patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
claims | 1. A method of RAID restriping in a disk drive system, comprising:selecting a RAID device for migration from a plurality of RAID devices based on a comparison between an initial score and at least one second score calculated for each of the plurality of RAID devices, wherein:the initial score relates to the RAID device in its present state and is calculated based on one or more scoring factors; andthe second score relates to at least one hypothetical RAID device located in available disk space and is calculated based on one or more scoring factors;creating at least one alternate RAID device based on the at least one hypothetical RAID device;moving data stored at the selected RAID device to the at least one alternate RAID device; andremoving the selected RAID device. 2. The method of claim 1, wherein the at least one second score comprises a replacement score relating to at least one hypothetical RAID device located in existing available disk space. 3. The method of claim 1, wherein the at least one second score comprises an overlay score relating to at least one hypothetical RAID device located in a combination of existing available disk space and at least a portion of the disk space taken up by the RAID device. 4. The method of claim 1, wherein the one of one or more scoring factors comprise one or more of the RAID level, RAID stripe size, RAID extent size, disk category, location on disk, disk enclosure, disk enclosure power supply, and communication path to the disk. 5. The method of claim 4, wherein the factors have varying weights for use in the calculation. 6. The method of claim 4, wherein selecting a RAID device for migration based on a comparison between an initial score and at least one second score calculated for each of a plurality of RAID devices comprises selecting the RAID device if the least one second score is better than the initial score. 7. The method of claim 1, wherein the initial score and the at least one second score are each calculated using the same scoring factors. 8. The method of claim 1, wherein the steps of selecting a RAID device for migration, creating at least one alternate RAID device, moving data, and removing the selected RAID device are done automatically without manual intervention. 9. The method of claim 8, wherein the steps are performed without loss of server data access to the disk drive system and compromised resiliency of the data. 10. The method of claim 8, wherein the steps are performed at least one of periodically, continuously, after every RAID device migration, upon addition of disk drives, and before removal of disk drives. 11. The method of claim 1, wherein the steps of selecting a RAID device for migration, creating at least one alternate RAID device, moving data, and removing the selected RAID device are done manually. 12. The method of claim 1, wherein moving data stored at the selected RAID device to the at least one alternate RAID device further comprises creating at least one temporary RAID device. 13. The method of claim 12, further comprising moving data stored at the selected RAID device to the at least one temporary RAID device and then from the temporary RAID device to the at least one alternate RAID device. 14. A disk drive system, comprising:a RAID subsystem; anda disk manager having at least one disk storage system controller configured to automatically:select a RAID device from the plurality of RAID devices based on a comparison between an initial score and at least one second score calculated for the plurality of RAID devices, wherein the initial score relates to the RAID device in its present state and is calculated based on one or more scoring factors and the second score relates to at least one hypothetical RAID device located in available disk space and is calculated based on one or more scoring factors;create an alternate RAID device based on the at least one hypothetical RAID device;move at least a portion of the data stored at the selected RAID device to the alternate RAID device; andremove the selected RAID device. 15. The disk drive system of claim 14, wherein the at least one second score comprises an overlay score related to at least one second hypothetical RAID device located in a combination of existing available disk space and at least a portion of the disk space taken up by the RAID device. 16. The disk drive system of claim 15, wherein the at least one second alternate RAID device is based on one of the first and second hypothetical RAID devices. 17. The disk drive system of claim 14, wherein the disk drive system comprises storage space from at least one of a plurality of RAID levels including RAID-0, RAID-1, RAID-5, and RAID-10. 18. The system of claim 17, further comprising RAID levels including RAID-3, RAID-4, RAID-6, and RAID-7. |
|
047624027 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 diagrammatically shows an example of a system according to the invention. This system comprises a sealed enclosure 9 containing the substance from which it is wished to extract a chemical or isotopic species, said substance being in the form of a vapour flow. Laser sources emit towards said enclosure 9 a beam S.sub.1, which can be formed from one or more beams S'.sub.1, S".sub.1, . . . , S.sub.1.sup.(n), with n being an integer at least equal to 1, and a beam S.sub.2. Means 11 make it possible to superimpose the different beams S'.sub.1, S".sub.1. . . S.sub.1.sup.(n) to obtain several beams S.sub.1, whereby said means 11 will be described in FIG. 6. A beam S.sub.1 corresponding to the selective excitation of the species to be extracted is introduced at several regularly distributed points into enclosure 9, whilst beam S.sub.2 corresponding to the transformation of said species is only introduced once. The means for introducing beams S.sub.1 and S.sub.2 into enclosure 9 are represented by Glan prisms 13, whilst the means for inverting these beams along parallel arms 15 are represented by plane mirrors 17, 19, 21. Thus, these mirrors successively reflect by 90.degree. beams S.sub.1 and S.sub.2, so that they traverse the complete enclosure 9 and along their passage create interaction zones 23 between the photons and certain molecules or atoms of the substance present. As a function of the case, these molecules or atoms are at energy levels corresponding to that of the photons of beams S.sub.1 and S.sub.2 injected into enclosure 9. The remainder of the description provides an