Some residual activity which arises from lead and other radio isotopes which are not dissolved in the solvent: these isotopes are decay products of radium and have originally been incorporated in the scale with the barium and the radium sulfates. Although they are not removed chemically by the present scale removal technique, the dissolution of the barium scale together with the other alkaline earth metal sulfates enables these other components of the scale to be removed by simple abrasion, for example, by scrubbing with or without a detergent/water scrub solution. In this way, the residual activity level may be reduced to a very low value, below the appropriate regulatory standards. Thus, by using the present chemical scale removal technique in combination with a simple mechanical removal of loose, non-adherent material, previously radioactive pipe may quickly and readily be restored to useful, safe condition. In order to demonstrate the barium sulfate scale-dissolving capacities of the composition, several aqueous solutions have been tested in laboratory tests the results of which are described in the discussions which follow. The experiments described below were, except as noted below, carried out in a cylindrical glass vessel having a height of 10 cm and an internal diameter of 7.5 cm. Barium sulfate or, when applicable, other sulfates or solid scale components, were agitated with the selected solvents and the rates of dissolution and final dissolved concentrations determined. The results are reported graphically in the FIGS. As shown in FIG. 1, DTPA alone and DTPA with various substituted acetic acids were compared at 100.degree. C. The results demonstrate that the DTPA/carboxylate combination complexes more barium sulfate than DTPA alone. FIG. 2 compares the relative rates of barium sulfate dissolution using DTPA alone and DTPA in combination with salicylic acid. As shown in the FIG., the addition of salicylic acid is effective to almost double the degree of barium sulfate dissolution. Distilled water was used in the majority of the above tests (except the continuous flow loop tests) for determination of the rate of barium sulfate dissolution and saturation. Minor decreases in efficiency may be observed with tap water and more significant decreases with seawater, e.g. about 20 percent decrease with seawater. This is reasonably to be expected since seawater has interfering ions, e.g. calcium and magnesium. These interfering ions complex with the chelating agent, either DTPA or EDTA, and reduce the overall dissolving power. Additionally, it has been determined that halide ions have a negative effect on dissolving power as a function of the size of the halide ion. Dissolution rate is increased as the halide ion size is reduced and the charge density is increased, i.e. in the order of iodide, bromide, chloride and fluoride. Fluoride ion enhances the effect of EDTA-based solvents, but not DTPA: fluoride inhibits most DTPA/catalyst solvents. As noted above, the effect of cations is also very important to the success of the scale solvent, especially when added with the sizable portion of caustic required to adjust the pH to 12. Dissolution is enhanced as the size of the cation is increased, i.e. lithium, sodium, potassium and cesium. Lithium and sodium hydroxides in the presence of EDTA, or DTPA, and catalysts are not soluble at a pH of 12, the optimum value. Cesium is too difficult to obtain, both in quantity and price. Therefore, potassium hydroxide, in the form of caustic potash, is the pH adjusting reagent of choice. |
claims | 1. A method of using an online service implemented on computing equipment, comprising:aggregating logs from a plurality of wireless electronic devices using the online service, wherein each wireless electronic device is operable to transmit at a plurality of transmit power levels, wherein the log of each wireless electronic device includes information indicating the amount of time that wireless electronic device spends at each of the plurality of transmit power levels and is received from that wireless electronic device;storing the logs that are aggregated from the plurality of wireless electronic devices using the online service on a power optimization server;with the power optimization server, organizing the aggregated logs into a plurality of data sets, wherein each data set in the plurality of data sets corresponds to a respective geographical region;with the power optimization server, calculating a plurality of cumulative distribution functions each of which corresponds to a respective data set in the plurality of data sets, wherein each cumulative distribution function in the plurality of cumulative distribution functions has at least one peak that corresponds to a radio-frequency transmit power level at which a typical wireless electronic device that resides in the corresponding geographical region spends the greatest amount of its time transmitting radio-frequency signals;with the power optimization server, identifying optimum transmit power settings that correspond to the peaks of the plurality of cumulative distribution functions; andproviding the identified optimum transmit power settings to the plurality of wireless electronic devices from the online service through a network. 2. The method defined in claim 1, wherein aggregating the logs from the plurality of wireless electronic devices comprises gathering the logs from the plurality of wireless electronic devices while the wireless electronic devices are docked to personal computers. 3. The method defined in claim 2, further comprising:with the personal computers, running a client portion of the online service. 4. A method of using a service implemented on computing equipment, comprising:gathering radio-frequency power amplifier data logs from a plurality of wireless electronic devices using the service implemented on the computing equipment, wherein each wireless electronic device is operable to transmit at a plurality of transmit power levels, wherein the data log gathered from each wireless electronic device in the plurality of wireless electronic devices includes information indicating how much time that wireless electronic device has spent at each of the plurality of transmit power levels and is received from that wireless electronic device;generating a distribution function based on the information in the radio-frequency power amplifier data logs gathered from the plurality of wireless electronic devices, wherein the distribution function has at least one peak that corresponds to a transmit power level at which a typical wireless electronic device spends the greatest amount of its time transmitting radio-frequency signals;obtaining optimum radio-frequency power amplifier settings for the plurality of wireless electronic devices by identifying the at least one peak of the distribution function; andwith the service implemented on the computing equipment, providing the optimum radio-frequency power amplifier settings to at least some of the plurality of wireless electronic devices over a network. 5. The method defined in claim 4, wherein analyzing the radio-frequency power amplifier data logs comprises:determining which of the radio-frequency power amplifier settings are optimal for a first type of geographic region; anddetermining which of the radio-frequency power amplifier settings are optimal for a second type of geographic region that is different than the first type of geographic region. 6. The method defined in claim 5, wherein the first type of geographic region comprises a metropolitan region. 7. The method defined in claim 6, wherein the second type of geographic region comprises a suburban region. |
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claims | 1. A pinhole collimator assembly comprising a plurality of pinhole apertures therein, wherein each pinhole aperture has an adjustable aperture size and wherein the pinhole collimator assembly is configured so that gamma rays emitted by a subject being imaged pass through the plurality of pinhole apertures in the pinhole collimator assembly, but the remainder of the pinhole collimator assembly is substantially gamma ray absorbent. 2. The pinhole collimator assembly of claim 1, wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein, wherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assembly. 3. The pinhole collimator assembly of claim 2, wherein the pinhole collimator assembly is configured so that movement of at least one of the inner collimator or the outer collimator adjusts the aperture size of each of the one or more pinhole apertures in the pinhole collimator assembly. 4. The pinhole collimator assembly of claim 3, wherein the pinhole collimator assembly is configured so that the one or more pinhole apertures maintain a square shape while the aperture size is adjusted. 5. The pinhole collimator assembly of claim 2:wherein the one or more outer pinhole apertures open to an outer surface of the outer collimator; andwherein the one or more inner pinhole apertures open to an inner surface of the inner collimator. 6. The pinhole collimator assembly of claim 2, wherein the inner collimator and the outer collimator are generally cylindrically shaped, and wherein the pinhole collimator assembly is configured so that rotation and/or translation of at least one of the inner collimator or the outer collimator adjusts the aperture sizes of each of the one or more pinhole apertures in the pinhole collimator assembly. 7. The pinhole collimator assembly of claim 2, wherein the inner collimator and the outer collimator are generally non-cylindrically shaped, and wherein the pinhole collimator assembly is configured so that axial translation of at least one of the inner collimator or the outer collimator adjusts the aperture sizes of each of the one or more pinhole apertures in the pinhole collimator assembly. 8. The pinhole collimator assembly of claim 7, wherein the pinhole collimator assembly is configured so that the one or more pinhole apertures maintain a square shape while the aperture size is adjusted. 9. The pinhole collimator assembly of claim 2, wherein the inner collimator comprises a cylindrical body having the one or more inner pinhole apertures therein, and wherein the outer collimator comprises a cylindrical body having the one or more outer pinhole apertures therein, and wherein either the inner or outer collimator has an alignment pin extending radially from the cylindrical body and correspondingly either the outer or inner collimator has an alignment slot sized to receive the alignment pin. 10. The pinhole collimator assembly of claim 1, wherein the pinhole collimator assembly comprises a diaphragm, wherein the diaphragm comprises a plurality of blocks arranged to define a respective pinhole aperture, wherein the diaphragm is configured so that positioning the blocks with respect to one another adjust an aperture size of the respective pinhole aperture. 11. The pinhole collimator assembly of claim 10, wherein the plurality of blocks comprises four blocks that are arranged so that the respective pinhole aperture is four sided. 12. The pinhole collimator assembly of claim 10, wherein the plurality of blocks comprises a first pair of parallel blocks and a second pair of parallel blocks, wherein each pair of the parallel blocks are spaced a distance apart, and wherein the first pair of parallel blocks are generally perpendicular to the second pair of parallel blocks. 13. The pinhole collimator assembly of claim 12, wherein each of the first pair of parallel blocks is slidably interlocked with each of the second pair of parallel blocks. 14. The pinhole collimator assembly of claim 12, wherein each of the first pair of blocks are configured to move in a generally opposite direction with respect to one another, and wherein each of the second pair of blocks are configured to move in a generally opposite direction with respect to one another. 15. The pinhole collimator assembly of claim 12, wherein the diaphragm comprises a plate coupled to the plurality of blocks, wherein the plate comprises a central opening aligned with the respective pinhole aperture defined by the plurality of blocks and a plurality of slots, wherein each of the blocks comprises a body and one or more pins extending from the body and through a corresponding one of the slots in the plate. 16. The pinhole collimator assembly of claim 15, wherein the diaphragm comprises a ring coupled to the plate, wherein the ring comprises a central opening aligned with the respective pinhole aperture defined by the plurality of blocks and a plurality of slots in the ring, wherein each of the blocks comprises a body and one or more pins extending from the body and through a corresponding one of the slots in the ring. 17. The pinhole collimator assembly of claim 16, wherein the pinhole collimator assembly is configured so that rotation of the ring positions the blocks with respect to one another so as to adjust the aperture size of the respective pinhole aperture defined by the diaphragm. 18. The pinhole collimator assembly of claim 1:wherein the pinhole collimator assembly comprises a plurality of diaphragms arranged in a generally circular configuration;wherein each diaphragm comprises a plurality of blocks that defines a pinhole aperture in the pinhole collimator assembly; andwherein each diaphragm is configured so that positioning the blocks with respect to one another adjusts the size of the pinhole aperture. 19. An imaging system comprising:a pinhole collimator assembly comprising a plurality of pinhole apertures therein, wherein each pinhole aperture has an adjustable aperture size; anda detector assembly configured to generate one or more signals in response to gamma rays emitted by a subject being imaged that pass through the one or more apertures in the pinhole collimator assembly. 20. The imaging system of claim 19, wherein the imaging system comprises a single photon emission computed tomography system or a combined single photon emission computed tomography system/x-ray computed tomography system. 21. The imaging system of claim 19, wherein the detector assembly comprises at least one of an array of solid-state detector elements or a scintillator assembly coupled to light sensors. 22. The imaging system of claim 19, comprising:a module configured to receive the one or more signals and to process the one or more signals to generate one or more images; andan image display workstation configured to display the one or more images. 23. The imaging system of claim 19:wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein;wherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assembly; andwherein the collimator is configured so that movement of at least one of the inner collimator or the outer collimator adjusts the aperture size of one or more pinhole apertures in the pinhole collimator assembly. 24. The imaging system of claim 19, wherein the pinhole collimator assembly comprises a diaphragm, wherein the diaphragm comprises a plurality of blocks arranged to define a respective pinhole aperture in the pinhole collimator assembly, wherein the diaphragm is configured so that positioning the blocks with respect to one another adjust an aperture size of the respective pinhole aperture. 25. The imaging system of claim 19:wherein the pinhole collimator assembly comprises a plurality of diaphragms arranged in a generally circular configuration;wherein each diaphragm comprises a plurality of blocks that defines a pinhole aperture in the pinhole collimator assembly;wherein each diaphragm is configured so that positioning the blocks with respect to one another adjusts the size of the pinhole aperture. 26. A method of adjusting collimator performance comprising:adjusting aperture sizes of a plurality of apertures in a pinhole collimator assembly;collimating gamma rays emitted by a subject being imaged with the pinhole collimator assembly; anddetecting the collimated gamma rays. 27. The method of claim 26:wherein the pinhole collimator assembly comprises an inner collimator comprising one or more inner pinhole apertures therein and an outer collimator comprising one or more outer pinhole apertures therein; andwherein the inner collimator and the outer collimator are arranged so that the one or more inner pinhole apertures and the one or more outer pinhole apertures align to define the one or more pinhole apertures in the pinhole collimator assemblywherein adjusting the aperture size of the one or more pinhole apertures comprises moving at least one of the inner collimator or the outer collimator. 28. The method of claim 26, wherein each of the one or more pinhole apertures is defined by a diaphragm comprising a plurality of blocks arranged to define an aperture, and wherein adjusting the aperture size of the one or more pinhole apertures comprises moving the blocks of each diaphragm with respect to one another. 29. The method of claim 26, wherein each of the one or more pinhole apertures is defined by a diaphragm comprising a first pair of parallel blocks and a second pair of parallel blocks arranged, and wherein adjusting the aperture size of the one or more pinhole apertures comprises moving the first pair of parallel blocks in an opposite direction with respect to one another and moving the second pair of parallel blocks in an opposite direction with respect to one another. |
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claims | 1. A nuclear reactor support system comprising:an elongated reactor vessel having a weight and an internal cavity configured for containing a primary coolant, the reactor vessel extending along a substantially vertical axis;a reactor core disposed within the internal cavity;an upper portion of the reactor vessel located above a ground plane and a lower portion of the reactor vessel located below the ground plane;the upper portion of the reactor vessel comprising a primary coolant outlet port fluidly coupled to the cavity;a first flange fixedly attached to the upper portion of the reactor vessel and contacting the ground plane, the first flange supporting the reactor vessel; a second flange fixedly attached to the upper portion of the reactor vessel above the ground plane, the second flange spaced vertically apart from the first flange; anda plurality of welded lugs extending vertically between the first and second flanges. 2. The system according to claim 1, wherein the first flange supports the entire weight of the reactor vessel in a cantilevered manner. 3. The system according to claim 2, wherein the lower portion of the reactor vessel is disposed in a reactor well below the ground plane. 4. The system according to claim 3, wherein a bottom of the reactor vessel is spaced vertically above a floor of the reactor well. 5. The system according to claim 4, wherein the lower portion represents a majority of a length of the reactor vessel. 6. The system according to claim 1, wherein the upper portion of the reactor vessel further comprises a primary coolant inlet port located above the ground plane and fluidly coupled to the cavity. 7. The system according to claim 6, wherein the primary coolant inlet and outlet ports are fluidly coupled to a steam generator. 8. The system according to claim 1, wherein the ground plane is defined by a top surface of a concrete slab. 9. The system according to claim 8, wherein the concrete slab forms a portion of a reactor well which accepts the lower portion of the reactor vessel, the reactor well further comprising a plurality of sidewalls and a floor. 10. The system according to claim 9, wherein a bottom end of the reactor vessel is spaced apart from the floor of the reactor well such that the first flange supports the reactor vessel in a cantilevered manner. 11. The system according to claim 2, further comprising a domed head detachably coupled to the upper portion above the first flange. 12. The system according to claim 11, wherein the upper portion of the reactor vessel is terminated with a first bolting flange coupled to a mating second bolting of the domed head via a plurality of bolts. |
