patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
description | The invention pertains to a method for obtaining images from slices of a specimen, the method comprising: repeatedly obtaining an image of the surface layer of the specimen, and removing the surface layer of the specimen, thereby bringing the next slice to the surface. Such a method of repeatedly removing a surface layer (also known as slicing) and obtaining an image of a specimen is known from e.g. particle-optical apparatus having both an ion-optical column and an electron-optical column, such as e.g. the DualBeam® instruments commercially available from FEI Company. It is remarked that ‘an image’ in the context of this invention is to be interpreted as an image displayed on a display unit as well as a representation thereof in e.g. a computer memory. Such a method is used in industry and laboratories, e.g. to analyse and inspect biological specimens and polymeric specimens and e.g. to form three-dimensional (3D) reconstructions of structures in biological tissues and polymers. The instrument used for performing the known method comprises an electron-optical column to obtain an image of a specimen by scanning a focused beam of energetic electrons, typically with an energy between 0.1 to 30 keV, over the specimen. The working of such a column is known from a Scanning Electron Microscope (SEM). Where the beam of electrons impinges on the specimen, secondary radiation, such as secondary electrons, backscattered electron, X-rays and light, may be emitted in response to the bombardment with the impinging electrons. By detecting the amount of e.g. secondary electrons emitted with e.g. a Secondary Electron Detector (SED), (place dependent) information of the surface of the specimen can be obtained. This information can be displayed as an image on a display, or the image can be stored for future retrieval or processing. After thus obtaining an image of the surface of the specimen, a surface layer may be removed using the ion column. The working of such a column is known from Focused Ion Beam (FIB) instruments. The column emits a focused beam of energetic ions, such as a beam of Ga+ ions with an energy of e.g. 40 keV. Where the beam of ions impinges on the specimen, material is removed. This removal is greatly enhanced by admitting certain gasses in the vicinity where the beam impinges on the specimen. This ion beam can be scanned over the surface, whereby the dwell time (together with the ion beam properties such as current density and energy) determines how much of the surface layer is removed. As a result a slice of material is removed. After the removal of the surface layer a fresh surface layer is exposed, and with the electron beam an image can be obtained of the thus exposed surface layer. By repeatedly obtaining an image of a surface layer and removing the surface layer from the specimen (removing a slice from the surface layer), a 3D reconstruction of the specimen can be made. Alternatively, a region of interest in the interior of the specimen can be brought to the surface to be examined by techniques that e.g. offer surface information. A problem when observing certain materials, such as polymers and biological tissues, is that the contrast of the specimen may be too poor to easily differentiate features of the specimen. As known to the person skilled in the art, in order to improve contrast, specimens may be stained to preferentially highlight some parts of the specimen over others. For stains to be effective, they have to preferentially bind to some parts of the specimen, thereby differentiating between different parts of the specimen. In electron microscopy, heavy metal salts may be used as a staining agent. Such heavy metal salts are commonly derived from gold, uranium, ruthenium, osmium, or tungsten. Heavy ions are used since they will readily interact with the electron beam and produce phase contrast, absorption contrast and/or cause backscattered electrons. Some of these heavy metal salts adhere to specific substances of the specimen. An example of that is OsO4 (osmiumtetroxide), which form a specific chemical reaction with the —C═C— double bonds of unsaturated fatty acids. Other staining agents that may be used are e.g. compounds of a heavy metal with e.g. an appropriate biologically active group, such as an antibody. Such staining agents are also known as labels. An example is colloidal gold particles absorbed to antibodies. Other examples of this group of staining agents are the Nanogold® particles, produced by Nanoprobes Inc., USA, which may be used to label any molecule with a suitable reactive group such as oligonucleotides, lipids, peptides, proteins, and enzyme inhibitors. To stain a specimen the specimen is exposed to the staining agent. The exposure can take the form of temporarily immersing the specimen in a liquid, such as a 1% solution of OsO4. Further steps in the staining process may include washing the specimen with water, alcohol, etc. Such staining processes are e.g. described by “Dermatan sulphate-rich proteoglycan associates with rat-tendon collagen at the d band in the gap region”, John E. Scott and Constance R. Orford, Biochem. J. (1981) 197, pages 213-216, more specific in the section ‘materials and methods’. The exposure can also take the form of exposing the specimen to a gas or vapour of the staining agent. This is e.g. described in “Observation on backscattered electron image (BEI) of a scanning electron microscope (SEM) in semi-thin sections prepared for light microscopy”, Y. Nagata et al., Tokai J. Exp. Clin. Med., 1983 May 8(2), pages 167-174. For a good contrast the specimen must be sufficiently stained. There is however an optimum in the staining dose: too much staining results in a decrease of the contrast as too much of the specimen becomes stained, whereby the (stained) structures of interest do not stand out to the background anymore. An adequate dose of staining must thus be found. A problem with certain combinations of staining agents and the materials to be stained is that the diffusion rate of the staining agent in the specimen is very low. Many of the heavy metal staining agents show a low diffusion rate in biological tissues, while in polymers the diffusion rate is even lower. As a result, when e.g. thick polymeric specimens are stained such that the surface is stained to an adequate level, the interior of the specimen is insufficiently stained to obtain a good contrast. If however the staining is such, that the interior is sufficiently stained, the surface is so heavily stained as to be unfit for obtaining a good image. There is therefore a need to stain thick specimens in such a way, that the whole specimen is stained to an adequate level. The invention intends to provide a method for staining thick specimens in such a way, that the whole specimen can be image with an adequate staining level. To that end the method according to the invention is characterized in that, after at least one of the removals of a surface layer the specimen is exposed to a staining agent. By re-staining the surface of the specimen every time that a surface layer is stripped, the surface can be stained to the optimum level as well as a constant level every time. It is remarked that it might be that re-staining is not necessary after every individual removal of a surface layer, but only after a predetermined number of layers. This may lead to a reduced processing time and thus shorter cycle time In an embodiment of the method according to the invention the images are obtained with a particle-optical apparatus. Although the method can be used with different kinds of microscopy, such as light microscopy and fluorescent microscopy, it is especially attractive for use with electron and ion microscopy. It is remarked that, when after each removal of a surface layer only a very thin layer of e.g. 20 nm is stained (e.g. by exposing the specimen for a short time to the staining agent), as an additional advantage the resolution of a Scanning Electron Microscope (SEM) image improves. This can be explained as follows: Stained specimens in a SEM are often observed by detecting backscattered electrons, as the heavy metals of the staining agent cause much backscattering. Such backscattered electrons can be generated deep within the specimen (e.g. 0.5 μm below the surface) and still be detectable. This implies that, when heavy metal atoms are present deep within the specimen, they are still detected. This results in an image that not only shows information of stained structures at the surface, but also information of stained subsurface structures. By staining only a thin layer of e.g. 20 nm only stained structures in this thin layer contribute to the image. The light atoms of the unstained specimen cause only very little backscattered electrons and will thus not substantially contribute to the image. The result is thus an image showing only stained structures in the uppermost layer of the specimen, and thus an improved resolution of the image. The same effect also improves the resolution of e.g. X-rays detected from the specimen, said X-rays being the result of the electron beam impinging on the heavy metal atoms in the stained specimen. In another embodiment of the method according to the invention the surface layer is removed using a particle beam. Removal of surface layers with an ion beam or an electron beam, assisted with etching gasses, is a well-known technique enabling the removal of layers of e.g. several tens of nanometers, although even thicker layers may be removed. A common thickness of the removed layer is approximately 30 to 60 nm. In yet another embodiment of the method according to the invention the staining is achieved by exposing the specimen to a gas or vapour. The method is best executed by exposing the specimen to a gas or vapour, so that no further drying of the stripped and re-stained surface is needed. Not only does this offer better results as the specimen does not deform to the repeated wetting and drying, but it also saves time, as staining by wetting followed by rinsing takes typically tens of minutes or more, while exposure to a gas or vapour yields good results in e.g. ten seconds. Another advantage is that it is possible to stain only a very thin layer of the specimen, which results—as mentioned before—in an improved resolution. In still another embodiment of the method according to the invention the staining takes place in a vacuum chamber, or at least in a chamber with a low pressure. Staining in a vacuum enables the staining of surfaces that may not be altered by reaction with atmospheric gasses, e.g. a chemical reaction with oxygen or e.g. hydration due to atmospheric water vapour. In other words: the surface of the specimen is kept fresh after the removal of the surface layer. In a further embodiment of the method according to the invention the specimen is stained in a vacuum chamber which is part of a particle-optical apparatus. By exposing the specimen to the staining agent in the vacuum chamber of the particle apparatus, the specimen need not be removed from the apparatus and its position with respect to the columns can be retained. This results in a much reduced processing time, as no time is lost to search for certain features. Also, as the specimen need not be re-positioned in the vacuum chamber (which commonly takes place by venting the vacuum chamber and then mounting the specimen, followed by the evacuation of the chamber) time is saved. In yet a further embodiment of the method according to the invention the specimen is exposed to more than one staining agent. A problem known in electron microscopy is that one kind of heavy metal staining agent is not well discernable from another kind of heavy metal marker. Both kinds of heavy metal markers will show the same behavior: the strong interaction with the electron beam. It is remarked that it can be envisaged to detect the characteristic X-ray radiation emitted from different heavy metals, but the efficiency of this is much lower than the efficiency of detecting e.g. backscattered electrons, resulting in a lower signal-to-noise ratio when detecting X-rays for a given exposure time to the electron beam. Therefore differential staining (using backscattered electrons) is not well possible in electron microscopy. By acquiring an image when the specimen is stained with a first staining agent and then acquiring an image of the specimen after it has been stained with a different staining agent, the effect of each staining agent individually can be observed. The staining agent used for one slice need not be used for another slice. It is conceivable that a first slice is observed using one staining agent, adhering to a certain type of tissue or material, after which a further slice is observed that is stained with another staining agent, adhering with another type of tissue or material. Therefore the method according to the invention also enables differential staining of specimens, using e.g. backscattered electrons. In still a further embodiment of the method according to the invention images of the specimen are obtained when the specimen is stained with one staining agent as well as with more than one staining agent, thereby enabling differential staining. By comparing the image obtained when the specimen is stained with one staining agent and the image obtained when the same slice of the specimen is additionally stained with another staining agent, differential staining can be observed. It is remarked that, by subtracting the image obtained while the specimen is stained by one staining agent from the image obtained while the specimen is additionally stained with another staining agent, thereby eliminating or at least greatly reducing the effect of the first staining agent, the effect of the second staining agent alone can be observed. In a yet still further embodiment of the method according to the invention an image of the specimen is obtained when the specimen is stained with one staining agent, after which the surface layer is removed, the specimen is exposed to another staining agent and another image is then obtained, thereby obtaining images of the specimen stained with one staining agent at a time. In another embodiment of the method according to the invention an image of the surface layer of the specimen is obtained in unstained condition as well as in stained condition, and the images thus obtained are combined in such a manner that topographical and topological information of the unstained specimen are eliminated, or at least greatly reduced, in the stained image. In yet another embodiment of the method according to the invention the staining agent comprises a molecule with a heavy metal and an organic group. In another aspect of the invention a gas injection system is equipped for administering a staining gas or vapour into the vacuum chamber of a particle-optical apparatus. FIG. 1 schematically depicts the method according to the invention. The method starts, after which in step 101 the specimen is stained. An image of the surface of the specimen is acquired and stored in step 102. As long as more slices of the surface must be removed (determined in step 103) a surface layer is removed in step 104. The decision in step 103 that more slices must be removed can e.g. be based on the structure of interest now being on the surface and visible in the image acquired in step 102, or it can e.g. be based on a predetermined number of slices, equivalent to a certain predetermined thickness of the specimen to be viewed. After the removal of a surface layer in step 104, the specimen is re-stained and a new image is acquired by repeating steps 101, 102 and 103 as long as needed. If no further surface layers need be removed (depending on the decision in step 103), e.g. a 3D image of the specimen may be constructed (step 105). FIG. 2 schematically depicts the method according to the invention, in which differential staining is applied. As in the method described in FIG. 1, the method starts after which in step 201 the specimen is stained with the first staining agent and acquiring a first image of this slice in step 202. Hereafter in step 203 the specimen is stained with another staining agent, the second staining agent. In step 204 a second image of this slice of the thus doubly stained specimen is acquired. By performing in step 205 suitable image processing, e.g. subtracting the information of the first image of this slice, acquired in step 202, from the second image of this slice acquired in step 204, an image of this slice can be acquired that shows only the information due to the staining with the second staining agent. This greatly simplifies the interpretation of the effect of differential staining. In step 206, equivalent to step 103 in FIG. 1, a decision is made whether it is necessary to remove a surface layer. If so, the surface layer is stripped in step 207 and the steps 201-206 are repeated, until the result of decision 206 is that no further surface layers need be removed. At the end, in step 207, a 3D image may be constructed of the specimen with any of the stains used, or any combination thereof. It is remarked that, instead of staining with two different staining agents, this method can also be used to stain with more than two staining agents, resulting in even more information obtained from the specimen. It is also remarked that this method, in which images are subtracted from each other, can also be used to obtain an image of the specimen of one staining agent only, while subtracting topological or other information of the unstained specimen. To achieve this step 201 should be skipped. FIG. 3 schematically depicts an apparatus equipped to perform the method according to the invention. FIG. 3 shows a particle-optical apparatus equipped with an ion-optical column 10 producing a focused beam of ions 11, and an electron-optical column 20 producing a focused beam of electrons 21. Both beams 11, 21 can be scanned independently of each other over the specimen 1, said specimen mounted on a specimen stage 2. Also, each of the beams 11, 21 can be blanked at any time so that it is possible to work with one of the beams 11, 21 at a time. When the specimen 1 is scanned with the electron beam 21 produced by electron optical column 20 in a fashion known from scanning electron microscopy, (place dependent) secondary radiation, is detected, such as secondary electrons detected by a secondary electron detector 30 (SED) of the well-known Everhart-Thomley type. The signal of this detector 30 is used by a Central Control & Processing Unit (CCPU) 40 and an image may be displayed on a viewing screen 50. Also other signals, such as X-rays detected by an X-ray detector 31, or backscattered electrons detected by a Backscattered electron Detector (BSD) 32, may be detected and subsequently processed by CCPU 40. Especially the information detected by the BSD 32 is important, as heavy metal markers cause a large amount of backscattered electrons, and thus a large BSD signal. The CCPU 40 also controls, among others, the ion column 10, electron column 20, the specimen stage 2, a gas injector 4 and staining unit 5. After obtaining the image of this slice of the specimen, the beam of ions 11 is scanned over the specimen 1, thereby removing the surface layer of the specimen. The removal rate is greatly enhanced by the admission of certain gasses in the vicinity where the ion beam impinges on the specimen. Such gasses can be admitted into the vacuum chamber 3 with the gas injector system 4. After removing a surface layer and thus exposing a fresh slice of the specimen, the specimen is stained by admitting a staining agent such as OsO4 gas to the specimen. The amount of staining is controlled by the partial vapour pressure as well as the time the specimen is exposed to the vapour. The staining agent is admitted into the vacuum chamber 3 by staining unit 5. The staining is completed by stopping the supply of staining gas or vapour, the remaining staining agent being removed from the vacuum chamber 3 by vacuum pumps (not shown), after which a further image can be obtained in the before mentioned manner. It is remarked that removal of surface material can also be achieved by an electron beam being scanned over the specimen while certain gasses are admitted. It is further remarked that to remove material the ion beam need not be focused. Also defocused ion beams and e.g. ion bombardment due to gas discharges are known to remove material. However, experimental results show that using a focused ion beam is the preferred method, as scanning the specimen with a focused beam results in a homogeneous removal of material, while otherwise the chance of preferential etching/milling is enhanced, resulting in a non-homogeneous removal of material from the specimen. It is also remarked that the method according to the invention can e.g. be used to automatically reconstruct a 3D image of the specimen, without human intervention or observation of intermediate images. |
|
050892134 | summary | BACKGROUND OF THE INVENTION The present invention relates to a nuclear fuel identification code reader and a fuel assembly, and more particularly to a nuclear fuel identification reader and a fuel assembly which are suitable for identification of a fuel assembly in a fuel storage pool. In the past, the identification of a nuclear fuel identification number of a fuel assembly loaded into a fuel storage pool has been effected by an operator by watching on a television monitor a video image taken by a marine TV camera. This is reported in Nuclear Technology, Vol. 72, March 1986, pp. 321-327. In the prior art method in which the video image of the TV camera is monitored through the TV monitor, there are some cases where it is not possible to identify the fuel identification number marked on the fuel assembly if clad (soft clad primarily consisting of Fe.sub.2 O.sub.3) is deposited on the fuel assembly. A solution to the above problem is disclosed in JP-A-57-53688, particularly FIG. 4 thereof. Eddy current sensors are inserted into recesses formed on a top surface of a handle of the fuel assembly to detect the fuel identification number. JP-A-60-207095 and JP-A-57-110994 disclose techniques to identify the fuel assembly by detecting a mark such as a groove formed at a top of the fuel assembly by ultrasonic wave. SUMMARY OF THE INVENTION It is an object of the present invention to provide a nuclear fuel identification code reader capable of identifying a nuclear fuel identification code marked on a fuel assembly in a short time and with a high accuracy. It is another object of the present invention to provide a nuclear fuel identification code reader capable of checking loss of a fuel assembly stored in a fuel storage pool. It is other object of the present invention to provide a nuclear fuel identification code reader capable of checking the presence of nuclear fuel in a stored fuel assembly. The first characteristic feature of the present invention resides in the provision of an optical sensor and an ultrasonic wave sensor for detecting the nuclear fuel identification code, means for identify the nuclear fuel identification code based on the information derived from the optical sensor, and means for identifying the nuclear fuel identification code based on the information derived from the ultrasonic wave sensor. In this arrangement, the nuclear fuel identification code can be identified in a short time. The second characteristic feature of the present invention resides in the provision of means for comparing a current recognition result for the nuclear fuel identification code with a past recognition result therefor. Thus, any loss of the stored fuel assembly can be checked. The third characteristic feature of the present invention resides in the provision of means for photographing a Chelencoff light generated in the fuel assembly and means for image processing an image signal of the Chelencoff light photographed by said photographing means. Thus, the presence of the nuclear fuel in the stored fuel assembly can be readily checked. |
claims | 1. A charged particle beam apparatus comprising:a charged particle beam source comprising:an emitter having an emitter needle with an emitter tip; anda supporting member configured to support the emitter;an emitter location measuring device configured to repeatedly measure the location of the emitter using the emitter needle as a measuring point; anda deflector system configured to compensate for variations in the location of the emitter. 2. A charged particle beam apparatus comprising:a charged particle beam source comprising:an emitter with an emitter tip; anda supporting member configured to support the emitter, wherein the supporting member comprises a base and a support wire;an emitter location measuring device configured to repeatedly measure the location of the emitter using the support wire as a measuring point; anda deflector system configured to compensate for variations in the location of the emitter. 3. The charged particle beam apparatus according to claim 2, wherein the support wire is a bent hairpin wire. 4. The charged particle beam apparatus according to claim 1, wherein the supporting member comprises a stabilization element. 5. The charged particle beam apparatus according to claim 1, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a first direction and comprises a first measuring assembly. 6. The charged particle beam apparatus according to claim 5, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a second direction essentially perpendicular to the first direction and comprises a second measuring assembly. 7. The charged particle beam apparatus according to claim 1, wherein the emitter location measuring device is a contact-less measuring device. 8. The charged particle beam apparatus according to claim 1, wherein the emitter location measuring device comprises a light source and a detector. 9. The charged particle beam apparatus according to claim 8, wherein the light source is a laser. 10. The charged particle beam apparatus according to claim 8, wherein the detector comprises at least two segments. 11. The charged particle beam apparatus according to claim 1, wherein the emitter location measuring device comprises multi-fiber optics. 12. The charged particle beam apparatus according to claim 1, wherein the emitter location measuring device includes an interferometer. 13. The charged particle beam apparatus according to claim 1, wherein the deflector system is a post-lens deflector system. 14. The charged particle beam apparatus according to claim 1, further comprising a scan unit. 15. The charged particle beam apparatus according to claim 1, further comprising an emitter location calibration amplifier configured to generate an emitter correction signal provided to the deflector system, wherein the emitter correction signal is based on an emitter location signal of the emitter location measuring device. 16. The charged particle beam apparatus according to claim 1, further comprising a stage location measuring device. 17. The charged particle beam apparatus according to claim 16, wherein the stage location measuring device is an interferometer. 18. The charged particle beam apparatus according to claim 16, further comprising a stage location calibration amplifier configured to generate a stage location correction signal provided to the deflector system, wherein the stage location correction signal is based on a stage location signal of the stage location measuring device. 19. The charged particle beam apparatus according to claim 16, wherein a combined correction signal is provided to the deflector system and wherein the combined correction signal is based on a stage location signal of the stage location measuring device and an emitter location signal of the emitter location measuring device. 20. A charged particle beam apparatus comprising:a charged particle beam source comprising:an emitter having an emitter needle with an emitter tip; anda supporting member configured to support the emitter;an emitter location measuring device configured to repeatedly measure the location of the emitter using the emitter needle as a measuring point; anda stage positioning system adapted to compensate for variations in the location of the emitter. 21. The charged particle beam apparatus according to claim 20, further comprising a deflector system for compensating variations in the location of the emitter. 22. The charged particle beam apparatus according to claim 21, further comprising dividing means for dividing a correction signal into a deflector system correction signal provided to the deflector system and a stage positioning correction signal provided to the stage positioning system. 23. The charged particle beam apparatus according to claim 20, wherein the supporting member comprises a base and a support wire. 24. The charged particle beam apparatus according to claim 23, wherein the support wire is a bent hairpin wire. 25. The charged particle beam apparatus according to claim 20, wherein the supporting member comprises a stabilization element. 26. The charged particle beam apparatus according to claim 20, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a first direction and comprises a first measuring assembly. 27. The charged particle beam apparatus according to claim 26, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a second direction essentially perpendicular to the first direction and comprises a second measuring assembly. 28. The charged particle beam apparatus according to claim 20, wherein the emitter location measuring device is a contact-less measuring device. 29. The charged particle beam apparatus according to claim 20, wherein the emitter location measuring device comprises a light source and a detector. 30. The charged particle beam apparatus according to claim 29, wherein the light source is a laser. 31. The charged particle beam apparatus according to claim 29, wherein the detector comprises at least two segments. 32. The charged particle beam apparatus according to claim 20, wherein the emitter location measuring device comprises multi-fiber optics. 33. The charged particle beam apparatus according to claim 20, wherein the emitter location measuring device includes an interferometer. 34. The charged particle beam apparatus according to claim 21 wherein the deflector system is a post-lens deflector system. 35. The charged particle beam apparatus according to claim 20, further comprising a scan unit. 36. The charged particle beam apparatus according to claim 21, further comprising an emitter location calibration amplifier configured to generate an emitter correction signal provided to the deflector system, wherein the emitter correction signal is based on an emitter location signal of the emitter location measuring device. 37. The charged particle beam apparatus according to claim 21, further comprising a stage location measuring device. 38. The charged particle beam apparatus according to claim 37, wherein the stage location measuring device is an interferometer. 39. The charged particle beam apparatus according to claim 37, further comprising a stage location calibration amplifier configured to generate a stage location correction signal provided to the deflector system, wherein the stage location correction signal is based on a stage location signal of the stage location measuring device. 40. The charged particle beam apparatus according to claim 37, wherein a combined correction signal is provided to the deflector system and wherein the combined correction signal is based on a stage location signal of the stage location measuring device and an emitter location signal of the emitter location measuring device. 41. A method of compensating variations in an emitter location of a charged particle beam apparatus including an emitter having an emitter needle with an emitter tip, comprising the steps of:measuring the emitter location using the emitter needle as a measuring point; andcompensating for variations in the emitter location. 42. The method according to claim 41, further comprising:measuring a stage location of a stage for supporting a specimen; andcompensating for variations in the stage location. 43. The method according to claim 41, wherein compensating for variations comprises deflecting a charged particle beam emitted by the charged particle beam emitter. 44. The method according to claim 42, wherein compensating for variations in the stage location comprises moving the stage. 45. The method according to claim 41, further comprising:generating an emitter location signal;transforming the emitter location signal to an emitter correction signal; andproviding the emitter correction signal to a deflector system. 46. The method according to claim 41, further comprising:generating a stage location signal;transforming the stage location signal to a stage correction signal; andproviding the stage correction signal to a deflector system. 47. The method according to claim 41, further comprising:generating an emitter location signal and a stage location signal;transforming the emitter location signal and the stage location signal to a first correction signal; andproviding the first correction signal to a deflector system. 48. The method according to claim 47, wherein transforming the emitter location signal and the stage location signal comprises analyzing the emitter location signal and/or the stage location signal with respect to different frequencies included in the variations in locations of the emitter and/or the stage. 49. The method according to claim 41, wherein the emitter is adapted for emitting ions. 50. The charged particle beam apparatus according to claim 2, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a first direction and comprises a first measuring assembly. 51. The charged particle beam apparatus according to claim 50, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a second direction essentially perpendicular to the first direction and comprises a second measuring assembly. 52. The charged particle beam apparatus according to claim 2, wherein the emitter location measuring device is a contact-less measuring device. 53. The charged particle beam apparatus according to claim 2, wherein the emitter location measuring device comprises a light source and a detector. 54. The charged particle beam apparatus according to claim 53, wherein the light source is a laser. 55. The charged particle beam apparatus according to claim 53, wherein the detector comprises at least two segments. 56. The charged particle beam apparatus according to claim 2, wherein the emitter location measuring device comprises multi-fiber optics. 57. The charged particle beam apparatus according to claim 2, wherein the emitter location measuring device includes an interferometer. 58. The charged particle beam apparatus according to claim 2, wherein the deflector system is a post-lens deflector system. 59. The charged particle beam apparatus according to claim 2, further comprising a scan unit. 60. The charged particle beam apparatus according to claim 2, further comprising an emitter location calibration amplifier configured to generate an emitter correction signal provided to the deflector system, wherein the emitter correction signal is based on an emitter location signal of the emitter location measuring device. 61. The charged particle beam apparatus according to claim 2, further comprising a stage location measuring device. 62. The charged particle beam apparatus according to claim 61, wherein the stage location measuring device is an interferometer. 63. The charged particle beam apparatus according to claim 61, further comprising a stage location calibration amplifier configured to generate a stage location correction signal provided to the deflector system, wherein the stage location correction signal is based on a stage location signal of the stage location measuring device. 64. The charged particle beam apparatus according to claim 61, wherein a combined correction signal is provided to the deflector system and wherein the combined correction signal is based on a stage location signal of the stage location measuring device and an emitter location signal of the emitter location measuring device. 65. The charged particle beam apparatus according to claim 2, wherein the charged particle beam source is adapted for emitting ions. 66. The charged particle beam apparatus according to claim 20, wherein the charged particle beam source is adapted for emitting ions. 67. A charged particle beam apparatus comprising:a charged particle beam source comprising:an emitter with an emitter tip; anda supporting member configured to support the emitter, wherein the supporting member comprises a base and a support wire;an emitter location measuring device configured to repeatedly measure the location of the emitter using the support wire as a measuring point; anda stage positioning system adapted to compensate for variations in the location of the emitter. 68. The charged particle beam apparatus according to claim 67, further comprising a deflector system for compensating variations in the location of the emitter. 69. The charged particle beam apparatus according to claim 68, further comprising dividing means for dividing a correction signal into a deflector system correction signal provided to the deflector system and a stage positioning correction signal provided to the stage positioning system. 70. The charged particle beam apparatus according to claim 68, wherein the deflector system is a post-lens deflector system. 71. The charged particle beam apparatus according to claim 68, further comprising an emitter location calibration amplifier configured to generate an emitter correction signal provided to the deflector system, wherein the emitter correction signal is based on an emitter location signal of the emitter location measuring device. 72. The charged particle beam apparatus according to claim 68, further comprising a stage location measuring device. 73. The charged particle beam apparatus according to claim 72, wherein the stage location measuring device is an interferometer. 74. The charged particle beam apparatus according to claim 72, further comprising a stage location calibration amplifier configured to generate a stage location correction signal provided to the deflector system, wherein the stage location correction signal is based on a stage location signal of the stage location measuring device. 75. The charged particle beam apparatus according to claim 72, wherein a combined correction signal is provided to the deflector system and wherein the combined correction signal is based on a stage location signal of the stage location measuring device and an emitter location signal of the emitter location measuring device. 76. The charged particle beam apparatus according to claim 67, wherein the support wire is a bent hairpin wire. 77. The charged particle beam apparatus according to claim 67, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a first direction and comprises a first measuring assembly. 78. The charged particle beam apparatus according to claim 77, wherein the emitter location measuring device is adapted to measure variations in the location of the emitter along a second direction essentially perpendicular to the first direction and comprises a second measuring assembly. 79. The charged particle beam apparatus according to claim 67, wherein the emitter location measuring device is a contact-less measuring device. 80. The charged particle beam apparatus according to claim 67, wherein the emitter location measuring device comprises a light source and a detector. 81. The charged particle beam apparatus according to claim 80, wherein the light source is a laser. 82. The charged particle beam apparatus according to claim 80, wherein the detector comprises at least two segments. 83. The charged particle beam apparatus according to claim 67, wherein the emitter location measuring device comprises multi-fiber optics. 84. The charged particle beam apparatus according to claim 67, wherein the emitter location measuring device comprises an interferometer. 85. The charged particle beam apparatus according to claim 67, further comprising a scan unit. 86. The charged particle beam apparatus according to claim 67, wherein the charged particle beam source is adapted for emitting ions. 87. A method of compensating variations in an emitter location of a charged particle beam apparatus comprising an emitter with an emitter tip and a supporting member for supporting the emitter, wherein the supporting member comprises a base and a support wire, the method comprising the steps of:measuring the emitter location using the support wire as a measuring point; andcompensating for variations in the emitter location. 88. The method according to claim 87, further comprising:measuring a stage location of a stage for supporting a specimen; andcompensating for variations in the stage location. 89. The method according to claim 88, wherein compensating for variations in the stage location comprises moving the stage. 90. The method according to claim 87, wherein compensating for variations comprises deflecting a charged particle beam emitted by the charged particle beam emitter. 91. The method according to claim 87, further comprising:generating an emitter location signal;transforming the emitter location signal to an emitter correction signal; andproviding the emitter correction signal to a deflector system. 92. The method according to claim 87, further comprising:generating a stage location signal;transforming the stage location signal to a stage correction signal; andproviding the stage correction signal to a deflector system. 93. The method according to claim 87, further comprising:generating an emitter location signal and a stage location signal;transforming the emitter location signal and the stage location signal to a first correction signal; andproviding the first correction signal to a deflector system. 94. The method according to claim 93, wherein transforming the emitter location signal and the stage location signal comprises analyzing the emitter location signal and/or the stage location signal with respect to different frequencies included in the variations in locations of the emitter and/or the stage. 95. The method according to claim 87, wherein the emitter is adapted for emitting ions. |
|
052590097 | abstract | A boiling water reactor fuel rod assembly is provided having a plurality of fuel rod spacers which are slidably receivable within an outer channel. Each of the rod spacers is formed of at least one lattice which defines a plurality of fuel rod retaining cells. The lattice is constructed of a plurality of pairs of oppositely facing springy support strips, with each support strip having a plurality of spring-loaded indentations. In an unloaded condition, oppositely facing indentations of each pair of strips, which define each cell, are displaced closer to one another. In a loaded condition, the oppositely facing cell indentations are forced away from each other by the fuel rods so that the springloaded indentations support and retain the fuel rods. |
abstract | An X-RAY CONVERTER having a light-proof housing with an X-ray-transparent wall behind which there are fastened an X-ray-to-optical converter, a filter of residual X-radiation, an objective lenses unit, and a photodetector containing at least two optoelectronic converters with partly overlapping fields of view and separated electrical outputs for connection to a system for processing of fragmentary video signals and generating an integral output video signal. For improving the efficiency of suppression of internal interferences in optical channels and the operating reliability, within the housing, parallel to the X-ray-to-optical converter, there is rigidly fastened an additional light- and X-ray-opaque partition with through-holes which in the number and placement correspond to objective lenses and optoelectronic converters and are blocked by washers of the filter of residual X-radiation, and ahead of the washers there are installed blinds, length A of each of which and distance D from the front surface of the X-ray-to-optical converter to the plane of front end faces of objective lenses are related by the ratio A/D=(0.50 . . . 0.95). |
|
summary | ||
description | This invention was made with government support under Contract No. DE-AC02-06CH11357 awarded by the United States Department of Energy to UChicago Argonne, LLC, operator of Argonne National Laboratory. The government has certain rights in the invention. This invention relates to a method for determining corrosion behavior in metals and more specifically, the invention provides an experimental method and model based on electrode-kinetics theory that can be used for predicting corrosion rates and lifecycle characteristics of metals and alloys including the release of constituent elements into a contacting fluid (e.g., in the body or environment). Medical implants, building structures, pipe lines, waste forms, and other industries incorporate various metals into their products. These metals require a particular set of characteristics to adequately perform their intended use. As such, relevant metals and their corrosion characteristics continue to be researched. Medical implants need to function for decades in rapidly changing biochemical conditions (e.g., blood plasma pH and medication levels). For example, the corrosion of alloys, which comprise implanted medical devices used in biological environments, release contaminants that could be hazardous or desirable, depending on their release rates. These material corrosion and constituent release rates will depend on the alloy composition and microstructure and the environmental (i.e., in vivo) conditions. Construction metals and pipelines are subjected to mechanical stress (e.g. elastic, deformable), environmental stress (e.g., acid rain, oxidation), and other chemical insults. For example, pipelines are widely used to carry natural gas, oil, water, and sewerage. The alloys used for pipelines are susceptible to corrosion when placed underground and subsequently exposed to seawater, salts, ground shifts, etc. Corrosion can deteriorate the mechanical properties and cause failure of the pipelines leading to the release of hazardous materials into the fluid being transferred or the surrounding environment. Corrosion of military equipment and infrastructure under the U.S., Department of Defense costs about $20B annually. A wide range of single and multiphase materials are used in various and changing service conditions. The use of standard electrochemical tests to predict their failure is not reliable because they do not represent the corrosion conditions. Long-term performance depends on the mechanistic understanding of the corrosion behavior of the constituent phases present on and below the materials' surface and test methods that quantify the rates of the controlling processes. Corrosion assessment techniques are widely applied for materials used in the automotive industry. However, for enhanced performance, new lightweight materials with excellent corrosion resistance are required. Their performance directly depends on the environment, microstructure, and phase composition. 3D printed materials are increasingly used in various applications as biomaterials, automotive, medical, nuclear etc. There are insufficient standards for evaluating the corrosion and mechanical properties of these materials. Finally, many types of wastes and their containers comprise metal. For example, one type of waste form includes radioactive spent fuel waste alloyed with shredded metal cladding. These waste forms must resist corrosion for many hundred thousand years after burial. Coatings deposited by techniques such as atomic layer deposition, plasma spray, chemical and physical vapor deposition, high velocity oxygen fuel, and laser cladding are used to provide corrosion protection in high temperature, chemically aggressive, and high tribological wear environments. The performance of these coated materials needs to be evaluated reliably. Key aspects of waste form development include (1) the capacity to accommodate waste constituents in durable phases, (2) reliable production methods that generate waste form products having consistent properties, and (3) confidence that the waste forms will meet regulatory requirements for radionuclide containment during handling, storage, transport, and permanent disposal. The major performance requirement for metal waste forms is to maintain sufficient corrosion resistance so that the disposal system will remain compliant with regulations as contaminants are leached or otherwise released from waste forms throughout the regulated service life of the disposal system. The primary pathway for radionuclide release is by seepage water contacting and degrading the waste form. Subsequently, groundwater transports the released radionuclides away from the burial site and into the surrounding biosphere. State of the art electrochemical corrosion experiments on metals measure and/or control the potential and net current of the oxidation and reduction reactions by manipulating and measuring two variables: the electrochemical redox and the pH of the solution. But these measurements fail to represent the range of the redox conditions under which the material must perform and the effects of those conditions on the material's surfaces over the long term. Potentiodynamic scans of polished surfaces indicate regions of passive and active corrosion behavior based on changes in the measured current at various applied potentials. But the polished surfaces used in these measurements do not represent surfaces that have equilibrated under the redox and chemical conditions in the test. Also, currents measured during potentiodynamic scans do not represent the steady corrosion of a stabilized surface. Steady corrosion occurs when the net current neither increases nor decreases over time. Most electrochemical measurements are made only at the resting-potential of the alloy in the test solution at one point in time or during very brief sampling periods. (The resting potential is the voltage/potential at which the oxidation and reduction reaction rates are equal and the net current is zero.) Every environment and material combination will have a resting potential or Ecorr that will vary as the surface passivates or is leached. It is the potential that is attained in the system (i.e., the combination of the material and the environment) in the absence of an imposed voltage, and is also referred to as the open circuit potential. Therefore, potentiodynamic scans of polished surfaces do not represent (and cannot be extrapolated to represent) the corrosion behavior of surfaces that have stabilized at any in vivo potential over time. The method fails to take into account effects of oxides which accrue on the surface of the material and leaching (dealloying) that may occur during the service life of the material. Reverse polarization and cyclic polarization methods are used to indicate changes in the corrosion behavior in representative solutions as pitting or passivation occurs. However, the responses represent transient behavior that may depend on the scan conditions, and may occur at the upper end of the scanned voltage range that does not represent service conditions. The effect of cyclic polarization is to drive oxidation reactions (to higher potentials) during the anodic scan and then drive reduction reactions (to lower potentials) during the cathodic scan. Applied potential is increased or decreased with time while the current is constantly monitored. Then the process is reversed after the potential is scanned to a predetermined current density or potential and the potential is decreased with time. Measurements can be made by using one or multiple cycles. However, and as discussed supra, this method fails to generate stabilized surfaces representing those formed over long periods of time in the in vivo redox conditions in which the material must perform. Another method, known as galvanodynamic, controls the current and measures the potential as the current is varied, plotting the change in potential versus time. This method provides the redox at which a particular corrosion process occurs, which may or may not represent in vivo redox conditions of interest. These and other standard testing methods such as linear polarization resistance and Tafel are not conducted under service conditions and do not represent corrosion of alloy surfaces that have stabilized under service conditions. Contrarily, those methods destabilize the surface by imposing cathodic potentials at the beginning of the scan. These state of the art methods do not measure the effects of passivation or leaching on corrosion rates. Those effects must be included to characterize long-term behavior of materials under relevant service conditions c. As such, unequivocal tests to determine the suitability of certain materials for a particular industry or application over the course of a typical service life do not exist. Coupon immersion tests are also commonly used to measure corrosion rates. But these tests only provide information regarding corrosion at the corrosion potential (Ecorr), which will drift in response to changes in both the solution composition (e.g., Eh and pH) and coupon surface properties that occur during the tests. Also, coupon immersion tests do not represent the electrochemical conditions that occur in the service environment. Rather, coupon test responses represent the cumulative corrosion occurring during the test period and only average rates can be derived, whereas most corrosion occurs (and therefore should be studied) in the early stages of most tests. Models need to be developed to represent degradation of materials in assessments that are conducted to ensure performance requirements will be met throughout the anticipated service-life of the material, be it a medical implant venue, an oil/gas transport line, or in a waste disposal facility. Specifically, a need exists in the art for a method to assess the corrosion behavior of homogenous materials, multiphase alloys, alloy/ceramic composites, and coated materials under controlled chemical and redox conditions. The method should include the use of techniques that are consistent with the mechanistic understanding of the corrosion process and provide corrosion rates that can be related to the material, the chemical surroundings, and the phase composition at the corroding surface for modeling purposes. The method should also be sensitive to the effects of physiological or environmental variables to which the material is subjected. In buried waste scenarios, the method should relate the electrochemical corrosion behavior to the release rates of radionuclides from waste forms. For medical devices and implants, the method should represent the effects of human activity on corrosion and the release of metal particles that may be toxic. For coated materials, the method should represent and be sensitive to thermal cycling, tribology and wear conditions and should provide the corrosion rates of the coating and the underlying substrate. An object of this invention is to provide a method for determining the corrosion characteristics of a material under specific controlled redox and chemical conditions that represent specific points in service environments/lives for industrial, environmental, and biological applications. It is noteworthy that the method does not average corrosion characteristics and other in-service phenomenon. Rather, the method provides a means for pinpointing corrosion status at any time during the service life of a work piece. Another object of the present invention is to provide a method for determining corrosion characteristics of a material in changing in vivo or in situ environments. A feature of the invention is the use of electrochemical analysis on the material over an extended period of time to measure the response of the surface to the chemical and redox conditions to which the material is typically subjected. (This includes engineered facilities in geological formations related to waste disposal, industrial applications, and in the body related to medical implants). An advantage of the invention is that it enables the identification of shortcomings in proposed medical implants, construction hardware, or radioactive waste forms that can be rectified prior to permanent insertion or disposal, including multiphase and coated materials. Yet another object of the invention is to provide a testing protocol to assess the corrosion behavior of homogenous and multiphase alloy, alloy/ceramic composite, and coated materials under controlled chemical and redox conditions. A feature of the invention is that it combines several electrochemical techniques with scanning electron microscopy (SEM) and solution analysis to evaluate in vivo or in situ effects of physical, chemical, and electrochemical changes on both the solid and solution phases. (In many applications, the release of constituents into solution is the primary concern rather than degradation of the material, per se, and the invention can determine when during service life, this release occurs.) An advantage of the invention is that it evaluates the material after it has stabilized at potentials representing the service conditions other than the resting (open circuit) potential of the material in the test solution. This allows the corrosion rates and stabilized surfaces to be measured directly at any solution redox to represent the effects of radiolysis, bioactivity, or corrosion itself. When dealing with hazardous waste form materials, another advantage of the protocol is that it provides greater confidence in predicting both the releases of contaminants and the longevity of the material in a given environment, including as that environment changes over time. Still another object of the invention is to establish functional dependencies on environmental variables that can be used in computer simulations of material corrosion in any redox environments based on electrode kinetics theory, mixed potential theory, passivation theory, and electric circuit analysis. A feature of the invention is exposing materials to various solutions simulating a range of real world conditions to determine the functional dependencies of materials' corrosion characteristics on key environmental variables. (For example, the imposition of a potentiostat represents Eh (redox) conditions that could possibly occur in the environment.) An advantage of the invention is that the results of the exposure provide a mechanistic understanding of the corrosion process and quantify the corrosion rate as a function of the materials' phase compositions, and also a function of key variables of the environment. Another object of the invention is the utilization of electrochemical tests on multiphase materials to develop and parameterize degradation models for metallic waste forms, where the alloys represent waste forms are made with metal (e.g. steel, zirconium) cladding and metallic fuel waste. Features of the models include enabling the design of waste forms to accommodate waste constituents in durable phases, and demonstrating that production methods generate waste form products having consistent properties. An advantage of the implementation of these models is that they instill confidence that the waste forms will meet regulatory requirements during storage, transport, and permanent disposal. Further, an object of the invention is to provide a test method supporting the design of radiological waste forms which are corrosion resistant in a range of seepage water compositions likely to occur throughout the regulated service life of a disposal facility. A feature of the method is that it subjects prototype materials used in the formulation of alloy waste forms to actual service conditions (and during the development of those service conditions) to ensure that the waste forms will be durable under the full range of environmental conditions, possible in disposal systems. An advantage of the invention is that siting and useful life determinations are more accurate, eliminating unscheduled downtime and catastrophic failure of buried structures. Another advantage of the invention is improving safety and performance assessment calculations by relating the electrochemical processes controlling the oxidation rate to the mass release rates of radionuclides of interest, and at specific points during the service life. Yet another object of the present invention is to provide medical material tests which can be conducted under service conditions (e.g., blood pH and Eh) with representative surfaces (passivated, leached, or actively corroding) of the material at different service ages. A feature of this invention is that biomaterial corrosion behaviors are measured in simulated in vivo conditions, those conditions which represent various physical activities/health of a patient. The results of these measurements are used to predict long-term performance based on an individual's body composition and plasma properties, the concentrations of medications present or anticipated as a person ages, and physical activity level during the service life of the implant. Further, an object of the invention is to provide a test method to test and predict the performance of coatings at specific life cycle points in realistic service environments. A feature of the method is that it subjects prototype coated materials to tribology and wear situations. An advantage of the method is that it ensures that the coatings are both physically and electrochemically durable under service conditions. Still another object of the present invention is providing a model circuit that represents the electrical properties of the stable material surface measured by using electrochemical impedance spectroscopy (EIS). The circuit relates the electrical properties to the physical nature of the stable surface. A feature of the invention is that the test parameters can be selected to represent the type of material, service conditions, and performance measures relevant to the industry. An advantage of the invention is that the method can be applied to durable and degradable materials representing a wide range of applications. Briefly, the invention provides a method for assessing the corrosion behavior of materials, the method comprising combining multiple electrochemical processes and modeling techniques to develop an electrochemical corrosion profile for a material of interest; wherein the imposed test conditions represent in vivo conditions; analyzing currents measured in the electrochemical processes; and comparing corrosion behavior of the material under several different environmental conditions to quantify dependencies for use in simulation models. Specifically, the invention provides a method for predicting corrosion rates of a material under a plurality of service conditions, the method comprising: determining a first phase composition of the material surface prior to corrosion; exposing the material to a solution representing one chemical service condition; applying an electrical potential to the exposed material to represent the redox strength of a second service condition; identifying the corrosion activity for first and second service conditions; and determining a second phase composition of the material after corrosion. The chemical and electrochemical conditions used in the tests are selected based on the anticipated service conditions for the material and the performance aspects to be modelled. The invention further provides a system for predicting release of radionuclides from buried waste forms, the system comprising a potentiodynamic scan to associate redox values at the surfaces of the waste forms to corrosion behavior of those forms; a potentiostatic analysis to determine current at the surfaces as they corrode; an electrochemical impedance spectrograph to reveal changes in electrical properties of the surface during corrosion; relating the changes to measured corrosion currents; current and surface electrical properties during corrosion; and a circuit representative of the surface properties as derived by the spectrograph, wherein the circuit can be related to physical models. Also provided is a method for determining radionuclide source terms, the method comprising supplying a multiphase waste form containing the radionuclides; immersing the waste form in a solution representing repository chemistry; and oxidizing the immersed waste form for a period of time and at a particular voltage representing the redox strength of the repository chemistry to establish a steady corrosion rate of the waste form. The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (e.g., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. Electrochemical Basis of Invention The invention provides a method of combining multiple processes and modeling techniques to produce a comprehensive understanding of a material's suitability for various medical, commercial and industrial uses based on its electrochemical corrosion behavior. Electrochemical corrosion occurs through chemical reactions that involve the transfer of electrons from the solid to solution species at solid/solution interfaces. The invention utilizes electrochemical tests to quantify the corrosion behaviors (tendencies to passivate, currents, elemental preferences, de-alloying, and corrosion products) of representative multiphase alloys, alloy/ceramic composites, and coated materials under a range of conditions relevant to the intended service environments. The use of electrochemical methods to represent the corrosion rates of passivated waste forms pertinent to long-term disposal is based on the fact that the redox reactions occurring between the solution and a particular metallic surface fix the electrical potential of the surface at a voltage that depends on the redox strength of a solution, which is quantified as the solution Eh value, in volts. In most systems, redox reactions involving H+ and dissolved O2 in the solution are coupled with oxidation reactions of metals at the surface through electron transfer. This is represented in terms of the various oxidation and reduction half-reactions for different species in the solution and on the surface. Some half reactions are as follows: Solution Reduction ReactionsMaterial Oxidation Reactions2H+ + 2e− → H2Fe → Fe2+ + 2e−O2 + 4e− → 2 O2−Fe2+ → Fe3++ e−SO42− + H2O + 2e− → SO32− + 2 OH−Cr → Cr3+ + 3e−H2O2 + 2e− → 2H+ + 2 O2−Zr → Zr4+ + 4e−Tc → Tc4+ + 4e−Tc4+ → Tc7+ + 3e−U → U4+ + 4e−U4+ → U7 + 2e− Each half reaction has a threshold potential that affects which coupled redox reactions can occur and will dominate under particular conditions. For example, in acidic solutions with low dissolved oxygen contents, coupling the Fe and Cr oxidation reactions with the H+ reduction reaction will dissolve steel to release Fe2+ and Cr3+ into solution. In contrast, acidic solutions with high dissolved oxygen contents will favor coupling of the Fe and Cr oxidation reactions with the O2 reduction reaction. Initial corrosion will lead to the formation of Fe2O3, but the steel will quickly passivate by forming a film of Cr2O3. However, coupling of the Fe and Zr oxidation reactions with the O2 reduction reaction will lead to active corrosion and the formation of Fe2O3 and ZrO2. Mildly oxidizing conditions will lead to sparingly soluble TcO2, but moderate and highly oxidizing conditions will form soluble TcO4−. The different kinetics of competing reactions will further complicate the observed behavior. The invention provides direct measurements of the preferred reaction paths under each service condition. The invention provides a more sensitive method to measure the effects of alloy composition and processing methods, such as casting, powder metallurgy, and 3D printing, on long-term corrosion behavior of multiphase alloys being developed for use in the biomedical, automotive, and aerospace industries. The invented method uses data from several sources, including the type of material, service conditions, and performance requirements to arrive at corrosion propensities and characteristics of the material to be measured. For example, the invention provides a means for mimicking the acid-base environment and effects of the oxygen content of blood so as to subject target materials to that environment over sustained periods of time. This enables profiles to be measured as the behavior of those materials change over time under the relevant range of in vivo conditions to support development of implant materials having ideal corrosion properties for those in vivo conditions. The invention also provides a sensitive method to quantify effects of microstructures resulting from different processing methods, such as casting, hot isostatic pressing, wrought, and 3D printing on corrosion behaviors of alloys, alloy/oxide composites, and semiconductor materials. The invention provides a sensitive method to quantify the corrosion behavior of small specimen areas (on the order of 100 square micrometers). This aids to distinguish the corrosion behavior of different regions of the heat affected zones in welds and other inhomogeneities. The invention provides a sensitive method to measure the quality and performance of the interface between a substrate and coating, including metal/metal, metal/ceramic, and oxide/semiconductor interfaces. Electrochemical test methods are used to quantify metals and their alloys for a myriad of applications, including medical, industrial, and waste burial. Analytical expressions are provided herein to represent ranges of environmental dependencies and conditions. (These conditions are not practical to simulate using state of the art immersion test methods). The expressions enable the modeling of long-term material performances. Electrochemical techniques including potentiodynamic (PD) and potentiostatic (PS) tests, and EIS analysis provide corrosion rates of metallic waste forms and engineering materials under the range of Eh-pH conditions that could occur as the surfaces stabilize under service conditions. The results of electrochemical tests with multiphase alloys were used to develop and parameterize a degradation model for metallic waste forms. A test protocol was developed combining the electrochemical methods with microscopy and solution analysis to measure the corrosion behavior and kinetics under imposed redox (Eh) and chemical conditions. The results provide a means to quantify the effects of passivation and leaching on the corrosion rates of multi-phase metals, show effects of specific elements in waste (e.g., noble metals) or added as trim to improve passivation, derive analytical dependencies of rate based on environmental variables, and improve waste formations. Specimens cut from cast ingots were fashioned into electrodes used to measure the corrosion kinetics under a range of conditions. Potentiostatic tests were conducted at several voltages spanning the range of redox potentials that could occur in seepage waters accumulating in breached waste packages to quantify the effect on the degradation rate. Currents were monitored for several days at applied voltages leading to steady cathodic, active, passive, or transpassive corrosion behaviors. Electrochemical impedance spectroscopy scans were performed daily to relate the measured currents to changes in the electrical properties of the corroding surface due to the formation or degradation of passivating films during those tests. The corroded electrode surfaces were characterized with scanning electron microscopy to correlate the electrochemical responses with the corrosion of specific phases or interfaces. The results show how distributions of passivating elements in constituent phases affect the corrosion behavior and illustrate how long-term degradation is being modeled. The analytical model based on an oxidative-dissolution mechanism of alloy corrosion assists in the formulation of alloys that are durable under a myriad of service environments and for different applications, such as geological repositories, nuclear reactor sarcophagus venues, chemical processing systems, structures, pipelines, and medical implant systems. The model relates the electrochemical processes controlling the oxidation rate to the mass release rates of constituents of interest, such as radionuclides, wherein the oxidation rate limits the release rate. Source Term Applications The invented model is used to calculate radionuclide source terms needed for safety and performance assessment calculations that will be conducted as part of the design and licensing of geological high-level radioactive waste repository facilities in the US. (The “source term” represents the amount of a radioactive contaminant that becomes available for transport (for example via underground aquifer) over time, and is one of the terms in a linear differential equation used to model contaminant transport.) Using accurate radionuclide source terms in performance assessments improves the design and confidence for licensing of geological high-level radioactive waste repositories in the United States. The source term model for metal waste forms is based on electrochemical principles, but the application of those principles to a multiphase waste form necessitates that the analytical formulations of dependencies on environmental variables and values of model parameters be determined empirically. The semi-empirical analytical model developed to calculate radionuclide source terms includes analytical functions that take into account the following effects: environmental variables on the electrochemical oxidation reactions with the alloy phases during active and passive corrosion; the attenuating effect of surface passivation on the oxidation reactions; and the dissolution behaviors of oxidized radionuclides. The dependencies of the oxidation reaction rates on key environmental variables and parameter values are measured for several alloyed materials that represent a range of possible metallic waste form compositions under conditions spanning the range of environments that may occur in geological disposal systems. The invented source term model uses process models based on electrode kinetic theory to represent the oxidation rates of constituent alloy phases and reaction affinity theory to represent the dissolution rates of radionuclide-bearing oxides to calculate radionuclide source terms. The electrometallurgical reprocessing of used metallic fuel to recover and recycle U and Pu generates two waste streams: salt wastes comprised of electrorefiner salt contaminated with oxidized fission product fuel wastes and metallic wastes comprised of activated cladding hulls and metallic fission product fuel wastes that were not oxidized under the processing conditions. Metallic waste forms are made by directly melting the cladding and fuel wastes with small amounts of trim metals to form a multi-phase alloy in which radionuclides and other waste constituents become immobilized in various intermetallic and solid solution phases. The durability of each phase controls the release of the radionuclides it contains. Electrochemical principles are applied to multi-phase waste forms incorporating radionuclides to determine the overall corrosion rates of the waste forms, which depend on the coupled corrosion of all constituent phases. The principles use analytical formulations of dependencies on environmental variables that can be used to calculate radionuclide source terms used in contaminant transport models. Subsequent transport is controlled by various processes acting on the contaminant, including advection, diffusion, sorption, precipitation, etc. The conceptual model for the release of radionuclides into groundwater as the waste form corrodes is based on a two-step process in which oxidation of the radionuclides and host alloys is the first step and dissolution of the oxides to release radionuclides into solution (or transportable colloids) is the second step. Oxidation of metal atoms in the waste form occurs through electrochemical reactions with (or facilitated through) the contacting solution at rates that can be modeled by using electrode kinetics theory. The suite of redox-sensitive solutes in the solution establishes the corrosion potential at the alloy surface that controls the oxidation rate of each metal atom. Oxidation of radionuclides can occur directly through redox reactions with solutes or indirectly through reactions catalyzed by the metal surface, and can be affected by galvanic couples and other processes that either protect or sacrifice particular elements or phases. The oxidation state of the oxidized radionuclide determines the propensity for dissolution into a solution of interest. For example, relatively little Tc4+ will be released into solution from Tc(IV)-bearing phases such as TcO2 but essentially all Tc7+ will be released (e.g., as TcO4−) if Tc is oxidized to Tc(VII). The higher oxidation states of transuranics generally have higher solubility limits, so both the oxidation and dissolution steps are sensitive to the solution Eh and pH, since H+ is an important oxidizing agent. The invented method includes taking into account the effects of environmental variables on the electrochemical oxidation reactions with the alloy phases during corrosion, the attenuating effect of the surface passivation, and the release of dissolved or colloidal species into solution. Understanding the reaction kinetics of the material of interest improves the understanding of the corrosion properties particular to the material. Thus, knowing that a stable measured current indicates stable redox reaction kinetics are occurring at the surface of the material. This provides confidence in predicting the long-term performance of the material of interest. FIG. 1A-D is a schematic depiction of the invented system and method. A potentiodynamic scan (FIG. 1A) may be performed to identify potential ranges having similar or unique behaviors 120 as a basis for selecting potentials to be used in the electrochemical tests. (Potentiodynamic tests provide information on the passivation behavior of a material.) The scan subjects the surface to a predetermined range of voltages in order to measure the dependencies of the anodic corrosion rate on the solution Eh and other environmental variables (namely, pH, T, and chloride ion concentration) and parameterize performance models. To generate the potentiodynamic scan shown in FIG. 1A, a range of potentials was applied, starting at the lower potential at −0.6 VSCE and scanning to the higher potential at +0.7 VSCE. A Nearly constant current (vertical line) is measured as the potential is scanned between about 0 and 0.5 VSCE, (thereby indicating passivation). Transpassive corrosion occurs above about 0.5 VSCE wherein the current increases rapidly as the potential increases. Metal dissolution rate is proportional to the current. The metal dissolves rapidly under active or transpassive behavior but very slowly under passive behavior. The arrows in FIG. 1A drawn at potentials of 0.2 and 0.4 VSCE indicate potentials used in potentiostatic tests conducted on freshly polished electrodes. Both voltages are in the passive region of the potentiodynamic curve in the graph 120. All reported voltages are with reference to a saturated calomel electrode (as VSCE). SEM analyses (125 in FIG. 1B) performed after the potentiodynamic scan (FIG. 1A) are used to identify phases that corroded actively during the scan and any alteration products that formed. Potentiostatic Test Detail Chemical control of the solution redox (Eh) is difficult due to the very strong effect of dissolved O2, even at very low concentrations in controlled atmosphere gloveboxes. However, the surface potential at any solution Eh can be simulated by using a potentiostat to fix the potential at the desired value. Using a potentiostat compensates for fluctuations in the environmental effects on the surface potential (such as changing chemistry due to material dissolution) during the test, so the measured current corresponds to a known surface potential. Furthermore, using a potentiostat to control the surface potential allows any potential of interest identified by the potentiodynamic step to be applied to a surface that is contacted by any solution composition of interest. This allows the effects of the solution Eh and the effects of the solution chemistry (particularly the pH and C− content) on the material corrosion behavior and corrosion rate to be distinguished. This provides a means for generating databases for parameterizing a mathematical model that can be applied to a wide range of conditions, including those not readily simulated in a laboratory. Potentiostatic tests (element number 130 in FIG. 1B) therefor are applied to measure the corrosion rates at all identified electrical potentials of interest. Specifically, the tests are analyzed to relate the mass release rates to the electrochemical corrosion rate. The results of potentiostatic tests at voltages indicated by the arrows in FIG. 1A at 0.2 and 0.4 VSCE (element number 130 in FIG. 1C). Passive corrosion is observed at 0.2 VSCE with a stable current density near 0.7×10−6 cm-2 achieved after about 5 days but active corrosion is observed at 0.4 VSCE with a stable current density near 0.01 A cm-2 achieved within 1 day. This shows the passivation shown in the PD scan at 0.4 VSCE could not be sustained. FIG. 1C compares Bode phase angle plots of the EIS analyses during the PS test at 0.2 VSCE, which show stable responses are obtain after 5 days. Aliquants of solution removed from the test solutions during testing and after testing are analyzed to measure the amounts of constituents released during corrosion. Concentrations can be measured before and after passivation layers form at each potential to provide insight into the degradation model. The masses of dissolved metals released into the solution are calculated from the measured concentrations and solution volume. To determine the mass released during the intervals between two solution collections in the same PS test, the mass calculated at the end of the first sampling interval is treated as background mass and subtracted from the mass calculated at the end of the second interval. The masses released to solution are used to calculate the normalized corrosion rates by dividing the mass of an element released during the test interval by the surface area of the electrode, the overall fractional mass fraction of that element in the material, and the reaction time over which the element accumulated in the solution. The normalized release rate based on the mass of species i in solution, NR(i), is calculated as N R ( i ) = m ( i ) S x f ( i ) x t where m(i) is the mass of species i in solution, S is the surface area of the electrode, f(i) is the mass fraction of i in the material, and t is the test interval. The normalizations allow for direct comparisons of NR(i) values for different electrodes, dissolved elements, imposed potentials, leachant solutions, and test intervals. Mass fractions were calculated from the gross compositions of the electrode material and the areas of electrodes were determined from SEM images used. The normalizations allow for direct comparisons of NR(i) values for different electrodes, dissolved elements, imposed potentials, leachant solutions, and test intervals. The combination of the measured current, SEM analyses of the corroded electrode, and solution analyses provides insight into the relative release rates from different constituent phases. Separate potentiostatic tests 130 are performed at each potential of interest over an extended period. Voltages used in PS tests are chosen based on features seen in the PD scan or based on the service environment of interest. That is, if a particular industrial process imposes a particular range of voltages, potentials within the range are chosen. If a change in behavior is observed at a particular voltage, then more potentiostatic tests may be performed at and near that voltage to comprehensively understand and quantify how the changes in the environment and/or the material affects performance. If a change in the surface conditions of the material is observed to occur over time at a particular potential, the potentiostatic tests 130 are continued until a stable current is attained. This may occur due to the stabilization or destabilization of passivation layers over time. The stable current density attained in each potentiostatic test 130 is used to calculate the material corrosion rate under those specific environmental conditions. The results of a series of potentiostatic tests in which one or more variables are changed (such as the applied potential representing the solution Eh, the pH or chloride concentration in the solution, and/or the temperature) can be used to derive an analytical equation representing the dependence on key variables such as Rate=fn(Eh, pH, Cl, T). The analytical expression may relate the measured current density to individual or combinations of variables by multivariate regression analysis. The potentiostatic tests 130 depicted in FIG. 1C show a stabilized passivation layer formed at 0.2 VSCE but transpassive corrosion at 0.4 VSCE. This data allows material developers to realize that one or more of the metallic phases will corrode rapidly under redox conditions above 0.4 VSCE in those chemical conditions. As such, this portion of the invented protocol advises developers that their proposed material may not provide suitable performance at redox conditions above 0.2 VSCE. The SEM analyses of the electrode from the PD scan (FIG. 1B) indicate which phase(s) corroded and what corrosion products formed. EIS analyses (graph number 140 in FIG. 1D) may be performed during the potentiostatic test 130. EIS is used to determine electrical properties of the material surface by measuring the impedance of the surface as it passivates. As such, EIS provides a means to monitor the changes in the material's electrical properties. Electrochemical impedance is usually measured by applying an AC potential to the working electrode in an electrochemical cell and measuring the AC current passing through the cell. A sinusoidal potential excitation is applied, and the response to the potential is an AC current signal which can be modeled as a sum of sinusoidal functions am devaluated as a function of the applied AC frequency. Usually electrochemical impedance is measured using a small excitation signal so that the cell's response is pseudo linear. The current response to a sinusoidal potential will be a sinusoid at the same frequency but shifted in phase, where the excitation signal is expressed as a function of time (Et=E0 sin(ωt)). Et is the potential at time, E0, is the amplitude of the signal, and ω is the radial frequency. The relationship between radial frequency ω (expressed in radians/second) and frequency f (expressed in hertz) is ω=2πf. In a linear system, the response signal It, is shifted in phase (ϕ) and has a different amplitude than I0. It=I0 sin(ωt+ϕ). An expression analogous to Ohm's law allows for the calculation of the impedance of the system as: Z = E t I t = E 0 sin ( ω t ) I 0 sin ( ω t + ∅ ) = Z 0 sin ( ω t ) sin ( ω t + ∅ ) . The impedance is expressed in terms of a magnitude Z0, and a phase shift, ϕ. As such, EIS quantifies the electrical impedance properties of the material's surface that can be interpreted as capacitive and inductive characteristics. Differences in the EIS results indicate the different passive layers that form under different redox and chemical conditions. Conversely, EIS that remain constant as the PS test proceeds indicate the surface has stabilized. The EIS 140 measures the electrical impedance properties of the passivation layer based on the AC current response to an AC voltage scanning over a user-defined range of frequencies. The combination of a stabilized current in the potentiostatic tests and evidence of a stabilized passivating layer in the EIS responses is a means to indicate the formation of a stable material in service. Specifically, these measured corrosion currents and the calculated corrosion rate represent the electrochemical properties of a stable (and therefore viable, long lasting) electrode surface formed under test conditions representing a particular environment. (The electrode material is selected as the single alloy or a multiphase composite material actually put into service.) Furthermore, an equivalent circuit model (discussed infra and depicted in FIG. 10B) based on the EIS results is used to postulate a physical model of the surface that is consistent with the material's electrical properties under those conditions. As such, the circuit model may be used to represent the corrosion characteristics of the metal under the environmental conditions represented by the test over time as long as the passivating layers can be sustained. The EIS spectra may be analyzed using standard analyses and represented using Bode and Nyquist plots. The expression for Z(ω) is composed of real and imaginary parts. In a Nyquist plot, the real part is plotted on the X-axis and the imaginary part is plotted on the Y-axis. Each point on the plot represents the impedance at one frequency. The impedance may be represented as a vector (arrow) from the origin of length |Z|. The angle between this vector and the X-axis, called the phase angle, is f (=argZ). Because Nyquist plots do not indicate what frequency was used to record that point, Bode plots showing the frequency information are also used to display EIS results. In the Bode plots, the log frequency is plotted on the X-axis and the absolute value of the impedance (|Z|=Z0) and the phase-shift are plotted on the Y-axes. These are referred to as Bode magnitude and Bode phase angle plots, respectively. A sample of the solution of interest is used to quantify the amounts of oxidized (i.e., dissolved) species released into solution as the material corroded during the potentiostatic test 130. The dissolved species may enter the solution by leaching or surface dissolution mechanisms. A surface analysis of the material of interest may be performed to determine by which process the dissolved species is released into the solution. For example, if the material exhibits active current, then leaching from one or more constituent phases may be occurring. Alternatively, if the material exhibits passive current, then dissolution of passivating layers is more likely. FIG. 2 comprises two panels: FIG. 2A and FIG. 2B. FIG. 2A shows electrochemical corrosion conditions in the natural corrosion environment. The electrochemical corrosion conditions imposed by the invented system is depicted in FIG. 2B. As to FIG. 2A, the composition and redox strength (Eh) of the in vivo solution establish the chemical environment and electrochemical potential at the alloy surface. As such, coupled redox reactions in the natural system shown in FIG. 2A transfer electrons from the alloy to solution species. This establishes a corrosion current that depends on the solution redox properties and chemical resistance to electron transfers between coupled species. As depicted in FIG. 2B, a surrogate solution is used to represent in vivo conditions and control environmental variables such as pH, chloride ion content, and temperature. A potentiostat is used to fix the electrochemical potential of the alloy surface at the desired value. The imposed surface potential is independent of the Eh of the surrogate solution. The generation of passivating oxides on the alloy surface impedes corrosion in both systems, and the experimental system quantifies the impedance provided by the passivating layers and the passive current. The potential at the alloy surface in FIG. 2B is controlled relative a reference electrode (RE) via the potentiostat by using the alloy as the working electrode (WE), with current flowing to or from the WE through a counter electrode (CE). The voltage that is fixed by the potentiostat can be selected to maintain a surface potential representing that imposed by any solution of interest, including values that may be very difficult to attain experimentally by using a solution and controlled atmosphere. Different electrolyte solutions can be used to represent the chemistries of seepage waters in a breached waste package that have been affected by radiolysis, container corrosion, and the degradation of other waste forms. Thus, these different electrolyte solutions can impose a range of chemical effects anticipated to occur during burial while the potentiostat maintains the working electrode at the desired potential to mimic the Eh effects. In addition to test conditions that represent the range of service conditions, potentiostatic (PS) tests can be conducted under extreme combinations of Eh and solution chemistry (e.g., pH and [Cl−]) that may not be physically realistic, but can be used to derive environmental dependencies used in the model. The current density that occurs as the electrode surface corrodes at an applied potential (either passively or actively) can be monitored in PS tests performed for many days until steady values representing stable systems and long-term behavior are attained. (The term “corrosion current” is traditionally used only to represent the current generated by corrosion at the open circuit potential. In this specification, the stable current density that is measured at an imposed potential is deemed to represent the current for environmental conditions being simulated under which the open circuit potential will correspond to the imposed potential.) Different constituent phases are expected to passivate, pit, or corrode actively at various imposed potentials, but each phase is expected to eventually attain a steady corrosion rate that can be used to represent the long-term corrosion rate of the multi-phase material. Changes from initial transient behaviors of the polished surfaces can occur due to leaching, stabilization of metastable pitting, or the degradation of passive layers that form initially but cannot be sustained by the underlying alloy phases. (This was shown in the PS test at 0.4 VSCE in FIG. 1C.) Mass corrosion rates can be calculated from the stable currents that are measured in PS tests by using Faraday's law. FIGS. 3A-3C are detailed views of an electrode construct. FIG. 3A is a perspective view of an electrode, in accordance with features of the present invention. FIG. 3B is a side view of the electrode, in accordance with features of the present invention. FIG. 3C is a perspective view of a micro-electrode mated with a commercial holder 115. For example, small electrodes are used to facilitate SEM examination of the entire electrode surface and measure the corrosion behavior of local regions, such as heat-affected zones in weldments. Selected regions of a material; full size electrodes, and standard 1 cm2 electrodes in commercial holders may also be used. A material of interest, such as a metal and/or its alloy (e.g., an alloy of stainless steel, Zr, Mo, Ru, Pd, Tc, and/or other metallic fuel waste), may define an elongated substrate 110 as an electrode. The elongated substrate 110 is surrounded by resin 111 to form a construct 112. The resin 111 may comprise an electrically non-conductive acrylic or epoxy which almost entirely encompasses the material, leaving approximately 2 mm2 of a first end of the elongated substrate exposed to define an exposed surface 113. An electrical lead wire connected to a second end of the elongated substrate 110 is also embedded in the resin and extends from the second end of the electrode. The exposed surface 113 is placed in a solution representing the chemistry of the service conditions that are of critical interest. Such critical chemistry parameters may include temperature, pH, chloride concentrations, dissolved salts (in the case of structural materials), radiation products such as H2O2 and H2 (in the case of radioactive waste forms), and protein/medicament concentrations (in the case of medical implants). In summary of this point, test conditions may mimic those found in ground water, pressurized crude oil/natural gas pipelines, irradiated seepage water, biological fluids, etc. Electrochemical tests are performed at potentials representing specific solution redox conditions or the range of redox spanned by the service conditions 315 that are of interest. EIS and Model Circuit Detail Using the results from the potentiostatic tests and EIS, an equivalent circuit 150 is derived to quantify electrical properties of the passivated surface and support a physical model of the corrosion system. The model circuit is designed to be consistent with the response seen in the EIS tests. The various resistors and capacitors represent the impedances to electrochemical anodic and cathodic reactions and transport barriers to electron and mass flow provided by the passive layers and interfaces. The circuit is applicable to the range of potentials for which the surface is stabilized by the same passivating oxides. The equivalent circuit is used to estimate the passive current for the stabilized surface over the range of applied voltages for which the circuit applies by treating the capacitors and constant phase elements as open circuits. This eliminates the need to measure currents for intermediate voltages directly with additional potentiostatic tests. As such, the circuit provides a means to estimate for specific voltages between empirically measured voltages. The equivalent circuit provides insights into the corrosion behaviors of the individual phases. The electrical properties of multiphase materials are often well-represented as single phases. FIG. 4 is a flowchart of the initial tests to characterize the corrosion behavior of materials. The electrode surface is polished to a predetermined finish (e.g. 1 μm finish) and characterized using SEM to document the phase composition 210. A potentiodynamic scan may be conducted in a solution of interest to identify the ranges of applied potential 220 for which the material shows propensities for active, passive, and transpassive behavior, based on the current response. The electrode surface is characterized 230 with SEM afterwards to identify phases corroded during the potentiodynamic scan. Once the effects of the potentials on the corrosion behaviors are identified in the potentiodynamic scan 220, a series of potentials is selected for use in the potentiostatic tests to quantify the corrosion behavior 240 in the regions of interests. The surface is repolished to remove any changes to the workpiece resulting from corrosion during the potentiostatic tests. Alternatively, a different or fresh electrode may be used. A reproducible surface finish within the range of 0.05 μm to 30 μm is suitable and a 1-2 μm finish is typical. Preferably the surface is consistent for all tests on the same material. Smoother polishes allow for better characterization of the initial microstructure. The objective of repolishing is to establish a fresh surface representing the bulk material. The material's microstructure and phase compositions are then characterized by scanning electron microscopy with x-ray emission spectroscopy 250. The compositions and relative areas of constituent phases in multiphase materials and composition variations within each phase are measured 260. The relative areas of constituent phases are determined using image analysis of SEM images or surface composition maps. The electrode surface is polished and examined using an SEM to characterize and document the microstructures 270 in several regions having features that can be used to locate the same regions for examination after testing. Several regions are documented before testing because corrosion does not occur uniformly across the electrode. If carbon coating is required to evaluate the non-conductive phases during SEM analysis, that coating is wiped off or otherwise removed from the electrode surface after the SEM analysis. Otherwise the coating may interfere with the electrochemical responses measured in the tests. FIG. 5 is a flowchart of the potentiostatic test protocol utilized by the claimed method. Potentiostatic tests are used to characterize the corrosion behavior of a metal surface in contact with the electrolytes of interest. The metal sample is known as the working electrode, while a reference electrode is used to monitor the potential at the working electrode surface. A potentiostat is used to maintain a constant potential at the working electrode surface and measure current passed through the electrolyte between the counter electrode and the working electrode to maintain that potential. Specifically, the potentiostatic tests evaluate changes in the current from when the potential is imposed on the bare surface of the material prior to, during, and after the formation of stabilizing passivation layers or leaching occurs to destabilize the surface. The potentiostatic test protocol (FIG. 5) is conducted separately by holding an electrode at each potential of interest in each solution, as follows: The material electrode, appropriate reference, and counter electrodes are placed in an electrochemical test cell containing a solution 305. The open circuit potential is measured 335 immediately for a period of time (e.g., one second) to orient the potentiostat 310. The electrode surface is electrochemically cleaned 315 by applying cathodic voltage 0.5 V below the measured open circuit potential until a stable cathodic current is attained. The selected potentiostatic voltage 320 is applied and the electrode current recorded for the desired duration (typically 1 to 7 days). EIS 325 is performed while continuing to apply the selected DC potentiostatic test voltage throughout the analysis. Each EIS analysis may be conducted over the range 100 kiloHz to 1 microHz, although other ranges may be appropriate for characterizing the layers that form on some materials. For example, potential layers that may form include, but are not limited to, Iron-based oxides (Fe2O3, Fe3O4), chromium oxide (Cr2O3), molybdenum oxide (MoO2), nickel oxides (NiO, Ni2O3), nickel-molybdate (NiMoO4), titanium oxide (TiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), zinc oxide (ZnO), Copper oxides (CuO, Cu2O), silver oxide (AgO), palladium oxide, tantalum oxide (Ta2O5), tin oxide, cobalt oxides (CoO, Co2O3, Co3O4), and technetium oxide (TcO2). The potentiostatic hold is continued and EIS analyses are performed periodically until a constant current and several constant EIS responses are attained 330. The frequency with which EIS analyses are performed is selected to monitor the evolution of passivation layers and indicate when they have stabilized. Daily analyses through one week are expected to be appropriate for most materials and environments, but longer durations may be required for some systems and actively corroding materials such as low alloy steels. For example, FIG. 1D shows Bode phase angle plots for EIS analyses performed during a potentiostatic hold after about 1, 2, 5, 6, and 7 days. The plots after 5, 6, and 7 days are essentially identical and indicate the surface has attained a stable state. Once a constant current and stable EIS responses are obtained, the surface has attained a stable state under the test conditions of electrolyte composition and imposed potential. Then the applied voltage is removed and the electrode is removed. An aliquant of the solution is immediately harvested for composition analysis 340. The surface of the corroded electrode is allowed to dry and then examined using SEM to identify specific phases, phase boundaries, or regions that corroded 345 during the potentiostatic test. (The extent of corrosion may be undetectable on electrodes that passivated in potentiostatic tests.) The recovered solution also is analyzed for constituents released during the test, which may indicate release from particular constituent phases based on their compositions 350. The solution composition is more sensitive to corrosion than SEM analysis, but less sensitive than the measured current. The series of EIS spectra obtained during a potentiostatic test are analyzed 360 (FIG. 5) to assess changes in the electrical properties due to surface degradation, the development of passive layers, and the stabilization or degradation of those layers. The stabilization of the EIS response is compared to the stabilization of the current measured in the potentiostatic test 365 to assess the stability of the surface. Stable non-zero anodic passive currents indicate that the surface is undergoing anodic corrosion at a much lower rate than was measured initially for the bare surface, due to presence of passivating layers. In summary, the invention enables measurement of the current in the presence of the passive layer likely to occur throughout the service life (so long as the underlying alloy can maintain that layer). Referring to FIG. 5, a Kramers-Kronig analysis was performed to confirm that the EIS spectra are reliable and extrapolate the results to low frequencies 370. The equivalent circuit analysis 375 for the stable EIS spectra collected near the end of the potentiostatic test at 0.2 VSCE shown in FIG. 1D represents the electrical properties of the stable passivated surface. Parameter values for the circuit components are determined by using commercial software. The DC current at any imposed potential is calculated from the EIS circuit using Ohm's law by treating the capacitors and constant phase elements as open circuits. Comparison of the measured and modelled currents 376 provides a method to determine if the equivalent circuit is appropriate. Large differences in the modelled and measured currents indicate that the equivalent circuit model is not appropriate. Small differences between the modelled current and the stable currents measured during the potentiostatic holds usually can be attributed to leakage current through the passivating layers that behave as imperfect capacitors. Comparison of the measured and modelled currents provides a means to determine the appropriate equivalent circuit. The steady currents measured at different applied voltages in potentiostatic tests conducted in the same solution are compared to determine the dependence of the material corrosion rate on the potential. Based on this comparison, an analytical expression is derived relating the measured passive or active current to the potential for potential ranges in which the corrosion behavior is the same. Likewise, the steady currents measured at the same applied voltage in the potentiostatic tests in a series of solutions in which one variable is changed (e.g., tests at different pH) are compared to determine the dependence of the current on that environmental variable. Based on these comparisons, an analytical expression that relates the stable current to individual or combinations of variables can be derived using multivariate regression analysis. The potential represents the solution redox and the current represents the material corrosion rate. Therefore, the analytical expression represents the corrosion behavior of a particular material in any environment of interest. FIGS. 6A and 6B are SEM images of a surface region before and after a Potentiodynamic scan. Specifically, FIG. 6A shows the material of interest 400 before the potential was applied and indicates areas representative of two different phases in the material, e.g., a first phase 405 is not visibly corroded. FIG. 6B depicts the material of interest 420 after corrosion at a fixed potential. As shown in FIG. 6B, significant corrosion has occurred in regions of the second phase 410 (specifically the spot 411 is completely corroded), while material of the first phase 405 has remained stable in the solution at the applied potential. The invention shows how corrosion may be localized and phase-specific. FIG. 7 depicts an example of how the EIS and potentiostatic tests are used in conjunction with each other to determine if a steady current is attained. FIG. 7A depicts current profiles for potentiostatic tests 505 performed at 0.2 VSCE and 0.4 VSCE in a solution with a 0.01M NaCl concentration at pH 3 and at room temperature. Those steady rates are compared with potentiodynamic scans 515 in FIG. 7B. The shapes of the current profiles and the constant currents that are achieved in potentiostatic holds at different voltages 355 (In FIG. 5) indicate whether active (curve 510 in FIG. 7A) or passive corrosion (curve 530) occurred. They provide additional insights to the corrosion process. For example, the random spikes in the current profile (curve 530), indicates the occurrence of metastable pitting. In contrast, the periodic current spikes 510 are instrumental artifacts from the electrochemical impedance spectroscopy scans run daily during the potentiostatic test. If the current profile reveals a sudden increase, then that may indicate a passive layer failed or could not be sustained by the underlying alloy phase during the potentiostatic test. A stable passive current (530) is attained in the PS test at 0.2 VSCE and stable active current (510) is attained in the PS test at 0.4 VSCE. The stable passive current (530) measured in the PS test at 0.2 VSCE and stable active current (505) measured in the PS test at 0.4 V are shown as small square symbols and compared with the potentiodynamic scan (530). The passive current attained in the PS test at 0.2 VSCE is about 10-times lower than the current measured in the PD at 0.2 VSCE, but the active current in the PS test at 0.4 VSCE is about 100-time higher than the current measured in the PD at 0.2 VSCE. This is because the high scan rate used in potentiodynamic scans excludes effects of the kinetically slow passivation occurring at 0.2VSCE and transpassive corrosion occurring at 0.4 VSCE. Those effects dominate the responses in the potentiostatic tests and are quantified by this method. The EIS graph 505 is a combination of sequential EIS analyses performed during potentiostatic tests. It depicts the current density over time in tests conducted at 0.4 VSCE (510) and 0.2 VSCE (530). The decreases in current density with time in the profiles of the 520, 530, and 540 curves indicate stabilization by formation of passive layers, whereas the increase in the 510 curve indicates active corrosion. The stable current density 530 attained represents the passive current for the stabilized surface and that attained in the 510 curve represents the active current expected to be maintained until the material is completely corroded. Plot 515 compares the passive current densities measured for the stabilized surfaces in the potentiostatic tests (squares) from graph 505 with the current densities measured for the bare surface during the potentiodynamic scan. This shows the degree of stabilization by the passive layers decreasing at increasing applied potentials until transpassive behavior occurs at a potential between about 0.3 VSCE (520) and 0.4VSCE (510). FIG. 8 shows the evolution of the surface electrical properties with the EIS results shown in Bode magnitude and phase angle plots. Both plots indicate how the passive layers stabilize over time: the impedance magnitude at the low frequency limit increases to a maximum value and the phase angles increase and become frequency-independent over time. Specifically, FIGS. 8A-D are examples of potentiostatic EIS results that show how surface electrical properties evolved in potentiostatic tests conducted at 0.2 VSCE and 0.4 VSCE. Results are shown as Bode magnitude plots (620 in FIG. 8A and 640 in FIG. 8B) and Bode phase angle plots (621 in FIG. 8C and 641 in FIG. 8D). The numerals indicate the reaction time (in days) at which the EIS was performed. Differences in the Bode magnitude and phase angle plots indicate different passivation layers formed in tests at different voltages. The layers formed at 0.2 VSCE 620 stabilized to yield high impedance and phase angle values within 5 days, while the layers formed initially at 0.4 VSCE 640 destabilized to yield low impedance and phase angle values within one day. FIG. 9 shows potentiostatic EIS data as Nyquist plots for passivating material. The EIS were performed after 1, 2, 3, and 5 days (graph 705). Nyquist plots (graph 710) were also generated for actively corroding material from EIS performed after 1, 2, and 3 days. The sequence of EIS Bode and Nyquist plots shows the evolution of the material surface electrical properties as the passive layers stabilize over time, as well as indicating when different layers have formed. The EIS results are evaluated using equivalent circuit analyses, wherein the measured electrical behavior is represented by an electrical circuit having the same frequency dependency. Specifically, FIG. 10 is an example of how the EIS analysis showing the measured values and theoretical values is used to develop an equivalent circuit having the same frequency dependencies measured in the EIS analysis of the stabilized surface in the PS test at 0.2 VSCE. FIG. 10 shows the relationship between measured EIS observations (FIG. 10A) and an electrical circuit (FIG. 10B) derived from those observations. The circuit comprises elements representing the impedances provided by charge transfer resistance (Rct), solution resistance (Rs), double layer capacitance (Qdl), and an RC-sub-circuit (Qα and Rα, Qβ and Rβ) representing the passive layer. (Constant phase elements Qdl, Qα, and Qβ are used to represent imperfect capacitors, which represent imperfect passive layers.) Both the circuit configuration and values of the circuit elements are selected such that the AC frequency response of the circuit matches that measured experimentally. Furthermore, the DC current calculated to flow through the equivalent circuit at the voltage imposed in the test is compared with the stable current measured during the test to discriminate between alternative equivalent circuits. This provides confidence that the circuit is physically meaningful. The circuit elements quantify the physical and chemical processes affecting the alloy corrosion rate in the natural system that imposes the same surface potential. The derived circuit 900 in FIG. 10B, is designed to be consistent with the EIS data (820, in FIG. 10A) collected at the end of each PS test to represent the stabilized surface. As such, the circuit verifies predictions derived from EIS and electrochemical tests.) In the plots shown as graph 820, the data are shown as squares 822 and the model results using the equivalent circuits are shown as circles 821. The equivalent circuits for the EIS results from PS test at 0.2 VSCE 815 and 820 are consistent with the visual similarities in the shapes of the Bode plots, and both are different from results of EIS from the PS test performed at 0.1 VSCE. The various capacitors, resistors, and constant phase elements (CPEs) used in the circuit (FIG. 10B) represent the physical processes affecting the materials corrosion as discussed, supra. However, different or additional circuit elements may be required to represent different surface behaviors. For example, there can be separate R and Q elements when more than one passive layer forms. (Only the alpha layer is shown in the figure.) Further, there may be an O circuit element when the working electrode is a rotating disk electrode. (O element is known as an open-finite-length-diffusion circuit.) This element may also be used when coatings or passive films are present. A T circuit element may be included to represent a film which contains a particular amount of electroactive substance. As such, it can be used in thin layer electrochemistry scenarios. Once the electroactive materials have been consumed, they cannot be replenished. (The behavior is observed in batteries or supercapacitors, such that a T circuit element yields relevant characteristic data for those applications.) The best fit values of the circuit components determined during the equivalent circuit analyses 815 are used to calculate the theoretical DC current at the imposed potential used in the PS test it represents. The CPEs are treated as open circuits and the Warburg components are treated as short circuits in these calculations. Close agreement (e.g., within a factor of 10 times) between the stable current measured during the PS test and the DC current calculated by the equivalent circuit provides confidence that the equivalent circuit represents the stabilized surface. Significant differences between the measured and modelled currents indicate the equivalent circuit is not appropriate. FIG. 11 shows a physical model of the stabilized surface (shown as a cross section). As discussed above, the EIS analyses were performed periodically during the potentiostatic tests to quantify the electrical impedance properties of the surface layers that attenuated the alloy corrosion rate. The total impedance includes contributions from surface layers which form over the constituent phases. A physical model may be derived that relates the elements in the equivalent circuit 900 to the surface layer structure 910. In these diagrams, the left side of the equivalent circuit in 900 corresponds with the bottom surface of the alloy in 910 and the right side of the equivalent circuit in 900 corresponds with the reference electrode in the solution above the material surface (not shown). The capacitor QDL 909 represents the double layer capacitance at the solution/oxide surface layer interface and resistor Rs 907 represents the resistance of solution between the double layer and the reference electrode in the solution (not shown). The resistor RCT 911 represents the combined charge transfer resistance of all anodic reactions occurring on all alloy surfaces. The two RC sub-circuits 913 and 914 represent the impedances provided by the passive layers that form and are referred to generically as the α and β sub-circuits. As discussed supra, the circuit can be used to estimate current at applied voltages other than that used in the potentiostatic test from which the circuit was derived. The range of potentials for which the circuit is appropriate is related to the stability ranges of the passivating oxides represented by the α and β sub-circuits. The component values quantify the electrical properties of the stable passive surface. In this example, the physical model shows that the Warburg element 915 in the α sub-circuit 913 represents degradation of the oxides formed over ZrFe2 phases that provide the primary current path during passive corrosion. This assignment is based on SEM analyses that show Phase 1 corrodes preferentially during potentiodynamic scans (FIG. 1B). The key aspects of the equivalent model 900 and physical models 910 are (1) the oxides represented by the α and β sub-circuits form over all constituent phases of the multiphase material, and (2) the Warburg element in the α sub-circuit represents less stable regions of the oxides that form over domains of the least durable alloys. Warburg elements can be used to represent degradation of weakly passivating layers that provide the primary current path during passive corrosion. This assignment is based on SEM analyses that shows a particular phase corrodes preferentially during potentiodynamic scans (FIG. 1A). The key aspects of the equivalent model 900 and physical models 910 are (1) the oxides represented by the α and β sub-circuits form over all constituent phases of the multiphase material, and (2) the Warburg elements represents less stable regions of the oxides that form over domains of the least durable alloys. Scanning Electron Microscopy Detail The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at and near the surface of solid specimens, including backscattered electrons, scattered secondary electrons, and X-rays. The signals that derive from electron-sample interactions reveal information about the sample including external morphology, chemical composition, and crystalline structure and orientation of materials which make up the sample, and a 2-dimensional image is generated that displays spatial variations in these properties. Areas with dimensions ranging from approximately 1 cm-1 micrometers can be imaged in a scanning mode using conventional SEM techniques. The SEM allows for precise measurement of very small features and objects. Secondary electron images are sensitive to contour. Backscattered electron images (BSE) are sensitive to atomic number and can be used for rapid discrimination of phases in multiphase samples. Analysis of the X-rays that are generated when the incident and scattered electrons interact with the specimen provide compositional information. In the claimed method, SEM analyses with associated energy-dispersive X-ray emission spectroscopy (EDS) are used to identify phases based on qualitative chemical analysis and electron backscattering efficiency. Application of Faraday's Law The steady-state corrosion rate calculated with Faraday's law relates the mass corrosion rate to the current density and alloy composition based on the number of electrons consumed during the anodic corrosion reactions as Rate = i corr W F where icorr is the corrosion density, W is the equivalent weight of the alloy, and F is Faraday's constant (96,485 coulomb mol−1). The equivalent weight of an alloy is a weighted average of values M/z for each of the major alloying elements in the alloy calculated as 1 W = 1 ∑ j M ( j ) f ( j ) z ( j ) where M(j) is the atomic weight of component j, f(j) is the mass fraction of component j in the material, and z(j) is the number of electron equivalents per mole of oxidized component j.Waste Forms Waste forms need to be designed to be corrosion resistant when contacted by the range of seepage water compositions likely to occur in a breached waste package throughout the regulated service life of a disposal facility. The chemistries of those seepage waters will be affected by container corrosion products, radiolysis, and the range of corrosion products generated during the degradation of backfill materials, neighboring waste forms, and the waste form itself. In the US, generic disposal systems constructed in granitic, argillite, and salt formations must be evaluated for the possible co-disposal of glass, glass/ceramic, and metal waste forms with directly-disposed spent fuel. This requires that the degradation behaviors of waste forms in a wide range of possible seepage water compositions be considered during the design of the waste forms and other EBS components. The phases formed in an alloy waste form depend on the compositions and relative amounts of cladding, fuel wastes, and added trim metals used to produce it. Steel cladding dominates most waste streams generated during the processing of fast reactor fuels. The predominant phases present in the waste forms will be Fe-based intermetallics and solid solutions. Zirconium-based cladding is used for commercial fuel and various Zr—Cr based systems forming Zr intermetallics and solid solutions are being evaluated as possible waste forms. Stainless steel-based waste forms were developed in the 1990s to immobilize high-level radioactive wastes from the electrometallurgical treatment of used sodium-bonded nuclear fuel. These metal waste forms were produced by alloying residual metallic fuel wastes and steel cladding hulls recovered from the electrorefiner with small amounts of trim metals. A multiphase alloy resulted, comprised of physically, chemically, and radiologically durable intermetallic and solid solution phases that host radionuclides. Most of the current inventory of used fast reactor fuel is in AISI Type 316L stainless steel cladding but future fuels may be clad in HT9-like stainless steel. The alloy waste forms made with Type 316L steel are being used as benchmarks for the metal waste forms being developed for HT9-clad fuels by adding trim Cr and Ni to attain overall waste form compositions similar to those made with Type 316L cladding. Therefore, the impact of the different steel-based cladding materials on the waste form composition will be due primarily to the amounts of passivating constituents added as trim. The material may comprise a metal or alloy, including homogenous or multiphase alloys and alloy-oxide composites, or any combination thereof. Further, the material may comprise any conductive material which corrodes by a mechanism involving electron transfer. The materials' microstructure and phase composition are characterized by scanning electron microscopy with x-ray emission spectroscopy to identify phases and alteration products. The overall dependencies on the environmental conditions measured using multi-phase materials represent the dependence of whichever constituent phase provides the dominant anodic corrosion current at the potential of interest. While this makes it possible to model the overall alloy degradation, Tc-99 and other radionuclides are not uniformly distributed between the constituent phases. The dependence of the release rate of Tc-99 (and other radionuclides) on the potential will probably have a different functional form than does the dependence of the overall corrosion current. Therefore, measuring the Tc-99 released to solution during electrochemical experiments is as important as measuring the anodic corrosion current. The sensitivity of the Tc-99 release to the electrochemical potential must be determined as an empirical parameter. Whereas the anodic current represents the sum of several oxidation reactions that lead to waste form degradation, the cathodic current represents the sum of many cathodic reactions taking place on the surfaces of the constituent phases that are coupled with the anodic reactions. The key processes controlling the cathodic current are electron transfer (reduction) at the charge transfer surface and mass transport of the oxidizing agents to the charge transfer surfaces. Parameters to be used in the model to take into account the partial anodic and cathodic processes are obtained from experimental data that provide the overall response for multiple species and reactions. Preferably, only the contributions of reactants that are tracked in performance assessment calculations for a disposal facility re considered explicitly, while the effects of minor reactions should be taken into account implicitly through the measured values of the model parameters. These are represented by the standard solutions (and relevant variations) that bracket possible environments in the disposal system. Specific experiments focus on the responses to the combined effects of pH, dissolved oxygen, and dissolved Cl— in several solutions to determine analytical expressions to model those variables. This approach is consistent with environmental variables that are tracked in performance assessment calculations. A representative alloy waste (RAW) form is analyzed by a potentiodynamic scan to measure the propensity for corrosion in the solution of interest. The solution in this example is 0.01 M NaCl adjusted to a pH of 3 at room temperature. The scan indicates the corrosive potential, the range in which it is passivated, and the potential at which it becomes transpassive. An SEM scan is performed to show the preferential corrosion of Phase 1 in Fe—Ni—Zr. Laboratory-scale ingots of the exemplary waste forms materials were produced by melting mixtures of AISI Type 316L stainless steel chips with Zr wire and metal powders in an ultra-pure argon atmosphere at about 1650° C. and 1600° C., respectively, for about 2 h. Polished cross sections of each material were prepared to characterize the microstructure and measure the compositions of the constituent phases by using an SEM (Hitachi S-3000N) with associated energy-dispersive X-ray emission spectroscopy (EDS; Thermo-Noran System Six or Thermo Scientific UltraDry). The consistencies of the microstructures and phase compositions in each ingot were assessed by areal analyses of broad cross sections, spot analyses of individual phases at locations throughout the cross-sections, and line profiles spanning phase domains and phase boundaries. Specimens used in the electrochemical tests were cut from each ingot as parallelepipeds with dimensions of about 1×2×15 mm3 by using a low-speed saw with a diamond wafering blade and water lubrication. Each test specimen was first fixed in acrylic resin and a copper wire was attached to the back end of the specimen using conductive epoxy. The assembled specimen and lead wire was then core-drilled and embedded in epoxy to produce a rod-like electrode with one end of the specimen exposed at the front end of the electrode and the wire protruding from the back end. Each electrode was made to be about 6 mm in diameter and 6 cm long, which is long enough for use in the microcell reactor during the electrochemical tests but short enough to fit into the sample holder of the SEM for microscopic characterization. Several electrodes were made with specimens cut from each material for use in electrochemical tests and care was taken to polish all electrodes to a similar final surface finish. The approximately 1×2 mm2 specimen surface exposed at the face of each electrode was polished to a final 1-μm finish with a series of abrasive papers and water lubrication followed by a final polish with a silica slurry. The face of each polished electrode was characterized with SEM to ensure no gaps had formed between the specimen and acrylic resin during production of the electrode. The detailed microstructures in several areas on the electrode surface were documented for later comparisons with analyses to be conducted after the tests were completed to determine which phases had corroded. Regions with phases having recognizable shapes or other unique features that served as fiducial markers were selected to help locate the same areas after corrosion. The exposed geometric surface area of the RAW material in each electrode was measured by using the SEM to normalize the currents measured during the electrochemical tests as current densities for direct comparisons. The normalized current densities can also be scaled to represent full-size waste forms. All electrochemical tests were conducted at room temperature in about 15 mL of an air-saturated acidic NaCl solution (0.1 mmolal H2SO4+10 mmolal NaCl adjusted to pH 4) in a 20-mL glass microcell (Princeton Applied Research). These conditions are used to represent seepage water that has interacted with bentonite backfill and then been acidified by corrosion of the waste package and radiolysis to about pH 4. Electrodes made from specimens of two different materials (RAW-2 and RAW-4) were used as the working electrodes in separate tests conducted in a cell with a KCl-saturated calomel reference electrode (SCE) and graphite counter electrode. Unless stated otherwise, voltages are reported relative to the SCE as VSCE. Tests were performed using a computer-controlled potentiostat, such as VersaSTAT 4 (Princeton Applied Research, Oak Ridge Tenn.) programmed with the protocols for each method, including scan ranges and rates, applied potentials, and hold times. Commercial software such as Versa Studio (Princeton Applied Research) was used to analyze the data and generate standard plots. Tests were conducted using parameter values that exceed the anticipated ranges for disposal conditions to determine analytical expressions for the effects of environmental variables that can be used in the degradation model. For example, solution redox potentials higher than 0.6 VSCE may not be physically achievable in disposal systems, but tests at even higher potentials are being used to augment the mechanistic understanding of the degradation process and reliably quantify the dependence of the corrosion rate on the environmental redox, including strongly reducing and strongly oxidizing conditions that could occur in localized microenvironments. Responses of small electrodes are sensitive to differences in the relative amounts of constituent phases that occur on the mm-scale due to cutting different specimens from the ingot and minor differences on the μm-scale due to polishing the specimen surface for reuse of the electrode in several tests. Small but significant differences in test responses highlight the effects of the relative amounts of constituent phases exposed at the face of the electrode on the corrosion behavior and the contributions of phase and grain boundaries. Series of PS tests were conducted at applied voltages selected to represent the cathodic, active, passive, and transpassive regions for each material observed in the PD scans to measure the evolution of the currents until they attained a constant rate representing the steady corrosion of a passivated surface or active corrosion. The voltages applied in the PS tests were used to represent the corrosion potentials that would be attained at the alloy surface when contacted by seepage water having a chemical composition with that redox. Therefore, the currents measured in a PS test at a particular imposed potential represent the corrosion currents that would be attained when the material is contacted by a solution with that value. Although the corrosion rates of the stabilized surfaces that form at fixed voltages representing the range of solution redox (Eh) values are of primary interest for modeling waste form performance, the electrical properties of those surfaces and the capacity of the waste form to maintain them provide confidence in their long-term stability. The use of a potentiostat ensures the potential will remain constant throughout the test to quantify the dependence of the corrosion rate on the Eh, while simultaneously measuring the dependencies on the solution composition and temperature. The potential at which the cathodic and anodic currents are equal and the measured current density is zero is traditionally referred to as the corrosion potential (ECORR). Electrodes made from specimens of two different materials (RAW2 and RAW4) were used as the working electrodes in separate tests conducted in a cell with a KCl-saturated calomel reference electrode (SCE) and graphite counter electrode. The gross compositions in mass percent of the different materials were as follows: FeCrNiMoMnSiZrUTcRuPdRhNbRAW239117.44.61.00.39.72.43.711.37.62.00RAW451149.71.71.20.415211111 Scoping tests indicated neither RAW-2 nor RAW-4 completely stabilized in the acidic NaCl test solution due to formation of slowly stabilizing passive films that we refer to as open circuit (OC) films. Therefore, the electrode was immersed in the test solution and cathodically cleaned at about −0.3 VSCE for a few minutes and then left at open circuit (i.e., with no applied voltage) for about eight hours to equilibrate with the solution and form the OC film prior to each PS test. This step as was done to provide a consistent surface at the beginning of each PS test, even though it was not fully equilibrated with the solution. EIS analyses were performed prior to the PS tests to characterize the OC film and then characterize the initial response of the surface to the voltage applied during the PS test. All EIS analyses were conducted with scans from 10 kHz to 1 mHz with the electrode held at the PS voltage and required about 2 hours to complete. The PS tests were conducted as sequential loops of PS hold and EIS analyses to assess the surface corrosion behavior as it stabilized at different potentials. Potentiostatic tests measure the corrosion rates under a range of potentials to represent solution redox (Eh) values that could occur in a disposal system during and after the generation of passivating or leached layers on constituent phases. Tests are conducted under different conditions to derive equations for the corrosion rate dependence on alloy composition and environmental variables. (Such variables include solution Eh, pH, chloride concentration, etc.). An equivalent circuit having the same AC frequency dependency as measured in the EIS of the stabilized surface is derived. The direct currents calculated from that circuit at the same voltages can be compared with the stable currents measured in the potentiostatic tests to verify that the circuits represent the stabilized surfaces. The tests are designed to span a range of possible conditions which could occur in geological disposal facilities. The environmental changes occurring in each facility will be due to several differing factors which cause the natural Eh (redox potential) to rise or fall. The method of this invention characterizes the corrosion behavior of a material in most of the possible environments, both present and future, giving a better idea of the long-term performance likely to be observed in each environment. Tests were being conducted using several representative alloyed waste form (RAW) materials for steel-clad fuel that provide a range of waste form compositions. Also used were several electrolytes representing the range of chemical conditions that could occur within breached waste packages in various disposal systems due to the effects of radiolysis and corrosion of other EBS components and waste forms. A potentiostat is used to directly apply surface potentials on specimens that represent the range of solution redox (Eh) conditions that could occur in seepage waters. Potentiostatic (PS) tests are conducted at several fixed voltages to measure the evolution of the corrosion current as the waste form surface corrodes or stabilizes over several days. Voltages were selected to characterize alloy corrosion under conditions expect to lead to cathodic, active, passive, or transpassive behaviors based on the results of a potentiodynamic (PD) scan conducted in the same solution to show the propensity of the bare surface for passivation. A series of PS tests quantify the effect of the solution chemical and redox conditions on the anodic current as either active corrosion continues or the surface equilibrates under the applied conditions and stable passivating layers form. The current is monitored continuously during the PS hold and the electrical properties of the surface are measured daily by using electrochemical impedance spectroscopy (EIS). The cycle of PS hold-EIS is repeated to assess the stability of the electrode surface in the solution based on the capacities of the alloy phases that constitute the waste form to maintain effective passive layers. The electrochemical responses are correlated with changes in the microstructure of the electrode surface based on examinations made before and after the tests by using a scanning electron microscope (SEM) and with the measured concentrations of radionuclides (or surrogates) and host phase constituents that are released into the solution during the PS test to identify the reactive phases. The combined results are used to derive equivalent circuit and physical models of the waste form degradation behavior. In summary, the invention provides a method for predicting corrosion rates of a material during service conditions. Service conditions are defined by particular solution composition and redox potential. The invented method comprises creating the service conditions, determining the redox potential of the service conditions, exposing the material to the service conditions, and maintaining the redox potential of the service conditions by using a potentiostat for a time sufficient to evaluate changes of the exposed material. Subsequent solutions analysis identifies elements of each phase and characterizes element distribution of each phase. Solutions analysis identifies elements of each phase and characterizes element distribution of each phase. Dependencies of the redox reaction on environmental variables and parameter values are measured empirically for several alloyed materials to represent a range of metallic waste form compositions under conditions which span a range of environmental conditions which occur in a geological disposal system. Separate tests are conducted, measuring the stable current density, surface properties, and radionuclide release into a solution at several potentials. The tests are conducted in several solutions determining empirical dependencies on solution properties; wherein the properties include pH and CI concentrations, at several imposed surface potentials, and at several temperatures. The electrochemical reactions resulting from the material contacting solution(s) representing the service conditions are modeled using electrode kinetics theory. Through the use of potentiostatic scans, potentiostatic hold tests and electrochemical impedance spectroscopy, key variables affecting corrosion rates of a material are identified. The derived degradation model is therefore based on analytical functions that take into account the effects of environmental variables on the electrochemical oxidation reactions with a multiphase alloy during active and passive corrosion, the attenuating effect of surface passivation, and the release of oxidized radionuclides into the solution. The electrical properties of a surface are characterized periodically using EIS while the material is maintained at a polarized potential determined by the potentiostatic tests. Potentiostatic tests measure the corrosion rates of a material stabilized at a voltage representing a particular solution redox. EIS is performed simultaneously with the potentiostatic hold tests and periodically to assess passivation of the surface. EIS measures the electrical stability of the material surface, characterizing the interface between the material and the solution. The electrochemical processes are performed at a constant voltage in different chemical environments that are held constant during each test. Tests in environments that differ by a single variable are used to derive an analytical equation relating the corrosion rate to key environmental variables. The aforementioned variables are incorporated into analytical models quantifying the effects of environmental variables that can be used to calculate long-term corrosion performance in evolving conditions. For example, the invention relates electrochemical corrosion behaviors to the release rates of radionuclides of a waste form. This allows for the formulation of metal waste forms that are durable over the wide range of redox and chemical conditions that could occur in a geologic repository. An equivalent circuit quantifying passivation properties was also developed to add confidence to long-term predictions, wherein the circuit is based on the aforementioned parameterization of the electrochemical processes. The physical model consistent with the measured structural and electrical behaviors is based on electrochemical principles applied to a multi-phase waste form. It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” “more than” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. In the same manner, all ratios disclosed herein also include all subratios falling within the broader ratio. One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the present invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Accordingly, for all purposes, the present invention encompasses not only the main group, but also the main group absent one or more of the group members. The present invention also envisages the explicit exclusion of one or more of any of the group members in the claimed invention. |