understanding of the operation of the system shown in FIG. 2. The two beams S.sub.1 and S.sub.2 are introduced from a Glan prism 13 with orthogonal polarization directions 25, 27. Beam S.sub.1 has a polarity 25 in the plane containing the propagation directions of the laser beams, whilst beam S.sub.2 has a polarization 27 perpendicular to said plane. The polarization difference between the two beams S.sub.1 and S.sub.2 makes it possible to distinguish them in the overall system. After passing through the Glan prism 13, beams S.sub.1 and S.sub.2 are colinear. Thus, in the case of FIG. 2, the Glan prism 13 is positioned in such a way that beam S.sub.1 is transmitted and beam S.sub.2 reflected by 90.degree.. The two beams S.sub.1 and S.sub.2 are then superimposed and traverse the enclosure 9 containing the vaporized substance creating a photon - substance interaction zone 23. After passing through enclosure 9 along a first arm 15, the beams S.sub.1 and S.sub.2 are reflected by 90.degree. by a first plane mirror 17, then by a second plane mirror 19 enabling beams S.sub.1 and S.sub.2 to pass in the reverse sense along a second arm 15 parallel to the first. During the passage of these beams along said second arm 15, a second substance - photon interaction zone 23 is formed. At the end of this arm, a plane mirror 21 makes it possible to reflect these beams on to a second Glan prism 13. During the passage of said prism, beam S.sub.2 is again reflected by 90.degree. due to its polarization, whilst beam S.sub.1, which is very attenuated, following the various interactions with the substance is transmitted by the prism and is lost in the system. A beam S.sub.1 of the same polarization is as previously then injected through said second Glan prism 13, and after passing through the latter, the transmitted beam S.sub.1 is superimposed on the reflected beam S.sub.2. Thus, the same conditions occur as during the first introduction of the beams S.sub.1 and S.sub.2 into the system. The sequence of operations is the same as that described hereinbefore and is repeated in such a way that the entire enclosure is scanned by beams S.sub.1 and S.sub.2 along parallel arms, thus producing substantially adjacent interaction zones 23. As a function of the substance - photon interaction type, it can be of interest to have a circular polarization 28 of beams S.sub.1 and S.sub.2. In this case, it is merely necessary to introduce into the overall system a quarter-wave plate 31 between the Glan prism 13 and the entrance to enclosure 9 in a beam propagation direction corresponding to an arm 15 and a further quarterwave plate 32 on an arm 15 traversed in the reverse sense by the beams between the outlet of enclosure 9 and Glan prism 13 and so on throughout the apparatus. These quarter-wave plates 31, 32 are e.g. constituted by Fresnel parallepipeds. The association of a quarter-wave plate 31, 32 with each prism 13 makes it possible to obtain from linearly polarized beams S.sub.1, S.sub.2 a circular polarization and vice versa. In the example of FIG. 2, beam S.sub.1 successively passes twice into enclosure 9 before being reinjected into the enclosure, but if it is not excessively attenuated following the different interactions with the substance, its utilization can be optimized by making it perform several passages of enclosure 9 in both senses and in directions forming parallel arms 15 until it is very attenuated. For this purpose, series of plane mirrors are added on the passage or path of beams S.sub.1 and S.sub.2, so that the latter are reflected as many times as is necessary, as hereinbefore. In order to synchronize the pulses of the reinjected beams S.sub.1 and those of beam S.sub.2, use is made of not shown delay lines, which can be constituted by a succession of plane mirrors, between which successive reflections take place. Various modifications can be made to the aforementioned system. Thus, FIG. 3 shows an embodiment of the system according to the invention permitting a better utilization of the photons and the vapour. The plane mirror 21 is replaced by a Glan prism 20 arranged so as to reflect only beam S.sub.2 by 90.degree. and to transmit the highly attenuated beam S.sub.1. Another beam S.sub.1 is then reinjected into the inlet of enclosure 9 at said level, i.e. at the end of arm 15 traversed in the reverse sense by the preceding beam S.sub.1. Thus, said beam S.sub.1 will travel the path in the reverse sense and this also applies throughout the remainder of the system. Moreover, a beam S.sub.2 is reinjected level with the outlet of beam S.sub.2, i.e. at the end of the passage of beam S.sub.2 through enclosure 9. Thus, the beams S.sub.1 and S.sub.2 traverse the vapour in both senses, thereby adequately interacting with the molecules or atoms located at the end of the paths of said beams. A variant of the latter device to bring about a better utilization of beam S.sub.2 is obtained by adding a mirror 22 at the end of the path of beam S.sub.2 in enclosure 9, so as to reflect it back into the latter in the same propagation directions as those of the incident beam S.sub.2. Following a double passage in enclosure 9, S.sub.2 is then almost completely absorbed. FIGS. 4a and 4b show other embodiments of the system according to the invention, in which beams S.sub.1 are introduced at the opposite end of enclosure 9 on each arm 15. Thus, in FIG. 4a, a second laser source identical to the first has been added and permits the symmetrical introduction with respect to the beams S.sub.1 from the superimposing means 11, of beams S.sub.1 coming from superimposing means 12 which are identical to means 11. A variant of this system, as shown in FIG. 4b, comprises reflecting back on to itself each beam S.sub.1 by using a plane mirror 26 positioned at the opposite end from the entrance of beam S.sub.1 and also for each arm 15. In these two systems, a second Glan prism 24 is placed on each arm 15 upstream of the entry of beam S.sub.1 from the second laser or upstream of the mirror, so as to deflect beam S.sub.2 towards the remainder of enclosure 9. Use is made of Glan prisms in the aforementioned system, but it is also possible to use any other apparatus making it possible to superimpose two light beams of orthogonal polarity entering the same in perpendicular directions or to separate such beams entering the same with the same direction. In place of the plane mirrors, it is possible to use any other apparatus making it possible to reflect polarized beams by 