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043702988 | claims | 1. A method of generating thermal energy and isotopes in a contained fission explosion, breeder reactor system, comprising the steps of providing a pressure vessel having an explosion chamber, introducing a pair of slugs each containing a sub-critical mass of actinides into said chamber propelling at least one of said slug pair, said pairs being introduced successively and at predetermined time intervals into the chamber along a flight path where they intercept at or near the center of the chamber and where the combining slug masses become more than critical to produce an explosion injecting a major portion of a working fluid into the chamber in the form of a plurality, draining the working fluid heated by the explosion from the vessel for conversion into useful work, collecting fissile, fertile and irradiated isotopes and debris from the exploded slugs as a precipitate from the working fluid, and fabricating the precipitate into additional slugs. 2. The method according to claim 1, including the steps of injecting said major portion of the working fluid through a plurality of concentric circular rows of passageways extending through an upper wall portion of the vessel such that the working fluid flows downwardly through the chamber in concentric relationship to a major axis passing longitudinally through the center of the vessel, controlling the flow of the working fluid through at least one innermost row of said passageways to form a tubular curtain extending along the entire length of the chamber at the instant of an explosion, and controlling the flow of working fluid through the remaining concentric rows of passageways extending outwardly of said innermost circular rows of passageways to form a plurality of outer tubular curtains of decreasing length from an inner to an outermost curtain thereof, said outer tubular curtains falling through the chamber to form a substantially spherically shaped body of working fluid which is concentrated near the center of the chamber at the instant of the explosion at the point of interception of the slugs. 3. The method according to claim 1, including the steps of injecting said minor portion of the working fluid as a spray into the chamber through a plurality of circular rows of passageways extending through top and bottom wall portions of the vessel inwardly of the concentric tubular curtains and in a direction toward a major axis passing longitudinally through the center of the vessel, and controlling the flow of the working fluid through the circular rows of passageways to spray the working fluid in front of the barrel openings before an explosion. 4. The method according to claim 1, including the steps of injecting said minor portion of the working fluid as a spray into the chamber through a plurality of circular rows of passageways extending through the wall of the vessel outwardly of the concentric tubular curtains, and controlling the flow of the working fluid through said circular rows of passageways such that the working fluid is sprayed adjacent to the internal surface of the chamber wall for cooling the chamber wall. 5. The method according to claim 1, including the steps of propelling each slug through a barrel by means of a rapidly expanding propelling gas, evacuating the propelling gas from the barrel through vent openings in the barrel, and recirculating the expanded gas to a storage and supply tank for re-use in propelling additional slugs into the chamber. 6. The method according to claim 5, including the steps of evacuating from the chamber residual amounts of the propelling gas escaping from the barrels into the chamber, evacuating from the chamber gaseous and non-gaseous explosion products, working fluid and propelling gases, separating and recirculating the propelling gas from the chamber to the storage and supply tank, separating the working fluid from the explosion products and returning the working fluid to the vessel, and returning the non-gaseous explosion products for re-use in the manufacture of additional slugs, and separating and storing the gaseous explosion products. 7. The method according to claim 1, including the steps of circulating a neutron absorbing fluid through a passageway in the wall of the vessel, passing said neutron absorbing fluid through a heat exchanger for cooling the fluid and the wall, and periodically withdrawing the neutron absorbing fluid from the passageway and introducing new fluid into the passageway. 8. The method according to claim 1, including the steps of propelling a pair of said slugs through barrel openings at opposite ends of the vessel, positioning said barrel openings so that they extend along a major vertical axis of the vessel, closing said barrel openings before said pair of combining slugs explode, opening said barrel openings after the explosion, and evacuating solid and gaseous materials from the chamber through the barrel openings, and through vents in the barrel. 9. In the method according to claim 1, including the step of producing tritium by irradiation of a working fluid containing lithium. 10. In a contained fission explosion breeder reactor system for generating thermal energy and for breeding isotopes: a pressure vessel having an explosion chamber; means for injecting a predetermined quantity of a working fluid into the chamber and for heating the working fluid by a fission explosion taking place near the center of the chamber, and means for draining the heated working fluid from the chamber for use in the production of useful work, the improvement comprising a plurality of re-useable accelerating mechanisms positioned externally of said vessel, each accelerating mechanism having a barrel in alignment with a barrel opening in said vessel for propelling a slug of a sub-critical mass of actinides into the chamber along a flight path such that the slugs from the accelerating mechanisms intercept near the center of the chamber where the combining slug masses become more than critical for producing an explosion, a closure mechanism for closing each barrel after passage of a slug into the barrel opening and before an explosion means for injecting a major portion of a working fluid into the chamber in the form of a plurality of concentric tubular curtains surrounding the flight path of the slugs, means for injecting a minor portion of the working fluid in the form of a spray adjacent the internal surface of the vessel wall and in front of the barrel openings through which said slugs pass into the chamber, said working fluid being selected from the group consisting of sodium, lithium, lead, or alloys thereof, of concentric tubular curtains surrounding the flight path of the slugs, injecting a minor portion of the working fluid in the form of spray adjacent to an internal surface of the vessel wall and in front of the barrel openings through which said slugs pass into the chamber, selecting the working fluid from the group consisting of sodium, lithium, lead, or alloys thereof, means for collecting fissile, fertile and irradiated isotopes and debris from the exploded slugs, and means for recirculating and fabricating said debris into additional slugs. 11. In the system according to claim 10, wherein said pressure vessel is substantially ellipsoidal in shape having a wall which is substantially elliptical in cross-section, said barrel openings extending through the wall at opposite ends of the vessel and being in alignment with a major axis extending vertically through the center of the vessel, a projection extending into the chamber and forming a collection trough at the bottom of the chamber for collecting the working fluid, one of said barrel openings extending centrally through the projection, a plurality of passageways extending from a bottom surface in the trough through the wall of the vessel for continuously draining the working fluid from the vessel, and a sump connected to the passageways externally of said vessel for collecting the heated working fluid from the vessel. 12. In the system according to claim 11, including a closure mechanism for closing each barrel opening before an explosion, each closure mechanism comprising a closure plate having an opening, and means for actuating said closure plate for moving the opening in said plate into alignment with the barrel opening in the vessel and with the barrel for passage of a slug therethrough into the vessel. 13. In the system according to claim 10, wherein said slugs are propelled from the accelerating mechanisms through the barrels by a rapidly expanding propelling gas, a plurality of vent openings in each barrel extending over a portion of its length, a containment jacket surrounding the barrel portion provided with said vent openings and forming an expansion chamber therewith, means for continuously evacuating propelling gas from said barrel and expansion chamber, and means for recirculating said propelling gas to a gas storage and supply tank for use in propelling additional slugs. 14. In the system according to claim 11, including a closure mechanism for closing the barrel opening at the bottom of the vessel before an explosion, said closure mechanism comprising a main and an auxiliary plate each having one opening therein, said main plate being positioned between the barrel opening in the vessel and an upper end portion of the barrel, said auxiliary plate being positioned below the main plate and between said upper end portion and a lower end portion of said barrel, an actuating mechanism for sequentially opening said plates such that the openings in plates are in alignment with the barrel and barrel openings as a slug is propelled through the barrel, said upper end portion of the barrel between the plates and the lower end portion of the barrel below said auxiliary plate having a plurality of vent openings, a pair of containment jackets surrounding the barrel portions provided with said vent openings to form a pair of expansion chambers, said slugs being propelled through the barrel by means of a propelling gas, means for continuously evacuating said propelling gas through the vent openings in the barrel and from the expansion chambers, and means for recirculating said propelling gas to a gas storage and supply tank for use in propelling additional slugs. 15. In the system according to claim 11, including at least one passageway within the wall of said vessel, and means for circulating a neutron absorbing and cooling fluid through the passageway. 16. In the system according to claim 11, including a first plurality of concentric circular rows of passageways extending through an upper wal portion of the vessel for injecting the working fluid into the vessel in the form of a plurality of falling, concentric, tubular curtains of working fluid, a second plurality of circular rows of passageways extending through said upper wall portion and through a lower wall portion of the vessel inwardly of said first rows of passageways for injecting the working fluid into the chamber as a spray in front of the barrel openings, and a third plurality of circular rows of passageways extending through the wall of the vessel outwardly of said first rows of passageways for injecting the working fluid as a spray adjacent to an internal surface of the wall for cooling the wall. 17. In the system according to claim 10, wherein the isotopes generated by the explosion include Pu.sup.239, Pu.sup.241, and/or U.sub.233. 18. In the system according to claim 10, wherein said slug comprises: (1) a major portion of substantially cylindrical shape formed from a metal or metal alloy selected from the group consisting of sodium, lithium and lead, said cylindrical portion having a flat frontal surface and a hemispherical depression centrally positioned in the frontal surface, and (2) a minor hemispherical portion, formed of a sub-critical mass of a fissile-fertile material, which has a flat frontal surface. 19. In the system according to claim 18, wherein the composition of the material in the minor hemispherical portion of the slug consists of a mixture of fertile and fissile actinides, said fissile actinides comprising Pu.sup.239, Pu.sup.241 and/or U.sup.233. 20. In the system according to claim 18, wherein said major cylindrical slug portion opposite of said flat frontal face, has a substantially ellipsoidal rear portion. |
045132046 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to the field of nuclear medicine. In particular, it relates to the field of radiation diagnosis and to examinations of a patient by means of a scintillation camera. Still more particularly, this invention relates to a housing or container for carrying a radioactive isotope which housing is to be attached to the patient's body, the isotope thereby serving as a motion detector or as an anatomical marker for nuclear images. 2. Description of the Prior Art In nuclear medicine, a radioactive tracer such as technicium is administered to a patient undergoing examination, and the distribution of the tracer in the patient's body is viewed by aid of a scintillation camera. A problem associated with this kind of nuclear examination is the movement of the patient. When the patient moves during examination, a blurred image may result. In order to overcome this disadvantage, a diagnostic motion correction scheme has been developed, see U.S. patent application Ser. No. 324,090, filed by Mark W. Groch and James T. Rhodes, under the title "Motion Correction Circuitry and Method for a Radiation Imaging Device", on Dec. 1, 1981. The disclosure of this application is incorporated herein by reference. According to this motion correction scheme, a blurring of e.g. .sup.99m Tc gated blood pool images due to patient motion is corrected. This is accomplished by introducing a special radioactive point source, in particular a gamma ray emitting radioisotope, whose energy window lies outside that of .sup.99m Tc, into the field-of-view of the scintillation camera. The point source remains outside of the patient's body; thus, no gamma rays emitted from the source are scatter events. Then the centroid of the point source is monitored. When a change in the centroid of the point source is detected due to patient motion, the .sup.99m Tc events are corrected and repositioned to take into account the motion artifact. In cardiac studies, for instance, the movement of a special radioactive source which is fixed to the chest of the patient is detected. This movement is subtracted from the detected radiation coming from the tracer isotope of different energy signature flowing in the blood through the heart. Thus the "dual isotope motion correction scheme" eliminates the motion blur in the images as they are acquired. There are two problems that one must keep in mind when using such a centroid (point) source external to the patient's body during image acquisition. First, the special radioactive point source must be within the field-of-view and the events emitted must be detected through the collimator of the camera. Second, since the point source should be encased in a shielding medium which will attenuate .sup.99m Tc events emanating from the patient's body, the point source must not obstruct any important anatomical structures in the field-of-view. SUMMARY OF THE INVENTION 1. Objects An object of this invention is to provide a housing for a radioactive point source which is to be attached to a patient in nuclear medical examinations. Another object of this invention is to provide such a housing which reliably retains and shields the point source, but leaves an opening free for emission of radiation towards a radiation detection system such as a scintillation camera. Still another object of this invention is to provide a housing for a radioactive point source which can be used in routine nuclear examinations either as a motion detector or as an anatomical marker for nuclear images. 2. Summary According to this invention, a housing for a radioactive source comprises a first shielding body, a second shielding body, and connecting means for connecting the two bodies. The first shielding body has a protrusion which contains a first recess for inserting the radioactive source. The second shielding body has a second recess in its surface. The second recess is shaped so that the protrusion fits therein. When the radioactive source is inserted into the first recess and the protrusion is located in the second recess, the radioactive source will emit radiation into the environment primarily through the conical aperture. According to a preferred embodiment, a .sup.241 Am centroid source is encased in a disk shaped tungsten alloy holder. The bottom part of the disk is to be laid on the patient so that the top part which contains the gamma ray escape aperture, faces away from the patient's body. The escape aperture is cone-shaped at an angle of e.g. approximately 120.degree. with an exit hole of approximately 2 mm. The first of the two aforementioned problems is solved by insuring that the source is in the field-of-view and that the disk holder not be tilted by more than 60.degree. from a plane perpendicular to the collimator holes. The second of the aforementioned two problems has a different solution depending on the view and collimator used in imaging. 1. RAO with slant hole collimator: The point source should be placed anatomically below the heart and just to the left side of the chest wall center. 2. ANT with parallel hole collimator: The point source should be placed anatomically anywhere below the heart, as long as the source faces anteriorly. 3. LAO with parallel hole collimator: The point source should be placed anatomically below the heart and on the central left to far left side of the chest wall. Adhesion of the centroid point source to the patient is preferably accomplished by placement of surgical tape in an X-pattern over the top side of the source, adhering the source firmly to the patient, thus insuring that patient and source motion is unified. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. |
claims | 1. A nuclear reactor in-core detector system including an in-core nuclear instrument thimble assembly comprising:a self-powered, fixed, in-core detector for monitoring a reactor core parameter indicative of a state of a reactor core and providing an electrical output representative of the monitored parameter;a wireless transmitter connected to receive the electrical output, wherein the wireless transmitter comprises a number of electronic components at least one of which is a Vacuum Micro-Electric Device configured as a vacuum diode placed in a grid circuit of an amplifier which is connected to the electrical output of the self-powered, fixed, in-core detector and responds substantially logarithmically, thus enabling the electronic components to follow the monitored neutron flux from startup through full power of a nuclear reactor in which the in-core detector system is disposed; andwherein substantially the entire in-core nuclear instrument thimble assembly is wholly contained within an instrument thimble within a nuclear fuel assembly without any in-core detector wiring external to the instrument thimble, inside a reactor vessel in which the in-core detector system is disposed. 2. The nuclear reactor in-core detector system of claim 1 wherein in addition to the amplifier the electronic components include a current-to-voltage converter and a voltage controlled oscillator with an output of the amplifier connected to an input of the current-to-voltage converter whose output is connected to an input of the voltage controlled oscillator that provides a frequency output proportional to a voltage on the input of the voltage controlled oscillator so that a current which is the electrical output representative of the monitored parameter which is connected to the amplifier is converted to a corresponding frequency that can be transmitted by the wireless transmitter wirelessly. 3. The nuclear reactor in-core detector system of claim 2 wherein the voltage controlled oscillator comprises a Micro-Electronic reactance tube. 4. The nuclear reactor in-core detector system of claim 1 wherein the electronic components comprise an input of a first amplifier connected to the electrical output of the self-powered, fixed, in-core detector, an input of a current-to-voltage converter connected to an output of the amplifier, an input of a voltage controlled oscillator connected to an output of the current-to-voltage converter, an input of a second amplifier connected to an output of the voltage controlled oscillator and a wireless transmission circuit connected to an output of the second amplifier for wirelessly transmitting the output of the second amplifier. 5. The nuclear reactor in-core detector system of claim 1 including a wireless receiver circuit and signal conditioning component designed to be situated remote from the reactor vessel, substantially including conventional solid state components. 6. The nuclear reactor in-core detector system of claim 1 including:a wireless receiver at least in part positioned outside and within the vicinity of the reactor vessel for receiving signals from the wireless transmitter; anda re-transmitter for transmitting to an area remote from the reactor vessel the signals received from the wireless transmitter. 7. The nuclear reactor in-core detector system of claim 6 wherein the re-transmitter is a second wireless transmission circuit that transmits the signals received from the wireless transmitter to a second wireless receiver that communicates the signals received from the wireless transmitter by way of the wireless receiver and the re-transmitter to processing circuitry remote from the reactor vessel. 8. The nuclear reactor in-core detector system of claim 7 wherein the second wireless receiver is positioned within the vicinity of a containment wall that shields a reactor power facility in which the in-core detector system is placed. 9. A nuclear fuel assembly having a top nozzle and a bottom nozzle and a plurality of thimble tubes extending between and substantially connected to the top nozzle and the bottom nozzle, at least one of the thimble tubes comprising an instrumentation thimble that houses a fixed in-core detector system comprising:a self-powered, fixed, in-core detector for monitoring a reactor core parameter indicative of a state of a reactor core and providing an electrical output representative of the monitored parameter;a wireless transmitter connected to receive the electrical output, wherein the wireless transmitter comprises a number of electronic components at least one of which is a Vacuum Micro-Electronic Device configured as a vacuum diode placed in a grid circuit of an amplifier which is connected to the electrical output of the self-powered, fixed, in-core detector and responds substantially logarithmically, thus enabling the electronic components to follow the monitored neutron flux from startup through full power of a nuclear reactor in which the in-core detector system is disposed; andwherein substantially the entire in-core nuclear instrument thimble assembly is wholly contained within an instrument thimble within a nuclear fuel assembly without any in-core detector wiring external to the instrument thimble, inside a reactor vessel in which the in-core detector is disposed. 10. The nuclear reactor in-core detector system of claim 9 wherein in addition to the amplifier the electronic components include a current-to-voltage converter and a voltage controlled oscillator with an output of the amplifier connected to an input of the current-to-voltage converter whose output is connected to an input of the voltage controlled oscillator that provides a frequency output proportional to a voltage on the input of the voltage controlled oscillator so that a current which is the electrical output representative of the monitored parameter which is connected to the amplifier is converted to a corresponding frequency that can be transmitted by the wireless transmitter. 11. The nuclear reactor in-core detector system of claim 10 wherein the voltage controlled oscillator comprises a Micro-Electronic reactance tube. 12. The nuclear reactor in-core detector system of claim 9 wherein the electronic components comprise an input of a first amplifier connected to the electrical output of the self-powered, fixed, in-core detector, an input of a current-to-voltage converter connected to an output of the amplifier, an input of a voltage controlled oscillator connected to an output of the current-to-voltage converter, an input of a second amplifier connected to an output of the voltage controlled oscillator and a wireless transmission circuit connected to an output of the second amplifier for wirelessly transmitting the output of the second amplifier. 13. The nuclear reactor in-core detector system of claim 9 including a wireless receiver circuit and signal conditioning component designed to be situated remote from the reactor vessel, substantially including conventional solid state components. 14. The nuclear reactor in-core detector system of claim 9 including:a wireless receiver at least in part positioned outside and within the vicinity of the reactor vessel for receiving signals from the wireless transmitter; anda re-transmitter for transmitting to an area remote from the reactor vessel the signals received from the wireless transmitter. 15. The nuclear reactor in-core detector system of claim 14 wherein the re-transmitter is a second wireless transmission circuit that transmits the signals received from the wireless transmitter to a second wireless receiver that communicates the signals received from the wireless transmitter by way of the wireless receiver and the re-transmitter to processing circuitry remote from the reactor vessel. 16. The nuclear reactor in-core detector system of claim 15 wherein the second wireless receiver is positioned within the vicinity of a containment wall that shields a reactor power facility in which the in-core detector system is placed. |