|
062263404 | summary | TECHNICAL FIELD This invention relates to a control rod for a nuclear reactor and, more specifically, to a thermal reactor lumped control material having increased control worth by virtue of hermaphroditic absorber loading. BACKGROUND Control materials (poison), such as control rods, are employed in, for example, nuclear reactors to perform duel functions of power distribution and reactivity control. Power distribution in the core is controlled during the operation of the reactor by manipulation of selected patterns of rods that enter from the bottom of the reactor core. Each control rod in its power distribution function may experience a similar or a very different neutron exposure than other control rods in the control system. Control rods are generally cruciform in cross section and typically comprise a plurality of absorber tubes extending axially in each wing of the rod. In one design, the tubes are filled with boron carbide powder and seal-welded at their ends with end plugs. The powder is separated into sections or segments. In another design, the tubes are filled with capsules of discrete lengths containing the boron carbide powder. A plurality of stainless steel capsules are stacked in each tube with the tubes lying side by side in each wing of the control rod, generally in parallel with the long axis of the rod. These capsules or segments, for example, may have lengths of one foot or more. Control materials such as control rods having higher worth are important to obtain adequate control for thermal reactors that incorporate mixed oxide fuels and may have an economic benefit for uranium-fueled thermal reactors. Thermal reactor poison loadings are usually characterized by periodically distributed masses of strong thermal absorbers, particularly boron carbide. Because of the short mean free path of thermal neutrons in such a mass, most of the absorptions occur near the surface of the mass, and the remainder of the poison mass is less effective as a thermal absorber. This effect can be better understood by a lumped mass of boron carbide in a neutron flux field, where the neutrons are assumed to have a spectral distribution consistent with a thermal reactor spectrum. The thermal neutrons in this field are strongly absorbed by the poison at the surface of the boron carbide (the "onion skin" effect). The resulting neutron distribution in the interior of the poison mass has a much lower fraction of thermal neutron than the external field. Therefore, the absorber in the interior of the poison mass has a much lower neutron absorption rate. This effect is compounded by the fact that boron carbide is a "1/v" absorber--i.e., its cross section is inversely proportional to the neutron energy; therefore, boron carbide in the center of a poison mass is much less effective at absorbing neutrons than the same material at the surface of the mass due to spectral hardening. The strength of the control rods in a nuclear reactor helps define the amount of fissile material that may be loaded in the core while assuring that the fission reactions in the core may be curtailed at any time. Stronger control rods permit the loading of a larger fissile inventory without corresponding increases in integral burnable absorbers (e.g., Gadolinia). Similarly, they also ease the introduction of mixed-oxide fuel. Because of the larger thermal absorption cross section of plutonium, such fuel makes conventional boron carbide loaded control rods less effective, not only because of the spectral change due to absorption hardening, but also because of a decrease in the flux in the vicinity of the lumped poison (for a fixed number of neutrons, there is a greater fraction absorbed in the more strongly absorbing discrete fuel masses). As with all high worth absorbers, higher worth implies faster destruction of absorber atoms. Unless a chain absorber (an element where nuclides transmute with neutron absorption, either directly or indirectly through radioactive decay, to other nuclides with large absorption cross sections) is used, the time span that such a lumped poison may be used is shorter than a lumped poison with a lower worth. DISCLOSURE OF THE INVENTION According to the present invention, the control worth of a thermal reactor lumped control material such as a control rod is increased by spatially varying the absorber material to adjust for changes in the neutron spectrum within the lumped absorber mass. The invention exploits the inherent spatial change in the neutron spectrum within a lumped poison mass in a thermal reactor neutron flux field. This is done by creating a hermaphroditic poison mass--i.e., a poison mass that incorporates two types of absorbers, the first being a strong thermal absorber near the surface of the mass, and the second being a strong resonance absorber in the interior of the poison mass. The outer regions of the poison mass are comprised of a strong "1/v" thermal absorber such as boron carbide. The inner region of the poison mass is comprised of a resonance absorber, such as hafnium. This resonance absorber more appropriately exploits the hardened characteristics of the neutron spectrum within the absorber mass by selectively absorbing the epi-thermal neutrons. Alternatively, a mixture such as a mixture of hafnium, dysprosium and europium, or a single material that has both large thermal and resonance neutron absorption cross sections may be used as the resonance absorber with the thermal absorber such as boron carbide disposed surrounding the mixture or single material. The creation of the hermaphroditic poison mass permits an increase in the control material worth while maintaining the external dimensions of the structure containing the control material, such as the control rod. |
abstract | The invention relates to a method for obtaining images from slices of a specimen, the method comprising: repeatedly obtaining an image of the surface layer of the specimen (1) and removing the surface layer of the specimen, thereby bringing the next slice to the surface; characterized in that after at least one of the removals of a surface layer the specimen is exposed to a staining agent. |
|
claims | 1. An isotope energy recovery system, the system comprising:a shielded spent nuclear fuel storage cask being sized to contain nuclear fuel rods including the isotope;reflective surfaces within the storage cask and around the fuel rods;an excimer medium surrounding the fuel rods in the path of radiation decay from the isotope, wherein the excimer absorbs the radiation decay and emits photons in response;a photovoltaic cell disposed to receive the photons;connections external to the storage cask for a load to draw power from the photovoltaic cell. 2. The system of claim 1, wherein the isotope comprises an alpha emitter. 3. The system of claim 2, wherein the isotope consists of an alpha emitter. 4. The system of claim 1, wherein the isotope comprises a beta emitter. 5. The system of claim 4, wherein the isotope consists of an beta emitter. 6. The system of claim 1, wherein said excimer medium comprises a gas excimer. 7. The system of claim 6, wherein said excimer medium comprises a gas plenum contained in said storage cask under pressure. 8. The system of claim 1, wherein said excimer medium comprises a liquid. 9. The system of claim 8, further comprising a lightpipe to isolate said photovoltaic cell and to direct photons toward said photovoltaic cell. 10. The system of claim 1, wherein said excimer medium comprises a solid. 11. The system of claim 1, wherein said storage cask comprises opposite top and bottom ends and said photovoltaic cell is disposed on one of the top and bottom ends of said cask and is shielded with material transparent to photons. 12. The system of claim 1, wherein said photovoltaic cell lines walls of said reflective surfaces. 13. The system of claim 1, further comprising a heat to energy conversion device attached to the storage cask. 14. The system of claim 1, wherein the storage cask is table top sized and the fuel rods are processed to fit with the table top sized storage cask. 15. The system of claim 1, wherein the fuel rods are unprocessed. |
|
051611767 | claims | 1. An exposure apparatus, comprising: a light source for emitting a light beam and for exposing a wafer through a mask along an exposure path; light blocking means being movable and effective to block the light beam emitted from said light source to limit an exposure zone; positional deviation detecting means for detecting positional deviation between the mask and the wafer and for producing a detection signal; and drive control means for moving said light blocking means to execute position control therefor, on the basis of the detection signal produced by said positional deviation detecting means, wherein said light blocking means is disposed along the exposure path between said light source and the mask and is disposed between said position detecting means and the mask. detecting means for detecting the relative position of the mask and the wafer said detecting means supplying a light beam to alignment marks of the mask and the wafer for detection of the relative position therebetween; and aperture means for variably defining a zone for irradiation of the mask with the X-rays, said aperture means being disposed between the mask and said detecting means with respect to the direction of supply of the X-rays, and said aperture means having a plurality of blades and a plurality of independent blade driving means associated with the plurality of blades, respectively; wherein a clearance is defined between adjacent blades, in the direction of the supply of the X-rays; wherein each blade has an irradiation zone limiting side edge having an end face which is inclined so as not to be irradiated with the X-rays; and wherein each of the plurality of blade driving means is adapted to support an associated one of said blades substantially at the middle thereof with respect to the zone limiting side of the blade. projecting, from a mark detecting means, a light beam to an alignment mark provided for mask-to-wafer alignment; moving a movable blade of an aperture means to variably define a range for X-ray irradiation of the mask, wherein the movable blade is disposed between the mark detecting means and the mask with respect to a direction of projection of the X-rays; detecting the position of the blade by using the light beam; controlling the movement of the blade on the basis of the detection; and projecting X-rays to the mask through the aperture means. 2. An apparatus according to claim 1, wherein the wafer is divided into plural exposure zones and wherein the exposure of the wafer is executed in a step-and-repeat manner in which the divided exposure zones are exposed in sequence. 3. An apparatus according to claim 1, wherein said light blocking means comprises four light blocking members corresponding to four sides of each exposure zone of rectangular shape and wherein each light blocking member is movable reciprocatingly along a straight line. 4. An apparatus according to claim 1, wherein said positional deviation detecting means comprises optical detecting means for optically detecting the relative position of the wafer and an alignment mark which is provided outside a circuit pattern forming area of the mask. 5. An exposure apparatus for exposing a mask and a wafer with X-rays to print a pattern of the mask on the wafer, said apparatus comprising: 6. In a semiconductor device manufacturing exposure method for exposing a wafer to a mask with X-rays to print a pattern of the mask on the wafer, the improvement comprising the steps of: 7. A method according to claim 6, wherein the movable blade blocks the X-rays but transmits the light beam. |
062352237 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention and its advantageous will be explained in further detail below in terms of a reference sintered nuclear fuel body or compact, which has been produced approximately in accordance with German Published, Non-Prosecuted Patent Application DE 38 02 048 A1, and for sintered nuclear fuel bodies according to the invention including (U, Pu)O.sub.2 mixed crystal: In order to produce the reference sintered nuclear fuel body, 70 g of UO.sub.2 powder and 30 g of PuO.sub.2 powder are mixed with 1 g of zinc stearate powder and ground for 16 hours in a ball mill. The ground product is then granulated in a granulating vessel and mixed in a conical mixer with a further 400 g of UO.sub.2 powder. Some of this mixed powder is then compressed into a body with a density of from 5.4 g/cm.sup.3 to 6.5 g/cm.sup.3 . This compressed body or compact is sintered in the sintering atmosphere, which includes 4% hydrogen and 96% nitrogen. The natural oxygen impurities in the nitrogen bring about an oxygen partial pressure of 10.sup.-20 atmospheres. After a holding time of 3 hours for the sintering, the sintered nuclear fuel body is cooled down in the sintering atmosphere. The final result is a reference sintered nuclear fuel body with a sintering density that is 95.7% of the theoretical density and an open porosity of 1.9% of the total volume of the reference sintered nuclear fuel body. The (U, Pu)O.sub.2 mixed crystal of the reference sintered nuclear fuel body has a mean particle size of 5.1 .mu.m. In order to produce a first sintered nuclear fuel body according to the invention, the same starting quantities of powdered UO.sub.2 and powdered PuO.sub.2 as in the production of the reference sintered nuclear fuel body are mixed, but together with one gram of powdered aluminum distearate, and compressed and sintered in the same way as in the production of the reference sintered nuclear fuel body. The result is a first sintered nuclear fuel body according to the invention, having a density of 95.5% of the theoretical density, an open porosity of 1.3% of the total volume of the sintered nuclear fuel body, and a mean particle size of the (U, Pu)O.sub.2 mixed crystal of 8.2 .mu.m. In order to produce a second sintered nuclear fuel body according to the invention, 470 g of powdered UO.sub.2, 30 g of powdered PuO.sub.2 and 250 ppm of TiO.sub.2 are mixed together. The mixture is then ground for 45 minutes in an attritor mill with steel balls. The ground product is then granulated for 20 minutes, and some of this granulated ground product is finally compressed into a body having a density of 5.4 g/cm.sup.3 to 6.5 g/cm.sup.3. This body is sintered in the same sintering atmosphere and in the same way as the body for producing the reference sintered body. The result is a second sintered nuclear fuel body according to the invention, having a density of 96.3% of the theoretical density, an open porosity of 0.4% of the total volume of the sintered nuclear fuel body, and a mean particle size of the (U, Pu)O.sub.2 mixed crystal of 28 .mu.m. An identical body to that used for making the reference sintered nuclear fuel body is heated in the same sintering atmosphere as in the production of the reference sintered nuclear fuel body to 1750.degree. C. and held at this temperature for one hour. CO.sub.2 gas is then added to the sintering atmosphere in increasing amounts until an oxygen partial pressure in the sintering atmosphere of 10.sup.-8 atmospheres is brought about. At the same time, the sintering temperature of 1750.degree. C. is maintained for a further two hours. The feeding of CO.sub.2 is then terminated, and the sintered body is cooled down in the hydrogen-containing sintering atmosphere. The result is a third sintered nuclear fuel body according to the invention, having a density of 95.3% of the theoretical density, an open porosity of 0.08% of the total volume of the sintered nuclear fuel body, and a mean particle size of the (U, Pu)O.sub.2 mixed crystal of 15 .mu.m. Finally, an identical body as in the production of the first sintered nuclear fuel body according to the invention is sintered and cooled down in the same sintering atmosphere as in the production of the third sintered nuclear fuel body according to the invention and in the same manner as in the production of this third sintered nuclear fuel body. The result is a fourth sintered nuclear fuel body according to the invention, having a density of 95.2% of the theoretical density, an open porosity of 0.03% of the total volume of the sintered nuclear fuel body, and a mean particle size of the (U, Pu)O.sub.2 mixed crystal of 29 .mu.m. Similarly advantageous values for the density, open porosity and mean particle size of the mixed crystal and therefore a correspondingly good retention capability of the sintered nuclear fuel bodies for gaseous fission products can be attained by the method according to the invention even if the UO.sub.2 powder that is used is produced, not by the ammonium uranyl carbonate (AUC) method as is the UO.sub.2 powder for the reference sintered nuclear fuel body and the four sintered nuclear fuel bodies according to the invention, but rather by the ammonium diuranate (ADU) method or by dry conversion (see the book entitled "Gmelin Handbuch der Anorganischen Chemie" [Gmelin Manual of Inorganic Chemistry], Springer-Verlag Berlin, Heidelberg, N.Y., 1981; Uran, Erganzungsband A3 [Uranium, Supplemental Volume A3], pp. 99-115). Using the four sintered nuclear fuel bodies according to the invention, including (U, Pu)O.sub.2 mixed crystal in a high-power nuclear reactor during four usage cycles showed that only about half as much fission gas is released during the four usage cycles, as compared with the reference sintered nuclear fuel body including (U, Pu)O.sub.2 mixed crystal. |
041893484 | summary | This invention relates to nuclear fuel elements formed with a large number of depending fuel rod assemblies attached to and depending from an overhead support having a manifold system connected to each fuel rod assembly for the extraction of fission product gases generated by nuclear fuel during fission. Nuclear fuel rod assemblies having solid nuclear fuel therein are often supported or hung by their upper ends to a grid-like support formed of interconnected beams having a manifold passageway system within the beams connected to each of the respective fuel rod assemblies for conveying gases therefrom. Such a fuel rod manifold and support system is disclosed in U.S. Pat. Nos. 3,743,576 and 3,432,388; and, as disclosed therein, the fuel rod assemblies were welded to their overhead supporting beams with gas tight welds between the fuel rod assembly and the lower wall of the beam. Often, a large number of fuel rod assemblies comprise a given fuel element, e.g., as many as two hundred and seventy-one or more fuel rod assemblies per fuel element. Typically, these fuel rod assemblies are elongated pin-like structures, often called fuel pins, having an outer metallic cladding wall encircling the fuel and transferring heat to the coolant flowing past the outer surface of the cladding wall. Usually, the upper ends of fuel rod assemblies have a plug or shaft of metal which is hermetically sealed to the cladding wall and is formed with a central bore to allow fission product gases to flow upwardly to the manifold system in the supporting beams. To convey the fission product gases to the manifold system without leakage into the surrounding coolant, each of the upper plugs of the fuel rod assemblies were welded to their support beams. However, such a welding process is slow and expensive. Moreover, a leaking weld connection is difficult to correct particularly when it is located at an interior one of a large number of fuel rod assemblies attached to a common beam support. Heretofore, it has been proposed to drill and tap the beam support and to thread the upper ends of the fuel plugs for releasable threading of the fuel rod assemblies directly to the support beams. However, threading of the beams also was found to be costly, time-consuming and inefficient. Thus, there is a need for a new and improved releasable interconnection between the fuel rod assemblies and their support beams which also provides a tight leak-free seal between the fuel rod assemblies and the support. Accordingly, a general object of the present invention is to provide a new and improved fuel element having detachable fuel rod assemblies secured with a tight leak-free connection to a beam support having a manifold vent system therein. |
046817280 | summary | CROSS-REFERENCE TO RELATED APPLICATIONS Application Ser. No. 490,099 filed Apr. 29, 1983 to Luciano Veronesi et al. for Nuclear Reactor (herein Veronesi) pending and assigned to Westinghouse Electric Corporation is incorporated herein by reference. The reactor disclosed by Veronesi is sometimes referred to in the art as the Mechanical Moderator Controlled Reactor (MMCR). Application Ser. No. 490,097 filed Apr. 29, 1983 to Luciano Veronesi for Nuclear Reactor (herein Veronesi '097) pending and assigned to Westinghouse Electric Corporation is also incorporated herein by reference. BACKGROUND OF THE INVENTION This invention relates to nuclear reactors and has particular relationship to reactors having a large number of different rods moveable in and out of the core to control the neutron flux. In its specific aspects, this invention concerns itself with reactors of the type in which a flow-through screen and disclosed in Veronesi '097 encircles the neutron-absorption rod guides. The flow-through screen has the effect of reducing the radial velocity of the coolant as it flows through the upper internals. The Mechanical Moderator Controlled Reactor disclosed by Veronesi is such a reactor. It this reactor there are control rods, gray rods and water-displacement rods for adjusting the neutron flux. The rods are suspended from spiders in clusters which are moveable by drives to achieve the desired or required neutron flux. The control rods are substantially neutron absorbent and serve for load-follow operations and must be capable of deactivating the reactor during refueling and quickly and effectively during scram. The gray rods have substantially lower neutron-absorbent capability than the control rods and also serve for load follow. They are moveable in and out of the core to "fine tune" the neutron flux. The water-displacement rods are inserted in the core during the earlier part, typically 40%, of the fuel cycle and are removed from the core during the remainder of the fuel cycle. The water-displacement rods when inserted in the core reduce the low energy neutron flux during the early part of the fuel cycle when the flux is high by reducing the moderation by the water coolant. When the water displacement rods are removed from the core, their function of reducing low energy neutron flux is substantially reduced. Each control-rod and gray rod cluster is associated with a fuel assembly and is moveable by its drive in or out of the fuel assembly or relative to a fuel assembly. Each displacement-rod cluster is associated with a plurality of fuel assemblies. Typically, there are in a Mechanical Moderator Controlled Reactor eighty-eight control-rod clusters and gray-rod clusters. Each cluster is of cruciform shape and carries eight rods positioned along the axial member and cross member of the cruciform. Typically, there are ninety-seven water-displacement rod clusters (WDRC's). Each WDRC in a typical MMCR, except those along the periphery of the upper internals, carries forty rods. Those along the periphery carry fewer than forty rods. The water-displacement rods are carried by a plurality of radial arms in the form of crucifixes extending from a central sleeve. The control-rod clusters in their functioning for load follow, experience frequent and rapid movement relative to their associated fuel assemblies. The gray-rod clusters typically may be inserted or fully withdrawn from their associated fuel elements 5600 times during the life of an MMCR. Each WDRC is fully inserted in a number of fuel assemblies symmetrical about its axis during the earlier part of the fuel cycle, and is fully withdrawn from the fuel assemblies and held in the withdrawn position during the remainder, typically 60%, of the fuel cycle. For reliable operation of a nuclear reactor, it is necessary that the neutron-flux adjusting rod clusters be effectively guided as they move in and out of the core. It is indispensable that the clusters be moveable without binding or sticking. It is an object of this invention to provide a nuclear reactor of the type having a large number of neutron-flux adjusting rods, such as the MMCR, including guides for the neutron-absorption rods which shall effectively guide these rods as they move in and out of the core and in whose use the rods shall not bind or stick as they are moved. It is another object of this invention to provide a nuclear reactor of the type that includes a flow-through screen about the guide structure having such guides for the neutron-flux adjusting rods. SUMMARY OF THE INVENTION This invention is applicable to, and can be embodied in, nuclear reactors of all types, those which have a flow-through screen and those which do not have such a screen. The invention, however, has unique applicability to nuclear reactors which have a flow-through screen. In prior art reactors each control rod, when it is retracted, is protected, by a housing, which forms a part of the guide structure, from the forces exerted by the cross-flow or radial flow of the coolant. This invention arises from the realization that in reactors including a flow-through screen, the water-displacement rods, when retracted into the upper internals, can, at least to an extent, be exposed to the coolant because in such reactors the radial velocity of the coolant is low and the drag forces exerted by the coolant on the exposed rods would be low. An additional factor which leads to the conclusion that exposure of the retracted water-displacement rods is feasible is that the time of exposure of these rods is substantially less than the time for control rods or gray rods. In accordance with this invention there is provided a nuclear reactor whose upper internals include a plurality of generally vertical guides. Each guide is formed of a plurality of vertically coextensive guide sections; each section is best described as a can open at the ends. Each can is formed and dimensioned so as to accommodate the neutron-absorber-rod clusters. Specifically, each can may have a cruciform transverse cross-section so as to pass and guide the control-rod and gray rod clusters. A generally horizontal plate is supported on the tops of each array of guide sections which are at the same level. There are thus a plurality of generally horizontal plates in a vertical array. The plates are perforated, the perforations in each plate being shaped and coordinated so as to pass the others of the neutron-flux adjusting rods. Specifically, the perforations in each plate extend radially from a central opening and include cruciform radial slots so as to pass the WDRC's. The plates are oriented in the vertical array with corresponding perforations precisely aligned so that the plates serve as guides for the WDRC's. Typically, in an MMCR, the plates have a diameter of about one hundred seventy-five inches and are composed of stainless steel. Because the plates are perforated as described, they would not, if they were integral structures, be self-supporting so that they could be manipulated unless they were very thick. To facilitate manipulation of the structure during assembly or disassembly of the reactor, each plate is formed of separate plate sections which can be nested in the manner of a "jig-saw puzzle" during assembly. Each plate section is supported on one or a plurality of the vertical guide sections. The water-displacement rods are partially exposed to the cross-flow of the coolant. When the plate sections are nested to form a plate, each plate may be regarded as divided into areas defined by a plurality of cans. The columnar volume under each plate-section area, except those around the periphery of a plate, is bounded to a substantial extent by arms on the cruciforms configuration of the cans. The areas around the periphery of each plate sections are partly bounded by the arms of cans. The water-displacement rods, when retracted, are partially protected by the arms of the surrounding cans from the cross-flow of the coolant. In the case of reactors with flow-through screens, as disclosed in Veronesi '097, the radial velocity of the coolant is low and the water-displacement rods are subjected to relatively low cross-flow forces. The plates formed of the assembled plate sections serve as plate guides for the WDRC's The reduction of velocity achieved with the flow-through screen is particularly important in reactors including WDRC's. There are a large number of water displacement rods, typically forty in each cluster. These rods together with the guides for the control rods and gray rods occupy a substantial portion of the volume of the upper internals. The coolant is driven by powerful pumps and is sucked out of the outlet nozzles at a high velocity, typically 50 feet per second. In the absence of the flow-through screen, the coolant would flow to the outlet nozzles predominantly through the portion of volume of the upper internals which is defined by an imaginary cylinder having the transverse cross-sectional areas of the openings in these nozzles and through the region immediately adjacent these cylinders. The coolant would wash the parts of the control rod and gray-rod guides and the water-displacement rods in this volume. Because the parts of the guides and water displacement rods occupy a large portion of this volume, the coolant velocity in this region of the guides and the water-displacement rods would be very high and the guides and rods would be subjected to high stresses resulting in failures. The flow-through screen distributes the coolant over the whole volume of the upper internals, reducing the flow velocity. Typically the flow velocity is reduced to about 4 ft/sec. Failure of the guides and water-displacement rods is thus precluded. In assembling the reactor, each plate section is assembled into an integrated unit, external to the reactor vessel, with its associated guide section or sections. The guide sections of each plate section are welded to end plates. The guide sections and end plates of the plate section are then stacked and secured to form an integrated columnar unit with the like plate sections interposed between adjacent end plates. The guide sections which extend along the unit are each bolted between end plates properly oriented so that the perforations of these sections are precisely aligned. Each column includes a number of complete guides equal to the number of guide sections which support the corresponding plate sections. Once all of the plate sections are assembled in columns, they are positioned in the pressure vessel on the upper core support with the plate sections at each level nested to complete the array of plates in the manner of a "jig-saw puzzle". The integrated units are pinned to the upper core support properly laterally aligned. Before these integrated units are inserted, the flow-through screen had been inserted in the pressure vessel. The integrated units are centered within the flow-through screen. The neutron-flux adjusting rod clusters are then inserted in the guide structures with their drive rods extending above the upper-internals. The upper-internals top plate is then positioned on top of the assembly of integrated units. |
summary | ||
abstract | A high-energy ion implanter includes a beam generation unit that includes an ion source and a mass analyzer, a high-energy multi-stage linear acceleration unit, a high-energy beam deflection unit that changes the direction of a high-energy ion beam toward a wafer, and a beam transportation unit that transports the deflected high-energy ion beam to the wafer. The beam transportation unit includes a beam shaper, a high-energy beam scanner, a high-energy beam collimator, and a high-energy final energy filter. Further, the high-energy beam collimator is an electric field type beam collimator that collimates a scan beam while performing the acceleration and the deceleration of a high-energy beam by an electric field. |
|
abstract | A nuclear reactor support system that, in one embodiment, includes a reactor vessel, a reactor core disposed within the reactor vessel, 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 support system further includes 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, and a plurality of welded lugs extending vertically between the first and second flanges. The first flange supports the entire weight of the reactor vessel in a cantilevered manner. |
|
abstract | An extreme ultraviolet light source apparatus using a spectrum purity filter capable of obtaining EUV light with high spectrum purity. The apparatus includes a chamber; a target supply unit for supplying a target material; a driver laser using a laser gas containing a carbon dioxide gas as a laser medium, for applying a laser beam to the target material to generate plasma; a collector mirror for collecting and outputting the extreme ultraviolet light radiated from the plasma; and a spectrum purity filter provided in an optical path of the extreme ultraviolet light, for transmitting the extreme ultraviolet light and reflecting the laser beam, the spectrum purity filter including a mesh having electrical conductivity and formed with an arrangement of apertures having a pitch not larger than a half of a shortest wavelength of the laser beam applied by the driver laser. |
|
052805069 | claims | 1. A steam isolation valve means comprising: a valve body provided with inlet and outlet portions through which a steam flows and an end opening; a substantially cylindrical valve disk body accommodated in the valve body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion; a drive means secured to the valve body and operatively connected to the valve disk body for reciprocating moving the valve disk body in the valve body; and means applied to the end opening of the valve body for holding the valve disk body when the valve disk body is shifted to a position fully opening the inlet portion wherein: said valve disk body is composed of a cylindrical valve disk having an inner hollow portion and a closed bottom and an open end, and said valve disk body holding means is composed of a valve disk holding coupling having an inner hollow portion and an outer configuration so to as to engageable with the open end of the valve disk. a valve body provided with inlet and outlet portions through which a steam flows and an end opening; a substantially cylindrical valve disk body accommodated in the valve body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion; a drive means secured to the valve body and operatively connected to the valve disk body for reciprocatingly moving the valve disk body in the valve body; and a tubular wall member integrally formed with the valve body, said valve disk body being accommodated in an inner hollow portion of the tubular wall member with a gap therebetween when the valve disk body is shifted to a position fully opening the inlet portion. a valve body provided with inlet and outlet portions through which a steam flows and an end opening; a substantially cylindrical valve disk body accommodated in the valve body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion; a drive means secured to the valve body and operatively connected to the valve disk body for reciprocatingly moving the valve disk body in the valve body; and steam flow guide means disposed for the valve body for guiding the steam flow from the inlet portion of the valve body; wherein: said guide means comprises a central guide rib disposed at the inlet portion of the valve body and side guide ribs formed integrally with an inner peripheral surface of the valve body at portions circumferentially apart from the central guide rib; and said central guide rib is disposed at a portion shifted from a central portion of a steam flow passage at the inlet portion of the valve body. 2. A steam isolation valve means according to claim 1, wherein the open end of said valve disk has an inner periphery provided with an inwardly tapered surface and said coupling has an outer periphery provided with an outwardly tapered surface which is engageable with the tapered surface of the valve disk. 3. A steam isolation valve means according to claim 1, wherein the open end of said valve disk has an outer periphery provided with an outwardly tapered surface and said coupling has an inner periphery provided with an inwardly tapered surface which is engageable with the tapered surface of the valve disk. 4. A steam isolation valve means according to claim 1, wherein said coupling is composed of a plurality of arcuate portions to be engaged with the open end of the valve disk. 5. A steam isolation valve means according to claim 1, further comprising a steam flow guide means secured to the valve body for guiding the steam flow. 6. A steam isolation valve means according to claim 5, wherein said guide means comprises a central guide rib disposed at the inlet portion of the valve body and side guide ribs formed integrally with an inner peripheral surface of the valve body at portions circumferentially apart from the central guide rib. 7. A steam isolation valve means according to claim 6, wherein each of said side guide ribs is provided with a plurality of slits formed along the inner peripheral surface of the valve body with substantially equal intervals. 8. A steam isolation valve means according to claim 1, wherein said valve disk body has an outer diameter axially gradually reduced at a central portion thereof. 9. A steam isolation valve means according to claim 1, wherein said inlet end of the valve body is connected to a steam inlet duct, said inlet duct being arranged vertically in an actually installed state. 10. A steam isolation valve means according to claim 1, wherein the steam isolation valve is composed of a main steam isolation valve means to be disposed in a reactor plant including a reactor container and a reactor pressure vessel, said main steam isolation valve means being disposed inside and outside the reactor container. 11. A steam isolation valve means comprising: 12. A steam isolation valve means according to claim 11, wherein said valve disk body is composed of a valve disk having an inner hollow portion and a closed bottom, said bottom having an outer surface centrally protruded outwardly. 13. A steam isolation valve means according to claim 11, further comprising a steam flow guide means secured to the valve body for guiding the steam flow. 14. A steam isolation valve means according to claim 11, wherein said guide means comprises a central guide rib disposed at the inlet portion of the valve body and side guide ribs formed integrally with an inner peripheral surface of the valve body at portions circumferentially apart from the central guide rib. 15. A steam isolation valve means according to claim 11, wherein the steam isolation valve is composed of a main steam isolation valve means to be disposed in a reactor plant including a reactor container and a reactor pressure vessel, said main steam isolation valve means being disposed inside and outside the reactor container. 16. A steam isolation valve means comprising: 17. A steam isolation valve means according to claim 16, wherein said guide rib has an outer configuration for causing asymmetric steam flow on both sides of the central guide rib. 18. A steam isolation valve means according to claim 16, wherein said central guide rib comprises two parts symmetrically arranged with respect to an axis of the valve disk body. 19. A steam isolation valve means according to claim 16, wherein said valve body has wall portions having a thickness different from each other on both sides of the central guide rib for causing different steam flow on both sides of the central guide rib at the inlet portion of the valve body. 20. A steam isolation valve means according to claim 16, wherein the steam isolation valve is composed of a main steam isolation valve means to be disposed in a reactor plant including a reactor container and a reactor pressure vessel, said main steam isolation valve means being disposed inside and outside the reactor container. |
description | This application claims the benefit of DE 10 2011 006 451.6, filed on Mar. 30, 2011. The present embodiments relate to a radiation therapy apparatus for treating tumor diseases. In a radiation therapy apparatus, a gantry may be used to position a radiation head, from which therapeutic radiation is directed at a patient, around the patient. Different gantry designs are known. U.S. Pat. No. 5,751,781 discloses an annular gantry with a central cylindrical aperture, in which a patient may be positioned for irradiation. Inside the gantry, the radiation head may be rotated along a plane of rotation, thereby enabling radiation to be directed at the patient from different directions. U.S. Pat. No. 6,969,194 and U.S. Pat. No. 6,865,254 disclose gantry designs having a front and a rear supporting gantry (e.g., two supporting gantries). The radiation head may be positioned at different positions between the two supporting gantries. A patient may be positioned between the two supporting gantries for irradiation. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a radiation therapy apparatus that has a simple gantry design, while allowing flexible adjustment of the position of a radiation head, is provided. The radiation therapy apparatus according to the present embodiments includes a gantry having a central aperture that defines a space, in which a patient may be positioned for irradiation. The radiation therapy apparatus also includes a positioning device, with which the patient may be positioned in the central aperture of the gantry, and a radiation head for generating therapeutic radiation that is directed at the patient. The radiation therapy apparatus includes an extension mechanism for the radiation head. The extension mechanism moves the radiation head and may be operated such that different operating modes may be set. In a first operating mode of the radiation therapy apparatus, the radiation head is disposed inside the gantry, the gantry having a front surface on a side facing the positioning device. In the first operating mode, the front surface constitutes a front edge of the radiation therapy apparatus toward the positioning device. For example, in the first operating mode, there are no energy generating components (e.g., the radiation head) projecting from the front surface that may collide, for example, with the patient or with the positioning device. The radiation head and/or other space occupying, energy generating components are disposed behind the front surface (viewed from the positioning device). In the best-case scenario, no components project beyond the front surface in the first operating mode. The front surface therefore constitutes the limit of the radiation therapy apparatus in relation to the positioning device. Provided the patient and the positioning device are located in front of the front surface, collisions with rotating components of the gantry are not possible in the first operating mode. In a second operating mode, the radiation head is moved out using the extension mechanism (e.g., in front of the front surface (viewed from the positioning device), which in the first operating mode constitutes the limit of the radiation therapy apparatus toward the positioning device). In the second operating mode, there is therefore a risk of components that project from the front surface colliding with the positioning device or with a patient positioned thereon. However, the outward movement of the radiation head increases the spatial possibilities for applying the radiation, making irradiation altogether more flexible. The number of possible irradiation angles and irradiation directions may be increased. The gantry may be, for example, annular in shape (e.g., similar to a conventional computed tomography gantry) having a central aperture. The cavity defined by the central aperture is approximately cylindrical. Inside the gantry disposed around the cavity, the radiation head may be rotated about a central axis, thereby enabling the radiation head to be moved to different positions within the plane of rotation. The axis of rotation may coincide with the longitudinal axis of the cylindrical aperture. Using the extension mechanism, the radiation head, which may otherwise only be rotated in the plane of rotation inside the gantry, may be moved out of the plane of rotation, thereby executing a movement having a component that is perpendicular to the plane of rotation (e.g., points in the direction of the axis of rotation). In contrast to U.S. Pat. No. 6,865,254, similar movements of the radiation head are possible without necessitating a complex and space-occupying design with two supporting gantries. Using the extension mechanism, the radiation head is therefore cantilevered out of the gantry from a retracted position and may then project at least partially from the front surface of the gantry. The extension mechanism may therefore bring about a radiation head movement having a component in the direction of the longitudinal axis of the cavity, without the gantry surrounding the cavity having to be rotated. The gantry structure as such (e.g., the gantry ring carrying the radiation head) may remain spatially fixed, and the extension mechanism may be operated in order to place the radiation head in a projecting position by a movement relative to the gantry. In one embodiment, on the side facing away from the positioning device, the gantry may have a back surface that in the first operating mode, constitutes a rear limit of the gantry. The extension mechanism may be operated such that, in a third operating mode of the radiation therapy apparatus, the radiation head may be moved out behind the back surface (viewed from the positioning device), which in the first operating mode constitutes the rear limit, by the extension mechanism. In the first operating mode, the back surface therefore constitutes, similarly to the front surface, a limit in the sense that the radiation head and/or other space occupying, radiation generating components are disposed in front of the back surface (viewed from the positioning device). In the best case scenario, in the first operating mode, no components project beyond the back surface. The back surface and the front surface therefore represent gantry boundaries, within which, in the first operating mode, the essential components for radiation generation and/or imaging are disposed. It is in the second or third operating mode that a gantry configuration with projecting components (e.g., with a projecting radiation head) is produced by the extension mechanism. In one embodiment, the gantry may be tilted about a horizontal axis. The gantry may be mounted on a stand, for example, via a swivel joint enabling the gantry to be tilted horizontally. The movement of the radiation head executable by the extension mechanism may be superimposed on the tilting movement of the gantry about the horizontal axis. The central aperture of the gantry may have a longitudinal axis. The longitudinal axis may specify, for example, the direction, along which the positioning device is to be moved in order to position a patient in the aperture. In the case of a cylindrical aperture, the longitudinal axis may be the cylinder's longitudinal axis. The extension mechanism may be embodied such that the extension mechanism allows a translatory movement of the radiation head along a direction having a component along the longitudinal axis. In one embodiment, the extension mechanism is embodied such that only a translatory movement of the radiation head in the direction of the longitudinal axis is provided. This arrangement may be embodied mechanically (e.g., via a rail system). In a mechanically more complex embodiment, the extension mechanism is configured such that, in addition to the translatory movement, another movement of the radiation head may be executed. The other movement has a component in a direction perpendicular to the translatory movement. In this way, the distance of the radiation head from the patient or from the central axis of the radiation therapy apparatus may be increased or reduced. The extension mechanism may also be embodied such that, in addition to the translatory movement, a tilting movement of the radiation head may be executed. With this embodiment, the radiation head may be tilted relative to the extension mechanism. This enables the direction, in which the therapeutic treatment beam is emitted, to be adjusted. The extension mechanism may be configured such that, when the extension mechanism is extended out, the radiation head is moved along an isocentric circular segment. The focal point of the therapeutic radiation (e.g., the origin of the therapeutic radiation) thus maintains the same distance from the isocenter. By appropriate tilting of the radiation head, the central beam of the therapeutic radiation remains aligned isocentrically (e.g., toward the isocenter) even in the extended state. FIG. 1 shows an embodiment of a radiation therapy apparatus 11 with a radiation head in a retracted position. The radiation therapy apparatus 11 shown in FIG. 1 has an annular gantry 13 enclosing a central aperture 15 (e.g., a cylindrical aperture). In the central aperture 15, a patient 17 may be positioned from one side using a positioning device 19 located on one side of the radiation therapy apparatus 11. Disposed within the gantry ring 13 are components of the radiation therapy apparatus 11 (e.g., a radiation source for therapeutic irradiation, a collimator for beam limiting, an imaging device for diagnostic X-radiation and/or a detector for portal imaging). For the sake of clarity, only a radiation head 21 and an extension mechanism 23 for the radiation head 21 are shown. These components may be rotated inside a circular ring of the gantry 13. An axis of rotation coincides with a longitudinal axis of the cylindrical aperture 15. A plane of rotation runs parallel to a plane of the gantry ring 13, thereby enabling an irradiation direction of the therapeutic radiation to be adjusted. The gantry ring 13 has, parallel to the plane of rotation, an annular front surface 25 that is a limit of the gantry ring 13 on a positioning device 19 side. In a first operating mode, which is shown in FIG. 1, no components (e.g., no radiation generating components such as the radiation head 21) project beyond a front surface 25. As all the components are located inside the gantry ring 15, these components may also be rotated without risk of collision with a patient 17 or with the positioning device 19. In the first operating mode, coplanar irradiation may take place, as the radiation is emitted from a point located in a plane that contains the isocenter, and is perpendicular to the longitudinal axis of the cylindrical aperture 15. The gantry ring 13 has, also parallel to the plane of rotation, a back surface 27 that constitutes a limit of the gantry ring 13 on a side facing away from the positioning device 19. In the first operating mode, no components (e.g., no radiation generating components) project beyond the back surface 27. In the first operating mode, the radiation therapy apparatus 11 has a configuration similar to a computed tomography scanner (CT configuration). The annular gantry 15 is mounted on a stand 29. The annular gantry 15 may be tilted as a whole about a horizontal axis via a right- and a left-hand bearing 31, thereby tilting the plane of rotation of the gantry 15. FIG. 2 shows the radiation therapy apparatus 11 depicted in FIG. 1 in a second operating mode. The radiation head 21 is moved out from the gantry ring 13 by an extension mechanism 23. The radiation head 21 is viewed from the positioning device 19, in front of the front surface 25 of the gantry 13. The radiation head 21 extends beyond the front surface 25, being “cantilevered out.” The configuration of the radiation therapy apparatus 11 is similar to an L-shaped configuration of conventional radiation therapy equipment with a cantilevering arm. In this position, the irradiation may be non-coplanar, as the radiation head 21 is no longer in the plane of rotation that is characterized by the rotation of the radiation head 21 inside the gantry 13 in the first operating mode and in which the isocenter lies. The extension mechanism 23 enables the radiation head 21 to be moved out of the plane that is perpendicular to the longitudinal axis of the gantry aperture 15 and contains the isocenter, without the gantry 13 as a whole being moved or tilted. The gantry ring 13 remains in the same position. The extension mechanism 23 causes the radiation head 21 to be moved relative to the gantry 13. FIG. 3 shows a top view of the configuration of the radiation therapy apparatus 11 shown in FIG. 2. FIG. 3 shows the cantilevered radiation head 21, which has been moved out of the plane of rotation and projects in front of the front surface 25 of the gantry 13. In FIG. 3, the back surface 27 of the gantry 13 is shown more clearly (e.g., the rear boundary of the gantry ring 13). Also shown in FIG. 3 is a retaining structure 33 provided for mechanical reasons behind the back surface 27 of the gantry 13, although this structure is not necessary. The retaining structure 33 contains no beam shaping or radiation generating components. FIG. 4 shows another embodiment of the radiation therapy apparatus 11. The extension mechanism 23 is embodied as a semicircular segment disposed concentrically to the gantry ring 13. The radiation head 21 is disposed on the semicircular segment. The semicircular segment incorporating the radiation head 21 may be swung out from the gantry ring 13 so that the radiation head 21 is brought in front of the front surface 25 of the radiation therapy apparatus 11 by this movement. Non-coplanar isocentric irradiation may be carried out. The difference compared to the apparatus shown in FIG. 1 is in the extension mechanism 23. Whereas the extension mechanism shown in FIG. 1 allows purely linear displacement of the radiation head 21 in a direction orthogonal to the plane of rotation, the extension mechanism shown in FIG. 4 permits isocentric motion. The radiation head 21 may always be at the same distance from the isocenter, and the central ray of the therapeutic radiation may always be aligned to the isocenter. The central ray is tilted out from the gantry ring 13. This may be effected via a real pivoted joint. The extension mechanism 23 may be embodied so as to execute the same or a similar movement as in the case of implementation with a real pivoted joint, using a virtual pivoted joint. FIG. 5 shows a top view of the embodiment of the radiation therapy apparatus 11 shown in FIG. 4. The cantilevering, semicircular segment 23 that carries the radiation head 21 is shown in FIG. 4. The cantilevering, semicircular segment 23 is moved out of the plane of rotation and projects in front of the front surface 25 of the gantry 13, which in the first operating mode, constitutes the limit of the gantry 13 toward the patient 17. FIGS. 6a and 6b show a side view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 linearly using a rail system 41. FIGS. 7a and 7b show a side view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 linearly using telescopic cylinders 43. FIGS. 8a and 8b show a side view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 linearly using ball screws 45, the travel being comparatively short. The drives shown in FIGS. 6 to 8 are based on serial kinematics. The main motion of the individual components is a linear movement. FIG. 9 shows a top view of an extension mechanism that moves the radiation head 21 out using a swiveling cantilever arm 51. The radiation head 21 may be moved linearly relative to the cantilever arm 51. FIGS. 10a and 10b show a top view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 out using a cantilever arm 51 that is operable to swivel. FIG. 11a and FIG. 11b show a top view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 out using a circular rail 53. FIG. 12a and FIG. 12b show a top view and a perspective view, respectively, of an extension mechanism that moves the radiation head 21 out using pivot mounted arms 55 operating on the selective compliant articulated robot arm or selective compliant assembly robot arm (SCARA) principle. FIG. 13a and FIG. 13b show a side view and a perspective view, respectively, of an extension mechanism with a swing-out semicircular element 57. The drives shown in FIGS. 9 to 13 are based on serial kinematics. The main motion of the individual components is a rotatory movement. FIG. 14 shows a plan view of an extension mechanism that employs rail-mounted slides 61 that may be moved in opposite directions to one another. FIG. 15 shows a plan view of an extension mechanism that employs cylinder plungers 63 that may be moved parallel to one another. FIG. 16 shows a perspective view of an extension mechanism with three cylinder plungers 63 disposed in a tripod-like manner. While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. |
|
description | This application claims priority under 35 U.S.C. §120 to, and is a continuation of, U.S. patent application Ser. No. 12/272,175, filed Nov. 17, 2008, and entitled “STEAM GENERATOR FLOW BY-PASS SYSTEM,” the contents of which are incorporated herein by reference in their entirety. The present disclosure relates to a system for removing decay heat from a nuclear reactor. In nuclear reactors designed with passive operating systems, the laws of physics are employed to ensure that safe operation of the nuclear reactor is maintained during normal operation or even in an emergency condition without operator intervention or supervision, at 10 least for some predefined period of time. A nuclear reactor 5 includes a reactor core 6 surrounded by a reactor vessel 2. Water 10 in the reactor vessel 2 surrounds the reactor core 6. The reactor core 6 is further located in a shroud 122 which surround the reactor core 6 about its sides. When the water 10 is heated by the reactor core 6 as a result of fission events, the water 10 is directed from the shroud 122 and out of a riser 124. This results in further 15 water 10 being drawn into and heated by the reactor core 6 which draws yet more water 10 into the shroud 122. The water 10 that emerges from the riser 124 is cooled down and directed towards the annulus 123 and then returns to the bottom of the reactor vessel 2 through natural circulation. Pressurized steam 11 is produced in the reactor vessel 2 as the water 10 is heated. A heat exchanger 35 circulates feedwater and steam in a secondary cooling system 30 in order to generate electricity with a turbine 32 and generator 34. The feedwater passes through the heat exchanger 35 and becomes super-heated steam. The secondary cooling system 30 includes a condenser 36 and feedwater pump 38. The steam and feedwater in the secondary cooling system 30 are isolated from the water 10 in the reactor vessel 2, such that they are not allowed to mix or come into direct contact with each other. The reactor vessel 2 is surrounded by a containment vessel 4. The containment vessel 4 is designed so that water or steam from the reactor vessel 2 is not allowed to escape into the surrounding environment. A steam valve 8 is provided to vent steam 11 from the reactor vessel 2 into an upper half 14 of the containment vessel 4. A submerged blowdown valve 18 30 is provided to release the water 10 into suppression pool 12 containing sub-cooled water. During a loss of feedwater flow, the nuclear reactor 5 is designed to respond by scramming the reactor core 6, flooding the containment vessel 4 or depressurizing the reactor vessel 2. The latter two of these responses result in the nuclear reactor 5 being shut down and unable to generate electricity for an extended period of time. Furthermore, during a loss of coolant condition where coolant is expelled from the reactor vessel 2, a flow of coolant through the reactor core 6 is reduced. This increases the time needed to bring the reactor core temperatures down to a desired level. A power module assembly is disclosed as comprising a reactor housing, a reactor core located in a lower portion of the reactor housing, and a heat exchanger proximately located about an upper portion of the reactor housing. The primary coolant flows out of the reactor housing via the upper portion, and the primary coolant flows into the reactor housing via the lower portion. The power module assembly further comprises a passageway provided in the reactor housing intermediate the lower portion and the upper portion, wherein the passageway is configured to provide an auxiliary flow of primary coolant to the reactor core to augment the flow of the primary coolant out of the upper portion of the reactor housing and into the lower portion. A nuclear reactor module is disclosed as comprising a reactor vessel and a reactor housing mounted inside the reactor vessel, wherein the reactor housing comprises a shroud and a riser located above the shroud. A heat exchanger is proximately located about the riser, and a reactor core is located in the shroud. The nuclear reactor module further comprises a steam generator by-pass system configured to provide an auxiliary flow path of primary coolant to the reactor core to augment a primary flow path of the primary coolant out of the riser and into the shroud, wherein the auxiliary flow path of primary coolant exits the reactor housing without passing by the heat exchanger. A method of cooling a nuclear reactor is disclosed. A primary coolant is circulated through a reactor housing comprising an upper riser and a lower shroud. A primary flow path of the primary coolant passes by a heat exchanger proximately located about the riser, and the primary coolant enters the lower shroud. A loss of coolant accident (LOCA) or a depressurization event is detected, and a fluid level of the primary coolant is decreased below the top of the riser. The primary flow path of primary coolant exits the riser as steam. An auxiliary flow path of primary coolant is circulated through an auxiliary passageway provided in the reactor housing, wherein the auxiliary flow path of primary coolant exits the reactor housing without passing by the heat exchanger. The primary coolant from the auxiliary flow path is combined with the primary coolant from the primary flow path that enters the lower shroud. Other aspects will become more readily apparent from the following detailed description of the embodiments, which proceeds with reference to the accompanying drawings. Various embodiments disclosed or referred to herein may be operated consistent, or in conjunction, with features found in co-pending U.S. application Ser. No. 11/941,024 which is herein incorporated by reference in its entirety. FIG. 2 illustrates a power module assembly 50 comprising an internally dry containment vessel 54. The containment vessel 54 is cylindrical in shape, and has spherical, domed, or ellipsoidal upper and lower ends. The entire power module assembly 50 may be submerged in a pool of water 16 which serves as an effective heat sink. The pool of water 16 and the containment vessel 54 may further be located below ground 9 in a reactor bay 7. The containment vessel 54 may be welded or otherwise sealed to the environment, such that liquids and gas do not escape from, or enter, the power module assembly 50. The containment vessel 54 may be supported at any external surface. In one embodiment, the containment vessel 54 is suspended in the pool of water 16 by one or more mounting connections 80. A reactor vessel 52 is located or mounted inside the containment vessel 54. An inner surface of the reactor vessel 52 may be exposed to a wet environment including a coolant 100 or liquid, such as water, and an outer surface may be exposed to a dry environment such as air. The reactor vessel 52 may be made of stainless steel or carbon steel, may include cladding, and may be supported within the containment vessel 54. The power module assembly 50 may be sized so that it can be transported on a rail car. For example, the containment vessel 54 may be constructed to be approximately 4.3 meters in diameter and 17.7 meters in height (length). Refueling of the reactor core 6 may be performed by transporting the entire power module assembly 50 by rail car or overseas, for example, and replacing it with a new or refurbished power module assembly which has a fresh supply of fuel rods. The containment vessel 54 encapsulates and, in some conditions, cools the reactor core 6. It is relatively small, has a high strength and may be capable of withstanding six or seven times the pressure of conventional containment designs in part due to its smaller overall dimensions. Given a break in the primary cooling system of the power module assembly 50 no fission products are released into the environment. Decay heat may be removed from the power module assembly 50 under emergency conditions. The reactor core 6 is illustrated as being submerged or immersed in a primary coolant 100, such as water. The reactor vessel 52 houses the coolant 100 and the reactor core 6. A reactor housing 20 comprises a shroud 22 in a lower portion and a riser 24 in an upper portion of the reactor housing 20. The shroud 22 surrounds the reactor core 6 about its sides and serves to direct the coolant 100 (shown as coolant flow 65, 67) up through the riser 24 located in the upper half of the reactor vessel 52 as a result of natural circulation of the coolant 100. In one embodiment, the reactor vessel 52 is approximately 2.7 meters in diameter and includes an overall height (length) of 13.7 meters. The reactor vessel 52 may include a predominately cylindrical shape with ellipsoidal, domed or spherical upper and lower ends. The reactor vessel 52 is normally at operating pressure and temperature. The containment vessel 54 is internally dry and may operate at atmospheric pressure with wall temperatures at or near the temperature of the pool of water 16. The containment vessel 54 substantially surrounds the reactor vessel 52 and may provide a dry, voided, or gaseous environment identified as containment region 44. Containment region 44 may comprise an amount of air or other fill gas such as Argonne or other noble gas. The containment vessel 54 includes an inner surface 55 or inner wall which is adjacent to the containment region 44. The containment region 44 may include a gas or gases instead of or in addition to air. In one embodiment, the containment region 44 is maintained at or below atmospheric pressure, for example as a partial vacuum. Gas or gasses in the containment vessel may be removed such that the reactor vessel 52 is located in a complete or partial vacuum in the containment region 44. During normal operation, thermal energy from the fission events in the reactor core 6 causes the coolant 100 to heat. As the coolant 100 heats up, it becomes less dense and tends to rise up through the riser 24. As the coolant 100 temperature reduces, it becomes relatively denser than the heated coolant and is circulated around the outside of the annulus 23, down to the bottom of the reactor vessel 52 and up through the shroud 22 to once again be heated by the reactor core 6. This natural circulation causes the coolant 100 (shown as coolant flow 65) to cycle through the heat exchanger 35, transferring heat to a secondary coolant, such as the secondary cooling system 30 of FIG. 1 to generate electricity. FIG. 3 illustrates the power module assembly 50 of FIG. 2 during an emergency operation. The emergency operation may include a response to an overheating of the reactor core 6, or an over-pressurization event of the reactor vessel 52, for example. During some emergency operations, the reactor vessel 6 may be configured to release the coolant 100 into the containment region 44 of the otherwise dry containment vessel 54. A decay heat of the reactor core 6 may be removed through condensation of the coolant 100 on the inner surface 55 of the containment vessel 54. Whereas the containment vessel 54 may be immersed in a pool of water 16, the inner surface 55 of the containment vessel 54 may be completely dry prior to the emergency operation or over-pressurization event. A flow limiter 58 or steam vent may be mounted on the reactor vessel 52 for venting the coolant 100 into the containment vessel 54 during the emergency operation. The coolant 100 may be released into the containment vessel 54 as vapor 41, such as steam. The flow limiter 58 may be connected or mounted directly to an outer wall of the reactor vessel 52, without any intervening structures such as piping or connections. The condensation of the vapor 41 may reduce pressure in the containment vessel 54 at approximately the same rate that the vented vapor 41 adds pressure to the containment vessel 54. Coolant 100 that is released as vapor 41 into the containment vessel 54 condenses on the inner surface 55 of the containment vessel 54 as a liquid. The condensation of the vapor 41 causes the pressure in the containment vessel 54 to decrease, as the vapor 41 is transformed into the liquid coolant 100. A sufficient amount of heat may be removed from the power module assembly 50 through the condensation of the vapor 41 on the inner surface 55 of the containment vessel to manage the removal of decay heat from the reactor core 6. In one embodiment, there is no release of the liquid coolant 100 from the reactor vessel 52 even during an emergency operation. The condensed coolant 100 descends to the bottom of the containment vessel 54 and collects as a pool of liquid. As more vapor 41 condenses on the inner surface 55, the level of the coolant 100 in the bottom of the containment vessel 54 gradually rises. Heat stored in the vapor 41 is transferred through the walls of the containment vessel 54 into the pool of water 16 that acts as an ultimate heat sink. Heat stored in the coolant 100 located at the bottom of the containment vessel 54 is transferred through liquid convection and conduction heat transfer on the inner surface 55. Heat removed from the steam or vapor 41 may be transferred to the relatively cold inner surface 55 through condensation on the inside walls of the cold containment vessel 54 and by natural convection from the hot coolant to the inner surface 55. Heat may be transferred to the pool of water 16 by conduction through the containment vessel walls and through natural convection on an outside surface of the containment vessel 54. The coolant 100 remains confined within the power module assembly 50 after the reactor core 6 becomes over-heated and during the emergency operation. The heat transferred to the pool of water 16 may provide adequate passive decay heat removal for three or more days without any operator intervention. The containment vessel 54 may be designed to withstand the maximum pressure that would result given an instantaneous release of the high-pressure fluid from the reactor vessel 52 into the containment vessel 54. The pressure inside the containment vessel 54 may be designed to approximately equilibrate with the pressure inside the reactor vessel 52, reducing break flow caused by the pressure difference and resulting in coolant level 100A in the reactor vessel 52 and coolant level 100B in the containment vessel 54 as shown in FIG. 3. The coolant level 100B is shown elevated with respect to the coolant level 100A due to an amount of hydrostatic driving force required for flow through the lower valves 57 back into the reactor vessel 52. Differences in coolant levels 100A and 100B may also exist due to a pressure difference in the reactor vessel 52 relative to the containment vessel 54 due to the pressure drop of the steam flow valve 58. FIG. 3 shows that the coolant levels 100A and 100B may equilibrate as a result of a hydrostatic head that is generated by in imbalance of the coolant levels. Coolant level 100A in the reactor vessel 52 remains above the top of the reactor core 6, keeping the reactor core 6 covered with coolant 100 at all times. The coolant level 100A is maintained by steam or vapor being emitted from the riser 24 (shown as coolant flow 42) which condenses on the inner surface 55 of the reactor vessel 52 before collecting at the bottom of the reactor vessel 52 to be re-circulated through the reactor core 6. A flow valve 57 may be provided to allow the coolant 100 to flow from the containment vessel 54 back into the reactor vessel 52 once an appropriate or predetermined condition of the coolant levels 100A, 100B is achieved. Coolant 100 that is allowed to reenter the reactor vessel 52 through the flow valve 57 replenishes the coolant 100 that was vented as vapor 41 through the flow limiter 58. The flow of coolant 100 through the flow valve 57 may be achieved through the natural circulation of the passive system due to the different coolant densities and coolant levels that result from temperature differences and valve coolant flow in the vessels 52, 54. Whereas a complete or perfect vacuum may be commercially or technically impractical to achieve or maintain, a partial vacuum may be created in the containment vessel 54. Any reference to a vacuum herein is therefore understood to be either a partial or complete vacuum. In one embodiment, the containment region 44 is maintained at a vacuum pressure that significantly reduces convective and conductive heat transfer through the containment gases. By substantially removing gases from the containment region 44, for example by maintaining a vacuum within the containment vessel 54, an initial rate as well as subsequent rates of condensation of vapor 41 on the inner surface 55 are increased. Increasing the rate of condensation increases the rate of heat transfer through the containment vessel 54. In the event of a loss of the vacuum in the containment region 44, the introduced vapor or liquid provide a further passive safety cooling mechanism to transfer heat between the reactor vessel 52 and the containment vessel 54 through natural convection. For example, by reducing or eliminating the thermal insulation, for example as provided by a vacuum, a more effective heat transfer from the reactor vessel 52 can be made during an emergency operation due to the condensed liquid coolant 100 which pools at the bottom of the containment vessel 54. Heat is transferred from the reactor vessel 52 through the liquid coolant 100 to the containment vessel 54. FIG. 4 illustrates an embodiment of a power module assembly 40 comprising a steam generator flow by-pass system 45 during an emergency operation, such as a loss of coolant accident (LOCA) or an over-pressurization event. Whereas the power module assembly 40 is described with reference to embodiments illustrated in FIGS. 2-3, it should be understood that many or all of the features could be applied to the nuclear power system described with respect to FIG. 1 as well as conventional power systems. A reactor housing 20 is mounted inside the reactor vessel 52, wherein the reactor housing 20 comprises the shroud 22 and the riser 24 located above the shroud 20. The heat exchanger 35 is proximately located about the riser 24. The reactor core 6 is located in the shroud 22. The riser 24 is shown illustrated as being attached to the reactor vessel 52 by an upper attaching member 41, whereas the shroud is shown illustrated as being attached to the reactor vessel 52 by a lower attaching member 43. The steam generator flow by-pass system 45 is configured to provide an auxiliary flow 48 of primary coolant to the reactor core 6 to augment a flow of the primary coolant 100 out of the riser 24 and into the shroud 22. The auxiliary flow 48 of primary coolant exits the reactor housing 20 without passing by the heat exchanger 35. The steam generator flow bypass system 45 may provide a hydraulic connection through one or more components of the reactor housing 20. In one embodiment, the steam generator flow by-pass system 45 provides a hydraulic connection through the annulus (ref. 123 FIG. 1) located intermediate the riser 24 and the shroud 22. The coolant flow 42 out of the upper portion (e.g. riser 24) of the reactor housing 20 comprises steam, wherein the auxiliary flow 48 of primary coolant comprises a mixture of two-phase coolant, such as boiling water. Coolant flow 42 exiting the riser 24 may comprise less coolant 100 by mass flow rate as compared to the coolant flow 67 (FIG. 2) during normal operations (e.g. full power operation). Auxiliary flow 48 may therefore serve to make up some of the lost flow rate, such that the coolant flow 46 entering the shroud 22 is augmented to at or near the same flow rate as coolant flow 65 in FIG. 2 during normal operation. In contrast to the coolant level 100N being above the outlet or top of the riser 24 shown in FIG. 2 during normal operating conditions, in the embodiment illustrated by FIG. 4 the coolant level 100A is shown below the top of the riser 24 during the emergency operation. Whereas the reactor housing 20 is shown completely submerged in primary coolant 100 in FIG. 2, the reactor housing 20 is only partially submerged in the coolant 100 as illustrated in FIG. 4. The level of the primary coolant 100 remains above the passageway 45 during normal operation, as well as during an off-normal operation, shut-down or emergency operation, when steam generator by-pass occurs. During normal operating conditions, the coolant flow 65 may be comprised of predominantly or exclusively single phase coolant, for example in a pressurized water reactor design (PWR). Accordingly, a flow of single phase coolant circulates through the reactor core 6 as coolant flow 65 and out the riser 24 as coolant flow 67 (see FIGS. 2 and 5). This provides for single-phase convection heat transfer at the surface of the fuel cladding in the reactor core 6. When a LOCA occurs and the coolant level 100A drops below the top of the riser 24, as illustrated in FIG. 4, the flow of single phase coolant may be interrupted. When pressure or temperature variations provide for conditions where the saturation conditions are surpassed, phase-change heat transfer may occur. Two-phase coolant may develop as it passes through the reactor core 6 which may then exit the reactor housing 20 via coolant flow 42 as steam which condenses on the inside wall of the reactor vessel 52. By including the auxiliary flow 48 through the steam generator flow by-pass system 45, convective heat transfer is provided to the reactor core 6, in addition to the heat transfer that occurs through steam generation. The level of coolant 100C within the riser 24 during the LOCA, may drop down to a level that is approximately equal to that of the coolant level 100A on the outside (downcomer) of the reactor housing 20 when the power module achieves a steady state condition. A steady state condition may occur when the coolant flow 46 entering the shroud 22 is equal to the combined flow rate of the coolant flow exiting the riser 24 and the auxiliary flow 48 exiting the steam generator flow by-pass system 45. The steam generator flow by-pass system 45 is located above the reactor core 6 to optimize coolant flow through the fuel rods. In one embodiment, the steam generator flow by-pass system 45 comprises a passageway provided in the reactor housing 20 intermediate the lower portion (e.g. shroud 22) and the upper portion (e.g. riser 24) of the housing 20, wherein the passageway is configured to provide the auxiliary flow 48 of primary coolant to the reactor core 6 which augments the flow of the primary coolant 100 out of the upper portion of the reactor housing 20 and into the lower portion. The auxiliary flow 48 of primary coolant accordingly bypasses the heat exchanger 35, located proximately about the upper portion of the reactor housing 20. The passageway 45 may be closed during a full power operation of the power module assembly 40, whereas during an emergency operating procedure, the passageway 45 is configured to open. Similarly, the passageway 45 may be configured to open during a shutdown, or power-down operation, including a LOCA or over-pressurization event. In one embodiment, the passageway remains open during all modes of operation, whereas the auxiliary flow 48 is substantially minimized or reduced to zero during normal operations of the power module assembly 40. FIG. 5 illustrates an embodiment of a power module comprising a steam generator flow by-pass system 59 during normal operating conditions. The steam generator flow bypass system 59 comprises an opening or passageway through the reactor housing 120. For example, the passageway may be located between or through a lower end 60 of the riser 24 and an upper end 62 of the shroud 22. The coolant flow 65 passes through the reactor core 6 located in the shroud 22 before exiting the riser 24 as coolant flow 67. During normal operations, little or none of the coolant flow 65 escapes through the steam generator flow bypass system 59. By prohibiting or reducing a flow rate through the steam generator flow by-pass system 59, a maximum flow of coolant passes by the heat exchanger 35 to remove heat from the reactor core 6. Accordingly, the mass flow rate of coolant flow 65 is approximately equal to that of coolant flow 67. FIG. 6A illustrates an embodiment of a steam generator flow by-pass system 69 during normal operating conditions, such as when a power module is operating at full power. During normal operation, the power module generates an operating temperature that is typically higher than a temperature associated with reactor start-up, reactor shut-down, or other operating conditions. Different temperatures may be generated at different locations within the coolant 100 as a result of interaction with the heat exchanger 35 (FIG. 4). At normal operating temperatures, coolant flow 65 and 67 behave substantially as described with respect to FIGS. 2 and 5. Different components of the reactor housing 20 may undergo different amounts of thermal expansion, as a result of the difference in operating temperature or as a result of differences in thermal properties of the various components. For example, some components may be made out of different materials, composition, or amount (e.g. thickness), such that one component may expand or retract to a greater degree than another component. In one embodiment, a direction of expansion or contraction of the shroud 22 and the riser 24 are in opposite directions. For example, while the riser 24 expands toward the bottom of the reactor vessel 52 (FIG. 2), the shroud 22 expands toward the top of the reactor vessel 52. This relationship is diagrammatically illustrated by the downward and upward facing arrows at the lower end 60 of the riser 24 and the upper end 62 of the shroud 22, respectively. Expansion of the components in opposite directions may be accomplished by attaching the riser 24 to the upper attaching member 41 and by separately attaching the shroud 22 to the lower attaching member 43 (FIG. 4). A passageway 63 in the upper end 62 of the shroud 22 is shown dislocated with a passageway 61 in the lower end 60 of the riser 24. With the shroud 22 and riser 24 in the thermally expanded condition, the dislocated passageways 61, 63 do not line up, such that little or none of the coolant flow 65 is allowed to pass through the steam generator flow bypass system 69. FIG. 6B illustrates an embodiment of the steam generator flow by-pass system 69 of FIG. 6A during a power-down operation. The power down operation may include a reactor shut-down, reactor trip or SCRAM, LOCA, or over pressurization event, for example. During the power-down operation, temperatures in the reactor vessel 52 (FIG. 2) tend to decrease, which results in a contraction or retraction of various reactor components. For example, while the riser 24 contracts toward the top of the reactor vessel 52 (FIG. 2), the shroud 22 retracts toward the bottom of the reactor vessel 52. This relationship is diagrammatically illustrated by the upward and downward directed arrows at the lower end 60 of the riser 24 and the upper end 62 of the shroud 22, respectively. The riser 24 and the shroud 22 may expand or contract at different amounts for the same change in temperature, in which case the directions of expansion and retraction may be relative to each other. The passageway 63 in the upper end 62 of the shroud 22 is shown aligned with the passageway 61 in the lower end 60 of the riser 24, allowing an auxiliary flow 48 of coolant to pass through the steam generator flow by-pass system 69. With the shroud 22 and riser 24 in the thermally retracted condition, the co-located passageways 61, 63 line-up to form a through-passage, such that the auxiliary flow 48 is combined with coolant flow 42. In one embodiment, the passageway 61, 63 opens due to a change in temperature within the reactor vessel 52 (FIG. 2), wherein a difference in rate of thermal expansion between the shroud 22 and the riser 24 causes the passageway 61, 63 to open. A flow rate of the auxiliary flow 48 may vary according to the change in temperature, a degree of alignment between the passageways 61,63, or the number of passageways provided in the reactor housing 20. The auxiliary flow 48 of coolant exits the reactor housing 20 without passing by or through the heat exchanger 35 (FIG. 4). FIG. 7 illustrates an embodiment of a steam generator flow by-pass system 79 comprising a through-passage 70. The through-passage 70 may be formed between the lower end 60 of the riser 24 and the upper end 62 of the shroud 22. The lower end 60 and upper end 62 are shown overlapping each other, such that the auxiliary flow 48 circulates through the through-passage 70. FIG. 7 may be understood as representing the flow of coolant during a shut-down or power-down operation, in which coolant flow 42 provides a reduced flow rate as compared to coolant flow 67 of FIG. 5. In FIG. 5, during normal operation of the power module 40, coolant flows 65, 67 may be sufficiently strong such that little or no auxiliary flow escapes from the steam generator flow by-pass system 59. Flow paths through the riser 24 may provide the path of least resistance during normal operation. During a shut-down operation, or LOCA, where coolant flow 42 may be reduced, auxiliary flow 48 may be allowed to exit the through-passage 70 through natural convection, as coolant flow 46 exceeds the flow rate of coolant flow 42. In one embodiment, the primary coolant exits the steam generator flow by-pass system 79 as a result of a decrease in flow rate of the coolant flow 42 of the primary coolant out of the riser 24. The decrease in flow rate may correspondingly decrease an amount of eddies that otherwise form in the through-passage 70 during normal operating conditions, allowing the coolant to “boil over” through the steam generator flow by-pass system 79. In the embodiment illustrated in FIG. 7 as well as the other various embodiments described and illustrated herein, the auxiliary flow 48 of primary coolant may exit the reactor housing 20 due to natural convection, or natural circulation of the coolant. A two-phase state of the coolant may promote auxiliary flow 48 of coolant to pass through the steam generator flow by-pass system, whereas most or all of the coolant would otherwise exit out the riser 24 when the coolant is in a single-phase state (e.g. during normal operating conditions). Passively cooling the reactor core 6 (FIG. 5) reduces or eliminates the need for providing moving or mechanical parts, such as motors. In one embodiment, a distance between the overlapped section of the lower end 60 and upper end 62 increases or decreases with a change in temperature of the power module 40. During a decrease in reactor temperature, forces F1 and F2 may act on the ends 60,62 of the riser 24 and shroud 22 to increase the size of the through-passage 70 and provide for an increase in auxiliary flow 48. Whereas during an increase in reactor temperature, the size of the through-passage 70 may decrease as the distance between the overlapped section of the ends 60, 62 decreases, resulting in the auxiliary flow 48 decreasing or ceasing to flow. A flow rate of the auxiliary coolant 48 may vary with a change in reactor temperature and associated change in size or flow area of the through-passage 70. FIG. 8 illustrates an embodiment of a steam generator flow by-pass system 89 comprising a valve 80 positioned near the lower end 60 of the riser 24 and the upper end 62 of the shroud 22. Auxiliary flow 48 may be allowed to flow similarly as with regards to the description of FIG. 7, whereas the valve 80 may be provided to limit a direction of the coolant flow 48 in a single direction. In one embodiment, valve 80 is a unidirectional valve that limits the direction of coolant flow 48 from within the reactor housing 20 to outside of the reactor housing 20. In one embodiment, the valve 80 is always open, and the rate of auxiliary flow 48 is governed by the flow rate of coolant flow 42, 46 or coolant flow 65, 67 (FIG. 5). In another embodiment, valve 80 is actuated (e.g. opened) upon detection of a shutdown operation or reactor scram, for example, such that valve 80 is otherwise closed during normal (e.g. full power) reactor operation. FIG. 9 illustrates an embodiment of a steam generator flow by-pass system 99 comprising one or more baffles 90. The auxiliary flow 48 through the baffles 90 may operate or function similarly as described above with respect to the embodiments illustrated in FIGS. 4-8. For example, during normal operation of the power module 40, little or no auxiliary flow 48 may be allowed to exit through the one or more baffles 90. During a shut-down operation, auxiliary flow 48 through the baffles 90 may be enabled or increased. In one embodiment, the one or more baffles 90 rotate about a pivot to open or close. Baffle 90A illustrates a baffle in a closed position, whereas baffle 90B illustrates a baffle in an open position. The one or more baffles 90 may open or close depending on the flow rate of the coolant flow 42,46, as these flow rates may exert pressure PI, P2 on the one or more baffles 90. If a flow rate or pressure differential between pressures PI, P2 is great enough, the one or more baffles 90 may close, and prohibit a flow of coolant through the steam generator flow by-pass system 99. The steam generator flow by-pass system 99 may further comprise a return mechanism, such as a spring, that returns the one or more baffles 90 to an open position when the flow rate drops below some predetermined threshold. In one embodiment, the steam generator flow by-pass system 99 comprises a screen with miniature louvers or baffles that allow the passage of boiling coolant, but prohibit or limit the passage of single phase coolant. FIG. 10 illustrates an embodiment of a steam generator flow by-pass system 109 comprising a temperature activated passage 100. The passage 100 may be configured to open due to a change in temperature within the reactor vessel 52 (FIG. 4). In one embodiment, the steam generator flow by-pass system 109 comprises a bi-metallic cover located over the passageway, wherein the bi-metallic cover comprises materials having different thermal 5 expansion rates or properties. In one embodiment, the passageway is formed between the riser 24 and the shroud 22. A first end of the temperature activated passage 100 may be fixed or otherwise attached to the reactor housing 20 (FIG. 4). Due to the different thermal expansion properties, a second end of the temperature activated passage 100 may bend away from the reactor housing 20 with a force Fo as a reactor temperature decreases. A passageway through the reactor housing 20 may therefore be formed which allows the auxiliary flow 48 to exit the steam generator flow by-pass system 109. As the reactor temperature increases, the temperature activated passage 100 may relax, or bend back to cover the passageway (shown by reference 100A) and reduce or stop the auxiliary flow 48 from exiting the reactor housing 20. FIG. 11 illustrates an embodiment of a steam generator flow by-pass system 119 comprising a ball check valve 110. The ball check valve 110 may move in a bi-direction sense, such that in one position it allows the auxiliary flow 48 to pass through the steam generator flow by-pass system 119, whereas in a second position (e.g. shown as reference 110A) it limits or prohibits the release of auxiliary flow 48 out of the reactor housing 20. The steam generator flow by-pass system 119 may comprise a return spring 115 that urges the ball check valve 110 toward the open, first position. The amount of force exerted by the return spring 115 may exceed the force due to the coolant flow 48 during a shut-down condition, for example. During normal operation, a flow rate due to coolant flow 65 (FIG. 5) may overcome the force exerted by the return spring 115, and place the ball check valve 110 in the closed, second position 110A. In another embodiment, the weight of the ball in the ball check valve provides the downward force of the ball check valve 110, replacing the need for the return spring 115. In another embodiment, a spring is located near the bottom of the ball check valve 110, instead of as shown in FIG. 11. The spring expands during normal operation due to an increase in temperature, urging the ball check valve 110 toward the closed, second position 110A. The spring contracts during a power down condition due to a decrease in temperature, urging the ball check valve 110 toward the open, first position. FIG. 12 illustrates an embodiment of a steam generator flow by-pass system 129 actuated by control rods 125A, 125B. The steam generator flow by-pass system 129 may comprise one or more vents or valves 120 attached to the reactor housing 20. In one embodiment, the steam generator flow by-pass system 129 is attached to the reactor housing 20 intermediate the shroud 22 and the riser 24. When the control rods (identified as reference number 125B) are removed from the reactor core 6, the steam generator flow by-pass system 129 may be actuated to be closed, such that little or no auxiliary flow is allowed to exit the reactor housing 20. The steam generator flow by-pass system 129 may be closed, for example, during normal or full-power operation of the power module 40. When the control rods (identified as reference number 125A) are inserted into the reactor core 6, the steam generator flow by-pass system 129 may be actuated to be open, such that the auxiliary flow is allowed to exit the reactor housing 20. The steam generator flow by-pass system 129 may be open, for example, during shut-down or a power down operation of the power module 40. One or more switches or sensors may determine when the control rods 125A, 125B are inserted or removed from the reactor core 6, and send a signal to actuate the steam generator flow by-pass system 129. FIG. 13 illustrates an alternative embodiment of a steam generator flow by-pass system 139 actuated by control rods 135A, 135B. The steam generator flow by-pass system 139 may comprise one or more control rods designed such that when withdrawn (135A) for operation they obstruct the flow path of the by-pass system, and when inserted (135B) during power down conditions they provide an open passage to auxiliary coolant by-pass flow 48. The location of the control rods 135A, 135B allow or prevent the auxiliary flow of primary coolant to pass through the housing 20. In one embodiment, the steam generator flow bypass system 139 is attached to the reactor housing 20 intermediate the shroud 22 and the riser 24. One or more switches or sensors may determine when the control rods are inserted 25 (135B) or removed (135A) from the reactor core 6. FIG. 14 illustrates a novel method of cooling a reactor core using a steam generator flow by-pass system. The method may be understood to operate with, but not limited by, various embodiments illustrated herein as FIGS. 1-13. At operation 140 a primary coolant is circulated through a reactor housing comprising an upper riser and a lower shroud, wherein a primary flow path of the primary coolant passes by a heat exchanger proximately located about the riser, and wherein the primary coolant enters the lower shroud. At operation 150, a loss of coolant accident (LOCA) or a depressurization event is detected. The LOCA or depressurization event may indicate a reduced amount of coolant or pressure in the reactor vessel. At operation 160, a fluid level of the primary coolant is decreased below the top of the riser, wherein the primary coolant exits the riser as steam. In one embodiment, the primary coolant that exits the riser as steam condenses as liquid coolant before being combined with an auxiliary flow path of the primary coolant that is circulated through an auxiliary passageway in the reactor housing. At operation 170, the auxiliary flow path of the primary coolant is circulated through the auxiliary passageway provided in the reactor housing, wherein the auxiliary flow path of the primary coolant exits the reactor housing without passing by the heat exchanger. In one embodiment, the auxiliary flow path of the primary coolant circulates through the auxiliary passageway due to a difference in hydrostatic forces on either side of the passageway. At operation 180, the primary coolant from the auxiliary flow path is combined with the primary coolant from the primary flow path that enters the lower shroud. In one embodiment, chemical additives soluble in coolant of a nuclear reactor are combined with the primary coolant of a nuclear reactor, modifying the nuclear and chemical characteristics of the coolant. A loss of primary coolant inventory is detected, and a fluid level of the primary coolant is decreased such that the nominal flow path is interrupted or reduced. Production of steam occurs in the core region, and exits the riser as steam. Nonvolatile additives in the primary coolant are concentrated in the core, and coolant devoid of the non-volatile additives collects in regions observing condensation. The primary coolant is circulated through a passageway provided in the reactor housing, wherein the coolant devoid of additives is combined with the coolant with increased concentration of additives, providing mixing of the coolant streams and mitigating the concentration process. Circulating the auxiliary flow path of the primary coolant through the auxiliary passageway reduces a concentration of non-volatile additives in the primary coolant within the reactor housing. Although the embodiments provided herein have primarily described a pressurized water reactor, it should be apparent to one skilled in the art that the embodiments may be applied to other types of nuclear power systems as described or with some obvious modification. For example, the embodiments or variations thereof may also be made operable with a boiling water reactor or more generally to any other integrated passive reactor design. The rate of release of the coolant into the containment vessel, the rate of condensation of the coolant into a liquid, and the rate of increase of pressure in the containment vessel, as well as other rates and values described herein are provided by way of example only. Other rates and values may be determined through experimentation such as by construction of full scale or scaled models of a nuclear reactor. Having described and illustrated the principles of the disclosure in a preferred embodiment thereof, it should be apparent that aspects may be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims. |
|
050864432 | abstract | Background-reducing x-ray multilayer mirror. A multiple-layer "wavetrap" deposited over the surface of a layered, synthetic-microstructure soft x-ray mirror optimized for reflectivity at chosen wavelengths is disclosed for reducing the reflectivity of undesired, longer wavelength incident radiation incident thereon. In three separate mirror designs employing an alternating molybdenum and silicon layered, mirrored structure overlaid by two layers of a molybdenum/silicon pair anti-reflection coating, reflectivities of near normal incidence 133, 171, and 186 .ANG. wavelengths have been optimized, while that at 304 .ANG. has been minimized. The optimization process involves the choice of materials, the composition of the layer/pairs as well as the number thereof, and the distance therebetween for the mirror, and the simultaneous choice of materials, the composition of the layer/pairs, and their number and distance for the "wavetrap." |
summary | ||
claims | 1. A fuel bundle for a nuclear reactor comprising:a first fuel element including thorium dioxide;a second fuel element including a first uranium fuel having a first fissile content; anda third fuel element including a second uranium fuel having a second fissile content;wherein the first fissile content and the second fissile content are substantially the same,wherein the first fuel element, the second fuel element, and the third fuel element are arranged such that a common coolant flows over each of the first fuel element, the second fuel element, and the third fuel element; andwherein the first uranium fuel and the second uranium fuel are each blended uranium fuel;wherein the blended uranium fuel comprises a blend of at least two of recycled uranium (RU), depleted uranium (DU), and slightly enriched uranium (SEU);wherein the fuel bundle is substantially free of post processed plutonium. 2. The fuel bundle of claim 1, wherein the first fuel element includes a first plurality of tubes containing the thorium dioxide. 3. The fuel bundle of claim 2, wherein the first plurality of tubes includes seven parallel tubes containing the thorium dioxide. 4. The fuel bundle of claim 2, wherein the first plurality of tubes includes eight parallel tubes containing the thorium dioxide. 5. The fuel bundle of claim 2, wherein the second fuel element includes a second plurality of tubes containing the uranium having the first fissile content and positioned radially outward from the first plurality of tubes containing the thorium dioxide. 6. The fuel bundle of claim 5, wherein the second plurality of tubes includes twelve parallel tubes containing the uranium having the first fissile content. 7. The fuel bundle of claim 5, wherein the second plurality of tubes includes fourteen parallel tubes containing the uranium having the first fissile content. 8. The fuel bundle of claim 5, wherein at least one of the second plurality of tubes is different in cross-sectional size than that of at least one of the first plurality of tubes. 9. The fuel bundle of claim 5, wherein the third fuel element includes a third plurality of tubes containing the uranium having the second fissile content and positioned radially outward from the second plurality of tubes containing the uranium having the first fissile content. 10. The fuel bundle of claim 9, wherein the third plurality of tubes includes eighteen parallel tubes containing the uranium having the second fissile content. 11. The fuel bundle of claim 9, wherein the third plurality of tubes includes twenty-one parallel tubes containing the uranium having the second fissile content. 12. The fuel bundle of claim 9, wherein at least one of the third plurality of tubes is different in cross-sectional size than that of at least one of the first plurality of tubes. 13. The fuel bundle of claim 9, wherein at least one of the third plurality of tubes is different is cross-sectional size than that of at least one of the second plurality of tubes. 14. The fuel bundle of any of claim 10, wherein the uranium included in at least one of second plurality of tubes and the third plurality of tubes is included with a burnable poison. 15. The fuel bundle of any of claim 10, wherein the thorium dioxide included in the first plurality of tubes is included with a burnable poison. 16. The fuel bundle of claim 9, comprising a fourth fuel element including at least one tube. 17. The fuel bundle of claim 16, wherein the first plurality of tubes is positioned radially outward from the at least one tube of the fourth fuel element. 18. The fuel bundle of claim 17, wherein the at least one tube includes thorium dioxide or a burnable poison. 19. A nuclear reactor comprising:a tube of pressurized fluid; andthe fuel bundle of claim 1. 20. The fuel bundle of claim 1, wherein the first fissile content and the second fissile content are greater than 1.8 wt %. |
|
description | This application claims benefit of priority to U.S. Provisional Patent Application No. 60/652,127, filed Feb. 11, 2005, and U.S. Provisional Patent Application No. 60/654,922, filed Feb. 22, 2005, both of which are incorporated herein by reference. 1. Field of the Invention This disclosure relates to the field of x-ray imaging, and more particularly to the dynamic low-dose imaging of an object or subject with a moving detector, as well as to the dynamic low-dose tomosynthesis and limited-angle tomographic imaging of a subject with a moving detector and a moving x-ray source. Specific applications are in the sub-fields of fluoroscopy, radiography, and cardiology. Other applications are in the fields of non-destructive testing, homeland security, and animal imaging. 