90.degree., whilst retaining the polarity thereof. FIGS. 5a and 5b show an embodiment of a system according to the invention operating in cavity manner. In this embodiment, to achieve optimum use of the molecules or atoms in the interaction zones 23, these zones are traversed several times by laser beams S.sub.1 and S.sub.2. Such an apparatus is shown in FIG. 5a. In FIG. 5a is shown a sealed enclosure 9 containing the substance in the form of a vapour flow and whereof it is wished to extract an isotopic or chemical species. Laser sources emit into said enclosure a beam S.sub.1, which can be constituted by several beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) with n being an integer at least equal to 1, as well as a beam S.sub.2. Means 11 make it possible to superimpose the different beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) to obtain several beams S.sub.1. A beam S.sub.1, corresponding to the selective excitation of the species to be extracted, is introduced at several regularly spaced points into enclosure 9 in parallel directions forming arms 15, whilst the beam S.sub.2, corresponding to the transformation of said species, is only introduced once into enclosure 9 and traverses the same in the same directions forming arms 15. The means for introducing beams S.sub.1 and S.sub.2 into enclosure 9 are represented by Glan prisms 29, 30, each beam S.sub.1 being injected through a prism 29, whilst beam S.sub.2 is injected through a prism 30. The means for reflecting beams S.sub.1 and S.sub.2 on to themselves are represented by plane mirrors 33, 35 respectively associated with Pockles cells 37, 39, whilst the means for inverting beam S.sub.2 towards other propagation directions forming parallel arms 15 are represented by a Pockles cell 41 associated with Glan prism 30. Thus, beams S.sub.1 and S.sub.2 are respectively injected across a Glan prism 29, 30 with the same polarization 27 perpendicular to the plane containing the propagation directions of the beams and in the same propagation directions forming arms 15. Thus, beams S.sub.1 and S.sub.2 have two opposite propagation senses making it possible to distinguish them in the complete system, despite their identical polarization 27. The assemblies constituted by plane mirrors 33, 35 and Pockels cells 37, 39 make it possible to cause beams S.sub.1 and S.sub.2 to traverse the same interaction zone 23 a number of times before transmitting beam S.sub.2 alone, through Pockels cell 41, into the following interaction zone 23. The voltages applied to the different Pockels cells as a function of time are shown in FIG. 5b. The remainder of the description provides a better understanding of the operation of the system shown in FIG. 5a. Beam S.sub.1 of polarization 27 is introduced into enclosure 9 by injecting through a Glan prism 29 following a reflection by 90.degree. on a plane mirror 43. This beam is reflected by the Glan prism 29 and then passes through a first Pockels cell 37. For a time t.sub.1 (FIG. 5b), a quarter-wave voltage V.sub..lambda./4, 45 is applied to said cell. Following the passage through cell 37, the polarization of beam S.sub.1 is circular. S.sub.1 is then reflected on itself by a plane mirror 33 perpendicular to the propagation direction of beam S.sub.1, the latter then again passing through cell 37. Following its second passage through cell 37, beam S.sub.1 has a polarization perpendicular to that of the incident beam and is therefore transmitted by the Glan prism 29. At the same time as beam S.sub.1, beam S.sub.2 is introduced into enclosure 9 at the other end of arm 15 in a symmetrical manner. It is then firstly injected through a Glan prism 30 with the same polarization 27, is then reflected by the latter and then passes through a Pockels cell 39 to which a quarter-wave voltage 47 is also applied for the same time t.sub.1. A plane mirror 35 perpendicular to the propagation direction thereof reflects the beam on itself and it then passes into the Pockels cell 39 again. Following its second passage in cell 39, beam S.sub.2 has a polarization perpendicular to that of the incident beam and the latter is then transmitted by the Glan prism 30. The Pockels cell 41 is passive, i.e. it does not modify the state of the radiation passing through it. Thus, the two beams S.sub.1 and S.sub.2 have the same propagation direction corresponding to an arm 15, but are of the opposite sense. Thus, during their passage in enclosure 9, they produce an interaction zone 23 between photons and substance. These beams are reflected towards interaction zone 23 whenever they reach the ends of an arm 15 by an assembly constituted by Pockels cell 37 (39) and a plane mirror 33 (35). The zero voltage applied to the Pockels cell 41 is maintained for as long as it is wished to pass beams S.sub.1 and S.sub.2 into the same interaction zone 23. When the number of outward and return passages performed in the same zone 23 by beams S.sub.1 and S.sub.2 is such that beam S.sub.1 is totally absorbed or highly attenuated, beam S.sub.2 is freed by applying to cell 41 a voltage V.sub..lambda./2, 49 at time t.sub.2. In a single passage of beam S.sub.2 in cell 41, the polarization of the resultant beam S.sub.2 is perpendicular to that of the incident beam. The latter is then reflected by 90.degree. by Glan prism 30 towards an assembly similar to that described hereinbefore. To ensure that beams S.sub.1 and S.sub.2 injected at each end of enclosure 9 are superimposed in interaction zones 23, the latter must have a length close to C.DELTA.t in which C represents the speed of light in the gaseous medium in question and .DELTA.t the mid-height width of the light pulses of the laser beams. The length of the optical cavity in which the system is located must be approximately twice as large as that of the interaction zone 23 so that during the injection, i.e. before time t.sub.1, the photons introduced by one end do not leave by the other. This cavity operation consequently makes it possible to act with all the initially available intensity on beam S.sub.2 and to simultaneously use all the energy emitted by the lasers. In the same way for the apparatus described in FIG. 2, the pulses of beam S.sub.1 must be synchronized with those of beam S.sub.2, the life of the transitions being approximately equal to that of the pulses, i.e. roughly a few dozen ns. For this use is made of a delay line, which is a "cavity without atoms". For this purpose, through a Glan prism is injected beam S.sub.1, which is reflected towards a zone outside the interaction zone 23. In said zone, beam S.sub.1 performs successive outward and return paths on itself as a result of plane mirrors positioned at each end of said cavity and is freed, as hereinbefore, by applying a voltage to a Pockels cell located on its path. FIG. 6 shows an embodiment of the means 11 making it possible to superimpose several beams constituting beam S.sub.1. As has been shown hereinbefore, the selective excitation beam S.sub.1 is generally formed from several beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) of respective wavelengths .lambda.'