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description | The present application is a continuation of application Ser. No. 10/896,092, filed Jul. 22, 2004 now abandoned, the contents of which are incorporated herein by reference. This invention relates to a technique for a preventive maintenance of boiling water nuclear power plant (hereinafter, referred to as “BWR”), and particularly to a method for mitigating a stress corrosion cracking (hereinafter, referred to as “SCC”) of nuclear power plant structural materials. In BWR, it is an important problem to suppress the SCC of the materials constructing the core structures and pressure boundaries (stainless steel, nickel-base alloys) from the viewpoint of improving the plant operating rate. SCC takes place when the three factors (materials, stress, environment) fail on one another. Accordingly, SCC can be mitigated by mitigating at least one of the three factors. When a plant is operated, the core cooling water is radioactively decomposed by the intense gamma and neutron rays emitted from the core. As its result, the structural materials constructing the in-core structures and pressure boundaries come to be exposed to the core cooling water containing oxygen and hydrogen peroxide (both are the products of radiolysis) in an amount of several hundreds ppb and having a high temperature (in this invention, a temperature of 100° C. or more is referred to as high temperature; and the outlet temperature of core is 288° C. at the time of normal power operation). FIG. 2 illustrates the relation between crack growth rate (hereinafter, referred to as “CGR”) and electrochemical corrosion potential (hereinafter, referred to as “ECP”). It is apparent from FIG. 2 that CGR decreases when ECP drops. FIG. 3 illustrates the results of measurement on the relation between the concentrations of oxygen and hydrogen peroxide and ECP of type 304 stainless steel (hereinafter, referred to as “304SS”) in high-temperature water. Both oxygen and hydrogen peroxide show a higher ECP at a higher concentration. Accordingly, for mitigating SCC of structural materials exposed to the cooling water of reactor, it is necessary to reduce ECP, or to lower the concentrations of oxygen and hydrogen peroxide present in the reactor water. As a technique for solving this problem, the technique of adding hydrogen from the feed water system (hereinafter, referred to as “hydrogen injection”) can be referred to. Hydrogen injection is a technique of reacting the injected hydrogen with the oxygen and hydrogen peroxide formed by the radiolysis of water to return them to water, and thereby decreasing the concentrations of oxygen and hydrogen peroxide in the reactor water. If the hydrogen injection is carried out, however, radioactive nitrogen 16 (hereinafter, referred to as “N-16”) formed by the radio-activation of water becomes readily migrating together with steam, and this N-16 enhances the dose rate of turbine building. FIG. 4 illustrates the relation between the concentration of hydrogen in the fed water and effective oxygen concentration ((oxygen concentration)+0.5×(hydrogen peroxide concentration)) and the relation between the concentration of hydrogen in the feed water and the relative value of main steam line dose rate. It is apparent from FIG. 4 that an increase in hydrogen concentration in the feed water brings about a rise in the relative value of main steam line dose rate, though it causes a decrease in the effective oxygen concentration. For solving this problem, a technique of making an element of the platinum group adhere to the surface of material and thereby accelerating the reaction between hydrogen and oxygen and hydrogen peroxide (for example, see: (1) JP Patent No. 2766422). By this technique, ECP can be decreased while suppressing the rise in the main steam line dose rate. If an element of the platinum group is made to adhere to the surface of a material in order to accelerate the reaction between hydrogen and oxygen and hydrogen peroxide, however, there arises a new problem that the concentration of radioactive cobalt Co-60 in the cooling water for the reactor rises. It is an object of this invention to provide a method for mitigating the stress corrosion cracking of reactor structural materials by which the rise in the main steam line dose rate can be suppressed without side reactions such as the elevation of radioactive cobalt Co-60 concentration in the cooling water of the reactor. A reductive nitrogen compound containing nitrogen having a negative oxidation number is injected into the reactor water of a boiling water nuclear power plant. By injecting a reductive nitrogen compound containing nitrogen having a negative oxidation number into the reactor water, the stress corrosion cracking of the structural material of the reactor can be mitigated without secondary effects such as the elevation of cobalt 60 (Co-60) concentration. Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 3—Filter demineralizer for condensate; 5—Feed water heating system; 6—Feed water line; 8—Bottom drain line; 10—Reactor water clean up system line; 12—Reactor water filter demineralizer; 16—Primary loop re-circulation system line. Elevation of the main steam line dose rate is dependent on the hydrogen concentration in the reactor water. The decreasing effect of the effective oxygen concentration in the reactor pressure vessel bottom water on the hydrogen concentration in the fed water is dependent on the designed conditions of the plant. As shown in FIG. 4, however, the hydrogen concentration in the fed water at which the main steam line dose rate begins to rise is not greatly dependent on the kind of plant, and stays at about 0.4 ppm. This is for the reason that most of the boiling water type reactors are so designed that the ratio of flow rate of feed water to flow rate in the core (average steam quality) comes to about 13%, so that the amount of hydrogen injected into the reactor water is not greatly different from one plant to another so far as the concentration of the feed water is fixed. Accordingly, the chemical reactions participated by N-16 in the core progress roughly under the same conditions, and the change in the main steam line dose rate shows a similar behavior. Accordingly, when a compound decreasing the concentrations of oxygen and hydrogen peroxide in the reactor water without greatly affecting the hydrogen concentration and giving the changes of pH and electro conductivity falling in the standard of control is injected into the reactor water, ECP can be decreased and SCC can be suppressed without causing a rise in the main steam system does rate. The present inventors have discovered that nitrogen compounds containing a nitrogen atom having an oxidation number smaller than that in molecular nitrogen, such as hydroxylamine, carbohydrazide, hydrazine, ammonia, diazine and the like, (hereinafter, these nitrogen compounds are referred to as “reductive nitrogen compounds”) are reductants satisfying the above-mentioned conditions. As the first reason therefor, it can be mentioned that these compounds decrease ECP of the material by oxidation reduction reactions of the reductive nitrogen compounds themselves, even in the period in which dose rate of the irradiation is small. FIG. 5 illustrates results of measurement of ECP of 304SS in the presence of oxygen in water having a high temperature of 280° C., wherein the injected reductive nitrogen compound is hydrazine. As concentration of hydrazine becomes higher, ECP decreases. If hydrazine consumes oxygen and the decrease in oxygen concentration causes a decrease in ECP, ECP should decrease to −0.5 VvsSHE in the presence of excessive hydrazine. According to the result of actual measurement, nevertheless, there is seen a tendency of saturation at −0.2V (SHE), which is probably attributable to an oxidation reduction reaction of hydrazine. Further, from the results of the measurement, it has become apparent that ECP reaches a saturation when concentration of added hydrazine exceeds a definite value. This means that the time period of the hydrazine-oxygen reaction is in an order of second, in water of high temperature. Accordingly, it can be expected that, even in the case of BWR where it takes a time period of second order from entrance of the water to its arrival at the core, the decrease will show a tendency of saturation. Thus, the inventors have confirmed that ECP can be decreased by injecting a reductive nitrogen compound, and have found that ECP can be decreased economically by placing an upper limit on the amount of injection. As the second reason, it can be pointed out that a reductive nitrogen compound reduces oxygen and hydrogen peroxide according the (Equation 2) and (Equation 3), when the reductive nitrogen compound is oxidized to form a molecular nitrogen according to (Equation 1). In the time period when the irradiation has a high dose rate, this reaction is accelerated by formation of radials, etc.2N−n—RN2+2ne−+R2n+ (Equation 1)O2+4H2O+4e−4OH− (Equation 2)H2O2+2e−2OH− (Equation 3)(R designates the residual part of the moleculeof reductive organic compound.) As the reductive organic compound, hydrazine is preferable. This is for the following three reasons. (1) Hydrazine reacts with oxygen and hydrogen peroxide as expressed by (Equation 4) and (Equation 5) to form nitrogen molecule and water which do not affect pH and conductivity. Accordingly, no release of hydrogen takes place. If the compound contains carbon, carbon dioxide is formed, which forms carbonic acid causing subsidiary effects of a rise in electro conductivity and a decrease in pH. However, hydrazine contains no carbon, and therefore such a problem does not arise.N2H4+O2N2+2H2O (Equation 4)N2H4+2H2O2N2+4H2O (Equation 5)(2) Hydrazine is higher than hydrogen in the reaction rate with oxygen and hydrogen peroxide. Accordingly, hydrazine rapidly reacts to form nitrogen and water, and the rise in electric conductivity, caused by its residence, is suppressed.(3) Hydrazine is a liquid substance and chemically stable, so that it is easy to handle. It can be injected by means of a pump even into a site of high pressure. However, when subjected to γ ray irradiation, hydrazine undergoes the reaction of (Equation 6), and releases ammonia and hydrogen in addition to nitrogen.N2H4NH3+(½)N2+(½)H2 (Equation 6) However, even in this case, due to the γ ray exposure, the reaction between N2H4 and radical forms a N2H3 radial which reacts with oxygen quite rapidly. The inventors have found that, so far as the amount of hydrazine is not excessive to oxygen or hydrogen peroxide, the quantities of ammonia and hydrogen formed by the reaction of (Equation 6) are only slight, and the influence on the water quality and main steam line dose rate can be minimized. In order to confirm the above-mentioned reaction, the inventors added hydrazine to oxygen-containing water having a high temperature of 280° C. and irradiated the system with Co-60, and followed the variations of oxygen concentration and by-product concentration based on hydrazine concentration. The results are shown in FIG. 6. When oxygen was excessive to the hydrazine concentration based on the stoichiometric quantities of the reaction of (Equation 4), the oxygen concentration decreased without formation of ammonia or hydrogen. On the other hand, when the concentration of hydrazine was excessive as compared with oxygen concentration, oxygen was consumed and at the same time ammonia and hydrogen were formed. From the results mentioned above, it was confirmed that, when oxygen is present in the system, hydrazine does not undergo the reaction of (Formula 6) even in exposure to γ ray, but the hydrazine reacts with oxygen to form nitrogen and water. Further, it became apparent that an excessive amount of hydrazine is decomposed into ammonia and hydrogen when exposed to γ ray. Based on this fact, the inventors found that the ammonia concentration in the cooling water in the reactor pressure vessel bottom can be used as an indication for controlling the amount of injected hydrazine. This is for the reason that existence of ammonia indicates that hydrazine is present at least in an amount enough for consuming the oxygen and hydrogen peroxide. Since ammonia forms ammonium ion and hydroxide ion in the neighborhood of room temperature, its existence can be indirectly confirmed by measuring conductivity or pH. On the other hand, when hydrazine is insufficient, ammonia is not formed. Accordingly, the ammonia concentration in the bottom of reactor is useful as an indication for judging the de-oxidant effect of is hydrazine in the cooling water of reactor. The effect of injection of hydrazine can be surely evaluated by measuring ECP by the measurement of oxygen concentration in the cooling water at the bottom of reactor pressure vessel or by using an ECP sensor provided on the drain line led from the bottom of reactor pressure vessel, and thereby combining the effect of hydrazine injection with a monitor. The inventors have found that the concentration of oxygen and hydrogen peroxide in the reactor water can be decreased more economically and with smaller subsidiary effects by combining the injection of reductive nitrogen compound and the injection of hydrogen and appropriately controlling their concentrations. Although the concentration of oxygen and hydrogen peroxide in the reactor water can be reduced by merely injecting the reductive nitrogen compound, it can generally be said that the price per mole of reductive nitrogen compound is higher than that of hydrogen. Further, in this technique, a reductive nitrogen compound is injected at a high concentration, and therefore the excessive reductive nitrogen compound emits ammonia to make an adverse influence, unless the amount of reductive nitrogen compound is strictly controlled so as to become an optimum amount for consuming oxygen and hydrogen peroxide. Accordingly, it is most desirable to convert the residual parts of oxygen and hydrogen peroxide which has not been consumed by hydrogen injection into water with the reductive nitrogen compound, because this technique can minimize the necessary amount of reductive nitrogen compound and gives a room to the control. FIG. 7 illustrates the results of analysis of effective oxygen concentration in the upper part of reactor which has been subjected to hydrogen injection. It is apparent that, if hydrogen injection is carried out, the concentrations of oxygen and hydrogen peroxide in the upper part of reactor are decreased. This is for the reason that the hydrogen present in the cooling water at the bottom of reactor pressure vessel suppresses the formation of oxygen and hydrogen peroxide caused by the radiolysis of water in the core. This effect is not readily obtainable even if a reductive nitrogen compound is added. If the concentrations of oxygen and hydrogen peroxide in the upper part of reactor is lowered, the amount of reductive nitrogen compound necessary for consuming the oxygen and hydrogen peroxide in the reactor cooling water can be decreased. As has been mentioned above, an increase in the main steam line dose rate takes place when the hydrogen concentration in the feed water has exceeded about 0.4 ppm. Accordingly, when hydrogen concentration in feed water is 0.4 ppm or below, no rise in the main steam line dose rate takes place, and even if a reductive nitrogen compound is added, the hydrogen concentration in the reactor cooling water does not increase greatly, so that combination of hydrogen injection and addition of reductive nitrogen compound does not lead to an increase in the main steam line dose rate. Further, when injection of hydrogen and addition of reductive nitrogen compound are combined, there arises a merit that the nitrogen molecule formed from reductive nitrogen compound is not readily oxidized into compounds having a higher oxidation number such as nitrous acid, nitric acid, etc. When the amount of reductive nitrogen compound is smaller than that of oxygen or hydrogen peroxide, the unreacted oxygen and hydrogen peroxide and the formed nitrogen coexist in the down-stream of the site where the reductive nitrogen compound has reacted completely. In such a site, there is a possibility that the nitrogen is oxidized to form nitrous acid and nitric acid, in some cases. Nitrous acid and nitric acid are not desirable, because they make a cause of a rise in electric conductivity and a decrease in pH. Although these oxidative anions do not cause a marked acceleration of SCC, so far as they are present in the cooling water for reactor only in a small amount, there is a fear that they can cause a decrease in pH and thereby a decrease in the stability of the oxides present on the line surface or fuels, and they can exercise an influence on the radioactivity concentration of core water. It is preferable, accordingly, to use hydrogen injection in combination and thereby maintain the cooling water for reactor in a reductive atmosphere, even after the reductive nitrogen compound has become unable to react. The amount of hydrogen injection can be optimized by monitoring the main steam line dose rate or by measuring the hydrogen concentration in the cooling water at the bottom of reactor pressure vessel. Further, the inventors have found that alcohols (CnH2n+1OH; wherein n is a natural number) are compounds capable of decreasing the concentrations of oxygen and hydrogen peroxide in the reactor cooling water without greatly affecting the hydrogen concentration. An alcohol reacts with oxygen or hydrogen peroxide according to (Equation 7) or (Equation 8) to yield carbon dioxide and water.C2nH2n+OH+(3n/2)O2nCO2+(n+1)H2O (Equation 7)C2nH2n+1OH+3nH2O2nCO2+(4n+1)H2O (Equation 8) However, unlike the case of hydrazine, the reactions of Equations 7 and 8 do not take place in the absence of γ ray irradiation. In order to confirm this fact, an alcohol (methyl alcohol) was injected into water of high temperature (280° C.) and ECP of 304SS was measured in the case of carrying out γ ray irradiation and in the case of not carrying out γ ray irradiation. The results are shown in FIG. 8. It is apparent from FIG. 3 that ECP of 304SS is about 0.1V (SHE) when the dissolved oxygen concentration is 300 ppb, and ECP decreases as the dissolved oxygen concentration decreases, and ECP reaches about −0.5V (SHE) when dissolved oxygen is 10 ppb or less. It is considered that, when γ ray irradiation is not carried out, oxygen remains without reacting with methanol and therefore ECP has become about 0.1V (SHE), while when γ ray irradiation is carried out, oxygen reacts with methanol to decrease the oxygen concentration so that ECP has become about −0.25V (SHE). Based on this result, it has been confirmed that methanol reacts with oxygen only when 7 ray irradiation is carried out. On the other hand, when an alcohol reacts with oxygen and hydrogen peroxide, CO2 is formed, which reacts with water according to (Equation 9) to form carbonate ion.CO2+H2OH2CO3H++HCO3−2H++CO32− (Equation 9) Thus, alcohols are disadvantageous in that they make higher the conductivity of reactor water and lower the pH value thereof. Accordingly, it is considered appropriate to use alcohols in combination with a reductive nitrogen compound such as hydrazine. Reductive nitrogen compounds such as hydrazine are reactive with oxygen and hydrogen peroxide even in the absence of γ ray irradiation, while alcohols such as methanol do not react with oxygen and hydrogen peroxide in the absence of γ ray irradiation. Therefore, it is considered that reductive nitrogen compounds such as hydrazine are higher in reactivity than alcohols such as methanol, and preferentially react with oxygen and hydrogen peroxide. Thus, by injecting a reductive nitrogen compound such as hydrazine in an amount somewhat smaller than the stoichiometric amount of the reaction with oxygen and hydrogen peroxide, and injecting the alcohol such as methyl alcohol in an amount needed for reacting the residual oxygen and hydrogen peroxide, the formation of ammonia which is a problem arising when a reductive nitrogen compound such as hydrazine is injected in itself alone can be suppressed. Further, there is a merit that pH can be returned to the neutral side by carbonate ion, even if the ammonia forms ammonium ion and shifts pH to the alkaline side. Additionally saying, it can be expected that, by adding an ion, an oxide or a hydroxide of manganese, zinc, molybdenum, tungsten or the like to the reactor water, an oxidation reduction reaction between these substances and reductive nitrogen compound takes place to accelerate the reactions of (Formula 4) and (Formula 5), and thereby the concentrations of oxygen and hydrogen peroxide are decreased, and thereby ECP is reduced. Next, BWR to which this invention is applied will be explained with reference to FIG. 1. In BWR, a condenser 13, a condensate filter demineralizer 3, a feed water pump 4, a feed water heater 5 and a reactor pressure vessel 1 charged with a nuclear fuel are connected by means of feed water line 6, and the reactor pressure vessel 1 and turbine 2 are connected by means of main steam line 14 to form a closed loop. Using water as the reactor coolant, water is converted to steam in the reactor pressure vessel 1. A turbine is rotated by the use of this steam, and thereby a generator (not shown in the figure) is rotated to generate electricity. The steam is returned to water in the condenser 13, made free from impurities in the condensate filter demineralizer 3, and returned to reactor pressure vessel 1 through feed water heater 5 by means of feed water pump 4. Apart from it, the lower part of reactor pressure vessel 1 and inlets of re-circulation pump 7 and jet pump 15 are connected by means of Primary Loop re-circulation system line 16. Heat output is increased by increasing the flow rate of cooling water flowing into the core by means of Primary Loop re-circulation pump 7. ABWR has no Primary Loop re-circulation system line 16, and the Primary Loop re-circulation pump 7, but has a structure of internal pump where the Primary Loop re-circulation pump 7 is provided in the pressure vessel 1. Hereinafter, an explanation will be made by referring to a reactor having a Primary Loop re-circulation system line 16. In this reactor, the upstream side of the Primary Loop re-circulation system line 16 and the reactor water clean up system 9, reactor water clean up system heat exchanger 11, reactor water filter demineralizer 12 and feed water system line 6 are connected by means of reactor water clean up system line 10, and the reactor water is passed to is the reactor water filter demineralizer 12 by means of reactor water clean up system pump 9 to remove impurities from the reactor water. Further, a bottom drain line 8 is provided to connect the bottom of reactor pressure vessel 1 to the reactor water clean up system line 10. Further, in the upper part of the core of the reactor pressure vessel 1, there is provided an emergency core cooling system for injecting water into the rector core in order to cool the core at the time of emergency and a control rod drive hydraulic system for injecting cooling water to drive the control rod for controlling the nuclear reaction of the fuel in the reactor are provided (not shown in the figure). Further, water qualities in the system lines are monitored by means of water quality monitors 21 to 25, and the dose rate of the main steam line 14 is monitored by means of the main steam line dose rate measuring equipment 26. In the case of ABWR, there is provided a reactor water clean up system line 10 for drawing out a part of the reactor water from the upper part of reactor pressure vessel 1, cooling it by passing it through reactor water clean up system heat exchanger 11, removing the impurities from the reactor water in the reactor water clean up equipment and returning it to the feed water line 6. In the above-mentioned BWR, the time at which a reductive nitrogen compound is injected in order to mitigate SCC is roughly classified into the following two times, and the site of injection varies depending on the time of injection. (1) At the times of start up and shut down—The time period of start up operation of the reactor, namely from the drawing out of the control rod to the injection of cooling water from water feed system; and the time period of shut down, namely from the time of stopping the injection of feed water from the water feed system to the time of wholly inserting the control rod.