2. Description of the Related Art A number of interventional procedures utilize x-ray as the preferred imaging modality for intervention planning, guidance, monitoring, and control. Although x-ray imaging systems for this purpose are widely available, prior-art systems and approaches are significantly limited. In particular, prior art interventional imaging poses the major impediments of high subject radiation dose and cumulative physician exposure to radiation. In certain procedures, the subject x-ray dose may be high enough to burn the subject's skin. Furthermore, a significant fraction of experienced radiologists and cardiologists are approaching or have reached their annual or life-time accumulated dose limit, and are therefore prevented from, or limited in, the practice of their skills. In a typical fluoroscopic procedure, an area detector is used to provide a fairly wide imaging field (typically 6 to 16 inches) at a high refresh rate (30 frames per second, or higher). Over the years, image-intensifier technology has evolved to provide electronic amplification and viewing of images. In general, the x-ray image formed on an input phosphor screen is amplified in intensity by a very large factor, by the electronics of a vacuum envelope within an image intensifier. The bright, but typically reduced-area output image is electronically recorded by a video system, and then displayed to the physician in essentially real time. Recently, a number of vendors have introduced digital detectors with refresh rate and x-ray absorption efficiency comparable to that of the image intensifier. However, these improvements have not resolved the issues of high subject and attendant dosage. Current technologies are further limited, in part, due to use of large area detectors and large exposure area beams. While a number of systems currently offered provide adjustable field-of-view imaging, a large exposure field is desirable to allow the physician to track the progress of an intervention and to maintain view of specific anatomical landmarks during a procedure. The requirement for a large exposed area translates into high detector costs and the need for a scatter-rejecting Bucky grid, which absorbs about one-half of emitted radiation and thus requires that the applied dose be increased by a factor of two. This adds to the aforementioned high subject and attendant dose; furthermore, the requirement for a large exposed area results in relatively low refresh rates over the entire image. For example, read-out of an entire large area detector, or a large area of such a detector, limits the imaging refresh rate. Cardiology and neurology interventions, which typically require the insertion of a catheter or similar interventional device in the subject's vasculature, can necessitate continuous or intermittent subject exposures for extended durations, resulting in high x-ray doses. For example, specific cardiology procedures using current, known technologies, such as in electro-physiology, can last for more than one hour, and accordingly necessitate very high subject doses. Interventional radiologists, cardiologists and other attending staff are also subject to significant x-ray exposure and dose, to such a degree that dose limitation regulations may prevent them from active work for a significant fraction of their available time, thus leading to underutilization of expensive resources. Three-dimensional (3D) imaging currently requires complex and expensive systems. In addition, most currently available 3D imaging systems also deliver high subject doses, and often limit access to the subject due to use of a gantry, a large area detector or a combination of area detectors. The methods and system disclosed herein allow for low-dose x-ray examinations as well as dynamic multispectral x-ray imaging in both radiographic and fluoroscopic modes, by translating and rotating a narrow-aperture detector and shaping a beam of x-rays accordingly, or by sweeping or rotating a beam of specific shape across the face of an area detector. Such innovations may facilitate real-time tracking and low-dose imaging of a catheter tip or other object (e.g., a biopsy needle or a surgical tool) inserted in a subject during an interventional procedure, for example as performed in interventional radiography, interventional neurology and interventional cardiology. In a more general sense, the disclosed methods and system facilitate real-time guidance of surgery. In one embodiment, x-ray examination of a subject or object involves scanning an x-ray fan-beam of specific shape across the subject or object. A detector is mounted on a movable assembly below the subject table, for example on a detector tray. The detector tray enables (a) independent scanning motions in two (preferably orthogonal) directions of a plane or other surface, typically chosen to be parallel to a subject table plane, and (b) independent rotation of the detector. The detector moves simultaneously along these degrees of freedom. In one embodiment, a method for dynamic x-ray imaging of a subject includes generating an x-ray beam having a non-circular shape about a beam central axis; and irradiating at least part of the subject with the non-circular beam while rotating the non-circular beam about the beam central axis. In one embodiment, a method for dynamic x-ray imaging of an object or part of an object includes moving a detector tray supporting a detector having a non-circular shape by rotating the detector tray. An x-ray beam is shaped to generally match the shape or part of the shape of the detector. The x-ray beam is moved or oriented to track the motion of the non-circular detector. A system for dynamic x-ray imaging of an object or part of an object includes a gantry to rotate a detector of non-circular shape, and a collimator to shape an x-ray beam to generally match the shape or part of the shape of the non-circular detector. An included beam orientation mechanism tracks the motion of the non-circular detector with the x-ray beam. The foregoing embodiments may also serve in dynamic, low-dose x-ray tomosynthesis and limited angle tomographic imaging systems. In a particular embodiment, an x-ray source and a detector of a specific shape are moved simultaneously along a number of motion axes, an x-ray beam from the source tracking location and motion of the detector. Multiple images are taken and may be mathematically processed to image a plurality of slices or horizons through a subject. In another embodiment, the x-ray source and detector may be stationary, while the subject is moved along one or more motion axes. One advantage to this type of tomosynthesis system is that it may be constructed and arranged for operation in a plurality of selectable imaging states including a tomosynthesis state and a non-tomosynthesis state. The use of a rotating collimator and/or rotating detector for low dose imaging permits, for example, the use of a narrow shaped beam in imaging performed as a fluoroscopic system, while also the same system may be operated by different control instructions to provide tomosynthesis. Still further, the disclosed instrumentalities may be incorporated in multi-spectral imaging systems with or without computer assisted diagnosis (CAD). One example of this would be to retrofit the system that is shown and described in U.S. Pat. No. 6,950,492, which is hereby incorporated by reference to the same extent as though fully disclosed herein. This type of system, for example, may be provided with a rotating collimator assembly as described herein, as well as a rotating detector driven in synchronicity with the collimator assembly. Other objects and advantages of the present disclosure will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, embodiments of the present invention are disclosed. Before proceeding with the detailed description, it should be noted that the matter contained in the following description and/or shown in the accompanying drawings may be embodied in various forms, and should therefore be interpreted as illustrative, and not in a limiting sense. Elements shown in the drawings are not necessarily to scale and may be exaggerated, enlarged or simplified, to facilitate understanding of the invention. The system implementation according to the various shown embodiments is amenable to automated controls. These may use circuitry including a controller or driver to interface with a computer. Processing may be accomplished using one or more processing units operably coupled with memory and data storage devices. System operations may be governed by program instructions and/or circuitry. Actuation, as described below, may be accomplished under motive force provided by step motors that are governed by these controls, where such motors are operably coupled with gears or drive belts to accomplished the desired movements. Motive force may alternatively be provided manually, as well as by pneumatic, hydraulic, or magnetic devices. In one aspect, servo mechanisms may be governed by feedback control to maintain alignment between a shaped beam that is emitted through a collimator and a shaped detector. This is particularly useful in embodiments that utilize a rotating collimator and a rotating detector that move in synchronicity with one another. In one example of this where the detector is slightly oversize relative to the beam, a detector sense signal indicating misalignment may result in the detector and/or the collimator being rotated to restore alignment. Furthermore, the detector sense signal may be interpolated for projection onto a uniform reference grid so that there is no loss of data. Turning now to FIG. 1A, a system 100 for dynamic low dose x-ray imaging is shown in a top orthogonal view. System 100 for example allows a significant reduction in subject and physician dose while permitting effective performance of an interventional procedure. A frame structure (or cradle) 102, designed for placement beneath or within a subject table (see, e.g., table 1110; FIG. 11), permits relative motion of a detector assembly 104 (shown bounded by a circle) with respect to the table. An x-ray tube apparatus assembly, such as a column or x-ray source assembly having an x-ray tube and a collimator, may for example be set upon rails that allow motion of the assembly in a direction generally parallel to the subject table. In one embodiment, a tube column assembly 106 is placed on one side of cradle 102 and the subject table, and may be dynamically rolled along rails 108 (or similar translation structure, such as a slide or roller assembly), which are for example parallel to the subject table, during the examination. In one embodiment, an x-ray tube 110 pivots with respect to a pivot axis (x′) 112 that lies generally parallel to the subject table (alternatively, image plane x O z). The combination of independent detector motion (relative to a surface that is often chosen to be parallel to the plane of the subject table), tube column translation and tube rotation, together with an adjustable collimator assembly (e.g., assembly 1010, described herein below with respect to FIG. 10), allows projection of an x-ray beam 114 of specific shape towards any area on the subject table. FIG. 1B depicts a front view and FIG. 1C depicts a side view of system 100. Combined FIGS. 1A-1C show a longitudinal subject axis (z) 116, a lateral axis (x) 118 and a table-to-source axis (y) 120. Axis y′ 122 (shown in FIG. 3) passes through the detector assembly 104 center of rotation and is orthogonal to a detector tray, e.g., rotable tray 204, FIG. 2. FIG. 1D is a perspective view illustrating exemplary geometry of system 100. An object or subject axis z′ 124 is for example generally parallel to longitudinal axis 116, and passes through the object or subject's center of gravity. In the case of subject imaging, this axis 124 may be collinear with the subject's main axis of elongation. In the case of inanimate object imaging, the object axis is chosen by convention to be parallel to longitudinal axis 116 and passing through the object's center of gravity. The x-ray source, e.g., projection source (S) 126 is located at a point that does not belong to the chosen object axis, and is retained as defining the vertex of a geometric projection source. A projection direction 128 is then defined as the line passing by the projection source 126 and the object axis 124 and orthogonal to the object axis 124; projection plane 130 is then defined as the plane containing object axis 124 and orthogonal to the projection direction 128. Sp represents the orthogonal projection of source 126 upon plane 130. An x-ray beam as shaped and defined by a collimator assembly, described herein below with respect to FIG. 10, presents at least one defined main direction, corresponding to the most elongated beam dimension as projected onto the projection plane 130. The intersection of the elongate beam axis and projection plane 130 defines a line 132 on the projection plane 130. The aforementioned directions may be determined according to a fixed, or laboratory reference system 134. Further, an x-ray beam shaped and defined by a collimator assembly according to the principles laid out herein presents a beam central axis 136 passing through the source 126 and generally passing through the geometric center of the beam projection in plane 130 or in the plane of detector assembly 104. In practice, such a beam central axis may be chosen to correspond to the rotational axis of a rotating collimator assembly, for example as described herein below with respect to FIGS. 10A-10B and 14. The beam central axis may also be chosen to pass through the detector assembly 104 center of rotation. It is noted that, in general, the beam projection onto plane (P) does not include point Sp, nor does the x-ray beam necessarily include projection direction 128. As shown in FIG. 2, system 100 may provide a fast, full-frame sampling detector assembly, designed according to the principles disclosed herein. Detector assembly 104 for example includes a detector 200 having detector cells 202 arranged as a matrix, shown as having a rectangular shape. Detector 200 may mount on a moveable assembly, such as a detector tray 204, itself assembled on sets of rails 206 and 208 underneath or within a subject examination table (e.g., table 606, FIG. 6), which enable independent motion along two directions x and z. As shown in FIG. 2, detector tray 204 is circular; however, alternate shapes may be utilized in connection with detector 200. In the embodiment illustrated in FIG. 2, detector tray 204 has three degrees of freedom: (1) translation Δz along the longitudinal table/subject axis 116, (2) translation Δx along the orthogonal direction 118 in the plane of the subject table, and (3) rotation Δθ with respect to axis y′ 122 (see FIG. 3), which is generally orthogonal to the plane of the subject table and generally in the direction of axis 120. These degrees of freedom may be activated independently, in combination, in turn or simultaneously. FIG. 2 illustrates part of the mechanical assembly that enables these motions. Detector tray 204 is mounted on an assembly (illustrated as two beams 210 parallel to axis 116). Beams 210 terminate at a system of wheels or similar translation structure, such as a slide or roller assembly (not shown) that allows motorized translation along rails 206, parallel to x axis 118. Rails 206 also terminate at a system of wheels or similar translation structure, such as a slide or roller assembly (not shown) that rolls on parallel rails 208, oriented parallel to z axis 116. Accordingly, the center or center of rotation O′ 212 of detector tray 204 can be juxtaposed with any location within a plane (or upon a surface) that is generally parallel to the subject table, for example, image plane x O z, shown in FIG. 5 (subject to mechanical limitations on excursion ranges), by actuation of motors for translation along rails 206, 210 (motors not shown). Further, as shown in FIG. 3, detector tray 204 is mounted with a rotation axis y′ 122 generally orthogonal to a plane that is locally tangent to the detector motion surface or plane (e.g., image plane x O z, FIG. 5). Detector tray 204 may freely rotate around axis 122. FIG. 3 provides a cross-sectional view of detector assembly 104 along the line AA′ 214 of FIG. 2. Line AA′ passes through detector center 212 and is parallel to the elongate axis of detector 200, e.g., parallel to a plane including detector cells 202. Power is for example provided to detector 200 via a brush link 302 and a slip-ring 304 assembly, although it is understood that power provision may be accomplished using alternate components. Transmission of detector data between rotating tray 204 and a detector base 306 may be provided by a transmitter and receiver assembly, for example including transmit and receive elements 308, 310, which transmit detector data through radio-frequency (RF) signals. However, other known methods of data transfer, such as brush-link data transfer, may provide data transmission from rotating tray 204 to base 306 (and from base 306 to tray 204). Detector base 306 is a non-rotating base, for example due to fixed mounting on a non-rotating portion of detector assembly 104. Transmit/receive elements 308, 310 may mount with rotating tray 204 and non-rotating detector base 306, respectively. The above-described combination of features facilitates unimpeded and unlimited rotation of detector tray 204 for any number of clockwise or counter-clockwise revolutions generally in the plane of the detector, and further enables transmission of power and data to and from detector assembly 104. Alternatively, and in other embodiments, detector motions may be restricted to two directions within a plane; or motion may be restricted to a single scan direction, either within a plane or along a curved path. FIGS. 4A-4D illustrate four of a number of possible detector cell arrangements upon detector tray 204. FIG. 4A shows a matrix of detector cells 402 arranged along a slot, as elongated rectangular matrix 403. In one embodiment, detector matrices are designed as a combination of square or rectangular detector modules that can be tiled along any dimension in a plane or surface. Current detector technologies allow design of such modules, possibly including backplane read-out; with such an arrangement, the spacing or gap between adjacent detector modules can be reduced to a dimension less than or equal to that of the detector cell pitch. FIG. 4A also shows the intersection 190 of an x-ray beam (not shown) central axis with the plane (e.g., image plane x O z, FIG. 5) of detector assembly 104. FIG. 4B shows rectangular matrix 403 of FIG. 4A with additional detector modules 404 provided near center of rotation 212. Such an arrangement, when properly matched by a source-collimator assembly, may provide effective trade-offs between the amount of area that is under continuous x-ray exposure and the areas more distal from center of rotation 212, which are exposed only twice for each full rotation of detector tray 204. As shown in FIG. 4C, alternate (or additional) detector module arrays 406 may be provided. Arrays 406 for example have various widths, lengths and detector cell sizes, along with other variable design parameters, and may be generally arranged along a plurality of radial lines passing through center of rotation 212. FIG. 4D illustrates the use of four additional detector module arrays 408 arranged as lines that are for example matched to a multi-slot collimator assembly. Many other arrangements of module arrays 408, such as areas of varying widths, lengths and detector cell resolution, are possible and may be designed to optimize specific performance. The fast, full-frame sampling detector allows refresh of the part of an image disk, such as a portion of the fixed image grid that is covered by tray 204, that is spatially coincident with a rotating detector at various rates. In one example of this, areas near rotation axis 122 may be refreshed at the intrinsic detector sample rate, while areas toward the periphery of the disk can be refreshed at a rate that is a function of detector sample rate, detector angular velocity, and detector cell arrangement. This flexibility facilitates relatively slow refresh of the outer part of an image, while faster refresh is provided at and near the image center, thus achieving an overall reduction in dose. In an interventional procedure using a catheter, for example, the faster refresh at the image center allows a physician to focus clearly on the catheter tip. The refresh rate at the image periphery is for example sufficient to provide landmark data for navigation, while still reducing overall dose to the patient, physician and any attending staff. Dose is reduced because at any given time, a much smaller total area is exposed to radiation as compared with conventional fluoroscopy procedures. Further, as a Bucky grid is not necessary when using a beam covering a reduced area, another two-fold dose reduction may be realized because the delivered dose does not have to be increased to compensate for Bucky grid absorption. An x-ray source filter (not shown) can be shaped to provide proportionally increased flux towards the extremities of the detector matrix (e.g., detector matrix 403) so that upon continuous rotation, the x-ray dose to various areas of an image disk can be further modulated, by design. In such an embodiment, the filter, located on the tube side of the imaging chain, provides more x-ray attenuation at the image center, and gradually less attenuation towards the side ends of the x-ray beam. Alternatively, the filter may be made of materials with essentially uniform attenuation properties. In other embodiments, such as those employing a plurality of detector lines or areas, the filter can be designed to essentially match the detector shape. Furthermore, different filter properties may be used for each of the corresponding detector areas or lines, therefore providing for simultaneous multi-spectral imaging. In a simple example with a detector array comprising two orthogonal rectangular cell arrays, one of the rectangular detector areas could be illuminated by a high energy beam, while the second rectangular area would be imaged by a low energy beam. FIG. 5 illustrates the relationship between detector samples 502 and image grid points 504. In a general case, a given detector sample contributes to a number of image grid samples in a local neighborhood. A number of algorithms have been described, such as the “gridding” algorithm first used in astronomy, that allow efficient interpolation and distribution of the detector samples to the image grid samples. As is seen from FIG. 5, in a general case, center of rotation 212 corresponds to the origin of the referential (x″ O z″) associated with the moving detector. The origin may be on any point with respect to the table or image plane (x O z), and rotation angle θ 506 may take any value. FIG. 6 illustrates the use of a real-time interventional device localization system 600 together with the dynamic x-ray system described herein above. In one embodiment, three radio-frequency emitters/receivers 604 (not to scale) are placed adjacent a subject table 606 and in such an arrangement as to provide sufficient signal separation for accurate three-dimensional device tip localization. A small assembly 608, for example having three coils, is contained within a device tip (which is for example within region of interest 612, shown bounded by a dotted circle). Analysis of the signals thus received at one or a multiplicity of frequencies permits accurate, real-time localization of the device tip with respect to the table coordinate system, as known in the art. This localization information is fed-back in real-time to the dynamic x-ray imaging system (e.g., system 100), and adjustments are dynamically made to the detector tray position (e.g., tray 204 position), x-ray tube column position (e.g., column 106 position), x-ray tube angle (e.g., tube 110 angle), and x-ray collimator assembly position (e.g., assembly 1010 position), as necessary to track the progress of the device tip with a detected x-ray beam. Further adjustments to detector raster mode, location and rotation may be made as necessary to enable dynamic tracking of the device tip. Scanning modes include translation of the detector along either the direction parallel to or the direction orthogonal to the short axis of the detector cell matrix (e.g., in directions z″ or x″ of FIG. 5); combinations of parallel and orthogonal translations; rotation of the detector with respect to center of rotation axis 122, and combinations of rotation and translation motions of the detector tray within the plane of the detector assembly. In a specific imaging mode, and for illustration, it might be desirable to ensure that the center 212 of detector tray 204 is always positioned with respect to table 606 and the system x-ray tube (e.g., tube 110) in such a manner that the x-ray shadow of the device tip projects onto center 212. Tracking may rely on automatic device tip detection in the projection image, motion of the detector assembly and/or motions of the x-ray imaging chain. A dynamic fluoroscopic image is obtained by simultaneously rotating tray 204 with respect to its instantaneous center, rotating the collimator assembly in synchronicity with the rotating tray 204, and/or translating and/or rotating the collimator across the x-ray port and/or rotating the x-ray tube, for acquiring x-ray data. Synchronicity between the tray and the collimator may be provided mechanically, by design, or through a feedback loop and sensing of relative motion of the x-ray beam with respect to the detector, for example feedback from pixels radiated by the beam penumbra may indicate misalignment between the tray and collimator. Other applications and modes of implementation are also possible. X-ray data acquisition may be performed in either a pulsed or a continuous mode. In addition, other device or object localization systems or instruments may be employed with system 100. FIG. 7 presents a block diagram showing system components. The system comprises an image acquisition and review workstation 710, an interface to an hospital or imaging network 730, and a gantry 740. The image acquisition and review workstation 710 has an acquisition workstation 712 with a graphical user interface (UIF) 713; a controller 714 which receives inputs from external devices such as an EKG and/or a device localization system, and drives x-ray emission, acquisition, system motions, and tracking; a data-preprocessing computer architecture 716 for data calibrations and corrections; an image reconstruction and decomposition engine 718; an image display 720; and, for specific application, a feature detection and characterization engine 722 interfacing to a database 724. The gantry 740 includes: a high-voltage generator and inverter 742 for the generation of time-varying kVp and mA waveforms; a controller 744 for the selection of an anode track and control of x-ray sources and x-ray focal spot parameters (the selection and control of which may vary as a function of time); a controller 746 for the activation of x-ray filters and collimation devices (such action also variable as a function of time); a motion control architecture 748 which itself comprises a controller 750 for the subject, detector cradle, and x-ray tube column positioning and a controller 752 for the motions of the detector assembly (e.g., along z, x axes 118, 116 and rotation Δθ about axis 122). FIG. 8 shows an exemplary data acquisition sequence 800. Following startup of the sequence, the user provides input information relating to the subject/object to be imaged, and type of data acquisition sequence to be performed, in step 802. Step 802 for example includes selection of acquisition parameters and input of body information at graphical UIF 713, of FIG. 7. The subject/object is then positioned, in step 804. The acquisition sequence and EKG and device localization feedback are initialized in step 806. Feedback from an EKG and/or feedback from device localization inputs may occur in essentially real time, or data acquisition may proceed according to a pre-determined imaging sequence. The synchronized acquisition sequence (indicated by dotted box 808) controls selection of spectra, including selection of: an anode track, in step 810; a focal spot geometry, in step 812; x-ray techniques, for example selection of KVp or mA waveforms, in step 814, and filtration, in step 816. The x-ray source and detector assembly are set in motion, in step 818, for example to perform a specific series of image acquisition sequence, to generate a particular imaging raster, or to dynamically track an interventional device tip such as a catheter, sheath, guide wire or other interventional object such as a biopsy needle or a radiation seed implant, e.g., in brachytherapy applications. Collimator controls are activated to dynamically track the detector location and orientation or to perform a specified acquisition sequence, in step 820. Collimator controls are for example activated as a function of body position of a subject upon a subject table, and/or other acquisition parameters. Data is acquired, in step 821, and calibration data is gathered, in step 822. Acquired data (gathered in step 821) is pre-processed, using the calibration data, in step 824. Calibrations and pre-processing is for example performed by computer architecture 716. An image reconstruction model is generated, in step 826, and an image decomposition model is generated, in step 828. Image reconstruction and decomposition is performed using the reconstruction and decomposition models of steps 826, 828, for example by image reconstruction and decomposition engine 718, in step 830. As may be desirable, the image data are automatically analyzed by a CAD engine, in step 832. The CAD engine, e.g., characterization engine 722, for example provides automatic detection, characterization, and classification of features by data processing and/or by accessing a database, in step 834. Acquired images are then displayed, in step 836, and reviewed, in step 838. A user for example provides inputs via UIF 713 as necessary, for image review. FIG. 9 details a method 900 for image reconstruction using an image reconstruction algorithm, e.g., as performed by engine 718, FIG. 7. Raw projection data are re-ordered and interpolated (if necessary depending on the specifics of the data acquisition sequence), in step 902. Following pre-processing of projection data, in step 904, the algorithm proceeds to image generation. Image generation commences with a determination of whether or not dynamic multispectral x-ray imaging (DXMI) is used, decision 906. In the case of a DMXI image acquisition sequence, a stack of multispectral projection images is obtained, in step 908. These images are decomposed using either a matrix inversion approach, step 910, or an iterative approach, step 912. A stack of decomposed projection images is acquired (via step 910 or 912), in step 914. The acquired images are then used to refresh the full field image, in step 916, thus providing a fluoroscopy or radiography image sequence, step 918. Alternatively, when DMXI is not used according to decision 906, a further case differentiation is made depending upon rotation of the detector tray, in decision 920. If the detector tray is not rotating, but translating (with the detector tray in an arbitrary angle), various simpler interpolation algorithms may be employed to dynamically build and refresh the full field image, e.g., by interpolating the detector raster to image grid, in step 922. The full field image is refreshed, step 916, and the fluoroscopic or radiographic image sequence generated, in step 918. Alternately, if the detector tray is rotating, decision 920, a more complex interpolation algorithm, such as a gridding algorithm, is employed, in step 924, for image field refresh, step 916, and generation of a fluoroscopic or radiographic image sequence, step 918. The choice of x-ray techniques as well as image frame rate contributes to the distinction between fluoroscopic and radiographic sequences. FIG. 10A schematically shows one embodiment of a collimator assembly 1010. A collimator 1020 is mounted on a rotatable ring 1022. Such ring can also be translated along an axis x″ 1024, by rolling along two rails 1026 parallel to x″. A system of collimator blades such as independently adjustable sets of blades 1028 and 1030 mount with the rotatable part of the collimator. Collimator blades 1028 and 1030 open or close along their respective axes, for example to effect an aperture 1032 and an aperture 1032 location that allow a narrow x-ray beam to be generated and to project onto a detector (e.g., detector assembly 104) for any position and/or orientation of the detector. A beam of specific shape, such as a beam including a number of fans (with or without a central wide area), may also be defined by blades 1028 and 1030 as subjected to suitable modifications (not shown). The shaped beam is then translated or rotated across the face of a large area detector or in synchronicity with the motion of a detector of specific shape. In one embodiment, the shape of the x-ray beam is adjusted to reflect a specific arrangement of detector cells. FIG. 10B shows an aperture 1050 shaped to match the arrangement of cells 402, 404 in FIG. 4B. Aperture 1050 is defined for example by an aperture plate 1052; however, aperture 1050 may also be defined by combining plate 1052 with blades 1028, 1030. Aperture 1050 size and shape may thus be controlled by any one of blades 1028, blades 1030 and aperture plate 1052, or by any combination of blades 1028, 1030 and plate 1052. To allow a continuous rotation mode, power is provided to the rotatable part of collimator assembly 1010, for example through a slip-ring and brush design (see, e.g., brush link 302 and a slip-ring 304 assembly, FIG. 3). Collimator assembly 1010 includes a filter (not shown), which may include filter materials of various attenuation and x-ray energy filtration properties. In one embodiment, filter attenuation varies from the center to the sides of collimator 1020; in another embodiment, different filters may be provided for each of the different areas of the collimator aperture 1050. Simplified collimator embodiments are also provided by use of an aperture plate 1052, providing for beam formation in a shape matching that of the detector cells such that variations in the projection imaging geometry during an imaging sequence are accounted for. For example, plate 1052 may ensure that a maximum beam width remains less than the width of the associated active detector array. The combination of x-ray aperture, collimator and filter shapes the x-ray beam both spatially and spectrally, as is known in the art. Shaping may also be accomplished using only an aperture and a filter, a collimator and a filter, or a lone collimator. Dynamically adjustable blades 1028, 1030 may provide a beam of specific width that in typical operation always projects onto the x-ray detector. Further, the width and position of the x-ray beam with respect to the detector matrix may be dynamically adjusted during the image acquisition sequence. This width adjustment, in particular, provides further control of the x-ray dose and noise properties of the image. Analysis of the full-frame data enables tracking of the beam umbra and penumbra onto the active detector. The location and orientation of the beam with respect to the detector as a function of time, for example, allows computerized, automatic prediction of necessary imaging chain (x-ray tube, collimator, detector) adjustments to either track the detector for a given imaging sequence, and/or to track a moving point such as the tip of an interventional device. Accordingly, detector motion may be tracked in real time based on detected x-ray profile information and/or instantaneous detector coordinate information. Tracking is for example achieved by a combination of the following motions: relative advance of the subject table with respect to the x-ray column, either by table motion or x-ray column motion; x-ray tube pivoting; collimator translations, for example along pivot axis 112, FIG. 1A and/or along an axis generally orthogonal to axis 112 (not shown); collimator rotation, and collimator blades adjustment (both with respect to the width and length of the collimator-defined aperture). In one embodiment, a specific raster and rotation sequence is programmed into both the detector tray controls and into the x-ray tube and collimator assembly controls. By these instrumentalities, the x-ray beam is spatially shaped to match at least part of the moving detector, in the sense that part of the active detector is illuminated by the beam umbra (largest intensity), and the beam penumbra (or area of drop in intensity) is also imaged by the active detector. For a detector of given shape, the collimator may be adjusted such that the x-ray beam illuminates only part of the detector, For example, if a detector has an elongated array with additional cells along a second, generally elongated array, the collimator may be adjusted such that the x-ray beam illuminates only one of the two elongated arrays. Many other geometries are possible for both the detector and the collimator, as guided by the choice of x-ray imaging sequence and application type. FIG. 11 illustrates one embodiment of a system 1100 for dynamic, low-dose x-ray imaging utilizing an additional degree of freedom. A subject-supporting table 1110 is adjustable via mechanical actuators 1112, allowing positioning of table 1110 with respect to detector cradle 102. This feature provides for variable geometry and variable magnification of a subject onto a detector plane. Both cradle 102 and subject table 1110 elevation along axis 120 can be adjusted via a cradle support 1114 and corresponding actuators (not shown). In one embodied image acquisition mode, both dynamic multi-spectral x-ray imaging (DMXI) acquisition and detector tray rotation occur simultaneously. FIG. 12 illustrates a corresponding method for image acquisition. Method 1200 is for example governed by an image acquisition algorithm. Each array or array cell may be subject to variable timing, depending on the specifics of a given acquisition sequence as well as location within the detector. Such variable timing may include both offsets and sample times. Thus, detector timing sequences are determined, in step 1210. Data read-out for each column of the utilized detector array is independently determined, based on image acquisition sequence parameters and detector rotation, in step 1220. Gridding image reconstruction (or similar interpolation method) is performed for the acquired frames, in step 1230. A stack of multispectral projection images is generated, in step 1240. These projection images are input to a decomposition algorithm that performs either a matrix inversion or similar analytical decomposition (e.g., SVD regularization), in step 1250, or an iterative inversion, in step 1260. Accordingly, a stack of decomposed projection images is generated, in step 1270. The acquired decomposed images are then used to refresh the full field image, in step 1280, and to generate a fluoroscopy or radiography image sequence, in step 1290. FIG. 13 illustrates use of a system for dynamic, low-dose x-ray imaging for imaging of parcels, inspection of parts, imaging of containers and the like. In one embodiment, system 1300 includes a conveyor belt 1310 for transporting a parcel 1320 to be imaged. Acquisition of a multiplicity of projections of the same object may be facilitated by simultaneous translation of the x-ray tube column along, for example, z axis 116. FIGS. 14A-14B depict a collimator assembly 1410 with collimator apertures 1420A, 1420B and collimator blades (not shown), shapes a beam to a specific shape 1430A, 1430B as projected onto a detector 1440. The beam 1450 is scanned and/or rotated across the face of detector 1440, which is for example a two-dimensional detector. Data is read out of detector 1440 either in a raster fashion or, as possible with newer technologies such as CMOS design, read-out of pre-determined areas in a specific sequence. FIGS. 14A and 14B present two embodiments for two specific x-ray beam shapes. FIGS. 15A-15C schematically present a set of detector motions with respect to a number of axes. Tomosynthesis or limited-angle tomographic imaging may be enabled by moving a detector of specific shape along motion axes of FIGS. 15A-15C, while simultaneously moving the x-ray source along motion axes of FIGS. 15A-15C and shaping an x-ray beam to track the location and motion of the detector. Alternately, one or both of the x-ray source and detector may remain stationary during all or part of the imaging sequence. Where both the source and detector are stationary, an object to be imaged may move through an x-ray beam emitting from source to detector. For example, an object such as a suitcase moving along a conveyor belt may pass through the beam generated by stationary column assembly 106. Such an embodiment may find particular use in security screening applications, such as airport security or customs inspections. In particular, FIG. 15A illustrates rotation of x-ray tube column assembly 106 by an angle φ 1510 with respect to rotation axis y′ 1515 shown in FIG. 15B. FIG. 15B in turn presents motion of tube column assembly 106 along axis x′ 1520 essentially including the x-ray tube 110 long axis. A displacement Δx′ 1530 enables acquisition of a multiplicity of projections at various angles. Column assembly 106 (or x-ray tube 110) may rotate to track motion of an associated detector, e.g., detector 200. Alternately, column assembly 106 may remain stationary while detector 200 rotates, for example upon tray 204. In another embodiment, for example as described above with respect to airport security, above, both column assembly 106 and detector 200 center 212 remain stationary while a subject or object to be imaged moves through a rotating x-ray beam. FIG. 15C illustrates rotation of angle δ 1540 of column assembly 106. This motion may also enable acquisition of a multiplicity of projections at various view angles; a similar effect may be enabled by translating x-ray tube 110 along z axis 116, as might be possible through rolling of the entire column 106 in this direction. In one embodied mode of operation, the detector performs an initial “scout” scan of either the entire table or of a sub-area as prescribed by the user. Based on this initial scout image, the user or the system computer prescribes an area to be imaged. A number of imaging modes are possible, including linear raster scan of the area (possibly including a multiplicity of raster scan lines), or a combination of translation of the detector tray rotation axis O′ together with continuous rotation of the detector around rotation axis y′. In a second embodied mode of operation, the system is set to track the progress of an interventional tool, such as the tip of a catheter or other interventional device. The system automatically selects the detector tray center O′ position so that the projection of the device tip is superimposed with the detector center O′. These automatic motions may be achieved either with or without simultaneous x-ray column translation along the subject table and associated x-ray tube pivoting with respect to axis x′, depending on the imaging mode selected. Once the device tip has reached the theatre of operation (such as the coronary arteries in a cardiology procedure), the detector continues rotation around O′, while minor adjustments to the O′ location are dynamically made to maintain the device tip at image or detector tray center. The point O′ may also be held at a given position, while fluoroscopic image refresh occurs through the continuous acquisition of data by the rotating detector. Alternatively, the detector trajectory may not include rotation, but be limited to a sequence of scans along specific raster lines, with the detector main axis either orthogonal or at a non-90-degrees angle with respect to the scan direction. In another embodied mode of operation, adjustment of various system parameters, including relative position of the x-ray tube apparatus with respect to the object and detector, allow dynamically acquisition of several images of the same object for various projection angles and projection geometries. The projections may be chosen dynamically by the user, or the system may automatically loop through a pre-determined sequence of projections. Dynamic operation of the system may also enable acquisition of image data at different levels of image noise, spatial resolution or spectral composition. In particular, the system may first be operated at a first level of resolution, noise, spectral composition or other imaging parameter, and then be switched to a higher resolution or reduced noise mode or different spectral composition, for example upon user or automatic detection of an abnormality or threat. Imaging acquisition may also take place at various levels of resolution, either dynamically in time or spatially; such various resolution and noise levels being for instance achieved through variable binning of the native resolution detector pixels. The various detector lines or arrays may have variable native pixel resolution as a function of the line or as a function of distance from detector iso-center. The present instrumentalities may be applied to the operation of flat-panels area detectors, either specifically designed or operated as follows: A beam of specific shape and spectral characteristics is swept across the active surface of the detector. In one embodiment, a fan-beam is scanned linearly and/or rotated using a collimator assembly and methods according to the principles described herein. In another embodiment, a beam of more complex shape (such as may be formed by a collimator plate as described above) and/or containing several fans and a central area, is scanned linearly and/or rotated. The flat-panel data are read out to allow image formation and image refresh at rates depending on the spatial location of a given image pixel. The present instrumentalities further apply to the operation of computed tomography (CT) systems, either specifically designed or operated as follows: A beam of specific shape and spectral characteristics is swept across the active surface of the detector, as described in the paragraph above. The beam sweeping may occur independently or simultaneously with gantry rotation. In all embodiments where the detected x-ray beam is under-collimated with respect to the active detector, detector cells that are not exposed by the primary beam or by the beam penumbra detect scattered radiation. These measurements may be leveraged to perform scatter correction and or further object analysis and characterization. Full-frame sampling of the active detector allows closed-loop dynamic adjustments to the x-ray beam parameters, including peak kilo-voltage, tube current, tube target location and selection, and filtration, to adapt x-ray imaging parameters to the composition of the object or anatomy being imaged. In a tomosynthesis or limited-angle tomographic imaging mode, the x-ray source is set in motion along at least one of axes z 116 (column rolling), x′ 1520 (tube translation along tube main axis), rotation of angle φ 1510 with respect to y′ 122, or rotation of angle δ, 1540, or any motion that similarly contributes to the acquisition of a multiplicity of views (or projections) of the object to be imaged. Given the dynamics of the x-ray tube and the dynamics of the detector, the tracking algorithm orients tube angle (rotation with respect to the axis x′) and/or collimator position and orientation, such that an x-ray beam of the appropriate shape projects onto the active part of the detector. This sequence of data acquisition results in the obtaining of a multiplicity of projection data that are then input to the 3D image reconstruction algorithm. A 3D image sequence can then be refreshed with the newly reconstructed information. Thus the system is designed for a fourth-dimensional data acquisition (time varying 3D data sets). The advantages of the above described apparatus embodiments, improvements, and methods should be readily apparent to one skilled in the art, as to enabling the design of low-dose dynamic x-ray imaging systems and low-dose tomosynthesis and limited-angle computed tomography. Additional design considerations may be incorporated without departing from the spirit and scope of the invention. It should thus be noted that the matter contained in the above description and/or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. Accordingly, the following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present methods, and systems which, as a matter of language, might be said to fall therebetween. |
|
049869582 | claims | 1. A fuel assembly having a plurality of fuel rods and a water rod occupying an area for accommodating at least four fuel rods, wherein, in the upper region of said fuel assembly, the proportion of fuel rods among fuel rods located in an outermost peripheral section of said fuel assembly whose enrichment in their respective upper regions is greater than the average enrichment in the upper region of said fuel assembly is not less than 50 percent, and in the lower region of said fuel assembly, the proportion of fuel rods among fuel rods located in the outermost peripheral section of said fuel assembly whose enrichment in their respective lower regions is greater than the average enrichment in the lower region of said fuel assembly is not greater than 20 percent. 2. A fuel assembly according to claim 1, wherein said average enrichment in said upper region of said fuel assembly is greater than said average enrichment in said lower region of said fuel assembly. 3. A fuel assembly according to claim 1, wherein the boundary between said upper region and said lower region is located within the range from 1/3 to 7/12 of the overall axial length of said effective fuel length portion when the lower end of said effective fuel length portion of said fuel assembly is determined as the base point. 4. A fuel assembly according to claim 2, wherein the quantity of burnable poison contained in said upper region of said fuel assembly is greater than the quantity of burnable poison contained in said lower region of said fuel assembly. |
055240429 | description | DETAILED DESCRIPTION OF THE INVENTION The continuously increasing production and resolution requirements for manufacturing semiconductor devices has led to the development of an electron storage ring (ESR) based X-ray lithography system (XLS). The major subunits of an ESR based XLS include a preaccelerator, beam transport line, electron storage ring (synchrotron), lithography beamlines and exposure stations (aligner/stepper). A typical beamline for an XLS is described in U.S. Pat. No. 5,031,199 the specification of which is hereby incorporated by reference thereto. One basic ESR XLS performance requirement is to support 0.25-0.10 micron lithography resolution with a given stepper. One of the resolution related optical parameters is the lithography exposure window. The elements that form the exposure window in the beamline and the stepper include mirrors, filters and an exit window. One of the functions of the exit window is to separate the beamline from the stepper (lithography chamber) and contribute to the formation of the exposure window. The beamline connects the synchrotron to the exposure chamber where the actual lithography takes place. The beamline operates at an ultra high vacuum (UHV) while the exposure chamber operates at about 760 mm Hg (atmospheric pressure). In order to ensure the vacuum integrity of the beamline, the exit window must be able to withstand at least this pressure differential. In addition, the material of the window must be transmissive to that portion of the spectrum which is required for lithography (between 800 eV and 1800 eV) and substantially attenuate X-rays above and below the desired energy band. Moreover, the effects on the X-ray beam power uniformity of the X-ray beam passing through the exit window must be considered. A high performance ESR based XLS requires that the power uniformity in the beam be 95% or better. The exit window of the present invention achieves all of the above requirements. Referring now to FIG. 1, there is shown a stationary exit window assembly 10 which can be utilized in accordance with the present invention. The assembly 10 includes a support structure 12 to support exit window 14. An X-ray beam 16 travels in the direction shown, from the beamline (not shown) through exit window 14 and finally to the stepper or exposure chamber (not shown). Bellows 18 are provided to maintain the pressure in the beamline at an ultra high vacuum and bellows 20 are provided to maintain the pressure in the exposure chamber at atmospheric pressure. Referring now to FIGS. 2, 3(a), 3(b) and 4 there is shown respective cross-sectional, front, detailed front, and perspective views of the exit window 14 of the present invention. The window 14 includes a thin material 22 having a window section 24 disposed within an opening 26 of a frame 28. The dotted lines 29 represent the separation between the beamline and the exposure chamber. As shown in FIG. 3(a), the width "a" represents the width of an exposure field 31 on a wafer (not shown) in the exposure chamber as well as the width of opening 26. As shown in the full front view of the window in FIG. 3(b), the window section 24 includes first and second end sections 30, 32 and a middle section 34 disposed between the first and second end sections 30, 32. The window 14 also includes a flat rectangular peripheral section 36 which is integral with each of sections 30, 32 and 34 of window section 24 and extends within frame 28. As shown in FIG. 3(b) and the one-quarter perspective view of FIG. 4, the first and second end sections 30, 32 have a substantially concave shape that tapers to a flat shape 38 near a periphery 41 of the opening 26. The shape of the end sections 30, 32 can be analogized to a dome that is cut in two having its upper lip pulled back. The middle section 34 has a shape that is substantially concave along its width and linear along its length and tapering to flat surfaces 42 near the periphery 41 of the opening 26. As will be described below, middle section 34 has a substantially constant surface radius R which is preferably as large as possible so as to minimize the effects on beam power uniformity of the X-ray beam passing through exit window 14. AS shown in FIG. 2, frame 28 is provided to securely fasten the thin material 22 in place. The frame 28 consists of first and second frame members 44, 46 each having an opening that is preferably rectangular and equal to the exposure field on the wafer. Each of members 44, 46 is tube shaped with a rectangular cross section and integral with rectangular shoulders 48, 50 respectively which extend perpendicularly from one end of each of members 44, 46. The members 44, 46 are held together, and the thin material 22 is secured by pins 52 on opposite sides of each of shoulders 48, 50 as shown in FIG. 3(a). In order to seal the UHV of the beamline from the atmospheric pressure in the exposure chamber a seal 54 is positioned within the member 44 and abuts the thin material 22 between the members 44, 46. The seal 54 completely surrounds the opening 26 and can be formed of aluminum. Although the frame 28 and opening 26 have been described as having rectangular shapes, it should be understood by those skilled in the art that other shapes, such as spherical and ellipsoidal can be utilized. However the rectangular shape is preferred because spherical and ellipsoid shapes require thicker exit window materials which increase the absorption of radiation and therefore decreases the radiation intensity passing through the window. By providing an exit window 14 having the shape described above, the present invention allows the window to withstand the 14.7 psi pressure differential between the beamline and the exposure chamber and the thin material to be thin enough to allow the desired energy spectrum through the window while substantially attenuating the energy band above and below the desired range. The exit window 14 can withstand a pressure differential of up to 44.1 psi. A preferred material for the thin material 22 of exit window 14 is beryllium having a thickness between 16-25 microns. Other materials that can be used for the thin material 22 include carbon (diamond), silicon, silicon carbide, and silicon nitrite having a thickness between 25-35 microns. Referring now to FIG. 5, there is shown a graph of the relative beam transmission as a function of exit window thickness for three different exit window materials. As shown in FIG. 5, beryllium is preferred since the silicon and carbon exit windows yield lower radiation transmissions and require more intensive cooling and which leads to a lower production throughput. Referring now to FIG. 6, there is shown a graph of the radiation intensity of the X-ray beam emitted through the exit window 14 of the present invention. The exit window had a thickness of 18 microns. As seen in FIG. 6, the exit window of the present invention allows the desired energy spectrum (800-1800 eV) through the window while substantially attenuating the energy band above and below the desired energy band. In a production X-ray lithography beamline application the exit window size is dictated by the size of the exposure field (chip size). A performance requirement for ESR based XLS is that the exposure field (chip sizes) on a wafer must be 25 mm.times.50 mm or larger with wafer diameters of 200 mm. By providing the exit window 14 having the shape described above, the present invention allows the exit window to meet this requirement by allowing the width "a" of opening 26 to be 25 mm or larger and the length "b" of opening 26 to be 50 mm or larger. In this embodiment, the width "e" of the thin material 22 can be 42 mm and the length "f" of the thin material 22 can be 120 mm. Thus, the present invention provides an exit window 14 that can support a stationary exit window. The cross-section of the X-ray beam scanned over the exit window is typically a few mm in the vertical dimension and 50 mm or wider. In order to fully illuminate the exposure field this beam is scanned over the entire vertical dimension of 25 mm or a stationary beam is used and the target (mask and wafer) is moved relative to the stationary beam. In either case, the present invention allows the exit window to be stationary. This is in marked contrast to prior art exit windows that require a synchronously scanning exit window to be scanned along with the X-ray beam. The stationary exit window of the present invention has a simpler design and operation over scanning exit windows which contribute to a longer lifetime. The stationary window has the advantage that no mechanical movement is required. In addition, no control system is required and the heat load is distributed on a larger surface area. The present invention is also directed to a method of scanning the X-ray beam emitted from the X-ray lithography beamline onto the exposure field 31 of a wafer (not shown). The method includes the step of positioning a stationary exit window having an opening 26 approximately equal to the exposure field 31 between the beamline and the wafer. The material 22 of the exit window has a shape and thickness such that it can withstand a pressure differential of at least 14.7 psi and is transmissive to the desirable energy band. A vacuum is created within the beamline such that there is a pressure differential of at least 14.7 psi between the beamline and the exposure chamber containing the wafer. Next, the X-ray beam is scanned between first and second positions 56, 58 such that the X-ray beam passes through the exit window 14 and is incident on the exposure field 31 between first and second edges 57, 59 thereof. The X-ray beam as passed through the exit window 14 has X-rays above and below the desired energy band substantially attenuated due to the thickness of the material 22 of the exit window 14. The beam power transmission variation generated by the beam deflection as a result of the shape of the exit window must be considered. As shown in FIG. 2, as the beam scans between first and second positions 56, 58 the beam only contacts the curved surface 60 having a substantially constant surface radius R. The scanned beam approaches the curved surface 60 of middle section 34 at various angles and thus passes through increasing thickness of material 22 as it moves away from the center line 62 (zero deflection) towards the top and bottom of the window. This virtual thickness is a function of the material thickness, the curvature of the surface 60 and the deflection angle "d". Referring now to FIG. 7, there is shown a graph of the relative beam power transmission variation over one half of the scanned field. It is clear from the graph that a window with a large surface radius R and a small deflection angle are desirable to minimize the virtual thickness and the accompanied beam power transmission variations. For example, FIG. 7 shows the beam power as a function of the scanning angle for three different values of R ranging from 1.3 inches to 3.0 inches. As shown in FIG. 7, an exit window with a surface radius R.gtoreq.2 inches would provide the required at least 95% power uniformity at the indicated 0.13.degree. beam deflection. Although shown and described in what we believed to be the most practical and preferred embodiments, it is apparent that departures from the specific methods and designs described and shown will suggest themselves to those skilled in the art and may be made without departing from the spirit and scope of the invention. We, therefore, do not wish to restrict ourselves to the particular constructions described and illustrated, but desire to avail ourselves of all modifications that may fall within the scope of the appended claims. |
description | The present application claims the benefit of U.S. Provisional Patent Application No. 62/458,377, titled “STEEL-VANADIUM ALLOY CLADDING FOR FUEL ELEMENT”, filed Feb. 13, 2017. When used in nuclear reactors, nuclear fuel is typically provided with cladding. The cladding may be provided to contain the fuel and/or to prevent the fuel from interacting with an external environment. For example, some nuclear fuels are chemically reactive with coolants or other materials that may otherwise come in contact with the nuclear fuel absent the cladding to act as a separator. The cladding may or may not be a structural element. For example, in some cases the nuclear fuel is a solid structural element, e.g., a solid rod of uranium metal or uranium dioxide, and the cladding is essentially a coating applied to the surface of the solid fuel. In other cases, nuclear fuel may be in a liquid form, powder form, or aggregate form, e.g., pellets or grains, that may require containment in a structural cladding. In any case, the cladding may take the form of a tube, box, or vessel within which the fuel is placed. The fuel and cladding combinations are often referred to as a “fuel element”, “fuel rod”, or a “fuel pin”. Fuel clad chemical interaction (FCCI) in metallic fuel systems refers to the degradation of fuel elements due to the chemical reaction between the fuel and clad components. The chemical interaction is due, at least in part, to multicomponent interdiffusion of species from the cladding into the fuel and vice versa. Specifically, diffusion couple and irradiation experiments both demonstrate migration of clad components (iron and nickel) into the fuel, while fission products (primarily the lanthanides like cerium, neodymium, and praseodymium) diffuse outward into the clad. FCCI leads to two primary concerns: reduction of clad mechanical properties from formation of brittle intermetallic compounds and wastage/thinning of the cladding, and formation of relatively low melting compositions within the fuel and clad interface. These concerns ultimately affect performance limits for the fuel system, with the peak inner clad temperature (PICT) being influenced by the low melting point (725° C.) of the uranium-iron eutectic that forms at 33 at % Fe. Additionally, the few occurrences of cladding breaches in the fueled region of rods irradiated in EBR-II exhibited extensive FCCI adjacent to the breach locations (max penetrations up to 170 μm into the clad), implicating FCCI as a primary contributor to these breaches. Although sodium-bonded metal fuel pins have been irradiated to peak burnups up to 20 at % with manageable amounts of FCCI, these irradiations typically were performed over the course of two to four years. Beyond the higher peak burnups (30 at %) required for a traveling wave reactor (TWR) application, the extended service time at temperature greatly compounds the concerns of degradation due to FCCI. This disclosure describes various configurations and components for bimetallic and trimetallic claddings for use as a wall element separating nuclear material from an external environment. The cladding materials are suitable for use as cladding for nuclear fuel elements, particularly for fuel elements that will be exposed to sodium or other coolants or environments with a propensity to react with the nuclear fuel. Structural Steel Layer with Carbon-doped Vanadium Liner FIG. 1 illustrates a cut away view of a linear section of cladding, or wall element, showing the two-layer construction of the cladding. The cladding 100 may be part of any structural component that separates nuclear fuel from a reactive, external environment. For example, the cladding 100 may be part of a wall of a tube containing nuclear fuel, a vessel or any other shape of storage container. In an alternative embodiment, rather than being a section of wall of a container, the cladding may be the resulting layers on the surface of a solid nuclear fuel created by some deposition or cladding technique. These techniques, such as electroplating, thermal spray coating, chemical vapor deposition, sputtering, ion implantation, ion plating, sputter deposition, laser surface alloying, hot dipping, and annealing to name but a few, are well known in the art and, depending on the desired end cladding properties, any suitable technique may be used. Regardless of the manufacturing technology used, the cladding 100 shown in FIG. 1 consists of two layers 102, 104 of material: a first layer 102 and a second, structural, layer 104 that is the structural element of the cladding. The first layer 102 separates the fuel, or the storage area where the fuel will be placed if the fuel has not been provided yet, from the structural layer 104. The first layer 102 acts as a liner that protects the structural layer 104 from contact with the fuel. The second layer 104 is between the first layer 102 and the external environment. Thus, the first layer 102 is a layer of material with one surface exposed to the fuel and the other surface exposed to the second layer 104 while the second layer 104 has a first-layer-facing surface and a surface exposed to the external environment. The cladding 100 illustrated in FIG. 1 has a first layer 102 of a material selected to reduce the effects of FCCI on both the properties of the first layer 102 and the stored fuel and also selected to reduce the effects of detrimental chemical interactions between the second layer 104 and first layer 102. In an embodiment, the first layer 102 is carbon-doped vanadium and the second layer is a steel. To reduce the interaction between the steel and the carbon-doped vanadium layers, in an embodiment the carbon-doped vanadium is doped with at least 0.001 wt. % (10 ppm) carbon. This will reduce the amount of decarburization observed in the steel and reduce the degradation of the steel while in use as a fuel element. In an embodiment the carbon-doped vanadium is a vanadium carbon alloy consisting of at least 99.0 wt. % V; 0.001-0.5 wt. % C; with the balance other elements, wherein the carbon-doped vanadium includes not greater than 0.1 wt. % of any one of the other elements, and wherein the total of the other elements does not exceed 0.5 wt. %. In more pure embodiments, the total of the other elements (i.e., the total of the composition that is not V or C) does not exceed 0.05, 0.025, or 0.01 wt. % of the alloy. In one specific embodiment, for example, the carbon range is from 0.1 to 0.3 wt. % C, the total of the other elements (everything that is not V or C) combined is less than 0.5 wt. %, and the balance is V. In another specific embodiment, for example, the carbon range is from 0.1 to 0.3 wt. % C, the total of the other elements (everything that is not V or C) combined is less than 0.1 wt. %, and the balance is V. The steel layer 104 may be any suitable steel. Examples of suitable steels include a martensitic steel, a ferritic steel, an austenitic steel, a FeCrAl alloy, an oxide-dispersion strengthened steel, T91 steel, T92 steel, HT9 steel, 316 steel, and 304 steel. The steel may have any type of microstructure. For example, in an embodiment substantially all the steel in the layer 104 has at least one phase chosen from a tempered martensite phase, a ferrite phase, and an austenitic phase. In an embodiment, the steel is an HT9 steel or a modified version of HT9 steel. In one embodiment, the modified HT9 steel is 9.0-12.0 wt. % Cr; 0.001-2.5 wt. % W; 0.001-2.0 wt. % Mo; 0.001-0.5 wt. % Si; up to 0.5 wt. % Ti; up to 0.5 wt. % Zr; up to 0.5 wt. % V; up to 0.5 wt. % Nb; up to 0.3 wt. % Ta; up to 0.1 wt. % N; up to 0.3 wt. % C; and up to 0.01 wt. % B; with the balance being Fe and other elements, wherein the steel includes not greater than 0.15 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %. In other embodiments, the steel may have a narrower range of Si from 0.1 to 0.3 wt. %. The steel of the steel layer 104 may include one or more of carbide precipitates of Ti, Zr, V, Nb, Ta or B, nitride precipitates of Ti, Zr, V, Nb, or Ta, and/or carbo-nitride precipitates of Ti, Zr, V, Nb, or Ta. FIG. 2 illustrates a tubular embodiment of the cladding of FIG. 1. In the embodiment shown, the wall element 200 is in the form of a tube with an interior surface and an exterior surface, the first layer 202 of carbon-doped vanadium forming the interior surface of the tube and the second layer 204 of steel forming the exterior surface of the tube. The fuel storage region is in the center of the tube. Fuel within the tube is thus protected from the reactive external environment at the same time the steel layer 104 is separated from the fuel. The general term wall element is used herein to acknowledge that a tube, vessel or other shape of container may have multiple different walls or sections of a wall of the cladding 100 as illustrated in FIG. 1. That is, the container has a shape that is defined by one or more continuously connected wall elements to form a vessel. However, embodiments of claddings include those that have one or more wall elements that are constructed of materials that are not the cladding 100 as illustrated in FIG. 1 as well as wall elements of the cladding 100. For example, a tube may have a cylindrical wall element of the cladding 100 described in FIG. 1 and FIG. 2 but have end walls of a different construction. Likewise, a cube-shaped fuel container may have sidewalls and a bottom wall constructed as shown in FIG. 1, but a top of different construction. FIG. 3 illustrates the wall element of FIG. 1, but this time with nuclear material 310, including but not limited to nuclear fuel, in contact with the carbon-doped vanadium layer 302. The steel layer 304 may be any thickness (i.e., the shortest distance between the exterior surface of the steel layer 304 that is exposed to the reactive environment and the vanadium layer 302) as necessary to provide the strength properties desired for the cladding. The carbon-doped vanadium layer 302 may have a thickness from that of a thin coating (0.1% of the thickness of the structural layer 304) up to 50% of the thickness of the structural layer 304. For example, embodiments of the carbon-doped vanadium layer have a thickness, as a percentage of the steel layer's thickness, of between any of 0.1%, 0.5%, 1.0%, 2.5%, 5%, 10%, 15%, 20% and 25% on the low end up to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% on the high end. Embodiments of the wall elements include the ranges that are any combination of the upper and lower limits provided above. For example, the above specifically includes embodiments of carbon-doped vanadium layers having ranges from 1-5%, from 0.1-10%, from 20-45%, and from 0.1-50% of the thickness of the steel layer. However, regardless of the thickness of the carbon-doped vanadium layer the primary structural element of the wall element 300 is the steel layer 304. FIG. 4, likewise, illustrates a tubular embodiment of the cladding of FIG. 2, but this time with nuclear material 410, including but not limited to nuclear fuel, in the hollow center of the tube 400. The steel layer 404, again, may be any thickness as necessary to provide the strength properties desired for the cladding. The carbon-doped vanadium layer 402 may have a thickness from that of a thin coating (0.1% of the thickness of the structural layer 404) up to 50% of the thickness of the structural layer 404. However, regardless of the thickness of the carbon-doped vanadium layer the primary structural element of the wall element 400 is the steel layer 404. In an alternative embodiment, the claddings shown in FIGS. 1-4 may be provided with a third, intermediate layer between the steel structural layer and the carbon-doped vanadium layer to further reduce interaction between the steel and the carbon-doped vanadium. Embodiments of suitable intermediate layers are described below with reference to FIGS. 9-12. For the purposes of this application, nuclear material includes any material containing an actinide, regardless of whether it can be used as a nuclear fuel. Thus, any nuclear fuel is a nuclear material but, more broadly, any materials containing a trace amount or more of U, Th, Am, Np, and/or Pu are nuclear materials. Other examples of nuclear materials include spent fuel, depleted uranium, yellowcake, uranium dioxide, metallic uranium with zirconium and/or plutonium, thorium dioxide, thorianite, uranium chloride salts such as salts containing uranium tetrachloride and/or uranium trichloride. Nuclear fuel, on the other hand, includes any fissionable material. Fissionable material includes any nuclide capable of undergoing fission when exposed to low-energy thermal neutrons or high-energy neutrons. Furthermore, fissionable material includes any fissile material, any fertile material or combination of fissile and fertile materials. A fissionable material may contain a metal and/or metal alloy. In one embodiment, the fuel may be a metal fuel. It can be appreciated that metal fuel may offer relatively high heavy metal loadings and excellent neutron economy, which is desirable for breed-and-burn process of a nuclear fission reactor. Depending on the application, fuel may include at least one element chosen from U, Th, Am, Np, and Pu. In one embodiment, the fuel may include at least about 90 wt. % U—e.g., at least 95 wt. %, 98 wt. %, 99 wt. %, 99.5 wt. %, 99.9 wt. %, 99.99 wt. %, or higher of U. The fuel may further include a refractory material, which may include at least one element chosen from Nb, Mo, Ta, W, Re, Zr, V, Ti, Cr, Ru, Rh, Os, Ir, and Hf In one embodiment, the fuel may include additional burnable poisons, such as boron, gadolinium, or indium. In addition, a metal fuel may be alloyed with about 3 wt. % to about 10 wt. % zirconium to dimensionally stabilize the fuel during irradiation and to inhibit low-temperature eutectic and corrosion damage of the cladding. Examples of reactive environments or materials from which the nuclear material is separated from includes reactor coolants such as NaCl—MgCl2, Na, NaK, supercritical CO2, lead, and lead bismuth eutectic. Structural Vanadium Alloy Layer with Steel Liner FIG. 5 illustrates a cut away view of a linear section of cladding, or wall element, showing the two-layer construction of a cladding having a structural vanadium alloy inner layer. Again, the cladding 500 may be part of any structural component that separates nuclear fuel from a reactive, external environment. For example, the cladding 500 may be part of a wall of a tube containing nuclear fuel, a vessel or any other shape of storage container. In an alternative embodiment, rather than being a section of wall of a container, the cladding may be the resulting layers on the surface of a solid nuclear fuel created by some deposition or cladding technique. These techniques, such as electroplating, thermal spray coating, chemical vapor deposition, sputtering, ion implantation, ion plating, sputter deposition, laser surface alloying, hot dipping, and annealing to name but a few, are well known in the art and depending on the desired end cladding properties any suitable technique may be used. Regardless of the manufacturing technology used, the cladding 500 shown in FIG. 5 consists of two layers 502, 504 of material. The first layer 502 is the primary structural element of the cladding and separates the fuel, or the storage area where the fuel will be placed if the fuel has not been provided yet, from the second layer 504. The second layer 504 is between the first layer 502 and the external environment. Thus, the first layer 502 is a layer of material with one surface exposed to the fuel and the other surface exposed to the second layer 504 while the second layer 504 has a first-layer-facing surface and a surface exposed to the external environment. Similar to the cladding described above with reference to FIGS. 1-4, the cladding 500 illustrated in FIG. 5 has a first layer 502 of a material selected to reduce the effects of FCCI on both the structural properties of the first layer 502 and the stored fuel and also selected to reduce the effects of detrimental chemical interactions between the second layer 504 and first layer 502. In an embodiment, the first layer 502 is a vanadium alloy containing at least 90% V and the second layer 504 is a steel. Vanadium alloys that may be used in the first layer 502 include without limitation vanadium carbon alloys, V-20Ti, V-10Cr-5Ti, V-15Cr-5Ti, V-4Cr-4Ti, V-4Cr-4Ti NIFS Heats 1 & 2, V-4Cr-4Ti US Heats 832665 & 8923864, and V-4Cr-4Ti Heat CEA-J57. In an embodiment, the vanadium alloy consists of 3.0-5.0 wt. % Cr; 3.0-5.0 wt. % Ti; and no more than 0.02 wt. % C; with the balance being V and other elements, wherein the vanadium alloy includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. This purity requirement may require special refining of the V and Ti, such as double- or triple-melting of the Ti or electro-refining of the V. In more pure embodiments, the total of these other elements does not exceed 0.4, 0.25, or even 0.1 wt. % of the alloy. The carbon range, depending on the embodiment, may be from 0.0001 to 0.02 wt. % C. The vanadium alloy may include one or more carbide precipitates of Cr, Ti and/or other elements. One particular V-4Cr-4Ti embodiment is provided in TABLE 1, below. TABLE 1ElementWt. FractionVBal.Cr3.5-4.5Ti3.5-4.5Si400-1000 ppmO<200 ppmN<200 ppmC<200 ppmAl<200 ppmFe<200 ppmCu <10 ppmMo <10 ppmNb <10 ppmP <10 ppmS <10 ppmCl <2 ppmTotal of all<100 ppm and not greater thanother elements0.001 wt. % of any one of theother elements. For the embodiment shown in TABLE 1, one suitable manufacturing process is as follows. The source of raw materials may be iodide or electro-refined vanadium with low impurity content and, in an embodiment, the calcium-reduction process is not used to obtain the vanadium. In an embodiment, the titanium source does not include sponge titanium in order to reduce Cl, K, and Na impurities and double- or triple-melting of the titanium feedstock is to be performed to achieve the necessary purity level. The V-4Cr-4Ti may be melted using an appropriate method such as laser beam melting, vacuum arc melting, or cold cathode induction melting, in order to prevent contamination. The ingot is then homogenized to reduce local inhomogeneity of Cr and Ti to <+/<0.3 wt. %. The subsequent ingot is then encapsulated in stainless steel and extruded or hot worked at a temperature from 1100-1300° C. and subsequently warm-rolled at a temperature from 300-900° C. to the final billet size required for bimetallic cladding tube fabrication. One or more intermediate anneals during hot work may be performed at 800-1200° C. for up to three hours in a vacuum furnace. One or more similar anneals may be performed as part of any cold work processing. The anneals during cold work may involve a sequence of anneals from 900-1000° C. (e.g., at 950±10° C.) to soften the vanadium followed by one or more anneals from 700-780° C. to transform the HT9 from martensite to ferrite. Final heat treatment of the bimetallic cladding tube product is performed at 1075±10° C. for 20 minutes with an air cool to room temperature followed by 650-700° C. for 1-3 hours and a rapid cooling rate. The steel layer 504 may be any suitable steel as described above with reference to FIGS. 1-4. For example, in one embodiment the steel is the modified HT9 steel having 9.0-12.0 wt. % Cr; 0.001-2.5 wt. % W; 0.001-2.0 wt. % Mo; 0.001-0.5 wt. % Si; up to 0.5 wt. % Ti; up to 0.5 wt. % Zr; up to 0.5 wt. % V; up to 0.5 wt. % Nb; up to 0.3 wt. % Ta; up to 0.1 wt. % N; up to 0.3 wt. % C; and up to 0.01 wt. % B; with the balance being Fe and other elements, wherein the steel includes not greater than 0.15 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %. In other embodiments, the steel may have a narrower range of Si from 0.1 to 0.3 wt. %. The steel of the steel layer 104 may include one or more of carbide precipitates of Ti, Zr, V, Nb, Ta or B, nitride precipitates of Ti, Zr, V, Nb, or Ta, and/or carbo-nitride precipitates of Ti, Zr, V, Nb, or Ta. As mentioned above, the vanadium alloy layer 502 is the primary structural element of the cladding. That is, the vanadium alloy layer 502 is the layer that provides most of the solid structure maintaining the shape of the fuel element and preventing failure of the cladding and release of nuclear material. The steel layer 504 may be nothing more than a coating of steel on the external surface of the vanadium alloy layer 502. In these embodiments, the vanadium alloy layer is at least twice as thick as the steel layer 504. That is, the steel layer 504 may be as little as 0.001% the thickness of the vanadium alloy layer 502 and up to 50% the thickness of the vanadium alloy layer 502. In various embodiments, the steel layer thickness may be from 0.01%, 0.1% or 1% of the thickness of the vanadium alloy layer 502 and up to 5%, 10%, 15%, 20% or 25% of the thickness of the vanadium alloy layer 502. FIG. 6 illustrates a tubular embodiment of the cladding of FIG. 5. In the embodiment shown, the wall element 600 is in the form of a tube with an interior surface and an exterior surface, the first layer 602 of vanadium alloy forming the interior surface of the tube and the second layer 604 of steel forming the exterior surface of the tube. The fuel storage region is in the center region of the tube. Fuel within the tube is thus protected from the reactive external environment at the same time the steel layer 604 is separated from the fuel. Again, the general term wall element is used herein to acknowledge that a tube, vessel or other shape of container may have multiple different walls or sections of a wall of the cladding 500 as illustrated in FIG. 5. FIG. 7 illustrates the wall element of FIG. 5, but this time with nuclear material 710, including but not limited to nuclear fuel, in contact with the vanadium layer 702. The steel layer 704, again, may be any thickness from a thin coating up to 50% of the thickness of the vanadium alloy structural layer 702. FIG. 8, likewise, illustrates a tubular embodiment of the cladding of FIG. 6, but this time with nuclear material 810, including but not limited to nuclear fuel, in the hollow center of the tube 800. The steel layer 804, again, may be any thickness from a thin coating up to 50% of the thickness of the vanadium layer 802, however, the primary structural element is the vanadium alloy layer 802. In an alternative embodiment, the claddings shown in FIGS. 5-8 may be provided with a third, intermediate layer between the vanadium alloy structural layer and the steel layer to further reduce interaction between the steel and the vanadium alloys. Embodiments of suitable intermediate layers are described below with reference to FIGS. 9-12. In addition to the bi-metallic cladding embodiments, tri-metallic versions of the above claddings may also be useful. Tri-metallic cladding embodiments involve providing an intermediate layer between the steel and vanadium layers described above to reduce interaction between the steel and the vanadium layers. These embodiments include claddings in which the steel layer is the structural layer and claddings in which the vanadium layer is vanadium alloy and acts as the structural layer. In either embodiment, the intermediate layer acts as a barrier to prevent interaction between the steel and the vanadium. In the embodiments in which the steel layer the structural element of the cladding, any of the vanadium materials described herein are suitable for the vanadium layer. In FIGS. 9-12, the tri-metallic cladding embodiment having an intermediate layer with a structural steel layer is specifically illustrated, however, the description discusses multiple tri-metallic cladding embodiments. FIG. 9 illustrates a cut away view of a linear section of another embodiment cladding, or wall element, having a three-layer construction. As with the cladding embodiments discussed above, the vanadium material used in the first layer 902 is again selected to reduce the effects of FCCI on both the properties of the first layer 902 and the fuel to be used in the fuel element. The outer layer 904 is steel, also as described above. In the cladding 900 illustrated, the middle, or intermediate, layer 906 acts as a liner between the steel layer 904 and the vanadium layer 902. In the embodiment shown, the steel layer 904 is the primary structural component of the fuel cladding 900. In this embodiment the steel layer 904 is the thickest layer in order to provide the structural support for the cladding 900. The steel layer 904 may be 50% or more of the total thickness of the cladding 900. For example, embodiments of the steel layer 904 range from lower bounds of 50, 60, 70, 75, 80, 90, 95, 99 or even 99.9% of the total thickness of the cladding 900. The upper bound is limited to some amount less than 100% in which the middle and vanadium layers are sufficient to provide some protection from FCCI. For example, upper bounds of from 75, 80, 90, 95, 99, 99.9 or even 99.999% of the total thickness of the cladding 900 are contemplated. The balance of the thickness is made up by the other two layers. Thus, in a broad embodiment, the cladding may be considered a thick, steel layer facing the coolant, a thin, fuel-side vanadium alloy or carbon-doped vanadium layer, and a thin, protective layer between the two wherein by ‘thin’ it is meant no more than 10% of the total thickness of the cladding. For example, specifically in one embodiment the steel layer 904 of the cladding 900 is at least 99% of the total cladding thickness with each of the middle layer 906 and vanadium alloy layer 902 being from 0.0001% to 0.9% of the total cladding thickness. The materials used in the first layer 902 may be any of those vanadium materials described with reference to FIGS. 1-4 or vanadium alloys described with reference to FIGS. 5-8, above. Likewise, the materials used in the outer steel layer 906 may be any of those steels described with reference to FIGS. 1-8, above. In one embodiment, for example, the steel is the modified HT9 steel defined above. The middle layer 906 is made of a material that has less chemical interaction with the vanadium layer 902 than the steel in the steel layer 904 has with the vanadium alloy layer 902. In this way, the middle layer 906 acts as a protective barrier between the fuel-side vanadium layer 902 and the outside steel layer 904. In an embodiment, the material of the middle layer 906 is selected from nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy. In nickel embodiments, the material is substantially pure, that is, at least 99.9 wt. % Ni; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. In more pure embodiments, the total of these other elements does not exceed 0.025; 0.01, or 0.005 wt. % of the material. In nickel alloy embodiments, the material is at least 90.0 wt. % Ni; with the balance other elements, wherein the material includes not greater than 5.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 10.0 wt. %. In more pure embodiments, the total of these other elements does not exceed 2.5; 1, or 0.5 wt. % of the nickel alloy. In chromium embodiments, the material is substantially pure, that is, at least 99.9 wt. % Cr; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. In more pure embodiments, the total of these other elements does not exceed 0.025; 0.01, or 0.005 wt. % of the material. In chromium alloy embodiments, the material is at least 90.0 wt. % Cr; with the balance other elements, wherein the material includes not greater than 5.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 10.0 wt. %. In more pure embodiments, the total of these other elements does not exceed 5, 2.5; 1, or 0.5 wt. % of the chromium alloy. In zirconium embodiments, the material is substantially pure, that is, at least 99.9 wt. % Zr; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. In more pure embodiments, the total of these other elements does not exceed 0.025; 0.01, or 0.005 wt. % of the material. In zirconium alloy embodiments, the material is at least 90.0 wt. % Zr; with the balance other elements, wherein the material includes not greater than 5.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 10.0 wt. %. In more pure embodiments, the total of these other elements does not exceed 5, 2.5; 1, or 0.5 wt. % of the zirconium alloy. In the embodiment shown, the steel layer is structural support for the cladding, having thicknesses as described above with reference to FIGS. 1-4, and the middle layer 906 and vanadium layer 902 are the thinner layers of the cladding. In an embodiment not shown, the vanadium layer 902 is the thicker, structural layer, having thicknesses as described with reference FIGS. 5-8, and the middle layer 906 and steel layer 904 are the thinner layers of the cladding. As with FIGS. 1-8, however, the steel layer 904 is the outer layer and the vanadium layer 902 is the inner layer. FIG. 10 illustrates a tubular embodiment of the cladding of FIG. 9. In the embodiment shown, the wall element 1000 is in the form of a tube with an interior surface and an exterior surface, the first layer 1002 of vanadium alloy forming the interior surface of the tube and the second layer 1004 of steel forming the exterior surface of the tube, the first and second layers being separated by the middle layer 1006. The fuel storage region is in the center region of the tube. Fuel within the tube is thus protected from the reactive external environment at the same time the steel layer 1004 is separated from the fuel. Again, the general term wall element is used herein to acknowledge that a tube, vessel or other shape of container may have multiple different walls or sections of a wall of the cladding 900 as illustrated in FIG. 9. FIG. 11 illustrates the wall element of FIG. 9, but this time with nuclear material 1110, including but not limited to nuclear fuel, in contact with the vanadium layer 1102 of the wall element 1100. The vanadium layer 1102 is separated from the steel layer 1104 by the middle layer 1106. FIG. 12, likewise, illustrates a tubular embodiment of the cladding of FIG. 9, but this time with nuclear material 1210, including but not limited to nuclear fuel, in the hollow center of the tube 1200. Again, the vanadium layer 1202 is separated from the steel layer 1204 by the middle layer 1206. The three layer steel-vanadium claddings have the benefits of (a) having a steel outer layer to protect the fuel element from exposure to the reactive coolant environment; and (b) the reduced FCCI due to the fuel side vanadium alloy layer. The main structural element may be either of the steel or vanadium layers. FIG. 13 illustrates a method of manufacturing a two or three layer wall element for separating a nuclear material from an external environment, such as those described above. The method 1300 includes manufacturing a first layer, the first layer including at least a steel layer in a first layer manufacturing operation 1302. The first layer is then connected to the second layer that includes at least a layer of vanadium alloy, in a layer connection operation 1304. In an embodiment of the layer connection operation 1304, the vanadium layer is manufactured prior to connecting the second layer to the first layer. In an alternative embodiment of the layer connection operation 1304, the second layer is created by depositing it onto the first layer. In an embodiment of the layer connection operation 1304, the second layer consists only of the vanadium alloy layer and includes connecting the steel layer directly to the vanadium alloy layer. In an embodiment of the first layer construction operation 1302, manufacturing the first layer includes manufacturing a first layer consisting of the steel layer connected to a third layer made of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy and the layer connection operation 1304 includes connecting the first layer to the second layer so that the third layer is between the steel layer and the vanadium alloy layer. In an alternative embodiment, in which the second layer consists of the vanadium alloy layer connected to the third layer of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy, the layer connection operation 1304 includes connecting the first layer to the second layer so that the third layer is between the steel layer and the vanadium alloy layer. FIG. 14a provides a partial illustration of a nuclear fuel assembly 10 utilizing one or more of the claddings described above. The fuel assembly 10, as shown, includes a number of individual fuel elements (or “fuel rods” or “fuel pins”) 11 held within a containment structure 16. FIG. 14b provides a partial illustration of a fuel element 11 in accordance with one embodiment. As shown in this embodiment, the fuel element includes a cladding 13, a fuel 14, and, in some instances, at least one gap 15. Although illustrated as a single element, the cladding 13 is composed of, entirely or at least in part, of the two layer or three layer claddings described above. A fuel is sealed within a cavity created by the exterior cladding 13. In some instances, the multiple fuel materials may be stacked axially as shown in FIG. 14b, but this need not be the case. For example, a fuel element may contain only one fuel material. In one embodiment, gap(s) 15 may be present between the fuel material and the cladding, though gap(s) need not be present. In one embodiment, the gap is filled with a pressurized atmosphere, such as a pressured helium atmosphere. In one embodiment, individual fuel elements 11 may have a thin wire 12 from about 0.8 mm diameter to about 1.6 mm diameter helically wrapped around the circumference of the clad tubing to provide coolant space and mechanical separation of individual fuel elements 11 within the housing of the fuel assemblies 10 (that also serve as the coolant duct). In one embodiment, the cladding 13, and/or wire wrap 12 may be fabricated from ferritic-martensitic steel because of its irradiation performance as indicated by a body of empirical data. The fuel element may have any geometry, both externally and for the internal fuel storage region. For example, in some embodiments shown above, the fuel element is cylindrical and may take the form of a cylindrical rod. In addition, some prismatoid geometries for fuel elements may be particularly efficient. For example, the fuel elements may be right, oblique, or truncated prisms having three or more sides and any polygonal shape for the base. Hexagonal prisms, rectangular prisms, square prisms and triangular prisms are all potentially efficient shapes for packing a fuel assembly. The fuel elements and fuel assembly may be a part of a power generating reactor, which is a part of a nuclear power plant. Heat generated by the nuclear reaction is used to heat a coolant in contact with the exterior of the fuel elements. This heat is then removed and used to drive turbines or other equipment for the beneficial harvesting of power from the removed heat. FIGS. 15A and 15B are micrographs of a trimetallic cladding having an intermediate layer of Ni electroplated to a first layer of vanadium doped with carbon on one side and a second layer of HT9 steel on the other. FIG. 15B is an enlargement of the area of the trimetallic cladding shown within the dashed box in FIG. 15A. In the cladding, the vanadium is doped with 0.2 wt. % C. FIG. 15C shows the chemical composition mapping for the trimetallic claddings of FIGS. 15A and 15B. In FIG. 15C the amount and distribution of Cr, Fe, V, Ni, C and Mo through the region around the middle layer are shown. This analysis shows that at least some vanadium diffused into the middle layer, but little or no vanadium made it into the HT9 layer. Notwithstanding the appended claims, the disclosure is also defined by the following clauses: 1. A wall element consisting of: a first layer of steel; a second layer of at least 90% vanadium; and a third layer of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy between the first layer and the second layer. 2. The wall element of clause 1, wherein the second layer has a thickness that is from 0.1% to 50% of the thickness of the first layer and the third layer has a thickness that is from 0.1% to 50% of the thickness of the first layer. 3. The wall element of clause 1, wherein the second layer has a thickness that is from 1% to 5% of the thickness of the first layer and the third layer has a thickness that is from 1% to 5% of the thickness of the first layer. 4. The wall element of clauses 1-3, wherein the second layer is selected from the vanadium alloys V-20Ti, V-10Cr-5Ti, V-15Cr-5Ti, V-4Cr-4Ti, V-4Cr-4Ti NIFS Heats 1 & 2, V-4Cr-4Ti US Heats 832665 & 8923864, and V-4Cr-4Ti Heat CEA-J57. 5. The wall element of clause 4, wherein the second layer is V-4Cr-4Ti. 6. The wall element of clause 4, wherein the second layer consists of: 3.0-5.0 wt. % Cr; 3.0-5.0 wt. % Ti; and no more than 0.02 wt. % C; with the balance being V and other elements, wherein the vanadium alloy includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. 7. The wall element of clause 5, wherein the second layer consists of: 3.5-4.5 wt. % Cr; 3.5-4.5 wt. % Ti; 0.04-0.1 wt. % Si; up to 0.02 wt. % O; up to 0.02 wt. % N; up to 0.02 wt. % C; up to 0.02 wt. % Al; up to 0.02 wt. % Fe; up to 0.001 wt. % Cu; up to 0.001 wt. % Mo; up to 0.001 wt. % Nb; up to 0.001 wt. % P; up to 0.001 wt. % S; and no more than 0.0002 wt. % Cl; with the balance being V and other elements, wherein the vanadium alloy includes not greater than 0.001 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.01 wt. %. 8. The wall element of clauses 1-4, wherein the second layer consists of: 0.001-0.5 wt. % C; the balance being V and other elements, wherein the second layer includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. 9. The wall element of clause 8, wherein the second layer includes from 0.1 to 0.3 wt. % C in addition to V. 10. The wall element of any of clauses 1-9, wherein the steel of the first layer is selected from a tempered martensitic steel, a ferritic steel, an austenitic steel, an oxide-dispersion strengthened steel, T91 steel, T92 steel, HT9 steel, 316 steel, and 304 steel. 11. The wall element of any of clauses 1-10, wherein the steel of the first layer consists of: 9.0-12.0 wt. % Cr; 0.001-2.5 wt. % W; 0.001-2.0 wt. % Mo; 0.001-0.5 wt. % Si; up to 0.5 wt. % Ti; up to 0.5 wt. % Zr; up to 0.5 wt. % V; up to 0.5 wt. % Nb; up to 0.3 wt. % Ta; up to 0.1 wt. % N; up to 0.3 wt. % C; up to 0.01 wt. % B; the balance being Fe and other elements, wherein the steel includes not greater than 0.15 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %. 12. The wall element of any of clauses 1-11, wherein the steel includes one or more of carbide precipitates of Ti, Zr, V, Nb, Ta or B, nitride precipitates of Ti, Zr, V, Nb, or Ta, and/or carbo-nitride precipitates of Ti, Zr, V, Nb, or Ta. 13. The wall element of any of clauses 5-7, wherein the vanadium alloy includes one or more carbide precipitates of Cr, Ti and/or other elements. 14. The wall element of any of clauses 1-13, wherein the first layer is at least 99% of the total thickness of the wall element and wherein with each of the third layer and second layer being from 0.0001% to 0.5% of the thickness of the first layer. 15. The wall element of any of clauses 1-14, wherein the wall element is in the form of a tube with an interior surface and an exterior surface, the first layer forming the interior surface of the tube and the second layer forming the exterior surface of the tube. 16. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 99.9 wt. % Ni; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. 17. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 90.0 wt. % Ni; with the balance other elements, wherein the material includes not greater than 1.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 5.0 wt. %. 18. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 99.9 wt. % Cr; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. 19. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 90.0 wt. % Cr; with the balance other elements, wherein the material includes not greater than 1.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 5.0 wt. %. 20. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 99.9 wt. % Zr; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. 21. The wall element of any of clauses 1-15, wherein the third layer consists of: at least 90.0 wt. % Zr; with the balance other elements, wherein the material includes not greater than 1.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 5.0 wt. %. 22. A container made, at least in part, from wall elements of any of clauses 1-21. 23. A container for holding a nuclear fuel comprising: at least one wall element separating a fuel storage volume from an external environment; the wall element having a first layer of steel separated from a second layer of at least 90% vanadium by a third layer between the first layer and the second layer; the first layer of the wall contacting the external environment and the second layer contacting and the fuel storage volume; and wherein the third layer consists of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy. 24. The container of clause 23, wherein the container has a shape that is defined by one or more continuously connected wall elements to form a vessel. 25. The container of clause 23, wherein the container is shaped as a cylindrical tube, at least one wall element forming a cylindrical wall of the tube and the fuel storage region being the inside of the tube. 26. The container of any of clauses 23-25, wherein the container includes a bottom wall and one or more sidewalls and at least one wall element forms a bottom wall or sidewall of the container. 27. An article, comprising: an amount of nuclear material; a wall element disposed exterior to the nuclear fuel and separating at least some of the nuclear material from an exterior environment, the wall element consisting of: a first layer of steel in contact with the external environment; and a second layer of at least 90% vanadium in contact with the nuclear material; and a third layer between the first layer and the second layer, the first layer of nickel inhibiting the transfer of carbon from the steel into the vanadium alloy; wherein the third layer consists of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy. 28. The article of clause 27, wherein the nuclear material includes at least one of U, Th, Am, Np, and Pu. 29. The article of clause 27 or 28, wherein the nuclear material includes at least one refractory material chosen from Nb, Mo, Ta, W, Re, Zr, V, Ti, Cr, Ru, Rh, Os, Ir, Nd, and Hf. 30. The article of any of clauses 27-29, wherein the first layer includes a steel, substantially all of which has at least one phase chosen from a tempered martensite phase, a ferrite phase, and an austenitic phase. 31. The article of any of clauses 27-30, wherein the cladding layer includes at least one steel chosen from a martensitic steel, a ferritic steel, an austenitic steel, an oxide-dispersed steel, T91 steel, T92 steel, HT9 steel, 346 steel, and 304 steel. 32. The article of any of clauses 27-31, wherein the nuclear fuel and the wall element are mechanically bonded. 33. The article of any of clauses 27-32, wherein the exterior environment includes molten sodium and the first layer of steel prevents contact between the sodium and the vanadium in the second layer. 34. The article of any of clauses 27-33, wherein the first layer and the second layer are mechanically bonded to opposite sides of the third layer. 35. The article of any of clauses 27-34, wherein the nuclear material includes at least 90 wt. % of U. 36. The article of any of clauses 27-35, wherein the nuclear material is a nuclear fuel and the article is a nuclear fuel element. 37. The article of any of clauses 27-36, wherein the third layer consists of: at least 99.9 wt. % Ni; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. 38. The article of any of clauses 27-36, wherein the third layer consists of: at least 90.0 wt. % Ni; with the balance other elements, wherein the material includes not greater than 5.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 10.0 wt. %. 39. The article of any of clauses 27-36, wherein the third layer consists of: at least 99.9 wt. % Cr; with the balance other elements, wherein the material includes not greater than 0.05 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.1 wt. %. 40. The article of any of clauses 27-36, wherein the third layer consists of: at least 90.0 wt. % Cr; with the balance other elements, wherein the material includes not greater than 5.0 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 10.0 wt. %. 41. The w article of any of clauses 27-36, wherein the second layer consists of: 0.001-0.5 wt. % C; the balance being V and other elements, wherein the second layer includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. 42. A wall element consisting of: a first layer of steel; a second layer of vanadium doped with at least 0.001 wt. % carbon on the first layer of steel, the second layer having no more than 0.5 wt. % of other elements besides V and C. 43. The wall element of clause 42 comprising: a third layer between the first layer and the second layer, the third layer being made of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy. 44. The wall element of clause 42 or 43, wherein the second layer consists of: 0.001-0.5 wt. % C; the balance being V and other elements, wherein the doped vanadium of the second layer includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. 45. The wall element of any of clauses 42-44, wherein the doped vanadium of the second layer includes from 0.1 to 0.3 wt. % C. 46. The wall element of any of clauses 42-45, wherein the steel of the first layer is selected from a tempered martensitic steel, a ferritic steel, an austenitic steel, an oxide-dispersion strengthened steel, T91 steel, T92 steel, HT9 steel, 316 steel, and 304 steel. 47. The wall element of any of clauses 42-46, wherein the steel of the first layer consists of: 9.0-12.0 wt. % Cr; 0.001-2.5 wt. % W; 0.001-2.0 wt. % Mo; 0.001-0.5 wt. % Si; up to 0.5 wt. % Ti; up to 0.5 wt. % Zr; up to 0.5 wt. % V; up to 0.5 wt. % Nb; up to 0.3 wt. % Ta; up to 0.1 wt. % N; up to 0.3 wt. % C; up to 0.01 wt. % B; the balance being Fe and other elements, wherein the steel includes not greater than 0.15 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %. 48. The wall element of any of clauses 42-47, wherein the steel includes one or more of carbide precipitates of Ti, Zr, V, Nb, Ta or B, nitride precipitates of Ti, Zr, V, Nb, or Ta, and/or carbo-nitride precipitates of Ti, Zr, V, Nb, or Ta and/or wherein the vanadium alloy includes one or more carbide precipitates of Cr, Ti and/or other elements. 49. The wall element of clause 42, wherein the second layer has a thickness that is from 0.1% to 50% of the thickness of the first layer. 50. The wall element of any of clauses 42-49, wherein the second layer has a thickness that is from 1% to 5% of the thickness of the first layer. 51. The wall element of any of clauses 42-50, wherein the wall element is in the form of a tube with an interior surface and an exterior surface, the first layer forming the interior surface of the tube and the second layer forming the exterior surface of the tube. 52. The wall element of clause 51 further comprising: an amount of nuclear material within the tube. 53. The article of clause 52, wherein the nuclear material includes one or more elements selected from U, Th, Am, Np, and Pu. 54. The article of clause 52 or 53, wherein the nuclear material includes at least one refractory material chosen from Nb, Mo, Ta, W, Re, Zr, V, Ti, Cr, Ru, Rh, Os, Ir, Nd, and Hf 55. A container for holding a nuclear fuel comprising: at least one wall element separating a fuel storage region from an external environment; the wall element having a first layer of steel attached to a second layer of vanadium doped with at least 0.001 wt. % carbon and having no more than 0.5 wt. % of other elements. the first layer of the wall contacting the external environment and the second layer contacting the fuel storage region. 56. The container of clause 55, wherein the container has a shape that is defined by one or more continuously connected wall elements to form a vessel. 57. The container of clauses 55 or 56, wherein the container is shaped as a cylindrical tube, at least one wall element forming a cylindrical wall of the tube and the fuel storage region being the inside of the tube. 58. The container of any of clauses 55-57, wherein the container includes a bottom wall and one or more sidewalls and at least one wall element forms a bottom wall of the container. 59. The container of any of clauses 55-58, wherein the container includes a bottom wall and one or more sidewalls and at least one wall element forms at least one of the one or more sidewalls of the container. 60. A wall element consisting of: a first layer of steel; a second layer of vanadium alloy on the first layer of steel, wherein the first layer of steel is from 0.1% to 50% of the thickness of the second layer. 61. The wall element of clause 60 comprising: a third layer between the first layer and the second layer, the third layer being made of nickel, nickel alloy, chromium, chromium alloy, zirconium or zirconium alloy. 62. The wall element of clauses 60 or 61, wherein the second layer is selected from the vanadium alloys V-20Ti, V-10Cr-5Ti, V-15Cr-5Ti, V-4Cr-4Ti, V-4Cr-4Ti NIFS Heats 1 & 2, V-4Cr-4Ti US Heats 832665 & 8923864, and V-4Cr-4Ti Heat CEA-J57. 63. The wall element of clause 62, wherein the second layer consists of: 3.0-5.0 wt. % Cr; 3.0-5.0 wt. % Ti; and no more than 0.02 wt. % C; with the balance being V and other elements, wherein the vanadium alloy includes not greater than 0.1 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.5 wt. %. 64. The wall element of clause 62, wherein the second layer consists of: 3.5-4.5 wt. % Cr; 3.5-4.5 wt. % Ti; 0.04-0.1 wt. % Si; up to 0.02 wt. % O; up to 0.02 wt. % N; up to 0.02 wt. % C; up to 0.02 wt. % Al; up to 0.02 wt. % Fe; up to 0.001 wt. % Cu; up to 0.001 wt. % Mo; up to 0.001 wt. % Nb; up to 0.001 wt. % P; up to 0.001 wt. % S; and no more than 0.0002 wt. % Cl; with the balance being V and other elements, wherein the vanadium alloy includes not greater than 0.001 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.01 wt. %. 65. The wall element of any of clauses 60-64, wherein the steel of the first layer is selected from a tempered martensitic steel, a ferritic steel, an austenitic steel, an oxide-dispersion strengthened steel, T91 steel, T92 steel, HT9 steel, 316 steel, and 304 steel. 66. The wall element of clauses 60-64, wherein the steel of the first layer consists of: 9.0-12.0 wt. % Cr; 0.001-2.5 wt. % W; 0.001-2.0 wt. % Mo; 0.001-0.5 wt. % Si; up to 0.5 wt. % Ti; up to 0.5 wt. % Zr; up to 0.5 wt. % V; up to 0.5 wt. % Nb; up to 0.3 wt. % Ta; up to 0.1 wt. % N; up to 0.3 wt. % C; up to 0.01 wt. % B; the balance being Fe and other elements, wherein the steel includes not greater than 0.15 wt. % of each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %. 67. The wall element of any of clauses 60-66, wherein the steel includes one or more of carbide precipitates of Ti, Zr, V, Nb, Ta or B, nitride precipitates of Ti, Zr, V, Nb, or Ta, and/or carbo-nitride precipitates of Ti, Zr, V, Nb, or Ta and/or wherein the vanadium alloy includes one or more carbide precipitates of Cr, Ti and/or other elements. 68. The wall element of any preceding clause, wherein the first layer has a thickness that is from 1% to 5% of the thickness of the second layer. 69. The wall element of any preceding clause, wherein the wall element is in the form of a tube with an interior surface and an exterior surface, the first layer forming the interior surface of the tube and the second layer forming the exterior surface of the tube. 70. A container for holding a nuclear fuel comprising: at least one wall element separating a fuel storage region from an external environment; the wall element having a first layer of steel attached to a second layer of vanadium alloy, wherein the first layer of steel is from 0.1% to 50% of the thickness of the second layer; the first layer of the wall contacting the external environment and the second layer contacting the fuel storage region. 71. The container of clause 70, wherein the container has a shape that is defined by one or more continuously connected wall elements to form a vessel. 72. The container of clause 70 or 71, wherein the container is shaped as a cylindrical tube, at least one wall element forming a cylindrical wall of the tube and the fuel storage region being the inside of the tube. 73. The container of any of clauses 70-72, wherein the container includes a bottom wall and one or more sidewalls and at least one wall element forms a bottom wall of the container. 74. The container of any of clauses 70-73, wherein the container includes a bottom wall and one or more sidewalls and at least one wall element forms at least one of the one or more sidewalls of the container. 75. An article, comprising: an amount of nuclear material; a wall element disposed exterior to the nuclear fuel and separating at least some of the nuclear material from an exterior environment, the wall element consisting of: a first layer of steel; and a second layer of vanadium alloy between the first layer and the nuclear material, wherein the first layer of steel is from 0.1% to 50% of the thickness of the second layer and the first layer of steel separates the second layer from the exterior environment. 76. The article of clause 75, wherein the nuclear material includes at least one of U, Th, Am, Np, and Pu. 77. The article of clauses 75 or 76, wherein the first layer includes at least one steel chosen from a martensitic steel, a ferritic steel, an austenitic steel, an oxide-dispersed steel, T91 steel, T92 steel, HT9 steel, 316 steel, and 304 steel. 78. The article of any of clauses 75-77, wherein the nuclear fuel and the wall element are mechanically bonded. 79. The article of any of clauses 75-78, wherein the exterior environment includes molten sodium and the first layer of steel prevents contact between the sodium and the vanadium alloy in the second layer. 80. The article of any of clauses 75-79, wherein the first layer and the second layer are mechanically bonded. 81. The article of any of clauses 75-80, wherein the nuclear material includes at least 90 wt. % of U. 82. The article of any of clauses 75-81, wherein the nuclear material is nuclear fuel and the article is a nuclear fuel element. 83. A power-generating reactor including the article of any of clauses 27-41 and 75-82. 84. A method of manufacturing a wall element for separating a nuclear material from an external environment, the method comprising: manufacturing a first layer, the first layer including at least a steel layer; and connecting the first layer to a second layer, the second layer including at least a vanadium alloy layer. 85. The method of clause 84 further comprising: manufacturing the second layer prior to connecting the second layer to the first layer. 86. The method of clauses 84 or 85, wherein connecting further comprises: connecting the steel layer to the vanadium alloy layer. 87. The method of any of clauses 84-86, wherein manufacturing the first layer includes manufacturing a first layer consisting of the steel layer connected to a chromium layer and connecting includes connecting the first layer to the second layer so that the chromium layer is between the steel layer and the vanadium alloy layer. 88. The method of any of clauses 84-87, wherein the second layer consists of the vanadium alloy layer connected to the chromium layer and connecting includes the first layer to the second layer so that the chromium layer is between the steel layer and the vanadium alloy layer. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the technology are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. It will be clear that the systems and methods described herein are well adapted to attain the ends and advantages mentioned as well as those inherent therein. Those skilled in the art will recognize that the methods and systems within this specification may be implemented in many manners and as such are not to be limited by the foregoing exemplified embodiments and examples. In this regard, any number of the features of the different embodiments described herein may be combined into one single embodiment and alternate embodiments having fewer than or more than all of the features herein described are possible. While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope contemplated by the present disclosure. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure. |
|
047042478 | claims | 1. Apparatus in combination with a fuel rod assembly containing nuclear fuel rods therein for compacting nuclear fuel rods in a fuel rod assembly for storage in a fuel rod storage canister, said apparatus including a fuel rod storage canister for storing compacted nuclear fuel rods, a fuel rod directing chamber having an entrance end defining a plurality of spaced apart openings for alignment with nuclear fuel rods of a first array of nuclear fuel rods in a fuel rod assembly, the spacing between fuel rods in the plurality of spaced apart openings ever decreasing from the entrance end of the fuel rod directing chamber to a discharge end thereof for merging by ever increasing the density of the fuel rods while moving through the directing chamber to the discharge end of said chamber, nuclear fuel rods emerging from the discharge end of said directing chamber forming a compacted second array of nuclear fuel rods for storage in said storage canister, and means to discharge nuclear fuel rods in the direction of their lengths from the fuel rod assembly, said fuel rod directing chamber being arranged in a tandem relation between said fuel rod assembly and said storage canister for confining a given nuclear fuel rod so that portions reside in said fuel rod assembly and said fuel rod directing chamber, and said storage canister and said fuel rod directing chamber while advanced by said means in the direction of the length thereof into said storage canister. 2. The apparatus according to claim 1 wherein said means to discharge nuclear fuel rods include gripper number to engage said nuclear fuel rods of said fuel assembly. 3. The apparatus according to claim 1 wherein said fuel rod directing chamber includes spaced apart end walls connected by tapered side walls. 4. The apparatus according to claim 1 wherein each of the said openings at the entrance end of said fuel rod directing chamber is joined to an opening in said discharge end by means of a tube. 5. The apparatus according to claim 4 wherein each said tube merges toward others of the said tubes from said entrance end to said discharge end of said fuel rod directing chamber. 6. The apparatus according to claim 1 wherein the said compacted second array is an equilateral triangular array. |
claims | 1. A method of detecting concealed fissile material in an article, where the presence of the concealed fissile material is unknown, comprising:providing at least one solid state fast neutron detector and at least one source of irradiating fast neutrons, the irradiating fast neutrons characterized by a particle energy, a pulse strength, a pulse width and a pulse frequency, wherein said pulse width is about 4 ns to 200 μs, said pulse frequency is about 100 to 10,000,000 Hz and said pulse strength is approximately 107 to 1012 neutrons per second;irradiating said article with said irradiating fast neutrons to effect emission of prompt, fast neutron radiation from said fissile material directly resulting from fissions occurring from neutron irradiation by said at least one neutron source, if the fissile material is present in the article and determine the presence of fissile material in the article;monitoring the emissions of such prompt fast neutron radiation directly resulting from fissions occurring from the neutron irradiation by said at least one neutron source, with the solid state fast neutron detector capable of discriminating between fast neutrons and thermal and epithermal neutrons and collecting counts of the prompt fast neutrons detected in the time between pulse widths without saturating;acquiring prompt fast neutron data indicative of a number of prompt fast fission neutrons emitted from said fissile material during a predetermined time period; andanalyzing said data to determine the presence or absence of said fissile material. 2. The method of claim 1, wherein said neutron detector is comprised of SiC. 3. The method of claim 1, wherein said neutron detector is comprised of a material selected from the group consisting of silicon carbide, cadmium zinc telluride (CZT), cadmium telluride, gallium arsenide and diamond. 4. The method of claim 1, wherein said particle energy of said neutron source irradiating the article is between 1 Mev and 25 Mev. 5. The method of claim 1, wherein said particle energy of said neutron source irradiating the article is selected from the group consisting of 2.5 Mev and 14 Mev. 6. The method of claim 1, wherein said article is a cargo container. 7. The method of claim 1, wherein said at least one neutron source is a plurality of neutron sources. 8. The method of claim 1, wherein said at least one neutron detector is a plurality of neutron detectors. |
|
abstract | Herein is described a method for identifying semiconductor radiation detector materials based on the mobility of internally generated electrons and holes. It was designed for the early stages of exploration, when samples are not available as single crystals, but as crystalline powders. Samples are confined under pressure in an electric field and the increase in current resulting from exposure to a high-intensity source of ionization current (e.g., 60Co gamma rays) is measured. A pressure cell device is described herein to carry out the method. For known semiconductors, the d.c. ionization current depends on voltage according to the Hecht equation, and for known insulators the d.c. ionization current is below detection limits. This shows that the method can identify semiconductors in spite of significant carrier trapping. Using this method and pressure cell, it was determined that new materials BiOI, PbIF, BiPbO2Cl, BiPbO2Br, BiPbO2I, Bi2GdO4Cl, Pb3O2I2, and Pb5O4I2 are semiconductors. |
|
claims | 1. A device for measuring back pressure in open-ended chemical reactor tubes, comprising:a wand body having upper and lower ends;a plurality of injector tubes mounted adjacent said lower end;a gas inlet on said wand body;a test gas path from said gas inlet through said injector tubes;at least one pressure sensor in fluid communication with at least one of said injector tubes for measuring the back pressure in said one injector tube;wherein said wand body and said injector tubes are rigidly mounted together to form a single unit which is sufficiently rigid that said plurality of injector tubes can be inserted simultaneously into their respective reactor tubes by moving said wand body. 2. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 1, and further comprising inflatable seals on said injector tubes and inflation gas paths from said gas inlet to said inflatable seals. 3. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 2, and further comprising an interlock means for ensuring that said injector tubes are inserted into their respective reactor tubes before inflating said inflatable seals. 4. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 1, and further comprising slidable mounting means which mount said injector tubes on said wand body. 5. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 4, wherein said slidable mounting means include a frame portion having a bottom surface; wherein said injector tubes project downwardly from said bottom surface; and further comprising seals on said injector tubes below the bottom surface of said frame portion. 6. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 5, and further comprising an interlock means for ensuring that said injector tubes are inserted into their respective reactor tubes before inflating said seals. 7. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 1, and further comprising an umbilical wand body including an umbilical handle and an umbilical injector tube, and a flexible tube connecting said umbilical wand body to said wand body so the umbilical wand body can move independently of the wand body. 8. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 1, and further comprising:a plurality of measurement paths between said at least one pressure sensor and said injector tubes; anda multiplexing valve in fluid communication with said measurement paths, including means for selectively putting said at least one pressure sensor in fluid communication with each of said injector tubes. 9. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 1, and further comprising:a laser measuring means on said wand body for automatically measuring the distance from said wand body to a reflecting surface. 10. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 9, and further comprising means for automatically determining which reactor tube is being measured based on the distance measured by said laser measuring means; means for automatically associating the pressure measurement with the reactor tube being measured; and means for electronically transmitting the pressure measurement together with an identifier for the chemical reactor tube being measured to a remote location. 11. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 10, and further comprising a slidable mounting means which mounts said injector tubes on said wand body. 12. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 11, wherein said at least one pressure sensor is mounted on said wand body. 13. A device for measuring back pressure in open-ended chemical reactor tubes, comprising:a wand body having upper and lower ends;a plurality of injector tubes mounted adjacent said lower end;a gas inlet on said wand body;a test gas path from said gas inlet through said injector tubes;at least one pressure sensor;at least one measurement path from one of said injector tubes to said at least one pressure sensor for measuring the back pressure in said one injector tube; an inflatable seal on each of said injector tubes;inflation gas paths from said gas inlet to said inflatable seals; andan interlock means for ensuring that said injector tubes are properly inserted into their respective chemical reactor tubes before inflating the inflatable seals. 14. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 13, and further comprising:a plurality of measurement paths between said pressure sensor and said injector tubes; anda multiplexing valve in fluid communication with said measurement paths, including means for selectively putting said pressure sensor in fluid communication with each of said injector tubes. 15. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 14, and further comprising:a laser measuring means on said wand body for automatically measuring the distance from said wand body to a reflecting surface. 16. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 15, and further comprising means for automatically determining which reactor tube is being measured based on the distance measured by said laser measuring means; means for automatically associating the pressure measurement with the reactor tube being measured; and means for electronically transmitting the pressure measurement together with an identifier for the chemical reactor tube being measured to a remote location. 17. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 16, and further comprising means for receiving the pressure measurements at the remote location; anddisplay means, in communication with said receiving means, for graphically displaying the layout of the tubes and the pressure data. 18. A device for measuring back pressure in open-ended chemical reactor tubes as recited in claim 13, and further comprising a slidable mounting means which mounts said injector tubes on said wand body. |
|
051907208 | abstract | A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting for fuel decay during reactor shutdown, or heat produced during a mishap. The reactor system is enhanced with sealing means for excluding external air from contact with the liquid metal coolant leaking from the reactor vessel during an accident. The invention also includes a silo structure which resists attack by leaking liquid metal coolant, and an added unique cooling means. |
043808557 | claims | 1. The method of filling a laser target having a hollow shell with gas which comprises the steps of drilling a hole through the wall of the shell, locating a plug having a melting temperature lower than that of the shell over the hole, placing the drilled shell with the plug in a vessel, introducing the gas into the shell through the hole while the plug is located on the shell over the hole, heating the vessel, thereby melting the plug to seal the hole to form a barrier against the escape of the gas from the shell thereby providing a gas-filled shell, removing said gas-filled shell from said vessel, and mounting said shell upon a stalk with the top of the stalk and the melted plug in contact with each other to provide an assembly for use in a laser fusion target chamber. 2. The method as set forth in claim 1 wherein said shell is a glass microballoon and further comprising the step of mounting said microballoon on a substrate having a light reflective layer thereon and testing said microballoon on said substrate. 3. The method as set forth in claim 2 wherein said step of testing comprises interferometrically measuring the optical path length of light which passes through said microballoon and is reflected by said layer thereby indicating the pressure of said gas contained in said microballoon. 4. The method as set forth in claim 1 further comprising the step of introducing material for coating the inside of said shell through said hole, and coating said shell on the inside thereof with said material. 5. The method as set forth in claim 1 wherein said drilling step is carried out by directing a beam of laser radiation in the form of at least one pulse which is less than 100 psec in duration to produce a high aspect ratio hole which is smaller than the plane wave diffraction limited focal spot size. 6. The method as set forth in claim 1 wherein said plug is a sphere. 7. The method as set forth in claim 6 wherein said sphere is of spherical latex material. 8. The method as set forth in claim 1 wherein said plug is selected from material in the group consisting of glass and thermoplastic material. 9. The method as set forth in claim 8 wherein said material of said plug is solder glass. 10. The method as set forth in claim 8 wherein said plug material is a polymer thermoplastic material having fractional crystallinity therein sufficient to limit the diffusion of the gas through the plug. 11. The method as set forth in claim 10 wherein said polymer thermoplastic is polystyrene of high fractional crystallinity. 12. The method as set forth in claim 1 wherein said step of introducing said gas is carried out by placing said drilled shell with said plug thereon in a vessel, introducing gas into said vessel and thereby allowing said gas to permeate through said hole around said plug. 13. The method as set forth in claim 12 wherein said gas is introduced into said vessel at greater than atmospheric pressure. 14. The method as set forth in claim 13 wherein said melting step is carried out while said pressurized gas is contained in said vessel. 15. The method as set forth in claim 14 further comprising reducing the pressure in said vessel to atmospheric pressure after said plug has melted and has formed said seal. 16. The method as set forth in claim 1 wherein said shell is a glass microballoon having an outside diameter from about 50 to 400 um and a wall thickness from about 0.5 to 3.5 um and further comprising the step of mounting said microballoon on a substrate with the aid of an adhesive selected from the group consisting of hydroscopic salt, methyl cellulose and collodion prior to said drilling step, and carrying said microballoon on said substrate during said drilling, plug locating, and plug melting steps. |
054328284 | description | FIG. 1 shows the head 1 of a vessel of a pressurized water nuclear reactor, having a hemispherical shape and including a convex outer surface 1a and a concave inner surface 1b. The head 1 has been shown in the position which it occupies when it is laid on the mating surface of the nuclear-reactor vessel or on an inspection and repair stand. The head 1 is penetrated by openings 2, the axes of which are parallel and of vertical direction, in the of the head shown in FIG. 1. An adaptor 3 of tubular shape is fixed inside each of the openings 2, the adaptor including a widened upper portion 3a to which it is possible to fix a mechanism for moving a rod for controlling the reactivity of the reactor, or a device for bearing and for gripping a thermocouple column assembly (not shown in FIG. 1). Inside the adaptors providing the penetration of a drive shaft of a rod for controlling the reactivity are also disposed thermal sleeves such as 4 which rest by means of a widened upper portion on a bearing surface inside the portion 3a of the adaptor. The adaptors 3 have a nominal outer diameter slightly greater than the diameter of the openings 2 and are shrink-fitted with nitrogen inside the openings 2 and are then fixed in a sealed manner by means of an annular weld 5 deposited inside a bevel machined in the concave inner surface 1b of the vessel head 1. The thermal sleeves 4 include a portion projecting in relation to the lower portion of the adaptor carrying a flared engagement cone 4a providing the reinsertion of the drive shafts of the control rods into the adaptors, while the head 1 is being laid on the vessel mating surface. The flared portions 4a of all the adaptors for penetration of the drive shafts are located at the same level in the vertical direction, while the lower end portions of the adaptors are located at different levels depending on their position on the vessel head, on account of the hemispherical shape of the head. The adaptors for penetrating the vessel heads of pressurized-water nuclear reactors are generally made of a nickel alloy, the vessel head itself being made of steel. A "buttering" layer made of stainless steel is deposited on the concave inner surface 1b of the vessel head in the bottom of the bevels in which the welds 5 for fixing the adaptors are deposited. After the nuclear reactor has been operated for a certain time, it is noticeable that some of the adaptors are liable to have cracks, in particular in the area of the welds 5 on the vessel head. In some cases, it is necessary to change completely the adaptor which has a crack, so as to be able to guarantee perfect safety of the vessel head during the operation of the nuclear reactor. In order to carry out such a replacement, the head is placed on a repair stand 6, such as shown in FIG. 2. The head 1 rests on a support block 7 of the repair stand, so that its convex upper surface 1a faces upwards and its concave lower surface 1b faces downwards and towards the interior of the repair station 6. The support block 7 includes, in particular, walls 8 of radial direction in relation to the head 1, to which walls columns 9 are fixed whose upper end 9a constitutes a pin for engagement of a passage opening 10 of a stud for fixing the vessel head 1. The repair station 6 also includes a biological-shield chamber 11, the upper portion of which constitutes a horizontal mechanism plate located immediately beneath the engagement cones 4a of the thermal sleeves 4 disposed inside the adaptors 3 providing the passage of a drive shaft of a control rod. The biological shield 11 enables some operations to be carried out beneath the lower surface 1b of the head, through an opening such as 12, despite the significant radioactivity of the inner lower face of the head 1. FIG. 2 shows the head 1 after it has been deposited on the repair stand 6, in an initial phase of the method of replacing an adaptor 3' placed in a central position on the vessel head. The mechanisms 13 fixed to the upper end portions 3a of the adaptors 3 are disposed side-by-side and in a lattice having square lattice cells, as may be seen in FIG. 3. Prior to a repair on an adaptor, such as the adaptor 3', in order to replace it by a new adaptor, it necessary to dismount the mechanism 13 of this adaptor 3' as well as the thermal sleeve disposed inside the adaptor. These operations are performed from above the head, which has advantages as regards the dimensions of the repair tools to be used and the simplicity of the implementation of the replacement operation; the costs relating to replacement are consequently reduced. In order to replace the adaptor 3', it is necessary to machine some portions of the adaptor and of the inner surface 1b of the head. In order to do this, a machine 14 is used which rests on and is fixed to the upper portion 3'a of the adaptor 3' being replaced and at the end of a telescopic arm 15 by means of its upper end portion so as to be held in a stable manner, during the machining operations, in the extension of the adaptor 3'. The telescopic arm 15 constitutes an element of a support jib 16 which is engaged and fixed in an opening 10 intended for the passage of a stud for fixing the vessel head 1. In order to install the arm 15 between the mechanisms 13 of the adaptors of a row of radial direction in relation to the head 1, the mechanisms 13 of three adaptors of the radial row are dismounted, the locations of these mechanisms 13 which have been dismounted being shown by the broken lines in FIG. 3, and thus access is gained to the central adaptor 3' from the edge of the head. It is obvious that, in the case of replacing an adaptor located on the periphery of the head, it is not necessary to dismount the mechanisms of other adaptors. In general, it is possible to dismount any number of mechanisms in order to make it easier to have access to the adaptor being replaced. As may be seen in FIG. 4, which shows an embodiment of the machine given solely by way of non-limiting example, the machine 14 can include a casing 17 and a column 18 mounted so as to rotate about its axis in relation to the casing 17, in the downward extension of the casing 17. The casing 17 includes a tubular lower portion 19 which can be engaged in the upper portion of an adaptor 3 virtually without clearance in order to hold the casing 17 on the upper portion 3a of the adaptor 3 which includes a bore having a shoulder on which the tubular support 19 rests. Furthermore, the column 18 of the machine 14 includes a ring 20 in which the column 18 is mounted so as to rotate and which enables the column 18 to be guided along the axial direction inside the adaptor 3. The column 18 is also mounted so as to rotate and to slide inside the tubular support 19 of the casing 17. Inside the casing 17, mounted so as to rotate in an axial direction aligned with the direction of the axis of the adaptor 3, is a tubular shaft 21 connected via a mechanism plate 22, at its lower portion, to the upper end of the column 18. The tubular shaft 21, which is mounted inside rolling bearings, is rigidly attached to a drive pinion 23 which meshes with a pinion 24 fixed to the output shaft of a geared motor 25 mounted in the casing 17. In this manner, the tubular shaft 21 and the column 18 can be driven rotationally about their common axis. The tubular shaft 21 is splined on the outside and is engaged in a ring which includes corresponding internal splines, this ring being rigidly attached to the pinion 23 and mounted so as to rotate in the casing 17 by means of a rolling bearing. In this manner, the tubular shaft 21 is rotationally integral with and translationally free to move axially in relation to the pinion 23. The tubular shaft 21 is mounted so as to rotate in a tubular support 26 which is itself mounted so as to slide in the axial direction inside the casing 17. The tubular support 26 carries on the outside a nut 27, the axis of which is parallel to the axis of the tubular shaft 21. A screw 28, meshing with the nut 27 and directed along the axial direction, is mounted so as to rotate in the casing 17 and is rigidly attached at its end to a pinion 29 meshing with a pinion 30 fixed to the output shaft of a geared motor 31. The geared motor 31 rotates the screw 28 which drives the tubular support 26 and the shaft 21 in axial translational movement by means of the nut 27. A pneumatic cylinder 32 disposed inside the tubular shaft 21 includes a rod connected, via a coupling bar 33 disposed inside the tubular column 18, to a boring tool 40 which engages in the end portion of the column 18 so as to be rotationally integral with the column 18. It is thus possible to drive the tool 40 rotationally and to move it axially, so as to machine the lower end portion of the adaptor 3 and a portion of the weld 5. The machining is performed by rotating the tool 40, using the geared motor 25, and by translationally moving this tool in the axial direction, by means of the column 18, using the geared motor 31. In addition, the tool is held by the coupling bar 33 connected to the rod of the pneumatic cylinder 32. After the installation of the machining device 14, as shown in FIGS. 2 and 3, the lower portion of the column 18 is equipped with a tool 40 making it possible to mill the lower portion of the adaptor 3 and to rebore the weld 5 and a portion of the penetration opening 2 of the vessel head 1. The boring tool 40 is fixed to the end of the column 18, from inside the biological-shield chamber 11 shown in FIG. 2, through the opening 12. This operation can be performed very rapidly, the tool 40 including means for rapid assembly to the end of the column 18 and to the bar 33 rigidly attached to the rod of the cylinder 32. As may be seen in FIG. 5, in which the members equipping the machine 14 have been shown in the position which they occupy after completing the machining of the lower portion of the adaptor, the bore diameter of the tool 40 is slightly greater than the external diameter of the adaptor 3 and than the nominal diameter of the opening 2. The bore 34 formed by the tool 40 makes it possible to remove completely, in the form of chips, the lower portion of the adaptor 3 up to a certain level inside the head 1, a portion of the weld 5 in contact with the external wall of the adaptor and, possibly, a thin inner skin of the penetration opening 2 for the adaptor. After the bore 34, as shown in FIG. 5, has been formed, the tool 40 is dismounted and a measurement device is mounted on the end of the column 18 from beneath the biological-shield chamber 11. The measurement tool is used to determine, in an extremely precise manner, the position of the lower surface of the weld 5 remaining, so as to adjust an operation for machining a welding bevel, inside the weld 5, for fixing the replacement adaptor. In particular, the position of a point constituting the reference and the origin for starting the machining of the bevel is determined in a very precise manner. FIG. 6 shows a tool 35 for machining a bevel in the metal of the weld 5, so as to weld the replacement adaptor. The machining tool 35 is mounted on the end of the column 18 of the machine 14, from inside the biological-shield chamber 11, through the opening 12. Depending on the previously determined reference and origin position, the machining tool 35 is adjusted in order to commence the machining of the bevel 36. The machining tool 35 includes a milling head 37 fixed to the output shaft of a geared motor 38 mounted on the support for the tool 35. The tool 35 includes means 39 for adjusting the position of the milling head 37 by means of pinions. The bevel 36 has to be formed in a position inclined in relation to the horizontal plane and with a complex shape which depends on the shape of the weld 5 filling the original bevel machined around the penetration opening 2, in the metal of the head 1. Depending on the distance of the adaptor 3 from the axis of the head 1, the bevel filled by the weld 5 is inclined to a greater or lesser extent and has a shape which is complex to a greater or lesser extent, which makes it necessary to adapt the conditions for machining the bevel 36 inside the weld 5 to the position of the adaptor 3. The tool 35 and the milling head 37 are rotated about the axis of the adaptor 3 and the milling head 37 is moved simultaneously and in an adjusted manner in the axial direction of the adaptor 3, in order to follow the surface of the weld 5 in which the bevel 36 is machined. These movements are controlled by coders, such as 41 and 42, associated with the means for moving the column 18, at the end of which is fixed the tool 35 which can be adjusted, prior to the machining operation, by using the means 39. After having machined the bevel 36, the tool 35 is dismounted and the machine 14 is equipped with a boring bar 43 carrying, at its end, a boring head 44. The boring bar 43 is mounted so as to rotate and to slide in the axial direction inside the bore of the adaptor 3 by means of a bearing 45. The boring head 44 forms a bore 46 inside the upper portion of the adaptor, the diameter of which is slightly less than the external diameter of the adaptor 3, so that, after boring the upper portion of the adaptor, a thin tubular wall 47 is left inside the opening 2 penetrating the vessel head 1. In an advantageous manner, the thickness of the residual wall 47 is very small and, for example, is of the order of 0.5 mm. Attached to the machine 14 are means 64 for laterally holding the upper portion of the adaptor 3, which is no longer held in the opening 2, after completing the reboring, except by the wall 47. The means for holding the machine and the adaptor enable rupture or bending of the thin wall 47, still engaged in the opening 2, to be prevented. The wall 47 remains held by shrink-fitting inside the opening 2, so that the adaptor 3 to be replaced cannot be completely extracted without the risk of causing a tensile rupture of the wall 47 or damage to the inner wall of the opening 2. Before extracting the thin wall 47, this wall is deformed, from above the head, by using compression cylinders engaging with the outer surface of the wall 47, in its portion located on the outside and just above the head 1. A compressional deformation is achieved by inwardly pushing-in the wall 47, so as to stress-relieve it and to disbond it from the wall of the opening 2, so that it can be extracted very easily without damaging the surface of the bore. The opening 2 penetrating the head 1 can then receive a replacement adaptor which is inserted and installed inside the opening 2 at liquid-nitrogen temperature. The replacement adaptor is held in position in the opening 2 as it heats up, the corresponding expansion resulting in the replacement adaptor shrink-fitting inside the opening 2. FIG. 8 shows the replacement adaptor 50 in position inside the penetration opening 2 of the head 1 and held by shrink-fitting with nitrogen. Also shown is the machine 14 which has been installed on the adaptor 50, so that its column 18 is mounted so as to rotate and to slide in the axial direction inside the bore of the replacement adaptor 50. An automatic TIG welding machine 48 is fixed, from beneath the head, to the end of the column 18, enabling the bevel 36 to be filled with filler metal in order to perform the welding and to seal around the adaptor 50. The bevel 36 has been machined with a cross-section such that it can be filled by successive welding beads superimposed on each other in the axial direction. Such welding is usually designated by the name of narrow-bevel welding. As mentioned in a previous Patent Application of the FRAMATOME Company, filed under the number FR-A-93/00980, such narrow-bevel welding, in the case of an adaptor whose bevel 36 is inclined, has to be performed by varying the speed of rotation of the welding head 49 about the axis of the adaptor during the welding, so as to provide a constant rate of deposition of the filler metal. In addition, the welding head has to be simultaneously moved rotationally and translationally along the axial direction of the adaptor 50 in order to follow the shape of the welding bevel 36. Adjustment of the movements of the welding head 49 can be provided by the means for controlling the machine 14. FIG. 9 shows a variant of the welding device used for filling the bevel 36. The welding machine 51 is suspended from a support part 52, the upper portion 52a of which constitutes a rotation spindle mounted inside a bearing 53 which can be fixed and locked in the bore of the adaptor 50, this mounting being able to be carried out from beneath the head, from inside the biological-shield chamber 11. The spindle 52a is connected to the output shaft of a geared motor 54 fixed to the support of the bearing 53. The geared motor 54 includes control means enabling its speed of rotation to be varied and adjusted during the welding. A slideway 56, on which a slide 57 carrying a TIG welding head 59 is mounted so as to move in the vertical direction, is mounted on the support 52 by means of an adjustment device 55. The slide 57 also carries a support 60 to which are fixed a reel 58 for supplying the head 59 with filler-metal wire and means for fastening the cable 61 for supplying the welding head with electric current. FIG. 10 shows the lower portion of the replacement adaptor 50, following the welding operation which has just been described. A weld bead 62 made of filler metal has been deposited in the bevel 36 machined in the metal of the weld 5. A gap 63 exists above the weld 62, between the external surface of the adaptor 50 and the internal surface of the bore 34, so that the bore 34 is slightly greater than the opening 2. Despite the presence of this gap 63, the adaptor 50 is fixed perfectly by shrink-fitting and by means of the weld 62. As may be seen in FIG. 10, the bore 34 is machined over an axial length of the opening 2 such that the adaptor 50 is nowhere in contact with the remaining portion of the weld 5 of the adaptor which has been replaced. The method according to the invention makes it possible to perform all the operations necessary for the replacement from an area located above the head 1, with the exception of operations for mounting and dismounting the tools, which are performed from the biological-shield chamber beneath the head. Furthermore, the adaptor can be replaced in a simpler and more rapid manner than by having access to the adaptor from beneath the head. The invention is not limited to the embodiment which has just been described. It is thus possible to use tools having a shape other than those which have been described for performing the various machining or welding operations. The invention applies to the replacement of any adaptor for penetrating the vessel head of a nuclear reactor. |
063079135 | abstract | A shaped plasma discharge system is provided in which a shaped radiation source emits radiation at a desired frequency and in a desired shape. In one embodiment, a laser source provides an output beam at a desired intensity level to shaping optics. The shaping optics alters the output beam into a desired shaped illumination field. In an alternate embodiment, plural laser sources provide plural output beams and the shaping optics can produce a compound illumination field. The illumination field strikes a target material forming a plasma of the desired shape that emits radiation with a desired spatial distribution, at a desired wavelength, preferably in the x-ray, soft x-ray, extreme ultraviolet or ultraviolet spectra. In another embodiment an electric discharge generates the required shaped radiation field. The shaped emitted radiation proceeds through an optical system to a photoresist coated wafer, imprinting a pattern on the wafer. |