.sub.1, .lambda.".sub.1, . . . .lambda..sub.1.sup.(n) with n being an integer at least equal to 1. Thus, these beams must be split and then superimposed in order to be injected into the system according to the invention. Thus, for splitting and superimposing several beams use is made of a group of plane mirrors positioned at 45.degree. with respect to the propagation direction of these beams. In the case of FIG. 4, as in the case of the isotopic separation of U.sup.235 from uranium vapour, consideration is given to three beams S'.sub.1, S".sub.1 and S.sub.1 '"of respective wavelengths .lambda.'.sub.1, .lambda.".sub.1, and .lambda..sub.1 "'. These beams are split and superimposed by successive beam splitting plates 51, 53, 55, 57 of reflection coefficient 0.5, the resultant beams S.sub.1 being directed in parallel propagation directions by total reflection plane mirrors 59, 61, 63, 65 towards different inlets of the enclosure of the system according to the invention. In this embodiment, the plane mirrors 60 and 62 solely make it possible to transmit beams S'.sub.1 and S.sub.1 '" respectively to beam splitting plates 51 and 57. Thus, half the beams S'.sub.1 and S".sub.1 reaching plate 51 in two orthogonal directions is transmitted, whereas the other half is reflected. Each transmitted half of one of the beams is superimposed on the reflected half of the other beam and vice versa. These halves of the superimposed beams are again split into two by two plates 53 and 55. In the same way, beam S.sub.1 "' is split into two by plate 57, the resultant beams being again split by plates 53 and 55, thus being superimposed on the split beams from S'.sub.1 and S.sub.1 ". This leads to four beams S.sub.1 resulting from the superimposing and splitting into four of beams S'.sub.1, S.sub.1 " and S"'.sub.1. By successive splitting operations, it is possible to obtain the same number of beams S.sub.1 of the same wavelength as is required by the system according to the invention. FIG. 7 shows a known installation making it possible to vaporize the substance, whereof it is wished to extract an isotope and collect it when it is ionized. This type of installation is used for separating the isotope U.sup.235 from uranium or for purifying palladium by eliminating isotope Pd.sup.107. The matter, in the form of ingot 67 is heated by electron bombardment along line 69 up to the evaporation temperature of said matter. The vaporized atoms have a high kinetic energy. The atoms vaporized within an angle .theta. are then irradiated by laser beams S.sub.1 and S.sub.2 introduced into said installation in accordance with a system according to the invention. Beam S.sub.1 selectively excites U.sup.235, whilst beam S.sub.2 ionizes the previously excited atoms. On either side of the laser beams traversing the vapour and interacting therewith are arranged collecting plate 71 between which an electric field is created. The ionized atoms are deflected by this field and then collected by plate 71. The non-ionized neutral atoms continue their path towards a target 72, where the vapour condenses. The number of plates 71 necessary for the optimum exploitation of the atoms emitted in angle .theta. is determined by the maximum spacing between the plate 71 compatible with a minimum charge exchange between the ions and the neutral atoms. As has been shown hereinbefore, the system according to the invention is also applicable to the molecular isotopic separation process. In this case, the molecules are firstly excited by a first beam S.sub.1 and are then photodissociated by a second beam S.sub.2. The separation of these dissociated molecules in particular takes place by condensation. Thus, no matter what the variants used, the system according to the invention makes it possible to compensate the small effective transition section corresponding to the transformation of the species to be extracted, i.e. the ionization or photodissociation, whilst optimizing the photon - matter/substance interaction. |
description | The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 10 2009 056 722.4 filed Dec. 2, 2009, the entire contents of which are hereby incorporated herein by reference. At least one embodiment of the invention generally relates to a collimator module for the modular assembly of a collimator for a radiation detector and/or a radiation detector. Scattered radiation is substantially generated by the interaction between primary radiation, emanating from the focus of a radiation source, and the object to be examined. Scattered radiation impinging on a radiation convertor of a radiation detector from a different spatial direction than the primary radiation as a result of this interaction causes image artifacts in the reconstructed image. Thus, collimators are placed upstream of the radiation convertors in order to reduce the detected proportion of scattered radiation in the detector signals. By way of example, known collimators comprise absorber elements, which are arranged next to one another in a collimation direction and are aligned in a unidirectional fashion in respect of their longitudinal extent. In the radial direction, the absorber surfaces of the absorber elements are aligned in a fan-shaped fashion with respect to the focus of a radiation source, and so only radiation from the spatial direction in the direction of the focus can impinge on the radiation detector. By contrast, scattered radiation proportions are absorbed by the absorber surfaces of the absorber elements. A slight tilt of the absorber elements compared to an intended alignment, or erroneous positioning of the absorber elements, or the entire collimator, compared to the radiation convertor, already leads to shadowing of the active regions of the radiation convertor and hence to falsification of or reduction in an attainable signal-to-noise ratio. Hence, a particular challenge when assembling a