(2) At the time of operation—The time period of starting up the reactor, the time period of normal operation, and the time period of shut down; provided that the period of (1) is excepted. The time periods of start up and shut down are period in which hydrogen and reductive nitrogen compound cannot be sent into the pressure vessel of the reactor, even if hydrogen and reductive nitrogen compound are injected into the cooling water from the feed water system. Therefore, it is necessary to inject hydrogen and reductive nitrogen compound into the cooling water flowing in at least one systems selected from the Primary Loop re-circulation system, reactor water clean up system, emergency core cooling system and control rod drive hydraulic system which can feed cooling water to reactor pressure vessel, for injecting hydrogen and reductive nitrogen compound into the reactor pressure vessel. At the time of start up and shut down, the radiation emitted from the core has a weak intensity, so that in the case of hydrogen injection, the efficiency of removal of oxygen and hydrogen peroxide is considered to be low. Thus, injection of reductive nitrogen compound reactive with oxygen and hydrogen peroxide even in the absence of the action of irradiation is particularly effective. Since steam flows into the condensation tank only when the steam flow rate is low and the turbine by-path valve is open, the influence of flying out of ammonia can also be neglected. Further, since the allowable range of ammonia concentration in the core water is broader than at the time of normal operation, the effect of injection of reductive nitrogen compound is very great in this period. On the other hand, at the time of normal operation, a reductive nitrogen compound is injected from at least one system selected from the water feed system, Primary Loop re-circulation system, reactor water clean up system, emergency core cooling system and control rod drive hydraulic system. Since the point of hydrogen injection is usually selected from the sucking-in side of the condensate pump having a low pressure, there is no problem in the positioning of hydrogen injection point and reductive nitrogen compound injection point, so that hydrogen injection and reductive nitrogen compound injection can be carried out simultaneously. The main place at which oxygen and hydrogen peroxide are formed by radiolysis of water is the core of the reactor. The emergency core cooling system and the control rod drive hydraulic system, capable of directly feed cooling water to the core, can directly inject hydrogen and reductive nitrogen compound into the generation source of oxygen and hydrogen peroxide, and therefore they have a merit of capable of decreasing oxygen and hydrogen peroxide in the early stage. Further, water is usually stagnated on the inner surface of emergency core cooling system and the surface is exposed to intense irradiation, as a result of which such areas are apt to generate SCC. Thus, if reductive nitrogen compound is passed constantly, SCC of the lines can be prevented and integrity of the system used at the time of emergency can be secured. In the case that a reductive nitrogen compound is injected from the feed water system line 6, it is preferable to feed the water to a downstream point of the feed water heater 5. Carbon steel is used as a material of the feed water system line 6, and oxygen is injected into the cooling water flowing therein in order to suppress corrosion of the pipe line. There is a possibility that the reaction with oxygen is catalyzed by the material surface, so that the reaction between oxygen and reductive nitrogen compound can be unnegligible at the position having a large surface area per unit volume of fluid as in the feed water heater 5, which can lead to a drop in utilization rate of the reductive nitrogen compound. Further preferably, it is desirable to inject the reductive nitrogen compound from downstream of water quality monitor 21 for the cooling water of feed water system line 6. In the water quality monitor 21, the impurities present in the cooling water taken into the reactor pressure vessel is monitored by checking electric conductivity. This is for the reason that, if the reductive nitrogen compound is injected into upstream thereof, the electric conductivity rises when the reductive nitrogen compound is dissociated into ions, and the presence of impurity becomes impossible to monitor. In the case where a reductive nitrogen compound is injected from the reactor water clean up system line 10, it is preferable to inject it from a down-stream point of the reactor cooling water filter demineralizer 12. This is for the reason that, when the reductive nitrogen compound is ionized, the ions are caught at the reactor water filter demineralizer 12, and the utilization rate of reductive nitrogen compound in the reactor pressure vessel 1 becomes lower. Further preferably, the reductive nitrogen compound is injected from the down-stream point of water quality monitor 24 which is located at downstream of the reactor water filter demineralizer 12. In the water quality monitor 24, the impurities in the cooling water passing through the reactor water filter demineralizer 12 are monitored by electric conductivity. If it is injected from the upstream thereof, the ionization of reductive nitrogen compound brings about a rise in electric conductivity, which makes it impossible to monitor the presence of impurities. Hereunder, examples relating to injection of reductive nitrogen compound into cooling water, according to this invention, will be mentioned. As the first example of this invention, an example in which only a reductive nitrogen compound is injected at the times of start up and shut down will be mentioned. At the times of start up and shut down, temperature is low and γ-ray exposure is small, so that the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide does not take place readily. FIG. 5 illustrates hydrazine concentration dependence of ECP of 304SS, wherein hydrazine was added as a reductive nitrogen compound. If the ECP dependence of CGR shown in FIG. 2 is taken into consideration, it is necessary to add hydrazine in an amount of 50 ppb or more or further preferably in an amount of 100 ppb or more in order to reduce CGR to 1/10 of that in the case of no hydrazine injection. On the other hand, addition of 300 ppb or more brings about no change in the ECP-lowering effect. From the electric conductivity dependence of CGR shown in FIG. 2, it is apparent that, even when ECP is the same, a higher electric conductivity gives a greater CGR. Accordingly, it is not desirable to add hydrazine in an excessive amount in order to increase electric conductivity of cooling water. Based on the above-mentioned facts, it can be said that it is preferable to control the hydrazine concentration so as to come to 300 ppb or less or to control reductive nitrogen compound concentration so as to come to 9.4×10-6 mol/liter or less; and it is further preferable to control hydrazine concentration to 50 ppb to 300 ppb, namely to control the reductive nitrogen compound concentration so as to come to from 1.5×10-6 to 9.4×10-6 mol/liter. FIG. 1 illustrates one example of the system chart in a case that a reductive nitrogen compound solution stored in the reductive nitrogen compound solution tank 41 is injected into Primary Loop re-circulation system line 16 by means of reductive nitrogen compound solution injecting pump 42. In order to adjust the concentration of reductive nitrogen compound to a prescribed concentration, the reductive nitrogen compound of which amount is calculated by the following Equation 10 is injected:(Amount of injected reductive nitrogen compound)=(Prescribed concentration of reductive nitrogen compound)×(Amount of cooling water in the pressure vessel of reactor)+(concentration of reductive nitrogen compound in the reductive nitrogen compound solution tank) (Equation 10) After once completing the injection, injection of the consumed amount of reductive nitrogen compound is enough for adjusting the reductive nitrogen compound concentration to the prescribed value. Concentration of the reductive nitrogen compound is determined by analyzing the concentration of reductive nitrogen compound in the sample taken out from the cooling water of the bottom part of reactor pressure vessel 1 through the water quality monitors 22 and 23. The amount to be re-injected is calculated from the following (Equation 11).(Amount of reductive nitrogen compound to be injected)={(Prescribed concentration of reductive nitrogen compound)−(Analyzed value of reductive nitrogen compound concentration)}×(Amount of cooling water in the reactor pressure vessel)÷(Concentration of reductive nitrogen compound in the reductive nitrogen compound solution tank) (Equation 11) By intermittently carrying out the above-mentioned procedures of analysis and re-injection, concentration of reductive nitrogen compound can be controlled so as to come to the prescribed value. It is also possible to carrying out a continuous monitoring by measuring the electric conductivity of the cooling water in place of intermittently analyzing the concentration of reductive nitrogen compound. This is for the reason that electric conductivity can be converted to concentration of reductive nitrogen compound by previously determining the coefficients a and b in (Equation 12) experimentally.(Concentration of reductive nitrogen compound)={(Electric conductivity)−b}÷a (Equation 12) In FIG. 1 is shown an example in which a reductive nitrogen compound injecting equipment is connected to the Primary Loop re-circulation system line 16. However, it is also possible to similarly control the injection of reductive nitrogen compound by connecting the reductive nitrogen compound injecting equipment to the reactor water clean up system line 10, as shown in FIG. 9. The other system lines are also similar. FIG. 10 illustrates one example of the reductive nitrogen compound injecting equipment preferably usable for the injection while controlling the amount of reductive nitrogen compound. This equipment is provided with a reductive nitrogen compound tank 51, in addition to which at least one of water level indicator 52, flowmeter 55 and integrated flowmeter 57 is provided. In addition to them, a reductive nitrogen compound solution injection pomp 54 for injecting a solution of reductive nitrogen compound into the cooling water, and a valve 53 and a check valve 56 for preventing erroneous injection of reductive nitrogen compound or back-flow of cooling water are equipped, and they are connected together by means of pipe lines. The tanks and lines are made of a steel material, the surfaces to be contacted with the reductive nitrogen compound are preferably coated with a resin material such as poly-tetrafluoroethylene resin to prevent a direct contact between steel material and reductive nitrogen compound. This is for the reason that a direct contact between steel material and reductive nitrogen compound can cause a decomposition of the reductive nitrogen compound. Further, there is a possibility that, if a reductive nitrogen compound comes into a direct contact with air, the reductive nitrogen compound can be decomposed. For preventing this decomposition, it is advisable to bubble the reductive nitrogen compound present in the tank with argon gas or to cover the liquid surface with argon or the like. Next, as the second example of this invention, an example in which only a reductive nitrogen compound is injected at the time of operation will be mentioned. Since temperature is high and γ-ray exposure is greatest at the time of operation, the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide is accelerated. Accordingly it is necessary to inject the reductive nitrogen compound continuously. In FIG. 6 are shown the changes of oxygen and by-products in a case of adding hydrazine as a reductive nitrogen compound to high-temperature water containing dissolved oxygen and carrying out a γ ray irradiation. In case that the concentration of reductive nitrogen compound does not reach the amount needed for converting oxygen to water, a residual part of oxygen remains. In case that the concentration of reductive nitrogen compound is higher than the amount necessary for converting oxygen to water, oxygen is consumed and ammonia is formed. Based on these facts, the proper amount of injected reductive nitrogen compound can be controlled by using the concentrations of oxygen and ammonia contained in the reactor pressure vessel bottom water as indications. One example of the controlling method will be explained blow with reference to FIG. 11. If the amount of injection is increased stepwise, the oxygen concentration in the cooling water reactor pressure vessel bottom decreases at first so as to match the step. The target value of oxygen concentration is 10 ppb, and further preferably 5 ppb. So far as the oxygen concentration is lower than the target, ECP can be lowered sufficiently and CGR can be made small. If the amount of injection of reductive nitrogen compound is stepwise increased, ammonia becomes detectable in the cooling water of reactor pressure vessel bottom. Since ammonia increases the load of reactor water filter demineralizer and leads to a rise in electric conductivity, a lower ammonia concentration is desirable. FIG. 12 shows the relations between ammonia concentration and pH at room temperature and electric conductivity. From the viewpoint of water quality management criteria of BWR, it is required that pH at room temperature is 5.6 to 8.6, and electric conductivity does not exceed 1 μS/cm. Accordingly, it is preferable that ammonia concentration in the reactor water does not exceed 4.2×10-6 mol/liter. The oxygen concentration can be analyzed by means of a dissolved oxygen meter; while the ammonia concentration can be analyzed by means of ion meter, calorimetric analysis or ion chromatography. It is also allowable to use electric conductivity or pH as an indication in place of analyzing ammonia concentration, because electric conductivity and pH can be converted to ammonia concentration based on FIG. 12. As above, the amount of injection of reductive nitrogen compound is stepwise increased, and the amount of injection of reductive nitrogen compound at which the ammonia concentration or the electric conductivity and pH comes to lower than the target value is previously determined. After that time of the operation, the designed amount of reductive nitrogen compound is injected. Otherwise, the range of amount of injection is determined, and reductive nitrogen compound is injected in that concentration range. It is also allowable to alter the amount of injection manually in the light of measured values of pH and ammonia, or to provide a control system into which measured values are fed back and thereby control the amount of injection. In this example, the mount of reductive nitrogen compound which must be injected has been determined by taking oxygen concentration as an indication. It is also possible to use ECP of the plant-constructing material immersed in the cooling water as an indication. This is for the reason that, as shown in FIG. 3, oxygen concentration has a 1:1 correlation with ECP, oxygen concentration can be determined from ECP. Next, as the third example of this invention, an example in which hydrogen and a reductive nitrogen compound are injected into the cooling water will be mentioned. In case that hydrogen is injected, the hydrogen concentration in the cooling water at the bottom of reactor pressure vessel increases. If the hydrogen concentration exceeds a definite value, dose rate of the main steam line can increase. Accordingly, it is necessary to control the amount of injected hydrogen together with the reductive nitrogen compound to obtain an optimum condition. Since hydrogen is usually cheaper in price than reductive nitrogen compound, it is preferable to increase the amount of hydrogen and decrease the amount of reductive nitrogen compound. FIG. 13 diagrammatically illustrates the changes of concentrations of oxygen, hydrogen and ammonia in the cooling water at the bottom of reactor pressure vessel, and the dose rate of main steam line, in the case of changing the amount of injection of reductive nitrogen compound while keeping the injection of hydrogen constant. In FIG. 13 is simultaneously shown a case of changing the amount of hydrogen injection. The dose rate of main steam line is taken to increase when the hydrogen concentration in the cooling water at the bottom of reactor has exceeded a definite value. In FIG. 13, a and d denote the amount of injection of reductive nitrogen compound at which dose rate of main steam line increases; while b and c are amount of injection of reductive nitrogen compound where oxygen concentration reaches the lowered target (b) by injection of reductive nitrogen compound. In the case of (2) where the injection of hydrogen is large, a small amount of reductive nitrogen compound is enough for reaching the lowered target of oxygen concentration (b), but the dose rate of main steam line begins to increase before reaching that amount of injection of reductive nitrogen compound (a). On the other hand, when the amount of injected hydrogen is small (1), the injected amount of reductive nitrogen compound is larger than that in the case of (2), but at such an amount the dose rate of main steam line does not rise (d). From the economical point of view, it is preferable to determine the maximum (1) as in the case of hydrogen injection (1). By stepwise changing the injected amounts of hydrogen and reductive nitrogen compound and determining the relation of FIG. 13, proper ranges of the injected amounts of hydrogen and reductive nitrogen compound can be determined. On the other hand, it is expected from the relation shown in FIG. 13 that, if the amount of injection of hydrogen is decreased, the amount of injection of reductive nitrogen compound necessary for reducing the oxygen concentration will increase. By utilizing this fact, proper ranges of injection of hydrogen and reductive nitrogen compound can be determined more efficiently. This method will be explained below by referring to FIGS. 14 and 15. As shown in FIG. 14, a reductive nitrogen compound and hydrogen are stepwise injected, by taking the oxygen concentration and ammonia concentration in the coolant in the reactor pressure vessel bottom as indications. Concretely saying, according to the flow chart of FIG. 15, the amount of injected hydrogen and the amount of injected reductive nitrogen compound are varied. At first, injection of hydrogen is carried out at the critical amount of hydrogen injection giving a dose rate, in the main steam line, not exceeding the lower limit of target value. Subsequently, the concentration of reductive nitrogen compound is stepwise increased. When main steam line dose rate has exceeded in this process, the amount of injected hydrogen is decreased by a definite amount. The concentration of reductive nitrogen compound is increased while aiming at that the oxygen concentration will reach a value not exceeding the lower limit of target. By this procedure, the amount of injection of the reductive nitrogen compound giving an oxygen concentration not exceeding the target value can be determined. Further, in the same manner as in Example 2, the amount of injected reductive nitrogen compound is stepwise increased to determine the range of the amount of injected reductive nitrogen compound giving an ammonia concentration not exceeding the upper limit. By the procedure mentioned above, an amount of injection of reductive nitrogen compound giving an oxygen concentration not exceeding the lower limit of target is taken as a minimum value, and the amount of injection just before the ammonia concentration exceeds the aimed upper limit is taken as the upper limit. In the subsequent period of operation, hydrogen and reductive nitrogen compound concentrations are so controlled as to come to the values determined above. It is also allowable to control the hydrogen injection by using the hydrogen concentration in the reactor pressure vessel bottom as an indication, in place of main steam line dose rate. In this case, injection of hydrogen only is previously carried out, and the relations of main steam line dose rate and hydrogen concentration in the bottom of reactor pressure vessel to the amount of hydrogen injection are determined, and further the relation between main steam line dose rate and hydrogen concentration in the bottom of reactor pressure vessel is determined. Hydrogen concentration can be continuously monitored by the use of dissolved hydrogen concentration meter. Further, it is also possible to use ECP of the plant-structural material dipped in cooling water as an indication, as has been mentioned in Example 2. Next, as the fourth example of this invention, a method of injecting hydrogen, a reductive nitrogen compound and an alcohol into cooling water will be mentioned. When hydrogen is injected, there is a possibility that the hydrogen concentration in the reactor pressure vessel bottom water increases, and if it exceed a definite value, main steam line dose rate increases, in the same manner as in Example 3. When an alcohol is injected, there is a possibility that, due to the carbonate ion, pH becomes low or electric conductivity becomes high. Accordingly, it is necessary to control the amounts of injection of alcohol and hydrogen together with reductive nitrogen compound, and optimize the condition. After determining the amount of injection of reductive nitrogen compound and hydrogen according to the method mentioned in Example 3, alcohol is injected so as to replace the reductive nitrogen compound and alcohol. Its amount is calculated according to the following equation 13:(Concentration of injected alcohol)=(Molar number of alcohol necessary for reacting with 1 mol of hydrogen peroxide)/(Molar number of reductive nitrogen compound necessary for reacting with 1 mol of hydrogen peroxide)×(Concentration of injected reductive nitrogen compound to be subtracted) (Equation 13) Concretely saying, it is advisable to replace the reductive nitrogen compound and alcohol stepwise while confirming that the change of electric conductivity of cooling water becomes smaller than the target value, as shown in FIG. 16. Otherwise, it is also allowable to determine the amount of alcohol injection giving an electric conductivity smaller than the target value and thereafter to inject the reductive nitrogen compound stepwise, as shown in FIG. 17. The concentration of dissolved CO2 formed from the alcohol can be calculated according to (Equation 7) and (Equation 8). From the relation between dissolved CO2 concentration and pH at room temperature and electric conductivity shown in FIG. 18, the concentration of dissolved CO2 giving an electric conductivity smaller than the target value can be read out. Accordingly, the alcohol concentration giving an electric conductivity not exceeding the target can be determined. However, since there is a possibility that the reductive nitrogen can be consumed prior to the alcohol, it is advisable to confirm the effect by taking the oxygen concentration in the cooling water and ECP of plant-structural material dipped in the cooling water as an indication. It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. According to this invention, a stress corrosion cracking of nuclear power plant structural material can be mitigated without secondary effects such as rise in the cobalt-60 concentration and the like, by injecting a reductive nitrogen compound containing a nitrogen having a negative oxidation number into a reactor water. |