abstract | A reactor pressure vessel assembly may include a housing surrounding a reactor core, steam separators, and a chimney. Inner surfaces of the chimney and reactor core define a conduit for transporting a two phase flow stream from the reactor core through the chimney to the steam separators. The housing defines an opening. An inner surface of the housing and outer surfaces of the chimney and reactor core define an annulus in fluid communication with the opening and conduit. A feedwater sparger in the housing is connected to the at least one opening and configured to deliver a sub-cooled feedwater into the annulus. A flow barrier structure between the chimney and the steam separators may force mixing between the sub-cooled feedwater and a downcomer fluid from the steam separators. An outer steam separator may be vertically over a portion of the flow barrier structure in a plan view. |
|
description | This application claims priority to applications GB 0700205.8 filed Jan. 5, 2007 and GB 0708452.8 filed May 1, 2007, the entire disclosures of which are expressly incorporated herein by reference The present invention relates to a method of treating radioactive sludge, commonly termed nuclear sludge, a form of wet intermediate level waste (ILW). Since the operation of the first nuclear power plants, there has been a need to safely dispose of waste that contains radioactive materials. Radioactive waste materials which need to be disposed of may also be produced in other industrial environments, such as hospitals, research establishments, decommissioning of nuclear power stations and in industry. The waste materials can arise from operational sources, e.g. during the process of spent fuel management, or during decommissioning activities. Fractions of such waste are typically found to be in a sludge form, due to the use of water as a moderator, shielding medium and as a thermal management tool, that contains both corrosion by-products and/or functional filtration media. A sludge may be defined as a liquid containing solid particles, at least some of which are radioactive for this class of waste. As part of the high profile nuclear clean up occurring in the UK there are requirements for facilities to condition radioactive Intermediate Level Waste (ILW) (which may be in the form of Magnox sludges, spent ion exchange media (natural or synthetic), organic ion exchange media, effluent management residues and sand) into a stable solid product suitable for interim, and ultimately, long term storage/disposal. These sludges are typically classified as intermediate level waste (ILW) because of their decay mode specific activity levels and their radiogenic heat characteristics, and, in the form in which they found, i.e. in bulk storage tanks and storage ponds, they are often thick mineral suspensions of approximately 50% v/v solids concentration of varying character. Recent developments for disposing of hazardous wastes include in-drum pyrolysis processes, such as that disclosed in the patent publication WO 2004/036117. This document discloses a process that involves pyrolysis and then steam reforming of waste containing organic materials and radionuclides, i.e. radioactive materials. The pyrolysis process volatises the organic materials within the drums at a temperature of between 200° C.-800° C. The resulting solid material remaining in the drums after the pyrolysis as a dry, inert inorganic matrix, which contains the radionuclides and their compounds. This inert inorganic matrix has a high carbon content, indicating the reactive form of the residues and the ineffectiveness of the thermal treatment. The remaining species in the gaseous phase following pyrolysis are water vapour, volatised organics and acid gases, which then are fed to a steam reformer, which operates at a temperature of 800° C. to 1000° C. This process is only of use for waste that is contained in drums and can only be carried out as a batch-wise operation. The drum material provides a barrier between a user handling the waste and the radioactive materials contained within the solid product material in the drum. However, it is not convenient to treat all waste in drums. Additionally, the present inventors have found that the final solid product produced with the in-drum process does not form a satisfactory physical and chemical barrier to the escape of radionuclides contained within the solid product as it takes the form of a clinker (particles fused at the edges), as opposed to a dense slag. This means that the hazardous components of the waste could potentially be remobilised physically. In the proceedings of GLOBAL 2005, held at Tsukuba, Japan, on Oct. 9-13, 2005, (gaper No. 016) a process for treating low and intermediate level nuclear waste in an incinerator and melting furnace was disclosed. The process involved the incineration of the waste in a plasma furnace that had a centrifuge chamber. When the waste was loaded into the plasma furnace, the centrifuge would force the waste to the sides of the rotating walls of the chamber. On initiating the plasma furnace, the waste melts and when the rotational velocity decreases the liquid waste runs towards the centre of the furnace floor and exits the chamber through an outlet in the floor into a mould beneath the outlet. The design of the chamber is complex and difficult to service, which presents health and safety risks as the refractory forms a large mass of contaminated secondary waste, which needs to be periodically replaced involving significant levels of direct physical handling. The process also results in a large amount of offgas containing many contaminants, due to the use of an auxillary gas burner, which must be treated in a separate part of the apparatus. The offgas treatment is an expensive and energy-consuming process. The most commonly used method of processing nuclear sludge is by cement or grouting techniques. These techniques have been used in the UK by the British Nuclear Group at the Trawsfynydd amongst other sites. The technique involves encapsulating nuclear waste with a cement-like material. If the nuclear waste is in liquid form, i.e. a sludge containing a sufficient amount of free water, dry cement powder can be added to the liquid, which will then set around the waste. The waste can be first placed in packages and then encapsulated in the cement to allow transportation of the waste. If the waste does not contain sufficient water for the grout to set, pre-prepared liquid cement can be poured onto the waste and allowed to set. These processes have the disadvantage that the resultant cement-encapsulated waste takes up considerably more volume than the original waste: typically, the original waste may constitute 25% or less of the volume of the final product and the active storage of waste is very expensive. It is an aim of the present invention to overcome or mitigate the problems associated with the prior art. The present invention provides a method for treating nuclear sludge comprising: subjecting the nuclear sludge to a plasma treatment in a plasma chamber to melt at least some of the inorganic components of the sludge, wherein the plasma chamber comprises a crucible having a cooled inner surface, this surface cooled sufficiently such that the inorganic components in contact with the inner surface are in a solid state and form a barrier between the part of surface of the crucible with which they are in contact and the molten inorganic components of the sludge. The present inventors have found that the inorganic components of the sludge, within the plasma furnace, form a vitreous liquid with a high radionuclide incorporation rate. This mass of waste accumulates as the process progresses until a predefined volume of vitreous product has been generated. At this point the material is transferred to an outer packaging container; where it is allowed to solidify as a monolith in line with regulatory requirements. The present inventors have surprisingly found that treating nuclear sludge within a plasma chamber has a number of advantages over the prior art. In contrast to the techniques of encapsulating nuclear waste in cement, the method of the present invention reduces the volume of the nuclear sludge and the end product is a solid, dense, vitrified material in which the radioactive nuclides are contained—the radionuclides have been found to be physically and chemically immobilised in the resultant solid waste material. Little, if any, leaching has been found to occur from the solid materials, which has been quantitatively determined to out perform traditional high-level waste borosilicate type glasses for silicon release under both neutral and alkaline conditions. By using a crucible with a cooled inner surface, a layer of solid, inorganic material has been found to develop on this surface from the waste material itself. Since this protects the material of the crucible and is effectively self-replacing on treating more radioactive sludge, the lining of the crucible does not need to be replaced. It also avoids the build-up of radioactive nuclides within the crucible walls or their lining, as its section can be varied and replaced through control of heat flux density, therefore preventing critical levels of nuclides occurring in the apparatus. The present inventors have found, for example, that the refractory linings traditionally used in the field are unsuitable for use in treating nuclear waste. The refractory linings are corroded by the corrosive chemical components typically present in the sludges, e.g. NaOH used in the management of wastes in ponds. Additionally, nuclides tend to build up in the refractory material, which may lead to critical levels of radioactive material and ultimately the production of a high level waste. A further advantage of the method of the present invention is that it does not require the presence of a host slag material, i.e. the radioactive sludge is converted to a solid form in the plasma chamber without the need for much, if any, additional uncontaminated solid material, blending agents. A “sludge” is a well known term in the art of processing radioactive material and generally refers to a liquid containing solid particles, at least some of which are radioactive. The sludges can have wide and varied rheological properties. The sludge can generally flow and the particles may be present as a suspension in the liquid or as a separate settled phase. The sludge may contain one or more materials including, but not limited to, magnesium, potassium, silicon, uranium, aluminium and sodium in elemental, oxide, hydroxide and/or carbonate form. The final product, i.e. wasteform, has been found to be vitreous and generally amorphous, but may contained mineralogical phases such as forsterite, cordierite, albite, clinoptilolite and other zeolites. The phases present in the final wasteform are dependent on both thermal history and wasteform composition, as shown in the Examples. The method may further involve oxidising the inorganic components of the waste by introducing an oxidant to the plasma chamber. The nuclear sludges that may be treated include, but are not limited to: a magnox sludge from ion exchange facilities, which may contain predominantly magnesium hydroxide. a sand/clino sludge from ion exchange facilities, which may predominantly contain clinoptilolite or an equivalent zeolite. a magnox legacy pond sludge, which may comprise one or more of the following: magnesium hydroxide, uranium oxides, magnesium carbonate and other minor constituents. The method of the present invention preferably includes the further step of removing the molten inorganic components derived from the sludge from the plasma chamber and allowing them to cool to form a vitrified solid material. Preferably, the one or more electrodes comprise graphite. Such electrodes have been surprisingly found to be particularly durable when used in the method of the present invention and resistant to corrosive chemicals such as halogens and highly alkali environments. Preferably the electrodes are coated with alumina, which will give more consistent wear characteristics and minimise lateral electrode carbon losses. The plasma chamber may comprise one or two plasma torches and/or electrodes. Preferably, the plasma chamber comprises two graphite electrodes, preferably operable in two modes. Preferably, the method involves maintaining at least some of the inorganic components in a molten state by directly coupling the arc from the graphite electrodes to the molten inorganic components. This is often termed a transferred arc mode. The electrodes may be operated in a first mode in which an electric arc is passed between the electrodes above the level of the nuclear sludge. This is preferably used to initiate the formation of the plasma in the process. The first mode allows the plasma process to be initiated easily and avoids the need for a conductive hearth which allows for flexibility in operation. If the plasma chamber comprises a single plasma electrode, the crucible may act as a live component of system. The plasma electrodes may be operated in a second mode in which an electric arc is passed between the torches through the sludge. This is preferably used to maintain the inorganic components of the sludge in a molten state once the plasma has formed, as the zone of influence of the process heat is extended. The second mode allows ohmic heating of the inorganic components of the sludge. This means that the electrical current passes through the material undergoing treatment and therefore provides for a higher power input per unit current that is spatially distributed, i.e. two arc attachment points, with a high coupling efficiency between the plasma and waste. Preferably, the plasma is generated using DC electricity. The inner surface of the crucible preferably comprises copper. Copper has been found to be particularly suitable because it is robust, thermally and electrically conductive inhibiting both chemical and thermal erosion processes, ductile and therefore tolerant of thermal cycling, dense with high thermal mass and therefore ensure safe containment. As is known to one skilled in the art, a plasma chamber comprises a crucible for holding the material to be treated, in this case the radioactive sludge. “Crucible” means a container suitable for use in a plasma chamber. The crucible used in the present invention has a cooled internal wall. Preferably, the crucible has a cooling system for maintaining the internal wall of the crucible at a temperature below 100° C., preferably below 50° C., irrespective of pressure, to avoid water film boiling and maintain good heat transfer. Preferably, the cooling system is a water-cooling system, wherein preferably water is passed between an outer wall and an inner wall of the crucible in order to cool the inner wall. The crucible containment device can also be refractory lined with indirect water-cooling, i.e. remote water-cooling to the process with conductive heat transfer into the working environment to provide for the desired temperature profile. Preferably, during the method of the present invention, the inner wall of the crucible is maintained below the liquidus, more preferably the solidus, temperature of the inorganic components of the sludge. (The liquidus and solidus temperatures of the inorganic components are readily measured by one skilled in the art by routine experimentation.) Preferably, the inner wall of the crucible is maintained at 100° C. or below, preferably 50° C. or below. Preferably, the process further comprises transferring the molten components of the sludge to a container for the storage of nuclear waste. Preferably, the plasma treatment is carried out at a temperature of 1000° C. or above, more preferably 1200° C. or above. In other words, the temperature of the plasma within the chamber is 1000° C. or above. Preferably, the plasma treatment is carried out at a maximum temperature of 1800° C., more preferably a maximum of 1600° C. More preferably, the plasma treatment is carried out at a temperature of from 1200 to 1500° C., most preferably at a temperature of about 1350° C. An oxidant may be present within the plasma chamber. The oxidant preferably comprises oxygen. The oxidant may comprise air, oxygen gas and/or steam. Preferably the oxidant comprises air. Air has been found to be particularly suitable and safe for use in the present invention. Any plasma gas known to the skilled person may be used in the method of the present invention, including, but not limited to, argon and nitrogen. Most preferably, argon is fed to the plasma chamber as a plasma gas. The plasma treatment is preferably carried out at a temperature at or above the liquidus temperature of the particles in the sludge, i.e. the inorganic components of the sludge. Additional material may be added to the sludge as required. Preferably, at least some of the particles within the sludge have a liquidus temperature of 1600° C. or below, more preferably 1500° C. or below, most preferably 1400° C. or below, and additional material may be added to ensure that the liquidus temperature of the particles is in the preferred range. For example, if the sludge contains one or more of Na2O, Al2O3 and SiO2, further amounts of one or more of these materials may be added to the sludge before or during plasma treatment to ensure that the relative ratios of the material are such that the material can form an albite material (Na2O—Al2O3-6SiO2). Alternatively, if the sludge contains magnesium species (for example magnesium oxides or hydroxides), Al2O3 and/or SiO2, then further amounts of one or more of these materials may be added to the sludge before or during plasma treatment to ensure that the relative ratios of the material are such that the material can form a forsterite and/or cordierite material (MgO-2Al2O3-5SiO2/2MgO—SiO2. Forsterite/cordierite materials have been found to have a liquidus temperature within the preferred range and also have a suitable viscosity when molten under plasma conditions. The method may further comprise carrying out the plasma treatment of the radioactive waste material in a receptacle removable from the plasma unit and that can be sealed following the plasma treatment, allowing the waste to be disposed of within the receptacle. A new receptacle can then be placed in the plasma unit and the process repeated. This avoids the need to transfer the molten and/or vitrified radioactive material following plasma treatment from the plasma unit (e.g. from a crucible) to a separate receptacle (e.g. a drum for the disposal of radioactive waste). The receptacle may, for example, be a receptacle having an inner surface lined with refractory or other material suitable for withstanding the conditions to which it would be exposed during plasma treatment. The receptacle may be in the form of a drum for the disposal of radioactive waste. The present invention further provides use of an apparatus for the treatment of nuclear sludge. The plasma chamber may comprise one or more inlets for an oxidant, e.g. an oxidising gas. The inlet for oxidant may be arranged such that the oxidant enters the plasma chamber through the sludge. Preferably, the apparatus is adapted such that the plasma power input and/or oxidant supply are controlled using automated control loops, rather than being set at predetermined levels throughout the treatment process. The plasma chamber will include a plasma gas, such as argon. Other gases that may be present in the plasma chamber include nitrogen, steam, and gases produced from the treatment of the waste, such as carbon monoxide and/or carbon dioxide. Nitrogen may be present from the inlet of air, which may be used to cool the gas stream, if required. Preferably, the plasma chamber is maintained at a power consumption rate of from 150 to 350 kW. Preferably, the plasma chamber comprises monitoring equipment, including, but not limited to equipment selected from: CCTV monitoring equipment for viewing the molten material within the plasma chamber, equipment for monitoring the amount of waste material and/or host slag material being fed to the plasma chamber, equipment for monitoring the internal temperature of the plasma chamber and equipment for monitoring the internal pressure of the plasma chamber. The apparatus may be operable using a sealed gravity feed mechanism. The apparatus may comprise a working upper chamber and a lower receptor chamber, wherein the upper chamber is adapted such that the molten slag material in the upper chamber can flow by gravity into the lower chamber. This is particularly advantageous in a continuous process, in which the blended waste is fed into the chamber continuously or periodically and avoids the requirement to run the process in a batch-wise manner. The upper and lower chambers are preferably sealed to prevent ingress of diatomic species into the plasma chamber from its exterior and egress of hazardous species. The nuclear sludge may be fed to the plasma chamber through an airlock device, which ensures positive displacement of the waste into the unit, and prevents ingress or egress of gases and heat to/from the interior of the plasma chamber. Feed ports containing airlock devices are known to the skilled person. The product material in the lower chamber can be removed after solidification. The present invention will now be illustrated with the following non-limiting Example. The Plasma Chamber A plasma chamber was provided as shown in FIG. 2 having a crucible 1 as shown in FIGS. 1b, 1c and 3. The crucible 1 had an inner wall 2 and an outer wall 3, both formed from cast, high conductivity copper. Between the inner and outer walls 2,3 were water cooling channels 3A for cooling the inner surface of the crucible. The plasma chamber further comprised one or more plasma torches/electrodes and more preferably two plasma torches/electrode, their longitudinal axis of location are shown at 4 and 5. The electrodes are manipulated using vertical and horizontal electromechanical actuation. The crucible sections were joined to the roof 6 at a flange. The crucible was lowered and removed using an electrically actuated jacked platform, for servicing away from the main furnace frame. The water-cooled, conical furnace roof 6 was lined with high-grade dense alumina refractory and fixed within the furnace-supporting framework. Within the plasma chamber was located a single plenum device (not shown) having an oxidant inlet. The device further comprised a jacket having an inlet and an outlet for water for cooling the device. The inlet and outlets were both connected to the inner water cooling circuit. The plenum device allows for distribution of oxidant within the plasma chamber and also allows good oxidant-feed contact, i.e. contact of the waste with the oxidant. The roof 6 contained the following ports: two ports for electrodes, one dual oxidant introduction port, one feeder discharge port, one temperature monitoring probe port and an exhaust mounted sight port with CCTV. FIG. 2 gives a general assembly drawing of the plasma chamber with the graphite electrodes and actuators in place. The crucible had an exit 11 at one side with a lip 12 extending downwards therefrom. A lower chamber (not shown) is positioned below the exit 11, such that molten material 13 during the reaction can flow by gravity out of the exit 11, down the lip 12 and into the lower chamber. The Off-Gas System The off-gas handling system comprised a refractory lined combustion chamber reactor off-gas duct extension of mild steel construction with temperature and pressure instrumentation. The system pressure and overall gas flow rates were controlled using an inverter drive induced draft (ID) fan. The particulate within the off-gas stream was removed using a reverse-jet-pulse baghouse, rated for a maximum gas flow rate of 6000 Am3 hr−1 at a temperature of up to 220° C. which was backed with a secondary panel HEPA filter to its baghouse to act as a fail-safe mechanism, in case of primary filter failure. Emissions data were recorded by a professional stack monitoring company in line with the Monitoring Certification Scheme (MCerts) and The United Kingdom Accreditation Service (UKAS) accreditation and certification. The exhaust gas composition was monitored by Envirodat Limited, using a Fourier Transform Infrared (FTIR) Spectroscopy gas analyser supplied by Quantitech Ltd. Using the Apparatus Because of the dangerous nature of radioactive materials, the method of the present invention was demonstrated using non-radioactive materials that were very similar in chemical and physical properties to radioactive waste from certain sources. Sludge #4 and its Simulant This is a sand/clino arising from an ion exchange facility (Sludge #4) sludge that is predominantly clinoptilolite with low levels of sand and other minor constituents. The chemical specification of the radioactive sludge and the associated simulant specification are given in Table 1. The trace radioactive species were dosed on top of the bulk chemistry of the sludge in the following proportions Sr90=0.35 mg/m3 settled sludge Cs137=5.18 mg/m3. Plutonium was not simulated with cerium as the amount used to simulate uranium would dominant any sensible retention assessment. TABLE 1Sludge #4 Simulant Chemical SpecificationRadioactive SludgeSimulant SludgeBulk ChemistryBulk ChemistryLiquid Phase% w/wLiquid Phase% w/wH2O27.86H2O33.21NaOH 9.14NaOH10.90C6H12O6—sawdust—(dextrose)Solid Phase% w/wSolid Phase% w/wSiO27.5SiO2 7.02Mg(OH)2—Mg(OH)2 4.97Al2SiO5—BNG43.89Clino In all cases the simulants were prepared by mixing the dry powder components together, followed by manual rotary blending to form a homogeneous mixture. The sodium hydroxide and water were mixed independently to form a solution; this was exothermic and so occurred well in advance of the material being charged to the plasma furnace to allow for the dissipation of heat. The only material that was not sourced through certified industrial and/or laboratory channels was the cellulose or dextrose representing the organic fraction. (Dextrose was used as a convenient representative for the organic fraction of the sludge in the thermochemical simulation.) This was simulated using sawdust sourced locally and was representative of the organic debris within the magnesium hydroxide rich sludges. Experimental Plan The process design criteria were determined using thermodynamic calculations based on the simulated chemistry of the ILW sludges combined with an understanding of the temperatures required for effective thermal treatment, as defined by phase stability and liquidus temperatures (phase diagrams), to produce a vitrified product. The thermodynamic code marketed by Outokumpu Research, called HSC Chemistry®. Version 5.1 was employed to model the system chemistry. Sludge #4 (Trials 1 & 2) A simulant was prepared in accordance with the Section entitled “Sludge #4 and its Simulant”. Enough material was blended to provide for approximately 100 kg of vitrified final waste-form. To the above 50 cc of CsNO3 as 1000 ppm solution equal to 50 mg Cs and 50 cc of Sr(NO3)2 1000 mg/liter solution equal to 50 mg Sr. The trial was started by adding 50 kg of simulant without the aqueous solution component to the hearth (the plasma chamber). This was vitrified while adding 20.595 kg solution (14.6 liters per hour for 1 hr 24 minutes) to make up the balance of the simulant. This arose due to the unforeseen reaction of dry sodium hydroxide with the balance of the simulant, i.e. the water contained within the clinoptilolite (≈14% w/w) reacted with the dry sodium hydroxide to form a cement. When steady state high temperature plasma conditions were reached with the mass of molten vitrified product in the furnace, feeding commenced under the following conditions: Gross Plasma Power=150 kW Assumed Steady State Losses=100 kW Solid Feed Rate=29.62 kg/hr Liquid Feed Rate=20.37 kg/hr (Water and NaOH) Duration=1 hour 24 minutes. Operating temperature=1600° C. Sludge #4 did not need any blend material addition as it automatically falls into the albite phase region (Na2O—Al2O3-6SiO2) of the Na2O—Al2O3-6SiO2 phase diagram. The vitrified material was anticipated to have a liquidus temperature of approximately 1100° C. The vitrified product was also predicted to have a low viscosity due to the presence of a large amount of soda (Na2O), to act as a silicate network modifier and disrupt the tetrahedral silica structure. The vitrified product is predicted to have a theoretical density of 2620 kg/m3. Mineralogical Information: albite Chemistry: NaAlSi3O8, sodium aluminium silicate. Class: Silicates Subclass: Tectosilicates Group: Feldspars Uses: ornamental stone, ceramics and mineral specimens. Sludge #4 Operational Results The simulant material was treated and vitrified. The simulant material of Sludge #4 was charged to the furnace as two separate streams: a liquid stream containing trace dopants of Cs and Sr using a positive displacement metering pump and the balance of the simulant, as a dry powder blend using a volumetric screw feeder. The two separate mechanisms were employed solely due to time limitations and the feeders available. The simulant material was charged and vitrified/oxidised in the cold crucible, twin electrode, plasma vitrification furnace using a twin graphite electrode system over a cold skull copper crucible. The furnace was pre-heated for approximately 20 minutes, using the plasma arc at a typical operating power of around 120 kW prior to the feeding of the simulant. The simulant was fed into the furnace after full-scale deflection (FSD) calibration of the feeding system, i.e. dosing pump and volumetric screw feeder. The feeder discharged into a gas purged, water-cooled, vertical pipe leading to the roof of the furnace and exiting directly between the arcs. Argon was charged to the furnace using a port at the distil end of the feed tube. The sludge simulant was processed at a feed rate approaching 40 kghr−1 (wet and dry components in combination) at an average operating gross input power of around 130-150 kW approximately 1 hours. The vitrified product residue within the furnace was allowed to solidify in-situ and was then sampled from the furnace mechanically. The electrodes used in this test-work were 50 mm in diameter with an 8 mm diameter bore hole down the centre for plasma gas. The graphite electrodes were manufactured from HLM graphite, which is an extruded grade; superior iso-statically pressed grades are available. These sections were 800 mm in length, with either female or male threads on the end and a gas fitting on the end, external to the furnace, for plasma gas connection. No direct measurements of temperature were made, i.e. within the plasma furnace, however a physically shielded ‘B’ type thermocouple in the sidewall of the plasma chamber recorded temperatures in the region of 200° C. The system thermal losses are acquired from instrumentation on the water-cooling manifold lines and was calculated using the following equation:Qloss=K′×FR×(Trtn−Tflw) Where: Qloss=Thermal loss (kW) FR=Water flow rate (l m−1) Trtn=Return water temperature (° C.) Tflw=Flow water temperature (° C.) K′=0.07 (kW min liter−1° C.−1) =Specific heat (Cp) of water corrected for volume and units As would be expected, the crucible loss dominated the thermal losses of the furnace, which were observed to have average values of 70-80 kW with vitrified sludge simulant. The total losses and power input were observed to balance after time indicating the system reached steady state. Overall, 69.6 kg of vitrified final wasteform should have been produced from the sludge #4 simulant charged to the furnace by calculation. The recorded mass of final waste-form recovered from the furnace is 64.2 kg. There was a very high level of material retention within the furnace and the discrepancy is well within the limits of compound accuracy associated with the techniques employed. Both the anode and cathode weighed 1660 g at the start of the test, the combined graphite wear rate was 2.87 kg MWh−1. These values of electrode mass loss per MWh of input energy give a parameter that is normalised for the contribution of the erosion due to input energy; i.e. it allows the erosion of different industrial processes to be compared. Both electrodes tended to wear to a conical shape as a result of erosion at the hot tip and lateral erosion due to oxidation. The cathode electrode also exhibited radial wear along its shaft exposing the channel. The wear rates were consistent with previous experimental data and compared favourably with the characteristics of other pyrometallurgical operations where wear rates can approach 15 kg MWh−1. Typical wear rates observed in plasma furnace operation are ≦5 kg MWh1, which suggests that there will be no fundamental problem in using graphite electrode systems for radioactive waste treatment on a larger scale. After the experiment the crucible was observed to be in good condition. Sludge #4 Final Waste-form The anticipated composition of the vitrified product/final waste form produced from sludge # 4 is shown in Table 2 below. The blended material charged to the plasma furnace consisted of 100% w/w sludge # 4 on a dry calcined based. Mass recovery of the oxide content of the fed simulant approached 100%. TABLE 2Anticipated Final Waste-form Composition ofThermally Treated Sludge #4Species% w/wNotesCeO20.00Approximate liquidus temperature =1100° C.MgO6.18Al2O316.31Mineralogical basis from ternary phaseSiO260.68diagram - resides within the albiteNa2O16.83phase fieldTotal100.00 The density of the vitrified product was measured to be 2340 kg m−3. The product had a green vitreous appearance. The X-ray diffraction pattern of the sludge #4 final waste-form and its phase diagram, derived from the chemical analysis, are presented in FIG. 4 and FIG. 5, respectively. This sludge contained 13.3% sodium oxide with the target phase albite, Na2O.Al2O3.6SiO2. The pattern shows that on rapid cooling it formed a soda-silica glass, instead of crystalline albite, with the other elements in solid solution, hence, complete reaction had occurred on processing. Information on the analysis techniques employed can be found below. The actual and revised predicted final waste-form composition is presented within Table 3. Good agreement is observed between the predicted and actual analysis results. The symbol ‘<’ indicates that the value lies below the limit of detection (LoD). TABLE 3Chemical analysis (% w/w) of the Final Waste-form of Sludge #4PredictionVitrifiedActualWaste-formproduct 4AnalysisCompositionNa2O13.3414.24MgO5.406.10Al2O39.709.12SiO265.6167.71P2O5<K2O1.201.31CaO1.661.51TiO20.13Mn3O4<V2O5<Cr2O3<Fe2O30.82ZrO2<ZnO<SrO0.26BaO0.19La2O30.09CeO2<Total98.40100.00 The anticipated concentration of both Cs and Sr from the dopant addition made was 0.59 ppm in both cases. However, this value is below the LoD of the analysis techniques employed and therefore it was a surprise to find that the reported Cs concentration in the final waste-form was 89 ppm. Similarly following the analysis of the composition of clinoptilolite which was reported to contain 0.33% strontium, it was no surprise to find that the strontium concentration of the vitrified product was 0.26% w/w. Therefore, inactive strontium accountability will be of little use for any simulant experiment containing clinoptilolite. The analysis of the clinoptilolite is presented in Table 4. TABLE 4Clinoptilolite Analysis (% w/w)ClinoptiloliteAnalysisNa2O3.35MgO0.70Al2O312.44SiO273.06P2O5<0.05K2O1.79CaO2.06TiO20.15Mn3O4<0.05V2O5<0.05Cr2O3<0.05Fe2O30.96BaO0.22ZrO2<0.05ZnO<0.05SrO0.33Water Content14.1 Technology Performance Assessment The experiments above demonstrate the suitability of the method of the present invention for the treatment of ILW radioactive sludge wastes. The work has clearly demonstrated the robust and tolerant characteristic of the plasma technology with respect to the compositional envelopes of the sludges and their associated transfer profiles. In all cases, the results have shown close agreement with the experimental predictions, the final waste-form being of a dense and homogeneous character. The bulk chemical analyses of the final waste-forms showed good agreement with the predicted compositions, allowing for the heterogeneous nature of the simulant feed materials. The phase analysis showed that the feed materials were transformed to a homogeneous product, which in most cases was a glass and in one case was a glass-forsterite mixture. This supported the predicted phase compositions. The operational prototype test facility was reliable and its performance was predominantly in line with the developed thermodynamic models. In all cases good levels of accountability were observed for both the transuranic simulant components and for the other simulant ingredients. In combination the data confirm the viability of plasma technology of the application. Material Analysis Techniques Chemical analyses were performed by LSM (London & Scandinavian Metallurgical Co. Limited), a UKAS accredited laboratory. For the vitrified product samples, XRF was employed to obtain quantitative compositional data on the bulk oxides after sample fusion into a glass bead using lithium tetraborate. Trace element analysis of caesium and strontium was carried out by inductively coupled plasma optical emission spectroscopy (ICP-OES). In addition, X-Ray diffraction (XRD) was used to evaluate the phases present in the final wasteform samples. Specific Gravity (SG) by Water Displacement SG—This is based on water displacement (immersion), however as the weights of samples become smaller, the water displacement methodology becomes less accurate. The test is reasonably simple to perform, but is only suitable for monolithic samples and not powder samples. A sample is weighed dry and then submerged in distilled water; the volume of water displaced is measured to determine the volume of the sample. The two values are then used to define the density. Final Wasteform Analysis Using XRF XRF-REO—Final Wasteform—This program is designed for Rare Earth based/containing materials and was used because of cerium content of the simulants. The analysis reported Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, Mn3O4, V2O5, Cr2O3, Fe2O3, BaO, ZrO2, ZnO, SrO and CeO in combination. XRF-OXIDE—Final Wasteform—This program is designed for a variety of ceramic/oxide based materials and was used to analyse the clinoptilolite feed material. Final Wasteform Analysis by ICP-OES Hydrofluoric (HF) acid digestion of the solid waste samples was conducted under microwave radiation, due to the aggressive nature of the preparation technique and its ability to take the materials into solution. This procedure allowed a direct analysis of solidified melt products to be made. An aqua-regia digestion medium (HCl/HNO3@3:1 w/w) was initially attempted but was found to be ineffective for taking silica into solution. Trace element analysis was carried out by inductively coupled plasma optical emission spectroscopy (ICP-OES). The samples were completely acid digested to all components and subsequently analysed by ICP-OES, to evaluate their compositions. Here, hydrofluoric acid was used to dissociate the silicate matrix and to dissolve the trace metal components. The resulting solution was passed into a plasma source in a flow of argon gas. Excitation of the elements present within the sample, and subsequent relaxation to their ground states, resulted in the emission of characterising elemental spectral lines. These were detected by a photometer, the intensity and wavelength of the emission being directly proportional to the concentration and identity respectively of the element in question. Final Wasteform Analysis Using XRD Inorganic phase identification of crystalline materials. X-ray diffraction measurements were obtained from solid specimens sectioned with a water-cooled diamond tipped cutting disc. The button specimens were sectioned radially to give two perpendicular surfaces, complementing the X-ray source/detector configuration. The samples were scanned across values of 2θ of X-X° with a step size of 0.02° in a continuous sweep. The important assumption was that the material was composed of an aggregate of tiny crystals in random orientations with respect to each other, even though the materials appeared homogeneous on a macroscopic scale. As the major constituents of the system were known, the types of phase formed could be predicted according to the ASTM index. Facilities' Commercial Characteristics The process design criteria developed for the trial were based on the simulated chemistry of the sludge waste materials, and the temperatures required for their effective thermal treatment, as defined by phase stability and liquidus temperatures data. The advantages of the method of the present invention as exemplified above are as follows: The gaseous environment and energy provided to the system can be controlled to give either oxidising or reducing conditions which offer some control over the volatility of radionuclide species to be engineered. Fine particle feed capabilities: the plasma chamber and plasma arc configuration allow direct feeding of particulate material into the plasma chamber at the arc confluence (point of arc contact). This minimises entrainment and physical carry-over of the feed material to the exhaust gas stream and makes it ideal for the treatment of sludges with particle sizes in the order of microns. The cold skull plasma chamber allows high temperatures and high energy fluxes during melt containment at elevated temperatures, i.e. above the liquidus temperature of the glasses, to be reached in a relatively short period of time. The term ‘cold skull’ means a water-cooled copper crucible. When in use, a solidified layer of waste-form glass forms at the internal surface of the crucible interface. This means that the crucible has minimal direct exposure to the inner working environment of the furnace and enhances the reliability, availability and maintainability (RAM) credentials of the facility. Graphite electrodes offer the advantages of low cost and high reliability and the elimination of the secondary waste problems associated with directly water-cooled plasma devices. The electrodes are regarded as a consumable; that is continuously fed into the plasma chamber as an operational consumable. This also eliminates the hazards associated with plasma device water leaks and avoids equipment longevity issues due to chemical environment; e.g. the stress corrosion cracking of water-cooled torches. The twin electrode configuration gives flexible operation. Two configurations can be employed; remotely coupled between two electrodes in free space, and directly coupled to a fluid melt. The latter allows ohmic heating of the melt, forming an additional heat dissipation mechanism within the plasma chamber. This configuration is the most suitable for heating a condensed phase due to its high current, low voltage characteristics and the direct passage of the plasma current through the material undergoing treatment. The remotely coupled configuration allows the plasma chamber to be started from cold, obviating the requirement for a conductive hearth, this also aids operation as is provides for easy recovery should solidification of the melt occur due to unexpected power outages. The plasma chamber offers the combined advantages of being able to gasify the combustible parts of wastes and oxidise and vitrify the non-combustible parts. In principle, this allows simultaneous volume reduction with effective immobilisation of metals, thereby transforming the contaminated wastes into a safe, leach-resistant, final waste-form. Combustibles present within the wastes are thermally destroyed (cracked) to recombine downstream in the off-gas system as simpler, innocuous molecules. Arc instabilities can be overcome during operation of the apparatus by using a pneumatically assisted, gravity feed, positive displacement metering pump mechanism that is completely sealed. This eliminates the unintentional ingress of diatomic atmospheric gases, which would otherwise cause some destabilisation of the plasma discharge. |
|
claims | 1. A method of extracting characters comprising: a first step of preparing design data having a hierarchy with regard to figure cells, the design data being design data of a device pattern for exposure; and a second step of extracting candidates for the figure cells corresponding to said characters from all levels of figure cells in said design pattern data by using the hierarchy with regard to the figure cells in said design pattern data, the candidates causing at least one of a number of kinds of characters and a number of shots of electron beams as a unit in performing an electron beam exposure of character projection system to be the smallest when said exposure is performed on at least a part of said device pattern. 2. The method of extracting characters according to claim 1 , wherein said second step, with regard to the figure cells of all levels in said design data, further comprises finding, respectively, for the electron beam sizes which can be irradiated, the following values: the size of the figure cells, the number of kinds of characters, the number of shots of electron beams required in performing the exposure of character projection system, and the number of shots of electron beams required in performing the exposure of variable shaping beam system, and claim 1 wherein candidates for the figure cells corresponding to said characters are extracted based on these values found. 3. The method of extracting characters according to claim 1 , wherein claim 1 said second step, candidates for the figure cells corresponding to said characters are extracted sequentially from the levels of a larger figure size to the levels of a smaller figure size based upon the magnitude of reduction of the number of shots of electron beams in comparison to the exposure of variable shaping beam system. 4. The method of extracting characters according to claim 1 , wherein claim 1 said second step, candidates for the figure cells corresponding to said characters are extracted sequentially from the levels of a larger figure size to the levels of a smaller figure size on the criterion that the number of kinds of characters required in performing the exposure of character projection system is smaller. 5. The method of extracting characters according to claim 1 , further comprising: claim 1 a first extracting step of extracting adjacent single-arranged figure cells together as one character when there are single-arranged figure cells among the candidates for the figure cells corresponding to said characters, the adjacent single-arranged figure cells causing more figure cells to be included in electron beam sizes; and a second extracting step of extracting adjacent figure cells in one newly array-arranged figure cell together as one character when there are adjacent array-arranged figure cells which can be treated as said one newly array-arranged figure cell among the candidates for the figure cells corresponding to said characters, the adjacent figure cells in the newly array-arranged figure cell causing more figure cells to be included in the electron beam sizes. 6. The method of extracting characters according to claim 5 , wherein claim 5 said first extracting step of extracting characters is performed using arrangement position coordinates of said adjacent single-arranged figure cells described in said design data and an external form size found by means of the calculations of the adjacent single-arranged figure cells grouped together into said one character; and said second extracting step of extracting characters is performed using the arrangement position coordinates of said adjacent any-arranged figure cells described in said design data and the external form size found by means of the calculations of the figure cells grouped together into one character in said one newly array-arranged figure cell. 7. The method of extracting characters according to claim 3 , wherein claim 3 said second step, from among the candidates for the figure cells corresponding to said characters, a candidate permitting a more effective exposure of character projection system is extracted preferentially one by one. 8. The method of extracting characters according to claim 4 , wherein claim 4 said second step, from among the candidates for the figure cells corresponding to said characters, a candidate permitting a more effective exposure of character projection system is extracted preferentially one by one. 9. The method of extracting characters according to claim 7 , wherein claim 7 said second step, from among the candidates for the figure cells corresponding to said characters, a candidate to be extracted preferentially is selected one by one on the criterion of the number of kinds of characters, the number of exposure shots required In performing the exposure of character projection system, and the magnitude of reduction of the number of exposure shots required in performing the exposure of variable shaping beam system using said extracted candidates for the figure cells. 10. The method of extracting characters according to claim 8 , wherein claim 8 said second step, from among the candidates for the figure cells corresponding to said characters, a candidate to be extracted preferentially is selected one by one on the criterion of the number of kinds of characters, the number of exposure shots required in performing the exposure of character projection system, and the magnitude of reduction of the number of exposure shots required in performing an exposure of variable shaping beam system using said extracted candidates for the figure cells. 11. The method of extracting characters according to claim 7 , wherein claim 7 said second step, for each of the candidates for the figure cells corresponding to said characters, a CP effectiveness defined by means of the equation of {(Number of VSB shots)xe2x88x92(Number of CP shots)}/{(Number of CP shots)xc3x97(Number of kinds of Characters)} is found, the number of kinds of characters and the number of exposure shots required in performing an exposure by means of the electron beam exposure of character projection system being the number of kinds of Characters and the number of CP shots respectively, and the number of exposure shots required in performing the exposure of variable shaping beam system using said extracted candidates for the figure cells being the number of VSB shots, and a candidate having a larger value of said CP effectiveness is extracted preferentially one by one. 12. The method of extracting characters according to claim 8 , wherein claim 8 said second step, for each of the candidates for the figure cells corresponding to said characters, a CP effectiveness defined by means of the equation of {(Number of VSB shots)xe2x88x92(Number of CP shots)}/{(Number of CP shots)xc3x97(Number of kinds of Characters)} is found, the number of kinds of characters and the number of exposure shots required in performing an exposure by means of the electron beam exposure of character projection system being the number of kinds of Characters and the number of CP shots respectively, and the number of exposure shots required in performing the exposure of variable shaping beam system using said extracted candidates for the figure cells being the number of VSB shots, and a candidate having a larger value of said CP effectiveness is extracted preferentially one by one. 13. The method of extracting characters according to claim 11 , wherein claim 11 from among the candidates for the figure cells corresponding to said characters, a candidate having a larger value of said CP effectiveness is extracted preferentially one by one when the number of the candidates for the figure cells corresponding to said characters is larger than the number of the available characters. 14. The method of extracting characters according to claim 12 , wherein claim 12 from among the candidates for the figure cells corresponding to said characters, a candidate having a larger value of said CP effectiveness is extracted preferentially one by one when the number of the candidates for the figure cells corresponding to said characters is larger than the number of the available characters. 15. A program product for operating a computer, said computer program product comprising: a first program instruction means for causing a computer to read in the design data including a hierarchy with regard to figure cells, the design data being design data of a device pattern for exposure; and a second program instruction means for extracting candidates for the figure cells corresponding to said characters from all levels of figure cells in said design pattern data by using the hierarchy with regard to the figure cells in said design pattern data, the candidates causing at least one of the number of kinds of characters and the number of shots of electron beams as a unit in performing an electron beam exposure of character projection system to be the smallest when said exposure is performed on at least a part of said device pattern. |
|
claims | 1. A method of monitoring a radiopharmaceutical synthesis process, comprising:generating, by at least one computer processor of a radiopharmaceutical synthesizer system, a set of data including at least a) a first activity measurement obtained at a first time point in the radiopharmaceutical synthesis process by at least one of a first radioactivity detector or a first sensor and b) a second activity measurement obtained at a second time point in the radiopharmaceutical synthesis process by at least one of a second radioactivity detector or a second sensor, wherein i) the at least one of the first radioactivity detector or the first sensor and ii) at least one of a second radioactivity detector or a second sensor are located differently in the radiopharmaceutical synthesizer system;generating, based on the set of data, a diagnostic fingerprint indicating activity measured with respect to time for execution of the radiopharmaceutical synthesis process; andoutputting the diagnostic fingerprint for quality control to adjust synthesizer hardware of the radiopharmaceutical synthesizer system in comparison to a successful synthesis process. 2. The method of claim 1, further comprising: implementing a modification to adjust the synthesizer hardware of the radiopharmaceutical synthesizer system based on a command received via a computer network. 3. The method of claim 1, further comprising: performing, using a quality control system, a check of the synthesizer hardware using at least one of the first activity measurement or the second activity measurement. 4. The method of claim 1, further comprising: configuring a plurality of radiodetectors located in the radiopharmaceutical synthesizer system to provide the first and second activity measurements. 5. The method of claim 1, wherein the set of data relates to a yield of the radiopharmaceutical synthesis process. 6. The method of claim 1, wherein the set of data includes data points measured and recorded at a predefined interval during the radiopharmaceutical synthesis process. 7. The method of claim 6, wherein the predefined interval includes one second intervals during the radiopharmaceutical synthesis process. 8. The method of claim 2, wherein the synthesizer hardware is to be adjusted using a correction factor to be automatically determined based on the quality control and implemented by the radiopharmaceutical synthesizer system. 9. The method of claim 1, wherein the radiopharmaceutical synthesizer system is configured to produce a particular radiopharmaceutical for use in conjunction with conducting a SPECT or a PET scan. 10. The method of claim 1, wherein the radiopharmaceutical synthesis process is a first radiopharmaceutical synthesis process, and the set of data is a first set of data, the method further comprising:comparing a second set of data from a second radiopharmaceutical synthesis process to the diagnostic fingerprint to evaluate the second radiopharmaceutical synthesis process by:processing the first set of data and the second set of data to generate a first extracted data and a second extracted data, respectively, wherein processing the first set of data further includes applying a first correlation factor to the first set of data to normalize the first set of data and wherein processing the second set of data further includes applying a second correlation factor to the second set of data to normalize the second set of data; anddetermining deviation of the second extracted data from the first extracted data to assess performance of the second radiopharmaceutical synthesis process; andwhen the deviation indicates a correction for the second radiopharmaceutical synthesis process, adjusting a subsequent radiopharmaceutical synthesis process by:determining a third correlation factor based on the determined deviation of the second extracted data from the first extracted data, the third correlation factor forming a correction factor; andimplementing the correction factor to adjust the subsequent radiopharmaceutical synthesis process according to the diagnostic fingerprint of the first radiopharmaceutical synthesis process. |
|
053496191 | claims | 1. A fuel assembly for a light water reactor comprising a plurality of fuel rods which contain a primary fissile material, wherein at least one of water rods, in which cooling water flows therein when said fuel assembly is provided in the reactor, is provided at least in one of each corner position of an outermost layer of a polygonal arrangement of the fuel rods and a position in the outermost layer adjacent to said corner position in such a manner that said water rods are located in rotation symmetry, each of said water rods being filled with water over a length at least corresponding to a fuel effective length, and the fuel rods are provided at positions in an adjacent layer to the outermost layer which are adjacent to those positions at which said water rods are located. 2. A fuel assembly for a light water reactor according to claim 1, wherein said fissile material includes primarily plutonium when exposure is zero. 3. A fuel assembly for a light water reactor according to claim 2, wherein one of said water rods is located in one of each corner position of the arrangement of the fuel rods and the position in the outermost layer adjacent to said corner position in rotation symmetry. 4. A fuel assembly for a light water reactor according to claim 2, wherein two of said water rods are provided in each corner position of the arrangement of fuel rods and in a position in the outermost layer adjacent to said corner position in such a manner that said water rods are located in rotation symmetry. 5. A fuel assembly for a light water reactor according to claim 2, wherein two of said water rods are provided in both positions in the outermost layer adjacent to each corner position of the arrangement of the fuel rods in such a manner that said water rods are located in rotation symmetry. 6. A fuel assembly for a light water reactor according to claim 2, wherein said polygonal arrangement has substantially a square shape. 7. A fuel assembly for a light water reactor according to claim 1, wherein some of said plurality of the fuel rods contain primary plutonium as a fissile material when exposure is zero, and the others of the fuel rods only contain uranium as a fissile material when exposure is zero. 8. A fuel assembly for a light water reactor according to claim 7, wherein said polygonal arrangement has substantially a square shape. 9. A fuel assembly for a light water reactor according to claim 7, wherein one of said water rods is located in one of each corner position of the arrangement of the fuel rods and the position in the outermost layer adjacent to said corner position in rotation symmetry. 10. A fuel assembly for a light water reactor according to claim 7, wherein two of said water rods are provided in each corner position of the arrangement of fuel rods and in a position in the outermost layer adjacent to said corner position in such a manner that said water rods are located in rotation symmetry. 11. A fuel assembly for a light water reactor according to claim 7, wherein two of said water rods are provided in both positions in the outermost layer adjacent to each corner position of the arrangement of the fuel rods in such a manner that said water rods are located in rotation symmetry. 12. A fuel assembly disposed in a light water reactor, said fuel assembly comprising a plurality of fuel rods which contain a primary fissile material, wherein at least one of solid moderator rods is provided in one of each corner position of an outermost layer of a polygonal arrangement of the fuel rods and a position in the outermost layer adjacent to said corner position in such a manner that said solid moderator rods are located in rotation symmetry, each of said solid moderator rods being filled with a solid moderator over a length at least corresponding to a fuel effective length, and the fuel rods are provided at positions in an adjacent layer to the outermost layer which are adjacent to those positions at which said solid moderator rods are located. 13. A fuel assembly according to claim 12, wherein said fissile material includes primarily plutonium when exposure is zero. 14. A fuel assembly according to claim 13, wherein said polygonal arrangement has substantially a square shape. 15. A fuel assembly according to claim 13, wherein one of said solid moderator rods is located in one of each corner position of the arrangement of the fuel rods and the position in the outermost layer adjacent to said corner position in rotation symmetry. 16. A fuel assembly according to claim 13, wherein two of said solid moderator rods are provided in each corner position of the arrangement of fuel rods and in a position in the outermost layer adjacent to said corner position in such a manner that said solid moderator rods are located in rotation symmetry. 17. A fuel assembly according to claim 13, wherein two of said solid moderator rods are provided in both positions in the outermost layer adjacent to each corner position of the arrangement of the fuel rods in such a manner that said solid moderator rods are located in rotation symmetry. 18. A fuel assembly according to claim 12, wherein some of said plurality of the fuel rods contain plutonium as a primary fissile material when exposure is zero, and the others of the fuel rods only contain uranium as a fissile material when exposure is zero. 19. A fuel assembly according to claim 18, wherein said polygonal arrangement has substantially a square shape. 20. A fuel assembly according to claim 18, wherein one of said solid moderator rods is located in one of each corner position of the arrangement of the fuel rods and the position in the outermost layer adjacent to said corner position in rotation symmetry. 21. A fuel assembly according to claim 18, wherein two of said solid moderator rods are provided in each corner position of the arrangement of the fuel rods and in a position in the outermost layer adjacent to said corner position in such a manner that said solid moderator rods are located in rotation symmetry. 22. A fuel assembly according to claim 18, wherein two of said solid moderator rods are provided in both positions in the outermost layer adjacent to each corner position of the arrangement of the fuel rods in such a manner that said solid moderator rods are located in rotation symmetry. 23. A core of a light water reactor comprising first fuel assemblies each including a plurality of fuel rods which only contain uranium as a fissile material when exposure is zero, second fuel assemblies each including a plurality of fuel rods which contain plutonium as a primary fissile material when exposure is zero, in which in said second fuel assembly at least one of moderator rods is provided at least in one of each corner position of an outermost layer of a polygonal arrangement of the fuel rods and a position in the outermost layer adjacent to said corner position in such a manner that said moderator rods are located in rotation symmetry, each of said moderator rods being filled with a filling substance over a length at least corresponding to a fuel effective length, and the fuel rods are provided at positions in an adjacent layer to the outermost layer which are adjacent to those positions at which said moderator rods are located. 24. A core of a light water reactor according to claim 23, wherein said second fuel assemblies are each arranged such that one of said moderator rods is located in one of each corner position of the arrangement of the fuel rods and the position in the outermost layer adjacent to said corner position in rotation symmetry. 25. A core of a light water reactor according to claim 23, wherein said second fuel assemblies are each arranged such that two of said moderator rods are provided in each corner position of the arrangement of fuel rods and in a position in the outermost layer adjacent to said corner position in such a manner that said moderator rods are located in rotation symmetry. 26. A core of a light water reactor according to claim 23, wherein said second fuel assemblies are each arranged such that two of said moderator rods are provided in both positions in the outermost layer adjacent to each corner position of the arrangement of fuel rods in such a manner that said moderator rods are located in rotation symmetry. 27. A core of a light water reactor according to claim 23, wherein said second fuel assemblies have substantially the same shape and dimensions as said first fuel assemblies. 28. A core of a light water reactor according to claim 23, wherein said polygonal arrangement has substantially a square shape. |
description | This application claims the benefit of U.S. Provisional Application Ser. No. 60/669,821 entitled “MICROSCOPE STAGE WITH FLEXURAL AXIS,” filed Apr. 8, 2005, the disclosure of which is hereby incorporated by reference in its entirety. Aspects of the present invention relate generally to stages, and more particularly to a microscope stage exhibiting predictable Z translation characteristics and limited cross-coupling translations. Microscope stages are generally required to be highly accurate and repeatable along all motion axes. Typically, a microscope stage will have three orthogonal axes: X, Y, and Z, which are generally defined by the optical axis of the microscope. For most applications, motion along the Z axis should be characterized by high resolution, for example step distances of less than about 0.10 μm, and high repeatability, for example error between multiple visits to the same targeted Z location of less than about 0.20 μm. Additionally, microscopy systems generally attempt to minimize cross-coupling between motion in the Z and X and Y coordinate axes, since such cross-coupling tends to distort the data captured during imaging operations, which in turn decreases quality and usability of the data acquired. A typical Z scan of a microscope slide may consist of 65 points taken on 0.20 μm intervals, for a total Z axis displacement of 13 μm. Ideally, cross-coupling movement in the X or Y axes in such applications would be limited to about 0.40 μm or less throughout the total 13 μm Z scan. In accordance with conventional stage technologies, as exemplified in the assignee's U.S. Pat. Nos. 6,781,753 and 5,812,310, the disclosures of which are hereby incorporated by reference in their entirety, a conventional microscopy system stage utilizes a series of linear slides in a ramp configuration. The slides and ramp cooperate to guide a microscope slide, disposed on the stage, in the Z dimension. Such multiple linear slide configurations required to create a Z translation, by necessity, are over-constrained. Consequently, parts tolerance, specifications, and assembly methods must be extremely accurate, otherwise the slides will “fight” each other during motion. This can cause binding along the Z axis, which results in high repeatability errors. Additionally, conventional systems are typically associated with attendant high costs, which result from the foregoing specification, tolerance, and assembly requirements. For example, six separate linear slides and multiple custom machined plates or slide mounts may be required in order to enable Z axis translation in a conventional system. Embodiments of the present invention overcome the above-mentioned and various other shortcomings of conventional technologies. The present invention provides a microscope stage exhibiting predictable Z translation characteristics, limited cross-coupling translations, high repeatability, and greater simplicity. The foregoing and other aspects of various embodiments will be apparent upon examination of the following detailed description thereof in conjunction with the accompanying drawing figures. A microscopy stage configured and operative in accordance with certain embodiments of the present invention may utilize a flexural design for Z axis motion or translation; in such an exemplary embodiment, a single Z plate may be pivotally mounted such that it is allowed to pivot on one or more flexural components at one end, while the other end may be translated in the Z dimension substantially parallel to the Z axis. It will be appreciated that, especially for small Z translations, cross-coupling in one axis perpendicular to the Z rotation axis, termed the X axis, may be negligible. In some applications, for example, a 13 μm Z scan may result in cross-coupling translations of only approximately 0.013 μm in X. This is a theoretical value based, in part, upon stage geometry; in some practical applications, expected cross-coupling translations along both X and Y axes may typically be greater due to other stage effects. The use of flexural components to translate in the Z dimension can greatly simplify microscope stage design and may reduce assembly time and component cost. The six linear slides and supporting structures currently employed in traditional Z translation implementations may be omitted in certain embodiments of the present invention. Turning now to the drawing figures, FIG. 1 is a simplified plan view, and FIGS. 2 and 3 are simplified cross-sectional views, of one exemplary embodiment of a microscope stage exhibiting predictable Z translation characteristics and limited cross-coupling translations. FIG. 4 is a detailed cross-sectional view of the microscope stage and one embodiment of a flexural component as illustrated in FIGS. 2-3. FIG. 5 is a perspective view of one embodiment of a flexural component. In accordance with the implementation depicted in FIGS. 1-3, an exemplary microscope stage 100 may include X-Y translation table base 110, Z plate 120, Z actuator 130, X and Y actuators 140, stage frame 150, and one or more flexural components 160. Actuators, such as for example, Z actuator 130 or X and Y actuators 140 may comprise manual, mechanical, electrical, electromechanical, or other devices or components to effect movement. Flexural components, such as flexural component 160, may comprise devices or components effecting rotation about a hinge axis. It will be appreciated that a typical microscopy system may include additional elements such as, for example, a metrology frame (not shown) to which various of the depicted elements may be fixedly or movably attached. Common elements of conventional microscopy systems such as, for example, optics, imaging and data acquisition apparatus, electrical or electronic control systems, and associated microscope stage components have been omitted from the drawing figures for clarity. It will be appreciated that a Z actuator 130 may be disposed on the side of the microscope stage 100 opposite the flexural components 160. For many applications, Z actuator 130 may be embodied in or comprise either a stepper or direct current (DC) motor-driven lead screw device, for example a piezoelectric actuator mechanism, a bellows coupling driven actuator system, or any other linear actuator mechanism currently available or developed and operative in accordance with known principles. The location or orientation of Z actuator 130 in X and Y, i.e., relative to the hinge axis 170 (see FIG. 5) of flexural components 160, and thus the torque exerted on the stage, may be adjusted or otherwise selectively modified to optimize performance of the complete design. In some embodiments, Z actuator 130 may be fixedly or rigidly attached, for example to stage frame 150. Alternatively, Z actuator 130 may be fixedly or rigidly attached to X-Y translation table base 110, or Z plate 120. In certain embodiments, Z actuator 130 may be configured to utilize linear slides in a ramp configuration to provide Z translation. In operation, Z actuator 130 may be operably coupled to, for example, Z plate 120 and employed to provide translation in the Z dimension. Z actuator 130 may be operably coupled to Z plate 120 through kinematic means such as, for example a Z actuator with a spherical actuator tip that slides on a planar surface of Z plate 120; or, alternatively, through a Z actuator tip contacting an X-Y linear slide operably attached to Z plate 120 and moving relative to the Z actuator tip. As best illustrated in FIG. 2, motion in the Z dimension of Z plate 120 on the side proximate to Z actuator 130 may be substantially linear, i.e., parallel to the Z axis; conversely, the distal side of Z plate 120 may be allowed to rotate about hinge axis 170 (see FIG. 5) associated with flexural component 160 situated on the side of Z plate 120 opposite Z actuator 130. Movement in the X dimension may be tolerable for many microscope imaging operations, particularly where total Z translations are expected to be small. As noted above, the total range of Z travel for many microscopy applications is typically expected to be on the order of approximately 1.0 mm, though a microscope stage such as illustrated and described herein may have utility where even greater Z travel is anticipated. In certain embodiments, flexural component 160 may be characterized by X-Y base coupling 180, Z plate coupling 190, and hinge axis 170. As illustrated in FIGS. 4 and 5, X-Y base coupling 180 may allow flexural component 160 to be rigidly attached to X-Y translation base 110 which is typically fixed in the Z dimension. Similarly, Z plate coupling 190 may allow flexural component 160 to be rigidly or fixedly attached to Z plate 120. During operation, as Z plate 120 is translated by Z actuator 130, flexural component 160 configured and operative as set forth herein may allow Z plate 120 to rotate about hinge axis 170. The distance and orientation of hinge axis 170 relative to X-Y base coupling 180 and Z plate coupling 190 may be selectively adjusted in accordance with overall Z translation requirements, material rigidity, design of Z plate 120, or a combination of the foregoing and other factors. In certain embodiments, hinge axis 170 is positioned in a substantially identical plane as the plane in which the object, specimen, or sample being observed is positioned. Specifically, it will be appreciated that the configuration and structural elements associated with flexural component 160 are susceptible of numerous variations. Size, shape, material selection, and respective configurations of X-Y base coupling 180 and Z plate coupling 190, for example, may be altered to accommodate stage design and overall system requirements. An example illustrated in FIGS. 2-5 employs certain embodiments in which flexural component 160 comprises a flexural type hinge, that is to say, a hinge that deflects in response to an actuation force. A suitable flexural hinge may be fabricated of aluminum, steel, titanium, nickel, brass, other metals, and various metal alloys exhibiting suitable hardness, rigidity, heat transfer characteristics, and other properties, or combinations thereof. Metal or metal alloy embodiments may be forged or milled, for example, depending upon the type of material used, the complexity of the shape of the flexural hinge, or a combination of these and other factors. Additionally, or alternatively, various sections or the entirety of the flexural hinge may be fabricated of or incorporate plastics, polymers, or composite materials which may be selected in accordance with strength, rigidity, heat transfer characteristics, and other properties as noted above with respect to metal embodiments. Those of skill in the art will appreciate that material selection and fabrication techniques for a suitable flexural hinge may be application specific, and may depend upon the myriad uses for which the stage, in conjunction with which the flexural hinge may be employed, is intended. In certain embodiments, flexural hinges may facilitate simpler fabrication and produce hinges with consistent flexural characteristics because the total range of anticipated travel for many microscopy applications is typically expected to be relatively small, typically on the order of approximately 1.0 mm. For greater expected translations in the Z dimension, a robust flexural hinge or a piano hinge assembly may alternately be employed. In certain embodiments, a flexural component may be embodied by a traditional type hinge. A traditional type hinge, also known as a piano hinge, comprises an axle or pin about which other parts can move relative to one another. A suitable piano hinge may be fabricated of various materials as described above for flexural hinges. Those of skill in the art will appreciate that material selection and fabrication techniques for a suitable piano hinge may be application specific, for example, and may depend upon the myriad uses for which the stage, in conjunction with which the piano hinge may be employed, is intended. In certain embodiments, flexural component 160 can be integrated into either Z plate 120 or X-Y translation table base 110. In such embodiments, a separate flexural component 160 can be omitted. In place of flexural component 160, hinge axis 170 can be integrated into Z plate 120, X-Y translation table base 110, or both Z plate 120 and X-Y translation table base 110. Integration of hinge axis 170 may be accomplished, for example, through machining Z plate 120, X-Y translation table base 110, or both Z plate 120 and X-Y translation table base 110, in various positions and to varying degree such that Z plate 120, X-Y translation table base 110, or both Z plate 120 and X-Y translation table base 110 typically exhibits predictable flexural characteristics. One embodiment of a stage design incorporating flexural hinge components as illustrated and described herein was tested in use on a laboratory microscopy system. Primary areas evaluated were Z scanning and point visiting. Results were compared to those obtained using two different traditional type stages. In general, results from the flexural stage testing protocol were at least as good as those obtained using the conventional stages. In order to minimize test variables, all data were acquired using a 40× water objective in order to provide a large working distance (allowing for large Z scans). All stages were operated using the same linear translation actuator mechanisms with the exception of the Z axis for the flexural stage, which employed a different make and model of actuator mechanism. Z PSF Tests To perform point spread function (PSF) tests, Z scans were taken using bead slides disposed at various positions of the stage's work volume. One aspect of the test sought to determine the possible effects of a flexural stage design on X-Z cross-sectioning. FIGS. 6-8 illustrate PSF's in the X-Z plane acquired during 150 μm Z scans taken with 5 μm scan intervals. The images in FIGS. 6-8 represent 150 μm Z scans on each stage under test. These scans were taken with 5 μm scan intervals. These types of images may assist in detection of any excessive stage cross-coupling evidenced by exhibition of non-symmetrical images, tilting images, or both. The scans were also used to look for changes in point symmetry throughout the 150 μm travel range, which would indicate varying Z performance. All three stages show similar image symmetry, indicating that Z sectioning performance was similar. FIGS. 9-11 illustrate PSF's taken on a flexural stage at three points throughout the Z travel range. These scans were the standard 13 μm distance with 0.20 μm scan intervals. Z home position was defined as the Z plate positioned horizontal (or normal to the optical axis). The three nominal scan locations were Z=−200 μm, Z=0 (home), and Z=+200 μm. This covered a Z range of 400 μm, which represents the prototype flexural stage design's capabilities. These scans were also used to look for irregularities in Z sectioning throughout the Z travel envelope. All three beads were scanned at approximately the same optical depth. X and Y positions also changed for each point, however due to limitations of the prototype design, travel was limited to an approximate 8 mm square area. This area did include end of travel conditions for the X axis slides, which created a minimum stiffness (worst case) scenario for Z stability. All three points show expected symmetry, indicating that the X-Z cross-coupling had no appreciable effect on data quality. As part of the testing Y-Z images PSF's were also created. These looked similar to the X-Z images. X-Y-Z Point Visiting Tests This series of tests was performed to validate stage repeatability during a typical point visiting experiment. The experiment consisted of a three point scan, with each point being visited ten times. As each point was visited, a Z scan was also performed. The total X-Y stage movement for each scan sequence was approximately 4 mm. Additional point visiting tests were also run on a flexural stage as illustrated and described above with reference to FIGS. 1-5 that included a larger number of point per sequence (up to ten), and experiments that also took 13 μm Z sections at each point visited. In general, X-Y repeatability error did not exceed 0.35 μm for all points collected at a given X-Y location. This error value included possible effects from thermal drift and “noisy” environment. The present invention has been illustrated and described in detail with reference to particular embodiments by way of example only, and not by way of limitation. Those of skill in the art will appreciate that various modifications to the exemplary embodiments are within the scope and contemplation of the present disclosure. Accordingly, other embodiments are within the scope of the following claims. |
|
description | The present application claims priority to Korean Patent Application No. 10-2021-0074119, filed Jun. 8, 2021, the entire contents of which is incorporated herein for all purposes by this reference. The present disclosure relates to a system for closing a drum unit for storing radioactive waste and, more particularly, to a system for closing a drum unit for storing radioactive waste, the system being configured to unmannedly close a top part of the drum unit for storing the radioactive waste through tightening units provided in a cover unit. In general, the amount of radioactive waste generated from nuclear power plants, research institutes, or the like is very small compared to that of household or industrial waste, but a fatal risk of radiation leakage is high and a treatment period is very long, so safety in a post-treatment process thereof is required to be secured. Treatment of radioactive waste is a method to reduce an effect of radiation on the environment, wherein the method solidifies the radioactive waste using a polymer, paraffin, cement, or the like. Here, radioactive liquid waste of the radioactive waste is made into granulated radioactive waste by concentrating and drying a large amount of moisture contained therein. Subsequently, the granulated radioactive waste is placed in a specified drum unit and is subject to solidification treatment by injecting a solidifying agent (solidifying resin) such as polymer, paraffin, cement, or the like into an inner side of the drum unit. On the other hand, in order to close the drum unit after injecting the radioactive waste into the drum unit, closure of the drum unit is performed by applying a mobile unmanned system to prevent workers from being exposed. At this time, in a process of closing a cover unit on a top part of the drum unit to block the radioactive waste after injecting the radioactive waste into the inner side of the drum unit, concerns are being raised due to serious problems that precise closure may not be made between the top part of the drum unit and the cover unit, so a trace amount of radioactivity may leak between the top part of the drum unit and the cover unit. Accordingly, research on a device for safely and unmannedly closing the drum unit containing the radioactive waste therein is being actively conducted. (Patent Document 1) Korean Patent No. 10-1146176 Accordingly, the present disclosure has been made keeping in mind the above problems occurring in the related art, and an objective of the present disclosure is to provide a system for closing a drum unit for storing radioactive waste, the system being configured to unmannedly close a top part of the drum unit for storing the radioactive waste through each of tightening units provided in a cover unit. Another objective of the present disclosure is to provide the system for closing the drum unit for storing radioactive waste for performing precisely fastening each of tightening units through a pair of keys and a pair of key grooves when each of the tool parts rotates to tighten each of the fastening bolts. The objectives of embodiments of the present disclosure are not limited to the above-mentioned objectives, and other objectives not mentioned will be clearly understood by those of ordinary skill in the art to which the present disclosure belongs from the following description. In order to achieve the above objective, according to one aspect of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, the system including: a supporting unit configured to be seated on the ground; a drum unit configured to be seated on a top part of the supporting unit and having a plurality of first fastening holes formed along an outer circumferential surface of a top part thereof; a moving unit configured to move to a side of the drum unit; a cover unit provided at an inside of the moving unit or at one side of the drum unit and having a plurality of second fastening holes formed along an outer circumferential surface thereof; tightening units configured to be inserted into the corresponding second fastening holes; a fastening unit configured to grip the cover unit through a gripping part provided on one side of the inside of the moving unit to move the cover unit to the top part of the drum unit simultaneously and to allow the cover unit to be seated by aligning axis lines of the first and second fastening holes to be matched, thereby closing a gap between the drum unit and the cover unit by tightening an upper part of each of the tightening units through associated one of a plurality of tool parts provided on a circumference of the gripping part; and a controller configured to control the fastening unit. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein each of the tightening units may include: a fastening bolt having a bolt head formed on an upper part thereof and a first screw thread formed on a lower part thereof; a first bushing having: a hollow first insertion portion into which the fastening bolt is inserted; a first step formed under the first insertion portion; and first latching portions formed so as to be symmetrical to each other in front and rear directions at a bottom part of the first step; a second bushing having: a hollow second insertion portion, into which outer circumferential surfaces of the first latching portions are inserted, and having a top part thereof being latched on the first step; and a plurality of fixing pieces formed into a plurality of incision portions on a circumference of a lower part of the second insertion portion; and a third bushing having: second latching portions formed so as to be symmetrical to each other in left and right directions at an upper part thereof, and inserted into the first latching portions; a second step formed at a side under the second latching portions; and a third hollow insertion portion formed under the second step. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein, when one of the tool parts tightens the bolt head, the third insertion portion formed with a second screw thread on an inner circumferential surface thereof may move to an upper part of the fastening bolt along the first screw thread, and at the same time, the second step may press a bottom part of each of the fixing pieces, and each of the fixing pieces may subsequently spread outward with a boundary line, which is formed at an upper end of each of the incision portions, as a reference, so as to surround an area around a bottom part of the first fastening hole, whereby the drum unit and the cover unit may be closed. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein the second step may be configured to be tapered at a predetermined angle in a direction from a bottom part to a top part. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein a pair of keys may be provided at a lower end of each of the tool parts, and a pair of key grooves into which the pair of keys are inserted may be provided on an outer circumferential surface of an upper part of the first insertion portion. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, the system further including an injection unit provided on the one side of the inside of the moving unit and configured to receive the radioactive waste from an outside to inject the radioactive waste into the drum unit. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein the controller may control positions of the fastening unit and the injection unit so as to move the fastening unit and the injection unit to a position where the drum unit may be seated. In addition, according to an embodiment of the present disclosure, there may be provided a system for closing a drum unit for storing radioactive waste, wherein the gripping part may be provided with an electromagnet, and the cover unit may be made of steel material so that the gripping part may grip a top part of the cover unit by a magnetic force of the electromagnet. According to the system for closing the drum unit for storing radioactive waste of the present disclosure, there is an effect in that the top part of the drum unit for storing the radioactive waste can be unmannedly closed through the tightening units provided in the cover unit. In addition, when each of the tool parts rotates to tighten each of the fastening bolts, there is an effect in that precise fastening of each of the tightening units can be performed through a pair of keys and a pair of key grooves. The following objectives, other objectives, features, and advantages of the present disclosure will be readily understood through the following exemplary embodiments related to the accompanying drawings. However, the present disclosure is not limited to the embodiments described herein and may be embodied in other forms. Meanwhile, the embodiments introduced herein are provided in order to allow the disclosed subject matter to be thorough and complete and the spirit of the present disclosure to be sufficiently conveyed to those skilled in the art. The embodiments described and illustrated herein also include complementary embodiments thereof. In the present specification, the singular also includes the plural, unless specifically stated otherwise in a phrase. As used herein, the terms “comprise” and/or “comprising” do not exclude the presence or addition of one or more other components. Hereinafter, the present disclosure will be described in detail with reference to the drawings. In describing the specific embodiments below, various specific contents have been prepared to more specifically explain and help the understanding of the disclosure. However, those skilled in the art and having the knowledge to a degree to understand the present disclosure may recognize that the embodiments may be used even without such various specific details. In some cases, it is mentioned in advance that parts, which are commonly known in describing the disclosure but not largely related to the disclosure, may not be described in describing the present disclosure in order to avoid confusion. FIGS. 1 to 2 are perspective views showing a system for closing a drum unit for storing radioactive waste according to an embodiment of the present disclosure, FIG. 3 is an exploded perspective view showing one of tightening units of the system for closing the drum unit for storing radioactive waste according to the embodiment of the present disclosure, FIG. 4 is a front view showing an exploded state of the one of the tightening units configured in the system for closing the drum unit for storing radioactive waste according to the embodiment of the present disclosure, FIG. 5 is a front view showing a coupled state of the one of the tightening units configured in the system for closing the container unit for storing radioactive waste according to an embodiment of the present disclosure, FIG. 6 is a partially enlarged view showing a state before the drum unit and the cover unit are closed in the system for closing the drum unit for storing radioactive waste according to the embodiment of the present disclosure, FIG. 7 is a partially enlarged view showing a state after the drum unit and the cover unit are closed in the system for closing the drum unit for storing radioactive waste according to the embodiment of the present disclosure, and FIG. 8 is a plan view showing a coupled state of a pair of keys and a pair of key grooves in the system for closing the drum unit for storing radioactive waste according to the embodiment of the present disclosure. As shown in FIGS. 1 to 8, the system for closing the drum unit for storing radioactive waste according to the present disclosure includes largely, a supporting unit 100, a drum unit 200, a moving unit 300, a cover unit 400, tightening units 500, a fastening unit 600, and a controller (not shown). More specifically, the system for closing the drum unit for storing radioactive waste according to the present disclosure includes: a supporting unit 100 configured to be seated on the ground; a drum unit 200 configured to be seated on a top part of the supporting unit 100 and having a plurality of first fastening holes 210 formed along an outer circumferential surface of a top part thereof; a moving unit 300 configured to move to a side of the drum unit 200; a cover unit 400 provided at an inside of the moving unit 300 or at one side of the drum unit 200 and having a plurality of second fastening holes 410 formed along an outer circumferential surface thereof; tightening units 500 configured to be inserted into the associated second fastening holes 410; a fastening unit 600 configured to grip the cover unit 400 through a gripping part 610 provided on one side of the inside of the moving unit 300 to move the cover unit 400 to the top part of the drum unit 200 simultaneously and to allow the cover unit 400 to be seated by aligning axis lines of the first and second fastening holes 210 and 410 to be matched, thereby closing a gap between the drum unit 200 and the cover unit 400 by tightening an upper part of each of the tightening units 500 through associated one of a plurality of tool parts 620 provided on a circumference of the gripping part 610; and a controller configured to control the fastening unit 600. First, the supporting unit 100 is configured to be seated on the ground of a radioactive waste disposal site and the like, wherein the supporting unit 100 may be adjusted to be horizontal with the ground. Through this, the supporting unit 100 prevents the drum unit 200, which will be described below, from being turned upside down by being tilted to any one side. When the supporting unit 100 is not leveled with the ground, in a process of injecting the radioactive waste into the drum unit 200 or after the radioactive waste has been injected into the drum unit 200, the drum unit 200 may be turned upside down because an axis line of the center of gravity thereof does not match vertically with a bottom surface thereof, and at the same time, the radioactive waste may leak. Therefore, in order to prevent such a problem, a top part surface of the supporting unit 100 may be provided to be parallel to the ground. In addition, the supporting unit 100 is manufactured in a structure in which pipes having a cross-section of a circular shape or square shape are coupled in horizontal and vertical directions, thereby supporting the load of the drum unit 200. In addition, the auxiliary supporting unit 110 may be further seated on and fixed to the top part of the supporting unit 100, wherein the auxiliary supporting unit 110 may be seated on and fixed to the top part of the supporting unit 100 with various heights, by taking into consideration a height between the bottom part of the fastening unit 600 to be described below and the top part of the drum unit 200, thereby being used as a means of supporting regardless of the height of the drum unit 200. The drum unit 200 is configured to be seated on the top part of the supporting unit 100 and to store radioactive waste generated in a radioactive waste disposal site and the like. Here, the radioactive waste, mixed materials, and the like are injected into the drum unit 200, and the radioactive waste may be injected through the injection unit 700, wherein the injection unit 700 is provided on one side of the inner side of the moving unit 300 to be described below and is configured to inject the radioactive waste into the drum unit 200 by receiving the radioactive waste from the outside. Here, the drum unit 200 may be manufactured in a drum shape having a cross-section such as a circle or square shape and may be manufactured to have various sizes, thereby receiving the radioactive waste. In addition, the drum unit 200 is formed with a plurality of first fastening holes 210 along the outer circumferential surface of the top part thereof, wherein the first fastening holes 210 are formed by being spaced apart from each other at regular intervals along the outer circumferential surface of the top part of the drum unit 200. In addition, after position adjustment (alignment of an axis line) of each of the first fastening holes 210 is made to correspond to each of the second fastening holes 410, each of the tightening units 500 to be described below is penetrated through and inserted into the associated one of the first fastening holes 210. On the other hand, a step (not shown) may be formed on an outer circumferential surface of the top part of the drum unit 200, thereby improving closing force with the cover unit 400 to be described below, and a sealing material (not shown) may be provided on an outer circumferential surface of the step (not shown), thereby improving the closing force between the drum unit 200, along with the step (not shown), and the cover unit 400. The moving unit 300 is configured to move to a side of the drum unit 200. Here, the moving unit 300 is a means to be used for unmanned operation at a radioactive waste disposal site after being moved to a radioactive waste disposal site located in various places, and it is implied that the moving unit 300 includes all moving means capable of loading such as a trailer, a cargo truck, and the like. On the other hand, the gripping part 610, the tool parts 620, and the like to be described below are loaded at the inside of the moving unit 300, thereby being allowed to move to a position where the drum unit 200 into which the radioactive waste has been injected has been seated. Here, the moving unit 300 is positioned by being spaced apart at a regular interval from the center of the drum unit 200 and may be positioned within an operating range of the fastening unit 600 and the injection unit 700 to be described below. The cover unit 400 is provided at the inside of the moving unit 300 or at one side of the drum unit 200 and is configured to close the top part of the drum unit 200. The cover unit 400 may be manufactured to have a cross-section in a cover shape such as a circle shape, a square shape, or the like and to have various sizes, thereby closing the top part of the drum unit 200. In addition, the cover unit 400 is formed with the plurality of second fastening holes 410 along the outer circumferential surface thereof, wherein the second fastening holes 410 are formed by being spaced apart from each other at regular intervals along the outer circumferential surface of the cover unit 400. In addition, after position adjustment (alignment of an axis line) of each of the second fastening holes 410 is made to correspond to each of the first fastening holes 210, each of the tightening units 500 to be described below is penetrated through and inserted into the associated one of the second fastening holes 410. On the other hand, a step (not shown) is formed on an outer circumferential surface of a bottom part of the cover unit 400 to correspond to the step (not shown) formed on the circumferential surface of the top part of the container part 200, thereby improving the closing force between the drum unit 200 and the cover unit, and a sealing material (not shown) may be provided on the outer circumferential surface of the step (not shown), thereby improving the closing force between the drum unit 200, along with the step (not shown), and the cover unit 400. On the other hand, the cover unit 400 is made of steel material (material that responds to magnetic force) and may be moved to the top part of the drum unit 200 in a state of the top part thereof being gripped by the gripping part 610, which will be described below, through whether current is supplied to the gripping part 610. Each of the tightening units 500 is configured to be inserted into associated one of the second fastening holes 410. Furthermore, in a standby state, each of the tightening units 500 has been inserted into the associated one of the second fastening holes 410 of the cover unit 400. When the cover unit 400 is seated on the drum unit 200 for closing the drum unit 200, axis lines of each of the first fastening holes 210 and each of the second fastening holes 410 are aligned to be matched, so that a lower part of each of the tightening units 500 is inserted into the associated one of the first fastening holes 210. Here, each of the tightening units 500 may mutually close the drum unit 200 and the cover unit 400 through the associated one of the tool parts 620 configured in the fastening unit 600 to be described below. The tightening units 500 will be described in detail below. The fastening unit 600 is configured to include a gripping part 610 provided on one side of the inside of the moving unit 300 and the tool parts 620 provided on the circumference of the gripping part 610. More specifically, the fastening unit 600 is configured: to grip the cover unit 400 through the gripping part 610 provided on one side of the inside of the moving unit 300 and to move the cover unit 400 to the top part of the drum unit 200, at the same time, thereby allowing the cover unit 400 to be seated by arranging the axis lines of each of the first fastening holes 210 and associated one of the second fastening holes 410 to be matched; and to close the gap between the drum unit 200 and the cover unit 400 by tightening an upper part of each of the tightening units 500 through associated one of a plurality of tool parts 620 provided around the gripping part 610. The gripping part 610 is provided with an electromagnet, and the cover unit is made of steel material to correspond to the gripping part 610. Accordingly, the gripping part 610 may grip the upper part of the cover unit 400 by the magnetic force of the electromagnet. That is, the electromagnet is connected to a separately provided power supply unit (not shown) to receive current and, when the current flows, the gripping part 610 is magnetized, so that the gripping part 610 may grip the top part of the cover unit 400 to move the cover unit 400 to the top part of the drum unit 200. In addition, when the current is cut off, the electromagnet returns to an original non-magnetized state, thereby allowing the cover unit 400 to be seated on the top part of the drum unit 200. Here, the fastening unit 600 is manufactured to be movable in front, back, left and right, and up and down directions through the control of the controller (not shown) to be described below and, after gripping the top part of the cover unit 400, may move to be matched with a position of the drum unit 200. Each of the tool parts 620 is configured to close the cover unit 400 that has been moved to the top part of the drum unit 200 through the gripping part 610. Each of the tool parts 620 is to be rotated by receiving a fluid supplied from the outside through a fluid supply means (not shown), wherein each of the tool parts 620 may be an electric drill. Here, a chamber (not shown) configured to collect the supplied fluid may be further included between the fluid supply means (not shown) and each of the tool parts 620. More specifically, the chamber (not shown) is connected to one side of the fluid supply means (not shown) to always collect the fluid supplied from the fluid supply means (not shown) and may supply the collected fluid to each of the tool parts. Accordingly, the shortage of fluid supply may be solved, thereby promoting an operation of each of the tool parts 620. On the other hand, each of the tool parts 620 is configured to tighten associated one of the tightening units 500 to be inserted into the cover unit 400. When each of the tool parts 620 grips the upper part of associated one of the fastening bolts 510, which will be described below, and rotates the associated one of the fastening bolts 510 to tighten, one side of the lower part of the associated one of the tightening units 500 surrounds a circumferential area around a bottom part of each of the first fastening holes 210, thereby closing the gap between the cover unit 400 and the drum unit 200. In this case, a magnet may be installed at an end of each of the tool parts 620 and grip a top part of the first bushing 520, which will be described below. Each of the above-stated tightening units 500 is configured to largely include a fastening bolt 510, a first bushing 520, a second bushing 530, and a third bushing 540. More specifically, the fastening bolt 510 is configured to include a bolt head 511 formed on an upper part thereof and a first screw thread 512 formed on a lower part thereof. The first bushing 520 is configured to include a hollow first insertion portion 521 into which the fastening bolt 510 is inserted, a first step 522 formed under the first insertion portion 521, and first latching portions 523 formed so as to be symmetrical to each other in front and rear directions at a bottom part of the first step 522. The second bushing 530 is configured to include a hollow second insertion portion 531 into which the outer circumferential surface of the first engaging portions 523 is inserted and a plurality of fixing pieces 533 configured as a plurality of incision portions 532 at a lower part of the second insertion portion 531. The third bushing 540 is configured to include: second latching portions 541 formed so as to be symmetrical to each other in left and right directions at an upper part thereof, thereby being inserted into the first latching portions 523; a second step 542 formed at a part under the second latching portions 541; and a third hollow insertion portion 543 formed under the second step 542. That is, when one of the tool parts 620 tightens the bolt head 511, the third insertion portion 543 formed with a second screw thread 544 on an inner circumferential surface thereof moves to an upper part of the fastening bolt 510 along the first screw thread 512, and at the same time, the second step 542 presses a bottom part of each of the fixing pieces 533, and each of the fixing pieces 533 subsequently spreads outward with a boundary line L, which is formed at an upper end of each of the incision portions 532, as a reference so as to surround an area around a lower part of one of the first fastening holes 210, whereby the drum unit and the cover unit are closed. On the other hand, a protrusion 534 protruding outward is provided at a lower end of each of the fixing pieces 533. When each of the fixing pieces 533 spreads outward with the boundary line L as the reference, each of the protrusions 534 latches and supports a spot around the bottom part of one of the first fastening holes 210, thereby enhancing closing force between the cover unit 400 and the drum unit 200. In addition, the second step 542 is configured to be tapered at a predetermined angle in a direction from a bottom part to a top part. Accordingly, when the third bushing 540 presses the bottom part of each of the fixing pieces 533, each of the fixing pieces 533 may be induced to be smoothly spread outward with the boundary line L as the reference. In addition, a pair of keys 420 are provided at a bottom part of each of the tool parts 620, and a pair of key grooves 430 into which the pair of keys 420 are inserted are provided on an outer circumferential surface of an upper part of the first insertion unit 521. Here, when each of the bolts 510 is being fastened by being rotated by associated one of the tool parts 620, each of the tightening units 500 may be prevented from being shaken through the pair of keys 420 and the pair of key grooves 430, whereby more precise fastening may be performed. On the other hand, the system may further include an injection unit 700 that is provided on one side of the inside of the moving unit 300 to receive the radioactive waste from an outside and to inject the radioactive waste into the drum unit 200. The controller (not shown) controls the fastening unit 600 and the injection unit 700 to move to a position where the drum unit 200 is seated by controlling positions of the fastening unit 600 and the injection unit 700, wherein the controller controls the positions according to an operator's decision by being interlocked with a controller provided to an operator. Here, the controller (not shown) may control the gripping part 610 to move the cover unit 400, may control each of the tool parts 620 to perform tightening associated one of the tightening units 500, or may control the position of the injection unit 700 to inject the radioactive waste into the drum unit 200. Here, the lengths of the fastening unit 600 and the injection unit 700 may be precisely adjusted through the controller (not shown) by being connected to length adjusting means such as a cylinder and the like, or may be precisely rotated through the controller (not shown) by being connected to a rotating means such as a rotating motor or the like. That is, the controller (not shown) is capable of moving the fastening unit 600 and the injection unit 700 to the position where the drum unit 200 is seated in the front and back directions, left and right directions, and up and down directions. Accordingly, the operator may unmannedly control a process even without being approached close to the drum unit 200 in which the radioactive waste is stored, so that the problem of exposure to radioactivity may be prevented. Therefore, according to the system for closing the drum unit for storing radioactive waste of the present disclosure, there is an effect in that the top part of the drum unit for storing the radioactive waste may be unmannedly closed through the tightening units provided in the cover unit. In addition, when each of the tool parts rotates to tighten associated one of the fastening bolts, there is an effect in that precise fastening of each of the tightening units may be performed through the pair of keys and the pair of key grooves. The embodiments described in the present specification and the configurations shown in the drawings are only the most exemplary embodiment of the present disclosure and do not represent all the technical spirit of the present disclosure, so it should be understood that there may be various equivalents and variations that may be substituted for the embodiments at the time of the present application. |
|
abstract | A column assembly of a radionuclide generator includes a column that retains a parent radionuclide that spontaneously decays to a relatively short-lived daughter radionuclide. A fluid path extends from an inlet port to the column and then to an outlet port and allows daughter radionuclide to be eluted from the radionuclide generator for use. Improved retention of parent radionuclide in the column is accomplished by preventing fluid from entering the flow path in a liquid state, such as during sterilization. Proper column chemistry is also promoted by preventing excess moisture from coalescing in the column, which may promote a higher and/or more reliable yield of daughter radionuclide from a radionuclide generator. |
|
summary | ||
abstract | An X-ray imaging apparatus is disclosed. The apparatus includes a radiator housing, an X-ray tube, a source of X-rays and at least one filtration material disposed on the X-ray tube. The X-ray tube is rotatable about a longitudinal axis and is disposed at least partially within the radiator housing. The source of X-rays emits at least one X-ray beam at least partially through the X-ray tube. The X-ray beam exits the X-ray tube at an annular X-ray window. The filtration material at least partially covers a portion of the annular X-ray window. Rotation of the X-ray tube causes the X-ray beam to pass through a plurality of locations in the annular X-ray window and at least a portion of the X-ray beam is filtered by the filtration material. |
|
048572624 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus for the singulizing of fuel rods shown in the above drawings is provided with a base plate 2 and a stand 4. A supporting table 6 for a fuel element 8 is attached to the stand 4 so as to be able to move in a vertical direction. The fuel element 8 is retained on the supporting table 6 in a position which can be determined by means of clamping jaws 10. Various mobile holders 12 are arranged in guides 11 at the top end of the stand 4 and serve as tool carriers. The drive mechanisms 14 for these holders 12 are arranged behind the stand 4. The fuel element 8 is provided with a foot piece and a head piece 19, 19', with a larger number of fuel rods 15 arranged between them and a smaller number of control rod guide tubes 15', which are retained by means of spacers 16 in a predetermined matrix arrangement in various planes at a distance from one another. In the fuel rod holder 12, grappling tools 20, 20' are arranged on both sides of each plane of spacers 18, which serve to maintain the rods in a defined position. A mobile cutting tool 24 is arranged on a separate mounting 22 between the grappling tools 20, 20'. At the lower end of this mounting 22, a cutting disk head 26 is arranged, which can be rotated over an angle of 90.degree.. Furthermore, a grappler 28 is arranged at the holder 22 of the cutting tool 24. Exposed fuel rods and control guide tubes are manipulated and deposited in a storage chamber 30 by means of this grappler 28. Operation of the fuel rod singularizer is as follows: As soon as the fuel element 8 is positioned in the right direction for the singulizing procedure and has been fixed in place by means of the clamping jaws 10, the foot piece and the head piece 19, 19' are simultaneously severed by means of the saw arrangement (not shown here), employing a state-of-the-art method. The fuel element is next decomposed or broken down layer by layer in the following manner. First of all, the outermost fuel rod in each spacer plane is firmly retained in the grappling tools. The outermost vertical spacer web of the spacer grid is then severed by means of the cutting tool at an angle of 45.degree.. The upper horizontal spacer web is then gripped in the corresponding grappler 28 and withdrawn upwards at an angle, as shown in FIG. 2. As a result, the next vertical spacer web becomes accessible to the cutting tool. After the second vertical spacer web has been severed, the third vertical spacer web can then be pulled into position by the grappler and thus be ready for cutting. All the vertical spacer webs in the first and uppermost layer of fuel rods can be severed in turn. In this way, the entire horizontal spacer structure in the first layer of fuel rods can be removed or bent upwards. In the next operation, the individual fuel rods can be lifted, in turn, inwards and out of the fuel element. This operation is accomplished with the help of the grappling tools 20, 20'. After being lifted inwards and out of this fuel element, the fuel rods are deposited in the storage chamber 30 in a compact, space-saving way. After the first layer of fuel rods has been dealt with, the above procedure is repeated for each subsequent plane of fuel rods, in turn, until the whole fuel element has been taken apart and all the fuel rods have been reshuffled. As stated above, each fuel element is provided with some more control rod guide tubes 32, 15'. See FIG. 3. The diameter of these tubes will generally exceed the diameter of the fuel rods, and this enables them to be identified by the grappling tools 20, 20' and stored in a separate chamber (not shown here). The remaining bent spacer grid and the head and the foot pieces are pressed in a special press and prepared for final storage (not shown here). The arrangement described here is suitable for use in reactor plants as well as in shielded cells. That is to say, the arrangement is suitable for operation in either dry or wet environments. This singularizing system can operate either horizontally or vertically, and it is operated entirely under remote control. |
claims | 1. An apparatus for producing radioisotopes comprising:an irradiation chamber;a compact, stand-alone, fast neutron generator disposed within the irradiation chamber configured to provide fast neutrons;NEU material disposed within the irradiation chamber;one or more NEU-receiving regions disposed within the irradiation chamber and configured to accommodate the NEU material; andone or more non-moderating neutron-reflecting regions disposed in the irradiation chamber; wherein the one or more non-moderating neutron-reflecting regions are configured to increase the path length traveled by at least some neutrons from the neutron generator before those neutrons leave the irradiation chamber; wherein the one or more non-moderating, neutron-reflecting regions disposed in the irradiation chamber comprise multiple elongated parallel outer tubular shells formed of non-moderating neutron-reflecting material; wherein each of the multiple elongated parallel outer tubular shells has an interior bore containing NEU; wherein the interior bore defines one of the one or more NEU-receiving regions; and wherein the irradiation chamber has a fill port disposed on the upward portion of the irradiation chamber and has a drain port disposed on the lower portion of the irradiation chamber. 2. The apparatus of claim 1 further comprising a neutron-absorbing outer containment vessel comprising walls that are disposed at least 0.5 meter from the outside of the irradiation chamber. 3. The apparatus of claim 1 further comprising a non-moderating neutron-reflecting wall disposed within the irradiation chamber and surrounding the multiple elongated parallel outer tubular shells formed of non-moderating neutron-reflecting material. |
|
abstract | The conventional detection technique has the following problems in detecting interference fringes: (1) Setting and adjustment are complex and difficult to conduct; (2) A phase image and an amplitude image cannot be displayed simultaneously; and (3) Detection efficiency of electron beams is low. The invention provides a scanning interference electron microscope which is improved in detection efficiency of electron beam interference fringes, and enables the user to observe electric and magnetic information easily in a micro domain of a specimen as a scan image of a high S/N ratio under optimum conditions. |
|
abstract | An ion source is disclosed for use in fabrication of semiconductors. The ion source includes an electron emitter that includes a cathode mounted external to the ionization chamber for use in fabrication of semiconductors. In accordance with an important aspect of the invention, the electron emitter is employed without a corresponding anode or electron optics. As such, the distance between the cathode and the ionization chamber can be shortened to enable the ion source to be operated in an arc discharge mode or generate a plasma. Alternatively, the ion source can be operated in a dual mode with a single electron emitter by selectively varying the distance between the cathode and the ionization chamber. |
|
summary | ||