radiation detector is, firstly, to manufacture the collimator in a very precise shape and, secondly, to align the collimator very precisely with respect to the radiation convertor. Here, positional accuracy of the order of a few 10 μm must be attainable and also verifiable by metrological means. The integration of the collimator into the radiation detector is complicated by the fact that the active regions of the detector elements in the radiation convertor are, for the most part, no longer visible from the outside when aligning the collimator. In indirect-conversion radiation convertors, in which the radiation is converted indirectly into electrical signals via the generation of light pulses by an incident X-ray quantum, the scintillator array used to generate the light pulses is covered by an opaque cover-reflector on the side of the beam incidence direction. Hence the structuring of the scintillator array is no longer visible from the outside during the integration of the collimator. JP 2003 177 181 AA and U.S. Pat. No. 6,982,423 B2 have disclosed radiation detectors, in which the collimator is produced in small units and, in the form of tiles or a matrix, is screwed to a radiation detector or radiation detector module. Moreover, embodiments are known in which the collimator modules are directly adhesively bonded onto the radiation convertor. Alternatively, the collimator modules in this case are aligned with respect to the outer edges of the radiation convertor. However, in the known cases, possible faulty positioning or tilting of the absorber elements of the collimator can only be detected in a subsequent test when the radiation detector has been completely assembled. Replacing a collimator module in such a collimator is very costly and requires much time. In at least one embodiment of the invention, a collimator module and/or a radiation detector are embodied such that the preconditions for a simpler assembly and simpler maintenance of the radiation detector are met. In at least one embodiment, this is achieved by a collimator module and/or by a radiation detector. Advantageous embodiments and developments are the subject matter of dependent claims. The collimator module according to at least one embodiment of the invention for the modular assembly of a collimator for a radiation detector comprises a multiplicity of absorber elements, which are arranged one behind the other in a collimation direction and held by a carrier, wherein the carrier has alignment device(s) for aligning the collimator module in the collimation direction, which alignment device(s) interact with positioning device(s) in a detector mechanism of the radiation detector when they are integrated into the radiation detector. Thus, the alignment device(s) are used for the precise alignment of the collimator module relative to the detector mechanism of the radiation detector. Hence, in this approach, the integration of the collimator module into the radiation detector is decoupled from an integration of a radiation convertor. This decoupling in particular allows a precise alignment or a precise readjustment of these components relative to one another with little effort, even after their integration into the radiation detector. By way of example, the assembly of a radiation detector may be implemented as follows: individual radiation convertor modules for assembling the radiation convertor on the one hand and, decoupled therefrom, the individual collimator modules on the other hand are inserted into the detector mechanism in separate process steps. The collimator modules are positioned on the base of the alignment device(s) provided in the carrier, which alignment device(s) interact with corresponding positioning device(s) in the detector mechanism. Corresponding alignment device(s) and positioning device(s) may be provided for integrating the radiation convertor modules. If necessary, the radiation convertor modules may be readjusted or aligned in a precise fashion relative to the collimator modules in a subsequent process step. Thus the preconditions for a simpler assembly and simpler maintenance of the radiation detector are created by the alignment device(s) provided in the carrier, which alignment device(s) interact with corresponding positioning device(s) in the detector mechanism. The alignment device(s) in the carrier are preferably recesses. Such alignment device(s), for example U-shaped recesses, can be produced very precisely in a simple fashion. The carrier preferably also has support device(s) for positioning the collimator module in a beam incidence direction, which support device(s) interact with abutment device(s) in the detector mechanism of the radiation detector when they are integrated into the radiation detector. During the insertion of the collimator module, the weight of the collimator module is supported from a direction in which gravity acts as well and hence not by the alignment device(s), and so the accuracy of the alignment is not reduced by an additional mechanical load on the alignment device(s). In the simplest case the support device(s) are edges of the carrier that abut against an abutment surface of the detector mechanism during integration. Such support device(s) can be produced in a particularly simple and precise fashion. In an advantageous embodiment of the invention, the carrier is formed from two carrier elements extending in the collimation direction, wherein the absorber elements are connected to the carrier elements in a cross-shaped fashion. Hence, the carrier elements as supporting parts form two sidewalls in which the absorber elements are held. Hence the carrier has very little complexity and can be produced with little effort. The cross-shaped connections between the absorber elements and the carrier elements ensure the necessary stability of the collimator. The carrier elements are ideally designed to be completely identical. The two carrier elements and/or the absorber elements preferably have a plate-like design. As a result of the possibility of stacking the elements connected with this, all carrier elements required for assembling the collimator can be produced in a single work step by simultaneous electric discharge wire cutting. The same holds true for the production of the absorber elements, in which up to 300 absorber elements can be produced in a single work step by simultaneous electric discharge wire cutting. The cross-shaped connections between the absorber elements and the carrier elements