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claims | 1. A system for the controlled fusion reaction of materials comprising:a. a concentric superconducting magnet defining a cavity;b. a concentric inner housing located within the cavity, the inner housing comprising an inner surface, the inner surface defining a controlled pressure chamber, wherein the chamber is configured to be cylindrical and oriented such that an axis of symmetry of the chamber is parallel to the magnetic field of the superconducting magnet;c. a concentric outer electrode located within the inner housing;d. a concentric inner electrode located at the radial center of the chamber, at least partially covered with insulation;e. a working gas inlet line located within the inner electrode, which introduces a first working material for forming an ionized plasma located within the chamber;f. a second material mounted on an inner surface of the outer electrode facing an exposed portion of the inner electrode;g. a photon source operatively coupled to the chamber, wherein the photon source is configured to irradiate at least the first working material to create a photon pressure sufficient to cause the first working material to rotate within the chamber;h. a continuous wave discharge circuit, which delivers a voltage between the inner electrode and the outer electrode to ionize a component of the first working material to create a plasma; andi. a pulse discharge circuit that delivers a current pulse through the plasma between the inner and outer electrodes of approximately 10 to 15 millisecond duration and induces rotation of the plasma and a surrounding neutral gas in conjunction with the Lorentz force caused by the superconducting magnet;wherein the rotation of the plasma and neutral gas within the chamber may reach up to about 100,000 RPS, which compresses the plasma against the second material mounted on the inner surface of the outer electrode by the centrifugal effect, and thereby providing conditions for a fusion reaction between the first working material and the second material during rotation of the plasma. 2. The system of claim 1, wherein the system is configured to cause the fusion reaction to be aneutronic. 3. The system of claim 1, wherein the system is configured to cause the fusion reaction to be neutronic. 4. The system of claim 1, wherein the first working material comprises hydrogen. 5. The system of claim 1, wherein the first working material comprises a material selected from the group consisting of hydrogen, deuterium, tritium, helium, argon, neon, xenon, nitrogen, and oxygen. 6. The system of claim 1, wherein the first working material comprises a vaporized solid. 7. The system of claim 1, wherein the first working material comprises a material selected from the group consisting of hydrogen, helium, argon, and a vaporized solid. 8. The system of claim 1, wherein the second material comprises a material selected from the group consisting of boron nitride and lanthanum hexaboride. 9. The system of claim 1, wherein the first working material and the second material comprise materials selected from the group consisting of boron, nitride, lanthanum hexaboride, hydrogen, deuterium, tritium, helium, argon, neon, xenon, nitrogen, oxygen, vaporized solids, hydrogen-1, boron-11, lithium-6, lithium-7, helium-3, and nitrogen-15. 10. The system of claim 1, wherein the superconducting magnet has the capability of creating a magnetic field of at least about 0.5 Tesla. 11. The system of claim 1, wherein the second material comprises boron. 12. The system of claim 11, wherein the second material comprises boron-11. 13. The system of claim 1, wherein the second material comprises lithium. 14. The system of claim 13, wherein the second material comprises lithium-6. 15. The system of claim 4, wherein the first working material comprises hydrogen-1. |
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049960210 | summary | FIELD OF THE INVENTION: This invention relates to nuclear reactor fuel assemblies for Pressurized Water Reactors (PWR) and in particular those assemblies which include spaced fuel rod support grids mounted in a reactor core as a unit. The fuel rods are held between an upper end fitting or top nozzle and a lower end fitting or bottom nozzle by means of spacer grids. Guide tubes or thimbles provide the structural integrity between the lower end fitting, the upper end fitting and the spacer grids intermediate the ends of the fuel assembly. BACKGROUND OF THE INVENTION: An attachment of the guide tubes to the lower end fittings is illustrated in U.S. Pat. No. 4,738,820. The guide tubes have plugs in their lower ends to facilitate attachment to the lower end fittings. The guide tubes and plugs are of zircaloy, an alloy of zirconium. The lower end fittings and cups attached thereto to receive the plugged lower ends of the guide tubes are of stainless steel, such as that known as 304. The cup acts as a mounting sleeve for the lowest grid which is also of a stainless steel, such as Inconel 625 or 718. The other grids are of zircaloy. Since the coefficient of expansion of zircaloy and stainless steels such as 304 and Inconel 625 or 718 are significantly different, attachments between zircaloy and stainless steel elements of a structure must accommodate the tendency of the elements to move at relatively different times, rates and magnitudes. Accordingly, attachments of these elements for structures which will maintain their integrity over time are difficult. For example, fuel assemblies may be used in a nuclear reactor, typically, for as many as three cycles of eighteen (18) months each. Many temperature cycles which potentially weaken bottom nozzle to guide tube connections occur during this period of time. SUMMARY OF THE INVENTION: In a fuel assembly having a stainless steel bottom nozzle or lower end fitting to zircaloy guide tube attachment constructed according to the principals of the invention, each zircaloy guide tube has a zircaloy lower end plug. A threaded central passageway in the guide tube plug receives a stainless steel threaded fastener which attaches the plugged tube and a tube receiving stainless steel cup or mounting sleeve to the lower end fitting. The stainless steel faster is an externally threaded bolt having a first end threadably received in the threaded central passageway of the plug in the lower end of the guide tube and a head at its other end in a countersunk hole on the side of the lower end fitting opposite said guide tube. An interruption is provided in the external threads of the bolt which forms a groove communicating the interior of the guide tube with the side of the lower end fitting opposite said guide tube and enhancing its frictional engagement with said threaded central passageway, thereby to hold and attach said guide tube and lower end fitting firmly together, even through a series of temperature cycles. Normally, the plug end receiving stainless steel cup with a fastener opening is secured between the zircaloy plugged guide tube end and the stainless steel lower end fitting. This fully accommodates the temperature expansion differences between zircaloy and stainless steel and provides a better attachment. The groove in the stainless steel fastener, permits lower end fitting fuel assembly reconstitution and provides for coolant flow through the end of the guide tube. These functions are accommodated with the advantage that the longitudinal slot or groove in the threads provides points of increased friction and holding power in the threaded connection and provide "give" for the zircaloy--stainless steel thermal expansion difference. The mean coefficient of thermal expansion.times.10.sup.2 (cm./cm./.degree. C.) in going from 70.degree. F. to 650.degree. C. or 21.1.degree. C. to 343.3.degree. C. for zircaloy-4 and 304 stainless steel are typically as follows: ______________________________________ zircaloy-4: 2.93 in./in./.degree.F. or 5.27 cm./cm./.degree.C. austenitic stainless steel: 9.87 in./in./.degree.F. or 17.77 cm./cm./.degree.C. ______________________________________ |
048633119 | summary | BACKGROUND OF THE INVENTION The present invention is directed to a lining or covering for bore holes in salt rocks used for storing radioactive materials, the bore holes consisting of superimposed tubular sections. Radioactive waste after suitable conditioning are inserted into final storage containers and terminally stored in geological formations. The terminal storage containers are so designed that they safely surroud the radioactive inventory, block the radioactive rays, withstand the pressure of the rocks and also are effectively protected against corrosion during the longterm storage. Therefore, it has been the practice to make such terminal storage containers very expensively of steel, constructed partially in multiple layers, and provided with special corrosion protection devices. There are needed a large number of pieces of such expensive and relatively difficult to handle containers which are stored in caverns or bores without any possibility of recovery for reuse. This point is also true for containers and packages made of ceramic material which are besides, sensitive to the pressure of the rocks. There are known from German No. OS 3034821 above ground intermediate storage members for radioactive materials in containers in which the shielding containers are located in superimposed tubular sections made of concrete. Likewise there are known storage tunnels lined or covered with concrete. The present invention is based on the problem of providing a covering for bore holes in salt rocks for the storage of radioactive materials comprising superimposed tubular sections which make possible the receiving of the static shielding and corrosion protection members of terminal storage containers so that these can be laid out in their stored containers of lower weight but simply and at low cost in order to be easily and conveniently handled. SUMMARY OF THE INVENTION The objects were obtained according to the invention by making the tubular sections of a metallic material and having each of them composed of an outer ring and an inner ring which are securely joined together by an intermediate ring of a electrochemically nobler material, welding the intermediate rings of the individual tubular sections together, the inner rings being not as high as the outer and intermediate rings in order to form a recess in the interior of the covering. The outer rings have upper and lower edges and directly engage an intermediate ring, whereby in each case there is applied in one of the recesses a support ring having twice the height of the depth of the recess and made of the same material as the intermediate ring and welded to the intermediate ring. In assembly, one inserts each support ring in the free recess of each adjacent outer ring, whereby the bottom of the recess in the outer ring sets deeper than the bottom of the recess in the inner ring. It is advantageous if the inserted side of the support ring grasp the free recess of the adjacent outer ring and there are provided manipulated recesses in the inner ring. Advantageously the inner rings and the outer rings comprise spherical case graphite. |
claims | 1. A method of forming a microscopic structure on a substrate of a material having a first ablation threshold using a laser beam, the laser beam having a spot size, the method comprising:forming a mask of a material having a second ablation threshold on the substrate surface using a fabrication process capable of producing mask features smaller than the laser beam spot size, the second ablation threshold being higher than the first ablation threshold; anddirecting the laser beam toward the substrate surface, the laser beam having a fluence above the first ablation threshold and having a spot size that is larger than the smallest design features of the mask, the mask protecting portions of the substrate that are covered by the mask to produce features in the substrate by laser processing, the features in the processed substrate being smaller than the laser beam spot size. 2. The method of claim 1 in which forming a mask on the substrate surface includes forming a mask using electron beam-assisted deposition or ion-beam assisted deposition. 3. The method of claim 1 in which forming a mask on the substrate surface includes forming a mask using photolithography. 4. The method of claim 1 in which forming a mask pattern on a substrate surface includes depositing a pattern that absorbs sufficient laser radiation to prevent damage to the substrate under the mask from the laser beam. 5. The method of claim 1 in which forming a mask pattern on the substrate surface includes depositing a pattern that reflects sufficient laser radiation to prevent damage to the substrate under the mask from the laser beam. 6. The method of claim 1 in which directing the laser beam toward the substrate surface comprises directing an ultra-fast pulsed laser beam toward the substrate surface. 7. The method of claim 1 in which forming a mask pattern on the substrate surface includes depositing multiple layers of materials to form the mask. 8. The method of claim 1 in which directing the laser beam toward the substrate surface includes selectively removing the substrate material and leaving mask material to protect masked portions of the substrate. 9. The method of claim 1 in which directing a laser beam toward the substrate surface includes removing material from the substrate in regions not covered by the mask. 10. The method of claim 1 in which directing the laser beam toward the substrate surface includes directing a laser beam having a fluence of between 001 J/cm2 and 100 J/cm2. 11. The method of claim 1 in which directing the laser beam toward the substrate surface includes directing a laser beam having a fluence just above the value required to micromachine the substrate. 12. The method of claim 1 in which directing the laser beam toward the substrate surface includes directing a laser beam having a fluence greater than the first ablation threshold and less than the second ablation threshold. 13. The method of claim 1 in which forming a mask includes forming a mask having an optical transmissivity sufficiently low so as to prevent damage to the underlying substrate through the mask. 14. The method of claim 1 in which forming a mask includes controlling the transmittance of the mask by controlling both the composition and thickness of the masking material. 15. The method of claim 1 in which forming a mask includes forming a mask mask that is sufficiently robust to prevent damage to the substrate during the micromachining operation. 16. The method of claim 1 which forming a mask includes forming a mask comprising a graded structure. 17. The method of claim 1 in which forming a mask comprises forming different regions of the mask have different thicknesses, materials, densities or other properties that influence the amount of optical transmission in different areas of the mask. 18. The method of claim 1 directing a laser beam toward the substrate includes removing the mask at a sufficiently slow rate so that the substrate under the mask is protected until the processing of the unprotected substrate is completed. 19. The method of claim 1 in which forming a mask includes forming a mask having properties at different positions on the substrate so that directing the laser beam toward the substrate surface creates three-dimensional structures as the mask is removed at different rates at different positions. 20. The method of claim 1 in which forming a mask includes forming a mask having different thicknesses or different compositions in different areas, so that portions of the mask are removed by the laser after a period of micromachining, so that areas that become exposed after the processing has begun are processed less than areas that had no mask at the beginning of the processing. 21. A system for modifying a work piece, comprising:a charged particle beam focusing column;a vacuum chamber for containing the work piece to be modified;an ultra-fast pulsed laser system having a maximum fluence;a work piece to be modified positioned in the vacuum chamber, the work piece including a substrate composed of a substrate material and a mask composed of a mask material, the ablation threshold of the substrate material being lower than the ablation threshold of the mask material, the maximum fluence of the laser system being greater than the ablation threshold of the substrate material. 22. The system of claim 21 in which the ultra-fast pulsed laser is operating with a fluence between the ablation threshold of the substrate material and the ablation threshold of the mask material. 23. The system of claim 21 in which the mask comprises multiple layers of materials. 24. The system of claim 21 in which different regions of the mask have different thicknesses, materials, densities or other properties that influence the amount of optical transmission in different areas of the mask. |
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059498366 | abstract | An apparatus, and method, are disclosed for producing a high specific activity of a radioisotope in a single increment of target material, or sequentially within in-series increments of target material, by exposing a targeted isotope in the target material to a high energy photon beam to isotopically convert the targeted isotope. In particular, this invention is used to produce a high specific activity of Mo.sup.99, of at least 1.0 Ci/gm or preferably at least about 10.0 Ci/gm, from Mol.sup.100. |
claims | 1. An apparatus, comprising:an imaging apparatus configured to perform an examination on an object;a treatment apparatus configured to develop a treatment plan based at least in part upon the examination and to perform a treatment on the object according to the treatment plan; anda support article configured to support the object in a substantially same orientation relative to the support article during both the examination and the treatment, the support article comprising one or more receptors for receiving at least a portion of the object and configured to pivot about an axis of rotation during at least one of the examination or the treatment. 2. The apparatus of claim 1, the support article substantially affixed to a floor of an operation room during both the examination and the treatment. 3. The apparatus of claim 1, the imaging apparatus configured to examine the object using x-ray radiation. 4. The apparatus of claim 3, the imaging apparatus configured to emit the x-ray radiation into a first plane and the treatment apparatus configured to emit photon radiation in a second plane substantially parallel to the first plane. 5. The apparatus of claim 4, the first plane and the second plane being substantially co-planar. 6. The apparatus of claim 1, the object comprising at least part of a patient, and the patient positioned in a prone position on the support article. 7. The apparatus of claim 1, the object comprising breast tissue and the one or more receptors configured to receive at least a portion of the breast tissue. 8. The apparatus of claim 1, the object comprising at least one of prostate tissue or testicular tissue and the one or more receptors configured to receive at least a portion of the at least one of prostate tissue or testicular tissue. 9. The apparatus of claim 1, the imaging apparatus configured to generate three-dimensional image data of the object under examination. 10. The apparatus of claim 1, the imaging apparatus remaining substantially fixed during the examination. 11. A method comprising:examining an object situated on a support article to develop a treatment plan;treating the object based upon the treatment plan while the object remains situated on the support article; androtating the object and the support article about an axis of rotation during at least one of the examining or the treating, the support article substantially affixed to a floor of an operation room during both the examining and the treating. 12. The method of claim 11, the examining comprising examining the object to generate three-dimensional image data of the object. 13. The method of claim 11, comprising maintaining an imaging apparatus configured to perform the examining in a substantially fixed position during the examining. 14. The method of claim 11, the examining comprising emitting x-ray radiation in a first plane. 15. The method of claim 14, the treating comprising emitting photon radiation in a second plane, the second plane substantially parallel to the first plane. 16. The method of claim 11, the examining and the treating performed while the object is in a prone position on the support article. 17. The method of claim 11, the object remaining in a substantially fixed orientation relative to the support article during both the examining and the treating. 18. The method of claim 11, the examining comprising rotating at least one of an x-ray source or a detector array relative to the object to generate three-dimensional image data of the object. 19. The method of claim 11, comprising:identifying a treatment area based upon the examining, wherein the treating comprises using radiation photons to treat the treatment area. 20. An apparatus for treating at least one of breast cancer, prostate cancer or testicular cancer, comprising:a support article comprising a receptor for receiving at least one of breast tissue, prostate tissue or testicular tissue of a patient;an imaging apparatus configured to perform an examination on the at least one of breast tissue, prostate tissue or testicular tissue while the patient is supported by the support article; anda treatment apparatus configured to perform a treatment on the at least one of breast tissue, prostate tissue or testicular tissue while the patient is supported by the support article,the support article configured to pivot about an axis during at least one of the examination or the treatment causing a position of the at least one of breast tissue, prostate tissue or testicular tissue to change relative to at least one of the imaging apparatus or the treatment apparatus,the examination and the treatment performed while the patient remains in a substantially fixed orientation relative to the support article. |