description | This application is a national phase entry under 35 U.S.C. § 371 of International Patent Application PCT/CN2016/089936, filed Jul. 13, 2016, designating the United States of America and published as International Patent Publication WO 2017/008746 on Jan. 19, 2017, which claims the benefit under Article 8 of the Patent Cooperation Treaty to Chinese Patent Application Serial No. 201510409138.1 and to Chinese Patent Application Serial No. 201520504843.5 filed Jul. 13, 2015. The present disclosure relates to the technical field of fluids machinery, and particularly, to a channel baffle structure. A High Temperature Gas-Cooled Reactor (HTR) applies graphite as a moderator and helium as a coolant, and it is an advanced nuclear reactor with good inherent safety, high-power generation efficiency and widespread usages. An overall structure of the primary circuit of an HTR nuclear power plant is illustrated in FIG. 1, which comprises a reactor pressure vessel 1′ and a steam generator pressure vessel 5′, wherein a hot gas duct 3′ is connected therebetween. The reactor core is cooled by helium. The HTR applies a helium circulator to drive the helium coolant circulating inside the primary circuit of the reactor. The helium circulator 4′ is arranged vertically and installed directly above the steam generator pressure vessel 5′. It can be seen from FIG. 1 that the entire helium circulator 4′ is located inside the primary circuit and connected with the reactor core. In order to prevent reverse natural flow with a high temperature up to 750° C. in the reactor core in an accident of reactor shutdown, a baffle should be installed at the inlet or outlet of the helium circulator 4′, which plays a role of blocking and isolating. Otherwise, the high temperature heat flow with a temperature up to 750° C. will flow through the outer wall of the hot gas duct 3′ and other boundaries of the primary circuit, whose design temperature is lower than 750° C. This causes pressure boundaries of the primary circuit to be damaged and the safety of the reactor to be seriously impacted. In addition, there is an operating condition of small flow for the HTR, which requires a small flow of helium to flow reversely (in an opposite direction of the helium flow of the helium circulator in normal operating conditions) through the helium circulator. At this time, the baffle of the helium circulator should be in a small opening state so as to guarantee a certain gas-flow speed. In order to be consistent with passive safety characteristics possessed by an HTR nuclear power plant, choosing a tongue plate structure similar to a check valve for the baffle structure is desirable. Generally, the tongue plate is to be opened and closed by the helium pressure and tongue plate gravity, which realizes a unidirectional flow of the helium. In addition, gas intake and gas exhaust directions of the helium circulator in the HTR are along an axial direction, and thus a swing check plate with the simplest structure must be chosen. Further, in order to satisfy the “diversity” requirements of design for nuclear power plants, a driving apparatus to drive the tongue plate of the swing check plate must be chosen. When passive characteristics of the swing check plate fail, active opening and closing of the tongue plate is realized, such that the baffle of the helium circulator have the active and passive characteristics at the same time. In addition, in the operating condition of small flow, it is difficult to control the opening and closing of the tongue plate only by the helium pressure and tongue plate gravity, and thus there is a need for a driving apparatus to complete the control. However, there is hardly any introduction about the specific connection structure between the driving apparatus and the swing check plate in the prior art. Therefore, it is a problem that a person skilled in the art needs to overcome to connect a driving apparatus and a swing check plate to realize the opening and closing as well as adjusting of the baffle of helium circulator of the HTR. The purpose of the present disclosure is to provide a channel baffle structure so as to realize that the channel is able to be opened and closed in both active and passive functions and to be able to adapt to work requirements of multiple operating conditions. In order to solve the above-mentioned technical problem, the present disclosure provides a channel baffle structure, which comprises a pipe, a swing check plate and a driving apparatus. The swing check plate comprises a tongue plate, a crank connecting rod and a rotating shaft. One end of the crank connecting rod is connected with the tongue plate through a nut, and the other end is welded on a shaft sleeve of the rotating shaft. The pipe wall of the pipe is provided with a circular opening for placing the tongue plate in a fully open state. The crank connecting rod and a circular branch pipe are welded at the circular opening. The axis of the circular branch pipe is perpendicular to the axis of the pipe, an end of the circular branch pipe is in a form of flange structure and connected with a pipe side cover plate by bolts. The tongue plate, the crank connecting rod and a part of the rotating shaft of the swing check plate are arranged within the pipe. The driving apparatus is arranged outside the pipe and the swing check plate and driving apparatus are connected through the rotating shaft, a bevel gear and a driving apparatus connecting shaft. One end of the rotating shaft is connected with the swing check plate, and the other end is connected with the bevel gear. One end of the driving apparatus connecting shaft is connected with the bevel gear, and the other end of the driving apparatus connecting shaft is connected with the driving apparatus. The channel baffle structure also comprises a special structure used for connecting the driving apparatus and the swing check plate, specifically, a key is installed on the rotating shaft connected with the crank connecting rod, an annular keyway is correspondingly set within the shaft sleeve of the rotating shaft, such that the shaft sleeve has an idle travel of 90-degree free rotation around the rotating shaft and the key is positioned within the annular keyway. Wherein, the rotating shaft is arranged at an inlet end of the pipe. Wherein, a supporting frame is welded at the outer wall surface of the pipe and the lower part of the rotating shaft so as to support the rotating shaft. Wherein, taking the axis of the rotating shaft as a reference direction, the radial height of the annular keyway is 0.1-0.3 mm higher than the radial height of the key, the circumferential angle α of the annular keyway is between 90° and 100°, and the axial length of the annular keyway is 0.1-0.3 mm longer than the axial length of the key. Wherein, the annular keyway is in clearance fit with the key. Wherein, a fully open position annular sealing surface adjacent to the pipe wall of the pipe is welded at an inner wall surface of the circular branch pipe of the pipe, and when the pipe is in the fully open state, the tongue plate is in contact with the fully open position annular sealing surface. Wherein, a fully closed position annular sealing surface is arranged at the inlet end of the pipe adjacent to the pipe wall, and when the pipe is in the fully closed state, the tongue plate is in contact with the fully closed position annular sealing surface. Wherein, when the driving apparatus controls the pipe to be opened or closed, the key is always directly above the rotating shaft in view from the direction parallel to the axis of the rotating shaft. Wherein, in the operating condition of small flow, after the pipe is opened or closed by taking the active characteristics of the driving apparatus to drive the tongue plate to move, it is required to rotate the rotating shaft reversely by the driving apparatus, such that the key rotates in the annular keyway reversely, until it is located directly above the rotating shaft, so as to prepare to open or close the pipe the next time. Wherein, in order to achieve a small opening state of the pipe when the fluid flows reversely, in view from the direction perpendicular to the page, the key has to be turned clockwise to a desired angle by the driving apparatus, such that the clockwise side of the key is adjacent to the clockwise side of the annular keyway. The channel baffle structure provided by the present disclosure comprises a pipe, a swing check plate and a driving apparatus, wherein a tongue plate of the swing check plate can be rotated under an external force so as to open or close the pipe. When the flow of fluid required to pass through the pipe is large, rotating of the tongue plate can be automatically realized by fluid pressure and tongue plate gravity, thereby realizing the opening and closing of the pipe; when the flow of fluid required to pass through the pipe is small or flows reversely, the rotating of the tongue plate can be controlled by the driving apparatus, thereby realizing the opening, closing and partial opening of the pipe. The control of opening and closing of the channel connected with the pipe can be realized by the tongue plate under both active and passive functions, and the baffle structure is simple in structure and can adapt to the requirements of multiple operating conditions of the channel. Detailed description of the present disclosure is further described in detail below in combination with the accompanying drawings and embodiments. The following embodiments are used to explain the present disclosure, but are not used to limit the scope of the present disclosure. As illustrated in FIG. 2, a channel baffle structure provided by an embodiment of the present disclosure comprises three parts of a pipe 1, a swing check plate and a driving apparatus 8, wherein the swing check plate comprises a tongue plate 2, a crank connecting rod 3 and a rotating shaft 4. One end of the crank connecting rod 3 is connected with the tongue plate 2 through a nut, and the other end is welded on a shaft sleeve 13 (FIG. 4). The rotating shaft 4 is arranged adjacent to an inlet of the pipe 1. The tongue plate 2, the crank connecting rod 3 and a part of the rotating shaft 4 of the swing check plate are arranged within the pipe 1. The swing check plate and the driving apparatus 8 are connected through the rotating shaft 4, a bevel gear 7 and a driving apparatus connecting shaft 9. One end of the rotating shaft 4 is connected with the swing check plate, and the other end is connected with the bevel gear 7; one end of the driving apparatus connecting shaft 9 is connected with the bevel gear 7, and the other end is connected with the driving apparatus 8. The rotating shaft 4 and the driving apparatus connecting shaft 9 play a role of connecting, and the bevel gear 7 plays a role of turning and transferring torque. The driving apparatus 8 is arranged outside the pipe 1, and the arrangement position is chosen as required. In order to support the rotating shaft 4, a supporting frame 6 is welded at the outer wall surface of the pipe 1 and the lower part of the rotating shaft 4. When the pipe 1 is installed vertically; the baffle structure can be used in the helium circulator of HTR. At this time, the pipe 1 is a conical pipe. This realizes the control of the opening and closing of the baffle of the helium circulator of HTR in the active and passive conditions. The baffle structure can also be used in non-return valves, check valves or other pipe circuits to control the opening and closing of pipes. That is, controlling the rotation of the tongue plate 2 using the pressure of the fluid that flows through the pipe 1 or the gravity of the tongue plate 2 and thus controlling the opening and closing of the pipe 1, or controlling the rotation of the tongue plate 2 by the driving apparatus 8 so as to control the opening of the pipe 1. When the pipe 1 of the baffle structure is horizontally installed, the tongue plate 2 is rotated by the driving function of the fluid pressure or the driving apparatus 8. The present embodiment is described by taking an example where the baffle structure is used in helium circulator of HTR, wherein the baffle structure is installed at the inlet of the helium circulator, and the driving apparatus 8 may be an electric driving apparatus, a pneumatic driving apparatus or an electromagnetic driving apparatus. In the present embodiment, the electric driving apparatus is chosen, and the pipe 1 is a conical pipe. Wherein, the conical pipe is an inlet pipe in front of an impeller of the helium circulator, and its small cross-section is adjacent to the impeller of the helium circulator. When the helium circulator is normally operated, gas-flow flows from the large cross-section to the small cross-section of the conical pipe, that is, the gas-flow flows into the helium circulator from bottom to top in an axial direction. In order to make the baffle structure have both active and passive characteristics at the same time, a particular set of specific connection structure is specially designed: as illustrated in FIGS. 4 and 6, a key 14 is installed at the rotating shaft 4 connected with the crank connecting rod 3, an annular keyway 15 is cut out at the inner surface of the shaft sleeve 13 adjacent to the rotating shaft 4, such that the shaft sleeve 13 has an idle travel of 90-degree free rotation around the rotating shaft 4. The key 14 is positioned within the annular keyway 15, and the key 14 is in clearance fit with the annular keyway 15. Taking the axis of the rotating shaft 4 as a reference direction, the radial height of the annular keyway 15 is 0.1-0.3 mm higher than the radial height of the key 14, the circumferential angle α of the annular keyway 15 is between 90° and 100°, and the axial length of the annular keyway 15 is about 0.1-0.3 mm longer than the axial length of the key 14. The cross-sectional view taken along the line A-A of the baffle structure of the present embodiment when controlling the conical pipe to be fully opened is illustrated in FIG. 3. As illustrated, the pipe wall of the conical pipe has a circular opening for placing the tongue plate 2 and the crank connecting rod 3 in a fully open state. A circular branch pipe 16 is welded at the opening, whose axis is perpendicular to the axis of the conical pipe 1. An end of the circular branch pipe 16 is in a form of flange structure and connected with a pipe side cover plate 10 by bolts, which plays a role of sealing and preventing dust from entering inside the helium circulator. A fully open position annular sealing surface 11 is welded at an inner wall surface of the circular branch pipe 16, which is adjacent to the pipe wall of the conical pipe. When the baffle of the helium circulator is fully opened, the tongue plate 2 and the crank connecting rod 3 are parallel to the pipe wall of the conical pipe, and the tongue plate 2 is in contact with the fully open position annular sealing surface 11. The cross-sectional view taken along the line A-A of the baffle structure of the present embodiment when controlling the conical pipe to be fully closed is illustrated in FIG. 5. As illustrated, the large cross-section of the conical pipe is an inlet of the helium circulator, and a fully closed position annular sealing surface 12 is arranged at the inlet adjacent to the pipe wall of the conical pipe. When the baffle of the helium circulator is fully closed, the tongue plate 2 and the crank connecting rod 3 are perpendicular to the axis of the conical pipe, and the tongue plate 2 is in contact with the fully closed position annular sealing surface 12, which closes the inlet of the helium circulator. The working principle and operating sequence of the baffle structure in the embodiment are as follows: Generally, the baffle structure relies on helium pressure and gravity of the tongue plate 2 and the crank connecting rod 3 to realize the opening and closing of the conical pipe, that is, the passive characteristics of how the baffle structure mainly functions. When helium flows reversely, that is, the helium flows in the same direction as that of gravity, or when the helium pressure is smaller than the gravity of the tongue plate 2 and the crank connecting rod 3, the tongue plate 2 rotates counterclockwise around the rotating shaft 4 under the action of gravity (referring to the direction perpendicular to the page, the same below), until in contact with the fully closed position annular sealing surface 12, which closes the inlet of the conical pipe and, in turn, closes the baffle of the helium circulator. When helium flows normally, that is, the helium flows in the opposite direction as that of gravity, or when the helium pressure is larger than the gravity of the tongue plate 2 and the crank connecting rod 3, the tongue plate 2 rotates clockwise around the rotating shaft 4 under the action of pressure, until in contact with the fully open position annular sealing surface 11 and parallel to the pipe wall of the conical pipe, such that the inlet of the conical pipe is not blocked and the baffle of the helium circulator is opened. When the baffle of the helium circulator is opened and closed by passive characteristics, since the rotating shaft 4 and the annular keyway 15 are clearance fit, when the tongue plate 2 rotates, the rotating shaft 4 and the key 14 do not move but only rotate with the shaft sleeve 13. In this process, the key 14 is always located directly above the rotating shaft 4. When the inlet of the conical pipe is in a closed state, the clockwise side of the key 14 is adjacent to the clockwise side of the annular keyway 15; when the helium circulator is in an open state, the counterclockwise side of the key 14 is adjacent to the counterclockwise side of the annular keyway 15. When the passive characteristics fail, the active characteristics of the baffle structure have to function, which rely on the driving apparatus 8 to drive the tongue plate 2 to move so as to realize the opening and closing of the baffle of the helium circulator. In order to close the baffle of the helium circulator, the driving apparatus 8 drives the rotating shaft 4 to rotate counterclockwise. Since the counterclockwise side of the key 14 is adjacent to the counterclockwise side of the annular keyway 15, the key 14 drives the shaft sleeve 13 to rotate counterclockwise, thereby driving the tongue plate 2 to rotate counterclockwise, until the tongue plate 2 is in contact with the fully closed position annular sealing surface 12. Likewise, in order to open the baffle of the helium circulator, the driving apparatus 8 drives the rotating shaft 4 to rotate clockwise. The key 14 drives the shaft sleeve 13 to rotate clockwise, thereby driving the tongue plate 2 to rotate clockwise, until the tongue plate 2 is in contact with the fully open position annular sealing surface 11, so as to open the baffle of the helium circulator. After the baffle of the helium circulator is closed, the rotating shaft 4 is rotated clockwise by the driving apparatus 8, such that the key 14 rotates clockwise within the annular keyway 15, and the shaft sleeve 13 of the rotating shaft 4 does not move, until the key 14 is reset to be directly above the rotating shaft 4, and the clockwise side of the key 14 is adjacent to the clockwise side of the annular keyway 15, so as to prepare to open the baffle of the helium circulator next time. After the baffle of the helium circulator is opened, the rotating shaft 4 is rotated counterclockwise by the driving apparatus 8, such that the key 14 rotates counterclockwise within the annular keyway 15, and the shaft sleeve 13 does not move, until the key 14 returns back to the position directly above the rotating shaft 4, the counterclockwise side of the key 14 is adjacent to the counterclockwise side of the annular keyway 15, so as to prepare to close the baffle of the helium circulator next time. In summary, after the baffle of the helium circulator is closed or opened by active characteristics, the key 14 is reset by being rotated in the opposite direction of the movement of the tongue plate 2 by the driving apparatus 8, so as to prepare to open or close the baffle of the helium circulator next time. In the operating condition of small opening and the helium flows reversely, the helium pressure is consistent with the gravity direction of the tongue plate 2 and the crank connecting rod 3. At this time, the baffle structure cannot passively maintain the small opening state, the active characteristics of the baffle structure has to function, so as to drive the tongue plate 2 to move to an intermediate position by the driving apparatus 8 to realize the small opening state of the helium circulator. When the initial state of the inlet of the conical pipe is in a open state, as illustrated in FIGS. 3 and 4, the key 14 is rotated clockwise to a required angle by the driving apparatus 8, and the tongue plate 2 will rotate counterclockwise under the action of the helium pressure and the gravity of the tongue plate 2 and the crank connecting rod 3, until the clockwise side of the key 14 is adjacent to the clockwise side of the annular keyway 15, thereby maintaining the helium circulator in the position of the required opening. When the initial state of the helium circulator is in a closed state, as illustrated in FIGS. 5 and 6, the key 14 is rotated clockwise to a required angle by the driving apparatus 8. Since the clockwise side of the key 14 is adjacent to the clockwise side of the annular keyway 15, which drives the tongue plate 2 to rotate clockwise to a required angle, the helium circulator is thereby maintained in the position of the required opening. In summary, in order to achieve a small opening state of the helium circulator, the key 14 has to be turned clockwise to a desired angle by the driving apparatus 8, such that the clockwise side of the key 14 is adjacent to the clockwise side of the annular keyway 15. Under accident conditions, for example, foreign matters may enter between the shaft sleeve 13 and the rotating shaft 4, if they are stuck and have to be synchronized with each other, the passive characteristics may fail. At this time, active characteristics have to function, that is, the rotating shaft 4; the shaft sleeve 13 and the key 14 are driven to be rotated together by the driving apparatus 8, thereby opening or closing the inlet of the conical pipe. It is to be noted that when the baffle structure is used in non-return valves, check valves or other pipes to control the opening and closing of pipe, when the flow of fluid required to pass through the pipe is large, the tongue plate can be automatically rotated by the fluid pressure and tongue plate gravity, thereby realizing the opening and closing of the pipe; when the flow of fluid required to pass through the valve is small or the fluid flows in the same direction as the closing direction of the non-return valve but the non-return valve has be to maintained in the open state, the rotating of the tongue plate can be controlled by the driving apparatus, thereby realizing the opening and closing of the pipe. The tongue plate can realize control effects of opening and closing of the pipe under both active and passive functions, and can adapt to the requirements of multiple operating conditions of the pipe. The channel baffle structure provided by the present disclosure is simple in structure, operates safely and conveniently, possesses passive and active characteristics at the same time, and can satisfy the requirements of multiple operating conditions of HTR and other pipes. The above-mentioned description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc., within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure. Industrial Utility The present disclosure provides a channel baffle structure, which comprises a pipe, a swing check plate and a driving apparatus, wherein the swing check plate comprises a tongue plate, a crank connecting rod and a rotating shaft, one end of the crank connecting rod is connected with the tongue plate through a nut, and the other end is welded on a shaft sleeve of the rotating shaft, the pipe wall of the pipe is provided with a circular opening for placing the tongue plate in a fully open state and the crank connecting rod, a circular branch pipe is welded at the circular opening, the axis of the circular branch pipe is perpendicular to the axis of the pipe, an end of the circular branch pipe is in a form of flange structure and connected with a conical pipe side cover plate by bolts, the tongue plate, the crank connecting rod and a part of the rotating shaft of the swing check plate are arranged within the pipe, the driving apparatus is arranged outside the pipe, the swing check plate and the driving apparatus are connected through the rotating shaft, a bevel gear and a driving apparatus connecting shaft, one end of the rotating shaft is connected with the swing check plate, and the other end is connected with the bevel gear, one end of the driving apparatus connecting shaft is connected with the bevel gear, and the other end is connected with the driving apparatus, and the channel baffle structure also comprises a special structure used for connecting the driving apparatus and the swing check plate, specifically, a key is installed on the rotating shaft connected with the crank connecting rod, an annular keyway is correspondingly set within the shaft sleeve of the rotating shaft, such that the shaft sleeve has an idle travel of 90-degree free rotation around the rotating shaft, the key is positioned within the annular keyway. When the flow of fluid passes through the pipe is large, the tongue plate can be automatically rotated by fluid pressure and tongue plate gravity, thereby realizing the opening and closing of the pipe; when the flow of fluid passes through the pipe is small or the fluid flows in the same direction as the closing direction of the non-return valve but the non-return valve has be to maintained in the open state, the rotating of the tongue plate can be controlled by the driving apparatus, thereby realizing the opening and closing of the pipe. The tongue plate can realize control effects of the opening of the inlet and outlet of the channel connected with the pipe under both active and passive functions, and can adapt to the requirements of multiple operating conditions of the channel. The present disclosure has strong utility. |
|
summary | ||
abstract | An electron beam apparatus and method are presented for collecting side-view and plane-view SEM imagery. The electron beam apparatus includes an electron source, some intermediate lenses if needed, an objective lens and an in-lens sectional detector. The electron source will provide an electron beam. The intermediate lenses focus the electron beam further. The objective lens is a combination of an immersion magnetic lens and a retarding electrostatic lens focuses the electron beam onto the specimen surface. The in-lens detector will be divided into two or more sections to collect secondary electrons emanating from the specimen with different azimuth and polar angle so that side-view SEM imagery can be obtained. |
|
044977689 | claims | 1. A method for quantitatively evaluating total fissile and total fertile nuclide content in samples, which comprises the steps of: a. generating repetitively pulsed gamma radiation; b. directing said gamma radiation onto a partially transparent target which generates photoneutrons while allowing a substantial portion of said gamma radiation to pass through; c. thermalizing said photoneutrons such that their reaction probability with fissile isotopes is substantially enhanced; d. causing said gamma radiation and said thermalized photoneutrons to impinge upon a sample; e. measuring the flux of said thermalized photoneutrons in the vicinity of the sample during time intervals in between the termination of a particular gamma radiation pulse and the commencement of the following one; f. measuring the intensity of said gamma radiation in the vicinity of the sample; g. measuring prompt and delayed fast neutron emission from the sample resulting from photofission of fertile and fissile nuclides interacting with said impinging gamma radiation, and from fission of fissile nuclides capturing said thermalized photoneutrons during said time intervals; h. accumulating a plurality of said prompt and delayed fast neutron emission measurements, and a plurality of said thermalized neutron flux measurements until statistically significant measurements are obtained; and i. relating said accumulated emitted prompt and delayed fast neutron measurements normalized by said accumulated thermalized neutron flux measurements and said intensity of said gamma radiation to known gamma and neutron cross sections for the fissile and fertile nuclides contained in the sample to obtain the quantitative assay. a. means for generating repetitively pulsed gamma radiation; b. means for filtering said gamma radiation to remove photons of energy lower than about 2 MeV; c. means for generating photoneutrons from a portion of said filtered gamma radiation, the remainder of said filtered gamma radiation impinging on a sample; d. means for thermalizing said photoneutrons, whereby said photoneutrons impinge upon the sample; e. means for measuring said thermalized photoneutron flux in the vicinity of the sample during time intervals in between the termination of a particular gamma radiation pulse and the commencement of the following one; f. means for measuring the intensity of said gamma radiation in the vicinity of the sample; g. means for measuring prompt and delayed fast neutron emission from the sample resulting from the photofission of fertile and fissile nuclides interacting with a substantial portion of said remainder of said filtered gamma radiation, and from fission of fissile nuclides capturing said thermalized photoneutrons during said time intervals; and h. means for accumulating a plurality of said prompt and delayed fast neutron emission measurements, and a plurality of said thermalized neutron flux measurements until statistically significant measurements are obtained, whereby said accumulated emitted prompt and delayed fast neutron measurements normalized by said accumulated thermalized neutron flux measurements and said intensity of said gamma radiation can be related to known gamma radiation and neutron cross sections for the fissile and fertile nuclides contained in the sample to obtain the quantitative assay. a. an electron accelerator capable of providing greater than about 1 ma of electron beam current in short duration pulses at a repetition rate between 1 and 60 Hz, and at energies in excess of about 10 MeV; and b. a target attached to the output of said linear accelerator which generates bremsstrahlung radiation when bombarded with said short pulses of electrons, said bremsstrahlung radiation thereby containing photons with energy in excess of about 10 MeV. 2. The method as described in claim 1, wherein said pulsed gamma radiation has photon energy in excess of about 10 MeV. 3. The method as described in claim 2, wherein said pulsed gamma radiation is filtered to remove photons of lower energy than about 2 MeV before impinging on the sample. 4. The method as described in claim 3, wherein said photoneutron thermalization step is caused to be substantially completed within about 0.5 ms after said termination of a particular gamma radiation pulse. 5. The method as described in claim 4, wherein said prompt fast neutron measurement step is performed between about 0.5 and 2.5 ms after said termination of a particular gamma radiation pulse in order to determine the number of thermal-neutron-induced fissions which are measurable during this time period, and wherein said delayed fast neutron measurement step is performed between about 5.5 ms after said termination of a particular gamma radiation pulse and said commencement of the following gamma radiation pulse in order to determine the number of photofissions from both fertile and fissile nuclides present in the sample which process is measurable during this later time period. 6. The method as described in claim 5, wherein said gamma radiation generated neutron flux is adjusted such that said emitted delayed fast neutron flux is comprised principally of neutrons from said photofission of fertile nuclides while allowing sufficient prompt fast neutron emission from said thermal neutron fission process in the fissile nuclides to enable said statistically significant neutron measurements to be obtained in a practical accumulation time period. 7. The method as described in claim 6, wherein said pulsed gamma radiation is derived from an electron accelerator having a beam current greater than approximately 1 ma, a pulse duration less than about 4 .mu.s, and a pulse repetition rate within the range of substantially 1-60 Hz, the electrons generated therefrom producing said gamma radiation by a bremsstrahlung process upon striking a heavy metal target. 8. An apparatus for quantitatively evaluating total fissile and total fertile nuclide content in samples, which comprises in combination: 9. The apparatus as described in claim 8, wherein said photoneutron thermalization means includes the walls of a chamber, said chamber surrounding the sample. 10. The apparatus as described in claim 9, wherein said thermalized photoneutron flux measuring means includes at least one bare low pressure .sup.3 He proportional counter located inside said chamber in the vicinity of the sample. 11. The apparatus as described in claim 10, wherein said prompt and delayed fast neutron emission measurement means includes at least one high pressure .sup.3 He proportional counter surrounded by polyethylene which is in turn surrounded by cadmium foil, in order to block said thermalized photoneutrons, and located within said chamber in the vicinity of the sample. 12. The apparatus as described in claim 11, wherein said pulsed gamma radiation means further comprises: 13. The apparatus as described in claim 12, wherein said filtering means includes a polyethylene slab placed between said target and said chamber. 14. The apparatus as described in claim 13, wherein said chamber wall includes a thick polyethylene inner wall surrounded by a layer of cadmium foil which is further surrounded by a thick outer wall of borated polyethylene, said cadmium and borated polyethylene layers being intended to reduce the effects of stray neutrons generated by said electron accelerator away from the direction of said electron beam. 15. The apparatus as described in claim 14, wherein said target includes niobium foil. 16. The apparatus as described in claim 15, wherein said neutron generating means includes a beryllium sheet. 17. The apparatus as described in claim 16, wherein each of said bare low pressure .sup.3 He proportional counters further comprises an about 2.5 cm diameter metal tube, approximately 51 cm long containing about 1% .sup.3 He and 99% .sup.4 He at low pressure. 18. The apparatus as described in claim 17, wherein each of said high pressure .sup.3 He proportional counters further comprises an about 5 cm diameter metal tube, approximately 34 cm long containing about 3 atmospheres of .sup.3 He and surrounded by about 1.25 cm of polyethylene which is in turn surrounded by about 1.7 mm thick cadmium foil. 19. The apparatus as described in claim 18, wherein said polyethylene inner chamber wall is about 10 cm thick, said surrounding cadmium foil is approximately 0.6 mm thick, and said borated polyethylene outer chamber wall is about 10 cm thick. |
claims | 1. A method of adjusting the weight of a control rod for use in a nuclear reactor, the control rod having an upper, generally cruciform absorber section and a lower velocity limiter attached to said section and including a vane, a transition piece and fins interconnecting with one another comprising the steps of: providing first and second sets of fins with said second set of fins being heavier than said first set of fins; providing first and second transition pieces, with said second transition piece being heavier than said first transition piece; selecting one of said first and second fins and one of said first and second sets of transition pieces; and forming a velocity limiter for said control rod containing said vane and said selected ones of said fins and said transition pieces thereby selectively adjusting the weight of the control rod and enabling the formed velocity limiter to be connected to the cruciform section by the fins. 2. A method according to claim 1 including selecting said second heavier transition piece and adjusting the weight of said second heavier transition piece to further selectively adjust the weight of the control rod. claim 1 3. A method according to claim 2 wherein the weight of the second heavier transition piece is adjusted by removing material from said heavier transition piece. claim 2 4. A method according to claim 3 wherein said transition piece has a generally cylindrical configuration about an axis and a bore through said transition piece along said axis, the weight of the heavier transition piece being adjusted by removing material from within said bore. claim 3 5. A method according to claim 1 wherein the difference in weight of said sets of fins is provided solely by a change in size of the first and second sets of fins. claim 1 6. A method according to claim 1 including a socket and welding said selected one of said transition pieces and said socket to one another. claim 1 7. A method according to claim 1 including selecting said first transition piece and adjusting the weight of said first transition piece to selectively adjust the weight of the control rod. claim 1 8. A method according to claim 7 wherein the weight of the first transition piece is adjusted by adding material to said first transition piece. claim 7 9. A method according to claim 1 including providing first and second sets of fins of different configurations with the second set being formed of more material than the material forming the first set and selecting said second set of fins. claim 1 10. A method according to claim 1 wherein the first and second sets of fins are of different configurations with the second sets of fins being formed of more material than the material of the first set of fins and selecting the first set of fins to selectively adjust the weight of the control rod. claim 1 11. A method according to claim 1 including selecting said second set of fins and said heavier transition piece and adjusting the weight of said second heavier transition piece by removing material from said heavier transition piece. claim 1 12. A method according to claim 1 including selecting said first set of fins and said first transition piece and adjusting the weight of said first transition piece by adding material to said first transition piece. claim 1 13. A method according to claim 1 including selecting said second transition piece and said first set of fins and adjusting the weight of said second heavier transition piece by removing material from said second transition piece. claim 1 14. A method according to claim 1 including selecting said second set of fins and said first transition piece and adjusting the weight of said first transition piece by adding material thereto to further selectively adjust the weight of the control rod. claim 1 15. The method of adjusting the weight of a control rod for use in a nuclear reactor the control rod having an upper, generally cruciform absorber section and a lower velocity limiter attached to said section and including a vane, a transition piece and fins, interconnecting with one another comprising the steps of: providing a set of fins; providing first and second transition pieces, with said second transition piece being heavier than said first transition piece; selecting one of said first and second transition pieces; and forming a velocity limiter for said control rod containing said vane and said selected one of said transition pieces and said set of fins thereby selectively adjusting the weight of the control rod and enabling the formed velocity limiter to be connected to the cruciform section by the fins. 16. A met hod according to claim 15 including selecting said second heavier transition piece and adjusting the weight of the second heavier transition piece by removing material therefrom. claim 15 17. A method according to claim 15 including selecting said firs transition piece and adjusting the weight of said first transition piece by adding material thereto. claim 15 |
|
claims | 1. A stage device to be used in a vacuum, comprising:a gas supply unit configured to generate a gas;a base member having upper, lower, right, and left surfaces;a slider formed in a frame shape surrounding the base member and having surfaces facing the respective surfaces of the base member, and disposed to be movable; andan air bearing configured to float the slider by supplying the gas to a space between the base member and the slider,wherein the slider includes an air chamber provided on the surfaces facing the base member to accumulate air, an air pad to emit the air for floating the slider above the base member, and an air supply groove to supply the air to the air pad;wherein the base member includes a slider-moving air flow passage buried therein to supply the gas from an inlet port to an outlet port to guide the gas generated by the gas supply unit for supplying the gas to the air chamber of the slider;wherein the base member further includes an air flow passage buried therein to supply the air from the gas supply unit to the air supply groove formed on the slider;wherein the air supplied to the air supply groove is sent to the air pad through an air flow passage buried inside the slider; andwherein the air supply groove is provided only in the slider positioned above the upper surface of the base member. 2. The stage device according to claim 1, whereinthe base member includes a pressure receiving plate to divide the air chamber of the slider into a first air chamber and a second air chamber, andthe slider-moving air flow passage includes a first slider-moving air flow passage and a second slider-moving air flow passage to supply the air from the outlet port of the first slider-moving air flow passage to the first air chamber and to supply the air from the outlet port of the second slider-moving air flow passage to the second air chamber. 3. The stage device according to claim 2, whereinthe slider includes the air chambers located on both the upper and lower surfaces or both the right and left surfaces of the slider that are opposed to each other and facing the base member, andthe outlet ports of the slider-moving air flow passages formed inside the base member respectively supply the air to the air chambers on both the surfaces of the slider. 4. The stage device according to claim 3, further comprising:a first slider and a second slider configured to move simultaneously in a direction perpendicular to a moving direction of the slider, whereinone end of the base member is connected to the first slider and another end of the base member is connected to the second slider, andthe air supplied to any of the slider-moving air flow passage and the air flow passage for air pad inside the base member is supplied through the first slider and the second slider. 5. The stage device according to claim 4, whereinthe first slider is formed into a frame shape around a first fixed member and the second slider is formed into a frame shape around a second fixed member,a flow passage inside the first slider is connected to a flow passage formed inside the first fixed member through a first air supply groove formed on a surface of the first slider facing the first fixed member, anda flow passage inside the second slider is connected to a flow passage formed inside the second fixed member through a second air supply groove formed on a surface of the second slider facing the second fixed member. 6. The stage device according to claim 5, whereinthe flow passage formed inside the first fixed member is formed along a moving direction of the first slider, and is branched at a predetermined position into two in a direction perpendicular to the flow passage to pass through the first fixed member,the flow passage formed inside the second fixed member is formed along a moving direction of the second slider, and is branched at a predetermined position into two in a direction perpendicular to the flow passage to pass through the second fixed member,a third air supply groove is formed on the first slider to be symmetrical to the first air supply groove with respect to the first fixed member, anda fourth air supply groove is formed on the second slider to be symmetrical to the second air supply groove with respect to the second fixed member. 7. The stage device according to claim 6, further comprising:a first end plate located between the base member and the first slider; anda second end plate located between the base member and the second slider, whereinthe slider-moving air flow passage formed inside the base member includes a first-slider moving air flow passage and a second-slider-moving air flow passage,the air is supplied to the first-slider-moving air flow passage through the flow passage formed inside the first fixed member, a passage hole formed inside the first slider, and a passage hole formed in the first end plate, andthe air is supplied to the second-slider-moving air flow passage through the flow passage formed inside the second fixed member, a passage hole formed inside the second slider, and a passage hole formed in the second end plate. 8. The stage device according to claim 5, whereinan air flow passage for air pad formed inside the first slider is connected to an air flow passage for air pad formed inside the first fixed member through an air supply groove formed on the surface of the first slider facing the first fixed member. 9. The stage device according to claim 8, whereinthe air flow passage for air pad formed inside the first fixed member is formed along the moving direction of the first slider, and is branched at a predetermined position into two in a direction perpendicular to the air flow passage for air pad to pass through the first fixed member, andan air supply groove is formed on the first slider to be symmetrical to the air supply groove with respect to the first fixed member. 10. The stage device according to claim 9, further comprising:an end plate located between the base member and the first slider, whereinthe air flow passage for air pad in the base member is supplied with the air through the air flow passage for air pad formed inside first fixed member, a passage hole formed inside the first slider, and a passage hole formed in the first end plate. 11. A stage device to be used in a vacuum, comprising:a gas supply unit configured to generate a gas;a base member having upper, lower, right, and left surfaces;a slider formed in a frame shape surrounding the base member and having surfaces facing the respective surfaces of the base member, and disposed to be movable; andan air bearing configured to float the slider by supplying the gas to a space between the base member and the slider,wherein the slider includes an air chamber provided on the surfaces facing the base member to accumulate air, an air pad to emit the air for floating the slider above the base member,wherein the base member includes a slider-moving air flow passage buried therein to supply the gas from an inlet port to an outlet port to guide the gas generated by the gas supply unit for supplying the gas to the air chamber of the slider; andwherein the base member further includes an air supply groove formed on a surface of the member facing the slider. |
|
abstract | A contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris from the radiation source. The contamination barrier includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. |
|
claims | 1. A system for facilitating a uniform loading condition for a steam dryer supported by a plurality of support members supporting a steam dryer in a nuclear reactor, comprising:a plurality of devices, each including,an actuator shaped to fit between a corresponding support member and a lower bearing surface of a portion of the dryer and configured to lift the corresponding dryer portion lower bearing surface relative to the support member,a measurement unit corresponding to the corresponding support member configured to measure a displacement value between the corresponding support member and the lower bearing surface of the corresponding dryer portion,a device housing supporting the actuator and measurement unit, anda pair of clamp arms connected to and extending downward from the device housing to a clamping cylinder, the clamping arms, the device housing, and the clamping cylinder defining an opening to receive the corresponding support member through the opening and to fixedly secure the device to the support member in relation to the corresponding dryer portion lower bearing surface. 2. The system of claim 1, wherein each device further includes a contact plate connected to the actuator, the contact plate configured to bear against the corresponding dryer portion lower bearing surface when connected to the actuator. 3. The system of claim 2, wherein the device housing further supports the contact plate, the device housing is configured to bear against an upper planar surface of the support member that extends into the opening, the contact plate is configured to bear against the corresponding dryer portion lower bearing surface, and the clamping cylinder is configured to bear against an underside of a lower planar surface of the support member that extends into the opening. 4. The system of claim 1, wherein the actuator is a hydraulic cylinder and the measurement unit is a transducer. 5. The system of claim 1, wherein the dryer portion lower bearing surfaces are dryer support ring bearing surfaces of the steam dryer, the dryer support ring bearing surfaces removable from the steam dryer based on the measured displacement values. 6. The system of claim 5, wherein the measured displacement value is a vertical distance between a given support member and the corresponding support ring lower bearing surface. 7. The system of claim 1, wherein the dryer portions are bearing surfaces of the dryer support ring attached to the steam dryer, and the plurality of support members are steam dryer support brackets spaced circumferentially around the steam dryer to connect a corresponding support ring to an upper shell of a reactor pressure vessel (RPV) enclosing the steam dryer. 8. The system of claim 7, wherein four of the support brackets are configured to attach to a corresponding support ring bearing area. 9. The system of claim 8, wherein the four brackets are arranged as a first pair of brackets configured in facing relation from each other and a second pair of brackets in facing relation to each other such that each of the brackets are in substantially equal spaced relation from one another at a corresponding support ring location. 10. The system of claim 7, wherein six support brackets are attached to a corresponding support ring location. 11. In a reactor pressure vessel (RPV) of a nuclear reactor, a lifting and measuring assembly connected to a plurality of support brackets supporting a steam dryer within the RPV, the assembly configured to fit between the support brackets and the dryer and configured to lift the dryer relative to the support brackets based on measuring displacement values between the support brackets and corresponding support ring bearing surfaces of the steam dryer, the assembly including a plurality of devices, each including,an actuator shaped to fit between a corresponding support member and a lower bearing surface of a portion of the dryer,a measurement unit corresponding to the corresponding support member,a device housing supporting the actuator and measurement unit, anda pair of clamp arms connected to and extending downward from the device housing to a clamping cylinder, the device housing, the pair of clamp arms, and the clamping cylinder defining an opening between the clamping arms to receive the corresponding support member through the opening so as to fixedly secure the device to the support member in relation to the corresponding dryer portion lower bearing surface. 12. The assembly of claim 11, wherein the assembly is configured so that a portion of a lower bearing surface of a support ring bearing on a corresponding support bracket is removable based on the measured displacement values. 13. The assembly of claim 12, wherein the assembly is provided at each support ring-support bracket interface in the RPV, and the measured displacement value is a vertical distance between a given support bracket and its corresponding support ring lower bearing surface. 14. The assembly of claim 11, wherein N support brackets support the steam dryer in the RPV, N ≧4. |
|
044735286 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention Nuclear power plants, because of the potential accidental release of radioactive materials, are required by practice to be designed in such a manner that the health and safety of the public is assured even in the event of the most adverse accident that can be postulated. In nuclear power plants utilizing light water as a coolant, the most adverse accident possible is considered to be a double-ended break of the largest pipe in the reactor coolant system and such an accident is commonly termed the Loss Of Coolant Accident, hereinafter sometimes referred to as LOCA. For accident protection, plants utilizing light water as the coolant employ containment systems designed to physically contain water, steam and any entrained fission products that may escape from the reactor coolant system. The containment system is normally considered to encompass all structures, systems and devices that provide ultimate reliability and complete protection for any accident that may occur. Engineering safety systems are specifically designed to mitigate the consequences of an accident, and the design goal of a containment system is that no radioactive material will escape from the nuclear power plant in the event of an accident. The passive containment system disclosed herein provides this desired level of protection for a loss of coolant accident and for other types of accident that are considered as a basis of design, and the concepts of the invention are considered to be effective for nuclear power plants employing either pressurized water reactors or boiling water reactors. 2. The Prior Art In order to provide containment for light water cooled nuclear power plants prior art techniques have basically utilized either full-pressure "dry-type" containment or pressure suppression containment. In a full-pressure containment the reactor building, completely enclosing the reactor coolant system, is capable of withstanding the pressure and temperature rise expected to occur in the event of a LOCA. The builidng is usually constructed either of steel or steel-lined reinforced concrete or prestressed concrete. Full-pressure containment systems may include double leakage control barriers and subatmospheric pressure operation. For the double leakage-control barrier any leakage into the control annulus is either pumped back into the primary containment, or the leakage is treated before being exhausted to the outside atmosphere. For subatmospheric operation the containment is normally maintained at partial vacuum, and following the LOCA, the pressure is reduced back to less than the outside atmosphere utilizing active engineered safety systems to terminate any potential release of radioactivity to the environment. The pressure-suppression containment consists of a drywell that houses the reactor coolant system, a pressure-suppression chamber containing a pool of water, and a vent system connecting the drywell to the pool of water. This containment structure is constructed of steel enclosed by reinforced concrete, or is steel-lined with reinforced concrete. The pressure-suppression containment is housed within a reactor building. In the event of a LOCA, the reactor coolant partially flashes to steam within the drywell, and the air, steam and liquid coolant flow through the connecting vents into the pool of water in the suppression chamber. The steam is condensed by the water and decreases the potential pressure rise in the containment. The air rises into the free space above the pool of water in the suppression chamber. Refinements in pressure-suppression containment utilizing water includes the inerting of the containment atmosphere. Inerting is aimed at preventing the burning of hydrogen produced from metal-water reaction of overheated nuclear fuel. A different type of pressure-suppression containment utilizes an ice-condenser. The ice is maintained in a refrigerated compartment surrounding the reactor coolant system. The ice-condenser containment is divided into an upper chamber and a lower chamber with the reactor coolant system in the latter. In the event of a LOCA a pressure rise of the lower chamber causes access panels located at the bottom of the ice-storage compartment to open. This provides a flow path for air and steam through the ice bed. The steam is condensed by the ice and decreases the potential pressure rise in the containment. The air passes into the upper chamber through top access panels forced open by the flow of air. Full-pressure containment and pressure-suppression containment are passive structures that require support systems for containment of the accident. Active systems such as residual heat removal systems and containment spray systems are used to dissipate heat to the environs. This prevents the containment design pressure and temperature from being exceeded and in the process, the containment pressure is reduced to limit the leakage of fission products. Active filtration systems are required in conjunction with the spray systems to reduce fission product concentration in the containment atmosphere. This also limits the amount of fission products that can leak out of the containment to the environs. Hydrogen recombiners are also being utilized to protect the containment from developing explosive concentrations of hydrogen. To be effective, both the full-pressure containment and the pressure-suppression require additional engineered safety systems that provide emergency cooling of the nuclear fuel. Pressurized water reactors require passive accummulator systems in addition to active high and low pressure injection systems to maintain an adequate amount of liquid coolant at the nuclear fuel. The residual heat removal systems used for containment pressure reduction also reject decay heat to the environs. Pressure suppression with gravity flooding has also been proposed as an engineering safety system for a LOCA. Active engineered safety systems are inherently required to function effectively in order to maintain the integrity of the containment system in the LOCA. Active systems require high integrity instrumentation and control equipment, rotating machinery, electric power sources and power distribution equipment. These systems need to function properly as part of a larger system under adverse containment environment conditions of high-pressure, high-temperature, high-humidity, high-radioactivity, and eroded thermal insulation. Malfunctioning of any active engineered safety system imposes even more adverse conditions on the operable system. For instance, an inadequate sourch of electric power may result in the malfunctioning of the emergency core cooling system for the nuclear fuel. Overheating of the fuel can result in melting of the fuel cladding with metal-water reactions occuring. The fuel core may slump and portions could collapse and overheat the bottom of the reactor vessel. Hydrogen is released from metal-water reactions and is subject to burning. The added energy from the metal-water reactions and from the burning of hydrogen imposes even more severe requirements on containment structure. Overheating of the fuel and melting of the cladding results in a gross release of fission products that are available for leakage from the containment system. This example points to the critical nature of active engineering safety systems that are an essential part of the containment system of the prior art. The prior art has proposed a variety of solutions to the containment of a nuclear power plant in the event of a LOCA, and in my U.S. Pat. Nos. 3,984,282 and 4,050,983, I have proposed passive containment systems for confinement of the coolant in the event of a LOCA, and for cooling the reactor assembly in the event of such an accident. Further, in my U.S. Pat. No. 3,865,688 I have disclosed a passive confinement system utilizing many of the concepts herein set forth, and this invention constitutes an improvement over that specifically set forth in U.S. Pat. No. 3,865,688. SUMMARY OF THE INVENTION The invention relates to a nuclear reactor containment arrangement, and more particularly, to an entirely passive containment system which encloses a reactor system using a high-pressure, high-temperature coolant and/or moderator such as light or heavy water. In this invention, the passive containment system is used to safely contain even the most adverse reactor accident wherein a sudden rupture of the reactor piping occurs resulting in the loss of coolant. The passive containment system herein provides equal protection for nuclear reactor system of the pressurized water or boiling water types. The containment system of the invention as used for a pressurized water reactor consists of interconnected cells; each cell housing a major component of the nuclear reactor system; i.e., reactor vessel, steam generators, pumps, pressurizer, regenerative heat exchanger, and piping. Cells are also provided for the engineered safety system components. Water-filled deluge tanks, quench tanks and reactor vessel refill tanks are located entirely within containment cells at an elevation above the reactor coolant system piping. Within the containment cells a primary container formed from interconnected steel shells encloses the entire reactor coolant system. The primary container is encased by reinforced or prestressed concrete. The water used within the reactor vessel refill tanks, within the deluge tanks, and within the quench tanks, is specially treated for accident containment purposes. The water is degassed and contains chemicals in solution that serve as a poision to neutrons, inhibitors of corrosion, oxygen "getters", and radio-nuclide getters. The water within the tanks is retained in a chilled condition by suitable refrigeration means such as a steam-jet refrigeration system or other refrigeration system. The passive containment system is housed within a reactor building. The arrangement of the cell structures permits the relocation of spent fuel storage pools and a refueling cavity and other equipment enclosures within the reactor building. In a typical response of the passive containment system hereof to a LOCA, decompression of the reactor coolant through the pipe break produces steam within the primary container which is normally maintained at a high vacuum. The steam pressurizes the containment and the steam overpressure is vented into the deluge and quench tanks. During reactor coolant blowdown, the hydrostatic pressure within the reactor vessel refill tanks causes check valves in the high-pressure injection pipe to lift, and treated water is injected into the reactor coolant system. The decompression of the refill tanks causes check valves in the steamlines between the steam generator secondaries and the refill tanks to lift. This initiates steam flow from the steam generators through jet injectors and steam flow through the injectors entrains treated water from the refill tanks. The steam and water are intimately mixed on passage through the diffuser sections of the injectors to provide a homogeneous solution of treated water that quenches the fuel elements, refills the reactor vessel and overflows through the pipe break into the containment. The elevated deluge and quench tanks include steam vent conduits communicating with the cooling liquid therein and with the containment. Thus, upon the containment being pressurized with steam due to the LOCA the steam within the containment will enter the deluge and quench tanks through their vent conduits and the chilled water in these tanks absorbs the heat energy within the steam. When coolant blowdown is arrested a gravity flow of the borated water from the deluge tanks continues emergency core cooling with flow through the pipe break that resulted in the loss of coolant. All stored energy within the reactor system is absorbed by the refill and deluge water flow, and sufficient heat capacity is provided in the chilled, stored water within the refill, deluge and quench tanks to reduce temperatures to low levels. The containment atmosphere is restored to the normal high-vacuum condition by the vapor carryover. The heat-sink capacity of the water in the quench tanks provides a vented containment for the term of the accident, and the borated water in the deluge tanks will provide four hours of passive decay heat removal. In the disclosed embodiment a four loop system is disclosed in conjunction with a single reactor vessel. Accordingly, four steam generators, four refill tanks, four deluge tanks, and four quench tanks are used with the preferred embodiment. A single pressurizer is employed to maintain the pressure within the reactor coolant system. Each steam generator includes a primary system receiving heat from the reactor coolant system and the steam generators transfer this heat to their secondary system which produces steam for utilization purposes, such as powering a turbine. In addition to utilizing the deluge tanks and quench tanks for steam venting and absorption purposes with respect to steam within the containment, these tanks also include steam absorbing means connected to the associated steam generator secondary system through electrically operated valves. Thus, thermal energy can be selectively absorbed within the deluge and quench tanks from the steam generator secondary system by operation of selective valves, and with certain types of malfunctions or leakage, this type of reactor cooldown is utilized. In such instance the transfer of heat from the generator secondary systems likewise cools the reactor coolant through the primary system and the heat absorption capacity of the deluge and quench tanks is sufficient to adequately cool the system for control purposes. In a major LOCA it is possible to use the thermal energy within one steam generator secondary system for the introduction of coolant into the reactor coolant system from refill tank injectors, while the energy within the generator secondary systems of other generators is being dissipated through direct injection of secondary steam into the associated deluge and quench tanks, thereby providing a simultaneous replenishing of reactor coolant and dissipation of the energy within the power plant. The quench tanks, in addition to absorbing vented steam, and steam injected therein from a secondary system, also include a steam-powered injector supplied with steam from the associated generator secondary system having a discharge communicating through a check valve with the associated generator secondary feedwater system. Thus, operation of the quench tank injector introduces auxiliary feedwater into the associated generator secondary system, and this operation is employed in the event of feedwater malfunctioning assuring a supply of feedwater in the event the accident restricts or eliminates the normal feedwater source. OBJECTS OF THE INVENTION It is a general object of the invention to provide a new and improved containment method and apparatus for any energy, toxic or radioactive materials released from a process system accommodated therein. It is a more particular object of the invention to provide a passive containment system process and apparatus for a nuclear reactor power plant system. Another object of the invention is to provide functional improvements in the complete containment of a nuclear reactor system through passive means actuated, controlled, powered and maintained by the forces of nature that are designed to be intrinsic to the containment system. A further object of the invention is to provide a reactor containment system which is less expensive to construct than similar prior systems in that the primary containment free volume is effectively reduced and less expensive materials are required. Another object of the invention is to provide a passive containment system that utilizes the forces of physics to provide the ultimate level of reliability in the containment of nuclear power plants. An additional object of the invention is to provide passive emergency core cooling utilizing passive reactor vessel refill decay heat transfer utilizing the energy within the reactor power plant system. Another object of the invention is to provide a nuclear power plant containment system which permits plant recovery from all design basis accident including the loss of coolant accident. An additional object of the invention is to provide a nuclear power plant heat removal system utilizing a plurality of coolant reservoirs wherein the coolant within the reservoirs may be selectively used for heat absorption by the venting of steam therein, and selected reservoirs permit coolant to be supplied directly to a reactor coolant system, in all events, the cooling capacity within the reservoirs being sufficient to achieve reactor cooldown. Yet another object of the invention is to provide a a nuclear reactor power plant system employing a plurality of steam generators and coolant reservoirs wherein energy within the steam generators may be selectively dissipated within the reservoirs, and energy within the generators may also be employed to introduce coolant directly into the reactor coolant system, and feedwater in the secondary system. |
description | The present invention relates, in general, to the vitrification of radioactive waste products and, more particularly, to a glass composition that is suitable for mixed waste products, which include flammable waste products, such as gloves, working clothes, plastic waste, and rubber, and low-level radioactive waste products, and which are discharged from a nuclear power plant, and a method of vitrifying the mixed waste products using the same. Flammable waste products, such as gloves, working clothes, plastic waste, and rubber, low-level radioactive waste products, and mixed waste products thereof, which are radioactive waste products discharged from a nuclear power plant, are treated by being encased in cement or contained in a waste drum. There is demand for a technology of manufacturing a solidified body, from which radioactive materials do not leak, or leak into underground water at a much slower speed compared to a cement-solidified body, when the solidified body comes into contact with underground water, and another technology of significantly reducing the number of radioactive waste drums so that a waste disposal site may be used over a long period of time, in consideration of the fact that it is becoming difficult to build waste disposal sites. Recently, various countries have actively made research into technologies for vitrifying radioactive waste products using glass media to meet this demand. Meanwhile, examples of the related art regarding a process of vitrifying radioactive waste products include Korean Patent No. 10-0768093 (a method of vitrifying middle- and low-level radioactive waste products using iron/phosphate glass) and Korean Patent No. 10-0432450 (a system for treating middle- and low-level radioactive waste products). However, since the middle- and low-level radioactive waste products are different from high-level waste products in terms of the type, production amount, and chemical composition thereof, the technology for vitrifying high-level waste products is not capable of being applied to middle- and low-level radioactive waste products without any modification, and, regardless, a glass composition for vitrifying mixed waste products, which include flammable waste products, such as gloves, working clothes, plastic waste, and rubber, and low-level radioactive waste products, is not disclosed in the patents. Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a glass composition which is most suitable for vitrifying mixed waste products. Another object of the present invention is to provide a method of vitrifying mixed waste products using a glass composition for use in the mixed waste products. In order to accomplish the above objects, the present invention provides a glass composition for vitrifying a mixed waste product, the glass composition including SiO2, Al2O3, B2O3, CaO, K2O, Li2O, MgO, Na2O, TiO2, and VO2. The glass composition may further include As2O5, CeO2, CoO, Fe2O3, MnO2, P2O5, and ZrO2. The glass composition includes 40 to 50 wt % of SiO2, 11 to 16 wt % of Al2O3, 8 to 15 wt % of B2O3, 3 to 6 wt % of CaO, 1 to 3 wt % of K2O, 1 to 3 wt % of Li2O, 1 to 3 wt % of MgO, 15 to 19 wt % of Na2O, 0.5 to 3 wt % of TiO2, and 0.5 to 3 wt % of VO2. When the glass composition further includes As2O5, CeO2, CoO, Fe2O3, MnO2, P2O5, and ZrO2, the glass composition includes 40 to 50 wt % of SiO2, 11 to 16 wt % of Al2O3, 8 to 15 wt % of B2O3, 3 to 6 wt % of CaO, 1 to 3 wt % of K2O, 1 to 3 wt % of Li2O, 1 to 3 wt % of MgO, 15 to 19 wt % of Na2O, 0.5 to 3 wt % of TiO2, 0.5 to 3 wt % of VO2, 0.5 to 3 wt % of As2O5, 0.5 to 3 wt % of CeO2, 0.1 to 2 wt % of CoO, 1 to 3 wt % of Fe2O3, 0.01 to 0.1 wt % of MnO2, 0.1 to 1.0 wt % of P2O5, and 0.5 to 3 wt % of ZrO2. In order to accomplish the above objects, the present invention also provides a method of vitrifying a mixed waste product, the method including adding the mixed waste product and a glass composition including SiO2, Al2O3, B2O3, CaO, K2O, Li2O, MgO, Na2O, TiO2, and VO2, together to a melting furnace. The glass composition may further include As2O5, CeO2, CoO, Fe2O3, MnO2, P2O5, and ZrO2. The glass composition includes 40 to 50 wt % of SiO2, 11 to 16 wt % of Al2O3, 8 to 15 wt % of B2O3, 3 to 6 wt % of CaO, 1 to 3 wt % of K2O, 1 to 3 wt % of Li2O, 1 to 3 wt % of MgO, 15 to 19 wt % of Na2O, 0.5 to 3 wt % of TiO2, and 0.5 to 3 wt % of VO2. When the glass composition further includes As2O5, CeO2, CoO, Fe2O3, MnO2, P2O5, and ZrO2, the glass composition includes 40 to 50 wt % of SiO2, 11 to 16 wt % of Al2O3, 8 to 15 wt % of B2O3, 3 to 6 wt % of CaO, 1 to 3 wt % of K2O, 1 to 3 wt % of Li2O, 1 to 3 wt % of MgO, 15 to 19 wt % of Na2O, 0.5 to 3 wt % of TiO2, 0.5 to 3 wt % of VO2, 0.5 to 3 wt % of As2O5, 0.5 to 3 wt % of CeO2, 0.1 to 2 wt % of CoO, 1 to 3 wt % of Fe2O3, 0.01 to 0.1 wt % of MnO2, 0.1 to 1.0 wt % of P2O5, and 0.5 to 3 wt % of ZrO2. According to the present invention, a glass composition that is suitable for mixed waste products, which include flammable waste products, such as gloves, working clothes, plastic waste, and rubber, and low-level radioactive waste products, and a method of vitrifying the mixed waste products using the same are provided to significantly reduce the volume of radioactive waste products and to vitrify the mixed waste products using the glass composition, which is suitable for vitrifying the mixed waste products, thereby maximally delaying or completely preventing the leakage of radioactive materials from a glass solidified body. A better understanding of the present invention may be obtained through the following Examples. It will be obvious to those skilled in the art that the Examples are set forth to illustrate the present invention but are not to be construed to limit the scope of the present invention. In order to vitrify target waste products for vitrification, discharged from the Uljin nuclear power plant, the type and the concentration of inorganic substances contained in each waste product were evaluated, and a suitable additive was added to the inorganic substances that were generated in the waste products to thus select glass compositions that were excellent in terms of process variables of a melting furnace, the quality of a molten solidified body, and the volume reduction effect. As shown in the flowchart of glass composition selection of FIG. 1, a process of selecting the candidate glass for each target waste product for vitrification included steps of selection of the additive (base glass frit), selection of the candidate glass, laboratory evaluation, and a pilot test. The inorganic substances in the target waste products for vitrification should be mixed with the additive to form the glass composition meeting the vitrification process and the quality of the molten solidified body. First, the suitable additive, that is, the base glass frit, was selected based on the analyzed concentration of the inorganic substance in the waste product. The properties of the candidate glass depend on the amount of the inorganic substance that is added to constitutional components of the base glass frit (the waste loading amount). As for main items which are evaluated by executing computer code, it is evaluated whether viscosity and electric conductivity values, which are important in views of the vitrification process, are in the range of 10 to 100 poise and 0.1 to 1.0 S/cm at an operating temperature of 1,150° C., and it is evaluated whether the 7-day PCT leaching rate, which is a factor for evaluating chemical robustness in view of the quality of the molten solidified body, is 2 g/m2 or less with respect to the elements B, Na, Li, and Si. When the aforementioned two aspects are satisfied, the volume reduction effects of the waste products are very different from each other, but the volume reduction ratio of each waste product, which is evaluated to be at a suitable level, is calculated in order to select the candidate glass. Whether the candidate glass that was selected using the computer code operation satisfied the properties required in views of the vitrification process and the quality of the molten solidified body was evaluated during the laboratory operation, and was finally verified using the pilot test. In order to vitrify the target waste products for vitrification, AG8W1 was selected as the candidate glass of the mixed waste product, which included the flammable waste product and the low-level radioactive waste product, (hereinafter, referred to as ‘W1 waste product’), DG-2 was selected as the candidate glass of the flammable waste product (hereinafter, referred to as ‘dry active waste’), and SG was selected as the waste resin using GlassForm 1.1 computation code. The components and main properties are described in Table 1. TABLE 1Properties of base glass frit and candidate glass (valuesat 1,150° C.)Dry active wasteW1 waste productBase/candidateWaste resinBase/candidateglassBase/candidateglassDG-glassAG8AG8W12BaseDG-2SG-BSGAl2O314.4212.308.007.077.57.36As2O51.040.62————B2O38.579.9715.0011.2915.0010.59BaO———0.04——CaO—4.82—9.77—18.1CeO21.040.62————CoO0.520.31—0.01——Cr2O3——————Cs2O——————CuO———0.01—2.86Fe2O3—1.78—0.35—2.86K2O—1.632.004.47—7.3Li2O2.071.247.005.257.505.13MgO—2.120.504.63—2.22MnO2—0.05—0.17—0.32Na2O24.1717.5711.0010.067.504.5NiO———0.11——P2O5—0.40—0.82——PbO———0.02——SiO244.5243.1455.0041.2562.5037.5SrO———0.14——TiO2—1.24—3.09——VO22.101.26—0.08——ZnO———0.22—1.26ZrO21.550.931.501.13——Loading040025040amount ofinorganicsubstance(wt %)Density2.592.672.402.652.622.65(g/cm3)Viscosity62673310864(poise)+Electric0.620.310.570.460.350.40conductivity(S/cm)+7-day PCT—Si, B,—Si, B,—Si, B,(g/m2)Li, Na <2Li, Na <2Li, Na <2 The viscosity, electric conductivity, phase homogeneity, liquidus temperature, transition temperature, softening point, thermal expansion coefficient, and compressive strength of the AG8W1 candidate glass of the W1 waste product, the DG-2 candidate glass of the dry active waste, and the SG candidate glass of the waste resin, which were selected in Example 2, were tested as follows. (1) Viscosity and Electric Conductivity From FIGS. 2 and 3, it was confirmed that the viscosity of the DG-2, AG8W1, and SG candidate glass was in the required range of 10 to 100 poise at the operating temperature of 1,150° C. when measured. Further, from FIGS. 4 and 5, showing the result of measurement of electric conductivity, it could be seen that all of the DG-2, AG8W1, and SG candidate glass satisfied the required value of electric conductivity at 1000° C. or higher. (2) Phase Hhomogeneity and Liquidus Temperature When the glass is melted over a long period of time, it is very important to maintain the glass at the liquidus temperature or higher in order to prevent crystals from being formed. When the homogeneous molten glass is formed at the melting temperature, normal production of the glass and long-term operation are feasible. On the other hand, when a crystal phase is formed, precipitation may occur, eventually clogging a glass outlet and possibly affecting the chemical robustness of the glass, that is, leachability. It is empirically known that the difference between the temperature of a melting state and the liquidus temperature of glass is preferably more than 100° C. The three kinds of candidate glass (AG8W1, DG-2, and SG) were subjected to a heat-treatment test at 950° C. for 20 hr, and analyzed using SEM/EDS. As a result, crystals were not formed at a meniscus and not at the boundary of a crucible. The minimum temperature, at which the crystals were not formed, determined from the result of the heat-treatment test for 20 hr, was defined as the liquidus temperature of the glass. From the result of the test, the liquidus temperature of the candidate glass was estimated to be 950° C. or less. Therefore, it could be seen that there was no possibility of the molten glass being converted into crystals during the long-term vitrification process. (3) Transition Temperature and Softening Point Glass has a transition region, making it unlike crystals in physical and chemical aspects. In other words, it can be seen that, with respect to a change in volume as a function of temperature when the molten liquid is supercooled, the volume of a crystal is rapidly changed at the melting temperature, but the volume of the molten glass body is slowly changed, reaching an equilibrium state when the molten glass body is supercooled. The volume of glass changes depending on the temperature. The temperature at which the slope is changed is called a glass deformation temperature or a glass transition temperature Tg, and refers to a thermodynamically meta-stable equilibrium state. The transition temperatures of the AG8W1 and SG candidate glass were evaluated to be about 498° C. and 466.7 to 498.1° C., respectively, when measured using analysis equipment. The softening points of the AG8W1 and SG candidate glass were measured to be 551° C. and 547° C., respectively. (4) Thermal Expansion Coefficient All existing constitutional elements of materials are vibrated by heat energy. Heat energy increases as the temperature is increased. Accordingly, a vibration width is increased, to thus increase the distance between two atoms connected by bonding force. In other words, expansion occurs as the temperature is increased. Vibration attributable to heat energy is limited by strong bonding in a solid state, but is not significantly limited in a liquid state, and accordingly, the expansion coefficient of liquid is large. The respective thermal expansion coefficients of the AG8W1 and SG candidate glass were 107×10−7 K−1 and 98×10−7 K−1 when measured. It can be seen that these values are similar to the thermal expansion coefficient of typical soda lime glass. (5) Compressive Strength The compressive strength of glass in use has been considered as an important property, and an effort has been made for a long time into investigating the cause of breakage to thus produce stronger glass. A breaking process is directly connected to a fatigue phenomenon, and influences attributable to hysteresis and the characteristic condition thereof need to be well understood. Surface bonding is a very important factor and needs to be sufficiently considered in order to increase strength. The strength of glass corresponds to a value until a breakage line is formed through an entire piece of glass. The AG8W1 and SG candidate glass was cooled from the transition temperature at a rate of about 2.7° C. per min to measure compressive strength, and the measured values were 2,146 psi and 7,985 psi. It is required that compressive strength be 500 psi or more based on US NRC requirements for cement, which is used to treat radioactive waste products. The aforementioned requirement may be applied to the molten solidified body, and accordingly, the compressive strength of the candidate glass may be evaluated as favorable. The molten solidified body, which is formed during the vitrification process, must be chemically stable in intermediate storage and final waste disposal environments. The most main reason why glass is selected as a treatment medium of radioactive waste products among many other materials is that glass prevents radioactive materials from leaking into the environment and is capable of storing the radioactive materials for a long period of time due to the excellent chemical robustness thereof. Accordingly, the selected candidate glass compositions were tested and analyzed using the internationally certified leaching test methods in order to compare and evaluate the chemical stabilities of the molten solidified bodies. In order to perform a robustness comparison with the glass selected by the Nuclear Environment Technology Institute, the high-level R7T7 candidate glass of France and the SRL-EA benchmark glass of the USA were tested together. (1) TCLP (Toxicity Characteristic Leaching Procedure) The US EPA TCLP (Toxicity Characteristic Leaching Procedure) test is the most important index indicating the stability of the solidified body to various kinds of accidents after the final disposal of the glass solidified body. The risk that the glass solidified body may face in the final waste disposal site is leakage of radioactivity and harmful materials into water when the solidified body comes into contact with water, and the TCLP test may be considered as a simulation of this situation. The molten solidified bodies (AG8W1, DG-2, and SG), which are obtained from research on selection of the glass composition, particularly contain vanadium (V), which is a strong oxidant, and chromium (Cr) and nickel (Ni), which are harmful materials, in small amounts in order to prevent the precipitation of reducing materials during the vitrification process. Accordingly, the TCLP test was performed using the three candidate glass compositions. In the TCLP test, the degree of elution of elements, which were regulated based on the Resources Conservation and Recovery Act (RCRA) (a total of 14 elements: Ag, As, Ba, Be, Cd, Cr, Hg, Ni, Pb, Sb, Se, Th, V, and Zn), into a leaching solution was analyzed. The concentrations of all target elements were analyzed to be the same as or lower than the detection limit of the analyzer, thereby satisfying all US EPA standards. (2) ANSI/ANS 16.1 (American National Standards Institute/American Nuclear Society 16.1) The ANSI/ANS 16.1 (American National Standards Institute/American Nuclear Society 16.1) leaching test, which was accomplished in a short period of time (three months), was performed as a leaching test for evaluating the chemical durability of the glass. The concentrations of main elements and simulated radionuclides, such as Co and Cs, which were leached from the molten solidified bodies, were analyzed to calculate effective diffusivity, and the average value of ten leaching indexes of each radionuclide, which were determined in ten leaching sections, was evaluated as the leachability index (Li) of the radionuclide. As seen in FIG. 6, showing the result of the ANSI/ANS 16.1 leaching test, Co and Cs did not leak into a leachate during a test period of three months, and the leaching indexes of all elements were 6 or more, which was the US NRC requirement. After pollutants were rapidly separated from the surface of the sample in an early stage of the test, initially observed leaching from the waste product solidified body was considered to be mainly attributable to diffusion. The leaching index of the radionuclides depends on the magnitude of the mobility of chemical elements in the single solidified substance. Therefore, the leaching indexes of all elements of the candidate glass satisfied the US NRC requirement, namely 6.0 or more, and cobalt, which was contained in the glass, and cesium, which was added in a small amount to the AG8W1 glass in order to perform the present test, were not detected. (3) PCT (Product Consistency Test) The US DOE PCT (product consistency test) as a robustness test for measuring the stability, the homogeneity, and the reproducible component ratio of a solidified body is a test for comparing leaching behavior of the elements in the molten solidified body for at least 7 days or over a long period of time (hundreds of days) to leaching behavior of the benchmark glass. DG-2, AG8W1, and SG, and R7T7 of France were used as the candidate glass, and the SRL-EA (environmental assessment) glass, which was manufactured by the Savannah River National Laboratory in the USA, was used as the benchmark glass. A PCT was performed on the DG-2, AG8W1, and SG candidate glass, the R7T7 candidate glass of France, and the SRL-EA benchmark glass for 7 days. As a result, the DG-2, AG8W1, and SG candidate glass exhibited relatively better leaching resistance than the R7T7 candidate glass and the benchmark glass, as shown in FIGS. 7 and 8. It is shown that the leaching rate of boron and sodium is higher than that of other elements. This is considered to be because a silicate compound is formed at a leaching boundary surface to thus reduce the concentration of the silicic acid in the leaching solution, but the leaching of other elements is increased. It is shown that the leaching resistance of four elements of the AG8W1 glass is relatively good compared to the DG-2 glass. The SG glass satisfied the US Hanford high/low-level vitrification limit, namely 2 g/m2 or less. The candidate glass and the SRL-EA benchmark glass were subjected to a long-term leaching test for 120 days, and the result is shown in FIG. 9. It could be seen that the leaching rate of each element in the candidate glass was better than that of SRL-EA and was lower than the US Hanford high/low-level vitrification limit, namely 2 g/m2 or less. (4) ISO (International Standards Organization) In order to evaluate the leaching mechanism of the elements constituting the molten solidified body and chemical integrity over a long period of time, a leaching test was performed using the ISO (International Standards Organization) standard test, which is a long-term leaching test. AG8W1 was subjected to the leaching test over a long period of time to thus evaluate the leaching behavior of the main elements, which leaked from the glass structure into the leaching solution. FIG. 10 shows the development of the leaching rate change of B, Na, and Si for 602 days. The three elements in AG8W1 exhibited a relatively stable leaching rate. FIG. 11 shows the cumulative fraction leached of the main elements. It could be seen that the curve of the cumulative fraction leached of B and Na rose with a very gentle slope but that Si, which constituted the main frame of the glass structure, was saturated. It is considered that the concentration of silicic acid in the leaching solution was reduced but that other elements were continuously diffused. In the result of the ISO leaching test for 602 days, cesium, which was added in a small amount to AG8W1 in order to check the leaching behavior of cesium, was not detected, but cobalt was intermittently detected in the leachate, thus exhibiting a very small cumulative fraction leached compared to other elements. Three types of candidate glass, which were selected in Example 2, were subjected to a pilot test using a pilot test device in order to check the ease of the vitrification process of the glass and the quality of the molten solidified body formed during the vitrification process. The pilot test was successfully repeated five times in order to analyze the pilot test characteristic of the AG8W1 candidate glass, the pilot test was repeated twice in order to check the pilot test characteristic of the DG-2 candidate glass composition, and the pilot test of the SG candidate glass composition was performed once. The main pilot test results of the waste products are arranged in the following Table 2. TABLE 2Summary of pilot test resultsSupply ratioSupplyNo.Operation variablesratioExpectedofIntegrityduringappropriateWastepilotInitialof moltentestsupply ratioSupplyproducttestsignitionglass(kg/h)(kg/h)typeW15FavorableFavorable1818Grainwaste(wasteproductresin)/cutting(dryactivewaste)Dry2FavorableFavorable2020CuttingactivewasteWaste1FavorableFavorable77Grainresin(wasteresin) The pilot test of the W1 waste product was continuously performed for a maximum of about 10 days, based on a single operation cycle, during which 70 kg of the AG8W1 candidate glass was used to prepare the initial molten glass, the waste product and the base glass frit AG8 were continuously supplied for 6 hours, residues were combusted for 1 hr, mixing was performed, and the glass was discharged in an increased amount. It was very easy to initially ignite the AG8W1 candidate glass used during the test and to control the molten glass when the waste product was not supplied. From the result of analysis of the discharged molten solidified body, it could be seen that a homogeneous molten solidified body was produced. It was evaluated that the dry active waste did not particularly affect the control of process variables and the quality of a molten solidified body even when the dry active waste was supplied in amounts of 20 kg and 25 kg per hour. When the dry active waste was supplied in an amount of 20 kg per hour, the dry active waste was capable of being continuously supplied together with the DG-2 base glass frit for 8 hrs, and an operation mode was capable of being successfully performed based on a single cycle for a total of 9 hrs by combusting residue for 1 hr, performing mixing, and discharging the glass in an increased amount. Even though PVC, rubber, lancing filters, and wood were supplied into the dry active waste at content levels (5, 15, and 1 wt %) that were higher than target values (0, 11.62, 03, and 0.5 wt %) for supply to a nuclear power plant, the concentration of generated harmful gas, the dust generation amount, and the color of the dry active waste were very favorable. Therefore, it was evaluated that there is no particular problem occurring in the case where a predetermined amount of waste product is mixed and supplied due to human error while the dry active waste is classified during a commercial operation. From the result of evaluation of the chemical robustness of the molten solidified body, which was discharged at early, middle, and final stages of the pilot test, it could be seen that the glass, which was discharged during the present pilot test, exhibited better robustness than that of the SRL-EA glass, which was the benchmark glass of the high-level molten solidified body of the USA. From the pilot test, it could be seen that it was very easy to control the operation variables of vitrification of the dry active waste and that it was possible to produce a high-quality molten solidified body compared to other flammable waste products (waste resin and the like). Accordingly, the simple volume reduction ratio that is expected when the used glass composition and operation mode for the vitrification process are applied to a commercialization process is evaluated to be high, namely about 175. However, in consideration of the occurrence of secondary waste products, such as the amount of discharged waste washing solution and high-temperature filters that are no longer of any use, it was judged that the overall volume reduction ratio was slightly reduced but, nonetheless, a very high volume reduction ratio of 100 or more was capable of being ensured. The pilot test of the waste resin was continuously performed, based on a single operation cycle, during which 70 kg of the SG candidate glass was used to prepare the initial molten glass, the waste product and the base glass frit SG-F were continuously supplied for 20 hours, residues were combusted for 1 hr, mixing was performed, and the glass was discharged in an increased amount. It was very easy to initially ignite the SG candidate glass used during the test and to control the molten glass when the waste product was not supplied. The simple volume reduction ratio, which is expected when the operation mode for the waste resin vitrification process is applied to a commercialization process, is evaluated to be about 50. Even in consideration of the occurrence of secondary waste products, it is judged that a volume reduction ratio of 30 or more was capable of being ensured. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. |
|
claims | 1. A method for preparing [18F]F2 , comprising the steps of: isolating [18F] fluoride from a water target by electrolysis in a reactor; then drying the [18F] fluoride and thereafter filling the reactor with a carrier gas or a metal fluoride to form plasma or a mixture comprising plasma thereof wherein the reactor also contains a controlled amount of fluorine gas; next igniting the plasma with at least a plasma induction by microwaves wherein the reactor comprises a microwave cavity and optionally also igniting the plasma with a fluorescent light tube driver circuit, or a high voltage discharge; and thereafter emptying the contents in the reactor into a stream of gas wherein [18F]F2 is trapped. 2. The method according to claim 1, wherein the metal fluoride is a deposition on the wall of the reactor or a powder on the wall of the reactor. 3. The method according to claim 1, wherein the carrier gas is a noble gas or a halogen gas. 4. The method according to claim 1, wherein the metal within the metal fluoride is Na, Ca, K, Mg, Mn or a salt thereof. 5. The method according to claim 1, wherein the controlled amount of fluorine gas is about 200 nanomoles to about 10 micromoles. 6. The method according to claim 1, wherein the high voltage discharge has a voltage of about 10 kV to about 50 kV. 7. The method according to claim 1, wherein the stream of gas is a halogen gas or a noble gas. 8. The method according to claim 1, wherein the reactor generates no heat. |
|
claims | 1. A nuclear power plant, comprising:a nuclear island, including one or more nuclear reactors located in one or more underground caverns;side by side with the one or more nuclear reactors, a centre for treating and conditioning radioactive wastes; andtwo repositories, located in the one or more underground caverns, the two repositories including a final repository being adapted to store low-intermediate level nuclear wastes, and a temporary repository being adapted to store spent fuel, high-level long-life radioactive materials, and spare nuclear rods for reactor refueling. 2. The underground nuclear power plant according to claim 1, further comprising:metallic doors for closing an entrance to the one or more underground caverns, and an interposition of walls made of injected concrete between said metallic doors. 3. The underground nuclear power plant according to claim 1, wherein the one or more underground caverns comprise an entrance provided with anti-intrusion devices to secure the nuclear island from attack from outside the one or more underground caverns. 4. The underground nuclear power plant according to claim 1, wherein the one or more underground caverns comprise an entrance provided with anti-flooding devices. 5. The underground nuclear power plant according to claim 1, wherein the one or more underground caverns is formed of rocks appositely formed to host the nuclear island, the centre for treating and conditioning radioactive wastes, and the two repositories. 6. The underground nuclear power plant according to claim 1, further comprising:storage facilities for radioactive wastes of low-intermediate level produced during a service life of the nuclear power plant for final underground storage in safe conditions to avoid transport of the radioactive wastes of low-intermediate level outside. 7. The underground nuclear power plant according to claim 1, wherein the temporary repository is adapted to operate as a final repository for all high-level long-life radioactive materials produced by the underground nuclear power plant. 8. The underground nuclear power plant according to claim 1, wherein substantially all components of the one or more nuclear reactors are underground. 9. The underground nuclear power plant according to claim 1, wherein the one or more nuclear reactors is constructed and arranged to use masses of natural water for cooling. 10. The underground nuclear power plant according to claim 1, wherein an access to an interior of the one or more underground caverns is horizontal. 11. The underground nuclear power plant according to claim 1, further comprising:a system for conditioning and disposing radioactive wastes provided inside the one or more underground caverns. 12. The underground nuclear power plant according to claim 1, wherein the one or more nuclear reactors is one or more commercial, high power PWR reactors. 13. The underground nuclear power plant according to claim 1, wherein the one or more underground caverns housing the nuclear isle and the the two repositories have a roof formed of an inverted arch and side-walls made substantially impermeable and provided with systems for collecting natural or accidentally released fluids. 14. The underground nuclear power plant according to claim 1, wherein the underground nuclear power plant is constructed and arranged to receive the radioactive wastes of the two repositories, thereby avoiding any danger of nuclear pollution to the surrounding environment. |
|
claims | 1. A method of inspecting a pressure vessel having a shell extending between an inner surface and an outer surface and a penetration extending through the shell from the inner surface to the outer surface, comprising the steps of:passing an eddy current probe through a penetration tube installed in the penetration with a clearance fit and welded at the inner surface of the pressure vessel;inducing eddy currents in the pressure vessel as the probe passes through the penetration tube; anddetermining the degradation of the pressure vessel shell in the region adjacent the penetration tube based upon eddy currents induced in the pressure vessel by the probe. 2. The method of claim 1, wherein the probe introduces eddy currents into the pressure vessel while it passes from either the inner or outer surface of the pressure vessel to the other surface of the pressure vessel. 3. The method of claim 2, wherein the pressure vessel is inspected in one pass of the probe through the penetration. 4. The method of claim 1, wherein the eddy currents are induced in the pressure vessel by at least one circumferential coil. 5. The method of claim 4, wherein the eddy currents are induced in the pressure vessel by a pair of circumferential coils. 6. The method of claim 1, wherein the probe also has a multiple array of eddy current coils, comprising the step of:inspecting the penetration tube with the multiple array of eddy current coils. 7. The method of claim 6, wherein the pressure vessel and the penetration tube are inspected in one pass of the probe through the penetration. 8. The method of claim 1, including the step of:inspecting the weld with an array of eddy current coils. 9. The method of claim 8, wherein the array of eddy current coils is rotated to inspect the weld. 10. The method of claim 9, wherein the weld is inspected in one 360° rotation of the array of eddy current coils. 11. The method of claim 10, wherein the pressure vessel and the penetration tube are inspected by one pass of the probe through the penetration from either the inner or outer surface of the pressure vessel to the other surface of the pressure vessel. 12. The method of claim 1, wherein the step of determining the degradation of the pressure vessel shell comprises determining the degradation across a gap of between 5 and 50 thousandths of an inch. 13. The method of claim 12, wherein the step of determining the degradation of the pressure vessel shell comprises determining the degradation across a gap of about 50 thousandths of an inch. 14. A method of inspecting a pressure vessel having an inner surface and an outer surface and a penetration extending therebetween, comprising the steps of:passing a first eddy current probe through a penetration tube installed in the penetration with a clearance fit and welded at the inner surface of the pressure vessel; andinspecting the entire thickness between the inner surface and the outer surface of the pressure vessel and the penetration tube in one pass of the first eddy current probe between the inner surface and the outer surface of the pressure vessel. 15. The method of claim 14, comprising the additional step of:inspecting the weld in one 360° rotation of a second eddy current probe. |
|
abstract | A system and method of employing patterning process statistics to evaluate layouts for intersect area analysis includes applying Optical Proximity Correction (OPC) to the layout, simulating images formed by the mask and applying patterning process variation distributions to influence and determine corrective actions taken to improve and optimize the rules for compliance by the layout. The process variation distributions are mapped to an intersect area distribution by creating a histogram based upon a plurality of processes for an intersect area. The intersect area is analyzed using the histogram to provide ground rule waivers and optimization. |
|
061750514 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The processes of the present invention are directed to the deactivation of alkali or alkaline earth metal used as liquid coolant and/or heat transfer agents in nuclear reactor systems. For purposes of explanation, sodium will be used as a representative of an alkali metal but this is not intended to be a limitation of the invention. Methods of the present invention can be demonstrated by reference to FIG. 1 which teaches that molten sodium can be accumulated in a storage tank 10 at a temperature ranging from about the melting point of 98.degree. C. to less than the boiling range of 883.degree. C. to maintain the sodium in a liquid state, and preferably, from about 110.degree. C. to 200.degree. C. The sodium can be pumped from the storage tank 10 or directly from a source such as the primary or secondary coolant system of a breeder reactor. From the storage tank 10, the molten sodium may be injected into a reaction vessel 14 which is charged with an ammoniacal liquid in a sufficient amount to dissolved the injected alkali metal. Preferably, the reaction vessel is charged with at least a stoichiometric excess (greater than a 1:1 mole ratio) of the ammoniacal liquid ammonia to dissolve the alkali metal. The ammoniacal liquid is preferably anhydrous liquid ammonia, but solutions of at least 50 percent-by-weight of ammonia in water can also be employed. The temperature and/or pressure in the reaction vessel is controlled to maintain the anhydrous ammonia in a liquefied state. The pressure may range from about 15 psi to about 200 psi. The pressure range will be dependent upon the temperature generated by the reaction within the vessel and whether the vessel is being cooled by an outside cooling system. Accordingly, if the reaction is carried out under normal atmospheric pressure then the temperature should be maintained at or below -30.degree. C. by any means known in the art. Alternatively, if the pressure within the reaction vessel is increased then the temperature may rise above -30.degree. C. The molten sodium may be injected or pumped under pressure into the reaction vessel through nozzle 15 that atomizes the sodium at a controlled rate to facilitate dissolution of sodium in the ammoniacal liquid under stirring conditions. The amount of sodium introduced into the reaction vessel should not exceed the solubility of sodium in anhydrous liquid ammonia at the specific temperature and pressure within the reaction vessel. When sodium and other alkali metals dissolve in an ammoniacal liquid, such as anhydrous liquid ammonia, solvated electrons are chemically generated. The sodium becomes a cation by losing a valence electron as illustrated in the following equation: ##STR1## The ammonia molecules of the solvent surround the charged electrons which provide stability so the sodium ions do not react with the solvated electrons. Instead, the sodium ions are free to react and/or combine with a reagent that provides a combinable anion to form a sodium salt precipitate or an easily separated sodium complex. The sodium cations and solvated electrons in the reaction vessel 14 are next introduced and combined with a precipitating agent that upon ionization in the liquid ammonia will provide an anion for combining with the sodium cation to form a salt precipitate. Generally, any precipitating agent that ionizes in ammoniacal liquid and provides an anion to combine with the sodium cation for precipitating a sodium salt may be used in the present invention. Preferably, the precipitating agent is selected from the group consisting of ammonium chloride, water, hydrogen chloride, ammonium nitrate, sodium nitrate, nitric acid, ammonium sulfate, ammonium chromate, ammonium dichromate, ammonium perchlorate, ammonium iodate, ammonium periodate, ammonium benzoate, and metal halides such as zinc halides, copper halides and nickel halides. More preferably, the precipitating agent is selected from the group including ammonium chloride, copper chloride and ammonium nitrate. The precipitating agent may be solubilized in an ammoniacal liquid in a precipitating agent tank 16 before introduction to the reaction vessel 14. The ionizable precipitating agent is added to the ammoniacal liquid in an amount not exceeding the solubility of the precipitating agent in the liquid ammonia at the specific temperature and pressure within the reaction vessel. The precipitating ammoniacal mixture may be introduced into the reaction vessel under stirring conditions to insure a homogenous reaction mixture. To form a salt precipitate, a sufficient amount of this mixture may be introduced so that the amount of the anion of the precipitating agent and the sodium cation brought together exceed the solubility of the ionic compound formed by their union. For instance, when using ammonium chloride NH.sub.4 Cl as the precipitating agent, the concentrations of the sodium cations Na.sup.+ and the chloride anions Cl.sup.- from NH.sub.4 Cl will exceed the solubility of sodium chloride NaCl in liquid ammonia thereby forming a salt precipitate. To insure the maximum amount of cations or Na.sup.+ to precipitate from the solution as NaCl an excess of the precipitating reagent Cl.sup.- may be added to the solution. ##STR2## Thus, a liquid ammonia solution of the active metal sodium reacts with ammonium chloride with the evolution of hydrogen and the formation of the corresponding alkali metal chloride. EQU 2Na+2NH.sub.4 Cl.fwdarw.H.sub.2 +2NaCl+2NH.sub.3 The precipitating salt can be removed from the reaction vessel by any means of separation including venting the liquid ammonia, removing the salt from the reaction vessel by filtration, spray drying, and or evaporation. Because ammonium chloride may cause the production of hydrogen gas an alternative precipitating agent may be utilized, that being a precipitating agent that upon ionization has an anion that can be reduced, such as ammonium nitrate. A solution of anhydrous liquid ammonia containing dissolved ammonium nitrate can form precipitates without the production of hydrogen. For instance, when the sodium is introduced either directly or indirectly into an ammoniacal solution of ammonium nitrate, the sodium is deactivated without the evolution of hydrogen. The alkali metal sodium is added in an amount to provide sufficient solvated electrons to reduce the anion of the dissolved precipitating agent. Preferably, the sodium is added in at least a 1:1 ratio, and more preferably, sodium and ammonium nitrate react in the approximate ratio of 2:1, a ratio required for the following reaction. EQU NH.sub.4 NO.sub.3 +2Na.fwdarw.NH.sub.3 +NaNO.sub.2 +NaOH The sodium metal is deactivated without the concomitant production of hydrogen gas when an excess of sodium is introduced into the ammonia solution containing ionized ammonium nitrate. It is believed that the solvated electrons formed during the dissolution of the sodium metal act as a powerful reducing agent and are consumed by the reduction of the nitrate anion forming a nitrite wherein the nitrogen atom has a lower oxidation number. Also, precipitating reagents that reduce the production of hydrogen gas when deactivating an alkali metal may include metal halide agents that upon ionization provide a cation that can be reduced, such as copper halides, zinc halides, magnesium halides, cadmium halides and mixtures thereof. The primary result upon the treatment of an alkali metal, such as sodium, with a metal halide, such as copper chloride, in liquid ammonia may be represented by the equation: EQU CuCl.sub.2 +2Na.fwdarw.Cu+2NaCl The metal cation is reduced to a free metal with a concomitant metal replacement reaction forming a metal salt. The free metal, acting as a catalyst, will frequently cause the formation of an amide, as a secondary reaction such as shown below: ##STR3## This secondary reaction may be minimized by having a shorter time of reaction, rapid addition of the alkali metal and the use of the alkali metal in only a slight excess over the stoichiometric quantity. When alkali metals dissolve in anhydrous liquid ammonia, several side reactions may also occur including the generation of amides, as shown above, and/or hydrides as shown by the following equations: ##STR4## During the processes, anhydrous liquid ammonia can be slowly vented from the reaction vessel to reduce the overall temperature within the reaction vessel. The unvented anhydrous liquid ammonia is allowed to expand slightly in the vessel with a concomitant cooling effect which is transferred to the reaction mixture. This reduction in temperature counteracts any heat generated by the reaction of the precipitating reagent with the sodium cation. Therefore, the formation of a precipitating alkali metal salt may proceed without overheating. Moreover, a reduced temperature decreases the possibility of an explosion of any hydrogen gas that may form during the reaction. The vented ammonia may be scrubbed in scrubber 18 which will remove any hydrogen gas that may form during the reaction and the cleaned ammonia can be stored in vessel 12 to be reused for recharging of the reaction vessel. Although the present invention has been described in terms of combining a reaction mixture with a precipitating ammoniacal mixture in a two step batch process, it should be clear that the deactivation methods of the present invention can be performed in a continuous process. In such a system, the formed precipitate is continuously removed while the reaction vessel is continuously recharged with anhydrous liquid ammonia. The alkali metal and precipitating agent can be introduced in a step process or simultaneously in controlled amounts. Additionally, the precipitating agent may be added directly to the reaction vessel for ionization in the ammoniacal liquid within the reaction vessel without first being ionized in a separate ammoniacal mixture. In the alternative, the alkali metal may be directly introduced into an ammoniacal liquid which already contains a dissolved precipitating agent. At some sites where a breeder reactor is being decommissioned, there may be an abundance of other hazardous agents or hazardous waste materials in addition to the radioactive materials associated with the breeder reactor. These hazardous wastes may be halogenated organics including chemical warfare agents, PCB compounds, highly halogenated toxic waste materials, halogenated insecticides and pesticides and other toxic materials or mixed waste stored on site waiting to be detoxified. Current methods of detoxification include incineration, neutralization and/or chemical processing. However, these methods can produce environmental concerns regarding atmospheric pollution and large quantities of additional waste material. Considering these facts, this invention further contemplates processes wherein the solvated electrons generated in the reaction vessel are used to decontaminate hazardous materials. Methods for decontaminating hazardous wastes including halogenated materials, nonradioactive metals or metalloids, and radioactive mixed wastes, using solvated electrons are disclosed in U.S. Pat. Nos. 4,853,040, 5,495,062 and 5,613,238 all of which are incorporated-by-reference herein. Accordingly, a halogenated hazardous waste material can be detoxified simultaneously with the deactivation of the alkali metal coolant thereby eliminating two different types of hazardous waste material with a single process. Briefly, this can be accomplished by introducing the halogenated hazardous waste material to the reaction vessel comprising an ammoniacal liquid, such as anhydrous liquid ammonia and an alkali metal wherein solvated electrons have been generated. The solvated electrons, acting as a reducing agent, should be in a sufficient amount to partially or completely dehalogenate a halogenated hazardous waste material to yield a compound(s) of lesser toxicity than the original waste material. In this process the uncombined halogen atoms that are removed from the halogenated compound may be combined with the alkali metal cation in the reaction vessel to form an insoluble alkali metal salt. The detoxified hazardous waste and alkali metal salts are removed from the reaction vessel for disposal. The anhydrous liquid ammonia is vented and scrubbed for possible reuse in the reaction vessel. Methods of the present invention further provide for the deactivation of alkali metal by dissolution of a precipitating agent in an ammoniacal liquid, such as anhydrous liquid ammonia with the subsequent addition of an alkali metal therein. Referring to FIG. 1, the closed reaction vessel 14 is charged with an excess of anhydrous liquid ammonia and the precipitating agent stored in tank 16 is introduced directly into the liquid ammonia. The precipitating agent is introduced in an amount so as to permit ionization of the agent. At this point, an alkali metal from storage tank 10 is introduced and dissolved in the anhydrous liquid ammonia thereby forming solvated electrons and cations. Upon dissolution, the alkali metal cations may combine with anions of the ionized precipitating agent and form a precipitating alkali metal salt. The precipitating salt may be removed from the reaction vessel or the liquid ammonia may be optionally vented for recovery and reuse. Liquid alkali metal drawn from the primary, intermediate and/or any contaminated circuit of a cooling system, such as in a pool system may initially warrant decontamination to reduce the radioactivity of the alkali metals. The radioactivity may be reduced to unrestricted levels before being treated by the processes of the present invention for final disposal. Molten sodium removed from the primary circulating loop is contaminated with radioactive isotopes such as Na-24 which occurs due to neutron bombardment. The sodium in the primary loop enters the core of the reactor, and therefore, can be contaminated with uranium dioxide and fission products as a result of direct contact with the irradiated uranium dioxide in the core. By removing some of the fission products, including plutonium-239, before deactivation by the present process, the precipitated alkali metal salt may be disposed of in a low-level radioactive site where storage is less restrictive and monitoring is reduced because of the removal of any plutonium-239. Any method that purifies and/or decontaminates sodium metal may be used as long as the sodium can be maintained in a liquid state or can resume a liquid state for further deactivation by the processes of the present invention. For instance, U.S. Pat. No. 3,854,933 discloses a method to remove impurities in metallic sodium, the contents of which are herein incorporated-by-reference. Briefly, calcium and/or magnesium and/or calcium-magnesium alloy are dissolved in the molten metallic sodium at a high temperature from about 450 to 850.degree. C. Thereafter, these dissolved metals are precipitated at a lower temperature, that being, a little higher than the melting point of sodium (97.5.degree. C.). As a result, nuclear fission products comprising elements from the group consisting of O, N, S, Sr, Ba, Sb, Sm, Pr, La, Ce, Ni, Si, Sn, Zn, Tl, Th, Pu, Rh, and Pb are separated from the sodium by chemically bonding with, adsorbing with and/or co-precipitating with the calcium and magnesium additives. Additionally, Na-24 formed in the molten metal by neutron bombardment is also removed because Na-24 acting as a magnesium atom precipitates when the molten solution is cooled to just above the melting point of sodium. After the impurities are removed the decontaminated sodium may be introduced directly into the reaction vessel for deactivation and precipitation by the methods of the present invention. In another embodiment of the present invention, the primary and secondary circuit loops of a breeder reactor may be deactivated in situ thereby removing any remaining solidified sodium metal after the bulk of the molten sodium has been drained. FIG. 2 illustrates a generic breeder reactor having separate and distinct primary and secondary circulating loops. The engineering design of the vessels and pipelines makes complete drainage of the system impossible, and therefore, the remaining sodium must be removed by other means. More important, by decontaminating the primary loop any radioactive fission products that may have contaminated the sodium in the loop are also removed thereby allowing the metallic hulk of the reactor to be shredded and disposed of as low-level radioactive waste. The processes of the present invention are ideal for decontaminating the coolant circulating loops and removing any remaining metal coolant that has solidified on surfaces or in crevices within the reactor system. The process comprises several steps. In the first step, anhydrous liquid ammonia is circulated through the circuit loops at a pressure and temperature to maintain the anhydrous ammonia in a liquefied state. The present process exploits the physical dissolution of sodium in liquid ammonia. The anhydrous liquid ammonia is circulated through the system until it becomes saturated with sodium and/or reaches an acceptable level of sodium ions dissolved in the ammoniacal solution and then is removed from the circulating system. After the ammoniacal liquid containing the dissolved sodium is removed from the system it may be directly introduced into the reaction vessel as shown in FIG. 1 for mixing with a precipitating agent. In the alternative, the anhydrous liquid ammonia with the dissolved sodium may be removed and evaporated to recover the sodium. This route may be utilized if the sodium removed from the primary loop must be decontaminated to remove radioactive fission products. The sodium can be reheated and the method discussed above may be used to remove unwanted fission products and the decontaminated sodium may then be deactivated by the processes of the present invention. The following specific examples demonstrate the invention, however, it is to be understood they are for illustrative purposes only and do not purport to be wholly definitive as to conditions and scope. EXAMPLE 1 The deactivation of sodium in an ammoniacal liquid with a precipitating agent solubilized in the ammoniacal liquid was demonstrated by the following experiment: A 5.3 gram sample of ammonium chloride was introduced into a 600 ml beaker containing 350 ml of NH.sub.3 and solubilized under stirring conditions forming a reagent mixture. Pieces of sodium metal were slowly added to the reagent mixture forming a reaction mixture from which sodium chloride was precipitated. The reaction mixture did not maintain a blue color in the vortex of the stirring mechanism until more than 2.3 grams of sodium were added. At this point all the chloride ions, being the limiting reagent, had combined with the sodium cations and precipitated. The addition of extra sodium above the 2.3 grams into the ammoniacal liquid maintained the expected blue solution due to unused solvated electrons. This example demonstrates the ability of ammoniacal liquid to deactivate sodium when a reagent is added that forms an alkali metal salt precipitate which has a reduced solubility in ammoniacal liquid when compared to that of the original reagent and alkali metal. EXAMPLE 2 A 7.0 gram sample of ammonium sulfate was introduced into a 600 ml beaker containing 350 ml of NH.sub.3 under stirring conditions forming a reagent mixture. Sodium was slowly added to the reagent mixture forming a reaction mixture. The addition of sodium precipitated a limited amount of sodium sulfate. The reaction mixture maintained a blue color in the vortex of the stirring mechanism and remained a permanent blue after only 0.59 grams of sodium were added. The reaction mixture containing ammoniacal liquid maintained the expected blue solution due to solvated alkali metal cations and electrons. This example demonstrates that some reagents are more aggressive in precipitating an alkali metal salt and this may be dependent on the solubility of the precipitating agent in liquid ammonia. EXAMPLE 3 A closed reaction vessel was charged with approximately 6 liters of liquid anhydrous ammonia. A 60 gram sample of metal sodium was introduced in the reaction vessel. The pressure within the vessel and the conductivity of the reaction mixture were monitored. With the addition of sodium to the reaction vessel the conductivity of the reaction mixture increased due to the sodium cations and solvated electrons formed during the solubilizing of sodium in liquid ammonia. This increase in conductivity is shown in FIG. 4 wherein the curve (labeled RxC1) rapidly increases. The pressure in the reaction vessel also increased as shown by the curve (labeled RxP1). The reaction vessel was vented to reduce the pressure with a concomitant reduction in the conductivity of the reaction mixture. 50 grams of water, which is a reagent soluble in liquid ammonia, was introduced into the reaction vessel. As evidenced by the decrease of the conductivity curve of the reaction mixture, the H.sub.2 O, which ionized in the ammonia, reacted with the sodium cations with the concomitant precipitation of sodium hydroxide. An additional 50 grams of water were added to the reaction vessel and the conductivity of the reaction mixture gradually decreased as the sodium cations combined with the hydroxyl ions forming the alkali metal salt precipitate. It is believed that the pressure in the reaction vessel increased as the solvated electrons combined with the hydrogen protons in solution and formed hydrogen gas. EXAMPLE 4 A 23 gram sample of metal sodium was introduced into a closable and pressurizable reaction vessel equipped with a stirring mechanism. The reaction vessel was assembled and charged with approximately 1.3 liters of anhydrous liquid ammonia. Upon completion of the ammonia addition the solution within the vessel had the typical blue color of a solution containing solvated electrons. The pressure within the vessel was initially about 110 psi which slowly increased to 120 psi with a temperature within the vessel of approximately 21-22.degree. C. The temperature was adjusted to approximately 5-6.degree. C. by venting the ammonia to reduce the internal temperature within the reaction vessel. The pressure was reduced to approximately 64 psi. 33 grams of ammonium nitrate were added to a separate lock hopper. Liquid anhydrous ammonia was introduced into the lock hopper for the purpose of dissolving and ionizing the ammonium nitrate before introduction into the reaction vessel. The lock hopper was connected to the reaction vessel via a top and bottom valve. The top valve of the hopper was opened allowing the ammonium nitrate solution to be pumped into the reaction vessel. Initially, as the ammonium nitrate ammoniacal solution was introduced into the reaction vessel the pressure and temperature within the vessel increased to 117 psi and 120.degree. C., respectively. After approximately 2 minutes, the pressure dropped to about 112 psi while the temperature held steady. The solution in the reaction vessel still maintained the blue color. At this point the bottom valve of the hopper was opened and an additional amount of the ammonium nitrate ammoniacal solution was introduced into the reaction vessel. At 3 minutes into the reaction, the pressure and temperature in the vessel increased to 190 psi and 26.degree. C., respectively and the blue color of the solution in the reaction vessel disappeared. As time progressed the pressure started to decrease within the reaction vessel while the temperature held steady. At 4 minutes into the reaction the pressure was approximately 148 psi and at 6 minutes the pressure was down to 144 psi. TIME TEMPER- PRESSURE EVENT (MIN) ATURE (C) (PSI) Reaction vessel containing sodium T = 0 8 67 in liquid anhydrous ammonia Top valve of hopper opened, T = .5 12 117 ammonium nitrate solution introduced into reaction vessel Bottom valve of hopper opened T = 2 17 106 T = 3 26 190 T = 4 29 148 T = 6 28 144 While not wishing to be bound by any specific mechanism of action, it is believed that several different reactions occurred including the deactivation of sodium and a secondary reaction that competed for the consumption of solvated electrons thereby reducing the formation of hydrogen gas. Solvated electrons are chemically generated as illustrated in the following equation: ##STR5## A possible explanation for the reduction of pressure within the vessel after the introduction of the ammonium nitrate ammoniacal solution may include the decrease of hydrogen gas produced because the solvated electrons acting as reducing agents are consumed in the reduction of the NO.sub.3.sup.- anion, wherein the N has a +5 oxidation state, to NO.sub.2.sup.- wherein the oxidation state is reduced to +3 such as shown in the following equation: EQU NH.sub.4 NO.sub.3 +2Na=NH.sub.3 +NaNO.sub.2 +NaOH Thus, if the formation of hydrogen gas is reduced the pressure in the vessel will decrease while the alkali metal salt precipitates are generated. It can be shown by the above examples and description that the present process provides a safe and efficient method for deactivating molten alkali metals removed from nuclear reactors by forming an easily disposable alkali metal salt precipitate. EXAMPLE 5 A 68 gram sample of copper chloride may be introduced into a closable and pressurizable reaction vessel that is equipped with a stirring mechanism. The reaction vessel is assembled and charged with approximately 3 liters of anhydrous liquid ammonia or a sufficient amount to dissolve and ionize the copper chloride therein and to dissolve the sodium metal that will be introduced subsequent to the addition of copper chloride. The temperature in the vessel may be adjusted to approximately 5-6.degree. C. by venting the ammonia to reduce the internal temperature within the reaction vessel and to maintain the anhydrous liquid ammonia in a liquefied state. 23 grams of molten sodium metal is introduced to a separate vessel for later introduction into the reaction vessel. The lock hopper is connected to the reaction vessel via a valve. The valve of the hopper is opened allowing the molten sodium metal to be injected or pumped into the reaction vessel. A solution of solvated electrons is formed from the reaction of the liquid ammonia with the sodium metal introduced into the reactor. The addition of the metal may be in a one-time injection or by serial mode of addition. The amount of molten sodium pumped into the reaction vessel is a slight amount greater than a stoichiometric amount for the reaction that being approximately twice the moles of the copper chloride according to the following equation: EQU CuCl.sub.2 +2Na.fwdarw.Cu+2NaCl When the blue color typical of solvated electrons persists, the addition of further metal is terminated to eliminate any unwanted secondary reactions that may generate hydrogen gas. The solvated electron solution is quenched and the ammonia is allowed to evaporate and is recovered for further use. The sodium metal is deactivated and a sodium metal salt is generated without the production of hydrogen gas. While not wishing to be bound by any specific mechanism of action, it is believed that the metal cation of copper chloride is reduced forming the free metal and the sodium chloride salt is formed. The solvated electrons are consumed by the reduction of the copper cation thereby competing with the possible production of hydrogen gas. The sodium chloride salt NaCl has a reduced solubility in the ammoniacal liquid when compared to that of the original precipitating agent CUCl.sub.2 and alkali metal Na which will make for easy separation from the ammonia solution. |
055747663 | abstract | An x-ray beam limiter includes a compressible disc 18 containing an aperture 20 and a slot 22 extending from the aperture to the outer edge 28 of the disc. The outer edge 28 of the disc 18 is covered with a bearing material and is retained within a groove 36 in a bearing retaining race 32 such that the disc 18 is rotatable within the retaining race 32. A beam limiter 54 is mounted to the disc 18. The disc 18 and beam limiter 54 are rotatable between at least two different positions. |