are preferably plug-in connections. Plug-in connections can be produced with little effort and at the same time offer a secure hold for the absorber elements in the respective carrier element. They can be formed in a particularly simple fashion by recesses or slits in the absorber elements and/or in the carrier elements. The position, the extent and the alignment of the recesses or the slits can moreover be prescribed very precisely in the region of a few μm by way of electric discharge wire cutting. The plugged-together elements can be aligned very precisely with respect to one another as a result thereof. In this case the plug-in connection satisfies a dual function. It is used both for mechanically fixing the elements amongst themselves and for aligning the elements with respect to one another. By way of example, the alignment is brought about in this case by guiding the one element in a guide channel formed by the slit. In this context, the use of electric discharge wire cutting has the additional advantage that the recesses or slits on the carrier-element side for holding the absorber elements and the alignment device(s) can be introduced without renewed insertion of the carrier elements. Possible erroneous positioning resulting from the renewed insertion are avoided as a result of this. Hence a collimator module can be produced, in which the alignment and position of the absorber elements in respect of the alignment device(s) have a tolerance of the order of the machine inaccuracy, that is to say a few μm. In an advantageous embodiment of the invention, the slits in the absorber elements interlock with the corresponding slits in the carrier elements in a cross-shaped fashion during the assembly of the plug-in connection. The elements are mutually guided by the two slits and thereby assume a predefined position with respect to one another. In a further advantageous embodiment, the absorber elements are additionally adhesively bonded to the carrier elements at the cross-shaped connection points. This additionally secures the plug-in connection and increases the strength of the collimator module. In order to increase the overall stability of the collimator, the collimator module according to one embodiment of the invention has at least one cover element in a beam incidence direction and/or a beam emergence direction, in which cover element the longitudinal edges of the absorber elements are guided at least in part. Guiding the longitudinal edges of the absorber elements to the cover element ensures that the absorber elements remain stably in position and alignment, even in the case of a large Z-coverage and high rotational speeds. This is because the transverse forces, which occur at the outer regions of the absorber elements, particularly when the recording system rotates, and are respectively directed in the opposite direction, are compensated by the affixed cover element. Moreover, the cover element protects the absorber elements from mechanical influences and hence from damages or dirt. The carrier elements preferably have a fixing device, by which the collimator module can be fixed to the detector mechanism. By way of example, such a fixing device(s) can be a bore for holding a fixing screw or a fixing element. This ensures that the position of the collimator module with respect to the detector mechanism, which position was imparted by the alignment device(s), is maintained. However, it would also be feasible for the alignment device(s) of the carrier additionally to satisfy the function of a fixing device as well. The radiation detector according to a second aspect of at least one embodiment of the invention has a detector mechanism for holding a collimator and a radiation convertor aligned with respect thereto, wherein the collimator is assembled from the above-described collimator modules, and wherein the alignment device(s) of the collimator modules engage in corresponding positioning device(s) in the detector mechanism for precisely positioning the collimator modules relative to the detector mechanism. In an advantageous embodiment of the radiation detector according to the invention, the radiation convertor is subdivided into radiation convertor modules, wherein the respective collimator module in each case covers two, three, four or five radiation convertor modules. As a result of such a segmentation of the collimator with respect to the radiation convertor, the collimator can be assembled quickly with a negligible error in the positioning accuracy. The collimator module can be produced as per the following steps: a) simultaneously producing the carrier elements by electric discharge wire cutting, in particular for all collimator modules required for the collimator, b) simultaneously producing the absorber elements by electric discharge wire cutting, in particular for at least one of the collimator modules, c) aligning the carrier elements relative to one another by way of a positioning tool, d) mounting the absorber elements in the carrier elements, wherein the absorber elements and the carrier elements have corresponding slits for producing a plug-in connection, e) adhesively bonding the absorber elements to the carrier elements, and f) placing and adhesively bonding cover elements on the longitudinal edges of the absorber elements in the beam incidence direction and/or beam emergence direction. Various example embodiments will now be described more fully with reference to the accompanying drawings in which only some example embodiments are shown. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The present invention, however, may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the present invention to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” or “directly coupled,” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. In the figures, parts that have the same effect have been provided with the same reference signs. In the case of repeating elements in a figure, such as the absorber elements 2, only one element is provided with a reference sign in each case for reasons of clarity. The illustrations in the figures are schematic and not necessarily to scale, wherein the scale may vary between the figures. FIG. 1 shows a computed tomography scanner 16, which comprises a radiation source 17 in the form of an X-ray tube, with an X-ray beam fan 19 emanating from the focus 18 thereof. The X-ray beam fan 19 penetrates an object 20 to be examined or a patient, and impinges on a radiation detector 3, in this case on an X-ray detector. The X-ray tube 17 and the X-ray detector 3 are arranged opposite one another on a gantry (not illustrated here) of the computed tomography scanner 16, which gantry can be rotated in a φ-direction about a system axis Z (=patient axis) of the computed tomography scanner 16. The φ-direction thus represents the circumferential direction of the gantry and the Z-direction represents the longitudinal direction of the object 20 to be examined. When the computed tomography scanner 16 is operational, the X-ray tube 17 and the X-ray detector 3, respectively arranged on the gantry, rotate about the object 20, with X-ray recordings of the object 20 being obtained from various projection directions. In each X-ray projection, X-ray radiation that has passed through the object 20 and has been attenuated thereby impinges on the X-ray detector 3. In the process, the X-ray detector 3 generates signals that correspond to the intensity of the incident X-ray radiation. The X-ray radiation is converted into electrical signals by way of a radiation convertor 13, which is structured in the form of radiation convertor modules (not illustrated here). Each radiation convertor module has detector elements 23 that have been arranged to form an array. Each detector element 23 generates a signal by way of a photodiode 26, which is optically coupled to a scintillator 27. An evaluation unit 21 subsequently calculates one or more two-dimensional or three-dimensional images of the object 20 in a well-known fashion from the signals registered thus by the X-ray detector 3, which images can be displayed on a display unit 22. The primary radiation emitted by the focus 18 of the X-ray tube 17 is scatted in different spatial directions in, inter alia, the object 20. This so-called secondary radiation generates signals in the detector elements 23 that cannot be distinguished from the signals of primary radiation required for the image reconstruction. Thus, without a further measure, the secondary radiation would lead to misinterpretations of the detected radiation and hence to a significant reduction in the quality of the images obtained by the computed tomography scanner 16. In order to limit the influence of the secondary radiation, a collimator 1 is used to substantially only let the proportion of the X-ray radiation emitted by the focus 18, i.e. the proportion of the primary radiation, pass unhindered onto the radiation convertor 13, while the secondary radiation is ideally completely absorbed by the absorber surfaces of the absorber elements 6. The collimator 1 is formed from a plurality of collimator modules 2, which are arranged one behind the other in the collimation direction φ, which in this case coincides with the φ-direction. The modular-like assembly of the collimator 1 reduces the integration complexity due to the improved manageability and reduces costs and complexity of maintaining the X-ray detector 3 because in the case of a fault it is merely a small part, namely an individual collimator module 2, and not the entire collimator 1 that needs to be replaced. FIG. 2 shows such a collimator module 2 in a partly fitted state and FIG. 3 shows it in a state where it has been fully fitted with absorber elements 6. The collimator module 2 is fitted with a multiplicity of absorber elements 6 that are arranged one behind the other in a collimation direction φ and are held by a carrier 4. In this exemplary embodiment, the carrier 4 consists of two carrier elements 5 extending in the collimation direction φ. The carrier elements 5 are held in a positioning tool (not illustrated here) during the fitting process in order to ensure a precise alignment of the carrier elements 5 with respect to one another. The absorber elements 6 are connected to the carrier elements 5 in a cross-shaped fashion via a plug-in connection. To this end, slits 8, 9 have been introduced into the absorber elements 6 and into the carrier elements 5, with respectively one slit 9 in the carrier element 5 corresponding to respectively one of the two slits 8 in the absorber element 6. When the absorber element 6 (illustrated as hovering in FIG. 2) is inserted into the carrier elements 5, the corresponding slits 8, 9 interlock in a cross-shaped fashion. Here the slits 8, 9 have a constant breadth over their axial length and form a guide channel for the respective counterpart, in which channel the counterpart is guided. Hence the absorber elements 6 assume a defined position with respect to the carrier elements 5 when the plug-in connection has been established, and are also mechanically coupled to said carrier elements. In order to increase the mechanical stability the two elements 5, 6 are additionally adhesively bonded to one another at the corresponding connection points. Each of the carrier elements 5 furthermore has alignment device(s) 7 in the form of recesses, which are used to align the collimator module 2 in the collimation direction φ when the alignment device(s) are integrated into the X-ray detector 3. To be more precise, the alignment device(s) 7 of the carrier elements 5 engage in corresponding positioning device(s) 14 in the form of protrusions on the detector mechanism 12, as illustrated in FIG. 10. The recesses 7 in the carrier element 5 and the protrusions 14 on the detector mechanism 12 form an interlocking connection in the collimation direction φ. The recess 7 has a U-shaped profile in the present example. It goes without saying that it would also be feasible for the protrusions 14 to be on the carrier elements 5 and the recesses 7 to be in the detector mechanism 12. What is decisive is that in this approach the respective collimator module 2 can be installed into the detector mechanism 12 in a way that is decoupled from a radiation convertor 13 of the X-ray detector 3. This decoupling simplifies the replacement of the collimator modules 2 and the readjustment of the relative position between the collimator modules 2 and the radiation convertor 13. Moreover, the carrier elements 5 have support device(s) 28, here in the form of the longitudinal edge of the carrier elements 5 in the beam emergence direction 25. These support device(s) 28 are used to position the collimator module 2 with respect to the detector mechanism 12 in the beam incidence direction 24. As explained below with respect to FIG. 10, the edges 28 in the installed state lie on abutment device(s) 29 in the form of projections on the detector mechanism 12. Additional