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abstract | Embodiments of a method for determining a mask pattern to be used on a photo-mask in a lithography process are described. This method may be performed by a computer system. During operation, this computer system receives at least a portion of a first mask pattern including first regions that violate pre-determined rules associated with the photo-mask. Next, the computer system determines a second mask pattern based on at least the portion of the first mask pattern, where the second mask pattern includes second regions that are estimated to comply with the pre-determined rules. Note that the second regions correspond to the first regions, and the second mask pattern is determined using a different technique than that used to determine the first mask pattern. |
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055330894 | summary | BACKGROUND OF THE INVENTION This invention relates to an instrument for use in limiting the transmission of x-rays from a radiological source to a particular area of the body of a patient while at the same time shielding surrounding areas of the body from such rays. It is an instrument that is independent of and employed as an accessory to the x-ray source. It is designed, when put to use, to interpose and support between the x-ray source and the patient a unit that is adjustable to collimate and limit x-rays issuing from the source onto the particular area of the patient's body while also shielding surrounding areas of the patient from such rays. More particularly, it is an object of this invention to provide, as an accessory in the employment of x-ray issuing devices, a manually operable and adjustable instrument of a simple and uncomplicated nature, an instrument which serves to achieve the beneficial results intended, primarily, limiting x-rays issuing from a radiological source to an area where needed upon the body of a patient and shielding surrounding areas of the body from such rays. A further object of the invention is to provide an instrument for the foregoing purpose, which is simple in structure, practical in its mode of use, and effective in accomplishing the results intended. BRIEF SUMMARY OF THE INVENTION In accordance with the invention there is provided an instrument which includes a unit having a multisided continuous frame defining the perimeter about a complementary aperture. To the sides of the frame are hinged depending panels in the nature of shields or shutters comprised of radio-opaque material. The unit is supported by its frame to an end of a rack. The rack is manually extendible to position the unit with the aperture of the unit exposed between an x-ray emitting source and a particular area of the patient's body. The shields are manually adjustable about the frame relative to the x-ray source and the body of the patient to vary the size of the aperture in a manner for the shields to collimate and limit flow of x-rays issuing from the source through the aperture to the particular area of the patient's body; and the radio-opaque material of the shields also serves to shield surrounding areas of the patient's body from the rays. The unit and the rack define an instrument embodying the invention. The foregoing, as well as other features, objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, when taken together with the accompanying drawing wherein an embodiment of the invention is illustrated. It is to be expressly understood, however, that the drawing is for purposes of illustration and description, and it is not to be construed as defining the limits of the invention. |
claims | 1. An x-ray generating system comprising:a microfocusing source of x-ray radiation;a waveguide bundle optic for capturing the x-ray radiation produced by the microfocusing source, the waveguide bundle optic having an input for receiving x-ray radiation from the microfocusing source and an output for outputting a collimated, or convergent x-ray beam;a diffractive optic with a diffractive reflection surface for focusing the x-ray beam from the wave guide bundle optic to a focal point; andwherein a sample receives radiation from the diffractive reflection surface, the sample being located adjacent to the focal point. 2. The system of claim 1, wherein the waveguide bundle optic is a polycapillary optic. 3. The system of claim 1, wherein the said focusing optic is a Kirkpatrick-Baez side-by-side optic having multilayer Bragg x-ray reflecting surfaces. 4. The system of claim 3, wherein the said Kirkpatrick-Baez-Baez side-by-side optic has two elliptical reflectors. 5. The system of claim 3, wherein the said Kirkpatrick-Baez-Baez side-by-side optic has two parabolical reflectors. 6. The system of claim 3, wherein the said Kirkpatrick-Baez-Baez side-by-side optic has two hyperbolical reflectors. 7. The system of claim 3, wherein the said multilayer Bragg x-ray reflecting surfaces have graded-d spacing. 8. The system of claim 7, wherein the graded-d spacing is laterally graded. 9. The system of claim 7, wherein the graded-d spacing is both laterally graded and depth graded. 10. An x-ray generating system comprising:a microfocusing source of x-ray radiation;a waveguide bundle optic for capturing the x-ray radiation produced by the microfocusing source, the waveguide bundle optic having an input for receiving x-ray radiation from the source and an output for outputting a collimated, or convergent x-ray beam;a diffractive optic with a diffractive reflection surface for focusing the x-ray beam from the wave guide bundle optic to a focal point;wherein the waveguide optic is a bundle of carbon nanotubes; andwherein a sample receives radiation from the diffractive reflection surface, the sample being located adjacent to the focal point. 11. The system of claim 1, wherein the said focusing optic is a doubly curved optic having multilayer Bragg x-ray reflecting surface. 12. The system of claim 11, wherein the said doubly curved optic has an ellipsoidal surface. 13. The system of claim 11, wherein the said doubly curved optic has a paraboloidal surface. 14. The system of claim 11, wherein the said doubly curved optic has a hyperboloidal surface. 15. The system of claim 11, wherein the said multilayer Bragg x-ray reflecting surfaces have graded-d spacing. 16. The system of claim 15, wherein the graded-d spacing is laterally graded. 17. The system of claim 15, wherein the graded-d spacing is both laterally graded and depth graded. 18. The system of claim 1, further comprising an aperture for removing unused portions of the x-ray radiation, the aperture located between the said focusing optic and the focal point. |
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description | This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/023,460 filed Jul. 11, 2014, and the subject matter thereof is incorporated herein by reference thereto. The present application contains subject matter related to concurrently filed U.S. patent application Ser. No. 14/696,322 filed Apr. 24, 2015. The related application is assigned to Applied Materials, Inc. and the subject matter thereof is incorporated herein by reference thereto. The present application contains subject matter related to concurrently filed U.S. patent application Ser. No. 14/696,331 filed Apr. 24, 2015. The related application is assigned to Applied Materials, Inc. and the subject matter thereof is incorporated herein by reference thereto. The present invention relates generally to extreme ultraviolet lithography, and more particularly to multilayer stacks, manufacturing systems, and lithography systems for extreme ultraviolet reflective elements for extreme ultraviolet lithography. Modern consumer and industrial electronic systems are growing ever more complex. Electronic devices require higher density electronic components in smaller and more flexible packages. As component densities increase, technology changes are required to satisfy the demand for higher density devices with smaller feature sizes. Extreme ultraviolet lithography, also known as soft x-ray projection lithography, is a photolithographic process for the manufacture of 0.13 micron, and smaller, minimum feature size semiconductor devices. Extreme ultraviolet light, which can generally in the 5 to 50 nanometers (nm) wavelength range, is strongly absorbed by most elements. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Extreme ultraviolet radiation can be projected through a series of reflective components, including mirror assemblies and a mask blank coated with a non-reflective mask pattern, and directed onto semiconductor wafers to form high density, small feature size semiconductor devices. The reflective components of extreme ultraviolet lithography systems can include reflective multilayer coatings of materials. Because of the high power levels of the extreme ultraviolet light, the remaining non-reflected extreme ultraviolet light causes thermal heating that can degrade reflectivity of the reflective components over time and can result in limited lifetimes for the reflective components. In view of the need for the increasingly smaller feature size of electronic components, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems. Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art. The embodiments of the present invention provides a method of manufacture of an extreme ultraviolet reflective element that includes: providing a substrate; forming a multilayer stack on the substrate, the multilayer stack includes a plurality of reflective layer pairs having a first reflective layer formed from silicon and a second reflective layer formed from niobium or niobium carbide for forming a Bragg reflector; and forming a capping layer on and over the multilayer stack for protecting the multilayer stack by reducing oxidation and mechanical erosion. The embodiments of the present invention provides an extreme ultraviolet reflective element that includes: a substrate; a multilayer stack on the substrate, the multilayer stack includes a plurality of reflective layer pairs having a first reflective layer formed from silicon and a second reflective layer formed from niobium or niobium carbide for forming a Bragg reflector; and a capping layer on and over the multilayer stack for protecting the multilayer stack by reducing oxidation and mechanical erosion. The embodiments of the present invention provides an extreme ultraviolet reflective element production system that includes: a first deposition system for depositing a multilayer stack on the substrate, the multilayer stack including a plurality of reflective layer pairs having a first reflective layer formed from silicon and a second reflective layer formed from niobium or niobium carbide for forming a Bragg reflector; and a second deposition system for forming a capping layer on the multilayer stack for protecting the multilayer stack by reducing oxidation and mechanical erosion. Certain embodiments of the invention have other phases or elements in addition to or in place of those mentioned above. The phases or element will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings. The following embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments would be evident based on the present disclosure, and that system, process, or mechanical changes may be made without departing from the scope of the embodiments of the present invention. In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. In order to avoid obscuring the embodiments of the present invention, some well-known elements, system configurations, and process phases are not disclosed in detail. The drawings showing embodiments of the system are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing FIGS. Similarly, although the views in the drawings for ease of description generally show similar orientations, this depiction in the FIGS. is arbitrary for the most part. Generally, the invention can be operated in any orientation. Where multiple embodiments are disclosed and described having some features in common, for clarity and ease of illustration, description, and comprehension thereof, similar and like features will be described with the same or similar reference numerals. For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of a mask blank, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane, as shown in the figures. The term “on” indicates that there is direct contact between elements. The term “directly on” indicates that there is direct contact between elements with no intervening elements. The term “processing” as used herein includes deposition of material or photoresist, patterning, exposure, development, etching, sputtering, cleaning, implantation, and/or removal of the material or photoresist as required in forming a described structure. The terms “about” and “approximately” indicate that the size of an element can be determined within engineering tolerances. Referring now to FIG. 1, therein is shown an exemplary diagram of an extreme ultraviolet lithography system 100 in a first embodiment of the present invention. The extreme ultraviolet lithography system 100 can include an extreme ultraviolet light source 102 for producing extreme ultraviolet light 112, a set of reflective elements, and a target wafer 110. The reflective components can include a condenser 104, a reflective mask 106, an optical reduction assembly 108, a mask blank, a mirror, or a combination thereof. The extreme ultraviolet light source 102 can generate the extreme ultraviolet light 112. The extreme ultraviolet light 112 is electromagnetic radiation having a wavelength in the range of 5 to 50 nanometers. For example, the extreme ultraviolet light source 102 can include a laser, a laser produced plasma, a discharge produced plasma, a free-electron laser, synchrotron radiation, or a combination thereof. The extreme ultraviolet light source 102 can generate the extreme ultraviolet light 112 having a variety of characteristics. The extreme ultraviolet light source 102 can produce broadband extreme ultraviolet radiation over a range of wavelengths. For example, the extreme ultraviolet light source 102 can generate the extreme ultraviolet light 112 having wavelengths ranging from 5 to 50 nm. The extreme ultraviolet light source 102 can produce the extreme ultraviolet light 112 having a narrow bandwidth. For example, the extreme ultraviolet light source 102 can generate the extreme ultraviolet light 112 at 13.5 nm. The center of the wavelength peak is 13.5 nm. The condenser 104 is an optical unit for reflecting and focusing the extreme ultraviolet light 112. The condenser 104 can reflect and concentrate the extreme ultraviolet light 112 from the extreme ultraviolet light source 102 to illuminate the reflective mask 106. Although the condenser 104 is shown as a single element, it is understood that the condenser 104 can include one or more reflective elements such as concave mirrors, convex mirrors, flat mirrors, or a combination thereof, for reflecting and concentrating the extreme ultraviolet light 112. For example, the condenser 104 can be a single concave mirror or an optical assembly having convex, concave, and flat optical elements. The reflective mask 106 is an extreme ultraviolet reflective element having a mask pattern 114. The reflective mask 106 creates a lithographic pattern to form a circuitry layout to be formed on the target wafer 110. The reflective mask 106 can reflect the extreme ultraviolet light 112. The optical reduction assembly 108 is an optical unit for reducing the image of the mask pattern 114. The reflection of the extreme ultraviolet light 112 from the reflective mask 106 can be reduced by the optical reduction assembly 108 and reflected on to the target wafer 110. The optical reduction assembly 108 can include mirrors and other optical elements to reduce the size of the image of the mask pattern 114. For example, the optical reduction assembly 108 can include concave mirrors for reflecting and focusing the extreme ultraviolet light 112. The optical reduction assembly 108 can reduce the size of the image of the mask pattern 114 on the target wafer 110. For example, the mask pattern 114 can be imaged at a 4:1 ratio by the optical reduction assembly 108 on the target wafer 110 to form the circuitry represented by the mask pattern 114 on the target wafer 110. The extreme ultraviolet light 112 can scan the reflective mask 106 synchronously with the target wafer 110 to form the mask pattern 114 on the target wafer 110. Referring now to FIG. 2, therein is shown an example of an extreme ultraviolet reflective element production system 200. The extreme ultraviolet reflective element can reflect extreme ultraviolet light. The extreme ultraviolet reflective element can include a mask blank 204, an extreme ultraviolet (EUV) mirror 205, or other reflective elements. The extreme ultraviolet reflective element production system 200 can produce mask blanks, mirrors, or other elements that reflect the extreme ultraviolet light 112 of FIG. 1. The extreme ultraviolet reflective element production system 200 can fabricate the extreme ultraviolet reflective elements applying thin coatings to source substrates 203. The mask blank 204 is a multilayered structure for forming the reflective mask 106 of FIG. 1. The mask blank 204 can be formed using semiconductor fabrication techniques. The reflective mask 106 can have the mask pattern 114 of FIG. 1 formed on the mask blank 204 for representing electronic circuitry. The extreme ultraviolet mirror 205 is a multilayered structure reflective in the range of extreme ultraviolet light. The extreme ultraviolet mirror 205 can be formed using semiconductor fabrication techniques. The mask blank 204 and the extreme ultraviolet mirror 205 can be similar structures, however the extreme ultraviolet mirror 205 does not have the mask pattern 114. The extreme ultraviolet reflective elements are efficient reflectors of the extreme ultraviolet light 112. The mask blank 204 and the extreme ultraviolet mirror 205 can have an extreme ultraviolet reflectivity of greater than 60%. The extreme ultraviolet reflective elements are efficient if they reflect more than 60% of the extreme ultraviolet light 112. The extreme ultraviolet reflective element production system 200 includes a wafer loading and carrier handling system 202 into which the source substrates 203 are loaded and from which the extreme ultraviolet reflective elements are unloaded. An atmospheric handling system 206 provides access to a wafer handling vacuum chamber 208. The wafer loading and carrier handling system 202 can include substrate transport boxes, loadlocks, and other components to transfer a substrate from atmosphere to vacuum inside the system. Because the mask blank 204 is used to form devices at a very small scale, the mask blank 204 must be processed in a vacuum system to prevent contamination and other defects. The wafer handling vacuum chamber 208 can contain two vacuum chambers, a first vacuum chamber 210 and a second vacuum chamber 212. The first vacuum chamber 210 can include a first wafer handling system 214 and the second vacuum chamber 212 can include a second wafer handling system 216. Although the wafer handling vacuum chamber 208 is described with two vacuum chambers, it is understood that the system can have any number of vacuum chambers. The wafer handling vacuum chamber 208 can have a plurality of ports around its periphery for attachment of various other systems. The first vacuum chamber 210 can have a degas system 218, a first physical vapor deposition system 220, a second physical vapor deposition system 222, and a pre-clean system 224. The degas system 218 is for thermally desorbing moisture from the substrates. The pre-clean system 224 is for cleaning the surfaces of the wafers, mask blanks, mirrors, or other optical components. The physical vapor deposition systems, such as the first physical vapor deposition system 220 and the second physical vapor deposition system 222, can be used to form thin films of materials on the source substrates 203. For example, the physical vapor deposition systems can include vacuum deposition system such as magnetron sputtering systems, ion sputtering systems, pulsed laser deposition, cathode arc deposition, or a combination thereof. The physical vapor deposition systems, such as the magnetron sputtering system, can form thin layers on the source substrates 203 including the layers of silicon, metals, alloys, compounds, or a combination thereof. The physical vapor deposition system can form reflective layers, capping layers, and absorber layers. For example, the physical vapor deposition systems can form layers of silicon, molybdenum, ruthenium, niobium, chromium, tantalum, nitrides, carbon, compounds, or a combination thereof. Although some compounds are described as an oxide, it is understood that the compounds can include oxides, dioxides, atomic mixtures having oxygen atoms, or a combination thereof. The second vacuum chamber 212 can have a first multi-cathode source 226, a chemical vapor deposition system 228, a cure chamber 230, and an ultra-smooth deposition chamber 232 connected to it. For example, the chemical vapor deposition system 228 can include a flowable chemical vapor deposition system (FCVD), a plasma assisted chemical vapor deposition system (CVD), an aerosol assisted CVD, a hot filament CVD system, or a similar system. In another example, the chemical vapor deposition system 228, the cure chamber 230, and the ultra-smooth deposition chamber 232 can be in a separate system from the extreme ultraviolet reflective element production system 200. The chemical vapor deposition system 228 can form thin films of material on the source substrates 203. For example, the chemical vapor deposition system 228 can be used to form layers of materials on the source substrates 203 including mono-crystalline layers, polycrystalline layers, amorphous layers, epitaxial layers, or a combination thereof. The chemical vapor deposition system 228 can form layers of silicon, silicon oxides, carbon, tungsten, silicon carbide, silicon nitride, titanium nitride, metals, alloys, and other materials suitable for chemical vapor deposition. For example, the chemical vapor deposition system can form planarization layers. The first wafer handling system 214 is capable of moving the source substrates 203 between the atmospheric handling system 206 and the various systems around the periphery of the first vacuum chamber 210 in a continuous vacuum. The second wafer handling system 216 is capable of moving the source substrates 203 around the second vacuum chamber 212 while maintaining the source substrates 203 in a continuous vacuum. The extreme ultraviolet reflective element production system 200 can transfer the source substrates 203 and the mask blank 204 between the first wafer handling system 214, the second wafer handling system 216 in continuous vacuum conditions. Referring now to FIG. 3, therein is shown an example of an extreme ultraviolet reflective element 302. The extreme ultraviolet reflective element 302 can be the mask blank 204 of FIG. 2 or the extreme ultraviolet mirror 205 of FIG. 2. The mask blank 204 and the extreme ultraviolet mirror 205 are structures for reflecting the extreme ultraviolet light 112 of FIG. 1. The extreme ultraviolet reflective element 302, such as the extreme ultraviolet mirror 205, can include a substrate 304, a multilayer stack 306, and a capping layer 308. The extreme