description | This is a continuation application, under 35 U.S.C. §120, of copending international application No. PCT/EP2011/003574, filed Jul. 18, 2011, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2010 035 509.7, filed Aug. 25, 2010; the prior applications are herewith incorporated by reference in their entireties. The invention relates to a method for depressurizing a nuclear power plant having a containment shell for containing activity carriers and having an outlet for a depressurization flow. The depressurization flow is conducted out of the containment shell into the atmosphere via a depressurization line provided with a filter system. The filter system contains a filter chamber having a filter chamber inlet, a filter chamber outlet and a sorbent filter lying therebetween. The depressurization flow is first conducted in a high-pressure section, then is depressurized by expansion at a throttle device, then is conducted at least partially through the filter chamber having the sorbent filter, and finally is blown out into the atmosphere. The invention also relates to a corresponding depressurization system for a nuclear power plant having a containment shell for containing activity carriers and having an outlet for a depressurization flow. A depressurization line provided with a filter system is connected to the outlet. The filter system contains a filter chamber having a filter chamber inlet, a filter chamber outlet and a sorbent filter lying therebetween. The depressurization line contains a high-pressure section, at the end of the high-pressure section, a throttle device is connected into the depressurization line. The depressurization line opens out downstream of the throttle device into the filter chamber inlet, and the filter chamber outlet is connected to a blow-out opening leading into the atmosphere. The invention finally relates to a nuclear power plant having such a depressurization system. To retain active gases or vapors occurring in accident situations, in particular in the unlikely event of a core meltdown, nuclear power plants are usually surrounded by a comparatively massive containment shell of concrete, reinforced concrete or steel that is hermetically sealed off from the outside world and is also referred to as a containment. Such containment shells are usually also configured to withstand high internal pressures, such as may occur in the case of an oxyhydrogen gas explosion or a major release of coolant vapor from the coolant circuit. Investigations into the behavior of the containment under significantly increased pressures that occur during accidents have shown, however, that, in unfavorable situations it may possibly happen that leakages occurring cause a relevant release of comparatively highly contaminated atmosphere into the surroundings. To minimize such unfiltered leakages, it is very advantageous if extensive depressurization can be carried out down to low excess pressures, or even to ambient pressure. This is of significant importance in particular in the case of containments for which the formation of cracks becomes more likely in such excess-pressure phases as a result of the structural design, such as for example in the case of a concrete containment, or in sensitive sealing regions, such as airlocks, etc. Therefore, various systems for excess pressure limitation and (filtered) depressurization of the containment in accident situations have already been installed in numerous nuclear power plants. These devices make it possible to retain the aerosols and to some extent also the elemental iodine. Effective retention of organoiodine from this depressurization flow—in passive operation without external energy being supplied—has so far not been possible. Recent findings in accident research show, however, that in such events the emitted organoiodine component in particular can contribute significantly to the radiation exposure of the population, and is consequently a risk factor. Within this application, organoiodine is understood in particular as meaning iodine in the form of organic compounds of a low carbon number, such as methyl iodine, etc. For example, in the case of the method mentioned at the beginning according to the international patent disclosure WO 90/16071 and the associated apparatus, a depressurization flow under comparatively high pressure and flowing out of the containment shell through a depressurization line is conducted through a filter chamber having a sorbent filter after it has undergone depressurization and expansion drying by a throttle valve that is also referred to as a throttle. Such sorbent filters are also referred to as molecular sieves, or mol sieves for short, and retain the elemental iodine in the depressurization flow by sorption comparatively well if the operating conditions are chosen such that there is no condensing out of the depressurization flow in the molecular sieve. In wet operation, on the other hand, the sensitive filter surfaces may be destroyed or become irreversibly “clogged”. In order to avoid this, according to WO 90/16071, a sufficiently high operating temperature of the iodine sorbent filter, in particular with a silver nitrate coating, is ensured by the comparatively warm depressurization flow in the high-pressure section of the depressurization line, that is to say upstream of the throttle, being conducted past the filter chamber (or else through heating pipes through individual filter elements) and the latter thereby being preheated by way of heat transfer. The device can be combined with a coarse and fine filtering device connected upstream, a metal-fiber screen for dehumidifying gas, and additionally with a freely discharging venturi scrubber. The achieved dew point difference of the depressurization flow in the low-pressure section is substantially determined by the (theoretical) throttle temperature and here is only about 5° C. on account of the structural design. As already mentioned above, according to recent investigations, the retention of organoiodine is not satisfactory, or at least not in economically acceptable operation without the use of external energy. Furthermore, significant amounts of afterheat occur especially in shutdown phases (no through-flow) because of the decay of the adsorbed activities. This can result in relevant heating of the molecular sieve, wherein the microcrystals are already destroyed at an operating temperature of about 210° C. owing to melting of the silver nitrate coating, and thus the separating effect is lost and activities are released. The process of pressure reduction in the containment shell by way of (filtered) blowing out of pressurized gas or vapor into the atmosphere is also referred to as venting. Accordingly, the depressurization flow is also referred to as a venting gas flow or similar. In terms of design and the possible activity emissions, the plants operated nowadays differ significantly from the new third-generation reactors (GEN 3), because in the latter case core meltdown was already taken into account in the design. Devices, such as for example scrubbers or sand-bed filter combinations, that have already been retrofitted do not solve the problem of organoiodine retention, to be regarded as something new, and the desired significant depressurization per se, in particular because of the high driving pressures required in scrubbers and the small reaction surface areas for mass transfer in the liquid phase and the very low separating effect for iodine in sand beds or molecular sieves in wet operation. An improvement of these devices, including in already existing plants, is of essential importance for achieving the higher safety standards of these nuclear power plants. A quantitative separation of all air-borne aerosol and iodine activities will also permit a significant reduction in costs in GEN3 plants, since the noble-gas activities that cannot be retained decay within a matter of days and thus a medium-term depressurization—without relevant releases—becomes possible. This permits a simplified design of the containment and of the associated safety systems, and consequently significant cost reductions. The present invention is therefore based on the object of providing a method for the depressurization of a nuclear power plant of the type mentioned at the beginning that is configured for particularly efficient and effective retention of activity carriers contained in the depressurization flow, in particular iodine-containing organic compounds. It is also intended to provide a depressurization system for a nuclear power plant that is particularly suitable for carrying out the method. With respect to the method, the object is achieved by providing that, immediately before it enters the filter chamber, the depressurization flow that has been depressurized by the throttle device is conducted through a superheating section, in which it is heated by direct or indirect heat transfer from the not yet depressurized depressurization flow in the high-pressure section to a temperature which is at least 10° C., preferably 20° C. to 50° C., above the dew-point temperature present there. It has surprisingly been found that the strong activity of a gas flow during the depressurization of a containment can be retained highly effectively by particularly effective passive-regenerative gas superheating downstream of the throttle by heat transfer from the excess-pressure region into the atmospheric region and subsequent sorbent filtering. As stated in more detail further below, the superheating of the depressurized depressurization flow in the low-pressure section may in this case take place on the one hand by direct heat transfer from the high-pressure section of the depressurization line with the venting gas as a heating heat transfer medium (first main variant: “dry” heating). On the other hand, an indirect, multistage heat transfer may take place via a washing liquid circuit of a wet filter/scrubber connected in terms of flow into the high-pressure section, with the washing liquid as an intermediate heating heat transfer medium, which for its part is heated up in the washing tank by the venting gas (second main variant: “liquid” heating). The two variants may also be combined with each other. The throttle, which is also referred to as a throttle valve or expansion valve, brings about a first drying of the depressurization flow by way of expansion, wherein it is also possible for the temperature to be significantly lower than the theoretical throttle temperature on account of gas humidities that are still contained and non-ideal throttling, depending on the operating phase. In the superheating section connected downstream of the throttle, the decisive superheating of the depressurization flow then takes place—largely independently of the effectiveness of the expansion drying—reliably avoiding condensing out in the region of the moisture-sensitive iodine-sorbent filter even under unfavorable operating conditions. The effective utilization of the surplus of heat present in the high-pressure region of the depressurization line for preheating the filter chamber on the one hand and for directly heating the depressurized depressurization flow immediately before it enters the filter chamber on the other hand makes it possible to dispense with the use of external energy, for instance in the form of electrical heating devices, in accordance with the principle of regenerative heat recovery with own-medium heating. This makes the method not only highly effective but also particularly energy-efficient. Advantageously, the depressurization flow is heated in the superheating section to a temperature which is—in the assumed case of design-basis accident events—at least 10° C., preferably 20° C. to 50° C., above the dew-point temperature present there. The dew point or dew-point temperature refers to that temperature at which a state of equilibrium of condensing and evaporating water is established in the depressurization flow, in other words condensate formation is just starting. As has surprisingly been found, the degree of separation for organoiodine, in particular if non-water-soluble silver coatings are used, increases greatly and, if for example such zeolite-based absorption materials are used, typically achieves values of up to 99.99% if the dew point difference is >10° C., preferably >20° C., even in the case of a depressurization flow with a high vapor content that has only been partially cleaned. Under some circumstances, even minor superheating, of for example 5° C. above the dew point, would suffice for effectively retaining organoiodine with high retention rates for a highly effective molecular sieve with a (water-soluble) silver-nitrate coating. However, it has been found that such a process in the plants known from the prior art depends greatly on largely achieving the theoretical throttling temperature, and on avoiding any residual moisture contents in the gas, which severely minimize superheating. In consideration of these new findings, such a plant of a conventional structural design, as is known for example from international patent disclosure WO 90/16071 mentioned at the beginning, with its immanent minor superheating cannot be operated effectively and safely. Only the concept according to the invention provides an effective remedy for this. The stated superheating of at least 20° C., particularly preferably at least 50° C., above the dew-point temperature is preferably achieved in the full-load operation of the depressurization system. This should be understood as meaning the initial depressurizing operation after a design-basis accident, when the pressure inside the containment is at a maximum and is typically about 3 to 8 bar, depending on the type of reactor and containment. Here, venting-gas mass flows of typically about 3 to 10 kg/s are reached. The dew-point temperature in the region of the sorbent filter is then typically around 80 to 100° C., depending on the vapor content, with the result that the temperature of the venting gas after superheating has taken place is preferably around 100 to 170° C. when it enters the sorbent filter. In part-load operation, when the venting-gas mass flows are around 25% of the corresponding values in full-load operation, the temperature increase is preferably still at least 10° C. The iodine sorption filtering can be achieved particularly effectively and compactly here with variable superheating and inverse residence times (short residence time under high superheating and long residence times under lower superheating) to almost atmospheric pressure—without auxiliary energy. Here, in the case of high containment pressure, a high volumetric flow is produced after throttling and, in spite of the resulting low sorption filter residence times, optimum reaction conditions with simultaneously increased diffusion are achieved on account of the now high gas superheating at the sorbent. Under low containment pressure, for example a quarter of the initial maximum pressure of, for example, 5 bar absolute, a low volumetric flow with reduced gas superheating is produced after throttling to almost atmospheric pressure, but effective iodine sorption is likewise made possible in spite of unfavorable sorption conditions on account of the now (around four times) higher sorption filter residence time. Effective sorption filtering is possible as a result, even up to complete depressurization and at containment temperatures of only 50° C. to 100° C., on account of the then still further increasing sorption filter residence time. In a first main variant of the method, the depressurization flow in the high-pressure section is conducted at least partially past the filter chamber and the chamber is thereby (“dry”) heated by almost direct heat transfer from the hot venting gas. That is to say from an apparatus viewpoint that at least a portion of the high-pressure section of the depressurization line is taken past the filter chamber and is thermally coupled to the filter chamber via heat-exchanger surfaces, with the result that the filter chamber is heated by the comparatively hot depressurization flow in the high-pressure section. In a particularly preferred configuration, the depressurization flow in the high-pressure section is conducted through a washing tank (“scrubber”) containing a washing liquid, preferably with inflow nozzles of the venturi scrubber type, before being conducted past the filter chamber. From an apparatus viewpoint, this therefore means that the washing tank is connected into the high-pressure section of the depressurization line upstream of the filter chamber around which the depressurization flow flows. The washing tank brings about effective fine filtering of the aerosols contained in the depressurization flow, preferably with an efficiency of >99%, in order to reduce the aerosol concentration that is typically encountered in the containment shell in the event of an accident of up to several g/m3 to an uncritical range of, for example, a few mg/m3. The effective wet filtering of the aerosols has the effect of avoiding relevant deposits on the downstream heat-exchanger surfaces. This succeeds in ensuring an effective and constantly high heat transfer for the superheating of the depressurization flow depressurized at the throttle and for the heating of the sorbent filter. The inflow nozzles, through which the depressurization flow enters the washing tank, preferably operate in this case on the venturi injection principle: the gas flow flowing through a constriction (throat) of a nozzle tube entrains washing liquid located in the surrounding washing tank by an inlet opening arranged at the constriction and configured for example in the manner of an annular slit, with the result that particularly intensive mixing between the gas flow and the sucked-in or entrained washing liquid droplets takes place in the manner of an (extremely fine) atomization. Aerosol particles and other particles entrained in the gas flow are thereby adsorbed in the washing liquid droplets. After emerging from the nozzle, the washing liquid and the gas flow separate again, in particular on account of the gravitational force, and the gas flow cleaned and freed of aerosols in such a way leaves the washing tank via a corresponding gas outlet line leading to the downstream heat-exchanger and sorbent-filter unit. The gas outlet line is for this purpose expediently connected to the washing tank above the so-called pool region, that is to say above the operational level of the washing liquid and above the discharge and separation zone. Alternatively or in addition, customary inflow nozzles directed into or entering the washing liquid may of course also be provided. Furthermore, in the pool region of the washing tank there may be arranged suitable flow internals, vortex generators, mixers, packers and the like, which increase the relevant interface for the (temporary) mixing of the venting gas and the washing liquid or the internal surface between them. The inflow nozzles and the depressurization line upstream of the inflow nozzles are preferably designed and dimensioned in such a way that the depressurization flow is conducted through the inflow nozzles into the washing tank at a flow rate of over 100 m/s. In the case of high-speed venturi separation, such rates are to be achieved in particular at the constrictions or throats of the venturi tubes, where the inflow openings for the washing liquid are located. The washing liquid in the washing tank is advantageously chemically conditioned by adding a caustic solution, preferably sodium hydroxide solution, and/or sodium thiosulfate, preferably as an aqueous sodium thiosulfate solution. This brings about a relevant increase in the retention of the activities contained in the venting gas flow, primarily of the elemental iodine. For this purpose, the washing tank is assigned corresponding metering devices and injectors, by which other chemicals can possibly also be added. Furthermore, a surface-reaction accelerator, in particular in the form of amines, is advantageously admixed with the washing liquid, promoting the adsorption/binding of the aerosols entrained in the venting gas flow in/on the washing liquid. Further filter elements may be connected into the high-pressure section of the depressurization line between the washing tank and the heat-exchanger/sorbent-filter unit, in particular metal-fiber or cartridge filters acting as fine filters, in order to reduce still further the aerosol content in the depressurization flow before it passes the heat-exchanger surfaces. Such filter elements may also be structurally integrated in the washing tank and are then expediently arranged above the pool region. If such filters are configured for (preferred) dry operation, liquid separators are expediently connected upstream of them to dehumidify the gas flow. In an alternative variant of the method, the depressurization flow is removed from a condensation chamber of a reactor, in particular of a boiling-water reactor, and conducted from there past the filter chamber and/or the superheating section to heat it, without an (external) washing tank being interposed. That is to say in terms of apparatus that the depressurization line is connected on the inflow side to the condensation chamber. A condensation chamber is usually understood in this connection as meaning a partial space that is partially filled with liquid (condensate), and separated from the rest of the space inside the containment (known as the pressure chamber) by a gas-tight separating wall and is connected to the rest of the space inside the containment via an overflow pipe entering the liquid and referred to as a condensation pipe. During the normal operation of the nuclear reactor, the overflow pipe is closed by a plug of liquid. In the event of an accident with an appreciable release of vapor and gases that cannot condense and a corresponding buildup of pressure in the pressure chamber, the gas/vapor mixture may enter the condensation chamber via the overflow pipe, the vapor component then condensing for the most part. The components that cannot condense collect above the level of the liquid in the condensation chamber and are removed from there, out of the condensation chamber and the containment shell, according to the variant described here of the invention via the depressurization line as a depressurization flow. The term “condensation chamber” is intended in this connection also to comprise other condensation pools that act in a similar way, for example condensation channel systems of a water-water energy reactor (WWER) of a Russian or other design. Since the condensation chamber acts to a certain extent itself as a scrubber and aerosol filter for the depressurization flow, it is therefore possible in a preferred configuration to dispense with a separate washing tank of the type described above arranged outside the containment. For a good heat transfer, the regenerative heat exchanger, forming the superheating section, and the filter chamber with the sorbent filter are preferably arranged in direct proximity at distances of <5 m, or are favorably integrated within one component. The combination may be arranged here in various chambers within a pressure vessel, in order to minimize heat losses and expenditure and in order to ensure optimum superheating and reaction conditions. In the aforementioned first main variant of the method, the sorbent filter is preferably arranged in an annular chamber surrounding the central chamber and having already integrated gas heating by way of the heat-exchanger tubes. The annular chamber has for example perforated tube sheet-metal screens with the sorbent. A fiber filter for retention of abraded sorbent particles can be connected downstream of the sorbent filter. Alternatively, a largely pressureless flat filter-chamber construction with interposed regenerative heat-exchanger elements may be provided. In this case, a modular structure is possible by joining together a number of modules. The heating of the sorption unit takes place here immediately before the flow passes through it; the filter chambers are favorably still partially heated externally by a medium. In a particularly advantageous configuration, the depressurization flow is at least partially conducted through a central chamber, which is surrounded by the filter chamber or adjoins it, the comparatively highly compressed depressurization flow in the high-pressure section being conducted through heat-exchanger elements arranged in the central chamber or protruding into it, in particular heat-exchanger tubes, and the depressurized depressurization flow, of a comparatively large volume, in the superheating section is conducted through the central chamber externally past the heat-exchanger elements. That is to say that the hot depressurization flow, still under high pressure, upstream of the throttle (also possibly only a partial flow of the same) gives off a significant part of its heat to the outside, to the already depressurized depressurization flow conducted around the heat-exchanger tubes, and consequently also indirectly to the even further out filter chamber to preheat the sorbent filter elements. From an apparatus viewpoint, this means that the filter chamber expediently surrounds or adjoins a central chamber, one or more heat-exchanger elements through which a flow can pass being arranged in the central chamber or protruding into it, and the conduction of the flow in the depressurization line being configured in such a way that the depressurization flow in the high-pressure section is conducted through the heat-exchanger elements and in the superheating section is conducted through the central chamber externally past the heat-exchanger elements. Expediently, one or more through-openings that form the filter chamber inlet are in this case provided between the central chamber and the filter chamber. For a particularly effective heat transfer, the heat-exchanger elements are preferably in the form of heat-exchanger tubes and are expediently provided on the outside with fins or projections that are arranged at regular intervals, run around them or extend in the longitudinal direction. Corresponding structures or internals may also be provided on the inside of the heat-exchanger tubes to generate turbulence or to form a swirling flow. The depressurization flow in the superheating section is advantageously conducted in counterflow or cross-counterflow with respect to the depressurization flow in the high-pressure section. From an apparatus viewpoint, this means for example that the heat-exchanger tubes forming the superheating section are arranged in the central chamber or protrude into it with a corresponding alignment, for instance as substantially vertical tubes or tubes bent in a zigzag form. By configuring the heating surfaces as dirt-repellent, smooth surfaces, with blast-resistant coatings or smooth high-grade steel surfaces, or additionally treated, such as for example polished, electropolished, and integrating condensate distribution systems in the heat exchanger region, such as for example tray or channel systems and/or spray systems, an effective heat transfer is effectively assisted on a sustained basis. For even more intensive preheating, a partial flow of the high-pressure depressurization flow may be taken from the depressurization line, in particular still upstream of the washing tank, via an additional heat exchanger device (tubes or annular chamber) and, for heating, be conducted directly through the sorbent filter or to a region connected upstream of it. This successfully achieves a further increase in the operating temperatures at the sorbent, in particular in situations with a significantly superheated containment atmosphere, and improves the organoiodine retention still further. A flow rate of the depressurization flow in the range from 10 m/s to 50 m/s is advantageously set in the high-pressure section. In the superheating section, a flow rate of the depressurization flow in the range from 10 m/s to 70 m/s is preferably set. The free flow cross section of the throttle is expediently set in such a way that the pressure in the high-pressure section is two to five times the pressure in the superheating section. In particular, if there is a (venturi) washing device in the high-pressure section, the wet filtering of the depressurization flow taking place there at a pressure of around 7 to 1 bar is preferably operated at two to five times the molecular sieve pressure at the sorbent filter, which is close to the atmospheric level. As already mentioned above, the aerosol-containing venting gas in the high-pressure section is advantageously conducted through the heat-exchanger tubes, which are favorably arranged in a channel-like structure (central chamber) to generate high gas rates, in particular of >10 m/s. Heat-exchanger elements (fins) on the raw-gas side are preferably configured with a mutual spacing of >1 mm, particularly preferably >5 mm, and are preferably vertically aligned. By choosing an appropriately over-dimensioned exchange surface on the aerosol-gas side, with an additional heating-surface reserve of >100%, while >500% is particularly robust and operationally reliable (based on the value without fouling), reliable operation can be ensured. Partial filtering of aerosols and iodine can also continue to take place selectively in the heat-exchanger unit. A configuration as a bare-tube heat exchanger and particularly high flow rates, for example of >10 m/s to 50 m/s, make it possible for the aerosol-containing gases to be conducted through the heat-exchanger tubes, such that relevant deposits in the tubes can be avoided. On the depressurized, atmospheric side, with maximum throughput phases, very high gas rates of >10 m/s to 70 m/s can likewise be set, with the result that high heat transfer values are achieved and very compact components are made possible. A high-speed regenerative heat recovery can be achieved preferably with a configuration of the heat exchanger according to the counterflow or cross-counterflow principle, as a finned-tube or plate heat exchanger. To achieve an effective heat transfer in cases with a low throughput, corresponding internals or structured tube surfaces (fins etc.) are preferably provided in/on the tubes to generate turbulent and/or swirling flow conditions. This successfully achieves a heat recovery coefficient of >0.5 with very compact units when there is a high containment pressure and high throughput, which can subsequently be increased to 0.8 when there is a low containment pressure and low throughput. The central chamber of the heat-exchanger/sorbent-filter unit is expediently connected in the bottom region to a condensate-collecting tank for condensate forming during operation. By injecting or charging sodium hydroxide or sodium hydroxide solution (NaOH) and/or sodium thiosulfate (Na2S2O3) and/or calcium peroxide (CaO2) into the condensate, for instance in the region of the condensate-collecting tank, or by spraying into the central chamber, a relevant increase in the iodine separation can additionally take place in the low-pressure section of the regenerative heat exchanger. Furthermore, the filtering and/or retention of chlorine-containing gases can be promoted in this way. In a particularly preferred configuration of the depressurization system, a prefilter (dry prefilter) is provided inside the containment shell, alternatively or additionally also outside the containment shell, for coarse aerosol filtering of the depressurization flow. Advantageously, a bypass line that can be closed by a controllable valve is connected parallel to the prefilter, such that if need be the depressurization flow can be conducted out of the containment shell to the filter systems located outside while partially or completely bypassing the prefilter. When venting the containment shell, the gas flow with a high activity content can therefore be conducted through the prefilter, where an extensive filtering of the coarse aerosols with diameters of >1 μm (retention rate preferably of >90%) and a partial filtering of the quantitatively low fine aerosol components with diameters of <1 μm (retention rate of preferably >50%) take place for example by metallic deep-bed filter cartridges or metal-fiber filters. The pre-filtering is preferably operated at two to five times the pressure at the sorbent filter (molecular sieve), in the pressure range of for example 7 to 1 bar. In order to limit the possible pressure losses at the prefilter and, in particular in the presence of a downstream (venturi) washing device at the inflow nozzles, for instance venturi nozzles, in order to allow comparatively high inflow rates to be set, if need be a bypass mode that bypasses the prefilter is provided. The opening of the bypass preferably takes place automatically and passively (that is to say without the use of external energy), by integration of an excess-pressure limiting device, such as for example a bursting disk or a spring-loaded overflow valve device. The opening mechanism may for example be set such that the bypass line is enabled when the pressure loss at the prefilter exceeds a value of >0.5 bar. The retention of the predominant amount of the aerosols from the initial high-concentration phase of the accident that is brought about by the prefilter when the bypass line is closed can then make it possible for the regenerative heat exchanger device to be operated effectively—even without a prefilter—in the later accident phase, with the bypass line open. Advantageously, the relevant plant components are dimensioned and the operating parameters in depressurization mode are chosen such that the pressure loss brought about by the possibly present prefilter and the regenerative heat exchanger in the high-pressure section is altogether <30% of the available total pressure loss up until release into the atmosphere, in order to ensure a high temperature level for the regenerative heating. In an advantageous configurational variant, an additional heating device, in particular an electrical heating device or a heating device operated with process steam from another plant, which can expediently be set or controlled independently of the operating conditions in the regenerative heat exchanger and in the superheating section, is provided for heating the depressurization flow in the depressurization line. The heating device may for instance be arranged downstream of the throttle. Alternatively or in addition, such heating elements may also be arranged upstream of the throttle in the high-pressure section of the depressurization line. Advantageous, for example, is an arrangement in the washing tank (if present), for instance in the washing liquid pool or above it, for example in the discharge zone or in the region of possibly present separators/additional filters. Such additional heating of the depressurization flow may also take place by way of a second heat accumulator that is previously heated up by the depressurization flow or by way of separate auxiliary energy sources. These devices may also be used to bridge the start-up operation. In a further expedient variant, a gas dryer or a drying cooler is connected into the depressurization line between the throttle device and the superheating section and brings about an additional drying and lowering of the dew point of the depressurization flow before it enters the superheating section. The cooling capacity of such a drying cooler is expediently <25% of the cooling capacity of the regenerative heat exchanger, preferably <10%. As a result, the dew point is lowered in the interposed cooling device by way of partial condensation and giving off heat to the surroundings or else to masses that are intended to be heated up and have a corresponding heat capacity in operating cases with an already low containment pressure and low temperatures, in other words with only little superheating potential, such as for instance also in the case of start-up. In the subsequent superheating section, a clear dew-point difference can then be ensured by heating up the depressurization flow to almost the high-pressure process temperature. An (additional) washing device which is configured for retaining chlorine-containing and/or nitrous gases may also be connected into the depressurization line between the throttle device and the sorbent filter, such that the depressurization flow is correspondingly cleaned in the washing device after it is depressurized at the throttle device and before it passes the sorbent filter. In an advantageous configuration, a suction blower with an electric-motor drive or a combustion-engine drive is connected into the depressurization line, or can be activated if need be, such that, in particular in long-term operation of the depressurization system, i.e. when the initial high internal containment pressure after an accident has already been largely reduced, the depressurization flow is “actively” sucked out from the containment shell by the suction blower through the depressurization line with the filter devices located therein. In other words, by activating a suction blower, the filter system can also remain active in long-term after-accident operation or else be used selectively to keep the containment under pressure, so as to completely avoid unfiltered containment leakages to the outside. The aforementioned measures, in particular the gas drying and the increase in the dew-point difference brought about as a result, now make it possible to reliably avoid a relevant coating of the large internal reaction surface of the sorbent filter with water-containing vapor, both in the macro-pore region and in the micro-pore region of the sorption means, and consequently to perform the iodine retention particularly effectively by way of adsorption on the surfaces and possibly chemisorption on the sorbent material. In an advantageous configuration, in particular when there is wet filtering in the high-pressure section by a corresponding washing device, the bypass line is connected into the depressurization line to bypass the filter chamber. In this case, the proportion of the depressurization flow that flows through the bypass line can expediently be set by suitable adjusting device. This makes possible an operating mode of the depressurization system in which a partial flow (that can be set) of the depressurization flow is blown out directly into the atmosphere via the bypass line while bypassing the filter chamber and the iodine sorption filter arranged therein. For pressure adaptation, a suitable pressure-reducing valve is expediently connected into the bypass line. This allows an effective retention of the activities as a whole, without having to make excessive use of the iodine absorption filter, when there are very high throughputs, for example in early phases of an accident with large amounts of gas and little occurrence of organoiodine, and the elemental iodine that is dominant in this phase largely being separated in the upstream scrubber device. In later phases—with relevant organoiodine formation that has in the meantime commenced, and thus a comparatively lower occurrence of gas—the full-flow filtering with inclusion of the iodine sorption filter then advantageously takes place with the bypass line largely or completely closed, in order to continue to ensure the high level of retention of the activities as a whole. The sorbent materials or sorption agents are preferably configured with >50 m2/g of internal surface and are made of inorganic materials. The then permanently acting superheating process consequently even makes it possible to use sorbent materials with a moisture-sensitive (water-soluble) silver-nitrate coating or doping. For example, use of silver-impregnated ceramic products, for example silica gel, makes it possible to achieve a very efficient iodine separation of >99.9% on a sustained basis. The molecular sieve may for example also be produced on a zeolite basis or with a different, preferably inorganic, carrier body and be coated or doped with silver nitrate (AgNO3), which is converted for example into silver iodide when iodine occurs. However, this is only favorable if sufficient superheating of the depressurization flow can be ensured in all operating phases. Advantageously, the organoiodine retention can be performed here highly effectively even in contaminated gases, for example gases containing nitrogen oxide and the like. An artificial zeolite, into which silver cations and/or heavy-metal cations have been introduced into the three-dimensional crystal lattice, for example by ion exchange, may be used as a more robust filter material. Combinations of binder-free zeolites, preferably with an open structure, are also possible. Such a binder-free molecular sieve, for example of the faujasite-structure type, is even better in terms of operational reliability, even in a highly superheated vapor atmosphere of for example >200° C., and also under short-term water-vapor sorption conditions (wet operation). Short-term wet operation therefore does not lead to destruction of these, for example silver-doped, zeolites. Similarly, a small introduction of caustic solution can be tolerated. Furthermore, an (additional) short-term gas superheating is achieved by way of moisture adsorption. It is particularly preferred if the sorbent filter contains a zeolite-based sorbent material as a mixture of zeolites with non-water-soluble doping, in particular a silver doping, and inorganic sorbent materials with water-soluble doping, for instance a silver-nitrate doping. In this case, the water-vapor adsorption advantageously takes place exclusively, or at least primarily, on the zeolite, even in short wet phases, the temporarily occurring release of adsorption heat being conducive to the process, with the result that elution of the water-soluble substances, such as for instance silver nitrate, can then be reliably avoided. This combination as a mixture of for example both zeolites with a silver doping and a molecular sieve with a silver-nitrate doping and/or also being accommodated on a common carrier body proves to be highly efficient and operationally reliable as a result of the dual separating mechanism. Furthermore, phosphazene molecules, phosphazene zeolites, in particular cyclo-triphosphazene zeolites, channel-type crystals, possibly with additional doping, may also be used as suitable sorbent materials for particularly effective and economical iodine retention. In a preferred configuration, the filter chamber may also contain in addition to the iodine sorbent filter further filter devices and retention devices, for instance for retaining chlorine-containing and/or nitrous gases and/or oil-containing compounds. For this purpose, sand-bed filters may be provided for example, and possibly the injection or charging of suitable chemicals. In addition, further short-term gas superheating can be achieved here in certain operating phases by specific partial adsorption of water vapor on the aforementioned zeolites (increase of the moisture by for example <2 percent by weight through sorption), and in this way the desired continuous organoiodine retention can be ensured. This is of interest in particular in start-up operation (known as start-up adsorption). To limit the temperatures in the occurrence of moisture, furthermore, a selective limitation of the catalytic activity of these sorption agents, for example by way of diffusion layers or mixed doping (for instance with silver cations and/or heavy-metal cations) and possibly with non-catalytic additives, can also be performed. As already indicated further above, during start-up operation of the depressurization system—at operating temperatures which are still comparatively low—at least partial vapor adsorption is advantageously permitted in the sorbent filter and the adsorption heat is used for superheating the depressurization flow and the sorbent filter. However, this is only meaningful if the sorbent filter is sufficiently insensitive to moisture, that is to say for example is configured on a zeolite basis with non-soluble doping. In a second main variant of the method, which is based on the presence of a washing tank for the wet filtering of the depressurization flow in the high-pressure section, the washing liquid is conducted out from the washing tank through a circulation line, at least a portion of which is in thermal contact with the filter chamber and heats the latter by heat transfer from the circulating washing liquid. That is to say from an apparatus viewpoint that a circulation line for the circulation of washing liquid is connected to the washing tank, the circulation line being taken past the filter chamber and being in thermal contact with it, with the result that a heat transfer takes place from the circulating washing liquid to the filter chamber. This therefore means that the amount of heat entrained by the venting gas flow in the high-pressure section of the depressurization line is in large part transferred in the washing tank to the washing liquid, which then circulates through the filter chamber or past it, whereby a renewed heat transfer takes place for the heating of the filter chamber with the sorbent filter and/or for the superheating of the depressurization flow depressurized by the throttle immediately before it enters the sorbent filter. It is particularly preferred if the depressurization flow depressurized by the throttle in the superheating section is in thermal contact with the circulation line and is heated by heat transfer from the circulating washing liquid. For this purpose, the superheating section of the depressurization line is thermally coupled to the circulation line via heat-exchanger surfaces, with the result that a heat transfer takes place there from the circulating washing liquid to the depressurization flow. In a preferred configuration, the flow of the washing liquid through the circulation line is driven by the impulse transferred from the depressurization flow to the washing liquid in the washing tank. For this purpose, at least one of the inflow nozzles is aligned in a suitable way, for instance directed toward the inlet of the circulation line, such that the impulse of the depressurization flow flowing through it that is transferred to the washing liquid drives the circulation of the washing liquid through the circulation line. Alternatively or in addition, however, corresponding motor-driven pumps may also be provided, in order to drive or assist the circulation flow. Advantageously, the circulation line has a washing liquid inlet, opening into the washing tank, and a washing liquid outlet, lying higher in relation to the washing liquid inlet and likewise opening into the washing tank. In this way, after flowing through the circulation line, the washing liquid removed from the washing tank is returned to the washing tank at a geodetically higher point. The washing liquid is preferably removed from the washing tank at a point at which the content of gas bubbles in the depressurization flow is particularly high, that is to say for example in the discharge region of the inflow nozzles. In a preferred configuration, a central chamber which surrounds or adjoins the filter chamber is provided, the circulating washing liquid being conducted through heat-exchanger elements arranged in the central chamber or protruding into it, in particular heat-exchanger tubes, and the depressurization flow in the superheating section being conducted through the central chamber externally past the heat-exchanger elements. The washing liquid flowing through the heat-exchanger tubes therefore gives off a large part of its heat content to the low-pressure depressurization flow flowing externally past the tubes, which is thereby superheated before it enters the filter chamber. In addition, before it enters the filter chamber, the low-pressure depressurization flow superheated in this way gives off a smaller part of its heat content to the further out filter chamber, which is thereby preheated to a certain extent. Furthermore, it is favorable if the low-pressure depressurization flow in the central chamber is conducted in counterflow or cross-counterflow with respect to the washing liquid flowing through the heat-exchanger elements. Furthermore, it is advantageously provided that the depressurization flow flows through the central chamber with a vertical main direction of flow from top to bottom and the washing liquid flows through the heat-exchanger elements with a vertical main direction of flow from bottom to top. A flow rate of the washing liquid in the circulation line of over 1 m/s, preferably of over 3 m/s, is preferably set, such that deposits from the washing liquid can be largely avoided and a particularly effective heat transfer is accomplished. In other words: the washing liquid serving as a heat transfer medium is driven by the impulse of the high-speed introduction of venting gas. The washing liquid is thereby removed from the washing tank close to where the venting gas is introduced and is transported through pipes into the heat exchanger of the heat-exchanger/sorbent-filter unit and subsequently back again into the pool of the washing tank. Specifically by selective removal of a liquid mixture containing more venting gas (containing bubbles) and conducting it in a rising manner through the heat exchanger device, the drive is further intensified on account of the lower density in comparison with the density of the (bubble-free) washing liquid in the pool of the washing tank, in particular if it is reintroduced at a geodetically higher point. The removal in the hottest zone of the scrubber, with a content of air and vapor bubbles, and the condensation of vapor bubbles during the heat transfer allow the temperature level to be increased further and the temperature difference in the heat exchange to be minimized further. The return into the washing tank preferably takes place above the sedimentation zone. It should also be noted that the statements made above in connection with the first main variant of the method/the device with regard to the filter materials and the temperature conditions at the sorbent filter, with regard to the pressure conditions and the flow rates in the lines carrying venting gas, with regard to the configuration of the washing tank and the inflow nozzles arranged therein, and with regard to the optionally provided components containing the gas dryer, blower, additional filter, etc., also readily apply to the second main variant, and therefore do not have to be repeated in detail at this point. The first and second main variants of the method and of the associated depressurization device may also be combined with one another, to be precise in particular in the sense that a heating of the filter chamber with the sorbent filter and/or of the depressurized depressurization flow in the superheating section is possible both directly by way of the depressurization flow in the high-pressure section (“dry”) and indirectly by way of the washing liquid (“liquid/wet”). For example, the structural design may be such that, at least in certain operating situations, heating takes place simultaneously in both ways (i.e. both “dry” and “liquid”), but in other operating situations, such as depending on the filling level of the washing liquid in the washing tank, only takes place in one of the two ways. In a further development of the concept, means for actively and deliberately switching over from one mode to the other are provided. Specifically in the case of the aforementioned combination of various heating concepts, but also in other cases, the washing tank and the heat-exchanger/sorbent-filter unit, possibly also only parts of the same, for instance the heat exchanger, may be structurally united or integrated in a common component. An example of this is explained in the detailed description of the figures. It is accordingly provided according to the invention that the depressurization line has between the throttle device and the filter chamber inlet a superheating section, which is thermally coupled to the high-pressure section via heat-exchanger surfaces, these heat-exchanger surfaces being dimensioned in such a way that the depressurization flow established under design-basis accident conditions in the superheating section is heated to a temperature which is at least 10° C., preferably 20° C. to 50° C., above the dew-point temperature present there. Further advantageous configurations of the device have already been described further above or follow analogously from the description of the corresponding method steps. The advantages achieved by the invention consist in particular in that a relevant coating of the reaction surfaces with water vapor and blocking by way of capillary condensation are reliably prevented by way of a selective superheating of the depressurization flow before it enters the iodine sorbent filter in the sorbent both in the macro-pore region and in the micro-pore region. The passive-regenerative configuration of the superheating process with heat recovery from the high-pressure region allows the method also to be used when there is a complete energy failure (“station blackout”) in the nuclear power plant to be depressurized. Furthermore, the decidedly high gas superheating of >10° C., preferably >20° C., for example in the temperature level from >120° C. to 170° C. and more (when there are high throughput rates and high gas superheating in the initial phase of the depressurization process), brings about a significant increase in the reaction rates in the iodine sorption filter. The then almost unlimitedly available, very great internal reaction surfaces and the improved diffusion succeed in achieving a passive, highly effective iodine sorption filtering, including for organoiodine compounds, with retention rates of >97%, preferably >99%. A resuspension (re-release) of the iodine from the iodine sorbent filter can be largely avoided by the chemical binding of the iodine and by the permanent heating of the iodine sorbent filter. The highly effective wet filtering of the depressurization flow in the high-pressure region, possibly in conjunction with further filter devices, in particular a metallic prefilter and/or a dry filter on a sand-bed or gravel-bed basis, consequently makes it possible for the first time for the active gases or vapors occurring in the containment in accident situations to be discharged to the surroundings after being filtered with an organoiodine retention of >99% to 99.9%—for ultimate pressure limitation in the containment. In this case, other air-borne activities and aerosols are also reliably retained in the filter system, even when venting operation continues over several days. 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 depressurizing a nuclear power plant, depressurization system for a nuclear power plant, and associated nuclear power plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Parts that are the same or have the same effect are provided with the same designations in all the figures. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a nuclear power plant 2 represented in the form of a detail has an outer containment shell 4, which is also referred to as a containment and has a massive reinforced-concrete shell. The containment shell 4 encloses an interior space 6. Arranged in the interior space 6 are the major nuclear components of the nuclear power plant 2, such as for instance the reactor pressure vessel with the reactor core and also further nuclear and non-nuclear plant components (not represented). The reinforced-concrete shell of the containment shell 4 is lined on its inside with a steel casing. The containment shell 4 forms a hermetic seal for the interior space 6 from the outside world and, in the unlikely event of an accident involving the release of radioactively charged gases or vapors, has the effect of retaining and containing them in the interior space 6. The containment shell 4 is configured for withstanding even comparatively high internal pressures of for example 3 to 8 bar in the interior space 6, as could occur for instance in accident situations involving a massive release of vapor, and at the same time remaining sealed over a relatively long period of time. At the same time, to increase the reactor safety further, and also to make the interior space 6 accessible again after an accident, a depressurization system 8 is provided, with the aid of which the gases and vapors contained in the interior space 6 can be blown out into the surroundings after being filtered and cleaned, and to the greatest extent free of any activity, with the result that a controlled reduction of pressure in the interior space 6 is made possible. The corresponding process is also referred to as venting. The depressurization system 8 is configured in the present case for particularly effective and low-energy retention of activity carriers contained in the venting gas, in particular of elemental iodine and iodine-containing organic compounds of a low carbon number (known as organoiodine). For this purpose, the depressurization system 8 contains a depressurization line 12, which is connected to an outlet 10, or to a penetration through the containment shell 4, and connected into which there are one behind the other, inter alia, a washing tank 14 and, further downstream, a sorbent filter 18, arranged in a filter chamber 16, to be specific an iodine sorbent filter. Further downstream, the filtered depressurization flow is blown out into the surrounding atmosphere via a flue 20 or chimney, generally a blow-out opening. The direction of flow of the depressurization flow is respectively indicated by arrows. As can be seen in FIG. 1, the depressurization line 12 may also contain an inner line section 22, which lies inside the containment shell 4 and into which there is optionally connected a prefilter 24, in particular a metal prefilter, for retaining the coarse aerosols. For bypassing the prefilter 24 if need be, a bypass line 26 connected parallel to it is provided and can be opened or closed as and when required by a control valve 28. One or more shut-off valves 30, which are connected into the depressurization line 12 and are closed during the normal operation of the nuclear power plant 2, may be arranged outside the containment shell 4, as can be seen in FIG. 1, alternatively or in addition also inside the containment shell 4. In order to initiate the depressurizing process in the event of an accident involving an increase in pressure in the interior space 6, the respective shut-off valve 30 is opened, which preferably takes place automatically and without the use of external energy, for instance by way of a pressure-dependent triggering device. For setting operating conditions that are as optimum as possible with regard to the filtering objective on the sorbent filter 18, a series of technical measures are provided. On the one hand, the depressurization flow (venting gas flow) coming from the interior space 6 of the containment shell 4 and under comparatively high pressure is conducted through a washing liquid 32 in the washing tank 14 and thereby cleaned, in particular freed of coarse aerosols. For this purpose, in the standby state of the depressurization system 8, the washing liquid 32 is kept in the washing tank 14 at a minimum filling level 34. For the chemical conditioning of the washing liquid 32, in particular for improving the filtering and retaining properties, suitable reagents, for example sodium thiosulfate solution, may be fed into the washing liquid 32 via a metering device 36 that is only schematically indicated here. In venting operation, that is to say in the case of depressurization, the depressurization flow is conducted via the line section 38 of the depressurization line 12 into the washing tank 14 and leaves via a manifold 40, and subsequently a plurality of inflow nozzles 42 connected in parallel in terms of flow. The inflow nozzles 42 are located below the minimum filling level 34 in what is known as the washing liquid pool 44, pool for short, of the washing tank 14 and are configured here as venturi nozzles. For this purpose, the respective inflow nozzle 42 has a partly narrowing venturi tube 46, an annular-slit feed (not represented) for the surrounding washing liquid 32 being provided at the construction, which is also referred to as a throat. The depressurization flow flowing through the venturi tube 46 during venting operation consequently entrains washing liquid 32 entering at the throat. Therefore, an intimately swirled-together washing-liquid/venting-gas mixture is discharged from the upwardly directed outlet openings 48 of the inflow nozzles 42, the contaminants and aerosols contained in the venting gas flow largely being adsorbed in the washing liquid 32. In the discharge zone 50 located above the washing liquid pool 44, the liquid and gaseous components of the washing-liquid/venting-gas mixture are separated again by gravitational force. The washing liquid 32, possibly augmented with condensate from the venting gas flow and enriched with aerosols and contaminants (particles, soluble gases) sinks back down into the washing liquid pool 44. Excess washing liquid 32 or condensate is carried away if need be via a liquid-discharge line 54, which is connected to the bottom of the washing tank 14 and is provided with a shut-off valve 52, with the result that the liquid level in the washing tank 14 does not exceed a predetermined maximum filling level 56. Once it has passed through moisture separators 58 and possibly further filter elements 60 arranged above the discharge zone 50 and above the maximum filling level 56, the venting gas cleaned by the washing process and still under high pressure leaves the washing tank 14 upwardly via the outlet opening 62 and enters the downstream line section 64 of the depressurization line 12. On the other hand, during depressurizing operation, the filter chamber 16 with the sorbent filter 18 is itself preheated via associated heat-exchanger surfaces 66, 68, by the depressurization flow coming from the line section 64, which has previously been cleaned in the washing tank 14, is still approximately (at least in terms of the order of magnitude) at the level of the pressure in the interior space 6 of the containment shell 4 and is comparatively hot. Only after the heat dissipation and transfer in the high-pressure section 70 of the depressurization line 12 is the depressurization flow depressurized in a further downstream throttle valve, throttle 72 for short, to approximately (at least in terms of the order of magnitude) ambient pressure and thereby dried. The part of the depressurization line 12 that is upstream of the throttle 72 forms the high-pressure section 70, the part that is downstream forms the low-pressure section 74. Following the expansion drying by way of the throttle 72, the depressurization flow is conducted through an (optional) additional gas dryer 76 with an associated condensate separator and condensate-collecting tank 78. Further downstream, the depressurization flow in the low-pressure section 74 of the depressurization line 12 is conducted past the high-pressure section 70 in such a way that heat transfer from the gas flow in the high-pressure section 70 to the gas flow in the low-pressure section 74 takes place on corresponding heat-exchanger surfaces 68 of a superheating section 80. Only after the superheating brought about as a result is the depressurized depressurization flow conducted through the filter chamber 16 with the sorbent filter 18. The thermal energy contained in the not yet depressurized depressurization flow in the high-pressure section 70 is therefore used in two ways: on the one hand, a heating of the filter chamber 16 with the sorbent filter 18 contained therein takes place via the heat exchanger surfaces 66, 68. On the other hand, a superheating of the depressurized depressurization flow takes place via the heat-exchanger surfaces 68 immediately before it enters the filter chamber 16. In this case it is ensured by suitable dimensioning and design of the flow-carrying and heat-conducting components, and possibly by suitable setting of the throttling cross section of the throttle 72 and further operating parameters, that the depressurization flow in the superheating section 80, that is to say immediately before entry into the filter chamber 16, is heated to a temperature which lies at least 10° C. above the dew-point temperature present there, in the full-load operation of the depressurization system 8 even at least 20° C. above it. The combination of these two measures reliably avoids condensation of the depressurization flow in the filter chamber 16, which could lead to an impairment of the efficiency or even to permanent destruction of the sorbent filter 18. FIG. 2 shows in somewhat more detail an actual configuration of the heat-exchanger/sorbent-filter unit 82 containing the heat-exchanger surfaces 66 and 68. The filter chamber 16 is configured as an annular chamber, which surrounds the, for example cylindrical or cuboidal, central chamber 84 in an annular and, in particular, coaxial manner. The longitudinal axis of the heat-exchanger/sorbent-filter unit 82 is vertically aligned. The filter chamber 16 and the central chamber 84 are separated from each other—at least in a lower region—in a gas-tight manner by a highly heat-conducting separating wall 86. The filter chamber 16 is for its part divided by filter elements 88 arranged in it in an annular manner into an inner inflow space 90, inwardly bounded by the separating wall 86, and an outer outflow space 92. As an alternative to the annular chamber type of construction, a plain box type of construction may also be provided, a cuboidal central chamber 84 being adjoined for example on one side by a cuboidal filter chamber 16 separated by a straight separating wall 86. Of course it is also possible for a central chamber 84 to be assigned a number of filter chambers 16, which are separate from one another and are then connected in parallel in terms of flow with respect to the depressurized depressurization flow in the low-pressure section 74. The line section 64 of the depressurization line 12 leading away from the washing tank 14, as seen in the direction of flow of the depressurization flow, is connected to a system of heat-exchanger tubes 98 connected in parallel in terms of flow and provided with fins 96 on their outside, and possibly also on their inside, arranged in the interior space 94 of the central chamber 84 (the heat-exchanger tubes 98 are drawn in half-perspective in the end regions, in between are only represented as simple lines). For this purpose, at the end of the line section 64, the depressurization line 12 is taken through a housing aperture 102, which is arranged in the cover housing 100 of the central chamber 84 and closed in a gas-tight manner on its outside, into the central chamber 84 and connected to the heat-exchanger tubes 98, possibly via a branching piece 104. Alternatively, plate heat exchangers or other heat-exchanger elements may also be provided. The heat-exchanger tubes 98 are led in a meandering manner from top to bottom in the interior space 94 of the central chamber 84, into the bottom region 106, where they come together again in a header 108. Connected to the header 108 downstream is a pipeline 114, which is taken through a further housing aperture 110 of the central chamber housing 112 and opens out into the line section 116 of the depressurization line 12 that leads to the throttle 72. The line section 118 of the depressurization line 12 that leads away from the throttle 72 returns into the central chamber 84 after the optionally provided gas dryer 76. The central chamber 84 therefore has in the bottom region 106 a central chamber inlet 120, to which the line section 118 coming from the throttle 72 or from the gas dryer 76 is connected (also see FIG. 1). Provided at the upper end of the central chamber 84, in the vicinity of the cover housing 100, are a plurality of through-openings 122, which penetrate the separating wall 86, lead from the interior space 94 of the central chamber 84 into the inflow space 90 of the filter chamber 16 and consequently together form the filter chamber inlet 124. The outflow space 92 of the filter chamber 16 is connected to the line section 130 of the depressurization line 12 that leads to the flue 20 via the filter chamber outlet 128, which is arranged downstream of the filter elements 88 on the outside of the filter chamber housing 126, for example in the bottom region thereof or else at another point (in FIG. 2, two outlet openings connected in parallel in terms of flow along with associated line connections are provided, and may be brought together again further downstream in a way that is not represented). In this way, the depressurization flow in the line section 64, coming from the washing tank 14, is under high pressure and is comparatively hot, is conducted via the housing aperture 102 into the central chamber 84 and flows through the heat-exchanger tubes 98 arranged therein with a main direction of flow pointing substantially vertically from top to bottom. Subsequently, the venting gas is conducted via the line section 116 to the throttle 72, dried by expansion and then conducted through the gas dryer 76. The depressurized gas flow enters the central chamber 84 again via the line section 118. It is conducted in counterflow or cross-counterflow with respect to the high-pressure depressurization flow in the heat-exchanger tubes 94 substantially from bottom to top past the heat-exchanger tubes 98, to pass finally via the through-openings 122 of the filter chamber inlet 124 into the filter chamber 16, where the desired organoiodine filtering and retention take place. When it flows through the heat-exchanger tubes 98, a heat transfer takes place from the hot high-pressure depressurization flow in the heat-exchanger tubes 98 to the surrounding low-pressure depressurization flow that is conducted in counterflow past the heat-exchanger tubes 98, depressurized by the throttle 72 and dried. The tube walls of the heat-exchanger tubes 98 thereby form the heat-exchanger surfaces 68 of the superheating section 80 formed by the interior space 94 of the central chamber 84, in which the superheating already described above of the depressurized depressurization flow takes place before it enters the inflow space 90 of the filter chamber 16 in the superheated state via the filter chamber inlet 124 formed by the through-openings 122, subsequently flows through the filter elements 88 and finally reaches the flue 20 in a filtered state via the outflow space 92, the filter chamber outlet 128 and the line section 130. At the same time, a heat transfer takes place—usually to a lesser extent—via the highly heat-conducting separating walls 86 that effectively act as heat-exchanger surfaces 66, from the low-pressure depressurization flow heated up in this way to the filter chamber 16, which as a result is likewise correspondingly heated. To improve the heat transfer, the heat-exchanger tubes 98 may also be suitably structured in their interior, for example provided with fins or have other internal fittings that generate turbulence or a swirling flow. The depressurization system 8 according to FIG. 1 is also configured for the purpose that, if need be, a partial flow of the depressurization flow in the high-pressure section 70 can be conducted past the heat-exchanger/sorbent-filter unit 82, that is to say does not flow through the heat-exchanger tubes 98, the throttle 72, the central chamber 84 and the filter chamber 16. This bypass partial flow consequently does not contribute to the superheating of the low-pressure depressurization flow in the superheating section 80 and to the heating of the filter chamber 16. For this purpose, at the branching point 142 downstream of the washing tank 14 and upstream of the heat-exchanger tubes 98, a bypass line 144 is connected to the line section 64 of the depressurization line 12, and opens out again into the depressurization line 12, to be specific into the line section 130, at the opening point 148 downstream of the filter chamber outlet 128. For setting the conditions of the partial flow, suitable adjusting and controlling devices (not represented) may be provided. Furthermore, a pressure-reducing valve 150 may be connected into the bypass line 144 for adapting the pressure level. Condensate 132 forming as the flow passes through the heat-exchanger tubes 98 may be removed if need be by way of a condensate-discharge line 134 branching off from the pipeline 114 of the line section 116, and be conducted for example to a condensate-storage tank. As represented in FIG. 1, the condensate-discharge line 134 may be brought together with the liquid-discharge line 54 from the washing tank 14. The filter elements 88 of the sorbent filter 18 are preferably produced from materials sorbing iodine and organoiodine, for example from binder-free zeolites with an open structure, that is to say an open-pore system, and with silver doping that is non-soluble in wet operation. If the occurrence of moisture in the sorbent filter 18 can be reliably ruled out in all operating states of the depressurization system 8, for instance by correspondingly designing the superheating capacity in the superheating section 80, zeolites with a silver-nitrate doping or coating, the retaining effect of which for organoiodine has surprisingly been found to be particularly high with a sufficiently high dew-point difference of the depressurization flow, may alternatively also be provided as filter materials, or at least admixed. For reliable control over particular operating states, for instance during start-up operation, an additional heating device 136, which is operated with an external energy source (for example electrically), is optionally thermally coupled to the depressurization line 12. Here in FIG. 2, it is arranged for example in/on the central chamber 84 of the heat-exchanger/sorbent-filter unit 82, alternatively or in addition in the filter chamber 16, in particular in the inflow space 90 thereof. It goes without saying that other mounting locations are also conceivable. Furthermore, devices for vacuum restriction 138 may be provided for example in the line section 38 between the outlet 10 from the containment shell 4 and the washing tank 14. This is used to avoid or quantitatively restrict the formation of a vacuum in the containment shell 4, for example after venting and subsequent partial condensation of the vapor that is present (for example by activating a spray system or other cooling system) by way of air-intake suction into the containment shell 4 as and when required. For an active extraction of the gas-vapor mixture located in the containment shell 4, a suction blower 140, which is supplied with driving energy by way of an external energy source, may be optionally connected into the depressurization line 12, for example upstream of the washing tank 14, but preferably downstream of the sorbent filter 18, or able to be activated if need be. The suction blower 140 is advantageously designed such that, in combination with a low water coverage of the inflow nozzles 42 and comparatively low nozzle speeds (<50 m/s), here only a coarse aerosol precleaning takes place, but it is subsequently possible for optimum speeds to be set in the downstream filter devices, with less than ¼ of the maximum throughput. It is thereby possible to bring the interior space 6 of the containment shell to a (slight) subatmospheric pressure with respect to the ambient atmosphere, and keep it at this subatmospheric pressure, and consequently to avoid external leakages completely. In the case of an alternative configurational variant that is likewise represented in FIG. 1, there is no need for the washing tank 14 (set up outside the containment shell 4) in the case of a boiling-water reactor. Instead, a wet filtering of the depressurization flow leaving the containment shell 4 takes place while it is still inside the containment shell 4, in a condensation chamber 152 located there. The condensation chamber 152 is separated from the remaining interior space 6 in the containment shell 4 by way of a gas-tight and pressure-stable separating wall 154. A connection in terms of flow between the two spatial regions is realized only by way of one or more overflow pipes 156, which are immersed in the condensate liquid 158 that is present in the condensation chamber 152. That is to say that the outflow opening 160 of the respective overflow pipe 156 is located below the minimum filling level 162 of condensate liquid 158. The depressurization line 12′ (drawn here with dashed lines) is in this case connected to a condensation chamber outlet 164, which is arranged above the maximum filling level in the gas-collecting space 170 lying above the condensate liquid 158. In the example shown here, the condensation chamber outlet 164 coincides with the outlet 10′ from the containment shell 4. The depressurization line 12′ is led from the outlet 10′ directly to the heat-exchanger/sorbent-filter unit 82 without a scrubber being interposed. Finally, it should be mentioned that the depressurization system 8 may have a number of strands of the same or similar type of construction that are connected in parallel in terms of flow. It is also possible for only individual sections of the depressurization line 12 to be duplicated by connecting identical components in parallel. It may be advisable in this case to set up a number of the heat-exchanger/sorbent-filter units 82 that are represented in FIG. 2 in the manner of a modular system directly adjoining one another and thermally coupled to one another, to be precise preferably with an alternating arrangement of for example box-shaped central chambers 84 and corresponding filter chambers 16. This is illustrated in FIG. 3. Also in the case of the variant of the depressurization system 8 that is represented in FIG. 4, the depressurization flow coming from the containment shell 4 is initially cleaned in a washing tank 14, depressurized further downstream at a throttle 72, possibly dried in a gas dryer 76, then conducted through a superheating section 80, in which a regenerative heating takes place, and finally conducted through the filter chamber 16 with the sorbent filter 18, before it is blown out into the surroundings via the flue 20. As in the case of the variants described above, a comparatively high dew-point difference of at least 10° C., preferably at least 20° C., is ensured in full-load operation by the superheating of the depressurization flow immediately before it enters the filter chamber, in order to prevent condensing out in the region of the sorbent filter 18, and in order to achieve particularly effective retention of iodine-containing activity carriers. As a difference from the variants described above, in the case of the system according to FIG. 4 the thermal energy required for the superheating of the low-pressure depressurization flow and for the heating of the filter chamber 16 is not transferred directly from the high-pressure depressurization flow. Rather, here the washing liquid 32 that is kept in the washing tank 14, and is for its part heated by the inflowing high-pressure depressurization flow, is used as a heat-transporting and heating medium. For this purpose, the inlet end 118 of a circulation line 182 is connected to the washing tank 14 in the lower region of the washing liquid pool 44, that is to say for example well below the minimum filling level 34. The outlet end 184 of the circulation line 182 is connected to the washing tank 14 at a geodetically higher point than the inlet end 180, for instance as represented here just below the minimum filling level 34 or else somewhat higher in the discharge zone 50. During venting operation—driven by the flow impulse of the venting gas flow flowing into the washing tank 14 through the inflow nozzles 42—the circulation line 182 is flowed through in the direction of flow 186 by a (bubble-containing) washing-liquid/venting-gas mixture. The washing liquid 32 mixed with the venting gas is consequently removed from the washing tank 14 at a comparatively low point and—after an interposed rising section 188—is circulated back into it again at a higher point in the manner of a washing liquid circuit. For particularly good utilization of the driving pulse, at least one of the inflow nozzles 42 is in this case aligned with the inlet end 180 of the circulation line 182, that is to say is directed (obliquely) downward here. The circulation is in this case assisted in accordance with the principle of natural circulation by the differences in density between the (clean) washing liquid 32 and the (bubble-containing) washing-liquid/venting-gas mixture. In the rising section 188 of the circulation line 182, the circulating washing liquid 32, mixed with venting gas, is conducted from bottom to top through a number of heat-exchanger tubes 98 connected in parallel in terms of flow (or else other heat-exchanger elements), which are arranged in approximately vertical alignment within the central chamber 84 of the heat-exchanger/sorbent-filter unit 82. The depressurization flow in the line section 192 of the depressurization line 12, coming from the washing tank 14 via the throttle 72 and the gas dryer 76 and cleaned in the wet filtering, is in turn conducted through the central chamber 84 in counterflow with respect to the washing liquid 32 circulating through the heat-exchanger tubes 98, i.e. from top to bottom, externally past the heat-exchanger elements 98. The depressurization flow flows through the central chamber 84 before it passes over into the filter chamber 16 with the sorbent filter 18 by way of through-openings 122 arranged in a lower region in the separating wall 86 between the central chamber 84 and the filter chamber 16 and forming the filter chamber inlet 124 (the filter chamber inlet 124 will generally be further down, in the region of the bottom of the separating wall 86, than how it is represented here in the purely schematic FIG. 4). By analogy with the variant described in conjunction with FIG. 1 and FIG. 2, the tube walls of the heat-exchanger tubes 98 and the separating wall 86 consequently form heat-exchanger surfaces 66 and 68 for a heat transfer from the circulating washing liquid 32 to the low-pressure depressurization flow on the one hand and the filter chamber 16 on the other hand. The section of the central chamber 84 that is flowed through by the low-pressure depressurization flow thereby forms the superheating section 80, which in terms of flow is connected directly upstream of the filter chamber 16. Finally, a further variant of the depressurization system 8 is represented in the form of a detail in FIG. 5. It contains a combined scrubber/heat-exchanger/sorbent-filter unit 200. Conceptually, it can be imagined that, for this purpose, the washing tank 14 and the heat-exchanger/sorbent-filter unit 82 of the depressurization system 8 according to FIG. 1 are arranged and integrated in a common housing 202. In actual fact, the scrubber/heat-exchanger/sorbent-filter unit 200 represented in longitudinal section in FIG. 5 contains a washing region 206, which is arranged in the lower section of the housing 202 and is filled with washing liquid 32, at least up to a minimum filling level 204. A depressurization flow taken from the containment shell of a nuclear power plant is conducted to a plurality of inflow nozzles 42 connected in parallel in terms of flow, via a pipeline 208, which is led through a housing aperture, and a manifold 40 adjoining in terms of flow. When it leaves into the washing liquid pool 44, the venting gas flow is subjected to a wet filtering, entirely analogous to the washing tank 14 known from FIG. 1. Following separation of the washing-liquid/venting-gas mixture, the venting gas flow, cleaned and freed of coarse aerosols and under high pressure, flows through the central space 210 and further upwardly adjoining flow channels or corridors 212 and 214, which are partly taken past the outer annular filter chamber 16 and are in thermal contact with it, up to the cover region 216 of the housing 202, is deflected there and enters moisture separators 58 and filter elements 60 via flow channels 218. For more intensive preheating, a partial flow of the high-pressure depressurization flow may be removed via an additional heating device 228 and, while bypassing the downstream heat-exchanger tubes 98 (see below), conducted directly through the sorbent filter 18 or the upstream region. On the downstream side of the respective filter element 60, the depressurization flow is fed via a flow channel 220 in the downward direction to a throttle 72 and depressurized there. In the adjoining low-pressure section, the depressurized venting gas flows initially further down through a plurality of heat-exchanger tubes 98 connected in parallel in terms of flow, is forced into a reversal of direction in the reversing sections 222, by a suitable contouring of the flow-conducting elements, and flows through adjoining heat-exchanger tubes 98, lying in series in terms of flow and geometrically parallel to the downwardly leading heat-exchanger tubes 98, back up to the through-openings 128 into the filter chamber 16, forming the filter chamber inlet 124. The filter chamber is constructed in a way analogous to the filter chamber 16 in the case of the device according to FIG. 1 or FIG. 2. The depressurization flow filtered in the sorbent filter 18 leaves via the filter chamber outlet 128 into a pipeline leading to a flue (not represented here). A heating of the filter chamber 16 takes place via the flow channels 214 for the high-pressure depressurization flow that are taken past the filter chamber 16. The heat-conducting separating walls 86 between the flow channels 214 and the filter chamber 16 thereby form heat-exchanger surfaces 66. Furthermore, the tube walls of the heat-exchanger tubes 98 form heat-exchanger surfaces 68 between the comparatively hot high-pressure depressurization flow flowing through the central space 210 and the low-pressure depressurization flow, to be superheated to a dew-point difference of at least 10° C., preferably more than 20° C., before it enters the filter chamber 16, in the heat-exchanger tubes 98. The heat-exchanger tubes 98 consequently represent the superheating section 80 for the depressurization flow previously depressurized at the throttle 72. In the case of the operating state represented in FIG. 5, the liquid level 224 of the washing liquid 32 lies approximately in the region of the minimum filling level 204, and consequently below the reversing sections 222 and the heat-exchanger tubes 98 lying above them. The heat-exchanger tubes 98 are therefore exclusively, or at least predominantly, “dry”-heated by the high-pressure depressurization flow conducted externally past them that has previously been cleaned in the washing liquid pool 44. With a greater filling level, and consequently a liquid level 224 that is further up in the region of the heat-exchanger tubes 98, on the other hand, a partial or even complete “wet” heating of the heat-exchanger tubes 98 is also possible by way of the washing liquid 32, which for its part is heated by the venting gas flowing in via the inflow nozzles 42. The admissible maximum filling level 226 lies just below the moisture separators 58 or filters 60. 2 Nuclear power plant 4 Containment shell 6 Interior space 8 Depressurization system 10, 10′ Outlet 12, 12′ Depressurization line 14 Washing tank 16 Filter chamber 18 Sorbent filter 20 Flue 22 Line section 24 Prefilter 26 Bypass line 28 Control valve 30 Shut-off valve 32 Washing liquid 34 Minimum filling level 36 Metering device 38 Line section 40 Manifold 42 Inflow nozzle 44 Washing liquid pool 46 Venturi tube 48 Outlet opening 50 Discharge zone 52 Shut-off valve 54 Liquid-discharge line 56 Maximum filling level 58 Moisture separator 60 Filter element 62 Outlet opening 64 Line section 66 Heat-exchanger surface 68 Heat-exchanger surface 70 High-pressure section 72 Throttle 74 Low-pressure section 76 Gas dryer 78 Condensate-collecting tank 80 Superheating section 82 Heat-exchanger/sorbent-filter unit 84 Central chamber 86 Separating wall 88 Filter element 90 Inflow space 92 Outflow space 94 Interior space 96 Fins 98 Heat-exchanger tube 100 Cover housing 102 Housing aperture 104 Branching piece 106 Bottom region 108 Header 110 Housing aperture 112 Central chamber housing 114 Pipeline 116 Line section 118 Line section 120 Central chamber inlet 122 Through-opening 124 Filter chamber inlet 126 Filter chamber housing 128 Filter chamber outlet 130 Line section 132 Condensate 134 Condensate-discharge line 136 Additional heating device 138 Vacuum restriction 140 Suction blower 142 Branching point 144 Bypass line 148 Opening point 150 Pressure-reducing valve 152 Condensation chamber 154 Separating wall 156 Overflow pipe 158 Condensate liquid 160 Outflow opening 162 Minimum filling level 164 Condensation chamber outlet 170 Gas-collecting space 180 Inlet end 182 Circulation line 184 Outlet end 186 Direction of flow 188 Rising section 192 Line section 200 Scrubber/heat-exchanger/sorbent-filter unit 202 Housing 204 Minimum filling level 206 Washing region 208 Pipeline 210 Central space 212 Flow channel 214 Flow channel 216 Cover region 218 Flow channel 220 Flow channel 222 Reversing section 224 Liquid level 226 Maximum filling level 228 Heating device\ |
|
description | This application is a divisional application of U.S. application Ser. No. 11/674,262, filed Feb. 13, 2007, now U.S. Pat. No. 7,700,931 and which application claims priority from Japanese application JP 2006-072600 filed on Mar. 16, 2006, the contents of which are hereby incorporated by reference on to this application. The present invention relates to a manufacturing technology for electronic parts such as semiconductor devices. More particularly, the present invention is concerned with an ion beam processing technology for processing a section of a sample with an ion beam, or for processing a sample so as to separate a micro test piece from the sample or make preparations for the separation. Manufacture of electronic parts such as semiconductor memories represented by a dynamic random access memory (DRAM), microprocessors, semiconductor devices including a semiconductor laser, and magnetic heads is requested to offer a high yield. This is because a decrease in the yield derived from production of a defective invites degradation of cost-effectiveness. Therefore, it is a critical problem how a defect or a foreign matter causing a defective or an imperfectly processed good is discovered in an early stage and what measures are taken. For example, at a site of manufacturing an electronic part, efforts are made to discover a defective by performing close inspection and to analyze the cause of occurrence of the defect. In an actual electronic part manufacturing process in which wafers are treated, a wafer that is being processed is inspected in order to track down the cause of an abnormality such as a defect in a circuit pattern or a foreign matter, and a countermeasure is discussed. Normally, a scanning electron microscope (SEM) offering a high resolution is used to observe an abnormality in a sample. In recent years, a complex FIB-SEM machine that uses a focused ion beam (FIB) in combination with the SEM has been employed. In the FIB-SEM machine, the FIB is irradiated in order to form an angular hole in a desired region so that the section can be observed using the SEM. For example, Japanese Patent Application Laid-Open No. 2002-150990 has proposed an apparatus that forms a rectangular hole near an abnormality in a sample using the FIB, observes the section of the rectangular hole using the SEM, and thus observes or analyzes a defect or a foreign matter. Moreover, PCT International Publication WO99/05506 has proposed a technology for extracting a micro test piece, which is to be observed using a transmission electron microscope (TEM), from a bulk sample using the FIB and a probe. Moreover, Japanese Patent Application Laid-Open No. 2000-156393 has proposed a technique of extracting a micro test piece to be inspected from a wafer without breaking the wafer, and returning the wafer, from which the micro test piece is extracted, to a production line. According to the technique, a progress in a machining process is monitored using a monitor, and a wafer is inspected or analyzed. Moreover, Japanese Patent Application Laid-Open No. 7-320670 has proposed a technology for processing a sample, which is to be observed using the SEM, with an argon ion beam whose beam spot has a diameter of 0.1 μm and which is generated by a helicon wave ion source. The technology for processing a sample with an ion beam so as to form a section and observing the section using an electron microscope, or the technology for separating a micro test piece from a sample using an ion beam, and observing the micro test piece using the electron microscope has an issue that should be overcome and that will be described below. In analysis of a defective included in products of an electronic part such as a semiconductor memory or a microprocessor, simultaneous analysis of multiple regions or swift feedback of the results of analysis is intensely requested. Specifically, an analytical test piece is extracted or prepared from a discovered defective region as quickly as possible, and then inspected or analyzed. The results are fed back to a manufacturing process as quickly as possible. This is important to reduce a cost of manufacture. Under current circumstances, it takes a time ranging from 5 to 10 min to form a section using an ion beam, and it takes a time ranging from 30 to 60 min to extract a micro test piece using the ion beam. These times cannot be said to be short enough to comply with a request for a production line. How to shorten the time required for preparing an observational or analytical test piece from a sample has become an issue that should be overcome. In the past, an ion beam whose beam spot is circular has been employed in processing that is performed using an ion beam. When the circular beam is employed, the precision in processing a section of a sample is determined with a beam diameter (a curvature of an ion beam spot). Moreover, a processing time during which the ion beam is employed is inversely proportional to an ion radiation current. In other words, the larger an ion beam current is, the shorter an ion beam processing time is. However, once the diameter of an ion beam is determined, the maximum value of the ion beam current is determined depending on the performance of an ion source or an ion optical system. The characteristics of the ion current and beam diameter are determined with a lens control value and an aperture diameter. When the aperture diameter is increased, the current increases. However, since aberrations caused by a lens are intensified, the beam diameter gets larger. FIG. 2 illustratively shows a conventional processing procedure that employs three beam modes, which are associated with ion beam currents, for the purpose of forming a section using an ion beam. Three beam modes A, B, and C are characterized by respective beam diameters and currents. The A mode is associated with a beam diameter of approximately 1 μm and a current of approximately 10 nA, the B mode is associated with a beam diameter of approximately 200 nm and a current of approximately 3 nA, and the C mode is associated with a beam diameter of approximately 30 nm and a current of approximately 200 pA. To begin with, an A-mode ion beam is rectangularly swept in order to form a rectangular hole. Herein, since a current is large and a beam diameter is large, a processed section is moderately curved and is therefore unsuitable for observation. A B-mode ion beam is then swept over the section in order to process the section steeply. A C-mode ion beam is then used to finish the section, whereby the section to be observed is completed. In FIG. 2, sections of electrodes and sections of plugs are seen bared on an observational section. Moreover, even when a thin film to be observed using a transmission electron microscope (TEM) is produced, a section is processed as mentioned above from both ends thereof. Herein, since the B-mode or C-mode ion beam carry a small current, it takes a long time, which is inversely proportional to the current, to complete processing. It takes a long time to complete observation. Observation of a section cannot be completed for a short period of time. Moreover, when contamination of a silicon wafer, of which section has been observed, with gallium is avoided so that the silicon wafer can be returned to a production line, ions employed should be of a non-contaminant ion species such as inert gas or oxygen. In this case, a plasma ion source is substituted for a liquid-metal ion source. However, a luminance level offered by the ion source is lower by two or three digits. When a beam diameter is set to 0.1 μm in order to finish a section, a current produced is on the order of several picoamperes. For processing a section, one hour or more is required. Therefore, observation of a vertical section of a specific region in a device using a non-contaminant ion species has not been realized. The present invention addresses the foregoing problems. An object of the present invention is to provide an ion beam processing technology for improving the precision in processing a section of a sample using an ion beam without extending a processing time, and shortening the time required for separating a micro test piece without breaking the sample or preparing the separation. According to the present invention, in order to improve the precision in processing while leaving a processing time unchanged, a stencil mask or any other pattern is used to mold an ion beam into, for example, a rectangular beam. At this time, an ion beam is molded so that the steepness of one of two pairs of sides, which extend in orthogonal directions, or two of four sides of a rectangle is smaller than that of the other pair of orthogonal sides. What is referred to as steepness is a concept representing a gradient at which the intensity of an ion beam decreases from a maximum domain to zero. Quantitatively, the steepness is expressed with the width of the skew of a beam profile. The steep sides are used to process a section or a thin film serving as an electron microscopic sample. A means for controlling the steepness or the beam profile will be described in relation to embodiments later. Moreover, for removal of neutral particles generated in an ion source or in the middle of an ion irradiation system, an axis along which an ion beam is drawn out of the ion source and an axis along which the ion beam is irradiated to a sample meet at an angle. Moreover, a mass separator is inserted into the ion irradiation system in order to remove impurity ions from the ion source. However, at this time, the steepness of an intensity profile representing an ion beam is decreased in a specific direction. Therefore, according to the present invention, a tilting direction in which the ion beam irradiation axis is tilted relative to the ion beam drawing-out axis, or a direction of mass diffusion in which the mass separator achieves mass separation and a tilting direction in which a stage is tilted are characterized for fear the specific direction will not adversely affect processing of a section or processing of a thin film serving as an electron microscopic sample. The details will be given later in relation with embodiments. According to the present invention, an ion beam is molded or controlled so that the beam on a sample will be asymmetrical (including axial asymmetry and asymmetry relative to 90° rotation with the irradiation axis as a center) with the ion beam irradiation axis (the ray axis of an ion beam) as a center. Thus, the problems are addressed. According to the present invention, an ion beam processing technology for improving the precision in processing of a section of a sample to be performed using an ion beam without making a processing time longer than a conventional processing time, and for shortening the time required for separating a micro test piece without breaking a sample or the time required for preparing the separation is realized to improve the yield for manufacturing a semiconductor device or the like. Embodiments of the present invention will be described with reference to the drawings. The present embodiment will be described on the assumption that an ion source is tilted relative to an ion beam column and a stencil mask is used to mold an ion beam. Now, an ion source shall be a plasma ion source that draws out an ion beam of inert gas or a gas element such as oxygen or nitrogen. If inert gas or an element species such as oxygen or nitrogen is selected as an ion species for the ion source, the electric characteristics of a device will not be affected at all. Therefore, after processing is completed using an ion beam, if a processed wafer is returned to a production line, a defective will hardly be produced. In such inline application, a very small amount of metal impurity is produced in the plasma ion source. When the impurity reaches a sample, the sample may become defective, though it is rare. One of impurities is metal ions, and other impurity is metal neutral particles. Neutral particles cannot be controlled using a lens or an electrostatic deflector but are broadly irradiated to a sample. Moreover, part of ions of a gas species is neutralized at the collision against gas molecules after released from the ion source. If the neutral particles are irradiated to a sample, a portion other than a desired portion of the sample is also processed. This poses a problem in that the sample is denatured. The present embodiment adopts a configuration in which an axis along which an ion beam is drawn out of an ion source and an axis along which the ion beam is irradiated to a sample meet at an angle for fear an impurity of neutral particles or gas neutral molecules may reach the sample. Moreover, luminance offered by a plasma ion source is generally lower by two or three digits than that offered by a liquid metal ion source that adopts gallium (Ga) or the like. In the present embodiment, a stencil mask having openings of predetermined shapes is inserted to the middle of an ion beam irradiation system in order to produce a molded beam that projects the shape of any of the openings on a sample. Furthermore, in the present invention, the skews of beam profiles representing an ion beam in two orthogonal directions are asymmetrical to each other. In this case, compared with the case where the skews of the beam profiles representing an ion beam in two orthogonal directions are symmetrical to each other, an ion beam current is increased and a processing time is shortened. FIG. 1 shows the configuration of an ion beam processing apparatus in accordance with the first embodiment of the present invention. The ion beam processing apparatus includes an ion beam irradiation optical system composed of a duoplasmatron 1 that releases gas ions of argon, neon, xenon, krypton, oxygen, or nitrogen, an ion beam deflector 20, an ion source aperture plate 26, a condenser lens 2, an objective lens 3, an ion beam scanning deflector 4, a stencil mask 5, and a tube 21 that serves as an ion beam column and accommodates these components. Moreover, the ion beam processing apparatus includes an electron beam irradiation optical system composed of an electron gun 7, an electron lens 9 that focuses an electron beam 8 released from the electron gun 7, an electron beam scanning deflector 10, and an electron beam column tube (scanning electron microscope (SEM) column tube) 22 that accommodates these components. A vacuum sample chamber 23 is located below the ion beam column tube 21 and SEM column tube 22. The vacuum sample chamber 23 accommodates a first sample stage 15 on which the sample 11 is mounted, a secondary-electron detector 12, and a depositional gas source 18. Moreover, the ion beam processing apparatus includes a probe 15 that carries a test piece extracted from the sample on the first sample stage by performing ion beam processing, a manipulator 16 that drives the probe, and a second sample stage 2 on which a micro test piece 303 is mounted. Needless to say, the interior of the ion beam column tube 21 is kept in vacuum. Herein, in the ion beam processing apparatus, an irradiated sample point or a point on a sample to which the ion beam 6 is irradiated and an irradiated sample point or a point on the sample to which the electron beam 8 is irradiated are deviated from the center of the sample mounting surface and are located at different positions. In other words, an ion beam irradiation axis 301 and an electron beam irradiation axis 302 will not intersect. Arranged as units for controlling the ion beam processing apparatus are a duoplasmatron control unit 91, an ion beam deflector control unit 92, an ion source aperture plate control unit 93, a lens control unit 94, a stencil mask control unit 95, an ion beam scanning deflector control unit 96, a first sample stage control unit 14, a second sample stage control unit 25, a manipulator control unit 17, a depositional gas source control unit 19, secondary-electron detector control units 27 and 28, an electron beam irradiation system control unit 97, and a computer system 98. Herein, the computer system 98 includes a display on which an image produced based on a detective signal sent from the secondary-electron detector 12 or information entered at an information input means is displayed. The first sample stage 13 includes a linear movement mechanism responsible for movements in two orthogonal directions on the sample mounting surface, a linear movement mechanism responsible for movement in a direction perpendicular to the sample mounting surface, and a rotation mechanism responsible for rotation on the sample mounting surface. The first sample stage control unit 14 controls the mechanisms in response to a command sent from the computer system 98. Moreover, the second sample stage 24 is rotated about a tilting axis thereof owing to a tilting ability, whereby an angle of irradiation at which an ion beam is irradiated to a test piece is varied. The second sample stage control unit 25 controls the second sample state 24 in response to a command sent from the computer system 98. Moreover, since the second sample stage 24 is disposed on the first sample stage 13, linear movements of the second sample stage 24 in two orthogonal directions on the first sample mounting surface, linear movement thereof in a direction perpendicular to the first sample mounting surface, and rotation thereof on the sample mounting surface are achieved by moving or rotating the first sample stage 13. The duoplasmatron 1 included in the ion beam processing apparatus is tilted with respect to the ion beam column tube 21, though the tilt is hard to see in FIG. 1. The duoplasmatron 1 is tilted in a Y direction in FIG. 1. A direction in which an ion beam is drawn out of the ion source and an ion beam irradiation axis meet at an angle. Next, movements made in the ion beam processing apparatus will be described below. By opening a gas valve located in the middle of a pipe extending from an argon cylinder, an argon gas is introduced into the duoplasmatron 1 so that plasma will be caused by gas discharge. An ion beam is then drawn out of the duoplasmatron 1. Herein, since an axis along which the ion beam is drawn out and an axis 301 along which the ion beam is irradiated to a sample meet at an angle, the ion beam deflector 20 refracts the path of the ion beam 6. Neutral particles generated in the ion source are unsusceptible to deflection by the ion beam deflector 20, and therefore move rectilinearly as they are. The movements of the duoplasmatron 1 and ion beam deflector 20 are controlled by the duoplasmatron control unit 91 and ion beam deflector control unit 97 respectively in response to a command issued from the computer system 98, or controlled by the computer system 98. The condenser lens 2 shall focus the ion beam at a point near the center of the objective lens. A voltage to be applied to the electrodes of the condenser lens 2 is set to a value, which is calculated in advance so that the condition will be met, by the computer system. The ion beam then passes through the stencil mask having a rectangular opening. The objective lens 3 controls the stencil mask 5 under the condition that an opening in the stencil mask 5 shall be projected on a sample. Herein, a voltage to be applied to the electrodes of the objective lens 3 is set to a value, which is calculated in advance so that the condition shall be met, by the computer system 98. Consequently, a rectangularly molded ion beam is irradiated to a sample. When the molded ion beam is kept irradiated, a rectangular hole is formed in the sample. Neutral particles collide against an aperture plate included in the ion beam irradiation system. At the time of the collision, secondary electrons may be generated due to sputtering. When a member against which the neutral particles collide is a metal, if the secondary electrons reach a sample, the sample are contaminated. Therefore, a member such as an aperture plate against which the neutral particles collide is made of an element that electrically hardly affects a sample, for example, a silicon. Moreover, an aperture plate and a mask to which an ion beam is irradiated are also made of the element. This eliminates a concern that the sample may be contaminated by sputtered metal particles. In other words, this is advantageous in improving a yield for a device manufacturing process. Next, a sequence of movements made in the electron beam irradiation system will be described below. The electron beam 8 released from the electron gun 7 is focused by the electron lens 9 and irradiated to the sample 11. At this time, the electron beam 8 is irradiated to a section of a sample while being swept by the electron beam scanning deflector 10. Secondary electrons released from the section of the sample are detected by the secondary-electron detector 12. At this time, the sample can be observed by converting the intensities of the secondary electrons into luminance values of an image. Owing to the sample observing ability based on the electron beam, an abnormality such as a defect in a circuit pattern formed on a sample or a foreign matter can be observed. In particular, the ion beam processing apparatus is preferable for acquisition of information on an abnormality in a hole, of which depth is large for the diameter thereof, because it has a structure that an electron beam is irradiated to a sample in a direction perpendicular to the sample. In the ion beam processing apparatus, the observing ability based on an electron beam is used to observe a section of a defect or a foreign matter in a sample, or to observe a section of an electron microscopic thin-film sample for the purpose of grasping a processing end point. Moreover, in the ion beam processing apparatus, an ion beam-irradiated sample point and an electron beam-irradiated sample point are deviated from the center of the sample mounting surface, and located at different positions. The objective lenses are disposed near a sample without spatially interfering with each other. Therefore, the distances of the objective lenses to respective working points are short. In other words, an ion beam and an electron beam can be thinned or excellent large current performance can be provided. Next, a procedure of extracting a micro test piece from a sample on the first stage 13 using a molded ion beam will be described below in conjunction with FIG. 3A and FIG. 3B. The left-hand drawings included in FIG. 3A and FIG. 3B are top views in which a sample is seen from above, and the right-hand drawings included therein are side views in which the sample is seen laterally. Since the ion beam processing apparatus employs a molded ion beam whose size is on the order of micrometers, it is not always recommendable to use the ion beam to mark a processed position. The ion beam processing apparatus therefore uses an electron beam, of which size is on the order of nanometers, for the marking. Incidentally, the procedure of extracting a micro test piece will be described on the assumption that a large-diameter aperture is selected from the ion source aperture plate. The ion beam is substantially not limited, whereby the same condition as the condition established when the ion source aperture plate is absent is established. The advantage of the ion source aperture plate will be described later. To begin with, the first sample stage 13 is moved so that an electron beam can be irradiated to a region from which a micro test piece is extracted. At a step shown in FIG. 3A (a), while a depositional gas is supplied, the electron beam 8 is irradiated in order to form a depositional film. Thus, two end marks 130 indicating an observational section are drawn. Specifically, while an image of a sample displayed on the screen of the display included in the computer system 98 is viewed, the marks are drawn to specify an observational position. Thus, although the ion beam processing apparatus uses a molded ion beam whose size is on the order of micrometers, the employment of the electron beam permits the drawing of the marks whose size is on the order of nanometers. Thereafter, the first stage 13 is moved so that a first molded ion beam 131 can be irradiated to a position shown in the vicinity of the marks. Herein, the openings in the stencil mask are switched to select the opening shown in FIG. 4 (a). At this time, a current of approximately 200 nA flows. The first molded ion beam 131 is irradiated so that the two marks will be encircled by the beam, whereby a first hole 132 of approximately 15 μm deep is formed. Thereafter, the openings of the stencil mask 5 are switched to select the circular opening shown in FIG. 4 (b). At this time, the cross section of the beam is nearly circular. However, since the ion beam 133 falls on the sample obliquely to the sample, the spot on the sample is elliptic. The sample can be observed by scanning the sample with the elliptic spot. Incidentally, the switching of the openings is executed when a user enters a switch command at an information input means or when the computer system 98 transmits a switching control signal to the mask control mechanism. Thereafter, as shown in FIG. 3A (c), the first sample stage control unit 14 causes the sample to rotate approximately 180° with an axis perpendicular to the surface of the sample as an axis of rotation. A secondary-electron image formed with secondary electrons generated from the sample due to the irradiation of the ion beam forming the elliptic spot is manipulated in order to recognize the initially formed hole. As shown in FIG. 3A (d), while the secondary-electron image produced by irradiating an ion beam 133 is viewed, the manipulator control unit is used to shift the position of the probe 15 so that the probe at the tip of a transporting means will come into contact with an end of the sample to be extracted. In order to fix the probe to the sample to be extracted, while a depositional gas is supplied, the ion beam is swept over the region containing the probe. Thus, a depositional film 134 is formed in the ion beam-irradiated region, and the probe is coupled to the sample to be extracted. Thereafter, the openings of the stencil mask 5 are switched to select the opening shown in FIG. 4 (c). At this time, a current of approximately 80 nA flows. An irradiated sample position or a position on the sample to which a second molded beam 135 is irradiated is adjusted in advance so that it can be determined with a circular beam. As shown in FIG. 3B (e), the ion beam control unit is used to control the ion beam-irradiated position on the basis of sample shape information acquired by irradiating a beam that forms an elliptic spot. The second molded ion beam 135 is irradiated so that the two marks will be encircled with the second molded ion beam as it is with the first molded beam, whereby a second hole 136 of approximately 15 μm deep is formed. The hole 136 communicates with the hole 132 formed with the first molded ion beam. Through the steps shown in FIG. 3A (a) to FIG. 3B (e), a wedge-like micro test piece 137 having a triangular section and encompassing the marks is held by the probe. Thereafter, the openings of the stencil mask are switched to select the circular opening shown in FIG. 4 (b). As shown in FIG. 3B (f), while a secondary-electron image obtained by irradiating an ion beam is viewed, the manipulator control unit is used to shift the position of the probe. The micro test piece coupled to the tip of the probe is extracted and moved to the sample holder 140 on the second sample stage 24. At the step shown in FIG. 3B (g), while a depositional gas is introduced, an ion beam is irradiated to a joint between the micro test piece and the sample holder. A depositional film 138 is formed in the ion beam-irradiated region, and the micro test piece 137 is coupled to the sample holder 140. At the step shown in FIG. 3B (h), an ion beam is irradiated to the depositional film that joins the probe 15 and micro test piece. The depositional film is removed by sputtering in order to separate the probe from the micro test piece 137. The ion beam processing apparatus in accordance with the present embodiment is characterized by the structure in which the ion beam column is tilted with respect to a sample. Owing to the structure, when a micro test piece is extracted using an ion beam, the sample stage need not be tilted but should merely be rotated. Next, a procedure of observing a section of a sample and producing an electron microscopic sample will be described below. In relation to the procedure, advantages provided by the features of the ion beam processing apparatus will be described in conjunction with FIGS. 5 (a), (b), and (c). FIG. 5 (a) shows a top view of the ion beam processing apparatus, FIG. 5 (b) shows a front view thereof, and FIG. 5 (c) shows a side view thereof. Referring to FIG. 5 (a), there are shown a tube 1001 accommodating a duoplasmatron, an ion beam column tube 1002 disposed under the duoplasmatron, and an electron beam column (SEM column) tube 1003 accommodating an electron source. For convenience' sake, X and Y axes are defined on the surface of the first sample stage 13, a Z axis is defined in the direction of a normal to the first sample stage, and an origin of a coordinate system is defined in the center of the first sample stage. The SEM column 1003 is disposed perpendicularly to the XY plane. Referring to FIG. 5 (c), the ion beam column 1002 is tilted on the XZ plane. The tilt angle is substantially 45° relative to the Z axis. Moreover, dot-dash lines 1004 drawn lengthwise and sideways in FIG. 5 (a) are the center lines in the X and Y directions of the first sample stage. An intersection between the dot-dash lines corresponds to the center of the sample mounting surface. As already described, an ion beam-irradiated sample point and an electron beam-irradiated sample point are deviated from the center of the sample mounting surface, and located at the mutually different positions. In other words, an ion beam irradiation axis 1100 and an electron beam irradiation axis 1102 will not intersect. As seen from the top view of FIG. 5 (a), the front view of FIG. 5 (b), and the side view of FIG. 5 (c), the duoplasmatron 1001 is tilted relative to the ion beam column tube 1002. Specifically, an axis 1101 along which an ion beam is drawn out of the ion source and an axis 1100 along which the ion beam 6 is irradiated to the sample 11 meet at an angle. Furthermore, the ion beam processing apparatus includes the probe 15 that carries the micro test piece 137 extracted from the sample 11 on the first sample stage 13 by performing ion beam processing, and the second sample stage 24 on which the micro test piece is mounted. The ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the micro test piece, by rotating the second sample stage about a tilting axis thereof. Moreover, the ion beam processing apparatus is characterized in that a segment drawn by projecting an axis, along which an ion beam is drawn out of the duoplasmatron 1001, on a plane perpendicular to the ion beam irradiation axis is at least substantially parallel to a segment drawn by projecting the tilting axis of the second sample stage 24 on the plane perpendicular to the ion beam irradiation axis. Otherwise, a segment drawn by projecting the axis 1101, along which an ion beam is drawn out of the duoplasmatron 1001, on the plane perpendicular to the ion beam irradiation axis is substantially parallel to the sample mounting surface of the first sample stage 13. The above relationship of the segment will be further described in conjunction with FIGS. 6 (a) and (b). In FIG. 5 (b), an X′ axis and a Z′ axis are defined by turning 45° the X and Y axes respectively with the Y axis as an axis of rotation. The Y axis is used as it is. Namely, a plane perpendicular to the ion beam irradiation axis shall be defined as the X′Y plane, and the ion beam irradiation axis shall be defined as the Z′ axis. FIG. 6 (a) shows the relationship of the ion beam irradiation axis 1100 on the YZ′ plane to an ion drawing-out axis 1101. Apparently, the ion beam irradiation axis 1100 and ion drawing-out axis 1101 meet at an angle. FIG. 6 (b) shows the plane perpendicular to the ion beam irradiation axis, that is, the X′Y plane. In FIG. 6 (b), a segment 1104 is drawn by projecting the axis 1101, along which an ion beam is drawn out of the duoplasmatron 1001, on the X′Y plane. A segment 1105 is drawn by projecting the tilting axis of the second sample stage 24 on the plane perpendicular to the ion beam irradiation axis. Apparently, the segments are substantially parallel to the Y axis. Otherwise, since the segment drawn by projecting the axis 1101, along which an ion beam is drawn out of the duoplasmatron 1001, on the plane perpendicular to the ion beam irradiation axis is substantially parallel to the Y axis, the segment is parallel to the sample mounting surface of the first sample stage 13. In contrast, the segment that is not parallel to the Y axis intersects the sample mounting surface of the first sample stage 13. In the structure having the ion source tilted relative to the ion beam column, neutral particles generated in the ion source fly in an ion drawing-out direction but will not reach a sample because they are intercepted by a stationary aperture plate or the like. Since the sample will not be contaminated with an impurity of neutral particles, a yield for manufacturing a device will not decrease. However, the refraction of an ion beam drawn out of the ion source into the direction of the ion beam column causes the width of the skew of an intensity profile representing a projected beam to expand, and interrupts formation of a steep section. This is attributable to the fact that energy exerted by an ion differs from ion to ion. When the ion beam deflector deflects an ion beam, the trajectory of the ion beam spreads in the deflecting direction according to a difference in energy. The same applies to a molded ion beam. The width of the skew of the intensity profile expands in the direction in which an ion beam is refracted by the ion beam deflector, that is, in the Y direction. Namely, the width of the skew of the intensity profile expands in the direction of a segment 1104 shown in FIG. 6 (b). Consequently, the molded ion beam to be actually irradiated to a sample has a processing edge, which is represented by a steep intensity profile, formed in the direction of a segment 1106 (X′ direction in FIG. 6 (b)), and has a processing edge, which is represented by a gentle intensity profile, formed in the direction of the segment 1104 (Y direction in FIG. 6 (b)). Needless to say, processing precision is higher in part of a section formed by the edge represented by the steep intensity profile, and the processed section is finer. Therefore, processing is proceeded with the edge, which is represented by the steep intensity profile, brought into contact with a section. A procedure of observing a section of a sample by utilizing the edge represented by the steep intensity profile will be described below. As shown in FIG. 7 (a), the second sample stage 24 is tilted approximately 45° with the micro test piece 137, which is extracted as mentioned above, mounted on the sample holder 140, so that the ion beam 6 will be irradiated substantially in parallel with the vertical section of the sample. The molded ion beam 6 is irradiated to the section of the sample in order to finish the section so that the section will be nearly vertical to the surface of the sample. The processing edge represented by the steep intensity profile is, as mentioned above, formed in the X′ direction shown in FIG. 7 (a). The first sample stage 13 is moved in the X and Y directions so that the electron beam 8 will be, as shown in FIG. 7 (b), irradiated to the section of the test piece. Thus, the section can be observed using the electron beam 8. FIG. 8 shows the movement of the first sample stage 13 made at this time. As seen from FIG. 8, an ion beam and an electron beam are alternately irradiated to the micro test piece 137 mounted on the second sample stage 24. Thus, a section of a sample can be steeply processed using a molded ion beam. Namely, a section of an abnormality such as a defect in a semiconductor circuit pattern or a foreign matter is formed, and the section of the defect or foreign matter is observed using the electron beam 8. Thus, the cause of the defect or foreign matter can be analyzed. A control method for controlling processing of a section with a molded ion beam by utilizing an ion source aperture plate will be described below. FIG. 9 shows an example of an ion source aperture plate 26 including axially asymmetric apertures and being employed in the present embodiment. The ion source aperture plate 26 has multiple apertures of different shapes formed therein. Any of the apertures is selected according to a processing method. The edges of the aperture plate are notched in relation to each aperture. The ion beam processing apparatus in accordance with the present embodiment includes an ion source aperture plate feeding mechanism, though FIG. 1 does not show the feeding mechanism. The notches are used to select any of the apertures. Dot-dash lines in FIG. 9 indicate the center lines in the X′ and Y directions of the apertures. The intersection of the center axes indicates a center axis of each aperture. When an ion beam passes through the aperture plate, the center of the beam generally passes the center axis. Incidentally, an axially asymmetric shape refers to shapes other than a circle. In the present embodiment, the shapes to which the axially asymmetric shape refers do not include a square. This is because if the shape of an aperture were a square, the width of the skew of a beam profile would be identical in two directions of the X′ and Y directions. In the present embodiment, the ion source aperture plate shown in FIG. 9 is disposed in the processing apparatus so that the direction of the major axes of the apertures will be aligned with the X′ direction shown in FIG. 5 (b) and the minor axes thereof will be aligned with the Y direction shown in FIG. 5 (b). Thus, when the minor axes of the apertures included in the ion source aperture plate, that is, the lateral sides of rectangles or the shorter diameters of the ellipses are aligned with the Y direction, the spread in the X′ direction of an ion beam passing through the objective lens becomes smaller than the spread in the Y direction thereof. Consequently, the adverse effect of aberrations caused by the objective lens gets smaller. Consequently, the skew in the X direction of a beam profile gets steeper than the skew in the Y direction thereof. Consequently, a section of a hole processed with a molded beam gets steeper in the X′ direction than in the Y direction. Moreover, an ion-beam current gets larger than it is when a beam is controlled so that it will exhibit steep profiles in the X′ and Y directions respectively. In particular, when the position of the stencil mask is adjusted so that one side of a rectangular opening in the stencil mask will coincide with an irradiation axis, the width of the skew of a beam profile can be controlled to be smaller. This is attributable to the fact that aberrations caused by lenses are minimized on the ion beam irradiation axis. FIGS. 10 (a), (b) shows the shapes of molded beams produced by selecting any of the apertures in the ion source aperture plate 26 and any of the openings in the stencil mask 5, and the beam profiles thereof. Selected apertures and openings are indicated with arrows in the drawings. FIG. 10 (a) is concerned with a case where the rectangular aperture in the ion source aperture place and the rectangular opening in the stencil mask are selected. A molded beam gets longer in the Y direction and has the X′-direction edge thereof represented by a steep intensity profile. FIG. 10 (b) is concerned with a case where the rectangular aperture in the ion source aperture plate and the square opening in the stencil mask are selected. A molded beam has a square cross section. Similarly to the beam shown in FIG. 10 (a), the beam has an X′-direction edge thereof represented by a steep intensity profile. When any of the apertures in the ion source aperture plate is selected as mentioned above, the skew of the intensity profile can be controlled independently of the shape of a molded ion beam. Namely, a region to be processed and processing precision can be determined independently of each other. For processing of a section of a sample on the sample holder, since an ion beam has the X′-direction edge thereof represented by a steep intensity profile, a steep section can be created. The X′ direction corresponds to the tilting direction of the second sample stage 24 or the direction of the sample mounting surface of the first sample stage. Namely, the direction of projection in which the tilting axis of the second sample stage is projected on the plane perpendicular to the ion beam irradiation axis, that is, the X′Y plane is the Y direction. The asymmetry of the apertures in the ion source aperture plate is determined so that an ion beam will have an X′-direction edge thereof represented by a steeper intensity profile than in a Y-direction edge thereof. In other words, the major axes of the apertures in the ion source aperture plate included in the ion beam processing apparatus are parallel to the Y direction that is the direction of projection in which the tilting axis of the second sample stage is projected. Otherwise, the major axes of the apertures in the ion source aperture plate are parallel to the Y direction that is the direction parallel to the sample mounting surface of the first sample stage. In other words, the ion beam processing apparatus extends control so that the width of the skew of an intensity profile, which represents an edge of a rectangular ion beam projected on a sample in a direction perpendicular to the direction of projection in which the tilting axis of the second sample stage is projected, will be smaller than the width of the skew of an intensity profile representing the other edge thereof in the direction parallel to the direction of projection in which the tilting axis of the second sample stage is projected. Owing to the foregoing arrangement, only a surface needed for observation is processed steeply. This is advantageous in that a throughput of processing improves. Moreover, in the ion beam processing apparatus, the ion source aperture plate may be projected on a sample using the condenser lens and objective lens. Namely, the sample can be processed in the shape of any of the apertures in the ion source aperture plate. In this case, since a magnification for projection can be varied using the two lenses of the condenser lens and objective lens, processing can be proceeded according to a desired size. Furthermore, if a lens equivalent to the condenser lens is interposed between the ion source and the ion source aperture plate, an intensity profile representing a molded beam to be irradiated to a sample can be controlled by varying the conditions for the lens. For observation of a section, the second sample stage need not be driven. Therefore, if the first sample stage is moved back to a position from which an ion beam is irradiated to a sample, a section that is located at a position deeper than and nearly parallel to a created section can be formed and observed. Herein, the position of a section can be identified based on a change in the intensity of secondary electrons generated by sweeping a molded ion beam at least in a direction perpendicular to the section. An ion beam-irradiated position can be determined during additional processing. Moreover, the tilting ability for the second sample stage may be used to orient a section in a direction perpendicular to an electron beam. In this case, the section can be closely observed in the perpendicular direction. Since the electron beam is irradiated in the perpendicular direction, a resolution will not be degraded by passage of the electron beam in a tilting direction. Moreover, the resolution is higher than that attained for observation of a sample at 45°. However, since a tilt angle cannot be highly precisely controlled, even if the tilt angle is returned to the original 45°, it is hard to irradiate an ion beam in parallel with a created section. In other words, even when the stage is not tilted, the structure of the ion beam processing apparatus permits repetition of processing of a section and observation. In the ion beam processing apparatus, cutting or processing to be performed with an ion beam in order to create a section and observation to be performed with an electron beam are repeated in order to acquire three-dimensional information on the inside of a sample. A three-dimensional image can be constructed using multiple two-dimensional view images. In the ion beam processing apparatus, the SEM column is disposed so that scanning electron microscopy (SEM) can be achieved in a perpendicular direction. However, the disposition of the SEM column need not always be perpendicular. The SEM column may be oriented in any direction as long as a section of a micro test piece can be observed. Next, a procedure of producing a thin film as an electron microscopic sample will be described below. The three openings in the stencil mask shown in FIG. 4 are used to produce a thin film. The rectangular openings are sequentially switched so that a beam current will get smaller in the order of roughing, semi-finishing, and finishing. Similarly to the foregoing processing of a section, the asymmetry of the apertures in the ion source aperture plate is determined so that the direction of projection in which the tilting axis of the second stage is projected on the X′Y plane perpendicular to the ion beam irradiation axis will be the Y′ direction, and that an ion beam will have an X′-direction edge thereof represented by a steeper intensity profile than a Y-direction edge thereof. Furthermore, the apertures in the ion source aperture plate are switched so that the steepness of the beam profile will be increased in order of roughing, semi-finishing, and finishing. Consequently, a section of a thin film can be processed steeply. As a result of processing, part of a thin film cut from a superficial position of a sample may be produced to be thinner than the other part thereof cut from a deep position thereof. As a countermeasure, the tilt angle of the sample stage relative to the horizon is set to an angle smaller than 45° in order to process the upper part of the thin film. The tilt angle thereof is set to an angle larger than 45° in order to process the lower part of the thin film. Thus, the thin film whose sides are nearly parallel to each other can be produced. Finally, the thin film is finished so that the thickness of an observational region will be about 100 nm or less, and thus produced as an electron microscopic sample. Thus, the TEM observational region is produced as a result of the foregoing processing. The observational region can be processed in the form of a thin film quicker than it conventionally is. In the foregoing example, an operator uses an input device included in the computer system to control the ion beam processing apparatus. Alternatively, a storage means such as a memory may be included in the computer system, and the conditions for control of all steps may be stored as a control sequence in the memory. In this case, sampling can be fully automated. After the thin film is produced as a micro test piece, the micro test piece is introduced into the TEM sample chamber. Transmission electron microscopy (TEM) makes it possible to observe a section of a defect or a foreign matter at a higher resolution than scanning electron microscopy (SEM) does. The cause of the defect can be closely analyzed based on the results of microscopy. Moreover, in the present embodiment, the ion beam irradiation axis and the electron beam irradiation axis will not intersect. Alternatively, the axes may intersect above a sample. The top view of FIG. 11 (a), the front view of FIG. 11 (b), and the side view of FIG. 11 (c) show the configuration in which the axes intersect above a sample. Specifically, in an ion beam processing apparatus having the configuration, the electron beam irradiation axis exists in a plane containing a segment drawn by projecting the ion beam irradiation axis perpendicularly on a sample and the ion beam irradiation axis. In other words, as shown in FIG. 11 (a), the ion beam irradiation axis and electron beam irradiation axis coexist on the same plane. As shown in FIG. 11 (b), the ion beam irradiation axis meets the sample mounting surface of the first sample stage at 45°. An angle at which the ion beam irradiation axis and electron beam irradiation axis meet is 90°. In the present ion beam processing apparatus, as shown in FIGS. 11 (b) and (c), unlike the processing apparatus shown in FIG. 1, a section processed with an ion beam can be observed without the necessity of moving the sample stage. Herein, the ion beam is used to repeatedly process the section, and a change in the section can be sequentially observed. The present ion beam processing apparatus gains an advantage over conventional apparatuses in that a section can be observed in a perpendicular direction. This is advantageous in that when a three-dimensional image is constructed using two-dimensional images produced according to the technique, a structure can be more faithfully reproduced. Moreover, the present ion beam processing apparatus includes a transmission electron detector 1201 that detects electrons scattering out of an electron beam, and can therefore produce a so-called scanning transmission electron microscopic image. Since the scanning transmission electron microscopic image is produced with the energy of an electron beam increased, the image offers a higher resolution than a scanning electron microscopic image. Prior to viewing of the scanning transmission electron microscopic image, a damaged layer formed on the surface of a sample is removed by irradiating an argon beam, which is produced with an accelerating voltage set to a lower voltage than that employed in the aforesaid processing, to the processed surface. At this time, the processed surface may be tilted more greatly than it is during the aforesaid processing. FIG. 12 (a) to (c) illustratively show the tilting. The damaged layer (30 mm thick) is an amorphous layer even when the sample is crystalline, and becomes an obstacle to observation of a crystal structure. In the present ion beam processing apparatus, the damaged layer can be removed in the sample chamber using only one ion source. This enables observation at a high resolution. Conventionally, gallium ions are irradiated in order to process a thin film, and a gas ion irradiation apparatus is used to remove a damaged portion. The ion beam processing apparatus is more low-cost than conventional apparatuses are and offers a higher throughput while successively removing the damaged portion. Moreover, when X-rays released from a sample to which an electron beam is irradiated are checked in order to analyze the elements of the sample, since the sample is, unlike conventionally, not contaminated with gallium, elemental analysis can be achieved despite the very low melting point of gallium. In an apparatus that uses gallium to process a thin film, the sample has to be taken out of the apparatus and to be cleaned for the purpose of obtaining a satisfactory effect. In the present ion beam processing apparatus, a sample can be kept placed in the same sample chamber. Consequently, a throughput can be improved drastically and laboriousness can be avoided. Incidentally, the present ion beam processing apparatus may include another electron beam irradiation system disposed perpendicularly to a sample, and may thus include two electron beam irradiation systems and one ion beam irradiation system. In the present embodiment, an axially symmetrical lens is adopted as the condenser lens. The axially symmetrical lens may be replaced with an axially asymmetrical ion beam lens realized with a double quadrupole lens. In this case, an ion beam is focused on a point near the center of the objective lens by means of the axially asymmetrical ion beam lens. The double quadrupole lens is designed to have the image plane at an equal distance in both the X′ and Y directions but exhibit different powers in the respective directions. The computer system 98 determines a voltage value so that the double quadrupole lens will focus an image at a point near the center of the objective lens in both the X′ and Y directions. An ion beam passes through the stencil mask that has rectangular openings. The objective lens is controlled so that it will project the stencil mask on a sample. Thus, a molded ion beam having a rectangular cross section is irradiated to the sample. Assuming that a voltage is determined so that the double quadrupole lens will exhibit a smaller power in the X′ direction than in the Y direction, the spread in the X′ direction of an ion beam passing through the objective lens is smaller than that in the Y direction. Consequently, the adverse effect of aberrations caused by the objective lens diminishes. At this time, the skew in the X′ direction of a beam profile is steeper than that in the Y direction. Consequently, an edge processed with the molded beam is steeper in the X′ direction than in the Y direction, and is thus shaped properly for observation of a section. Moreover, an ion beam current increases compared with a case where an ion beam is controlled to have the X′-direction and Y-directions edge thereof represented by respective steep beam profiles. In particular, when the position of the stencil mask is adjusted so that one side of a rectangular opening in the stencil mask will coincide with the irradiation axis, the width of the skew of a beam profile is controlled to get smaller. What counts herein is that a direction in which an axis along which an ion beam is drawn out of an ion source is tilted should be parallel to at least a processed section to be observed. Namely, the tilt of the ion source should not adversely affect formation of a section to be observed. In the present embodiment, a double quadrupole lens is adopted as the axially asymmetrical ion beam lens in order to control the width of the skew of a beam profile. As long as a lens is axially asymmetrically controllable, any of a quadrupole lens, an octupole lens, and a hexadecapole lens will do. A combination of the quadrupole, octupole, and hexadecapole lenses or a combination of any of the lenses with a symmetrical lens will do. In the present embodiment, the width of the skew of a beam profile is defined as a distance between a point indicating 16% of a maximum beam intensity and a point indicating 84% thereof in order to quantitatively handle the steepness of the skew thereof (see FIG. 10A and FIG. 10B). However, any definition other than the width of the skew of a beam profile may be adopted as the definition of the steepness of the edge of a beam forming a beam spot. Assuming that an ion beam is controlled to have both X-direction and Y-direction edges thereof represented by steep beam profiles, when the asymmetrical beam molding technique employed in the present embodiment is compared with a technique in which the ion beam is molded to be symmetrical, an ion beam current can be increased. Therefore, the beam molding technique employed in the present embodiment is preferable especially for an ion beam of a gas element such as argon or oxygen. The first embodiment has been described on the assumption that a gallium (Ga) ion beam is focused. In this case, gallium remains in a processed region. In a manufacturing process for a silicon device or any other semiconductor device, since gallium that is a heavy metal is highly likely to cause a defective, an ion beam of inert gas or a gas element such as oxygen or nitrogen that does not seriously affect the properties of a sample should preferably be used to produce a test piece. However, talking of a plasma ion source that generates gas-element ions and that is one of currently available ion sources, the luminance of the generated ion beam is lower at least by two or three digits than that of an ion beam generated by a liquid metal ion source using gallium or the like. Consequently, an ion beam is molded to be asymmetrical, and part of the ion beam represented by a steeper beam profile is used to perform actual processing. Even when the ion source suffering low luminance is employed, processing precision will not be degraded. This would prove advantageous for any ion source irrespective of whether an ion beam is of a gas element (for example, such an element as nitrogen, oxygen, neon, xenon, or krypton, or a mixture thereof). Moreover, when the beam profiles representing the X-direction and Y-direction edges of an ion beam are symmetric, an ion beam current can be set to any value by controlling the ratio of steepness levels of the beam profiles representing the two orthogonal-direction edges. Namely, if one of the beam profiles representing the X-direction and Y-direction edges is not relatively steep, the ion beam current increases. However, since the edge of the ion beam represented