ultraviolet mirror 205 can be used to form reflecting structures for use in the condenser 104 of FIG. 1 or the optical reduction assembly 108 of FIG. 1. The mask blank 204 can include the substrate 304, the multilayer stack 306, the capping layer 308, and an absorber layer 310. The mask blank 204 can be used to form the reflective mask 106 of FIG. 1 by patterning the absorber layer 310 with the layout of the circuitry required. In the following sections, the term for the mask blank 204 can be used interchangeably with the term of the extreme ultraviolet mirror 205 for simplicity. The mask blank 204 can include the components of the extreme ultraviolet mirror 205 with the absorber layer 310 added in addition to form the mask pattern 114 of FIG. 1. The mask blank 204 is an optically flat structure used for forming the reflective mask 106 having the mask pattern 114. For example, the reflective surface of the mask blank 204 can form a flat focal plane for reflecting the incident light, such as the extreme ultraviolet light 112 of FIG. 1. The substrate 304 is an element for providing structural support to the extreme ultraviolet reflective element 302. The substrate 304 can be made from a material having a low coefficient of thermal expansion (CTE) to provide stability during temperature changes. The substrate 304 can have properties such as stability against mechanical cycling, thermal cycling, crystal formation, or a combination thereof. The substrate 304 can be formed from a material such as silicon, glass, oxides, ceramics, glass ceramics, or a combination thereof. The multilayer stack 306 is a structure that is reflective to the extreme ultraviolet light 112. The multilayer stack 306 includes alternating reflective layers of a first reflective layer 312 and a second reflective layer 314. The first reflective layer 312 and the second reflective layer 314 can form a reflective pair 316. The multilayer stack 306 can include between 40-60 of the reflective pairs 316 for a total of up to 120 reflective layers. However, it is understood that more or fewer layers can be used as needed. The first reflective layer 312 and the second reflective layer 314 can be formed from a variety of materials. For example, the first reflective layer 312 and the second reflective layer 314 can be formed from silicon and niobium, respectively. The optical properties of niobium determine how well it performs in the multilayer stack. The real and imaginary components of the refractive index are similar to molybdenum. The first reflective layer 312 can be formed from silicon. The second reflective layer 314 can be formed from niobium. Although the multilayer stack 306 is described as having the first reflective layer 312 formed from silicon and the second reflective layer 314 formed from niobium, other configurations are possible. For example, the first reflective layer 312 can be formed from niobium and the second reflective layer 314 can be formed from silicon. However, it is understood that the alternating layers can be formed from other materials. In another example, the second reflective layer 314 can be formed with niobium carbide. The reflectivity of the mask blank 204 and the extreme ultraviolet mirror 205 is determined by the sharpness of the interface between the layers and the roughness of layers. Changing the material used to from the multilayer stack 306 can improve interface sharpness or layer roughness will increase the multilayer reflectivity. The multilayer stack 306 forms a reflective structure by having alternating thin layers of materials with different optical properties to create a Bragg mirror. Each of the alternating layers can have dissimilar optical constants for the extreme ultraviolet light 112. The multilayer stack 306 can be formed in a variety of ways. For example, the first reflective layer 312 and the second reflective layer 314 can be formed with magnetron sputtering, ion sputtering systems, pulsed laser deposition, cathode arc deposition, or a layer deposition technique. In an illustrative example, the multilayer stack 306 can be formed using a physical vapor deposition technique, such as magnetron sputtering. The first reflective layer 312 and the second reflective layer 314 of the multilayer stack 306 can have the characteristics of being formed by the magnetron sputtering technique including precise thickness, low roughness, and clean interfaces between the layers. The first reflective layer 312 and the second reflective layer 314 of the multilayer stack 306 can have the characteristics of being formed by the physical vapor deposition including precise thickness, low roughness, and clean interfaces between the layers. The physical dimensions of the layers of the multilayer stack 306 formed using the physical vapor deposition technique can be precisely controlled to increase reflectivity. For example, the first reflective layer 312, such as a layer of silicon, can have a thickness of 3.5 nm. The second reflective layer 314, such as a layer of niobium, can have a thickness of 3.5 nm. However, it is understood that the thickness of the first reflective layer 312 and the second reflective layer 314 can vary based on engineering needs, the wavelength of the extreme ultraviolet light 112, and the optical properties of the layer materials. In another example, the second reflective layer 314 can be formed with niobium carbide having a thickness of 3.5 nm. In another example, the first reflective layer 312 and the second reflective layer 314 can be formed from silicon and niobium carbide. The first reflective layer, such as a silicon layer, can have a thickness of 4.15 nm. The second reflective layer 314, such as a layer of niobium carbide, can have a thickness of 2.8 nm It has been discovered that forming the multilayer stack 306 with silicon and niobium provides similar reflectivity of the multilayer stack 306 as silicon and molybdenum. Based on the refractive index and other physical properties of niobium and silicon, the multilayer stack 306 having reflectivity comparable to that of molybdenum and silicon. It has been discovered that forming the multilayer stack 306 with silicon and niobium carbide provides similar reflectivity of the multilayer stack 306 as silicon and molybdenum. Based on the refractive index and other physical properties of niobium carbide and silicon, the multilayer stack 306 having a silicon layer of 4.15 nm and a niobium carbide layer of 2.8 nm provides a reflectivity comparable to that of molybdenum and silicon. It has been discovered that forming the multilayer stack 306 with niobium carbide increases the reliability of the multilayer stack 306. The hardness of the niobium carbide protects the multilayer stack 306 and increase operating life. The capping layer 308 is a protective layer transparent to the extreme ultraviolet light 112. The capping layer 308 can be formed directly on the multilayer stack 306. The capping layer 308 can protect the multilayer stack 306 from contaminants and mechanical damage. For example, the multilayer stack 306 can be sensitive to contamination by oxygen, carbon, hydrocarbons, or a combination thereof. The capping layer 308 can interact with the contaminants to neutralize them. The capping layer 308 is an optically uniform structure that is transparent to the extreme ultraviolet light 112. The extreme ultraviolet light 112 can pass through the capping layer 308 to reflect off of the multilayer stack 306. The capping layer 308 has a smooth surface. For example, the surface of the capping layer 308 can have a roughness of less than 0.2 nm RMS (root mean square roughness measure). In another example, the surface of the capping layer 308 can have a roughness of 0.08 nm RMS with a characteristic surface roughness length between 1/100 nm and 1/1 μm. The capping layer 308 can be formed in a variety of ways. For example, the capping layer 308 can be formed directly on the multilayer stack 306 with magnetron sputtering, ion sputtering systems, ion beam deposition, electron beam evaporation, radio frequency (RF) sputtering, atomic layer deposition (ALD), pulsed laser deposition, cathode arc deposition, physical vapor deposition, or a combination thereof. The capping layer 308 can have the physical characteristics of being formed by the magnetron sputtering technique including precise thickness, low roughness, and clean interfaces between the layers. One of the causes of reflectivity loss is oxidation of the multilayer stack 306 due to the periodic cleaning process. To prevent this oxidation the capping layer 308 can be formed directly on the top of the multilayer stack 306 before the absorber layer 310 is formed. Because most materials are opaque to the extreme ultraviolet light 112, the general contamination level in the extreme ultraviolet system must be minimized. Thus, the reflective mask 106 must be cleaned with greater frequency than with other lithographic systems. In order to remove the small particles and other contaminants commonly found on the reflective mask 106 during use, the cleaning procedure needs to be aggressive. However, the harsh cleaning procedure, such as the Megasonic process, can causes pitting and degradation of the capping layer 308, which can lead to reflectivity loss and oxidation of the multilayer stack 306. The capping layer 308 can be formed from a variety of materials having a hardness sufficient to resist erosion during cleaning. For example, ruthenium can be used as a capping layer material because it is a good etch stop and is relatively inert under the operating conditions. However, it is understood that other materials can be used to form the capping layer 308. The capping layer 308 can have a thickness of between 2 nm to 3 nm. In another example, a typically capping layer thickness can be 2.5 nm for ruthenium. It has been discovered that forming the capping layer 308 with niobium carbide increases the reliability of the extreme ultraviolet reflective element 302 by protecting the multilayer stack 306. The hardness of the niobium carbide protects the multilayer stack 306 and increase operating life by reducing erosion and oxidation of the multilayer stack 306. It has been discovered that forming the capping layer 308 with an additional layer of niobium carbide increases the reliability of the extreme ultraviolet reflective element 302 by protecting the multilayer stack 306. The hardness of the niobium carbide protects the multilayer stack 306 and increase operating life by reducing erosion and oxidation of the multilayer stack 306. After cleaning, the capping layer 308 can have the physical characteristics of being exposed to a cleaning process. The capping layer 308 can have physical characteristics of erosion marks, reduced thickness, uneven wear, solvent residue, residue from the absorber layer 310, or a combination thereof. The capping layer 308 can exhibit additional physical characteristics including chemical residue caused by the interaction of the cleaning solvents and the material of the capping layer 308. The extreme ultraviolet reflective element 302, such as the extreme ultraviolet mirror 205, can be formed with the substrate 304, the multilayer stack 306, and the capping layer 308. The extreme ultraviolet mirror 205 has an optically flat surface and can efficiently and uniformly reflect the extreme ultraviolet light 112. Protecting the multilayer stack 306 with the capping layer 308 prevents degradation of the reflectivity. The capping layer 308 can prevent damage to the multilayer stack 306 during manufacturing and cleaning operations. The capping layer 308 can prevent oxidation to maintain reflectivity and prevent reflectivity loss of the multilayer stack 306 during use and cleaning. For example, the multilayer stack 306 can have a reflectivity of greater than 60%. The multilayer stack 306 formed using physical vapor deposition can have reflectivity between than 63%-68%. Forming the capping layer 308 over the multilayer stack 306 with harder materials can reduce reflectivity by 1%-2%, but the capping layer 308 prevents damage to the multilayer stack 306 and prevents a reduction in the reflectivity of the multilayer stack 306. In some cases, reflectivity up to 70% can be achieved using low roughness layers, clean interfaces between layers, improved layer materials, or a combination thereof. The absorber layer 310 is a layer that can absorb the extreme ultraviolet light 112. The absorber layer 310 can be used to form the pattern on the reflective mask 106 by providing areas that do not reflect the extreme ultraviolet light 112. The absorber layer 310 can be a material having a high absorption coefficient for a particular frequency of the extreme ultraviolet light 112, such as about 13.5 nm. In an illustrative example, the absorber layer 310 can be formed from chromium, tantalum, nitrides, nickel, alloys, or a combination thereof. In another example, the absorber layer can be formed from an alloy of tantalum, boron, and nitrogen in various ratios. The absorber layer 310 can be formed directly on the capping layer 308. The absorber layer 310 can be etched using a photolithography process to form the pattern of the reflective mask 106. The extreme ultraviolet reflective element 302, such as the mask blank 204, can be formed with the substrate 304, the multilayer stack 306, the capping layer 308, and the absorber layer 310. The mask blank 204 has an optically flat surface and can efficiently and uniformly reflect the extreme ultraviolet light 112. The mask pattern 114 can be formed with the absorber layer 310 of the mask blank 204. It has been discovered that reflectivity can be increased by adding an interstitial layer of carbon between the top of the multilayer stack 306 and the capping layer 308. It has been discovered the forming a layer of carbon over the multilayer stack 306 increases reflectivity. It has been discovered that reflectivity can be increased by adding an interstitial layer of carbon or niobium carbide between the top of the multilayer stack 306 and the capping layer 308. It has been discovered the forming a layer of carbon or niobium carbide over the multilayer stack 306 increases reflectivity. It has been discovered that forming the capping layer 308 with niobium or niobium carbide over the multilayer stack 306 increases reflectivity and operational lifetime. Niobium carbide provides a hard protective layer. Forming the capping layer 308 from niobium or niobium carbide can protect the multilayer stack 306 formed from molybdenum and silicon layers. The capping layer 308 formed from niobium or niobium carbide can be used in addition to or an alternative to forming the capping layer 308 from ruthenium. The first reflective layer 312, the second reflective layer 314, the capping layer 308, and the absorber layer 310 can be formed with physical vapor deposition systems. The physical vapor deposition systems can include the first physical vapor deposition system 220 of FIG. 2, the second physical vapor deposition system 222 of FIG. 2, or a combination thereof. Although the extreme ultraviolet reflective element is shown with the substrate 304, the multilayer stack 306, the capping layer 308, and the absorber layer 310, it is understood that other layers may be included. Additional protective layers, passivation layers, or other layers can be included. For example, the extreme ultraviolet reflective element can include a planarization layer below the multilayer stack 306. Referring now to FIG. 4, therein is shown a second example of a multilayer stack 406. The multilayer stack 406 is similar to the multilayer stack 306 of FIG. 3 and uses similar element numbers. The multilayer stack 406 can be part of an extreme ultraviolet reflective element 402, such the mask blank 204 of FIG. 2 or the extreme ultraviolet mirror 205 of FIG. 2. The mask blank 204 and the extreme ultraviolet mirror 205 are structures for reflecting the extreme ultraviolet light 112 of FIG. 1. The extreme ultraviolet mirror 205 can include a substrate 404, the multilayer stack 406, and a capping layer 408. The mask blank 204 can include the substrate 404, the multilayer stack 406, the capping layer 408, and an absorber layer 410. The mask blank 204 can be used to form the reflective mask 106 of FIG. 1 by patterning the absorber layer 410 with the layout of the circuitry required. In the following sections, the term for the mask blank 204 can be used interchangeably with the term of the extreme ultraviolet mirror 205 for simplicity. The mask blank 204 can include the components of the extreme ultraviolet mirror 205 with the absorber layer 410 added in addition to form the mask pattern 114 of FIG. 1. The mask blank 204 is an optically flat structure used for forming the reflective mask 106 having the mask pattern 114. The substrate 404 is a structural element for supporting the extreme ultraviolet reflective element 402. The absorber layer 410 is a layer that can absorb the extreme ultraviolet light 112. The absorber layer 410 can be used to form the pattern on the reflective mask 106 by providing areas that do not reflect the extreme ultraviolet light 112. The capping layer 408 is a protective layer transparent to the extreme ultraviolet light 112. The capping layer 408 can be formed directly on the multilayer stack 406. The capping layer 408 can protect the multilayer stack 406 from contaminants and mechanical damage. The multilayer stack 406 is a structure that is reflective to the extreme ultraviolet light 112. The multilayer stack 406 can include alternating reflective layers of a first reflective layer 412 and a second reflective layer 414 with a barrier layer 418 between each alternating layer. The multilayer stack 406 can optionally include the barrier layer 418 between the first reflective layer 412 and the capping layer 408 and between the second reflective layer 414 and the substrate 404. The barrier layer 418 is a protective layer. The barrier layer 418 is for separating the first reflective layer 412 and the second reflective layer 414 to minimize the chemical interaction between the layers. For example, the barrier layer 418 can be formed from carbon, niobium carbide, or a material with similar properties. The first reflective layer 412 and the second reflective layer 414 can form a reflective pair 416. The multilayer stack 406 can include between 40-60 of the reflective pairs 416 for a total of up to 120 reflective layers. However, it is understood that more or fewer layers can be used as needed. The first reflective layer 412 and the second reflective layer 414 can be formed from a variety of materials. For example, the first reflective layer 412 and the second reflective layer 414 can be formed from silicon and niobium, respectively. The multilayer stack 406 can have a variety of configurations. For example, the first reflective layer 412 can be formed from silicon and the second reflective layer 414 can be formed from niobium or niobium carbide. In another example, the first reflective layer 412 can be formed from niobium or niobium carbide and the second reflective layer 414 can be formed from silicon. Although the multilayer stack 406 is described as having the first reflective layer 412 formed from silicon and the second reflective layer 414 formed from niobium, other configurations are possible. For example, the first reflective layer 412 can be formed from niobium and the second reflective layer 414 can be formed from silicon. However, it is understood that the multilayer stack 406 can be formed from other materials. In another example, the second reflective layer 414 can be formed with niobium carbide. As niobium carbide is has high hardness, the multilayer stack 406 can be fabricated from silicon and molybdenum and covered with a layer of niobium or niobium carbide. This can be used in addition to or an alternative to the capping layer 408 formed from ruthenium. The reflectivity of the mask blank 204 and the extreme ultraviolet mirror 205 is determined by the sharpness of the interface between the layers and the roughness of layers. Changing the material used to from the multilayer stack 406 can improve interface sharpness or layer roughness and increase the multilayer reflectivity. Because most materials absorb light at extreme ultraviolet wavelengths, the optical elements used must be reflective instead of the transmissive as used in other lithography systems. The multilayer stack 406 forms a reflective structure by having alternating thin layers of materials with different optical properties to create a Bragg reflector or mirror. Each of the alternating layers can have dissimilar optical constants for the extreme ultraviolet light 112. The alternating layers cause constructive interference when the period of the thickness of the reflective pair 416 is approximately half the wavelength of the extreme ultraviolet light 112. For example, for the extreme ultraviolet light 112 at a wavelength of 13 nm, the reflective pair 416 can be about 6.5 nm thick. The multilayer stack 406 can be formed in a variety of ways. For example, the first reflective layer 412, the second reflective layer 414, and the barrier layer 418 can be formed with magnetron sputtering, ion sputtering systems, pulsed laser deposition, cathode arc deposition, or a combination thereof. In an illustrative example, the multilayer stack 406 can be formed using a physical vapor deposition technique, such as magnetron sputtering. The first reflective layer 412, the second reflective layer 414, and the barrier layer 418 of the multilayer stack 406 can have the characteristics of being formed by the magnetron sputtering technique including precise thickness, low roughness, and clean interfaces between the layers. The physical dimensions of the layers of the multilayer stack 406 formed using the physical vapor deposition technique can be precisely controlled to increase reflectivity. For example, the first reflective layer 412, such as a layer of silicon, can have a thickness of 3.5 nm. The second reflective layer 414, such as a layer of niobium, can have a thickness of 3.5 nm. The barrier layer 418, such as a layer of carbon, can have a thickness of between 1 and 5 angstroms. However, it is understood that the thickness of the first reflective layer 412 and the second reflective layer 414 can vary based on engineering needs, the wavelength of the extreme ultraviolet light 112, and the optical properties of the layer materials. Protecting the multilayer stack 406 with the capping layer 408 improves reflectivity. The capping layer 408 can prevent damage to the multilayer stack 406 during manufacturing and cleaning operations. The capping layer 408 can be mounted directly on the multilayer stack 406 or directly on the barrier layer 418. For example, the multilayer stack 406 can have a reflectivity of greater than 60%. The multilayer stack 406 formed using physical vapor deposition can have reflectivity between than 63%-68%. Forming the capping layer 408 over the multilayer stack 406 formed with harder materials can improve reflectivity. In some cases, reflectivity up to 70% can be achieved using low roughness layers, clean interfaces between layers, improved layer materials, or a combination thereof. It has been discovered that forming the multilayer stack 406 with the barrier layer 418 formed from carbon or niobium carbide increases reflectivity and