by the steeper beam profile is used to process a sample, processing precision will not be degraded. Moreover, ion beam scanning deflection electrodes included in the ion beam processing apparatus shown in FIG. 1 may be used to sweep a beam over a section. In this case, if the beam sweeping direction coincides with a direction parallel to the section, the section can be efficiently processed. Taking for instance the beam profiles shown in FIGS. 10 (a) and (b), if the skew of the beam profile representing the X′-direction edge of an ion beam is steeper than that of the beam profile representing the Y-direction edge thereof, it is important for the computer system to determine a rectangular region, over which the beam is swept, so that at least one side of the rectangular region in the beam sweeping direction will be parallel to the Y direction. Moreover, when the beam is not swept, a processed shape is limited to the same shape as the beam. If the ion beam can be swept, there is freedom in a beam-processed shape. Moreover, a processed region can be arbitrarily determined irrespective of the beam shape. Moreover, the stencil mask may be provided with a mechanism for limiting one of the openings formed in the stencil mask to a small size. A molded beam having passed through the opening is swept over a sample in order to produce a sample image, and a processed position is determined using the sample image. In this case, the position can be determined highly precisely. Talking of the mechanism for limiting the opening in the mask, the stencil mask may be structured to have a small-diameter opening, or a microscopic aperture plate may be superimposed on the stencil mask. As a technique for routing a thin beam to a sample, the diameter of an ion release hole in an ion source or the diameter of an aperture for limiting a region from which ions are drawn out may be projected in a reduced size on the sample using a lens. However, in this case, since the conditions for the lens are different from those for a lens that is used to project an opening in the stencil mask on the sample, a beam irradiation axis may be deviated from a line with which it should coincide. It may therefore be necessary to adjust the beam irradiation axis. This is time-consuming. However, when an opening in the stencil mask is projected on a sample, since the conditions for the lens remain unchanged, the necessity of adjusting the beam irradiation axis is obviated. Assuming that the diameter of an opening in the stencil mask is controlled so that the diameter of a beam that falls on a sample via a lens after passing through the opening will be smaller than the diameter of a beam that falls on the sample via a lens after passing through an ion release hole in the ion source or an ion drawing-out limitation aperture in the ion source, an advantage described below will be provided. In general, projecting conditions under which a projection lens projects an opening in the stencil mask on a sample may be determined based on calculated values of lens conditions, but cannot be determined fully satisfactorily. However, when at least the above conditions are met, if an attempt is made to determine the conditions for the projection lens under which the diameter of a beam on the sample shall be minimized, the determined conditions nearly correspond to the conditions for a projection lens that projects an opening in the stencil mask on a sample. In contrast, when the above conditions are not met, even if an attempt is made to determine the conditions for a projection lens so that the diameter of a beam on a sample will be minimized, the determined conditions are conditions under which the ion release hole in the ion source shall be projected on a sample. The conditions for the projection lens cannot be established. Herein, the opening in the stencil mask is circular. Alternatively, the opening may be a square or a polygon at least one side of which is smaller than the diameter of the ion drawing-out limitation aperture. In this case, a nearly identical advantage is provided. Moreover, in the present embodiment, the duoplasmatron is adopted as the ion source. Alternatively, a plasma ion source employing microwaves, a multicusp ion source, a field ionization ion source, or a liquid metal ion source will do. In particular, when a silicon ion beam alone is irradiated to a sample by removing gold and an impurity from a gold-silicon alloy using a mass separator, it will prove advantageous in that a sample will not be contaminated with an impurity in the course of manufacturing a silicon device. Furthermore, a thin beam which is hard to draw out of the plasma ion source can be produced. Moreover, in the aforesaid embodiment, an electron beam is used to observe a section. Alternatively, an ion beam may be used for the observation. When a field ionization ion source is employed, a section can be observed at a high resolution. In this case, a shallower structure can be observed than that can with an electron beam. Otherwise, a higher resolution can be attained. As for the configuration of an apparatus, an ion beam irradiation optical system is substituted for an electron beam irradiation optical system that irradiates an electron beam to a sample. The same applies to all embodiments to be described later. Moreover, secondary radiation to be detected by the secondary-electron detector may include secondary electrons as well as reflected electrons and secondary ions. Moreover, two secondary-electron detector control units 27 and 28 are included. The secondary-electron detector control unit 27 amplifies a dc signal sent from the detector, while the other secondary-electron detector control unit 28 measures a signal intensity level by counting the number of pulses included in the signal sent from the detector. In the latter control unit, since the number of detective particles is directly counted, a noise occurring in the detector can be removed to offer high detective sensitivity. Conventionally, it is unnecessary to count the number of pulses because an ion beam or an electron beam to be irradiated to a sample is sufficiently intense. However, especially when the field ionization ion source is employed, an ion current is small. Therefore, the detector control unit 28 that counts the number of pulses to measure a signal intensity level would prove effective. Consequently, observation can be achieved at a higher resolution than it conventionally is. However, when the number of pulses is counted, the number of pulses that can be counted is limited to about one million pulses per second. If a current to be measured is equal to or larger than a pico-ampere, the number of pulses included therein cannot be counted. Consequently, the two control units are switched according to the magnitude of a current composed of ions or electrons to be irradiated. Alternatively, the computer system 98 may be used to automatically switch the control units by monitoring a current of charged particles to be irradiated to a sample. According to the sample production method and sample production apparatus described as the present embodiment, since neutral particles are removed, metal neutral particles generated in the plasma ion source will not reach a sample. Even when a processed wafer is returned to a production line, it is rare to generate a defective. Moreover, gas neutral particles will not be broadly irradiated to a sample. This is advantageous in overcoming an issue that a portion of a sample other than a desired portion thereof is processed and denatured. Moreover, according to the sample production method and sample production apparatus described as the present embodiment, the employment of the stencil mask permits high-precision processing to be achieved with a large current. In particular, even if an ion source suffers low luminance, a large beam current can be produced and processing precision can be improved. Therefore, processing of a section or production of a micro test piece can be achieved shortly. This means that in a semiconductor device manufacturing process, an ion beam of inert gas or a gas element such as oxygen or nitrogen that does not seriously affect the properties of a sample can be substituted for an ion beam of gallium that is highly likely to cause a defective. Consequently, a yield for manufacturing a semiconductor device or the like can be improved without contamination of a wafer with a metal such as gallium, and a section can be formed with an ion beam. Furthermore, since a micro test piece can be separated without the necessity of breaking a wafer or preparations can be made for the separation, there is provided a novel test/analysis method making it unnecessary to dispose of a wafer for the purpose of evaluation and making it possible to return a wafer, from which a sample to be tested is extracted, to a production line without occurrence of a defective. Moreover, a wafer can be evaluated without being broken, a defective will not be newly generated, and an expensive wafer will not be wasted. Eventually, a yield for manufacturing a semiconductor device improves. The sample production apparatus in accordance with the first embodiment includes the first sample stage and the second sample stage on which a test piece extracted by performing ion-beam processing is mounted. The present embodiment will be described as an apparatus that does not always include the second sample stage but has a tilting ability to vary an angle of irradiation, at which an ion beam is irradiated to a sample, by rotating the first stage about the tilting axis of the first stage. Moreover, in the first embodiment, an ion beam-irradiated sample point and an electron beam-irradiated sample point are deviated from the center of the sample mounting surface, and located at mutually different positions. In the apparatus of the present embodiment, the ion beam irradiation axis and electron beam irradiation axis intersects above a sample. In the present apparatus, an axis along which an ion beam is drawn out of an ion source and an axis along which the ion beam is irradiated to a sample meet at an angle. A segment drawn by projecting the axis, along which an ion beam is drawn out of the ion source, on a plane perpendicular to the ion beam irradiation axis may be substantially parallel to a segment drawn by projecting the tilting axis of the sample stage on the plane perpendicular to the ion beam irradiation axis. In other words, the segment drawn by projecting the axis, along which an ion beam is drawn out of the ion source, on the plane perpendicular to the ion beam irradiation axis is substantially parallel to the sample mounting surface of the sample stage. The relationship of the segment will be described below. Referring to FIG. 13 (a) to (c), an advantage provided by the features of the ion beam processing apparatus in accordance with the second embodiment of the present invention will be described below. FIG. 13 (a) shows a top view of the ion beam processing apparatus, FIG. 13 (b) shows a front view thereof, and FIG. 13 (c) shows a side view thereof. The inside of the apparatus is identical to that shown in FIG. 1. The iterative description will be omitted. In FIG. 13 (a), there are shown a tube 1001 accommodating a duoplasmatron, an ion beam column tube 1002 located under the duoplasmatron, and an electron beam column tube 1003 (scanning electron microscope (SEM) column tube) including an electron source. For convenience' sake, X and Y axes are defined on a first sample stage 13, a Z axis is defined in the direction of a normal to the first sample stage, and an origin of a coordinate system is defined at the center of the first sample stage. The SEM column 1003 is disposed perpendicularly to the XY plane. In FIG. 13C, the ion beam column 1002 is tilted on the XZ plane, and the tilt angle is substantially 45° relative to the Z axis. Moreover, dot-dash lines 1004 drawn lengthwise and sideways in FIG. 13 (a) are the center lines of the sample stage extending in the X and Y directions respectively. An intersection between the dot-dash lines coincides with the center of the sample mounting surface. An ion beam-irradiated sample point and an electron beam-irradiated sample point are aligned with the center of the sample mounting surface and located at different positions. Namely, an ion beam irradiation axis 1100 and an electron beam irradiation axis 1102 intersect nearly on a line passing the center of the sample mounting surface. As seen from the top view of FIG. 13 (a), the front view of the FIG. 13 (b), and the side view of FIG. 13 (c), the duoplasmatron 1001 is tilted relative to the ion beam column tube 1002. Namely, an axis 1101 along which an ion beam is drawn out of the ion source and an axis 1100 along which the ion beam 6 is irradiated to a sample 11 meet at an angle. The present apparatus may or may not include a probe 15 that carries a micro test piece 137 which is extracted from the sample 11 on the sample stage 13 by performing ion-beam processing. The present apparatus has a tilting ability to vary an angle of irradiation, at which an ion beam is irradiated to a micro test piece, by rotating the sample stage 13 about the tilting axis thereof. Moreover, in the present apparatus, a segment drawn by projecting the axis, along which an ion beam is drawn out of the duoplasmatron 1001, on a plane perpendicular to the ion beam irradiation axis may be at least substantially parallel to a segment drawn by projecting the tilting axis of the sample stage 13 on the plane perpendicular to the ion beam irradiation axis. Otherwise, the segment drawn by projecting the axis 1101, along which an ion beam is drawn out of the duoplasmatron 1001, on the plane perpendicular to the ion beam irradiation axis is parallel to the sample mounting surface of the sample stage 13. This positional relationship is identical to that shown in FIGS. 6 (a), (b) and observed in the apparatus in accordance with the first embodiment shown in FIG. 5 (a) to (c). Even in the present apparatus, neutral particles generated in the ion source fly in an ion drawing-out direction, and are intercepted by a stationary aperture plate or the like in the middle but will not reach a sample. Namely, the sample will not be contaminated with an impurity of neutral particles. A yield for manufacturing a device will not decrease. However, when an ion beam drawn out of the ion source is refracted to the direction of the ion beam column, the width of the skew of an intensity profile of a projective beam expands. In the case of a molded ion beam, the width of the skew expands in a direction in which an ion beam is refracted by an ion beam deflector, that is, in a Y direction in FIG. 13 (a) to (c). Namely, the width of the skew expands in the direction of the segment 1104 shown in FIG. 6 (b). A processing edge represented by a steep beam profile is formed in the direction of the segment 1106 (X′ direction in FIG. 6 (b)), and a processing edge represented by a gentle beam profile is formed in the direction of the segment 1104 (Y direction in FIG. 6 (b)). Naturally, part of a sample treated with the edge represented by the steep beam profile is processed with higher precision, and the processed section is satisfactory. Therefore, the edge represented by the steep beam profile is brought into contact with a section. A procedure of observing a section of a sample using the edge represented by a steep beam profile will be described below. As shown in FIG. 13 (b), the sample stage 13 is tilted approximately 45° with a sample 11 mounted thereon so that a direction perpendicular to the sample will coincide with the direction of the ion beam irradiation axis 1100. A molded ion beam 6 is irradiated to the sample so that a section will correspond to the YZ′ plane shown in FIG. 6 (a). The section is finished to become nearly perpendicular to the surface of the sample. As mentioned above, a processing edge represented by a steep beam profile is formed in the X′ direction shown in FIG. 6 (b). Thereafter, an electron beam 8 is irradiated to the section of the sample, whereby the section can be observed using the electron beam 8. Compared with the apparatus shown in FIG. 1, the present apparatus is characterized in that the sample stage need not be moved but that the section can be observed using the electron beam. Thus, the molded ion beam is used to steeply process a section of a sample. In other words, if a section of an abnormality such as a defect in a semiconductor circuit pattern or a foreign matter is formed, the section of the defect or foreign matter can be observed using the electron beam 8. The cause of the defect or foreign matter can be analyzed. Even in the present apparatus, when a section is processed using a molded ion beam, a profile representing an ion beam may be axially asymmetrically controlled using an ion source aperture plate or an asymmetric lens. For processing of a section of a sample on the sample stage, since an ion beam has the X′-direction edge thereof represented by a steep beam profile, the section is steeply processed. The X′ direction corresponds to a tilting direction in which the sample stage is tilted, or the direction of the sample mounting surface of the first stage. Namely, the direction of projection in which the stage tilting axis is projected on the X′Y plane perpendicular to the ion-beam irradiation axis is the Y direction. The asymmetry of the apertures in the ion source aperture plate is determined so that the X′-direction edge of an ion beam will be represented by a steeper intensity profile than the Y-direction edge thereof. Namely, the present apparatus is structured so that the major axes of the apertures in the ion source aperture plate will be parallel to the direction of projection in which the stage tilting axis is projected, that is, the Y direction. Otherwise, the present apparatus is structured so that the major axes of the apertures in the ion source aperture plate will be parallel to the sample mounting surface of the stage, that is, the Y direction. In other words, in the present apparatus, the width of the skew of an intensity profile representing an edge of an ion beam, which is projected on a sample and has a rectangular cross section, in a direction perpendicular to the direction of projection in which the stage tilting axis is projected on the sample stage surface is controlled to be smaller than the width of the skew of an intensity profile representing the other edge thereof in the direction parallel to the direction of projection in which the stage tilting axis is projected on the sample stage surface. Owing to the foregoing arrangement, only a section that should be observed is steeply processed. This is advantageous in that a throughput of processing improves. Moreover, even in the present apparatus, if cutting to be performed with an ion beam in order to form a section and observation to be performed using an electron beam are repeated, three-dimensional information on the inside of a sample can be acquired or a three-dimensional image can be constructed using multiple two-dimensional view images. In the present apparatus, the SEM column is disposed so that scanning electron microscopy can be achieved in a perpendicular direction. However, the SEM column need not always be disposed perpendicularly as long as a section of a micro test piece can be observed. According to a sample production method and sample production apparatus described as the present embodiment, neutral particles are removed. Therefore, metal neutral particles generated in the plasma ion source will not reach a sample. Even if a processed wafer is returned to a production line, a defective is rarely developed. Moreover, gas neutral particles will not be irradiated to a wide area of a sample. This is advantageous in overcoming an issue that a portion of a sample other than a desired portion is processed and denatured. Moreover, a section can be observed using an electron beam without the necessity of moving the sample stage after the completion of processing the section. Moreover, according to the sample production method and sample production apparatus described as the present embodiment, the employment of the stencil mask permits high-precision processing to be achieved with a larger current. In particular, even if an ion source suffering low luminance is employed, a large beam current can be produced and processing precision can be improved. Consequently, processing of a section and production of a micro test piece can be achieved shortly. This means that in a semiconductor device manufacturing process, an ion beam of inert gas or a gas element such as oxygen or nitrogen that does not seriously affect the properties of a sample can be substituted for an ion beam of gallium (Ga) which is highly likely to cause a defective. Consequently, a section can be produced with an ion beam without contamination of a wafer with a metal such as gallium. Moreover, a micro test piece can be separated without breakage of a wafer or preparations can be made for the separation. Consequently, a novel test/analysis method making it unnecessary to dispose of a wafer for the purpose of evaluation and making it possible to return a wafer, from which a test piece is extracted, to a production line without occurrence of a defective can be provided in order to improve a yield for manufacturing a semiconductor device or the like. Moreover, a wafer can be evaluated without being broken, a defective will not be newly developed, and an expensive wafer will not be wasted. Eventually, a yield for manufacturing a semiconductor device improves. In the sample production apparatuses in accordance with the first and second embodiments respectively, neutral particles generated in the plasma ion source or neutral particles generated in the middle of the column will not reach a sample. However, ions of an impurity such as a metal generated in the plasma ion source reach the sample. The present embodiment will be described as a sample production apparatus in which a mass separator is disposed in the middle of a path of an ion beam in order to trap the impurity ions. Even in the present embodiment, a beam molded by passing through an opening in a stencil mask and projected on a sample is employed. FIG. 14 shows the configuration of an ion beam processing apparatus in accordance with the third embodiment of the present invention. The ion beam processing apparatus includes an ion-beam irradiation optical system composed of a duoplasmatron 1 that releases ions of a gas such as argon, neon, xenon, krypton, oxygen, or nitrogen, a mass analyzer 61, an ion source aperture (limiting aperture) plate 26, a condenser lens 2, an objective lens 3, an ion beam scanning deflector 4, a stencil mask 5, and an ion beam column tube 21 that accommodates these components. Moreover, the ion beam processing apparatus includes an electron beam irradiation optical system composed of an electron gun 7, an electron lens 9 that focuses an electron beam 8 released from the electron gun 7, an electron beam scanning deflector 10, and an electron beam column tube (scanning electron microscope (SEM) column tube) 22 that accommodates these components. A vacuum chamber 23 is disposed below the ion beam column tube 21 and SEM column tube 22. The vacuum chamber 23 accommodates a first sample stage 13 on which a sample 11 is mounted, a secondary-electron detector 12, a depositional gas source 18. Moreover, the ion beam processing apparatus includes a probe 15 that carries a test piece extracted from a sample on the first sample stage by performing ion beam processing, a manipulator 16 that drives the probe, and a second sample stage 24 on which a micro test piece 303 is mounted. Needless to say, the inside of the ion beam column tube 21 is kept in vacuum. Herein, in the ion beam processing apparatus, an ion beam-irradiated sample point and an electron beam-irradiated sample point are deviated from the center of the sample mounting surface and located at different positions. Namely, an ion beam irradiation axis 301 and an electron beam irradiation axis 302 will not intersect. Disposed as units for controlling the ion beam processing apparatus are a duoplasmatron control unit 91, a mass separator control unit 62, an ion source aperture plate control unit 93, a lens control unit 94, a stencil mask control unit 95, an ion beam scanning deflector control unit 96, a first sample stage control unit 14, a second sample stage control unit 25, a manipulator control unit 17, a depositional gas source control unit 19, secondary-electron detector control units 27 and 28, an electron beam irradiation system control unit 97, and a computer system 98. Herein, the computer system includes a display on which an image produced based on a detective signal sent from the secondary-electron detector 12 or information entered at an information input means is displayed. Movements made in the ion beam processing apparatus are nearly identical to those made in the apparatus in accordance with the first embodiment. The mass separator 61 is moved instead of the ion beam deflector 20 in order to remove impurity ions included in an ion beam. The ability of the mass separator 61 is exerted when the mass separator control unit 62 is started in response to a command sent from the computer system 98. A molded ion beam having passed through the mass separator 61, condenser lens 2, stencil mask 5, and objective lens 3 is irradiated to a sample, whereby a rectangular hole is formed. Thereafter, an electron beam released from the electron beam irradiation system is used to observe a section of a sample. FIG. 15 (a) shows a top view of the ion beam processing apparatus, FIG. 15 (b) shows a front view thereof, and FIG. 15 (c) shows a side view thereof, thus clarifying the structure of the mass separator, the positional relationship thereof to the electron beam tube, and the relationship thereof to a section forming direction in FIG. 14. Moreover, FIG. 16 (a) to (c) shows the internal structure of the mass separator 61. In FIG. 15 (a) to (c), the secondary-electron detector, depositional gas source, and manipulator are not shown. In the top view of FIG. 15 (a), the front view of the FIG. 15 (b), and the side view of FIG. 15 (c), there are shown a sample stage 13 that holds a sample, an ion source 1001 that generates an ion beam, an irradiation optical system 1002 that irradiates an ion beam to the sample held on the sample stage 13, a charged beam irradiation optical system 1003 that is used to observe a section processed with an ion beam, and the mass separator 61. The mass separator 61 included in the present embodiment is a so-called E×B mass separator in which an electric field and a magnetic field are developed perpendicularly to an ion beam and the direction of the electric field and the direction of the magnetic field meet at right angles. In FIG. 16 (a) to (c), there are shown permanent magnets 1012, and electrostatic deflectors 1011 disposed perpendicularly to the permanent magnets 1012 and used to apply an electric field. In the present embodiment, the permanent magnets are used. Alternatively, electromagnets may be employed. Moreover, the magnetic field alone may be used for mass separation. In this case, a path of an ion beam is refracted. A segment drawn by projecting a direction of mass diffusion, which is included in mass separation, on a plane perpendicular to an ion beam irradiation axis should merely be at least substantially parallel to a segment drawn by projecting the tilting axis of the second sample stage on the plane perpendicular to the ion beam irradiation axis. In other words, the segment drawn by projecting the direction of mass diffusion, which is included in mass separation, on the plane perpendicular to the ion beam irradiation axis is parallel to the sample mounting surface of the first sample stage. The relationship between the direction of mass separation and the depositions of the columns will be described later. In FIG. 16 (a), an arrow 1015 indicates a direction in which mass separation occurs in the E×B mass separator. Among ions incident on the mass separator, ions whose masses cause the electric fields thereof to balance with the magnetic field induced by the permanent magnets are allowed to pass through a mass separation aperture 1013. However, the mass separation causes the width of the skew of an intensity profile of a projective beam to expand, and prevents formation of a steep section. This is attributable to the fact that energy exerted by an ion differs from ion to ion. When an ion beam has ions thereof separated by the mass separator, the trajectory of the ion beam spreads in the direction of diffusion due to the difference in energy. This affects even a molded ion beam. Consequently, the width of the skew of the intensity profile expands in the direction of mass separation performed by the mass separator. In the ion beam processing apparatus, the mass separator is disposed so that the direction of mass diffusion to be performed by the mass separator will not be parallel to a processing direction in which a section is kept dug up. Thus, an adverse effect on a processed section is avoided. The segment drawn by projecting the direction of mass diffusion, which is performed by the mass separator 61, on the plane perpendicular to the ion beam irradiation axis, that is, the X′Y plane shown in FIG. 6 (b) is parallel to the Y axis. The segment drawn by projecting the tilting axis of the second sample stage on the plane perpendicular to the ion beam irradiation axis (X′Y plane) is also parallel to the Y axis. Herein, since the Y axis is parallel to the sample mounting surface of the first stage, the segment drawn by projecting the direction of mass diffusion on the plane perpendicular to the ion beam irradiation axis can be said to be parallel to the sample mounting surface of the first stage. A technique for observing a section under the above depositions and a technique for producing an electron microscopic thin-film sample are identical to those described in relation to the apparatus shown in FIG. 1. Owing to the arrangement described in conjunction with FIG. 15 (a) to (c) and FIG. 16 (a) to (c), a steep section can be shortly formed using a molded ion beam, and can be observed at a high throughput using an electron beam. The present embodiment includes the first sample stage and the second sample stage on which a test piece extracted by performing ion beam processing is mounted. The second sample stage need not always be included. The ion beam processing apparatus may have the tilting ability to vary an angle of irradiation, at which an ion beam is irradiated to a sample, by rotating the first stage about the tilting axis thereof. At this time, the ion beam irradiation axis and electron beam irradiation axis generally intersect above a sample. Moreover, as described in relation to the first and second embodiments, the ion beam deflector for removing neutral particles generated in the ion source and the mass separator may be used in combination. Moreover, the mass separator may be tilted relative to the ion irradiation axis in order to perform removal of neutral particles and mass separation concurrently. At this time, the configuration of the apparatus can be simplified and a cost of manufacture can be reduced. Moreover, the present embodiment adopts an argon ion beam. Alternatively, an ion beam of such an element as nitrogen, oxygen, neon, xenon, or krypton, or an ion beam of a mixture thereof will do. Moreover, the present embodiment adopts the duoplasmatron as an ion source. Alternatively, a plasma ion source employing microwaves, a multicusp ion source, a field ionization ion source, or a liquid metal ion source will do. In particular, when the mass separator is used to remove gold or an impurity from a gold-silicon alloy for the purpose of irradiating a silicon ion beam alone to a sample, the sample will not be contaminated with the impurity in the course of manufacturing a silicon device. Furthermore, a thin beam which the plasma ion source can hardly produce can be produced. According to the sample production method and sample production apparatus described as the present embodiment, in addition to the advantages provided by the sample production method and sample production apparatus described as the first embodiment, impurity ions such as metal ions generated in the ion source can be removed by the mass separator and will not reach a sample, and the sample will not be contaminated with the impurity. This is advantageous in that a yield for manufacturing a device will not be decreased. Moreover, compared with a technique according to which an ion beam is controlled so that the X-direction and Y-direction edges thereof respectively will be represented by steep profiles, that is, compared with a case where the ion beam is molded symmetrically, the asymmetrical beam molding technique employed in the present embodiment can increase an ion beam current. Consequently, the beam molding technique employed in the present embodiment is preferable for an ion beam of a gas element such as argon or oxygen. In a manufacturing process for a semiconductor device such as a silicon device, an ion beam of inert gas or a gas element such as oxygen or nitrogen that does not adversely affect the properties of a sample should preferably be employed in production of a test piece. However, among currently available ion sources, a plasma ion source that generates gas-element ions suffers low luminance of a generated ion beam. Consequently, an ion beam is asymmetrically molded at the beginning, and an edge of the ion beam represented by a steeper beam profile is used to perform actual processing. Thus, even an ion source suffering low luminance may be employed without degradation of processing precision. This applies not only to ion sources that employ an ion beam of a gas element (for example, such an element as nitrogen, oxygen, neon, xenon, or krypton, or a mixture of the elements) but also to the other ion sources that suffer low luminance. Moreover, even when an ion beam is not molded rectangularly, the problems the present invention addresses can be solved. For example, the ion beam is molded to have an elliptic cross section. When the ion beam is elliptically molded, an ion beam having two diameters, that is, a long diameter along a major axis of an ellipse and a short diameter along a minor axis thereof is produced. The short-diameter direction of a beam spot is used to process a section of a sample. Compared with a case where a circular beam is employed, precision in processing a sample is improved. For actual processing of a sample, the positional relationship between an ion beam and a sample is controlled so that the short-diameter direction of the beam will be oriented to a processed section of the processed sample. Moreover, in the aforesaid embodiments, an electron beam is used to observe a section. Alternatively, an ion beam may be used for the observation. In particular, when a field ionization ion source is employed, a section can be observed at a high resolution. Moreover, a shallower structure can be observed than that is with an electron beam. As for the configuration of an apparatus, an electron beam irradiation optical system that irradiates an electron beam to a sample is replaced with an ion beam irradiation optical system. This is commonly applicable throughout the present application. The present invention has been described in terms of axially asymmetrical control of an ion beam profile. For example, when the widths of the skews of beam profiles representing the edges of an ion beam in two orthogonal directions are different from each other, the beam profiles representing the X-direction and Y-direction edges need not be axially symmetrical. For example, when one of the edges, that is, the X-direction edge extends in the axial center, the width of the skew of the beam profile is minimized and smaller than the width of the skew thereof representing the other edge of the ion beam. If the width of the skew of a beam profile is different from the width of the skew of a beam profile representing either of the edges or the Y-direction edge of the ion beam, it says that the ion beam is axially asymmetric. As described previously, according to the present invention, a processing method for shortening the time required for forming or processing a section using an ion beam, a processing method for shortening a processing time required for separating a micro test piece without breaking a wafer or a processing time required for making preparations for the separation, and an ion beam processing apparatus can be realized in order to improve a yield for manufacturing a semiconductor device. Furthermore, a processing method for shortening a section forming time in a case where inert gas ions, oxygen ions, or nitrogen ions are used as an ion beam, a processing method for shortening the time required for separating an analytic sample from a wafer or making preparations for the separation, and an ion beam processing apparatus can be realized. Furthermore, a novel test/analysis method making it unnecessary to dispose of a wafer for the purpose of evaluation and making it possible to return a wafer, from which a test piece is extracted, to a production line without occurrence of a defective can be realized. Moreover, when an electronic part manufacturing method in accordance with the present invention is adopted, a wafer can be evaluated without being broken, a defective will not be newly produced, and an expensive wafer will not be wasted. Eventually, a yield for manufacturing an electronic part improves. Furthermore, an ion beam processing apparatus in which a method for separating an analytic sample or making preparations for the separation, a test/analysis method, and the electronic part manufacturing method can be implemented can be realized. The present invention includes ion beam processing apparatuses and ion beam processing methods that are described below. (1) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and a charged beam irradiation optical system for use in observing a section processed with the ion beam, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam processing apparatus is structured so that an axis along which the ion beam is drawn out of the ion source and an ion beam irradiation axis along which the ion beam is irradiated to the sample will meet at an angle; and the ion beam processing apparatus is structured so that a segment drawn by projecting the axis, along which the ion beam is drawn out of the ion source, on a plane perpendicular to the ion beam irradiation axis can be at least substantially parallel to a segment drawn by projecting the tilting axis of the sample stage on the plane perpendicular to the ion beam irradiation axis. (2) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and a charged beam irradiation optical system for use in observing a section processed with the ion beam, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam processing apparatus further includes a mechanism for performing mass separation on the ion beam drawn out of the ion source; and the ion beam processing apparatus is structured so that a segment drawn by projecting a direction of mass diffusion, which is included in mass separation, on a plane perpendicular to an ion beam irradiation axis along which the ion beam is irradiated to the sample can be at least substantially parallel to a segment drawn by projecting the tilting axis of the sample stage on the plane perpendicular to the ion beam irradiation axis. (3) An ion beam processing apparatus including: a first sample stage that holds a sample; an ion source that generates an ion beam; an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage; an electron beam irradiation optical system that irradiates an electron beam to the sample; a probe means for carrying a test piece extracted from the sample by performing ion beam processing; and a second sample stage on which the test piece is mounted, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the test piece, by rotating the second sample stage about the tilting axis of the second sample stage; the ion beam processing apparatus further includes a mechanism for performing mass separation on the ion beam drawn out of the ion source; and the ion beam processing apparatus is structured so that a segment drawn by projecting a direction of mass diffusion, which is included in mass separation, on a plane perpendicular to an ion beam irradiation axis along which the ion beam is irradiated to the sample can be at least substantially parallel to a segment drawn by projecting the tilting axis of the second sample stage on the plane perpendicular to the ion beam irradiation axis. (4) The ion beam processing apparatus set forth in (1) or (2), wherein a beam irradiation axis of the charged beam irradiation optical system for use in observation is perpendicular to an apparatus installation plane, and the ion beam irradiation axis is tilted relative to the apparatus installation plane. (5) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and a charged beam irradiation optical system for use in observing a section processed with the ion beam, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam irradiation optical system is an irradiation optical system that irradiates the ion beam to the sample via a mask having a desired rectangular opening; and the ion beam processing apparatus further includes a control means for extending control so that the width of the skew of an intensity profile representing an edge of the rectangular ion beam, which is projected on the sample, in a direction perpendicular to a direction in which the tilting axis of the sample stage is projected on the sample stage surface will be smaller than the width of the skew of an intensity profile representing the other edge of the ion beam in a direction parallel to the direction in which the tilting axis of the sample stage is projected on the sample stage surface. (6) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; a limiting aperture through which ions are drawn out of the ion source; and an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage, wherein: the ion beam irradiation optical system is an irradiation optical system that irradiates the ion beam to the sample via a mask having an opening of a desired shape; and the mask has a polygonal or circular opening whose at least one side or whose diameter is so small that the diameter of a beam irradiated to the sample through the opening via a lens will be smaller than the diameter of a beam irradiated to the sample through an ion release hole in the ion source or the limiting aperture via the lens. (7) An ion beam processing apparatus including: a first sample stage that holds a sample; an ion source that generates an ion beam; an ion beam irradiation optical system that irradiates the ion beam to the sample held on the sample stage; an electron beam irradiation optical system that irradiates an electron beam to the sample; a probe means for carrying a test piece extracted from the sample by performing ion beam processing; and a second sample stage on which the test piece is mounted, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the test piece, by rotating the second sample stage about the tilting axis of the second sample stage; and an electron beam irradiation axis along which the electron beam is irradiated to the sample and an ion beam irradiation axis along which the ion beam is irradiated to the sample are tilted relative to the first sample stage, and the electron beam irradiation axis and ion beam irradiation axis exist on the same plane and intersect substantially perpendicularly to each other. (8) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage, wherein: the ion beam is used to process the sample so as to form a substantially vertical section, a test piece is extracted from the sample, or a transmission electron microscopic thin-film sample is produced; the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam processing apparatus is structured so that an axis along which an ion beam is drawn out of the ion source and an axis along which the ion beam is irradiated to the sample will meet at an angle; and a segment drawn by projecting the axis, along which the ion beam is drawn out of the ion source, on a plane perpendicular to the ion beam irradiation axis can be substantially parallel to the sample mounting surface of the sample stage. (9) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and a charged beam irradiation optical system for use in observing a section processed with the ion beam, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam processing apparatus is structured so that an axis along which the ion beam is drawn out of the ion source and an axis along which the ion beam is irradiated to the sample will meet at an angle; and a segment drawn by projecting the axis, along which the ion beam is drawn out of the ion source, on a plane perpendicular to the ion beam irradiation axis is substantially parallel to the sample mounting surface of the sample stage. (10) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and an electron beam irradiation optical system that irradiates an electron beam to the sample, wherein: the ion beam processing apparatus is structured so that an axis along which the ion beam is drawn out of the ion source and an axis along which the ion beam is irradiated to the sample will meet at an angle; the ion beam processing apparatus further includes a probe that carries a test piece extracted from the sample by performing ion beam processing, and a second sample stage on which the test piece is mounted; the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the second sample stage about the tilting axis of the second sample stage; and a segment drawn by projecting the axis, along which the ion beam is drawn out of the ion source, on a plane perpendicular to the ion beam irradiation axis is substantially parallel to the sample mounting surface of the sample stage. (11) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage; and a charged beam irradiation optical system for use in observing a section processed with the ion beam, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the sample, by rotating the sample stage about the tilting axis of the sample stage; the ion beam processing apparatus further includes a mechanism for performing mass separation on the ion beam drawn out of the ion source; and a segment drawn by projecting a direction of mass diffusion, which is included in mass separation, on a plane perpendicular to the ion irradiation axis is substantially parallel to the sample mounting surface of the sample stage. (12) An ion beam processing apparatus including: a first sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage; an electron beam irradiation optical system that irradiates an electron beam to the sample; a probe that carries a test piece extracted from the sample by performing ion beam processing; and a second sample stage on which the test piece is mounted, wherein: the ion beam processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the test piece, by rotating the second sample stage about the tilting axis of the second sample stage; the ion beam processing apparatus further includes a mechanism for performing mass separation on the ion beam drawn out of the ion source; and a segment drawn by projecting a direction of mass diffusion, which is included in mass separation, on a plane perpendicular to the ion irradiation axis is parallel to the sample mounting surface of the first sample stage. (13) An ion beam processing apparatus in which a beam irradiation axis of a charged beam irradiation optical system for use in observation is perpendicular to an apparatus installation plane, and an ion beam irradiation axis is tilted relative to the apparatus installation plane. (14) An ion beam processing apparatus in which a beam irradiation axis of an electron beam irradiation optical system is perpendicular to an apparatus installation plane, and an ion beam irradiation axis is tilted relative to the apparatus installation plane. (15) An ion beam processing apparatus structured so that an electron beam irradiation axis and an ion beam irradiation axis intersect substantially above a sample. (16) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; and an irradiation optical system that irradiates the ion beam to the sample held on the sample stage, wherein: the ion beam irradiation optical system is a projective ion beam irradiation optical system that irradiates an ion beam to the sample via a mask having an opening of a desired shape, and includes at least two ion beam lenses and at least two mask driving mechanisms or aperture driving mechanisms capable of changing openings. (17) An ion beam processing apparatus including: a first sample stage that holds a sample; an ion source that generates a first ion beam; an irradiation optical system that irradiates the first ion beam to the sample held on the sample stage; a field ionization ion source that generates a second ion beam; an ion beam irradiation optical system that irradiates the second ion beam to the sample; a probe that carries a test piece extracted from the sample by performing first ion beam processing; and a second sample stage on which the test piece is mounted, wherein: the ion processing apparatus has a tilting ability to vary an angle of irradiation, at which the ion beam is irradiated to the test piece, by rotating the second sample stage about the tilting axis of the second sample stage; and an irradiation axis along which the first ion beam is irradiated and an irradiation axis along which the second ion beam is irradiated are tilted relative to the first sample stage, exist on the same plane, and intersect substantially perpendicularly. (18) An ion beam processing apparatus including: a sample stage that holds a sample; a field ionization ion source that generates a gas ion beam; an irradiation optical system that irradiates the gas ion beam to the sample held on the sample stage; and a secondary-electron detector capable of detecting secondary electrons or reflected electrons released from the sample, wherein: the ion beam processing apparatus further includes at least two control units each including a signal amplifier for amplifying a signal sent from the secondary-electron detector; and one of the control units amplifies a dc voltage of a detective signal, and the other control unit measures a signal intensity level by counting the number of signal pulses. (19) An ion beam processing apparatus including: a sample stage that holds a sample; a field ionization ion source that generates a gas ion beam; an irradiation optical system that irradiates the gas ion beam to the sample held on the sample stage; and a secondary-electron detector capable of detecting secondary electrons or reflected electrons released from the sample, wherein: the ion beam processing apparatus further includes at least two control units each including a signal amplifier for amplifying a signal sent from the secondary-electron detector, measures a current to be irradiated to the sample, and switches the two secondary-electron detector control units according to the current value. (20) An ion beam processing method to be implemented in an ion beam processing apparatus which includes a sample stage that holds a sample, an ion source that generates a gas ion beam, and an irradiation optical system that irradiates an ion beam to the sample held on the sample stage, in which the gas ion beam irradiation optical system is a projective ion beam irradiation optical system that irradiates an ion beam to the sample through a mask, which has an opening of a desired shape, under the condition that the opening in the mask will be projected on the sample via a lens, and in which a gas ion beam produced using a first accelerating voltage is used to process the sample in order to produce a transmission electron microscopic thin-film sample, wherein: in the same vacuum sample chamber, the gas ion beam is irradiated to a processed surface of the transmission electron microscopic thin-film sample with an accelerating voltage set to a voltage lower than the first accelerating voltage. (21) An ion beam processing apparatus including: a sample stage that holds a sample; an ion source that generates an ion beam; an irradiation optical system that irradiates the ion beam to the sample held on the sample stage, wherein: the ion beam is used to process the sample in order to form a substantially vertical section, a test piece is extracted from the sample, or a transmission electron microscopic thin-film sample is produced; an axis along which the ion beam is drawn out of the ion source and an axis along which the ion beam is irradiated to the sample meet at an angle; and a member against which neutral particles generated in the ion source or an intermediate vacuum chamber collide is made of a silicon. |
|
summary | ||
summary | ||
claims | 1. A computed tomography apparatus comprising: a scanning unit which is rotatable relative to an examination zone, about an axis of rotation extending through the examination zone; a radiation source which generates a radiation beam; a diaphragm arrangement disposed between the radiation source and the examination zone in order to form a fan beam traversing the examination zone from the radiation beam; a two-dimensional detector arrangement having a plurality of detector elements and a measuring surface, a part of which detects primary radiation from the fan beam whereas another part of the measuring surface detects scattered radiation produced in the examination zone; and a collimator arrangement interposed between the examination zone and the detector arrangement, the collimator arrangement including a plurality of lamellas disposed in planes that subdivide the fan beam into a number of segments so that the detector elements that are situated in a column extending parallel to the axis of rotation essentially are struck only by primary radiation or scattered radiation from one and the same segment. 2. A computed tomography apparatus as defined by claim 1 , wherein the planes in which the lamellas are disposed intersect at the focus of the radiation source. claim 1 3. A computed tomography apparatus as defined by claim 1 , wherein the computed tomography apparatus includes a first mode of operation in which a part of the detector elements detect the scattered radiation that is generated in the fan beam, and a second mode of operation in which the detector elements detect the primary radiation that is generated in a cone beam whose dimensions in the direction of the axis of rotation are larger than those of the fan beam. claim 1 4. A computed tomography apparatus as defined by claim 3 , wherein in the first mode of operation a first diaphragm arrangement is disposed between the radiation source and the examination zone in order to generate the fan beam whereas in the second mode of operation a second diaphragm arrangement is active in the beam path in order to generate the cone beam. claim 3 5. A computed tomography apparatus as defined by claim 3 , wherein the computed tomography apparatus utilizes a first computer program for calculating the scatter density distribution in the part of the examination zone traversed by the fan beam from the detector signals acquired in the first mode of operation, and a second computer program for calculating the attenuation of the primary radiation in the part of the examination zone traversed by the cone beam from the detector signals acquired in the second mode of operation. claim 3 6. A computed tomography apparatus comprising: a scanning unit which is rotatable relative to an examination zone, about an axis of rotation extending through the examination zone; a radiation source which generates a radiation beam; a diaphragm arrangement disposed between the radiation source and the examination zone in order to form a fan beam traversing the examination zone from the radiation beam; a two-dimensional detector arrangement having a plurality of detector elements and a measuring surface, a part of which detects primary radiation from the fan beam whereas another part of the measuring surface detects scattered radiation produced in the examination zone; and a collimator arrangement interposed between the examination zone and the detector arrangement, the collimator arrangement including a plurality of lamellas disposed in planes that subdivide the fan beam into a number of segments so that the detector elements that are situated in a column extending parallel to the axis of rotation essentially are struck only by primary radiation or scattered radiation from one and the same segment; wherein the computed tomography apparatus utilizes a first computer program for calculating scatter density distribution in the part of the examination zone traversed by the fan beam, and a second computer program for calculating attenuation of primary radiation in the part of the examination zone traversed by a cone beam whose dimensions in the direction of the axis of rotation are larger than those of the fan beam. |
|
047284889 | description | DETAILED DESCRIPTION OF THE INVENTION Shown in FIG. 1 is a water displacement rodlet 1 which is composed of an elongate tubular zirconium base alloy (preferably Zircaloy-2 or 4) or a Zirconium-niobium alloy member 2 hermetically sealed at both ends and containing ZrO.sub.2 pellets and helium. The rodlet is one of a number of rodlets which is connected to a spider assembly 3. The spider assembly 3 has a drive line 5 for moving the rodlets into and out of the thimble tubes of a nuclear fuel assembly. Rodlet 1 is connected to the spider assembly by a rodlet flexure member 7 located at the end of one of the spider vanes 9. Distributed along the length of the rodlet 1 are plates 11 which exend transversely with respect to the longitudinal axis of the rodlet 1. Preferably there are six such support plates 11. Each support plate 11 is perforated through its thickness by holes 13 which are connected to each other by slots 15. Slots 15 and holes 13 are configured and sized to provide support to the rodlets while allowing the rodlets 1 and the spider assembly 3 to readily travel up and down through the support plates 11 without binding. The support plates are composed of a non-zirconium base alloy, preferably a stainless steel such as AISI 304 stainless. The rodlet flexure member 7 provides flexibility to prevent jamming of adjacent rodlets in the support plates. These flexures then permit small gaps to further reduce wear. As shown in FIG. 1 the rodlet in accordance with the present invention has been coated with a wear resistant ESD coating on the outside diameter surface of the zirconium base alloy tubular member 2 in those areas of the tubular member in the vicinity of the holes in support plates 11. This is more clearly shown in FIG. 2 which is an enlarged view of the zirconium base alloy tubular member 2 in the vicinity of a support plate 11. It is preferred, as shown in FIG. 2, that the length of tube, L, having tube ESD coating 16 thereon at any one location should exceed the thickness, T, of the support plate 11, and more preferably, the coated portion of the tube should extend below plane of the bottom face 17 and above the plane of the top face 19 of support plate 11. Most preferably the coated length, L, is at least about three times the thickness, T, of plate 11. As also shown in FIG. 2, it is preferred that surface wall 21 of hole 13 which communicates with top surface 19 and bottom surface 17 of the support plate 11, also have an ESD coating 23 on it. ESD coating 23 may be selected from those described in the aforementioned Johnson patent application relating to ESD coatings. Alternatively, an improved ferrous alloy for wear may be substituted for the 304SS support 11 eliminating the need for ESD coating 23. A transverse cross section through the tubular member 2 and the support plate 11 is shown in FIG. 3. The tubular member is preferably Zircaloy-2 or 4 in a fully recrystallized, partially recrystallized or cold worked and stress relief annealed condition. Metallurgically bonded to the outer surface of tube 2 is a relatively thin ESD coating 16. The Zircaloy tube may have an outside diameter of about 0.91 inches and a wall thickness of about 0.055 inches while the ESD coating has an average thickness between about 0.001 and 0.002 inches. At and near the metallurgical bond 25 between the coating 16 and the tube 2 is a diffusion zone and heat affected zone that may extend a few thousands of an inch into the wall of the tube 2, but leaves the bulk of the wall thickness in its original metallurgical condition. The ESD coating 16 is preferably obtained from a cemented Cr.sub.2 C.sub.3 electrode as described in the aforementioned Johnson patent application. The ESD coating 23 on the wall 21 of the aperture 13 in support plate 11 also has a thickness of about 0.001 to 0.002 inches, but does not necessarily have the same composition as that found in coating 16 on tube 2. In addition to differences in coating composition caused by the diffusion of base metal into the coating (e.g. Zr in the case of tube 2 and Fe in the case of plate 11), the coating composition itself may differ in order to optimize the resistance of the wear couple to fretting wear under water reactor operating conditions. For example the coating 23 may be selected from those ESD coatings in accordancw with the invention described in the aforementioned Johnson patent application. While FIGS. 2 and 3 indicate that the surface of wall 21 of hole 13 has been entirely coated, it is also contemplated that wall 21 may remain uncoated or coated in only certain areas, for example in the areas of wall 21 wich is in close proximity to the juncture 27 of wall 21 and top face 19 and the juncture 29 of wall 21 and bottom face 17. The preceding examples have clearly demonstrated the benefits obtainable through the practice of the present invention. Other embodiments of the invention will become more apparent to those skilled in the art from a consideration of the specification or actual 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. |
048790885 | description | DETAILED DESCRIPTION Referring to the drawings, FIG. 1 shows the basic probe structure 2 used in our test. It includes a torsionally flexible probe handle 3, near one end of which is a transducer 4. The transducer is mounted in an alignment tab 6, which is spaced from a leaf spring 8 (FIG. 4). At the other end of probe handle 3 is a mounting block 10 which serves as the connector for the electrical cable 12. Probe handle 3 is fabricated from two strips of stainless steel which are welded together. Signal wires 13 connect transducer 4 to cable 12. FIGS. 2, 3, and 3A show the operating means by which the probe is inserted into the fuel assembly. The mounting block 10 is carried on a support means 16, which rides on rails 18, 18', which provide for longitudinal movement, and on rails 20, which provide for transverse movement. A guide pin 22 slides in grooves 24 of index plate 26. The grooves 24 are open at one end, shown at the left in FIGS. 2 and 3 and are faced by deflection plate 28 which is provided with multiple deflecting surfaces 30, each of which faces one of the grooves 24. The actuating means, which are not shown on FIG. 2, are indicated diagrammatically on FIG. 3. A reciprocating hydraulic cyclinder 32 moves carrier 16 and probe 2 longitudinally of the latter so that the transducer is moved along a row of fuel rods 34 in fuel assembly 36. At the same time, another cylinder 38 exerts a continuous pressure laterally. Under the influence of these cylinders, the pin 22 moves longitudinally along a groove 24 to the right in FIG. 2, then returns. When it reaches the lefthand end of the groove, the force of pressure cylinder 38 forces it laterally along the deflecting surface 30 to the next groove 24, as best shown in FIG. 3A. These grooves are spaced apart the same distance as the spaces between the rows of fuel elements 34. The transducer, therefore, passes successively along the rows of fuel elements in the fuel assembly 36. When the pin 22 has moved in both directions along the last groove 24, indicated as 24', the operator reverses the direction of pressure exerted by cylinder 38. The pin 22 then moves back along the groove 40 at the end of index plate 26 to the starting position, carrying with it the carrier 16 and the probe 2. Members 37 and 39 are guide members, made in the same form as the fuel tubes 34. One of these members is open at both ends. When the system is immersed in water, it fills, so that it simulates a defective fuel tube. This provides a check on the operation of the system during actual testing. FIG. 4 shows the position of the transducer 4 relative to a tube 34 when a test is made. As the probe is inserted between the rows of tubes 34, the transducer 4 continuously emits a series of pulses. When the transducer is in most positions of its travel, no reflection from a tube is returned to it. However, when it is in the position shown in FIG. 4, the ultrasound waves follow the paths shown by the arrows, resulting in echoes received and recorded by the transducer. As can be seen in FIGS. 1 and 4 the transducer 4 is recessed within the alignment tab 6 which is pressed against the rod 34 which is being tested. This results in a "water path", indicated by arrows in FIG. 4, between the transducer and the outer surface of the rod 34. This water path is necessary to provide a suitable time interval between the transmission of the pulse and the reception of the echoes which will now be described. FIG. 5 shows typical examples of the form of the echo as recorded on an oscilloscope. The horizontal axis of the graph measures time while the vertical axis measures the amplitude of the echoes received by the transducer. FIG. 5 shows, in solid lines, the signals characteristic of a tube which contains no water, and, in dotted lines, those characteristic of a tube containing water. The transducer, as it travels past the rods, emits a series of pulses, one of which is shown at 36. The remaining peaks show various reflections which are received by the transducer when it is aligned so that the emitted beam is radial to the tube. The first peak, 38, is the reflection from the outer surface of the rod. It will be noted that this is received by the transducer about 2.0 microseconds after the transmitted pulse. During the next 1.7 (approximately) microseconds there is a series of closely spaced peaks 40a, 40b, 40c, and 40d. They are from the inner surface of the tube nearest the transducer and are the result of reflection of the ultrasound back and forth between the inner and the outer surface of the tube wall nearest to the transducer. This is termed "wall ringing". Finally, there is another pulse 42 which results from the reflection of the ultrasound from the outer wall, back to the transducer, again to the outer wall, and again to the transducer. This is termed the "second surface echo". The curves connecting the peaks show the decay of the "wall ringing" with time. It will be noted that the rate of decay is much greater for a tube containing water than for one free from water. This is because there is a relatively high degree of "coupling", i.e., transfer of energy, between the metal and water, and almost no coupling between the metal and a gas, such as helium. The effect is the same whether of not the portion of the tube being tested contains fuel. The reflected sound energy is a function of boundary condition on the inside of the cladding. As long as the water layer is thick relative to the wave length of the sound being used then material beyond this water layer will have no affect on the measurement. The amount reflected from the fuel, if present, will be small as compared to that reflected from the inner wall of the tube, perhaps 2 percent of it. In making the test, the instrumentation is so designed that when the transducer is centered on a rod, there is a recordation over a "time window" 44, which includes the peak 38. After a specified lapse of time, chosen to exclude the second surface echo 42, there is again a recording of the signal over the "time window" 46, which includes the fourth reflection from the inner surface, provided the signal at this time is above a predetermined amplitude. If the signal is below that level, no recording is made. A sample of such a record is shown in FIG. 6. In this figure, the upper row records the echo received in the time windows 44 from each rod traversed by the transducer, while the lower row indicates the signals received during the time windows 46. It will be noted that in some instances there is no recording 46 corresponding to a record 44. The relationship is shown in larger scale and in relation to the tubes in FIG. 7. This figure shows a row of tubes 34 including one defective tube 34' which contains water. The upper signal trace shows the echoes received during the time windows 44. The lower shows echoes received during the time windows 46. It will be noted that no signal 46 appears opposite the defective tube 34'. The entire traverse of the transducer along a row of tubes 34 (FIG. 2) requires only a very few seconds; hence, an assembly can be checked very quickly with this system. While we have described in detail one embodiment of our invention, it will be apparent to those skilled in the art that various changes can be made, we therefore wish our patent coverage to be limited solely by the scope of the appended claims. |
043022880 | description | DESCRIPTION The invention is described herein as employed in a water cooled and moderated nuclear reactor of the boiling water type, an example of which is illustrated in simplified schematic form in FIG. 1. Such a reactor system includes a pressure vessel 10 containing a nuclear fuel core 11 submerged in a coolant-moderator such as light water, the normal water level being indicated at 12. A shroud 13 surrounds the core 11 and a coolant circulation pump 14 pressurizes a lower chamber 16 from which coolant is forced upward through the core 11. A part of the water coolant is converted to steam which passes through separators 17 and dryers 18 thence through a steam line 19 to a utilization device such as a turbine 21. Condensate formed in a condenser 22, along with any necessary make-up water, is returned as feedwater to the vessel 10 by a pump 23 through a control valve 24 and a feedwater line 26. A plurality of control rods 27, containing neutron absorber material, are provided to control the level of power generation and to shut down the reactor when necessary. Such control rods 27 are selectively insertable among the fuel assemblies of the core under control of a control rod control system 28. For proper reactor operation it is necessary to maintain the water level in vessel 10 within predetermined upper and lower limits. A general approach to such water level control will now be discussed. A first aspect of such control is a comparison between the steam out-flow from the vessel with the feedwater in-flow. A signal proportioned to the steam flow rate is provided by a steam flow sensor which may be a well-known differential pressure transmitter 29 that senses the differential pressure from a pair of spaced pressure taps in a venturi 31 placed in the steam line 19. (A suitable venturi arrangement for such purpose is shown in U.S. Pat. No. 3,859,853.) Similarly, a signal proportional to the feedwater flow rate is provided by a sensor 32 which may be in the form of a differential pressure transmitter connected to a venturi 33 in the feedwater line 26. (A suitable venturi for use in the feedwater line is shown in U.S. Pat. No. 3,889,537.) The signals from flow sensors 29 and 32 are transmitted to a feedwater control system 34 wherein one is subtracted from the other. A difference of zero indicates that outflow and inflow are the same and the water level will remain constant. If the difference is other than zero, a signal corresponding in sign and proportional to the amplitude of the difference is applied to a valve controller 36 which adjusts the valve 24 in a manner to bring steam outflow and feedwater inflow toward balance. This arrangement provides rapid correction and maintains vessel water level within the bounds of a relatively narrow deadband. However, it does not sense or control the position of the water level in the vessel. Thus a second aspect of water level control is the provision of an upper water level pressure tap 37 and a lower water level pressure tap 38 which provide signals from which the position of the water level in the vessel may be determined. The pressure taps 37 and 38 communicate with the interior of the vessel 10 and are connected to a well-known differential pressure transmitter 39 which converts the difference in pressure at taps 37 and 38 to an output signal indicative of the position of the water level 12. This signal is applied to the feedwater control system 34 and is employed therein to modify the control signal to valve controller 36 whereby the valve 24 is controlled to maintain the position of the water level 12 within the prescribed upper and lower normal operating limits. (Although not shown here for clarity of drawing, it is noted that the usual system employs two or more sets of pumps 23, valves 24 and controllers 36 connected in parallel.) If for some reason, such as component failure, the feedwater control system 34 fails to maintain the water level within normal limits the water level may become excessively low or high. A level detector 40 is provided to detect an excessively low, out-of-limits, water level and to produce a signal .theta.L.sub.1. Similarly, a level detector 41 is provided to detect an excessively high water level and to produce a signal .theta.L.sub.h. These signals are received by a reactor protection system 42 which responds to an out-of-limits condition by signaling the control rod control system 28 to insert the control rods and shut down the reactor. As further background to a discussion of the present invention reference is made to FIG. 2 which illustrates a known prior water level control system. As in FIG. 1, signals proportional to the steam flow rate and feedwater flow rate are provided by differential pressure transmitters 29 and 32. These signals are applied to separate inputs of a first algebraic summer circuit 43 which provides an output signal proportional to the difference therebetween on a lead 44 connect to an input of a second summer circuit 46. Signals indicative of the water level in vessel 10 are provided on respective leads 47.sub.a, 47.sub.b from differential pressure transmitters 39.sub.a and 39.sub.b which are connected to suitably positioned differential pressure sensors. A switch 48 selects either the signal on lead 47.sub.a or lead 47.sub.b at the option of the reactor operator and the selected signal normally is applied over a lead 49 to a second input of summer circuit 46. The output signal of the summer circuit 46 is applied over a lead 51, a switch 52 and a lead 45 to a level control circuit 53. The control circuit 53 compares the signal from the summer circuit to level set points and applies a level correction signal over a lead 54 to the controller 36 of valve 24 in the feedwater line 26 whereby the valve 24 is controlled as described hereinbefore in connection with FIG. 1. The switch 52 allows the operator to connect the line 49 directly to level controller 53 so that the summer 46 is out of the circuit. A master control station 56, located at the operators position and connected to the level controller 53 provides suitable operator displays, allows operator adjustment of the water level set points and provides for manual control of the valve controller 36. Thus the prior system, illustrated in FIG. 2 allows manual selection of one or the other of the water level indicating signals on leads 47.sub.a and 47.sub.b and the switch 53 allows the steam and feedwater flow comparison arrangement to be switched out of the circuit. However, there is no means for taking action automatically in the event of faults. A water level control system according to the invention, which reduces the liklihood of reactor shutdown because of failure of a component of the system, is illustrated in FIG. 3. Features which distinguish this system from previous systems are the provision of at least one redundant level control channel, automatic transfer of control from one channel to another and automatic disconnect of the signal from the steam and feedwater flow comparison circuit. For the purpose of this discussion Channel A will be considered the normal control channel and Channel B the redundant channel. Channel A includes the following interconnected elements: pressure taps or sensors 37.sub.a and 38.sub.a, differential pressure transmitter 39.sub.a, high level trip circuit 57.sub.a, low level trip circuit 58.sub.a, summer circuit 46.sub.a, switching circuit 52.sub.a, and level control circuit 53.sub.a. Channel B includes similar interconnected elements with similar reference numbers but with b subscripts. Differential pressure transmitter 39.sub.a provides an output signal indicative of the water level in vessel 10. This signal is applied to an input of summer circuit 46.sub.a via lead 47.sub.a. The other input of summer circuit 46.sub.a is connected to lead 44 over which is transmitted the output signal of summer circuit 43 which, as described hereinbefore is proportional to the difference between steam outflow and feedwater inflow whereby the level indicating signal is modified by the flow difference signal. The output signal from summer circuit 46.sub.a normally is applied via lead 51.sub.a, switch 52.sub.a and lead 45.sub.a to the level control circuit 53.sub.a. Control circuit 53.sub.a provides the water level control signal on a lead 67.sub.a which normally is applied through a switch 68 to valve controller 36. Operation of channel B is similar with the output signal of summer circuit 46.sub.b normally being applied to level control circuit 53.sub.b. A feature of the invention is the provision of a rate of change circuit 59 which monitors the flow rate difference signal on lead 44 and actuates switches 52.sub.a and 52.sub.b in response to a predetermined rate of change in the difference signal. It is found that component failures tend to be catastrophic in nature. Thus such a failure in the steam-feedwater flow comparison circuit (e.g. elements 29,32,43) is likely to result in a high rate of change of the output signal of summer circuit 43 on lead 44. Such a rate of change is detected by circuit 59 which thereupon produces an output signal on a lead 61 which actuates switches 52.sub.a and 52.sub.b to connect the leads 47.sub.a and 47.sub.b directly to leads 45.sub.a and 45.sub.b, respectively, and thus the summer circuits 46.sub.a and 46.sub.b are bypassed. (A signal connection 62 from the master control station 56 provides for manual reset of the switches 52.sub.a and 52.sub.b.) Another feature of the invention is the transfer of water level control from Channel A to Channel B upon detection that the water level has drifted outside of upper or lower operating limits or upon detection of a rapid change in the water level control signal from control circuit 53.sub.a. To detect the event of water level drift outside of the predetermined limits, the water level signals from three separate differential pressure transmitters 39.sub.a, 39.sub.b and 39.sub.c are monitored. The differential pressure transmitter 39.sub.c can be connected to suitable pressure sensors 37.sub.c and 38.sub.c or it can be connected in parallel with transmitter 39.sub.b to pressure sensors 37.sub.b and 38.sub.b. Connected to monitor the water level signals on leads 47.sub.a, 47.sub.b and 47.sub.c from transmitters 39.sub.a, 39.sub.b and 39.sub.c are respective pairs of high and low level trip circuits including 57.sub.a and 58.sub.a connected to lead 47.sub.a, 57.sub.b and 58.sub.b connected to lead 47.sub.b and 57.sub.c and 58.sub.c connected to 47.sub.c. (The level trip circuits may be any well-known threshold circuit, such as a Schmitt trigger circuit, which produces an output signal only when the input signal exceeds, or falls below, a predetermined level.) The high level trip signals H.sub.a, H.sub.b and H.sub.c are applied to a 2-out-of-3 logic circuit 63. Similarly, the low level trip signals L.sub.a, L.sub.b and L.sub.c are applied to a similar logic circuit 64. The output signals from the logic circuit are fed to an OR circuit 65. Thus in response to the presence of any two of the high level or any two of the low level trip signals the OR gate 65 produces an output channel transfer signal on a lead 66 connected to the transfer switch 68. In its normal position, the transfer switch 68 connects the level control circuit 53.sub.a through lead 67.sub.a to the valve controller 36 for control of the feedwater flow control valve 24 by Channel A. A channel transfer signal from OR gate 65 on lead 66 actuates transfer switch 68 to connect level control circuit 53.sub.b, through lead 67.sub.b, to valve controller 36 whereby water level control is transferred to Channel B. (A connection 69 between switch 68 and the master control station 56 provides reset of the switch 68. It is to be understood that connections, not shown, provide visual indications at the operators station of various aspects of circuit operation, such as the states of switches 52.sub.a, 52.sub.b, and 68.) If a failure in Channel A causes a high rate of change in the water level control signal on lead 67.sub.a which results in a large change in feedwater flow to the vessel through valve 24, the capacity of the feedwater source (e.g. condenser 22, FIG. 1) to store or supply the feedwater may be exceeded before the change in water level is sufficient to produce the low level or high level trip signals necessary to transfer control to Channel B. To prevent such a possibility, a further feature of the invention is the provision of a rate of change detection circuit 70 connected to monitor the water level control signal to valve controller 36. In response to a high rate of change of this control signal the rate of change circuit produces an output signal on a lead 75 connected to an input of the OR gate 65. In response to such signal the OR gate 65 provides an output signal on lead 66 which actuates switch 68 whereby water level control is transferred immediately to Channel B. In the system illustrated herein the rate of feedwater flow is varied by valve 24. Other feedwater flow rate varying means may be used. For example, the feedwater flow can be varied by use of a variable speed drive for pump 23. In such case the valve 24 is eliminated and the flow control signal is applied to a speed controller of the variable speed drive (not shown) for pump 23. If control is transferred to Channel B because of a rapid change in the water level control signal of Channel A, there is no significant change in the vessel water level because of the immediacy of the transfer, for slow changes in vessel water level, transfer of control is not effected until the predetermined upper or lower operating limits are exceeded. An example of the operation of the water level control system of FIG. 3 for a slowly changing water level is illustrated by FIG. 4. The initial portion 71 of the curve illustrates normal level control operation under control of Channel A. At 72 it is assumed that a fault occurs in Channel A which results in a relatively slowly rising water level. At 73 the water level traverses the normal upper limit H. This event is detected by the high level trip circuits 57.sub.a -57.sub.c which thereupon produce at least two of the signals H.sub.a, H.sub.b and H.sub.c. In response to these signals the logic circuit 63 produces an output signal through OR gate 65 which actuates switch 68 and, thus automatically transfers level control to Channel B. Upon assuming control, Channel B reduces the water level to its normal position as indicated at 74. (Transfer of level control from Channel A to Channel B could cause a large change in feedwater flow if the water level set point of level control circuit 53.sub.b is significantly different from the actual vessel water level when the transfer is made. To prevent such a large change in feedwater flow the level set point established by control circuit 53.sub.b preferably is floating, rather than fixed, so that it tracks the actual vessel water level within the upper and lower operating limits, or other means may be provided to limit the rate of change of the water level control signal. In the absence of the automatic control channel transfer provided by the present invention (for example, with a prior system as shown in FIG. 2) the water level could continue to rise, as indicated by the dashed curve 76, until it reached the upper out of limits level OL.sub.h and the reactor would have been shut down unnecessarily. Studies of the operation and reactor scram history of a large nuclear reactor power plant indicate that use of the present invention in such plant will reduce the annual reactor scrams by about 6 percent with an annual savings in the cost of the unavailability of the reactor of several hundred thousand dollars per year. |
summary | ||
abstract | A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials. |
|
description | The present invention relates to a reactor containment vessel vent system for use in a nuclear power plant. In a nuclear power plant, even if an unlikely event in which a reactor core disposed in a reactor pressure vessel is melted (hereinafter, referred to as a severe accident) occurs, the accident is designed to stop if sufficient water injection is performed thereafter and the reactor containment vessel is cooled. However, in a case where the cooling of the reactor containment vessel at the time of the severe accident is insufficient, generation of steam is continued and pressure in the reactor containment vessel is increased. When the pressure of the reactor containment vessel is further increased, there is a risk of a severer accident in which the reactor containment vessel is damaged and a large amount of radioactive substance is released to the atmosphere. Therefore, when the pressure in the reactor containment vessel is increased to predetermined pressure or more, gas in the reactor containment vessel is released into the atmosphere and an operation of reducing the pressure in the reactor containment vessel is performed. The operation of reducing the pressure in the reactor containment vessel is referred to as a vent operation. When the vent operation is performed in a boiling water reactor, the gas in the reactor containment vessel (hereinafter, referred to as vent gas) is released into pool water of a suppression pool, and the radioactive substance is removed by a scrubbing effect of the pool water. Then, the vent gas from which the radioactive substance is removed is released into the atmosphere. In the boiling water reactor in the related art, the vent gas is released into the atmosphere after the radioactive substance is removed by the pool water of the suppression pool. However, it is not possible to remove all radioactive substances only by scrubbing the pool water. Therefore, there is a reactor containment vessel vent system as a system for further removing the radioactive substance from the vent gas released into the atmosphere. The reactor containment vessel vent system in the related art includes a tank containing water that scrubs the vent gas, a pipe that introduces the vent gas into the water in the tank, a metal filter and an iodine filter provided at an outlet that discharges the vent gas from the tank, and the like. In such a reactor containment vessel vent system, the vent gas is scrubbed by being released into the water in the tank to remove particulate radioactive substance. In addition, the particulate radioactive substance that cannot be removed by scrubbing is removed by the metal filter, and a gaseous radioactive substance such as iodine is removed by a chemical reaction or an absorption action in the iodine filter. A noble gas filter that does not permeate radioactive noble gases is disposed at a further downstream portion (exhaust port side) of these radioactive substance removing units. The noble gas filter also removes the radioactive noble gases. However, if the noble gas filter is simply installed, the gas containing the noble gases that cannot permeate the noble gas filter stays in a region in contact with an upstream side of the noble gas filter in a discharge pipe of the vent gas (hereinafter, referred to as immediate upstream portion). In this case, since partial pressure of the gas containing the stayed noble gases is increased, permeation performance of steam to be permeated by the noble gas filter is reduced. That is, the steam to be discharged cannot permeate the noble gas filter. As a result, even when the vent operation is performed, the reactor containment vessel vent system cannot continuously discharge the steam in the reactor containment vessel, and eventually the pressure in the reactor containment vessel cannot be lowered. Therefore, for example, a reactor containment vessel vent system described in Patent Literature 1 includes a pipe and a mechanism for gas containing the noble gases staying in the immediate upstream portion of the noble gas filter in the vent gas outlet pipe to return to the reactor containment vessel. In this case, since the gas containing the noble gases that cannot permeate the noble gas filter does not stay in the immediate upstream portion of the noble gas filter, the noble gas filter does not hinder the discharge of the steam. That is, the permeation performance of the noble gas filter can be continuously maintained. Patent Literature 1: JP-T-2016-521843 However, in the reactor containment vessel vent system described in Patent Literature 1, an active device such as a pump is used to return the gas stayed in the immediate upstream portion of the noble gas filter into the reactor containment vessel. In order to drive the active device such as the pump, supply of a power supply is indispensable. Therefore, when an unlikely event occurs in which the power supply is lost and the active device such as the pump cannot be driven, the noble gas filter may lose the permeation performance of the steam, and the pressure in the reactor containment vessel may not be continuously lowered. In order to allow the pressure in the reactor containment vessel to be continuously lowered, it is necessary to prevent the noble gas filter from losing the permeation performance of the steam even in the unlikely event that the power supply is lost. An object of the invention is to provide a reactor containment vessel vent system capable of continuously releasing steam generated in a reactor containment vessel to the atmosphere even when a power supply is lost. The reactor containment vessel vent system according to the invention reduces pressure in a reactor containment vessel by releasing gas in the reactor containment vessel to the atmosphere. The reactor containment vessel vent system includes: a vent line that forms a vent gas flow path through which vent gas is discharged from the reactor containment vessel and released to the atmosphere; a noble gas filter provided at a most downstream portion of the vent line, the noble gas filter allowing at least steam to pass through and not allowing radioactive noble gases to pass through among the vent gas; a return pipe that connects an immediate upstream portion of the noble gas filter in the vent line and the reactor containment vessel; and an intermediate vessel provided on the return pipe, in which gas containing the radioactive noble gases that cannot permeate the noble gas filter flows and is stored. According to the invention, it is possible to provide a reactor containment vessel vent system capable of continuously releasing steam generated in a reactor containment vessel to the atmosphere even when a power supply is lost. Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions thereof are omitted. FIG. 1 is a diagram schematically showing an example of a configuration of a reactor containment vessel vent system 15 according to a first embodiment of the invention. In FIG. 1, an example of a configuration of the reactor containment vessel vent system 15 according to the present embodiment is shown in a broken-line frame, and an example of a schematic cross-sectional structure of a reactor containment vessel 1 is shown on a left side of the frame. As shown in FIG. 1, a reactor pressure vessel 3 containing a reactor core 2 is installed in the reactor containment vessel 1. A main steam pipe 4 is connected to the reactor pressure vessel 3 to send steam generated in the reactor pressure vessel 3 to a turbine (not shown) for power generation. In the present specification, the term “steam” refers to water steam. The inside of the reactor containment vessel 1 is partitioned into a dry well 5 and a wet well 7 by a diaphragm floor 12 made of reinforced concrete. The wet well 7 refers to a region in which pool water is stored therein. A pool in the wet well 7 is referred to as a suppression pool 8. The dry well 5 and the wet well 7 communicate with each other by vent pipes 11, and vent pipe exhaust portions 11a are opened below a water surface of the suppression pool 8 in the wet well 7. A pipe break accident in which a part of a pipe such as the main steam pipe 4 is damaged and the steam flows into the reactor containment vessel 1 is generally known as a name of Loss of Coolant Accident (LOCA). Such an accident usually occurs in the dry well 5 through which the main steam pipe 4 passes. In an unlikely event that such an accident occurs and the steam flows out into the dry well 5 from a break hole of the main steam pipe 4 or the like, first, pressure in the dry well 5 rises. The steam flowing out into the dry well 5 is guided into the water of the suppression pool 8 in the wet well 7 through the vent pipe 11 due to a pressure difference between the dry well 5 and the wet well 7. At this time, since the steam is condensed by the pool water in the suppression pool 8, the pressure rise in the reactor containment vessel 1 is prevented. Most of the radioactive substances contained in the steam are removed by a scrubbing effect of the pool water in the suppression pool 8. In the reactor containment vessel 1 of a boiling water reactor, when the pressure in the reactor pressure vessel 3 or the main steam pipe 4 rises abnormally, a steam relief safety valve 6, a steam relief safety valve exhaust pipe 9, a quencher 10, and the like are provided as units that reduce the pressure. This is to prevent an accident such as the LOCA from occurring not only when the pressure rise is merely an abnormal pressure rise. That is, when the pressure in the reactor pressure vessel 3 or the main steam pipe 4 rises abnormally, the steam relief safety valve 6 provided in the main steam pipe 4 is opened, and the steam in the main steam pipe 4 is released into the water of the suppression pool 8 through the steam relief safety valve exhaust pipe 9 and the quencher 10. Since most of the steam is condensed by releasing the steam into the water in the suppression pool 8, the pressure in the reactor pressure vessel 3 and the main steam pipe 4 is reduced. Most of the radioactive substances contained in the steam are removed by the scrubbing effect of the pool water in the suppression pool 8. As described above, in the present embodiment, by condensing the steam in the suppression pool 8 and cooling the pool water in the suppression pool 8 with a residual heat removal system (not shown), it is possible to prevent temperature and pressure in the reactor containment vessel 1 from rising. That is, a steam outflow accident from the main steam pipe 4 or the like to the dry well 5 can usually be stopped. However, if the residual heat removal system loses function although unlikely, the temperature of the pool water in the suppression pool 8 rises. As the temperature of the pool water rises, since partial pressure of the steam in the reactor containment vessel 1 rises up to saturated steam pressure of the temperature of the pool water, the pressure in the reactor containment vessel 1 rises. When such pressure rise occurs, the pressure rise can be prevented by spraying cooling water into the reactor containment vessel 1. In addition, the spray can be operated by connecting a fire pump or the like from the outside. Further, the spray may not work although unlikely. In this case, the pressure in the reactor containment vessel 1 continues to rise. When the pressure rise in the reactor containment vessel 1 occurs, the pressure rise in the reactor containment vessel 1 can be prevented by releasing the gas in the reactor containment vessel 1 to the outside. The operation is referred to as a vent operation. In the boiling water reactor, the vent operation is performed by releasing the gas in the wet well 7 to the outside (atmosphere). Since the gas in the wet well 7 is gas in which most of the radioactive substances are removed from the pool water of the suppression pool 8, pollution caused by the radioactive substances in the atmosphere is minimized. When performing the above-described vent operation, the reactor containment vessel vent system 15 is provided as a device to remove the radioactive substances from the gas (hereinafter, referred to as vent gas) released from the reactor containment vessel 1. Hereinafter, the reactor containment vessel vent system 15 will be described in detail. In a portion surrounded by a broken line in FIG. 1 (reactor containment vessel vent system 15), an arrow on a side of a pipe represented by a solid line indicates a direction of flow of the vent gas, and Roman numerals indicate an approximate type of gas contained in the vent gas. As shown in FIG. 1, one end of a vent pipe 13 is branched and connected to both the dry well 5 and the wet well 7 of the reactor containment vessel 1, and isolation valves 14 are disposed in the branched vent pipe 13. The other end of the vent pipe 13 is connected to an inlet pipe 17 of a filter vent vessel 16, and a distal end portion of the inlet pipe 17 is open into the filter vent vessel 16. Scrubbing water 18 is stored in a lower side of the filter vent vessel 16, and a metal filter 19 and an iodine filter 38 are provided in series on an upper side of the filter vent vessel 16. One end of an outlet pipe 20 of the filter vent vessel 16 is connected to the metal filter 19 and the iodine filter 38. The other end of the outlet pipe 20 passes through a shield wall 21 and is guided to the outside of the shield wall 21, and finally connected to an exhaust column 22 via a noble gas filter 23. The vent operation is usually started by opening an isolation valve 14a on the wet well 7 side. That is, when the pressure in the reactor containment vessel 1 rises abnormally due to a severe accident or the like, the isolation valve 14a on the wet well 7 side is opened as the vent operation. At this time, high pressure gas filled in the reactor containment vessel 1 passes through the pool water of the suppression pool 8 and is released to the wet well 7 side. At this time, since the gas such as the steam released to the wet well 7 side is scrubbed by the pool water of the suppression pool 8, most of the radioactive substances are removed. This is a main safety feature of the boiling water reactor. Next, the gas in the wet well 7 passes through the isolation valve 14a opened by the vent operation as the vent gas, and is further released into the scrubbing water 18 in the filter vent vessel 16 via the vent pipe 13 and the inlet pipe 17. At this time, the vent gas passing through the vent pipe 13 contains steam (water steam), hydrogen, nitrogen, or the like as main components, and also includes an aerosol-shaped radioactive substance, radioactive noble gases, and the like. The vent gas released into the scrubbing water 18 is scrubbed by the scrubbing water 18, and most of the aerosol-shaped radioactive substance is removed. Further, a gaseous radioactive substance such as iodine is removed from the vent gas scrubbed by the scrubbing water 18 by the metal filter 19 and the iodine filter 38. Therefore, the vent gas passing through the outlet pipe 20 on a downstream side of the iodine filter 38 is removed of the aerosol-shaped radioactive substance, radioactive iodine, or the like. Further, in the present embodiment, the noble gas filter 23 is provided in the vicinity of the exhaust column 22 on the outlet pipe 20 extending from the filter vent vessel 16 to the exhaust column 22 via the iodine filter 38. The noble gas filter is formed of a filter material that does not allow the radioactive noble gases and nitrogen gas to pass through but allow the water steam or hydrogen gas to permeate. Therefore, only the water steam and the hydrogen gas are released to the atmosphere from the exhaust column 22. In the above-described reactor containment vessel vent system 15, a vent gas flow path including pipes, radioactive substance removing units, and the like from the reactor containment vessel 1 to the exhaust column 22 via the vent pipe 13, the filter vent vessel 16, the outlet pipe 20, and the like, is referred to as a vent line. In the above-described reactor containment vessel vent system. 15, the noble gas filter 23 can remove the radioactive noble gases no matter at which position the noble gas filter 23 is disposed on the vent pipe 13 and the outlet pipe 20. However, it is considered that a best selection for the noble gas filter 23 to be placed is at a most downstream portion of the outlet pipe 20. In this case, since the noble gas filter 23 is disposed on the downstream side of the filter vent vessel 16, the metal filter 19, and the iodine filter 38, it is possible to prevent the aerosol-shaped radioactive substance or the like from adhering to the noble gas filter 23. Therefore, in this case, it is possible to prevent performance degradation due to adherence of the radioactive substance or the like to the noble gas filter 23. In addition, it is possible to prevent exposure to influence of a molten fuel that may occur during the severe accident. Therefore, reliability of the reactor containment vessel vent system 15 can be improved. As described above, the reactor containment vessel vent system 15 according to the present embodiment can confine the radioactive noble gases and discharge the steam from the exhaust column 22 to the outside even if the severe accident occurs in which the steam or the radioactive substances are generated in the reactor containment vessel 1. Therefore, the pressure in the reactor containment vessel 1 can be reduced. Next, the filter material of the noble gas filter 23 will be described. The noble gas filter 23 is required to permeate the steam. In order to prevent the pressure rise in the reactor containment vessel 1, the hydrogen gas generated when the reactor core 2 is melted is also required to be permeated. A molecular diameter of the steam (water) or hydrogen that permeates the noble gas filter 23 is as small as 0.3 nm or less, and a molecular diameter of the radioactive noble gases that does not permeate (Kr, Xe, and the like) is considerably larger than that. Therefore, as a structural material of the noble gas filter 23, a molecular sieve film that selectively permeates the steam and the hydrogen gas having a small molecular diameter can be used. In the case of the boiling water reactor, the gas in the reactor containment vessel 1 is replaced with nitrogen. Therefore, when selecting the radioactive noble gases using the molecular sieve film that uses the molecular diameter, the molecular sieve film may not permeate nitrogen molecules having a molecular diameter close to the size of the molecular diameter of Kr or Xe. However, from the viewpoint of reducing the pressure in the reactor containment vessel 1, since the cause of the pressure rise is the steam and the hydrogen gas, it does not matter even if the molecular sieve film does not allow the nitrogen molecules to permeate. Examples of the filter material of the molecular sieve film suitable for the above condition include a polymer film containing polyimide as a main component, a ceramic film containing silicon nitride as the main component, a graphene oxide film containing carbon as the main component, and the like. These molecular sieve films are generally known as filters used for hydrogen purification. The filter material of the noble gas filter 23 may be any film as long as it is a film that does not permeate Kr or Xe but permeates molecules of hydrogen or water (steam). Since the noble gas filter 23 using the filter material as described above permeates the steam and the hydrogen gas and does not permeate the nitrogen and the radioactive noble gases, it is possible to release the steam and the hydrogen gas that cause the pressure rise in the reactor containment vessel 1 while removing the radioactive noble gases. However, when the radioactive noble gases are removed from the vent gas by the noble gas filter 23, there is a problem that the permeation performance of the noble gas filter 23 for the steam and the hydrogen gas reduces with the passage of time, which is also a technical problem in the related art. The problem is caused by staying of the nitrogen gas and the radioactive noble gases that cannot permeate the noble gas filter 23 in a region in the outlet pipe 20 that is in contact with the upstream side of the noble gas filter 23 (hereinafter, referred to as an immediate upstream portion of the noble gas filter 23 or simply an immediate upstream portion). That is, when the nitrogen gas and the radioactive noble gases that cannot permeate the noble gas filter 23 stays in the immediate upstream portion of the noble gas filter 23, partial pressure of the gas rises, and the permeation of the steam and the hydrogen gas to be permeated by the noble gas filter 23 is hindered. Therefore, the permeation performance of the steam and the hydrogen gas by the noble gas filter 23 is reduced, and eventually a permeation function is lost. When the permeation function of the steam and the hydrogen gas by the noble gas filter 23 is lost, the pressure of the immediate upstream portion of the noble gas filter 23 rises to the same level as the pressure in the reactor containment vessel 1. This means that the function of the vent is lost. In order to prevent such a situation, the reactor containment vessel vent system 15 according to the present embodiment includes an intermediate vessel 100 for separately storing the gas such as the nitrogen gas and the radioactive noble gases staying in the immediate upstream portion of the noble gas filter 23. The immediate upstream portion of the noble gas filter 23 is connected to the intermediate vessel 100 via a return pipe 24a. A relief valve 25 is provided on the return pipe 24a. The relief valve 25 is constituted by a diaphragm type relief valve or the like, and has a structure that opens when fluid pressure on a primary side exceeds a set pressure PA and closes when the fluid pressure on the primary side falls below a set pressure PB (PB<PA). Therefore, in the present embodiment, when the pressure of the immediate upstream portion of the noble gas filter 23 rises and exceeds the set pressure PA, the relief valve 25 is opened. At this time, the gas such as the nitrogen gas and the radioactive noble gases staying in the immediate upstream portion of the noble gas filter 23 flows into the intermediate vessel 100. Initial pressure in the intermediate vessel 100 is preferably vacuum pressure or atmospheric pressure, and it is desirable that the gas in an initial state has oxygen removed by nitrogen substitution or the like. Therefore, in the reactor containment vessel vent system 15 according to the present embodiment, the pressure of the gas staying in the immediate upstream portion of the noble gas filter 23 can be reduced to the set pressure PA of the relief valve 25 or less. That is, the partial pressure of a total of the nitrogen gas and the radioactive noble gases in the immediate upstream portion of the noble gas filter 23 does not exceed a predetermined value. Therefore, in the present embodiment, the noble gas filter 23 can continuously maintain the performance of permeating the steam and the hydrogen gas without permeating the nitrogen gas and the radioactive noble gases. That is, in the reactor containment vessel vent system 15 according to the present embodiment, the steam and the hydrogen gas that cause an increase in the pressure in the containment vessel 1 can be continuously released to the outside even at the time of the severe accident or the like so that the pressure in the reactor containment vessel 1 can be continuously reduced. Further, in the present embodiment, the intermediate vessel 100 and the reactor containment vessel 1 are connected via a return pipe 24b, and a check valve 26 is provided on the return pipe 24b. The check valve 26 blocks the flow of the fluid from the reactor containment vessel 1 to the intermediate vessel 100, and in the present embodiment, prevents the radioactive substance in the containment vessel 1 from flowing into the intermediate vessel 100. On the other hand, the check valve 26 does not block the flow of the fluid from the intermediate vessel 100 to the reactor containment vessel 1. Therefore, when the pressure in the intermediate vessel 100 becomes higher than the pressure in the reactor containment vessel 1, the gas stored in the intermediate vessel 100 flows into the reactor containment vessel 1. Therefore, in the present embodiment, it is possible to prevent the pressure in the reactor containment vessel 1 from reducing more than necessary. Incidentally, in order to cool the reactor pressure vessel 3 and the reactor containment vessel 1, when cooling water is sprayed into the reactor containment vessel 1 after the vent operation, the pressure in the reactor containment vessel 1 may reduce more than necessary. Alternatively, natural cooling for a long time may reduce the pressure in the reactor containment vessel 1 more than necessary. In such a case, the gas stored in the intermediate vessel 100 flows into the reactor containment vessel 1. The check valve 26 is not limited to a check valve, and a relief valve may be used instead. However, in this case, a set pressure of valve opening of the relief valve needs to be set to a value lower than initial pressure in the reactor containment vessel 1. FIG. 2 is a diagram showing an example of time transition of pressure in each of the reactor containment vessel 1, the immediate upstream portion of the noble gas filter 23, and the intermediate vessel 100 after the vent operation in the reactor containment vessel vent system 15 according to the first embodiment of the invention. In FIG. 2, a horizontal axis of the graph represents time, a vertical axis represents pressure, dashed-dotted lines represent pressure in the reactor containment vessel 1, thick broken lines represent pressure in the immediate upstream portion of the noble gas filter 23, and thick solid lines represent pressure in the intermediate vessel 100. Here, initial pressure in the reactor containment vessel 1 is P0, initial pressure of the immediate upstream portion of the noble gas filter 23 is P1, initial pressure of the intermediate vessel 100 is P2, set pressure of the valve opening of the relief valve 25 is PA, and set pressure of valve closing is PB. In FIG. 2, t10, t11, t12, . . . represent time of the valve opening of the relief valve 25, t20, t21, t22, . . . represent time of the value closing of the relief valve 25, and t3 represents time of the valve opening of the check valve 26. The initial pressure P1 of the immediate upstream portion of the noble gas filter 23 is approximately the same as the atmospheric pressure. However, when the vent operation is performed, the pressure of the immediate upstream portion of the noble gas filter 23 gradually rises due to the vent gas released from the reactor containment vessel. This is because the nitrogen gas and the radioactive noble gases stay in the immediate upstream portion of the noble gas filter 23 and the permeation of the steam and the hydrogen gas that permeate the noble gas filter 23 is hindered. When the pressure of the immediate upstream portion of the noble gas filter 23 exceeds the set pressure PA of the relief valve 25, the relief valve 25 opens (time t10), and the nitrogen gas and the radioactive noble gases staying in the immediate upstream portion of the noble gas filter 23 flows into the intermediate vessel 100. At this time, since the steam permeation performance of the noble gas filter 23 is recovered, the pressure at the immediate upstream portion of the noble gas filter 23 decreases. When the pressure at the immediate upstream portion of the noble gas filter 23 decreases to the set pressure PB of the relief valve 25 or less, the relief valve 25 is closed (time t20). Therefore, the nitrogen gas and the radioactive noble gases start to stay again at the immediate upstream portion of the noble gas filter 23, and the pressure turns to rise. After that, the same operation as those described above is repeated until the times t11 and t21, further until the times t12 and t22, and so on. Therefore, since the pressure of the immediate upstream portion of the noble gas filter 23 rises at most up to the set pressure PA of the relief valve 25, the permeation performance of the steam and the hydrogen gas by the noble gas filter 23 can maintain at a constant performance. Therefore, since the steam and the hydrogen gas is continuously discharged from the reactor containment vessel 1, the pressure in the reactor containment vessel 1 gradually reduces. The pressure in the intermediate vessel 100 gradually rises in accordance with the amount of the nitrogen gas and the radioactive noble gases flowing into the relief valve 25 at the time of the valve opening. When the pressure in the intermediate vessel 100 exceeds the pressure in the reactor containment vessel 1, the check valve 26 opens (time t3), and the nitrogen gas and the radioactive noble gases stored in the intermediate vessel 100 flow into the reactor containment vessel 1. Thus, the nitrogen gas and the radioactive noble gases are returned to the reactor containment vessel 1. As described above, in the present embodiment, the intermediate vessel 100, the relief valve 25, and the check valve 26 which are provided to reduce the pressure at the immediate upstream portion of the noble gas filter 23 are passive components that operate without external power such as a power supply. Therefore, when the pressure reaches the set pressure PA of the relief valve 25, the gas such as the nitrogen and the radioactive noble gases staying in the immediate upstream portion of the noble gas filter 23 moves into the intermediate vessel 100 without being supplied with the power supply. When the pressure of the gas in the intermediate vessel 100 becomes higher than the pressure in the reactor containment vessel 1, the gas stored in the intermediate vessel 100 moves, that is, returns to the reactor containment vessel 1 without being supplied with the power supply. Therefore, the reactor containment vessel vent system 15 according to the present embodiment can continuously reduce the pressure in the reactor containment vessel 1 without releasing the radioactive noble gases to the outside even when the unlikely event such as lost of the power supply occurs. At this time, it is also possible to prevent the pressure in the reactor containment vessel 1 from reducing more than necessary. In the present embodiment, the immediate upstream portion of the noble gas filter 23 and the reactor containment vessel 1 are connected by the return pipe 24a, the intermediate vessel 100, and the return pipe 24b of one system, and may be connected by the return pipe 24a, the intermediate vessel 100, and the return pipe 24b of a plurality of systems. In this case, capacity of the intermediate vessel 100 can be made smaller than in the case of one system. In this case, even when the intermediate vessel 100 and the return pipes 24a and 24b of one system cannot be used due to some reason, the pressure at the immediate upstream portion of the noble gas filter 23 can be reduced by using the intermediate vessel 100 and the return pipes 24a and 24b of remaining systems. Therefore, reliability of the reactor containment vessel vent system 15 can be improved. In the above description of the first embodiment, it is assumed that the reactor containment vessel vent system 15 is applied to an improved boiling water reactor, and it is needless to say that the reactor containment vessel vent system 15 can be applied to a reactor type other than a light water reactor such as a pressurized water reactor or a high-speed growth reactor. In the reactor containment vessel vent system 15 according to the first embodiment, a wet radioactive substance removing device such as the filter vent vessel 16 is used as the radioactive substance removing device, and a dry radioactive substance removing device can also be used. These circumstances are the same in second to fourth embodiments described below. FIG. 3 is a diagram schematically showing an example of a configuration of a reactor containment vessel vent system 15a according to a second embodiment of the invention. In FIG. 3, an example of a configuration of the reactor containment vessel vent system 15a according to the present embodiment is shown in a broken-line frame, and an example of a schematic cross-sectional structure of the reactor containment vessel 1 is shown on a left side of the frame. The configuration of the reactor containment vessel vent system 15a according to the present embodiment is different from the configuration of the reactor containment vessel vent system 15 (see FIG. 1) according to the first embodiment in that a bypass pipe 120, a steam trap 110, and a check valve 130 are newly added. Hereinafter, differences from the first embodiment will be described. In the first embodiment, the nitrogen gas and the radioactive noble gases staying in the immediate upstream portion of the noble gas filter 23 flow into the intermediate vessel 100, and the inflow of the steam is ignored. However, when the relief valve 25 is opened, not only the nitrogen gas and the radioactive noble gases but also a part of the steam may flow into the intermediate vessel 100. Therefore, in the present embodiment, in addition to the nitrogen gas and the radioactive noble gases, a part of the steam to be originally released into the atmosphere flows into the intermediate vessel 100. When the steam flows into the intermediate vessel 100, the steam cools and condenses in the intermediate vessel 100, and accumulates in the intermediate vessel 100 as condensed water. Therefore, in the present embodiment, the bypass pipe 120 connecting the intermediate vessel 100 and the filter vent vessel 16 and the steam trap 110 provided on the bypass pipe 120 are added to the configuration of the reactor containment vessel vent system 15 (see FIG. 1) according to the first embodiment. Specifically, the bypass pipe 120 connected to the filter vent vessel 16 is provided downward from a bottom of the intermediate vessel 100. The check valve 130 and the steam trap 110 are provided on the bypass pipe 120. Therefore, when the steam flowing into the intermediate vessel 100 cools and becomes condensed water, the steam flows into the filter vent vessel 16 via the bypass pipe 120 due to gravity. The steam trap 110 has a function of allowing only condensed water to pass through and not allowing a gas component (steam) thereof to pass through. Therefore, only the condensed water flows into the filter vent vessel 16. The check valve 130 prevents the condensed water from flowing back into the intermediate vessel 100, and may also be omitted. Here, a connection destination of the bypass pipe 120 from the intermediate vessel 100 to the filter vent vessel 16 is assumed to be inside the filter vent vessel 16, and may be either the upstream side or the downstream side of the filter vent vessel 16. As described above, according to the present embodiment, the steam flowing into the intermediate vessel 100 becomes condensed water and returns to the filter vent vessel 16. Therefore, more nitrogen gas and radioactive noble gases can be stored in the intermediate vessel 100. In consideration of the contrary, a volume of the intermediate vessel 100 can be reduced accordingly. Furthermore, in the present embodiment, since the condensed water is returned to the filter vent vessel 16, an effect of preventing a reduction in the scrubbing water 18 can also be expected. As described above, in the present embodiment, the intermediate vessel 100, the relief valve 25, and the check valve 26 which are provided to reduce the pressure at the immediate upstream portion of the noble gas filter 23 are passive components that operate without external power such as a power supply. Therefore, the reactor containment vessel vent system 15a according to the present embodiment can continuously reduce the pressure in the reactor containment vessel 1 without releasing the radioactive noble gases to the outside even when the unlikely event such as lost of a power supply occurs. At this time, it is also possible to prevent the pressure in the reactor containment vessel 1 from reducing more than necessary. FIG. 4 is a diagram schematically showing an example of a configuration of a reactor containment vessel vent system 15b according to a third embodiment of the invention. In FIG. 4, an example of a configuration of the reactor containment vessel vent system 15b according to the present embodiment is shown in a broken-line frame, and an example of a schematic cross-sectional structure of the reactor containment vessel 1 is shown on a left side of the frame. The configuration of the reactor containment vessel vent system 15b according to the present embodiment is different from the configuration of the reactor containment vessel vent system (see FIG. 1) according to the first embodiment in that a non-condensable gas collection system 200 is newly added. Hereinafter, differences from the first embodiment will be described. Nitrogen gas and radioactive noble gases staying in an immediate upstream portion of the noble gas filter 23 flow into the intermediate vessel 100 when the relief valve 25 is opened, and at this time, steam to be originally released to the outside also flows into the intermediate vessel 100. Therefore, in the present embodiment, in order to prevent the inflow of the steam, the non-condensable gas collection system 200 is added to the reactor containment vessel vent system 15 (see FIG. 1) according to the first embodiment. As shown in FIG. 4, the non-condensable gas collection system 200 is provided on the return pipe 24a that connects the immediate upstream portion of the noble gas filter 23 and the relief valve 25. Non-condensable gases such as the nitrogen gas and the radioactive noble gases that does not condense at a temperature of about room temperature is collected, and the collected non-condensable gases are caused to flow into the intermediate vessel 100. A principle of non-condensable gas collection in the non-condensable gas collection system 200 is basically to remove condensable gas by cooling condensable and non-condensable mixed gas and condensing the condensable gas such as the steam. In this case, cooling of the gas by natural convection of air or water can be used. FIG. 5 is a diagram schematically showing an example of a configuration of the non-condensable gas collection system 200 used in the reactor containment vessel vent system 15b according to the third embodiment of the invention. As shown in FIG. 5, the non-condensable gas collection system 200 includes a condensing pipe 201 that captures non-condensable gases 202 (excluding the hydrogen gas), a pipe jacket 203 that allows outside air 205 to flow between outer surface of a pipe and inner surface of the pipe jacket, and a check valve 204. The condensing pipe 201 branches from the immediate upstream portion of the noble gas filter 23 of the outlet pipe 20 and is provided substantially vertically from below to above. The condensing pipe 201 is connected to the return pipe 24a via the check valve 204, and is further connected to the intermediate vessel 100. Here, a vertical portion of the condensing pipe 201 including the check valve 204 is covered by the cylindrical pipe jacket 203 at its outer peripheral portion, and a gap is provided between the pipe jacket 203 and the outer peripheral portion of the condensing pipe 201 and the check valve 204 to allow the outside air 205 to flow between outer surface of the pipe and inner surface of the pipe jacket. In this case, the non-condensable gases 202 such as the high-temperature nitrogen gas and the radioactive noble gases stays in the condensing pipe 201, and the cold outside air 205 flows into the gap between the condensing pipe 201 and the pipe jacket 203. Therefore, the outside air 205 flowing into the gap between the condensing pipe 201 and the pipe jacket 203 is heated by the heat of the condensing pipe 201 side, and becomes a rising air flow due to a chimney effect. Therefore, the cold outside air 205 is taken into the gap between the outer peripheral portion of the condensing pipe 201 and the pipe jacket 203, and the gas including the non-condensable gases 202 staying in the condensing pipe 201 is cooled. The longer the pipe jacket 203, a larger chimney effect can be provided. Hereinafter, the principle of the non-condensable gases collection by the non-condensable gas collection system 200 will be described. When the nitrogen and the radioactive noble gases stay in the immediate upstream portion of the noble gas filter 23, the permeation performance of the steam by the noble gas filter 23 is reduced. Therefore, the nitrogen and the radioactive noble gases including the steam flow into the condensing pipe 201. The gas flowing into the condensing pipe 201 is cooled by the outside air 205 flowing through the gap between the pipe jacket 203 and the outer peripheral portion of the condensing pipe 201. At this time, when the temperature falls below a dew point of the steam, the steam included in the gas starts to condense. When the steam condenses, the volume decreases accordingly, and thus the pressure in the condensing pipe 201 reduces locally. At this time, the non-condensable gases 202 staying in the immediate upstream portion of the noble gas filter 23 is instantaneously supplied to the local portion where the pressure is reduced. At this time, although the steam also flows due to a density difference, it can be said that only the non-condensable gases 202 is supplied since the inflow steam instantaneously condenses. Eventually, the non-condensable gases such as the nitrogen and the radioactive noble gases stays in the condensing pipe 201. Thereafter, when the nitrogen and the radioactive noble gases further stay in the immediate upstream portion of the noble gas filter 23 and the noble gas filter 23 loses the permeation performance of the steam, the pressure in the condensing pipe 201 further rises. When the pressure exceeds the set pressure PA of the relief valve 25 (see FIG. 4) provided on the downstream side of the check valve 204, the relief valve 25 opens, and the non-condensable gases such as the nitrogen and the radioactive noble gases staying in the condensing pipe 201 flow into the intermediate vessel 100. In this manner, the non-condensable gas collection system 200 can collect the non-condensable gases and store the collected non-condensable gases in the intermediate vessel 100. Here, it is assumed that the condensing pipe 201 is disposed at a position higher than the filter vent vessel 16. In this case, the condensed water condensed in the condensing pipe 201 is returned to the filter vent vessel 16 by gravity via the outlet pipe 20. Therefore, the effect of reducing the decrease in the scrubbing water 18 in the filter vent vessel 16 can be expected. The check valve 204 may be a relief valve, and in this case, the relief valve 25 provided on the return pipe 24a can be used as the relief valve. In addition, the natural convection of water may be used to cool the condensing pipe 201. In this case, the condensing pipe 201 can be cooled by installing a cooling water vessel (not shown) at a position higher than the condensing pipe 201 and allowing cooling water to flow into the gap between the pipe jacket 203 and the condensing pipe 201 by a water head difference therebetween. FIG. 6 is a diagram schematically showing an example of a configuration of another non-condensable gas collection system 200a used in the reactor containment vessel vent system 15b according to the third embodiment of the invention. Here, the non-condensable gas collection system 200a is used in place of the non-condensable gas collection system 200 shown in FIG. 5 in the reactor containment vessel vent system 15b (see FIG. 4) according to the third embodiment. A difference between the configurations of the non-condensable gas collection system. 200 shown in FIG. 5 and the non-condensable gas collection system 200a shown in FIG. 6 is that the former uses the disk-shaped noble gas filter 23, while the latter uses a cylindrical noble gas filter 23a. That is, in the example of FIG. 6, the cylindrical noble gas filter 23a is disposed at a position connecting the outlet pipe 20 and the condensing pipe 201 disposed substantially vertically from below to above, and is installed coaxially with both pipes. Therefore, among the gases flowing into the outlet pipe 20, the steam and the hydrogen gas permeate the noble gas filter 23a in a radial direction and reach the exhaust column 22 via a pipe that covers the outside thereof, and are released from the exhaust column 22 to the outside atmosphere. On the other hand, the non-condensable gases 202 such as the nitrogen or the radioactive noble gases that does not permeate the noble gas filter 23a stays in the condensing pipe 201. When the pressure is increased, the gas flows into the intermediate vessel 100 via the check valve 204 and the relief valve 25. Also in the example of FIG. 6, the outer peripheral portion of the check valve 204 and the condensing pipe 201 is covered with the cylindrical pipe jacket 203. Therefore, the non-condensable gases 202 staying in the condensing pipe 201 is cooled by the cold outside air 205 flowing in the outer peripheral portion thereof. Therefore, even if the non-condensable gases 202 is mixed with the steam, the steam is removed by condensing so that only the non-condensable gases 202 flows into the intermediate vessel 100 and is stored therein. The principle of the non-condensable gas collection in the non-condensable gas collection system 200a as described above is almost the same as the principle of the non-condensable gases collection described with reference to FIG. 5. Therefore, even in the non-condensable gas collection system 200a in the example of FIG. 6, the non-condensable gases can be collected, and the collected non-condensable gases 202 can be stored in the intermediate vessel 100. Here, it is assumed that the condensing pipe 201 is disposed at a position higher than the filter vent vessel 16. In this case, the condensed water condensed in the condensing pipe 201 is returned to the filter vent vessel 16 by gravity via the outlet pipe 20. Therefore, the effect of reducing the decrease in the scrubbing water 18 in the filter vent vessel 16 can be expected. In addition, the natural convection of water may be used to cool the condensing pipe 201. In this case, the vessel of the cooling water is installed at a position higher than the condensing pipe 201, and cooling water flows into the gap between the condensing pipe 201 and the pipe jacket 203 by the water head difference to cool the outer peripheral surface of the condensing pipe 201. As described above, in the present embodiment, the intermediate vessel 100, the non-condensable collection mechanisms 200, 200a, the relief valve 25, and the check valve 26 which are provided to reduce the pressure of the immediate upstream portion of the noble gas filter 23 are passive components that operate without external power such as a power supply. Therefore, the reactor containment vessel vent system 15b according to the present embodiment can continuously reduce the pressure in the reactor containment vessel 1 without releasing the radioactive noble gases to the outside even when the unlikely event such as lost of the power supply occurs. At this time, it is also possible to prevent the pressure in the reactor containment vessel 1 from reducing more than necessary. Other non-condensable gas collection systems 200, 200a used in the reactor containment vessel vent system 15b according to the third embodiment described above may be applied to the reactor containment vessel vent system 15a according to the second embodiment. FIG. 7 is a diagram schematically showing an example of a configuration of a reactor containment vessel vent system 15c according to a fourth embodiment of the invention. In FIG. 7, an example of a configuration of the reactor containment vessel vent system 15c according to the present embodiment is shown in a broken-line frame, and an example of a schematic cross-sectional structure of the reactor containment vessel 1 is shown on a left side of the frame. The configuration of the reactor containment vessel vent system 15c according to the present embodiment is largely different from the reactor containment vessel vent system 15a according to the second embodiment (see FIG. 3) in that a non-condensable gas collection system 200b including the intermediate vessel 100 is provided. Another difference is that the relief valve 25 is provided not on an upstream side of the non-condensable gas collection system 200b but on a downstream side. Further, a pipe on a downstream side of the relief valve 25 is branched into two, one of which is connected to the reactor containment vessel 1 via the check valve 26, and the other is connected to the filter vent vessel 16 via the check valve 130 and the steam trap 110. Hereinafter, these differences will be described. FIG. 8 is a diagram schematically showing an example of a configuration that collects the non-condensable gases 202 by the non-condensable gas collection system 200b in the reactor containment vessel vent system 15b according to the fourth embodiment of the invention. As shown in FIG. 8, the non-condensable gas collection system 200b includes the intermediate vessel 100 that collects and stores the non-condensable gases 202, and the pipe jacket 203 that covers an outer peripheral surface of the intermediate vessel 100 in an up-down direction and allows the outside air 205 to flow through a gap formed between the intermediate vessel 100 and an outer peripheral surface thereof. In the present embodiment, the intermediate vessel 100 and the immediate upstream portion of the noble gas filter 23 in the outlet pipe 20 are connected by the return pipe 24a. Therefore, nitrogen and radioactive noble gases that cannot permeate the noble gas filter 23 stay and are stored in the immediate upstream portion of the noble gas filter 23 and the intermediate vessel 100 with the passage of time. However, at this time, it is considered that steam is also mixed in the intermediate vessel 100. Here, when the low-temperature outside air 205 flows into the gap between the intermediate vessel 100 and the pipe jacket 203 that covers the outer peripheral portion of the intermediate vessel 100, the temperature of the gas mixed with the steam stored in the intermediate vessel 100 is also reduced. When the temperature becomes equal to or lower than a dew point temperature of the steam, condensation of the steam starts, and the steam is removed from the gas stored in the intermediate vessel 100. When the pressure in the intermediate vessel 100 exceeds the set pressure PA of the relief valve 25 provided on a return pipe 24c, the gas from which the steam stored in the intermediate vessel 100 is removed, that is, the nitrogen and the radioactive noble gases are returned to the reactor containment vessel 1 via the return pipe 24b. The condensed water generated in the intermediate vessel 100 is returned to the filter vent vessel 16 via the relief valve 25, the check valve 130, and the steam trap 110 provided on the bypass pipe 120 provided in a downward direction. At this time, the condensed water basically passes through the bypass pipe 120 due to gravity and reaches the filter vent vessel 16. In the fourth embodiment described above, water may be used for cooling the intermediate vessel 100 by the pipe jacket 203. In this case, a cooling water vessel (not shown) is installed at a position higher than the intermediate vessel 100, and cooling water flows into the gap between the pipe jacket 203 and the intermediate vessel 100 by using the water head difference therebetween, thereby cooling the intermediate vessel 100. The relief valve 25 provided on the return pipe 24c is not necessary. If the check valve 26 is installed on the return pipe 24b, even if the relief valve 25 is not installed, the function of collecting and storing the non-condensable gases 202 by the non-condensable gas collection system 200b is maintained. A connection destination of the bypass pipe 120 may be either the upstream side or the downstream side of the filter vent vessel 16. Furthermore, the check valve 130 provided on the bypass pipe 120 is also not necessary. However, when the check valve 130 is provided, a backflow of the fluid from the filter vent vessel can be prevented. The noble gas filter 23 provided in the outlet pipe 20 may have a disk shape used in the example of FIG. 5 or a cylindrical shape used in the example of FIG. 6. As described above, in the present embodiment, the non-condensable collection mechanisms 200b, the relief valve 25, and the check valve 26 which are provided to reduce the pressure of the immediate upstream portion of the noble gas filter 23 are passive components that operate without external power such as a power supply. Therefore, the reactor containment vessel vent system 15c according to the present embodiment can continuously reduce the pressure in the reactor containment vessel 1 without releasing the radioactive noble gases to the outside even when the unlikely event such as lost of the power supply occurs. At this time, it is also possible to prevent the pressure in the reactor containment vessel 1 from reducing more than necessary. The invention is not limited to the above-described embodiments and modifications and includes various modifications. For example, the above-described embodiments have been described in detail in order to facilitate the understanding of the invention, but the invention is not necessarily limited to all of the described configurations. Apart of the configuration of one embodiment or modification can be replaced with the configuration of another embodiment or modification, and the configuration of another embodiment or modification can also be added to the configuration of one embodiment or modification. In a part of a configuration of each embodiment or modification, a configuration of another embodiment or modification can be added, removed, or replaced. 1 reactor containment vessel 2 reactor core 3 reactor pressure vessel 4 main steam pipe 5 dry well 6 steam relief safety valve 7 wet well 8 suppression pool 9 steam relief safety valve exhaust pipe 10 quencher 11 vent pipe 11a vent pipe exhaust portion 12 diaphragm floor 13 vent pipe 14 isolation valve 15, 15a, 15b, 15c reactor containment vessel vent system 16 filter vent vessel 17 inlet pipe 18 scrubbing water 19 metal filter 20 outlet pipe 21 shield wall 22 exhaust column 23 noble gas filter 24a, 24b, 25c return pipe 25 relief valve 38 iodine filter 100 intermediate vessel 110 steam trap 120 bypass pipe 130 check valve 200, 200a, 200b non-condensable gas collection system 201 condensing pipe 202 non-condensable gases 203 pipe jacket 204 check valve 205 outside air |
|
claims | 1. A synthesis system comprising:a cyclotron operable for bombarding a target material in a target cavity of a solution target with protons or deuterons; anda kit for isolation of a radionuclide from a solution including the radionuclide, the solution having been produced by the bombarding of the target material in the target cavity of the solution target with protons or deuterons, the kit comprising: a column including a sorbent to adsorb the produced radionuclide on the sorbent, wherein the sorbent comprises a hydroxamate resin; and an eluent for eluting the radionuclide off the sorbent,wherein the radionuclide is selected from 68Ga, 89Zr, 64Cu, 86Y, 63Zn, 61Cu, 99mTC, 45Ti, 52Mn and 44Sc. 2. The synthesis system of claim 1, wherein:the eluent comprises a phosphate. 3. The synthesis system of claim 1, further comprising:a radionuclide product vessel for receiving eluted radionuclide from the column. 4. The synthesis system of claim 1, further comprising:a first fluid conduit for placing the column in fluid communication with the cyclotron, anda second fluid conduit for placing the column in fluid communication with the vessel that receives the solution including the eluted radionuclide. 5. The synthesis system of claim 1, further comprising:a second column including a sorbent to adsorb impurities in the eluent used for eluting radionuclide from the column. 6. The synthesis system of claim 1, further comprising:a controller for automating the system. 7. The synthesis system of claim 6, wherein:the controller executes a stored program to: (i) deliver the solution including the radionuclide from the target cavity to the column, (ii) thereafter deliver the eluent to the column, and (iii) thereafter deliver the eluted radionuclide to a radionuclide product vessel. 8. The synthesis system of claim 6, wherein:the controller executes a stored program to: (i) deliver the solution including the radionuclide from the target cavity cyclotron to a collection vessel, (ii) deliver the solution including the radionuclide from the collection vessel to the column, (iii) thereafter deliver the eluent to the column, and (iv) thereafter deliver the eluted radionuclide to a radionuclide product vessel. 9. The synthesis system of claim 1 wherein:the eluent comprises hydrogen phosphate ions. 10. The synthesis system of claim 1 wherein:the eluent comprises an alkali metal hydrogen phosphate. 11. The synthesis system of claim 1 wherein:the eluent comprises HCl. |
|
abstract | A capsule for the transfer of a target material in a conveying system between a target irradiation station and a collecting station comprising: a beamline channel for the passage of an energetic beam irradiating the target material, a target holder holding the target material or a substrate backing the target material at a glancing angle with respect to the beamline channel axis, a degrader foil positioned across the beamline channel for degrading an energy of the energetic beam upstream of the target material, a target cooling inlet and a target cooling outlet for passage of a cooling fluid in a target cooling duct in a vicinity of the target holder such that the target material can be cooled during an irradiation, and a degrader foil cooling inlet and a degrader foil cooling outlet for passage of a cooling gas in a vicinity of the degrader foil. |
|
summary | ||
047132086 | summary | CROSS-REFERENCE TO RELATED APPLICATION The present invention is related, but in no way dependent upon, co-pending U.S. patent application Ser. No. 703,577, entitled STEADY-STATE INDUCTIVE SPHEROMAK OPERATION, filed Feb. 20, 1985, in the names of Alan C. Janos, Stephen C. Jardin and Masaaki Yamada. BACKGROUND OF THE INVENTION This invention relates generally to the generation and confinement of an energetic plasma by magnetic fields and is particularly directed to the initiation and sustaining of a fusion plasma in a sheromak reactor. A spheremak reactor uses toroidal and poloidal magnetic fields to confine a doughnut-shaped plasma. In a speheromak, the currents generation the toroidal field within the plasma itself, eliminating the large external toroidal field coils required in tokamak reactors. The spheromak geometry therefore provides various advantages over that of the tokamak such as improved access to the plasma for placement of thermal conversion blankets, the creation of plasmas with low aspect ratios and increased stability, a high current density minimizing the requirement for auxiliary heating, and a high beta value representing the ratio of plasm pressure to magnetic field pressure. The sustainment of the spheromak configuration is highly desirable for assisting in the attainment of fusion conditions from an initial discharge or for maintaining a steady-state fusion plasma. Sustainment is used to describe any method of actively driving plasma currents to either extend the discharge lifetime, maintain a steady-state discharge, or increase plasma currents after the formation phase. Steady-state or long-pulse (wherein the discharge time is much longer than a resistive decay time) operation has many advantages over pulsed operation including a reduction in mechanical fatigue due to cyclic magnetic and thermal stresses an an increase in energy efficiency by eliminating energy losses incurred during start-up of a discharge. Near term advantages of sustainment would be derived from the providing of a long lived, time-independent plasma so that the confinement properties of the spheromak could be easily studied. Various techniques have been proposed for the sustainment of spheromaks. These proposals, which have met with only limited degrees of success, include the merging of spheromaks, the application of oscillating field current drive (OFCD) using audio frequencies, radio frequency current drive, the application of direct current (DC) from electrodes, the Rotamak concept, and neutral as well as charged particle beam injection. Present Alfven electrode gun schemes have the advantage of a simple operation requirement that permits the plasma to be easily translated into the experimental area. In addition, the DC electrode gun approach has sustained spheromaks experimentally for much longer than a resistive decay time. However, this approach requires a substantial amount of electrode discharge to create the toroidal magnetic field and to propel the plasma through the electrode gun muzzle against poloidal field pressure. Furthermore, the possible advantage of inductive sustainment over DC current drive using electrodes is a potential reduction if impurity influx due to the elimination of a material surface, in contact with the plasma, through which large currents are drawn. Inductive sustainment is extendable to long time cycles and may be able to maintain a discharge indefinitely. U.S. Pat. Nos. 4,363,776 to Yamada et al and 4,436,691 to Jardin et al, both assigned to the assignee of the present application, disclose inductive approaches to the formation and sustainment of a spheromak plasma. However, because inductively produced spheromak plasmas are subject to resistive decay and because heretofore the poloidal and toroidal fields have not been sustainable as both are produced in part or in whole, respectively, by plasma currents, the aforementioned inductive approaches have been used only in a pulsed operation, i.e., the method is repeated at regular intervals, and have not been suitable for continuous, or steady-state, operation. The aforementioned, cross-referenced patent application also discloses an inductive approach to the sustainment of a spheromak plasma involving the initiating of a plasma discharge by means of the combination of poloidal and toroidal magnetic fields in an evacuated vacuum vessel containing a neutral species, wherein the poloidal magnetic field is comprised of first and second component poloidal magnetic fields of different strength. The thus produced plasma is allowed to expand in the direction of the weaker poloidal magnetic field, with a portion of the expanded plasma pinched off so as to produce a line-linked spheromak plasma partially connected to the toroidally shaped flux core within the vacuum vessel. The poloidal and toroidal magnetic fields .psi. and .phi. are then subject to oscillation such that .psi. and .phi. have different phases, where preferably the poloidal and magnetic fields are 90.degree. out of phase. The plasma may be partially pinched off by either energizing a set of pinching coils or by simultaneously reversing the directions of the poloidal and toroidal currents in the flux core. The present invention is directed to an arrangement for the inductive generation and sustainment of a spheromak plasma involving the use of a poloidal flux-amplifying inductive transformer aligned along the major axis of a flux core and comprised of a solenoidal coil. Reversal of the current in the solenoidal coil results in a poloidal flux swing and the conversion of a portion of the poloidal flux to toroidal flux for either plasma generation or sustainment. OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide for improved generation and sustainment of an energetic plasma in a spheromak fusion reactor. It is another object of the present invention to inductively induce a large poloidal magnetic flux in a spheromak-shaped plasma utilizing a reduced magnetic field-generating current in a current-carrying flux core. Yet another object of the present invention is to facilitate the formation and sustainment of a spheromak plasma using available technology which does not require an undue amount of research and development. A further object of the present invention is to provide a thermonuclear fusion reactor for forming and sustaining a low impurity spheromak plasma by means of large alternating poloidal and toroidal magnetic fields. The present invention contemplates a poloidal flux transformer in the form of a straight solenoidal coil positioned along the length of the major axis of a magnetic flux core for inductively inducing poloidal flux therein for the generation and sustaining of a spheromak plasma. The poloidal flux transformer may be used as an amplifier stage in a moving plasma reactor scenario to initiate the formation of a spheromak plasma as well as to translate and inject the plasma into a desired location. In the latter case, the initial or seed plasma is made by an inductive discharge around a flux varying core and its flux is increased during translation and injection of the plasma into a desired location by the poloidal flux transformer. The poloidal flux-amplifying inductive transformer makes use of the observed phenomenon of flux conversion wherein a poloidal flux is converted to a toroidal flux and vice versa, with the plasma assimilating the fluxes and relaxing toward a Taylor stable minimum energy equilibrium state. The present invention not only reduces the demanding current carrying requirements for the flux core, but also improves poloidal flux injection efficiency and reduces the impurities within the plasma. |
055725635 | claims | 1. A mirror unit comprising: a mirror having a reflecting surface; a holding member for supporting said mirror; and an airtight chamber incorporating said mirror, supported by said holding member, in an airtight state, wherein one of said mirror and said holding member constitutes a portion of a side wall of said airtight chamber and said mirror is detachably mounted to said airtight chamber through an opening in the side wall. a radiation source for generating a radiation beam; a mirror unit including a mirror for reflecting the radiation beam; and an exposure unit for exposing a substrate with the reflected radiation beam, wherein said mirror unit comprises: a mirror having a reflecting surface; a holding member for supporting said mirror; and an airtight chamber incorporating said mirror, supported by said holding member, in an airtight state, wherein one of said mirror and said holding member constitutes a portion of a side wall of said airtight chamber and said mirror is detachably mounted to said airtight chamber through an opening in the side wall. 2. A mirror unit according to claim 1, wherein said mirror comprises an X-ray mirror for reflecting X-rays. 3. A mirror unit according to claim 1, further comprising securing means for securing said mirror to said holding member. 4. A mirror unit according to claim 3, wherein said mirror secured to said holding member by said securing means comprises an integral member. 5. A mirror unit according to claim 4, further comprising means for mounting said integral member to said airtight chamber. 6. A mirror unit according to claim 5, further comprising a gasket provided between said integral member and said airtight chamber for assuring vacuum sealing of said airtight chamber. 7. A mirror unit according to claim 4, wherein said integral member further comprises means for cooling said airtight chamber. 8. An exposure apparatus comprising: 9. An exposure apparatus according to claim 8, further comprising securing means for securing said mirror to said holding member. 10. An exposure apparatus according to claim 9, wherein said mirror secured to said holding member by said securing means comprises an integral member. 11. An exposure apparatus according to claim 10, further comprising means for mounting said integral member to said airtight chamber. 12. An exposure apparatus according to claim 11, further comprising a gasket provided between said integral member and said airtight chamber for assuring vacuum sealing of said airtight chamber. 13. An exposure apparatus according to claim 10, wherein said integral member further comprises means for cooling said airtight chamber. 14. An exposure apparatus according to claim 8, wherein the substrate comprises a wafer, on which said exposure unit transfers a pattern by exposure. 15. An exposure apparatus according to claim 8, wherein said radiation source comprises a synchrotron orbit radiation apparatus for emitting a sheet-shaped radiation beam. 16. An exposure apparatus according to claim 15, wherein said mirror spreads the sheet-shaped radiation beam emitted from said synchrotron orbit radiation apparatus in a direction perpendicular to a sheet plane of the radiation beam. |
059237171 | summary | FIELD OF THE INVENTION This invention relates generally to nuclear reactors and more particularly, to identifying optimum fuel bundle loading arrangements in a nuclear core. BACKGROUND OF THE INVENTION A nuclear reactor core has many, e.g., several hundred, individual fuel bundles that have different characteristics. Such bundles preferably are arranged within the reactor core so that the interaction between the fuel bundles satisfies all regulatory and reactor design constraints, including governmental and customer specified constraints. In addition to satisfying the design constraints, since the core loading arrangement determines the cycle energy, i.e., the amount of energy that the reactor core generates before the core needs to be refreshed with new fuel elements, the core loading arrangement preferably optimize the core cycle energy. To optimize core cycle energy, the higher reactivity bundles generally are positioned at an inner core location. To satisfy some design constraints, however, higher reactivity bundles generally are positioned at an outer core location. Identifying the preferred core loading arrangement therefore is an optimization with constraints challenge. The number of bundle arrangements, or configurations, possible in the reactor core can be in excess of one hundred factorial. Of these many different possible configurations, only a small percentage of such configurations satisfy all applicable design constraints. In addition, only a small percentage of the configurations that satisfy all applicable design constraints are economical. Traditionally, core loading arrangement determinations are made on a trial and error basis. Specifically, and based on past experience of the engineers, a core loading arrangement is identified. The identified core loading arrangement is then simulated in a computer. If a particular design constraint is not satisfied by the identified arrangement, then the arrangement is modified and another computer simulation is run. Man-weeks of resources typically are required before an appropriate core loading arrangement is identified using the above described procedure. In addition, once a core loading arrangement that satisfies all design constraints has been identified using the trial and error approach, such identified core arrangement may not provide the actual maximum cycle energy. Therefore, the trial and error process continues until the engineers believe that the optimum core arrangement has been identified. In practice, however, it is possible that a particular core arrangement that is not necessarily consistent with the engineers' past experience may be the actual optimum core arrangement. Such actual optimum core arrangement, however, may not necessarily be identified through the trial and error process. Since the core arrangement problem generally is considered unique for each reactor and bundle characteristics, no known algorithm provides a viable solution for identifying optimum reactor core arrangements. In addition, expert systems have not been used on a broad basis since a standard set of rules typically are not applicable over a wide range of situations to the many unique and complex core loading arrangements which differ in all reactors. It would be desirable, of course, to reduce the time required to identify a core loading arrangement which optimize cycle energy and satisfies all design constraints. It also would be desirable to provide a methodology applicable to a wide range of reactors for consistently and reliably identifying optimum core loading arrangements. SUMMARY OF THE INVENTION These and other objects may be attained by the present invention which in one aspect is a method for identifying an optimum core loading arrangement. The method generally has two (2) phases. The first phase is an initialization phase and the second phase is the running, or search, phase. In the initialization phase, an initial core loading arrangement is identified based on the relative reactivity levels of the bundles to be loaded and the reactor core locations. Once the initial core loading arrangement is identified, such arrangement is then optimized, within the defined constraints, in the running phase. More specifically, in the running phase, each core location is analyzed to determine whether such core location reactivity level can be changed from the initial reactivity level to either satisfy a constraint or optimize cycle energy, or both. Subsequent to analyzing each core location as described above, random core loading arrangements are created and compared with the then best case loading arrangement identified. Such randomly generated core loading arrangements sometimes are referred to as "random jumps", and such "random jumps" are made to potentially identify previously unconsidered core loading arrangements that may be more optimum than the most optimum arrangement identified up to that point in processing. In another aspect, the present invention is a system including a computer programmed to execute the above described initialization and running phase routines. By programming a computer to perform such routines, the amount of engineer time required to identify a core loading arrangement which optimize cycle energy and satisfies all design constraints can be reduced. In addition, such a method and system are believed to be applicable to a wide range of reactors for consistently and reliably identifying optimum core loading arrangements. |
046726527 | summary | BACKGROUND OF THE INVENTION The invention relates to a radiodiagnostic apparatus with an X-ray tube, a diaphragm which is semitransparent in at least one region and which clears a slit of variable width to let radiation pass, with an x-ray image intensifier and a television camera coupled thereto for the generation of video signals, the camera being connected with a monitor for the reproduction of the video signals. German Offenlegungsschrift No. 1,800,879 discloses a primary ray diaphragm for x-ray examination apparatus. Here, a semitransparent diaphragm consisting of two diaphragm plates attenuates the lateral radiations in the x-ray beam. Otherwise, particularly in the case of extremities, the unattenuated beam would directly strike the x-ray image intensifier input screen. This would produce bright areas which impair the perception of details in the actual viewing area. By the use of the semitransparent diaphragm plates these overradiated (or "bloomed") lateral areas are attenuated, so that the visibility in the area of interest is increased, although high-contrast objects (for example, surgical instruments brought in from the side) are still clearly visible. To properly orient the test object with respect to the radiodiagnostic apparatus, the diaphragm plates are rotatable on a diaphragm disk. For manual adjustment of the width of the non-attenuated ray path, the two diaphragm plates can be moved toward each other, until (in the ideal case) overradiated areas have disappeared. In the normal case of non-rectilinear contours, contour adaptation cannot be achieved with the rectilinear end faces of the diaphragm plates. Either a large portion of the object to be examined is attenuated as well, or else large parts of the television picture are still overradiated, so that the visibility of details continues to be reduced. From German Offenlegungsschrift No. 29 05 202 a viewer ("light viewing box") is further known, where for the observation of transparent, rectangular pictures the image support can be darkened by a plurality of parallel and narrow cover strips. By placing pictures on the edge of the viewer, their size is picked up automatically. Subsequently only those strips which cover the picture are moved by a motor until the film is exposed also at its lower edge. Several films can be exposed simultaneously only if they are of the same vertical size. Adaptation to irregular contours is impossible by using the blades of this viewer. One object of the invention is to provide, for a radiodiagnostic apparatus of the initially mentioned kind, a semi-transparent diaphragm which adapts itself as exactly as possible to the contours of the object to be examined, so that only small areas of the object being examined, or none at all, are covered up, or only small areas in the vicinity of the object are uncovered. SUMMARY OF THE INVENTION According to the invention, the diaphragm comprises a plurality of individual blades, which abut and are parallel to each other. The blades are arranged into two opposed groups which are on both sides of the slit and are individually longitudinally slidable dependent on the size of the object to be viewed. There is connected to the television camera an evaluating circuit which supplies a control signal obtained from the video signal to a setting device for the individual blades. The blades of the diaphragm are automatically moved toward each other until each individual blade reaches the outer contours of the object being examined. Advantageously the longitudinal direction of the blades is perpendicular to the center line of the slit. A better adaptation of the blades to the contour of the object being examined can be obtained when the longitudinal direction of the blades makes an angle of between 20.degree. and 90.degree. with the center line of the slit. It has been found to be advantageous when the angle between the longitudinal direction of the blades and the center line of the slit is 45.degree.. A simple control of the blades results when each individual blade is displaced by a corresponding motor. The mechanical construction can be simplified when there are provided for each side of the diaphragm, i.e. each group of blades, a motor which drives a roller, and at least one coupling magnet, the motor and magnet being controlled by the evaluating circuit, and when the blades can be coupled with the roller by the coupling magnet. Reliable adjusting of the blades is achieved when at least one part of each of the blades is designed as a toothed rack and when the roller is designed as a toothed roller. The mechanical cost can be further reduced when a coupling magnet is provided which is displaced mechanically and couples the blades individually with the roller. Parallel actuation of the blades can be achieved when a coupling magnet is associated with each blade, the coupling magnet being individually actuated by the evaluating circuit. The evaluating circuit is further simplified when the coupling magnets are actuated individually, one after the other. Rapid adjusting of the blades can be achieved when the coupling magnets are actuated by the evaluating circuit alternately in multiplexing. The electronic engineering can be simplified when, in radio diagnostic apparatus in which the diaphragm is arranged on a rotatable diaphragm ring, the television camera and the diaphragm are coupled in their rotation in such a way that the longitudinal direction of the blades always lies in the direction of the television's horizontal scan. Advantageously, the evaluating circuit comprises a circuit for position determination of the blades within the video picture. To the circuit are supplied the clock pulses of the television camera and control signals, which identify the particular blade being actuated. The video signal is supplied to an adaptation stage, and the adaptation stage and the circuit are connected with a gate circuit to which a peak value detector is connected. The output signal of the detector is supplied to a comparator stage which compares the output signal with an adjustable threshold value, and the comparator stage controls the coupling magnets. Optimum control of the blades is achieved if the threshold value is selectable to correspond to the transmission characteristics of the organ under investigation. |
description | FIG. 1 shows the upper plate 1 of the frame system in a tridimensional view, wherein the upper plate 1 has a first opening 4 for radiation emission. Moreover a bore 9 is present which permits the placement of a touch contact to protect the radiation filter against breakage. FIG. 2 shows the lower plate 2 of the frame system in a tridimensional view, wherein a second opening 5 is present. A threaded opening 18 is provided for attaching a snap fastener. FIG. 2a shows the lower plate 2 from FIG. 2 in a plan view. FIG. 3 shows a suitable double spring clip 6 which is bent from a metal wire. FIG. 3a shows the double spring clip from FIG. 3 in a tridimensional view wherein the double spring clip 6 is to be fastened by its annular loop to a marginal member on the frame system. FIG. 4 shows a rectangular frame system with double spring clips 6a, 6b, 16a, 16b as in FIG. 3, with the upper plate 1, the lower plate 2 and the snap fastener 8 in the form of a pushbutton. FIG. 4a shows the rectangular frame system from FIG. 4 in section, the arrangement of a first radiation filter 7b and a second radiation filter 7a being shown. The upper plate 1 and the lower plate 2 are joined at the marginal member 3a by screws 18a. FIG. 5 shows the rectangular frame system from FIG. 4 in a tridimensional view wherein an additional marginal member 3b can be seen. FIG. 6 shows a tridimensional view of a plurality of tanning modules 19 with a housing 20 and the frame system of the invention. On the far left is shown a tanning module 19 with the frame system closed. In the center is a tanning module 19 with the frame system open including the tanning radiator, wherein the reflector 21, the lower plate 2 and the first radiation filter 7b can be seen. At the right end is shown a tanning module 19 without a radiation filter in the frame system and without a tanning radiator. All three tanning modules 19 are provided with air exhaust hoses 22. FIG. 7 shows in section three tanning modules 19 which are arranged as in FIG. 6. A first radiation filter 7b and a second radiation filter 7a are present. FIG. 8 shows a tanning module 19 with an opening 23 in the housing 20 for hooking on the frame system. The lower plate 2 and the marginal member 3b can be seen in the opening 23. The frame system is hooked in the opening 23 by a pin 25. |
|
abstract | Electromagnetic radiation sensitive mask materials are provided. The mask materials are chosen such a first percentage of electromagnetic radiation at a first wavelength is transmitted through the mask material prior to the exposure of the mask material to electromagnetic radiation at a second wavelength and a second percentage of electromagnetic radiation at the first wavelength is transmitted through at least a portion of the mask material after the at least a portion of the mask material is exposed to electromagnetic radiation at the second wavelength. Methods of patterning substrates using electromagnetic radiation sensitive mask materials are also provided. Compositions for producing masks are provided, and systems are provided. |
|
summary | ||
053533151 | abstract | Indicating the priority of a spatially fixed, activated alarm tile on an alarm tile array by a shape coding at the tile, and preferably using the same shape coding wherever the same alarm condition is indicated elsewhere in the control room. The status of an alarm tile can change automatically or by operator acknowledgement, but tones and/or flashing cues continue to provide status information to the operator. |
description | The invention generally relates to grating-based phase contrast imaging. Particularly the invention relates to an X-ray detector for a phase contrast imaging system, to the use of such X-ray detector in a phase contrast imaging system, to a phase contrast imaging system with such X-ray detector and to a method of fabricating an X-ray detector for a phase contrast imaging system. In X-ray phase-contrast imaging and/or differential phase contrast imaging (DPCI) a phase information of coherent X-rays passing through an object of interest is visualized. In contrast to classical X-ray transmission imaging approaches, in DPCI not only absorption properties of the object of interest along a projection line, but also a phase shift of the X-rays transmitted through the object of interest and/or the small angle scattering properties of the object are determined. This provides additional information, which may be used e.g. for contrast enhancement, material composition determination, revealing of micro-structures and/or dose reduction. Usually highly monochromatic and coherent X-ray radiation may be required in DPCI. For this purpose, conventional X-ray sources, such as e.g. X-ray tubes, may be used in combination with a source grating placed between the X-ray source and the object of interest. The source grating may ensure coherence by providing small openings, through which the X-ray beam is passed. In beam direction behind the object of interest, usually a phase-shifting grating, also known as phase grating (G1), is placed having the function of a “beam splitter”. When the X-ray beam passes through the phase grating, an interference pattern is generated, which contains the required information about the phase shift of the X-ray beam in a relative position of minima and maxima of beam intensity, wherein the relative position of minima and maxima is typically in the order of several micrometers. Since a common X-ray detector with a typical resolution in the order of 150 μm may not be able to resolve such fine structures, the interference pattern usually is sampled with a phase-analyzer grating, also known as absorber grating (G2), which features a periodic pattern of transmitting and absorbing strips with a periodicity similar to and/or matching that of the interference pattern. Due to the similar periodicity of the absorber grating, a Moiré pattern is generated behind the absorber grating, which may have a much larger periodicity and which may, thus, be detectable with a conventional X-ray detector. To finally obtain the differential phase shift, at least one of the gratings may be shifted laterally by fractions of a grating pitch, which is typically in the order of 1 μm. This technique is also referred to as “phase stepping”. The phase shift can then be extracted from the particular Moiré pattern measured for each position of the analyzer grating. In further developments, computed tomography of phase-shift with hard X-rays may also be performed. However, in particular in the case of a cone-beam geometry, rather strong phase contrast distortions may arise in regions outside a center of the field of view. It may be desirable to provide a robust and cost-efficient X-ray detector for a phase contrast imaging system and a phase contrast imaging with such X-ray detector producing improved images with reduced phase contrast distortions. This is achieved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims and the following description. It should be noted that the features which are in the following described for example with respect to the X-ray detector may also be part of the phase contrast imaging system, and vice versa. Furthermore, all features which are in the following described with respect to the X-ray detector and/or the imaging system correlate to respective method steps for fabricating the X-ray detector. A first aspect of the invention relates to an X-ray detector for a phase contrast imaging system. It is to be noted that the X-ray detector may equally be used for dark-field imaging. The X-ray detector comprises a scintillation device and a photodetector with a plurality of photosensitive pixels optically coupled to the scintillation device. The X-ray detector comprises a primary axis parallel to a surface normal vector of the scintillation device, and the scintillation device comprises a wafer substrate having a plurality of grooves, which are spaced apart from each other. Each of the grooves extends to a depth along a first direction from a first side and/or a first surface of the scintillation device into the wafer substrate, wherein each of the grooves is at least partially filled with a scintillation material. Further, the first direction of at least a part of the grooves is different from the primary axis and/or the surface normal vector, such that at least a part of the grooves is tilted with respect to and/or relative to the primary axis. According to an example, the first direction of at least a subset of the plurality of grooves and/or at least a part of the plurality of grooves is different from the primary axis and/or different from a direction of the primary axis, such that at least the subset of the plurality of grooves and/or at least a part of the plurality of grooves is tilted with respect to the primary axis. In other words, the first direction of at least some of the plurality of grooves is different from the primary axis and/or different from a direction of the primary axis, such that at least some of the plurality of grooves are tilted with respect to the primary axis. According to a further example, an angle between the first direction of a groove arranged in a center region of the scintillation device and the primary axis is smaller than an angle between the first direction of a groove arranged in an outer region of the scintillation device and the primary axis. In other words, an angle between the first direction of at least one groove, which is arranged in a center region of the scintillation device, and the primary axis is smaller than an angle between the first direction of at least one further groove, which is arranged in an outer region of the scintillation device, and the primary axis. The “scintillation device” may refer to a scintillator and/or a scintillator arrangement. The primary axis may refer to an axis of the X-ray detector which may be arranged in a direction towards an X-ray source, when the X-ray detector is installed in the phase contrast imaging system. Additionally or alternatively the primary axis may be parallel to an optical axis of the imaging system and/or parallel to a center axis of an X-ray beam. In this regard, the primary axis may also refer to a beam direction along the optical axis of the imaging system. The surface normal vector may refer to the surface normal vector of the first side of the scintillation device. Alternatively, the surface normal vector may refer to the surface normal vector of a second side of the scintillation device arranged opposite to the first side. The first side may be directed towards the photodetector, whereas the second side may be directed towards an X-ray source when the X-ray detector is installed in an imaging system. The scintillation device may have an arrangement of grooves. The grooves may also refer to trenches. Each of the grooves may have a specific first direction and/or groove direction, in which the respective groove extends from the first side of the scintillation device into the wafer substrate. Accordingly, the first direction of each of the grooves may be substantially parallel to a center axis and/or a center plane of the respective groove. By way of example, the first direction of each of the grooves may be defined by the center axis and/or the center plane of the respective groove. Each of the grooves may have a certain depth along the first direction, and each groove may be formed as elongated cavity in the wafer substrate extending along an extension direction of each groove, wherein the extension direction may be perpendicular to the surface normal vector and/or transverse to the first direction. Accordingly, each of the grooves may partly or entirely traverse the wafer substrate in the longitudinal extension direction. Further, each of the grooves may have an angle between the primary axis and the first direction of the respective groove, wherein in the following the angle may also be measured between the surface normal vector and the first direction of each groove. By forming at least a part of the grooves such that they are tilted relative to the primary axis and/or the surface normal vector, phase contrast distortions may advantageously be reduced. This way, e.g. in a cone-beam geometry, intensity losses may be reduced by increasing an effective aspect ratio of the grooves. Thereby, the phase shift and/or dark field signal may be detected more reliably and precisely. Hence, an overall image quality may be increased. The present invention may at least partly be regarded as being based on the following considerations and findings. Generally, grating-based differential phase contrast and/or dark-field imaging is a promising technology that may likely add additional diagnostic value in particular in the area of chest imaging, where the dark-field signal channel is highly sensitive to changes of a micro-structure of lung tissue. One of the most challenging problems related to this technology may be the fabrication of large area gratings, in particular the absorber grating G2, which is usually placed directly in front of the X-ray detector. Currently, this grating usually is a gold-grating. However, there may be a need to avoid usage of a gold grating for the G2 grating because gold has a rather weak attenuation in the medically important energy range, e.g. ranging from about 65 keV to about 82 keV. As a consequence, the G2 grating may have a rather large thickness and/or length and thus it may be rather expensive. By using the inventive X-ray detector with its scintillation device, in which a scintillator structure is provided by at least partly filling the grooves of the wafer substrate with the scintillation material, the absorber grating may be omitted, because the functionality of the absorber grating may be provided by the X-ray detector itself and/or the scintillation device. This may save cost for the X-ray detector and/or the imaging system. By means of the inventive X-ray detector and/or the scintillation device, only a desired part of X-ray radiation may be detected, such as a part of the interference pattern generated by a phase grating (G1), which contains relevant phase shift information. According to an embodiment of the invention, grooves arranged in the outer region of the scintillation device are more tilted with respect to the primary axis than grooves arranged in the center region of the scintillation device. According to an embodiment of the invention, the first side of the scintillation device is in direct contact with the photodetector. This way light emitted from the grooves and/or the scintillation material contained therein may be directly transmitted to the photosensitive pixels of the X-ray detector without any absorbing materials in between. This may increase the overall efficiency of the detector. According to an embodiment of the invention, an angle between the first direction of a groove arranged in a center region of the scintillation device and the primary axis is smaller than an angle between the first direction of a groove arranged in an outer region of the scintillation device. The X-ray detector may have a center region and/or area as well as a border region and/or area. The center region may e.g. be arranged at or adjacent to the optical axis of the imaging system, when the X-ray detector is installed therein, and the outer region may refer to a peripheral region and/or a border region of the detector, which may be arranged at a certain distance to the optical axis. i.e. it may be laterally spaced apart from the optical axis. The angles between the first directions of grooves arranged in the center region and the primary axis may be smaller than the angles of the first directions of the grooves arranged in the outer region, such that the grooves in the center region may be less tilted with respect to the primary axis than the grooves in the outer region. E.g. in a cone-beam geometry the beam may have a certain spread, such that X-ray particles impinge in different directions onto the X-ray detector with respect to the surface normal vector and/or the primary axis of the detector. By tilting the grooves arranged in the outer region more than those arranged in the center region, different impinging angles of the X-ray particles and/or the beam spread may be compensated and intensity losses may thus be reduced. According to an embodiment of the invention, the scintillation device comprises at least one groove with a first direction parallel to the primary axis, wherein the at least one groove is arranged in a center region of the scintillation device. The at least one groove may be arranged in a center of the scintillation device and may be aligned with the primary axis and/or the optical axis of the imaging system. Alternatively or additionally a plurality of grooves arranged in the center region may have first directions parallel to each other and/or parallel to the primary axis. According to an embodiment of the invention, an angle between the first directions of the grooves and the primary axis increases with increasing distance of the grooves to a center region of the scintillation device. The distance to the center region may be measured laterally, i.e. perpendicular and/or transverse to the primary axis, the surface normal vector and/or the optical axis. In other words, with increasing distance to the center region the grooves are sequentially more tilted and/or increasingly tilted with respect to the primary axis. This may allow to align and/or orient at least a part of the grooves or all of the grooves in direction of an X-ray source, in direction of a focal spot of the imaging system and/or in direction of a predetermined beam direction. This way, the overall intensity of X-ray radiation detected with the detector may be increased. Also an effective aspect ratio may be increased, thereby improving an overall image quality of an image acquired with the X-ray detector. According to an embodiment of the invention, each of the grooves is completely filled with scintillation material. This may further increase an overall light output of the grooves filled with scintillation material, thereby increasing the overall detector efficiency. According to an embodiment of the invention, each groove and/or the scintillation material contained therein is divided into a plurality of sections along a longitudinal extension direction of each groove. In other words, the scintillation material in each groove may be structured. This structure may be formed by one or more barriers ranging from the first side of the scintillation device to the depth of each groove into an inner volume of each groove and/or into the wafer substrate, wherein the barriers may separate adjacently arranged and/or directly adjoining sections. The barriers may be configured to block light generated by the scintillation material contained in a single section. Thus, light emitted in a single section may be confined within this section. According to an embodiment of the invention, each of the grooves extends from the first side of the scintillation device into an inner volume of the wafer substrate. Alternatively or additionally the scintillation device further comprises a layer of wafer substrate arranged on a second side of the scintillation device opposite to the first side of the scintillation device. In other words, the groove may not continuously traverse the wafer substrate in the first direction, but may rather extend to a certain depth into the wafer substrate. This generally may simplify a fabrication process of the X-ray detector. According to an embodiment of the invention, at least a part of the grooves has a rectangular, a trapezoidal, a tubular, a cylindrical, a conical, or an asymmetric shape. Accordingly, also a cross section of at least a part of the grooves may be rectangular, round, elliptic or oval. Depending on a beam geometry, certain geometries of the grooves may have certain advantages, such as trapezoid grooves in a focused geometry. According to an embodiment of the invention, the detector is a flat detector. Alternatively or additionally, the detector is configured for a focused geometry of the imaging system. Usually, in a focused geometry, the detectors and/or gratings may be bended in order to compensate a reduction in detected X-ray intensity in peripheral and/or outer regions of the detector. With the inventive X-ray detector such bending may not be required and a manufacturing process of the X-ray detector may be simplified. According to an embodiment of the invention, the wafer substrate comprises Silicon. Silicon may advantageously be used as rather large and homogenous wafer substrates may be available at low cost. Alternatively or additionally the scintillation material comprises at least one of CsI, NaI, CsI(Tl), CsI(Na), CsI(pure), CsF, KI(Tl), LiI(Eu) and gadolinium oxysulfide. Also other inorganic crystals may be used as scintillation material. These materials may have a rather high light output and are available at low cost. According to an embodiment of the invention, each of the grooves has a depth of 0.5 mm to 5 mm, particularly 1 mm to 3 mm. The depth may be measured along the first direction of each groove. Alternatively or additionally, each of the grooves has a width of 1 μm to 200 μm, particularly 2 μm to 100 μm. The width may be measured perpendicular and/or transverse to the first direction of the respective groove. The above mentioned dimensions of the grooves may be suitable for differential phase contrast imaging applications, particularly for efficiently detecting the interference pattern generated by a phase grating. In this regard, the dimensions of the grooves may be similar to, balanced with and/or correlated with a periodicity of the phase grating (G1) and/or the corresponding interference pattern generated by means of the phase grating. By way of example, an aspect ratio of the grooves and/or of each of the grooves may be in the range of 5 to 1000, particularly in the range of about 10 to 100. Therein, the aspect ratio may depend on the type and/or energy of radiation, e.g. X-rays, to be detected. Accordingly, the grooves should have a depth large enough to absorb enough radiation and/or X-ray photons. For CT applications, a stopping power of about 3 mm and for mammography applications a stopping power of about 1 mm may be suitable. Accordingly, the depth of each of the grooves may also be in this range. On the other hand, the width of the grooves may depend on the design of the phase contrast imaging system. A pitch of the grooves, a groove spacing and/or distance between two neighboring grooves may be about 1 μm to about 500 μm, particularly about 2 μm to about 100 μm, wherein a wall thickness of walls formed by the wafer substrate and separating two neighboring grooves may be about half of the pitch. According to an embodiment of the invention, each of the grooves has a length along a longitudinal extension direction of each groove, which length corresponds to a length of a single photosensitive pixel of the photodetector. The length may be measured in a direction perpendicular and/or transverse to the first direction of each groove. In other words, the wafer substrate and/or the scintillation device may be formed such that a single groove may be covered by a single photosensitive pixel. A typical length of a photosensitive pixel may be about 100 μm to about 300 μm. Accordingly, also the length of the grooves in longitudinal extension direction may be about 100 μm to about 300 μm. A second aspect of the invention relates to the use of an X-ray detector in a phase contrast imaging system, as described above and in the following. The imaging system may e.g. refer to an imaging system with focused geometry and/or with a cone-beam geometry. The imaging system may also refer to a computed tomography system and/or a C-arm system. A third aspect of the invention relates to a phase contrast imaging system comprising an X-ray source for emitting a beam of X-rays centered around an optical axis of the imaging system, an X-ray detector, as described above and in the following, and at least one grating arranged between the X-ray source and the X-ray detector. The optical axis may e.g. refer to a center axis and/or an axis of symmetry of the X-ray beam. The optical axis may point directly to the X-ray detector parallel to the primary axis and/or parallel to a surface normal vector of the detector. The imaging system may also comprise two gratings, wherein a first grating may be arranged between the X-ray source and the object of interest to be examined. The first grating may provide a coherent X-ray beam and/or the first grating may divide a large focal spot into several smaller ones each, wherein each of the smaller focal spots may have a spatial coherence and/or coherence length large enough to generate an interference pattern. Further, a second grating may be arranged between the object of interest and the X-ray detector, wherein the second grating may be the phase grating, which is configured for generating an interference pattern. Further, the primary axis of the X-ray detector is arranged parallel to the optical axis of the imaging system. According to an embodiment of the invention, the X-ray detector is arranged such that the first direction of each of the grooves is oriented and/or aligned towards a focal spot of the imaging system and/or the X-ray source. The X-ray source may be a point source and the focal spot may thus refer to the location of the X-ray source. By aligning all grooves towards the focal spot, an overall detected intensity may be further increased. A fourth aspect of the invention relates to a method of fabricating and/or manufacturing an X-ray detector. The method comprises the steps of: forming a plurality of grooves into a wafer substrate, such that the grooves are spaced apart from each other and such that each of the grooves extends to a depth along a first direction from a surface of the wafer substrate into the wafer substrate; at least partially filling each of the grooves with scintillation material; and arranging the wafer substrate with the at least partially filled grooves on a photodetector. Therein, the X-ray detector comprises a primary axis parallel to a surface normal vector of the wafer substrate, and the first direction of at least a part of the grooves is different from the primary axis, such that at least a part of the grooves is tilted with respect to the primary axis. According to an example of the fourth aspect, the first direction of at least a subset of the plurality of grooves and/or at least a part of the plurality of grooves is different from the primary axis and/or different from a direction of the primary axis, such that at least the subset of the plurality of grooves and/or at least a part of the plurality of grooves is tilted with respect to the primary axis. In other words, the first direction of at least some of the plurality of grooves is different from the primary axis and/or different from a direction of the primary axis, such that at least some of the plurality of grooves are tilted with respect to the primary axis. According to a further example of the fourth aspect, an angle between the first direction of a groove arranged in a center region of the scintillation device and the primary axis is smaller than an angle between the first direction of a groove arranged in an outer region of the scintillation device and the primary axis. In other words, an angle between the first direction of at least one groove, which is arranged in a center region of the scintillation device, and the primary axis is smaller than an angle between the first direction of at least one further groove, which is arranged in an outer region of the scintillation device, and the primary axis. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In principle, identical, similar and/or functionally similar parts are provided with the same reference symbols in the figures. The figures are schematically and not to scale. FIG. 1 shows a phase contrast imaging system 100 according to an exemplary embodiment of the invention. The phase contrast imaging system 100 may e.g. be used for differential phase contrast imaging. The phase contrast imaging system 100 comprises an X-ray source 102 for emitting a beam 104 of X-rays, X-ray radiation and/or X-ray photons. The X-ray source 102 may be an X-ray tube and/or a point source. The phase contrast imaging system 100 further comprises a focal spot 103. The X-ray beam 104 may be cone-like shaped and/or may be centered around an optical axis 106 of the phase contrast imaging system 100. The optical axis 106 may denote the direction of the smallest distance to the X-ray source 102 measured from a plane perpendicular to the optical axis 106. The X-ray beam 104 may be emitted in z-direction as depicted in FIG. 1. In order to provide spatial coherence of the beam 104 and/or in order to generate a spatially coherent beam 104 of X-rays, the phase contrast imaging system 100 further comprises a source grating 108 arranged between the X-ray source 102 and an object of interest 110, which is placed inside the beam 104 and which is to be examined by means of the phase contrast imaging system 100. The source grating 108 may be a one-dimensional grid with a plurality of parallel strips. The object of interest 110 may e.g. be a patient, a part of a patient and/or any other object. Spatial coherence of the beam 104 may alternatively be provided by means of special type of X-ray source 102, such that no source grating 108 may be required. The phase contrast imaging system 100 further comprises a phase grating 112 and an X-ray detector 10. The phase grating 112, also referred to as phase-shifting and/or G1 grating, is arranged between the object of interest 110 and the X-ray detector 10 and/or between the X-ray source 102 and the object 110. The phase grating 112 may be a one-dimensional grid with a plurality of parallel strips. The X-ray detector 10 comprises a scintillation device 12 and a photodetector 14 with a plurality of photosensitive pixels, as described in detail in following figures. Generally, the phase grating 112 is configured to generate an interference pattern, which contains information about the phase shift of the X-ray beam 104 in a relative position of minima and maxima of beam intensity. In other words, the relative position of minima and maxima depends on the phase-shift of a wave front incident on the phase grating 112. As a phase of X-rays passing through the object of interest 110 may be altered according to physical properties of the object of interest 110, such as e.g. a density and/or a thickness of material contained therein, the interference pattern generated by the phase grating 112 is also altered accordingly. Therefore, by analyzing the interference pattern, the phase-shift information may be extracted, which information may in turn be used e.g. to increase and/or improve the contrast of an X-ray absorption image. In conventional phase contrast imaging systems the interference pattern generated by the phase grating 112 is analyzed by means of an analyzer grating (G2 grating) arranged and/or placed in front of the X-ray detector 10. In the phase contrast imaging system 100 according to the invention the functionality of the analyzer grating is advantageously integrated into the X-ray detector 10, as explained in detail in the following figures. The phase contrast imaging system 100 further comprises a control unit, control module, controller and/or control circuitry 114 configured for controlling the X-ray detector 10, the X-ray source 102 and/or other components of the phase contrast imaging system 100. The control unit 114 may also be configured signal processing, for data read-out from the X-ray detector 10 and/or for data processing of data acquired by means of the X-ray detector 10. The phase contrast imaging system 100 optionally comprises an actuator 120, a piezo actuator 120, a stepper 120 and/or a stepping motor 120 configured to shift the phase grating 112 and/or the X-ray detector 10 and/or the source grating 108 laterally, i.e. perpendicular and/or transverse to the optical axis 106. This may allow to obtain the differential phase shift and is also referred to as “phase stepping”. The actual phase shift can then be extracted from the particular measurements for each position. FIG. 2a shows cross-sectional view of an X-ray detector 10 for a phase contrast imaging system 100 according to an exemplary embodiment of the invention. FIG. 2b shows a bottom view of an X-ray detector 10 for a phase contrast imaging system 100 according to an exemplary embodiment of the invention. If not stated otherwise, the X-ray detectors 10 of FIGS. 2a and 2b comprise the same elements and features as the X-ray detector 10 of FIG. 1. The X-ray detector 10 is a flat X-ray detector 10, which comprises a scintillation device 12 and a photodetector 14 with photosensitive pixels 15 optically coupled to the scintillation device 12. The photosensitive pixels 15 are schematically depicted in FIG. 2b as rectangles 15. The X-ray detector 10 has a primary axis 16, which is oriented and/or aligned parallel to a surface normal vector of the X-ray detector 10 and/or parallel to a surface normal vector of the scintillation device 12. The primary axis 16 may be aligned with the optical axis 106 of the phase-contrast imaging system 100, i.e. the primary axis 16 may be directed towards the focal spot 103 and/or towards the X-ray source 102, when the X-ray detector 10 is installed in the phase-contrast imaging system 100. The surface normal vector may denote a vector of a first side 13 and/or a first surface 13 of the scintillation device 12. However, the surface normal vector may also denote the respective vector on a further side/surface of the scintillation device opposite to the first side 13. The scintillation device 12 comprises a silicon wafer substrate 18, e.g. a silicon wafer substrate, having grooves 20 and/car trenches 20, which are spaced apart from each other in a direction perpendicular and/or transverse to the primary axis 16. As shown in FIGS. 2a and 2b, the grooves 20 are spaced apart from each other in x-direction, wherein between two neighboring grooves 20, the wafer substrate 18 is arranged. The grooves 20 may be equally spaced apart from each other in x-direction and/or they may be arranged with varying distance between two neighboring grooves 20. The grooves 20 thereby are spaced apart from each other by the wafer substrate 18. Each of the grooves 20 extends to a depth 22 along a first direction 21 from the first side 13 of the scintillation device 12 into an inner volume 19 of the wafer substrate 18. The first direction 21 is schematically depicted in FIG. 2a by an arrow 21 for two of the grooves 20. Accordingly, each of the grooves 20 has a specific first direction 21 and/or a specific depth 22, which may refer to groove direction 21 of each groove 20. The first directions 21 of at least a part of the grooves 20 are different from the primary axis 16 and/or the surface normal vector of the X-ray detector 10, such that at least a part of the grooves 20 is tilted with respect to the primary axis 16. In other words, the first directions 21 of at least a part of the grooves 20 are oriented transverse to the surface normal vector of the X-ray detector 10 and/or with a transverse component to the surface normal vector of the X-ray detector 10. Particularly, angles between the first directions 21 of grooves 20, which are arranged in a center and/or middle region 24 of the scintillation device 12, and the primary axis 16 are smaller than angles between the first directions 21 of grooves 20, which are arranged in an outer region 26 and/or peripheral region 26 of the scintillation device 12. Accordingly, grooves 20 arranged in the outer region 26 are more tilted with respect to the primary axis 16 than grooves 20 arranged in the center region 24. Further, at least one groove 20a arranged in the center region 24 has a first direction 21a parallel to the primary axis 16 and/or the surface normal vector of the detector 10. Also a plurality of grooves 20 in the center region 24 may have first directions 21a parallel to the primary axis 16 and/or the surface normal vector of the detector 10. Further, the grooves 20 may be formed in the wafer substrate 18, such that the angles between the first directions 21 of the grooves 20 and the primary axis 16 increase with increasing distance of the grooves 20 to the center region 24 of the scintillation device 12. In other words, the greater the distance of a groove 20 to the center region 24 and/or to a center of the scintillation device 12 is, the more is the respective groove 20 tilted with respect to the primary axis 16. Accordingly, the grooves 20 are increasingly tilted with increasing distance to the center region 24. Each of the grooves 20 has a depth 22 of about 0.5 mm to about 5 mm, particularly about 1 mm to about 3 mm, measured along the first direction 21. Further, each of the grooves 20 has a width_23 of about 1 μm to about 200 μm, particularly about 2 μm to about 100 μm, measured perpendicular to the primary axis 16 in x-direction as shown in FIG. 2a. Referring to FIG. 2b, each of the grooves 20 has length 25 along a longitudinal extension direction 27, wherein the length 25 corresponds and/or correlates with the length of a single photosensitive pixel 15. A typical length 25 of the grooves 20 may be in the range of about 100 μm to about 300 μm. The extension direction 27 of each groove 20 is oriented antiparallel to the y-axis in FIG. 2b. Each of the grooves 20 may entirely traverse the wafer substrate 18 along the longitudinal extension direction 27, i.e. in the example shown in FIG. 2b the length of a single groove 20 may be twice as large as the length of a photosensitive pixel 15. Alternatively, a single groove 20 may have a length 25 nearly equal to the length of the photosensitive pixel 15, i.e. in y-direction as shown in FIG. 2b two grooves 20 may be arranged, adjoining each other in y-direction and/or in the longitudinal extension direction 27. Further, as can be seen in FIG. 2b the extension directions 27 of the grooves 20 are parallel with respect to each other, and the grooves 20 are separated by the wafer substrate 18 in a direction perpendicular to the extension direction 27, i.e. in x-direction. Each of the grooves 20 is at least partly, preferably completely, filled with scintillation material. The scintillation material may comprise at least one of CsI, NaI, CsI(Tl), CsI(Na), CsI(pure), CsF, KI(Tl), LiI(Eu) and gadolinium oxysulfide. Also other crystals may be used as scintillation material. X-ray photons emitted from the X-ray source 102 and passing through the source grating 108, the object of interest 110 and/or the phase grating 112 impinge onto the X-ray detector 10 and the grooves 20. Inside the grooves 20, X-ray photons are converted to visible light, which in turn is converted to an electrical signal by means of the photosensitive pixels 15. Finally, the electrical signal may be processed and/or evaluated by the control unit 114. Since light generated by an impinging X-ray photon in the scintillation material of the scintillator device 12 is emitted in all directions, each groove 20 and/or the scintillation material comprised in each groove 20 is divided into several sections 28 along the longitudinal extension direction 27. In other words, the scintillation material in each groove 20 is structured. The sections 28 may be provided by forming appropriate barriers 29 in the scintillation material of each groove 20. The barriers 29 may extend from the first side 13 of the scintillation device 12 to the depth 22 of each groove 20. By means of the sections 28 and/or barriers 29 it may be ensured that light generated by an X-ray photon in a single section 28 is collimated and/or refined within the respective section 28. Accordingly, light generated in a specific section 28 may not cross a barrier 29. This may also increase a resolution of the X-ray detector 10. The section 28 may extend in extension direction 27 to be as large as an area covered by a single photosensitive pixel 15 in the extension direction 27. In other words, the section 28 and a single photosensitive pixel 16 may have identical extensions and/or dimensions in extension direction 27. Referring to FIG. 2a, a cross-sectional shape of the grooves 20 may be trapezoidal. However, other shapes, such as a rectangular, a tubular, a cylindrical, a conical, or an asymmetric shape may be feasible depending e.g. on beam geometry. It is to be noted that also a two-dimensional grid with grooves 20 may be fabricated and/or used for the X-ray detector 10. Accordingly, the grooves 20 may be arranged in a pattern, a two-dimensional grid and/or an array in the wafer substrate 18. This may allow to extract two-dimensional phase-shift information with the X-ray detector 10. FIG. 3 shows a cross-sectional view of a phase contrast imaging system 100 according to an exemplary embodiment of the invention. If not stated otherwise, the imaging system 100 of FIG. 3 comprises the same elements and features as the imaging system 100 of FIG. 1 and/or the X-ray detector 10 as described with reference to FIGS. 2a and 2b. For the sake of visibility, the X-ray detector 10 shown in FIG. 3 comprises only 3 grooves 20, 20a. However, the X-ray detector 10 may comprise many more grooves 20. In FIG. 3, three different impinging directions 104a, 104b, 104c of an X-ray beam 104 are schematically depicted to illustrate advantages of the inventive X-ray detector 10 and/or the imaging system 100. In this focused geometry shown in FIG. 3, each of the grooves 20, 20a and/or the respective first directions 21, 21a of each of the grooves 20, 20a is oriented and/or aligned towards the focal spot 103 of the imaging system 100 and/or towards the X-ray source 102. Accordingly, the first direction 21, 21a of each groove 20, 20a is direct antiparallel to the respective impinging direction 104a, 104b, 104c of X-rays. This design advantageously allows to reduce losses in an intensity detected with the X-ray detector 10 by increasing the effective aspect ratio. Accordingly, phase contrast distortions may be reduced and an overall image quality may be improved. Typically, a large area detector 10 may have size of about 50 cm times 50 cm, which is illuminated by the X-ray source 102 in a distance D of about 50 cm to 200 cm. This implies that the x-ray photons incident under an angle to the surface normal vector of the X-ray detector 10 and/or a respective detector plane, increases with increasing distance to the optical axis 106. Near the borders of the detector 10 and/or in the outer region 26 of the X-ray detector 10 the maximum angle α is equal to arcustangens(a/2/D)), wherein a refers to a dimension of the detector 10 in a direction perpendicular to the optical axis 16. Therefore, the visibility and also the detected intensity is reduced for the peripheral area 26 and/or outer region 26 of the detector 10. With the inventive detector 10 this problem may significantly be reduced and/or solved completely. FIG. 4 shows a flow chart illustrating steps of a method of fabricating an X-ray detector 10 according to an exemplary embodiment of the invention. In a step S1 a plurality of grooves 20 is formed into a wafer substrate 18, such that the grooves 20 are spaced apart from each other and such that each of the grooves 20 extends to a depth 22 along a first direction 21 from a surface 13 of the wafer substrate 18 and/or a first side 13 into the wafer substrate 18; In a second step S2 each of the grooves 20 is at least partially filled with scintillation material. In a third step S3 the wafer substrate 18 is arranged with the at least partially filled grooves 20 on a photodetector 14. The X-ray detector 10 fabricated and/or manufactured with this method may comprise the same features and/or elements as the X-ray detectors 10 described in previous FIGS. 1 to 3. Particularly the X-ray detector 10 comprises a primary axis 16 parallel to a surface normal vector of the wafer substrate 18, wherein the first direction 21 of at least a part of the grooves 20 is different from the primary axis 16, such that at least a part of the grooves 20 is tilted with respect to the primary axis 16. The grooves 20 may for instance be etched and/or drilled into the wafer substrate 18 in step S1. By way of example, the grooves 20 may be formed with a laser, and optionally surfaces of the grooves 20 may be smoothed with an etching process. In order to determine the first directions 21 of each of the grooves 20, a laser and/or an X-ray source may be used in combination with a shadow mask. This may allow to simulate impinging directions 104a, 104b, 104c of X-rays onto the X-ray detector 10 and/or simulating a beam geometry. This may allow each groove 20 and/or each first direction 21 to be aligned with the respective predetermined impinging direction 104a, 104b, 104c of X-rays, as illustrated in FIG. 3. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. |
|
abstract | A formic acid aqueous solution that contains Fe (II) ions is produced by dissolving metal iron in a formic acid aqueous solution. Nitrogen is supplied from a nitrogen supply device to a chemical liquid tank and then discharged from a discharge line to reduce the dissolved oxygen concentration in the aqueous solution. The chemical liquid tank is filled with the formic acid aqueous solution sealed with nitrogen, and transferred from a factory to a nuclear reactor building designated as radiation-controlled areas. Inside the nuclear reactor building, the chemical liquid tank is installed in a film deposition apparatus connected to a reactor water recirculation pipeline. The formic acid aqueous is supplied from the chemical liquid tank to the inside of the reactor water recirculation pipeline, and then a ferrite film is formed on the inner surface of the reactor water recirculation pipeline. |
|
claims | 1. A lithographic projection apparatus, comprising:a projection system configured to project a patterned radiation beam onto a target portion of a substrate;a positioning structure configured to move the substrate relative to the projection system during exposure by the patterned radiation beam;a single-faceted oscillatingly pivotable mirror configured to move the patterned radiation beam relative to the projection system during at least one pulse of the patterned radiation beam; andan actuator configured to oscillatingly pivot the mirror according to an oscillation timing that substantially corresponds to a pulse frequency of a radiation system and such that the patterned radiation beam is scanned in substantial synchronism with the movement of the substrate during the at least one pulse. 2. The apparatus of claim 1, wherein the actuator is controlled by a controller, wherein the controller, actuator and radiation system are interconnected in a control loop arrangement, and wherein the control loop is configured to maintain substantial synchronism between oscillation of the mirror and pulses of the radiation system. 3. The apparatus of claim 1, wherein the pivotable mirror is supported by a support assembly, and a frequency of the oscillation timing substantially corresponds to a resonance frequency of the mirror and its support assembly. 4. The apparatus of claim 3, wherein the support assembly further comprises the actuator. 5. The apparatus of claim 4, wherein the support assembly further comprises a counter-mass constructed and arranged to isolate forces produced by the actuator from a remaining part of the apparatus. 6. The apparatus of claim 1, wherein the actuator comprises a plurality of motors, constructed and arranged to impart rotational forces on the mirror. 7. The apparatus of claim 1, wherein, when in use, the mirror oscillates with a sinusoidal motion. 8. The apparatus of claim 7, wherein, when in use, the pulses of the radiation system substantially correspond in timing to a zero crossing of the sinusoidal motion of the mirror oscillation. 9. The apparatus of claim 1, wherein, when in use, a position of the patterned radiation beam relative to the projection system can be further shifted in order to compensate for an error of movement of the substrate during a pulse of the patterned radiation beam. 10. The apparatus of claim 1, wherein the actuator is configured such that it can control a position of a mid-point of an oscillation of the pivotable mirror. 11. The apparatus of claim 10, wherein the pivotable mirror is configured to oscillate about a first axis and the actuator is configured to control an angular position of the mid-point of the oscillation of the pivotable mirror about the first axis. 12. The apparatus of claim 10, wherein the pivotable mirror is configured to oscillate about a first axis and the actuator is configured to control an angular position of the mid-point of the oscillation of the pivotable mirror about a second axis, the second axis being substantially perpendicular to the first axis and lying in a plane substantially parallel to a surface of the pivotable mirror at a location on which the patterned radiation beam would be incident on the pivotable mirror. 13. The apparatus of claim 1, wherein the actuator is configured to control a relative phase of a pulse frequency of the radiation system and an oscillation of the pivotable mirror. 14. The apparatus of claim 1, wherein the actuator is constructed to oscillatingly pivot the pivotable mirror relative to a base of the actuator, and further comprising a second actuator configured to control the position of the base relative to the projection system. 15. The apparatus of claim 14, wherein the actuator is configured to oscillate the pivotable mirror about a first axis and the second actuator is configured to control an angular position of the base relative to the projection system about a second axis, the second axis being substantially parallel to the first axis. 16. The apparatus of claim 14, wherein the actuator is configured to oscillate the pivotable mirror about a first axis and the second actuator is configured to control an angular position of the base relative to the projection system about a third axis, the third axis being substantially perpendicular to the first axis and lying in a plane substantially parallel to a surface of the pivotable mirror at a location on which the patterned radiation beam would be incident on the pivotable mirror. 17. The apparatus of claim 14, wherein the second actuator comprises a Lorentz actuator and is configured to minimize transfer of a vibration from the actuator to the remainder of the lithographic projection apparatus. 18. The apparatus of claim 1, wherein the mirror is substantially planar. 19. The apparatus of claim 1, wherein the mirror is located proximate a pupil plane of the projection system, or a conjugate plane thereof. 20. The apparatus of claim 1, wherein the mirror is located at a conjugate plane of a pupil plane of the projection system. 21. The apparatus of claim 1, wherein the positioning structure is configured to move the substrate at a substantially constant velocity relative to the projection system during a plurality of pulses of the patterned radiation beam and during intervals therebetween, and wherein, when in use, the patterned radiation beam is moved in substantial synchronism with movement of the substrate for a duration of at least one pulse of the patterned radiation beam. 22. The apparatus of claim 1, wherein, when in use, the patterned radiation beam is scanned in substantial synchronism with movement of the substrate during a plurality of pulses of the patterned radiation beam, such that a pattern is projected onto substantially a same place on the substrate a plurality of times. 23. The apparatus according to claim 22, wherein (i) an intensity of the patterned radiation beam, (ii) an illumination of a programmable patterning structure, (iii) a pupil filtering, or (iv) any combination of (i) to (iii), are changed for at least one of a plurality of projections of the patterned radiation beam that are directed onto substantially the same place on the substrate. 24. The apparatus of claim 1, wherein, when in use, a configuration of a pattern is changed between a plurality of projections of the patterned radiation beam that are directed onto substantially the same place on the substrate. 25. A device manufacturing method, comprising:moving a substrate relative to a projection system that projects a patterned radiation beam onto a substrate during exposure;oscillatingly pivoting a single-faceted pivotable mirror according to an oscillation timing that substantially corresponds to a pulse frequency of the patterned radiation beam so as to alter a path of the patterned radiation beam in substantial synchronism with movement of the substrate; andprojecting the patterned radiation beam onto the substrate. 26. The method of claim 25, wherein moving the substrate includes moving the substrate at a substantially constant velocity relative to the projection system during a plurality of pulses of the patterned radiation beam and during intervals therebetween, and wherein the path is altered in substantial synchronism with the movement of the substrate for a duration of at least one pulse of the patterned radiation beam. 27. The method of claim 25, further comprising altering the path of the patterned radiation beam in substantial synchronism with the movement of the substrate during a plurality of pulses of the patterned radiation beam, such that a pattern is projected onto substantially a same place on the substrate a plurality of times. 28. The method of claim 27, further comprising changing a configuration of the pattern between a plurality of projections of the patterned radiation beam that are directed onto substantially the same place on the substrate. 29. The method of claim 27, further comprising changing (i) an intensity of the patterned radiation beam, (ii) an illumination of a programmable patterning structure, (iii) a pupil filtering, or (iv) any combination of (i) to (iii), for at least one of the plurality of projections that are directed onto substantially the same place on the substrate. 30. The method of claim 25, wherein the mirror oscillates with a sinusoidal motion. 31. The method of claim 30, wherein pulses of the patterned radiation beam substantially correspond in timing to zero crossings of the sinusoidal motion of the mirror. 32. The method of claim 25, wherein the path of the patterned radiation beam is further shifted in order to compensate for an error of movement of the substrate during a pulse of the patterned radiation beam. 33. An apparatus comprising a projection system, the projection system having:a single-faceted oscillatingly pivotable mirror configured to receive a patterned beam of radiation; andan actuator coupled to the pivotable mirror and configured to oscillatingly pivot the mirror. 34. The apparatus of claim 33, wherein the pivotable mirror is positioned in a pupil plane of the projection system, or a conjugate plane thereof. 35. The apparatus of claim 33, wherein the actuator is configured to oscillate the mirror at a frequency in the range of 1-10 kHz. 36. The apparatus of claim 33, further comprising a radiation source; and a patterning device constructed and arranged to receive a radiation beam provided by the radiation source and to pattern the radiation beam. 37. The apparatus of claim 36, wherein the patterning device is a programmable patterning device. |
|
050733052 | summary | BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a method of evacuating treating containers to a vacuum for use in compacting radioactive wastes by an HIP (hot isostatic press), hot press or the like. Such radioactive wastes include metals and bricks contaminated with plutonium or a transuranium element having a long half life. In recent years, attention has been directed to treatments by HIP or the like for compacting radioactive wastes into solid blocks for stabilization before storing the wastes (see, for example, Examined Japanese Patent Publication SHO 57-959). For example, the treatment of hulls will be described which are sheared cladding tubes. Hulls are hollow, have a low bulk density of 1.0 and are therefore precompressed to a true density ratio of at least about 70% by a press first. During the compression, a highly radioactive oxide formed by zircalloy on the surfaces of the hulls and having a thickness of about 10 .mu.m partly separates off. The compressed waste is then placed into a treating container of stainless steel or the like, which is then filled with a metal powder, stainless steel powder or the like to eliminate the space or clearances remaining in the container. A closure is then welded to the container, piping (hereinafter referred to as an "evacuating pipe") is thereafter attached to the closure for connection to a vacuum pump, and the interior of the container is evacuated to a degree of vacuum, e.g., about 10.sup.-2 torr. The container thus evacuated is completely sealed off to hold the vacuum therein, and the container is compressed by HIP or hot press under an external pressure with heating, whereby the container is compacted. The container is evacuated to prevent the container itself from breaking owing to the presence of air or like gas confined in the container when the container is compressed under a high pressure. However, if the container is thus evacuated after the waste has been placed thereinto, a particulate radioactive substance separating off the waste is led out of the container via the evacuating pipe to contaminate the vacuum pump and the inner surface of the evacuating pipe. The spillage of the radioactive substance due to aspiration can not be prevented completely even at a reduced evacuation rate. Further even if a filter is removably installed in the evacuating pipe and the like, the filter becomes contaminated and is therefore extremely difficult to replace, hence inconvenience is caused. SUMMARY OF THE INVENTION The main object of the present invention is to provide a method of evacuating treating containers to a vacuum free of the foregoing problem. To fulfill this object, the present invention provides a method of evacuating a container to a vacuum for use in treating radioactive wastes by placing the waste into the container, and evacuating, sealing off and thereafter compressing the container, the method being characterized by placing the waste into the container, forming over the waste a filter layer of particulate material fulfilling one of the following requirements, and thereafter aspirating a gas through the filter layer from thereabove to evacuate the container and sealing off the container. (1) A layer having a thickness of at least 5 mm and formed of a particulate material not smaller than 40 .mu.m to less than 105 .mu.m in mean particle size. PA0 (2) A layer having a thickness of D mm and formed of a particulate material not smaller than 105 .mu.m to not greater than 210 .mu.m in mean particle size d .mu.m, the thickness D and the mean particle size d having the relationship represented by: EQU D.gtoreq.(20/105).times.d-15 With the method described above, the gas within the container is drawn out through the interstices between the particles of the particulate material, whereas the radioactive substance separating off the waste is blocked by the filter layer fulfilling the specified requirement and is prevented from being led out of the container. Accordingly, the present method satisfactorily evacuates the container while reliably preventing the release of the radioactive substance from the container. The filter layer is subjected to the compacting treatment along with the container and therefore need not be replaced. The above and other objects, features and advantages of the present invention will become apparent upon a reading of the following detailed description and the accompanying drawings. |
055352537 | abstract | The method and the device are applicable to the penetrations (2) of a pressurised water nuclear reactor vessel head (1) during operation.. The device includes a double circuit for picking off two gas samples (100, 16, 17; 12, 13, 14, 15) and a measurement assembly (18) which regularly compares the content, especially of water vapour, in the two samples picked off. The first sample is taken from the volume of a chamber (7) where the possible leak (10) emerges, and the second in proximity to the head (1) outside the region immediately affected by the leak. The assembly (18) makes it possible to generate (19) an alarm in the event of a leak and to distinguish it from operational alarms.. Techniques and means are also provided for determining the flow rate of sweeping in the volume of the chamber (7) and for checking the pick-off and detection systems. |
claims | 1. A method of applying a burnable poison to a nuclear fuel rod having exterior cladding, which fuel rod is useful in a nuclear environment, and will be subject to exterior contact with aqueous coolant, the method comprising:(a) providing a nuclear fuel rod, said nuclear fuel rod having an axis, and an outer surface of cladding optionally having surface oxides and other surface deposits;(b) providing at least one application device adjacent said surface of said nuclear fuel rod;(c) rotating said nuclear fuel rod about said axis or moving the at least one application device and holding the rod still;(d) optionally removing at least a portion of any of said optional surface oxides and said other surface deposits on said outer cladding surface of said nuclear fuel rod by spraying an abrasive material onto said surface of said nuclear fuel rod via said at least one application device; and(e) applying burnable poison particles onto said cladding surface of said nuclear fuel rod by spraying a plurality of layers of said burnable poison particles onto said surface of said nuclear fuel rod via said at least one application device, where the burnable poison particles are applied at a velocity sufficient to cause adhesion to said outer surface of cladding, to form an outer layer of the burnable poison particles subject to oxidation by contact with an aqueous material, where the total thickness of the plurality of layers of the burnable poison particles is from 0.001 mils to 10 mils. 2. The method according to claim 1, further comprising applying a further protective coating onto said burnable poison layers via said application device while adjusting the position of said application device in relation to said nuclear fuel rod. 3. The method according to claim 2, further comprising applying as said further protective coating a metallic coating. 4. The method according to claim 1, wherein said adjusting the position of said application device involves adjusting the angle of said application device in relation to said nuclear fuel rod. 5. The method according to claim 1, wherein said adjusting the position of said application device involves adjusting the position of said application device in relation to said axis of said nuclear fuel rod. 6. The method according to claim 1, further comprising applying as said burnable poison a burnable poison selected from the group comprising elemental boron, elemental gadolinium, elemental hafnium, elemental erbium, HfB2, ZrB2, Gd2O3, Er2O3, and mixtures thereof. 7. The method according to claim 1, wherein the cladding is a metal, the method further comprising adjusting the rate at which said burnable poison particles exit said application device during the step of applying said burnable poison particles onto said cladding surface of said nuclear fuel rod, so as to improve surface adhesion to the particles to the surface of the cladding. 8. The method according to claim 1, wherein said nuclear fuel rod is continuously rotated. 9. The method of claim 1, wherein after step (e), said nuclear fuel rod is contacted by an aqueous material causing said outer layer of burnable poison to form a protective, adhering oxide. 10. The method of claim 1 wherein the velocity in step (e) is from 1,500 ft./second to 2,500 ft./second and the particle size of the burnable poison is from 1 micrometer to 500 micrometers. 11. A method of applying a burnable poison to a nuclear fuel rod having exterior cladding, which fuel rod is useful in a nuclear environment, and will be subject to exterior contact with aqueous coolant, the method comprising:(a) providing a nuclear fuel rod, said nuclear fuel rod having an axis and an outer surface of cladding optionally having surface oxides and other surface deposits;(b) providing at least one application device adjacent said surface of said nuclear fuel rod, said application device having a channel extending therethrough, said channel being in communication with a pressurized gas source and a particle source;(c) providing an image capture device adjacent said nuclear fuel rod, said image capture device being adapted to transmit an image to a remote viewing station;(d) rotating said nuclear fuel rod about said axis;(e) optionally introducing abrasive particles into said channel via said particle source and expelling pressurized gas from said pressurized gas source through said channel thereby spraying said abrasive particles onto said outer cladding surface of said nuclear fuel rod and removing at least a portion of said optional surface oxides and said other surface deposits on said outer surface of said nuclear fuel rod while adjusting the position of said application device in relation to said nuclear fuel rod; and(f) introducing burnable poison particles into said channel via said particle source and expelling pressured gas from said pressurized gas source through said channel thereby spraying a plurality of layers of said burnable poison particles onto said cladding surface of said nuclear fuel rod while adjusting the position of said application device in relation to said nuclear fuel rod, wherein the burnable poison particles are applied at a velocity sufficient to cause adhesion to said outer surface of cladding, to form an outer layer of the burnable poison particles subject to oxidation by contact with an aqueous material, where the total thickness of the plurality of layers of the burnable poison particles is from 0.001 mils. to 10 mils. 12. The method according to claim 11, further comprising applying a further protective coating onto said burnable poison layers via said application device while adjusting the position of said application device in relation to said nuclear fuel rod. 13. The method according to claim 12, further comprising applying as said further protective coating a metallic coating. 14. The method according to claim 11, wherein a portion of said adjusting the position of said application device involves adjusting the angle of said application device in relation to said nuclear fuel rod. 15. The method according to claim 11, wherein a portion of said adjusting the position of said application device involves adjusting the position of said application device in relation to said axis of said nuclear fuel rod. 16. The method according to claim 11, further comprising applying as said burnable poison a burnable poison selected from the group comprising boron, gadolinium, hafnium, erbium, HfB2, ZrB2, Gd2O3, and Er2O3 and mixtures thereof. 17. The method according to claim 11, wherein the cladding is a metal, the method further comprising adjusting the rate at which said burnable poison particles exit said application device during the step of applying said burnable poison particles onto said cladding surface of said nuclear fuel rod, so as to melt the particles into the surface of the cladding. 18. The method according to claim 11, wherein said nuclear fuel rod is continuously rotated. 19. The method according to claim 11, further comprising transmitting an image of said nuclear fuel rod from said image capture device to said remote viewing station. 20. The method of claim 11, wherein after step (f), said nuclear fuel rod is contacted by an aqueous material causing said outer layer of burnable poison to form a protective adhering oxide. 21. The method of claim 11, wherein the velocity in step (f) is from 1,500 ft./second to 2,500 ft./second and the particle size of the burnable poison is from 1 micrometer to 250 micrometers. |
|
summary | ||
claims | 1. A method implemented by a semiconductor device design system, the method comprising:generating, from a schematic description of a semiconductor device, a first set of data comprising descriptions of device elements and connectivity of the semiconductor device;generating a set of integrated circuit (IC) masks for the semiconductor device;identifying characteristics of mask device elements described by the set of IC masks;generating, from the determined mask device elements and the IC masks, a second set of data comprising descriptions of the identified IC mask device elements and connectivity of the semiconductor device;comparing each device element in the first set of data with a corresponding IC mask device element in the second set of data, wherein said comparing comprises reading information associated with a device element in the first set of data, whereinthe information associated with the device element in the first set of data comprises a location of the device element and an identifier of the type of device element,identifying physical mask layers associated with the type of device element, wherein the physical mask layers correspond to expected mask layers for the type of device element,reading information associated with the corresponding IC mask device element from the second set of data, whereinthe corresponding IC mask device element is at a maskset location corresponding to the location of the device element in the first set of data, andthe information associated with the corresponding IC mask device element comprises descriptions of mask layers at the maskset location, andcomparing the descriptions of the IC mask device element mask layers with the identified physical mask layers;recording differences, if any, between a device element in the first set of data and the corresponding IC mask device element in the second set of data, as a result of said comparing;generating a set of modified IC masks using the recorded differences; andfabricating the semiconductor device using set of modified IC masks. 2. The method of claim 1 further comprising:storing the first set of data in a first memory; andstoring the second set of data in a second memory. 3. The method of claim 1 wherein said generating the set of IC masks comprises:generating a design layout corresponding to information provided by the schematic description of the semiconductor device;generating one or more mask layers corresponding to the design layout; andgenerating one or more additional mask layers that do not correspond to the design layout. 4. The method of claim 3, wherein the descriptions of the identified mask device elements in the second set of data comprise:a location in the integrated circuit of a mask device element; andinformation associated with each mask layer in a predefined range of the location, wherein each mask layer comprises both the one or more mask layers corresponding to the design layout and the one or more additional mask layers. 5. The method of claim 4 wherein said identifying characteristics of mask device elements described by the set of IC masks comprises:performing a pattern matching between known mask features for a general device type and the set of IC masks. 6. The method of claim 5 further comprising:storing the known mask features for the general device type in a memory. 7. The method of claim 1 wherein said identifying the physical mask layers associated with the type of device element comprises:accessing a memory storing information associated with the physical mask layers for the type of device element. 8. The method of claim 1 wherein the differences between the device element in the first set of data and the corresponding IC mask device element comprise missing features for the IC mask device element. 9. The method of claim 1 wherein the differences between the device element in the first set of data and the corresponding IC mask device element comprise additional features for the IC mask device element. 10. A semiconductor device design system comprising:a design environment system, comprising a first set of processors and a first memory configured to store a first set of instructions executable by the first set of processors, the first set of instructions configured togenerate, from a schematic description of a semiconductor device, a first set of data comprising descriptions of device elements and connectivity of the semiconductor device;a CAD-to-Mask system, comprising a second set of processors and a second memory configured to store a second set of instructions executable by the second set of processors, the second set of instructions configured toreceive the first set of data, andgenerate a set of integrated circuit (IC) masks for the semiconductor device from the first set of data;a device recognition system, comprising a third set of processors and a third memory configured to store a third set of instructions executable by the third set of processors, the third set of instructions configured toreceive the set of IC masks for the semiconductor device,identify characteristics of mask device elements described by the set of IC masks, andgenerate, from the determined mask device elements and the IC masks, a second set of data comprising descriptions of the identified IC mask device elements and connectivity of the semiconductor device; anda comparator system, comprising a fourth set of processors and a fourth memory configured to store a fourth set of instructions executable by the fourth set of processors, the fourth set of instructions configured toreceive the first set of data and the second set of data,compare each device element in the first set of data with a corresponding IC mask device element in the second set of data, wherein said instructions to compare further comprise instructions configured toread information associated with a device element in the first set of data, whereinthe information associated with the device element in the first set of data comprises a location of the device element and an identifier of the type of device element,identify physical mask layers associated with the type of device element, wherein the physical mask layers correspond to expected mask layers for the type of device element,read information associated with the corresponding IC mask device element from the second set of data, whereinthe corresponding IC mask device element is at a maskset location corresponding to the location of the device element in the first set of data, andthe information associated with the corresponding IC mask device element comprises descriptions of mask layers at the maskset location, andcompare the descriptions of the IC mask device element mask layers with the identified physical mask layers; andrecord differences, if any, between a device element in the first set of data and the corresponding IC mask device element in the second set of data, as a result of said comparing. 11. The semiconductor device design system of claim 10 wherein the second memory, associated with the CAD-to-Mask system, is configured to store additional instructions, the additional instructions configured togenerate a design layout corresponding to information provided by the schematic description of the semiconductor device;generate one or more mask layers corresponding to the design layout; andgenerate one or more additional mask layers that do not correspond to the design layout. 12. The semiconductor device design system of claim 11, wherein the descriptions of the identified mask device elements in the second set of data comprise:a location in the integrated circuit of a mask device element; andinformation associated with each mask layer in a predefined range of the location, wherein each mask layer comprises both the one or more mask layers corresponding to the design layout and the one or more additional mask layers. 13. The semiconductor device design system of claim 12 wherein the third set of instructions, associated with the device recognition system, configured to identify characteristics of mask device elements described by the set of IC masks further comprises instructions configured to:perform a pattern matching between known mask features for a general device type and the set of IC masks. 14. The semiconductor device design system of claim 13 wherein the device recognition system further comprises:a fifth memory configured to store the known mask features for the general device type. 15. The semiconductor device design system of claim 10 wherein the instructions configured to identify the physical mask layers associated with the type of device element further comprises instructions configured to:access a memory storing information associated with the physical mask layers for the type of device element. 16. The semiconductor device design system of claim 10 wherein the differences between the device element in the first set of data and the corresponding IC mask device element comprise missing features for the IC mask device element. 17. The semiconductor device design system of claim 10 wherein the differences between the device element in the first set of data and the corresponding IC mask device element comprise additional features for the IC mask device element. 18. A non-transitory computer readable storage medium, storing instructions executable by a processor, the instructions comprising:a first set of instructions configured to generate, from a schematic description of a semiconductor device, a first set of data comprising descriptions of device elements and connectivity of the semiconductor device;a second set of instructions configured to generate a set of integrated circuit (IC) masks for the semiconductor device;a third set of instructions configured to identify characteristics of mask device elements described by the set of IC masks;a fourth set of instructions configured to generate, from the determined mask device elements and the IC masks, a second set of data comprising descriptions of the identified IC mask device elements and connectivity of the semiconductor device;a fifth set of instructions configured to compare each device element in the first set of data with a corresponding IC mask device element in the second set of data, wherein the fifth set of instructions further comprise instructions configured toread information associated with a device element in the first set of data, whereinthe information associated with the device element in the first set of data comprises a location of the device element and an identifier of the type of device element,identify physical mask layers associated with the type of device element, wherein the physical mask layers correspond to expected mask layers for the type of device element,read information associated with the corresponding IC mask device element from the second set of data, whereinthe corresponding IC mask device element is at a maskset location corresponding to the location of the device element in the first set of data, andthe information associated with the corresponding IC mask device element comprises descriptions of mask layers at the maskset location, andcompare the descriptions of the IC mask device element mask layers with the identified physical mask layers; anda sixth set of instructions configured to record differences, if any, between a device element in the first set of data and the corresponding IC mask device element in the second set of data, as a result of said comparing. |
|
description | This application is a continuation-in-part of U.S. patent application Ser. No. 10/434,796 filed May 9, 2003. 1. Field of the Invention The present invention relates to shipping pigs for radiopharmaceuticals that use lead for radiation shielding. In particular, lead shielding is encapsulated and sealed. 2. Discussion of the Prior Art Conventional shipping pigs for radiopharmaceuticals include those that use lead for radiation shielding. The lead shielding defines a cavity to accommodate the syringe. Some conventional pigs have a removable, puncture proof, inner liner or a removable sharps container positioned within their cavity to serve as a barrier between the radiopharmaceutical syringe and the lead shielding. Such a barrier prevents contamination of the lead shielding by leaks from the radiopharmaceutical syringe, such leaks are contained by the inner liner or sharps container. A sharps container is known conventionally to be made from a puncture resistant, if not puncture-proof, hard plastic material having a tubular housing that is securable to a tubular cap in a releasable manner. Both the tubular housing and the tubular cap of the sharps container are elongated with their distal ends (to each other) closed and their proximal ends (to each other) open. The sharps container is sized to accommodate inside a syringe. It would be desirable to provide a radiopharmaceutical pig that encapsulates and seals lead shielding without the need for a removable, puncture-proof liner or a sharps container to protect the lead shielding from contamination caused by leaks from the radiopharmaceutical syringe. One aspect of the invention resides in encapsulation of an inner facing surface of a lead shield of a radiopharmaceutical pig. The inner facing surface defines a chamber in which is inserted a radiopharmaceutical syringe. The encapsulation protects the inner facing surface against contamination from leaks of the contents of the radiopharmaceutical syringe and further obviates the need for a sharps container to enclose the syringe. If desired, a non-puncture resistant, disposable housing may be inserted into the lower portion of the chamber so that the lower portion of the radiopharmaceutical syringe (with the needle) may be inserted into a cavity of the housing, thereby also doing away with the need for a sharps container. The cavity of the housing catches any leaks from the syringe that may occur to prevent the leaks from reaching regions outside the housing that the leaks could otherwise contaminate. Turning to the drawings, FIGS. 1 and 2 identify lower assembly components, namely, a lower case 1, a lower lead shield 2, a lower liner 3, and an O-ring 4, all which may be collectively considered part of a lower assembly 13. FIGS. 1 and 2 also identify upper assembly components, namely, an upper lead shield 6, an upper liner 5 and an upper case 7, all which may collectively be considered part of an upper assembly 14. The lower case 1, upper case 7, lower liner 3 and the upper liner 5 may be made of plastic, metal or a combination of each. The lower case 1 and the lower liner 3 may be secured to the lead shield so that together they encapsulate and seal the lower lead shield 2. Alternatively, the lower case 1 and the lower liner 3 may be secured to each other to contain the lower lead shield 2, but without being secured to the lower lead shield 2 itself. In either situation, the lower case 1 and lower liner 3 may be made contiguous with each other and formed from the same material, as opposed to being separate components. Likewise, the upper case 7 and the upper liner 5 may be secured to the lead shield so that together they encapsulate and seal the upper lead shield 6. Alternatively, the upper case 7 and the upper liner 5 may be secured to each other to contain the upper lead shield 6, but without being secured to the upper lead shield 6 itself. In either situation, the upper case 7 and upper liner 5 may be made contiguous with each other and formed from the same material, as opposed to being separate components. To secure the lower case 1 to the lower liner 3 and/or to the lower lead shield 2 as applicable, and to secure the upper case 7 to the upper liner 5 and/or to the upper lead shield 6, as applicable, either a securing material 15, 16 (FIGS. 4–5) or mechanical fit components 17, 18 (FIGS. 6–7) may be employed. The securing material 15, 16 (FIGS. 4–5) may be an ultrasonic seal, a heat seal, adhering material, and/or laminating material or any combination of these. The mechanical fit components 17, 18 (FIGS. 6–7) may be pressure snap rings or other types of pressure fit components, such as screw locks, clamps or conventional mechanical fasteners. The O-ring 4, which may be made of neoprene or other elastomer, is securely attached into a groove 8, such as with glue or epoxy. The O-ring 4 seals the lower liner 3 to the upper liner 5 as the upper assembly 14 may be screwed onto the lower assembly 13 using the threads 9. Each of the lower liner 3 and the upper liner 5 may have outwardly directed flange surfaces that sandwich the O-ring 4 between them to seal a chamber defined by the lower and upper liners 3, 5. The threads 9 may be triple start threaded to reduce an amount of turns needed to screw the two assemblies 13, 14 together. In addition, the lower case 1 has flats 11 that are molded to prevent the lower assembly 13 from rolling on a flat surface. There may be a configuration with at least one corner such as a hexagon shape 12 molded onto the bottom of the lower case 1 such that the hexagon shape 12 can be secured in a hexagon shaped hole or recess. This way the upper assembly 14 can be screwed to, or unscrewed from, the lower assembly 13 without the user holding onto the lower assembly. This greatly reduces the amount and duration of hand exposure to radiation, because the user no longer needs to hold onto the lower assembly during the screwing and unscrewing operations. The syringe 10 contains a radiopharmaceutical and is placed into the lower liner 3 before the two halves of the upper and lower cases 1, 7 are screwed together by engaging thread connections. After the two halves have been screwed together, the syringe 10 is shipped filled within the two halves to a site. After arrival at the site, the syringe is removed from the two halves and used to administer the radiopharmaceutical from the syringe. When done, the empty syringe may be reinserted into the pig and then shipped back to the supplier for further handling. Otherwise, the empty syringe may be placed into a conventional, lead shielded container (not shown) for future disposal in accordance with government regulations for safe disposal of spent radiopharmaceutical syringes. The two lead shields 2, 6 have edges that face each other that are configured to overlap and engage each other so as to completely shield against penetration of radiation at the joint between the two lead shields 2, 6. Thus, lower lead shield 2 may have a tubular projection in the edge that complements a further tubular projection in the edge of the upper lead shield 6 and is of a reduced diameter relative to that of the further tubular projection. The lower lead shield 2 may have a lower projection that fits within a complementary recess inside at the base of the lower case 1. As a result of encapsulating, the lower and upper lead shields 2, 6 are sealed and thereby protected by the lower and upper liners 3, 5 against contamination from any radiopharmaceutical remnants from the syringe 10 and against exposing the lead shields to cleansing fluids such as water when cleaning them. The syringe 10 may be entirely free of any sharps container surrounding it, because the lower and upper liners 3, 5 obviate the need for it. Indeed, a sharps container would not need to be used in the radiopharmaceutical pig of the present invention to provide sufficient protection of the lead shields against contamination by the discharge of any remnants from within the syringe 10, because the encapsulation provides sufficient protection. The lower and upper liners 3, 5 themselves may be formed of an encapsulating material that adheres or otherwise clings to secure itself to the lead shield to which it is in contact, such as when subjected to a sufficient amount of heat. Turning to FIGS. 4 and 5, the lower shield 2 does not have to be secured to either the lower case 1 or to the lower liner 3. Instead, the lower liner 3 is secured directly to the outer case 1 around a periphery (contact diameter) with the securing material 15. Likewise, the upper shield 6 does not have be secured to either the upper case 7 or to the upper liner 5. Instead, the upper liner 5 may be secured to the upper case 7 about a periphery (contact diameter) with the securing material 16. The lower shield 2 and the upper shield 6 are thereby held in place. Turning to FIGS. 6 and 7, the lower liner 3 may be mechanically fastened to the lower case 1 using a mechanical fit component 17, such as snap rings, screw locks, clamps or conventional mechanical fasteners. The lead shield 2 need not be adhered to anything. Likewise, the upper liner 5 is mechanically fastened to the upper case 7 using a mechanical fit component 18, such as snap rings, screw locks, clamps or conventional mechanical fasteners. The lead shield 6 need not be adhered to anything. Turning to FIG. 8, a flexible, removable, disposable housing 19 is shown for the lower half of the pig. The housing 19 is not puncture-resistant, but would still serve to keep the pig clean, capturing anything that may come out of the syringe 10, because the housing 19 has a closed bottom end. The housing 19 is positioned to be out of contact with the tip of the needle of the syringe while the syringe is within the pig. The housing 19 may be made of any non-puncture-resistant material, such as a soft plastic. In accordance with the invention, sufficient clearance is provided within the cavity defined by the housing to accommodate insertion of the syringe so that the tip of the needle of the syringe will not contact the housing during insertion of same into the lower portion of the cavity and by configuring the upper and lower halves of the radiopharmaceutical pig to clamp outward flanges of the syringe between them so as to maintain the position of the syringe within the cavity in a stable manner during transport. Preferably, the clearance within the lower portion of the cavity is longer than the tip of the needle can reach when the lower portion of the syringe is fully inserted and is wider than the diameter of the body of the syringe and thus many times wider than the diameter of the needle. The housing 19 is elongated with a mouth at one end sized to accommodate insertion of the needle of the radiopharmaceutical syringe through the mouth and preferably accommodate the lower half of the syringe, and an opposite end that is closed to contain any leaks from the radiopharmaceutical syringe. If desired, a puncture resistant platform (not shown) may be inserted within the housing 19 to rest at the opposite end to prevent the tip of the needle from penetrating to reach the housing itself. A cap made of the same non-puncture resistant material as the housing 19 may likewise be used to accommodate the upper half of the syringe so that the entire syringe with attached needed is contained within confines of the housing 19 and the cap to prevent leaks of contents of the syringe from reaching areas of the pig beyond the housing. Such a cap and housing 19 serves the same role as a conventional sharps container, but would not be made from material that is puncture-resistant as is the sharps container and thus differs in that respect. The housing 19 and cap would be disposed of after use, but would serve the purpose of preventing contamination outside the housing and cap. While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various changes and modifications may be made without departing from the scope of the present invention. |
|
047449403 | summary | FIELD OF THE INVENTION This invention relates to an apparatus for compacting spent nuclear reactor fuel rods, and more particularly to an improved apparatus for transferring a spaced apart array of such spent fuel rods from a fuel assembly storage. STATEMENT OF THE PRIOR ART Nuclear reactor installations employ nuclear fuel materials in the form of fuel rods which are supported in fuel rod assemblies. The fuel rods are metal pipes which are filled with nuclear fuel material and are about 0.4-0.6 inch in diameter and from 8 to 15 feet in length. Groups of 64, 128, 220 or more such fuel rods are assembled in a fuel rod assembly which includes grids for alignment and support of the fuel rods, a lower end fitting, an upper end fitting, and guide tubes. The fuel rod assembly is introduced into a nuclear reactor as the fuel source. After the nuclear fuel in the fuel rod assembly is spent to a pre-established level, the entire fuel rod assembly is withdrawn from the nuclear reactor and stored vertically in appropriate metal racks in a wet pool until the radioactive properties have dissipated sufficiently for transfer to other storage locations. Within the fuel rod assembly, the individual fuel rods are spaced apart in a pre-established array, usually a rectangular array. The fuel rod assemblies are spaced apart in the metal racks and are maintained under water for the purpose of moderating or slowing the neutrons. In the fuel rod assembly, the ration of cross-sectional area of fuel rod to cross-sectional area of water is approximately 1:1. At the present time, spent nuclear fuel rod assemblies are withdrawn from the nuclear reactors and are stored vertically in appropriate storage racks under water in storage pools without any deliberate change in the fuel rod assembly. The fuel rod storage pools are filled with the spent fuel rod assemblies whose activity has dissipated as a result of extended storage in the pool. A number of suggestions have been made for removing long-term storage fuel rod assemblies from the pool and for withdrawing individual spent fuel rods from the fuel rod assembly and thereafter for assembling the individual spent fuel rods in new containers or canisters wherein the fuel rods are more closely aligned, i.e., more densely compacted, and for returning such newly-filled canisters to appropriate storage racks within a water storage pool for long-term storage or until appropriate fuel recovery processing is economically feasible. Some of the anticipated difficulties with the proposed fuel rod compacting processes which have been suggested arise form the knowledge that the fuel rods are twisted and bent out of alignment as a result of their long-term exposure in nuclear reactors. In some cases, the distortion may be as much as 5 inches in an 8-foot long rod. Such permanent distortion of the fuel rods will interfere with the proposed alignment techniques. The casing of the fuel rods should be handled by using procedures and equipment designed to accommodate embrittlement due to irradiation in the nuclear reactor. A further problem is that the long, thin fuel rods are shipped and therefore likely to impact with each other when pulled from the fuel assembly. Such impacting could cause fuel rod breakage. Moreover, the fuel rods may be difficult to manipulate. A still further problem relates to the inherent safety of compacting spent fuel rods. There is a possibility that the fuel rods might become spaced apart by a critical distance while removed from the fuel rod assembly and before compaction and confinement in a storage canister Moreover, the fuel rods might be dropped in the water pool or broken due to embrittlement during multimanipulation before confinement in a storage container. Such possibilities should be precluded. SUMMARY OF THE INVENTION According to the present invention, an apparatus is provided for transferring fuel rods from a fuel rod assembly in an underwater pool or in a hot cell to a fuel rod canister and vice versa, when desired, so that the density of the fuel rods in a canister greatly exceeds the density of fuel rods in the fuel rod assembly. A fuel rod consolidation funnel may be used to alter the spacing between the array of fuel rods during the transfer procedure. The apparatus for transferring adequate gripping forces can be produced to advance the fuel rods in the presence of frictional and other forces action on the fuel rods during the transfer process. The apparatus further embodies a design to establish alignment between fuel rod gripper openings in a gripper with the spaced apart array of fuel rods. According to the invention, an end of a fuel rod assembly is removed by cutting or otherwise and grippers of a movable gripper assembly are passed between rows of the exposed end portions of the array of fuel rods to simultaneously grip the fuel rods. The grippers are housed in a gripper plate having a face plate reaction wherein a web section separates passageways for fuel rods. Elongated, expandable grippers are seated in the face plate to extend across the face plate section so that expansion of the expandable grippers force fuel rods engaged therewith against a wall forming a fuel rod passageway. The gripper assembly is reciprocated along a rectilinear path between a fuel rod gripping position at the exposed end of the fuel assembly and a remote fuel rod release position which is adjacent an entry end of a fuel rod directing chamber such as a transition funnel which has fuel rod receiving openings corresponding to the array of fuel rods in the fuel rod assembly. The operation of the reciprocating gripper serves to withdraw an increment of length of all the fuel rods in unison from the fuel assembly in one axial direction for entry and passage in the fuel rod directing chamber. The transition funnel at its fuel rod discharge end has a relatively narrow cross section which corresponds to the cross section of the desired compacted bundle of fuel rods presented to the storage container. For each individual fuel rod, there can be a separate guide within the transition funnel for directing a fuel rod from the fuel rod assembly through the transition funnel into a permanent storage container. The fuel rod consolidation process is thus carried out by positioning the transition funnel between the fuel rod assembly and a permanent storage container in a tandem arrangement so that the spent fuel rods pass in only one direction directly from the fuel rod assembly through the transition funnel into the storage container. This tandem arrangement of components can be provided in a hot cell or it can be provided beneath the water surface in a water pool. In the either event, the spent fuel rods move along a generally horizontal path or a generally vertical path. In the latter event, the fuel storage container can be located either above or below the transition funnel. Thus, the storage container can be positioned so that the spent fuel rods either move upwardly into the storage container or downwardly into the storage container. The passageways through the transition funnel direct the spent fuel rods into pre-established storage positions in a compacted array of fuel rods within the container. The present invention further provides guide tube openings dispersed in the array of fuel rods to receive and portions of guide tubes which are included in the fuel rod assemblies for receiving control rods. The guide tubes are utilized in this instance to align and maintain alignment between the opening in the gripper and the face rods. A second gripper is arranged to reciprocate along a rectilinear path in a gap established between the discharge end of the transition funnel where the fuel rod bundle is gripped and the entry end of a storage canister where the fuel rod bundle is released. The second gripper can embody a construction for gripping the entire bundle of fuel rods since they are in a compacted array. The fuel rods are advanced into the storage container by reciprocating the second gripper in the same manner as the reciprocating motion of the first gripper. In some instances, it may be desirable to provide additional retention means to support the fuel rods during the return movement of each of the first and second grippers. Such retention means can be located at the entry side of the transition funnel and/or storage container. The retention means may, when desired, include the use of conventional grids provided in the fuel assembly to support the fuel rods at various spaced-apart locations along the length of the fuel assembly. In this regard, such grids conventionally provide resilient spring clips to apply a spring tension force against the outer cylindrical surface of the fuel rod. The spring forces can be utilized to prevent unwanted axial movement of the fuel rods while the grippers are returned from a release position to a gripping position as described hereinbefore. When desired, a gripper at the entry and or exit end of the transition funnel can be attached to the funnel and the funnel with one or both grippers attached thereto can be reciprocated along a rectilinear path between gripping and release positions to move the fuel rods from the fuel rod assembly. By providing fuel rod containers of the same cross-sectional dimensions as the fuel rod assemblies, the containers can be stored in the same underwater fuel rod storage racks which have been employed for the fuel rod assemblies. In addition, it is possible to transform the consolidated rods to other geometries, i.e., rhombic, to maximize storage in a cylindrical container which can be used for transporting and/or permanent storage at a local or remote storage site. Accordingly, it is an object of this invention to provide and improve gripper and/or guide spent fuel rod assembly directly into a fuel rod container for compact storage of the spent fuel rods. It is a further object of this invention to carry out the described apparatus wherein a reciprocating gripper moves a distance corresponding to only a small increment of the fuel rod lengths which minimizes the space required to consolidate the fuel rods while causing the fuel rods to move unidirectionally from a fuel rod assembly to a consolidation funnel. |
summary |
Subsets and Splits