increases reliability. The barrier layer 418 can reduce the formation of silicides and form smoother layers. Referring now to FIG. 5, therein is shown a third example of a multilayer stack 506. The multilayer stack 506 is similar to the multilayer stack 306 of FIG. 3 and uses similar element numbers. The multilayer stack 506 can be part of an extreme ultraviolet reflective element 502, such the mask blank 204 of FIG. 2 or the extreme ultraviolet mirror 205 of FIG. 2. The mask blank 204 and the extreme ultraviolet mirror 205 are structures for reflecting the extreme ultraviolet light 112 of FIG. 1. The multilayer stack 506 can include a substrate 504, the multilayer stack 506, a capping layer 508, and an absorber layer 510. The multilayer stack 506 can include a first reflective layer 512 and a second reflective layer 514 forming a reflective pair 516. Although the multilayer stack 506 can have the first reflective layer 512 formed from silicon and the second reflective layer 514 formed from niobium, other configurations are possible. For example, the first reflective layer 512 can be formed from niobium or niobium carbide and the second reflective layer 514 can be formed from silicon. The multilayer stack 506 is a structure that is reflective to the extreme ultraviolet light 112. The multilayer stack 506 can include alternating reflective layers of the first reflective layer 512 and the second reflective layer 514 with a boundary layer 520 between each alternating layer. The multilayer stack 506 can optionally include the boundary layer 520 between the first reflective layer 512 and the capping layer 508 and between the second reflective layer 514 and the substrate 504. The boundary layer 520 is a layer between the first reflective layer 512 and the second reflective layer 514. The boundary layer 520 is the result of a chemical reaction between the material of the first reflective layer 512 and the second reflective layer 514. For example, the boundary layer 520 can be a silicide. The silicide can be formed from silicon and a metal such as niobium. The multilayer stack 506 can include a barrier layer 518. The barrier layer 518 is a protective layer. For example, the barrier layer 518 can be formed from carbon having a thickness of between 1 and 5 angstroms inclusive. The barrier layer 518 can be formed between the multilayer stack 506 and the capping layer 508. Another of the barrier layer 518 can be formed between the multilayer stack 506 and the substrate 504. The barrier layer 518 can be formed between the first reflective layer 512 and the second reflective layer 514 to modify the boundary layer 520. The barrier layer 518 can reduce the thickness of the boundary layer 520 by inhibiting the formation of the silicide. Referring now to FIG. 6, therein is shown the structure of FIG. 3 in a provisioning phase of manufacturing. The provisioning phase can include a method to provide the substrate 304. For example, the provisioning phase can provide the substrate 304 formed from silicon. Referring now to FIG. 7, therein is shown the structure of FIG. 6 in a layering phase of manufacturing. The layering phase can include a method to form the multilayer stack 306 directly on the substrate 304. The multilayer stack 306 can form alternating layers of the first reflective layer 312 and the second reflective layer 314 on the substrate 304. For example, the multilayer stack 306 can have between 40 and 80 alternating layers of niobium and silicon. Referring now to FIG. 8, therein is shown the structure of FIG. 7 in a protective phase of manufacturing. The protective phase can include a method to form the capping layer 308 on the multilayer stack 306. The multilayer stack 306 can include alternating layers of the first reflective layer 312 and the second reflective layer 314 on the substrate 304. For example, the protective phase can use magnetron sputtering to deposit a metallic material on the multilayer stack 306. Referring now to FIG. 9, therein is shown the structure of FIG. 8 in a pre-patterning phase of manufacturing. The pre-patterning phase can include a method to form the absorber layer 310 directly on the capping layer 308. For example, the pre-patterning phase can form the absorber layer 310 on the capping layer 308. The capping layer 308 is over the multilayer stack 306. The multilayer stack 306 can include alternating layers of the first reflective layer 312 and the second reflective layer 314 on the substrate 304. Referring now to FIG. 10, therein is shown the structure of FIG. 4 in a provisioning phase of manufacturing. The provisioning phase can include a method to provide the substrate 404. For example, the provisioning phase can provide the substrate 404 formed from an ultra-low thermal expansion material. In another example, the substrate 404 can be formed from silicon, glass, or a combination thereof. Referring now to FIG. 11, therein is shown the structure of FIG. 10 in a layering phase of manufacturing. The layering phase can include a method to form the second reflective layer 414 on the substrate 404. Referring now to FIG. 12, therein is shown the structure of FIG. 11 in a depositing phase of manufacturing. The depositing phase can include a method to form the first reflective layer 412 and the barrier layer 418 on the second reflective layer 414. The layering phase and the depositing phase can be repeated as many times as needed to finish forming the reflective pairs 416 of FIG. 4 of the multilayer stack 406 of FIG. 4 on the substrate 404. For example, the multilayer stack 406 can have between 40-60 alternating layers of silicon and niobium with a carbon layer between them. The multilayer stack 406 can be formed on the substrate 404. Referring now to FIG. 13, therein is shown the structure of FIG. 12 in a finishing phase of manufacturing. The finishing phase can include a method to form the capping layer 408 on the multilayer stack 406 and the absorber layer 410 directly on the capping layer 408. The multilayer stack 406 can include the first reflective layer 412 and the second reflective layer 414 with the barrier layer 418 between the layers. Referring now to FIG. 14, therein is shown a flow chart of a method 1400 of manufacture of an extreme ultraviolet reflective element in a further embodiment of the present invention. The method 1400 includes: providing a substrate in a block 1402; forming a multilayer stack on the substrate, the multilayer stack includes a plurality of reflective layer pairs having a first reflective layer formed from silicon and a second reflective layer formed from niobium or niobium carbide for forming a Bragg reflector in a block 1404; and forming a capping layer on and over the multilayer stack for protecting the multilayer stack by reducing oxidation and mechanical erosion in a block 1406. Thus, it has been discovered that the extreme ultraviolet reflective element production system of the embodiments of the present invention furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects for an extreme ultraviolet reflective element production system. The resulting method, process, apparatus, device, product, and/or system is straightforward, cost-effective, uncomplicated, highly versatile and effective, can be surprisingly and unobviously implemented by adapting known technologies, and are thus readily suited for efficiently and economically manufacturing extreme ultraviolet reflective element production systems fully compatible with conventional manufacturing methods or processes and technologies. Another important aspect of the embodiments of the present invention is that they valuably supports and services the historical trend of reducing costs, simplifying manufacturing, and increasing performance. These and other valuable aspects of the embodiments of the present invention consequently further the state of the technology to at least the next level. While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the included claims. All matters hithertofore set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense. |
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052689514 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The scanning method in accordance with this invention avoids distortion errors by means of the steps as follows: 1. A collimating first mirror has the capability of altering the source to mirror location and/or grazing angle of incidence. PA0 2. A flat second mirror is capable of a scanning motion by translation with an optional accompanying change in the grazing angle of incidence. This invention employs a scanning method which greatly reduces or eliminates mirror scanning errors while presenting the possibility of producing a constant distortion (zero to some value determined by mask/wafer overlay distortion correction), a minimum of flux change throughout vertical scanning, and a nearly constant x-ray beam profile during scanning. The technique is independent of collimating mirror surface form. Alternative Mirror Scanning Method The alternative scanning method requires a second, flat, grazing incidence mirror M2 which is placed after the first, collimating, mirror M1. FIGS. 1A-1C illustrate the basic principle involved in maintaining collimation and performing vertical scanning by shifting the flat collimating mirror M1 parallel to the exposure field or along the input beam to the flat second mirror M2 (to minimize the length of the second mirror M2). The x-ray radiation beam 10 from source S is reflected over a range shown by beams 12 and 14 from the first mirror M1 and reflected by second mirror M2 as beams 16 and 18 which are directed at exposure field EF. Combinations of both shifts are not shown but are obvious. This method has existing analogs in conventional optics. Less obvious is the capability of this two mirror system M1 and M2 to allow some adjustment of the Xphase and Zphass errors at the mask during exposure scanning, independently, allowing independent control of (gap dependent) printing distortion in the vertical and horizontal directions. This capability is an important feature of this invention. Xphase adjustments may be made by modifications of the location of collimating mirror M1 (along and/or perpendicular to the beam path), mirror grazing angle, or combinations thereof. Changes in Zphase usually accompany the changes in Xphase produced, most noticeably in the mean value of the Xphase at the top and bottom of the exposure field while changes in Zphase in the horizontal direction are much smaller, often negligible. FIG. 1B shows the second mirror M2 of FIG. 1A making a linear vertical shift vertical to the path of x-ray beam 19 with mirror M2 moving to higher position M2' along the direction of scan 21 with x-ray beam 19 reflecting twice, at different times, from the collimating mirror M2, M2' as top and bottom beams 20 and 22 corresponding to the respective positions of mirror M2, M2'. FIG. 1C shows the second mirror M2 of FIG. 1A making a linear shift parallel to the path of x-ray beam 19 with mirror M2" moving along the direction of scan 23 to position M2'" with x-ray beam 19 reflecting from the collimating mirror M2",M2'" as top and bottom beams 20' and 22' corresponding to the respective positions of mirror M2", M2'". FIGS. 2A and 2B show the Zphase error introduced by altering the grazing angle of the collimating first mirror M1 with Zphase correction by the second flat mirror M2. By altering the grazing angle of the flat mirror M1 and shifting the mirror M1 as shown in FIGS. 2A and 2B, the mean Zphase of the rays 28, 30 in FIG. 2A and 30' in FIG. 2B arriving at the mask may be altered to a desired value, usually zero. In FIG. 2B, exposure scanning is accomplished by shifting the mirror M2 as shown in FIGS. 1A-1C. By this method the Zphase errors introduced by modifying the first mirror M1 are reduced to only the small horizontal component. FIG. 3 illustrates altering the grazing angle of the flat mirror M2 between positions M2' and M2" while it is scanned so a deliberate Zphase error may be introduced at the mask. This error is introduced solely by the second flat mirror M2. The distortion correction capability of this system is primarily a function of the gap and the specific design of the first, collimating, mirror. Typically, increasing the source to mirror distance for the first mirror allows larger phase changes to be made with position modification before adverse image effects are noted, such as nonlinear Xphase within the exposure field, or unacceptably large Zphase errors in the horizontal direction for a given Xphase error. Increasing the source to mirror distance also reduces the flux gathered from the source per unit length of horizontal exposure field, reducing throughput. These effects are engineering trade-offs, and performance of the scanning operations is not degraded by the scanning second mirror. The introduction of a second reflecting surface into the beam path reduces the flux available for exposure, requiring longer exposure times, and yielding lower system throughput. While this invention has been described in terms of the above embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. |
claims | 1. A charged particle lithography system for transferring a pattern onto the surface of a target, comprising:a beam generator for generating a plurality of charged particle beamlets, the plurality of beamlets defining a column;a beam stop array having a surface for blocking beamlets from reaching the target surface and an array of apertures in the surface for allowing the beamlets to reach the target surface; anda modulation device for modulating the beamlets to prevent one or more of the beamlets from reaching the target surface or allow one or more of the beamlets to reach the target surface, by deflecting or not deflecting the beamlets so that the beamlets are blocked or not blocked by the beam stop array, the modulation device comprising:a plurality of apertures arranged in arrays for letting the beamlets pass through the modulation device;a plurality of modulators associated with the plurality of apertures, each modulator being provided with electrodes extending on opposing sides of an associated aperture for generating an electric field across the aperture; anda plurality of light sensitive elements arranged in arrays, for receiving modulated light beams and converting the light beams into electric signals for actuating the modulators;wherein a surface area of the modulation device comprises an elongated beam area comprising an array of apertures and associated modulators, and a power interface area for accommodating a power arrangement for suitably powering elements within the modulation device, the power interface area being located alongside a long side of the elongated beam area and extending in a direction substantially parallel thereto. 2. The system according to claim 1, wherein the power interface area extends along the entire length of the long side of the elongated beam area. 3. The system according to claim 1, wherein the power interface area comprises a first portion positioned alongside a first long side of the elongated beam area and extending in a direction substantially parallel thereto, and a second portion alongside a second long side of the elongated beam area and extending in a direction substantially parallel thereto, the second long side being opposite to the first long side. 4. The system according to claim 1, wherein the surface area of the modulation device further comprises an optical interface area in which the light sensitive elements are placed, and the power arrangement is arranged for suitably powering the light sensitive elements. 5. The system according to claim 4, wherein the optical interface area has an elongated shape, and wherein the optical interface area is located between the beam area and the power interface area. 6. The system according to claim 4, further comprising a plurality of optical fibers for guiding the modulated light beams towards the light sensitive elements, wherein the optical interface area being reserved for establishing an optical interface between the plurality of optical fibers and the light sensitive elements. 7. The system according to claim 1, wherein the power arrangement extends in a direction substantially perpendicular to, and away from the modulation device. 8. The system according to claim 7, further comprising a power supply, the power supply being located at a short side of the power interface area, the power arrangement being connected to the power supply. 9. The system according to claim 8, wherein a projection of the power arrangement in a direction substantially perpendicular to the surface of the modulation device falls entirely within the power interface area. 10. The system according to claim 1, wherein the power arrangement comprises a ribbon cable. 11. The system according to claim 1, wherein the power arrangement comprises a slab. 12. The system according to claim 11, wherein the slab has a height that is equal to or greater than the long side of the beam area. 13. The system according to claim 1, wherein the long side of the beam area extends over substantially an entire width of the beamlet column. 14. The system according to claim 1, further comprising a wafer positioning system arranged for moving the target in a predetermined direction relative to the modulation device, and wherein the orientation of the long side of the beam area is substantially transverse to a relative direction of movement of the wafer positioning system. 15. The system according to claim 1, further comprising a wafer positioning system arranged for moving the target in a predetermined direction relative to the modulation device, and wherein the long side of the beam area has a skewed orientation with respect to the predetermined direction of movement between the wafer positioning system and the modulation device. 16. The system according to claim 15, wherein the slit has an orientation at an angle of less than 5 degrees with respect to a direction perpendicular to the predetermined direction of movement between the wafer positioning system and the modulation device. 17. The system according to claim 1, wherein the modulated light signals received by the light sensitive elements are multiplexed to provide information for controlling more than one modulator, and wherein each light sensitive element is communicatively coupled with a demultiplexer for demultiplexing the received signal for control of a plurality of modulators. 18. The system according to claim 1, wherein the light sensitive elements are arranged to provide a signal for controlling a plurality of the modulators, and wherein the modulation device further includes a plurality of memory elements, each memory element being arranged for storing a signal for control of one of the modulators. 19. The system according to claim 1, wherein the surface area of the modulation device is subdivided into a plurality of alternating beam areas and non-beam areas, the modulators being located in the beam areas, and the light sensitive elements being located in the non-beam areas;wherein the light sensitive elements in the non-beam areas are communicatively coupled to the modulators in an adjacent beam area. 20. The system according to claim 19, wherein the modulators in a beam area are controllable by light sensitive elements arranged in non-beam areas located on more than one side of the beam area. 21. The system according to claim 19, wherein the modulators in the beam areas are more densely packed together than the light sensitive elements in the non-beam areas. 22. The system according to claim 19, wherein the beamlets are arranged in groups and the modulators are arranged in groups, each group of modulators for deflecting or not deflecting one of the groups of beamlets, and wherein each group of modulators is located in a single one of the beam areas of the modulation device. 23. The system according to claim 22, wherein each group of modulators is arranged in a rectangular array in one of the beam areas, and is controlled by a single light sensitive element in an adjacent non-beam area. 24. The system according to claim 22, wherein each group of modulators is arranged in a radial arrangement around a centrally located axis of the corresponding groups of beamlets. 25. The system according to claim 19, further including a shielding structure for shielding electric fields generated within the non-beam areas. 26. The system according to claim 25, wherein the shielding structure, or a projection thereof in a direction perpendicular to the surface of the modulation device, surrounds a beam area. 27. The system according to claim 25, wherein the shielding structure comprises side walls forming an open-ended box-like structure. 28. The system according to claim 1, wherein the modulators are part of a CMOS device. 29. The system according to claim 28, wherein electrodes of the modulators are formed by conductive layers of the CMOS device. 30. A modulation device for use in a charged particle lithography system for patterning a plurality of charged particle beamlets in accordance with a pattern, the beamlets defining a column, the modulation device serving to modulate the beamlets to prevent one or more of the beamlets from reaching the target surface or allow one or more of the beamlets to reach the target surface, by deflecting or not deflecting the beamlets, the modulation device comprising:a plurality of apertures arranged in arrays for letting the beamlets pass through the modulation device and a plurality of modulators associated with the plurality of apertures, each modulator being provided with electrodes extending on opposing sides of an associated aperture for generating an electric field across the aperture; anda plurality of light sensitive elements arranged in arrays, for receiving modulated light beams and converting the light beams into electric signals for actuating the modulators;wherein a surface area of the modulation device comprises an elongated beam area comprising an array of apertures and associated modulators, and a power interface area for accommodating a power arrangement for suitably powering elements within the modulation device, the power interface area being located alongside a long side of the elongated beam area and extending in a direction substantially parallel thereto. 31. A method of transferring a pattern on to a target surface using a charged particle lithography system according to claim 1, the method comprising the steps of:generating a plurality of beamlets defining a column;modulating the beamlets by deflecting or not deflecting the beamlets, for the purpose of completely or partly preventing the beamlets from reaching the target surface, under control of a control unit;transferring the passed beamlets to the target surface;wherein the modulating further comprises the steps of:optically transmitting data as modulated light beams carrying the pattern, to light sensitive elements;converting the modulated light beams received by the light sensitive elements into electric signals;actuating one or more modulators, on the basis of the electrical signals, to selectively deflect the beamlets for blocking or not blocking the beamlets from reaching the target surface, by means of deflection in an electric field. |
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