fixing device(s) 11 are provided on the carrier elements 5, which fixing device(s) can fix the collimator module 2 in its position with respect to the detector mechanism 12. In the simplest case the fixing device(s) 11 are bores in the carrier elements 5. The carrier elements 5 are embodied in a symmetric and plate-shaped fashion. Hence all carrier elements 5 required for assembling the collimator 1 can be produced very precisely in a single work step by way of electric discharge wire cutting. It is also advantageous that the slits 8 and recesses 7 in the respective carrier element 5 can be produced without renewed introduction of the workpiece, and so the tolerances between alignment device(s), fixing device(s) and holding device(s) 7, 11, 8 for the absorber elements 6 are of the order of the machine inaccuracy and hence of the order of just a few μm. FIG. 4 shows the collimator module according to an embodiment of the invention, which has additionally been fitted with fixing elements 30 for fixing the collimator module 2 to the detector mechanism 12. FIG. 5 shows one of the fixing elements 30 in a detailed view. It has a basic body 31 with a bore 32 for guiding a fixing pin or a fixing screw. The bore 32 has been dimensioned across the axial direction 33 such that the fixing element 30, and hence the collimator module 2 connected thereto, can be adjusted with respect to the detector mechanism 12 within certain tolerances. A holding device 34 in the form of a pin or a stud has additionally been attached to the basic body 31. The pin 34 has been inserted into the corresponding bore-hole-shaped fixing device(s) 11 on the carrier element 5 in a tight-fitting fashion. The axial direction 35 of the pin 34 and the axial direction 33 of the bore 32 are perpendicular to one another, and so the collimator module 2 and the detector mechanism 12 can be fixed by the fixing pin or the fixing screw from the beam incidence direction 24. This direction offers the option of easier access to the X-ray detector 3 and hence simpler fixing and readjustment of the collimator module 2. In this example embodiment, the collimator module 2 is respectively fitted with five cover elements 10 in the beam incidence direction 24 and the beam emergence direction 25 for increasing the stability and protecting the absorber elements 6. FIG. 6 shows partial fitting of the collimator module 2 with cover elements 10 in the beam incidence direction 24. A section of the collimator module 2 can be seen in a detailed view in FIG. 7. FIG. 8 shows the collimator module 2 with partly fitted cover elements 10 from the perspective of the beam emergence direction 25. Each cover element 10 has precisely manufactured guide grooves 36, which guide and hold the longitudinal edges of the absorber elements 6. The cover elements 10 are produced from a material that is transparent to X-ray radiation. FIG. 9 shows part of the detector mechanism 12 without a collimator module 2 and FIG. 10 shows it with an installed collimator module 2. The detector mechanism 12 has positioning device(s) 14 in the form of studs, which are used to align the collimator module 2, engage into the alignment device(s) 7 of the collimator modules 2 and hence position the latter in the collimation direction φ. The collimator module 2 is carried in the detector mechanism 12 by virtue of the fact that the edges provided in the carrier elements 5 lie on corresponding projections 29 on the detector mechanism 12. The detector mechanism 12 moreover has bores that correspond to corresponding bores 11 in the carrier elements 5. These two parts are screwed together via these bores 11, 37 in order to fix them. Reference is made to the fact that the statements should not be considered to be restricted to a collimator module 2 that is merely used to suppress the scattered radiation in the φ-direction. It is immaterial to the invention whether the collimator module 2 furthermore has additional absorber elements 6 (not illustrated here), which are arranged one behind the other in the direction of the z-axis and are used for suppressing scattered radiation in the z-direction. Reference is furthermore made to the fact that beam incidence direction 24 and beam emergence direction 25 correspond to the directions of the incident and emergent radiation when the collimator module 2 is used as intended. In conclusion, the following statement can be made: At least one embodiment of the invention relates to a collimator module 2 for the modular assembly of a collimator 1 for a radiation detector 3 with a multiplicity of absorber elements 6, which are arranged one behind the other in a collimation direction φ and held by a carrier 4, wherein the carrier 4 has alignment device(s) 7 for aligning the collimator module 2 in the collimation direction φ, which alignment device(s) interact with positioning device(s) 14 in a detector mechanism 12 of the radiation detector 3 when they are integrated into the radiation detector 3. This provides the preconditions for integrating the collimator module 2 in a fashion that is decoupled from a radiation convertor 13, and so this allows easy assembly of a collimator 1 and adjustment to a position assumed between a radiation convertor 13 and the collimator 2. At least one embodiment of the invention moreover relates to a radiation detector 3 with such a collimator module 2. The patent claims filed with the application are formulation proposals without prejudice for obtaining more extensive patent protection. The applicant reserves the right to claim even further combinations of features previously disclosed only in the description and/or drawings. The example embodiment or each example embodiment should not be understood as a restriction of the invention. Rather, numerous variations and modifications are possible in the context of the present disclosure, in particular those variants and combinations which can be inferred by the person skilled in the art with regard to achieving the object for example by combination or modification of individual features or elements or method steps that are described in connection with the general or specific part of the description and are contained in the claims and/or the drawings, and, by way of combineable features, lead to a new subject matter or to new method steps or sequences of method steps, including insofar as they concern production, testing and operating methods. References back that are used in dependent claims indicate the further embodiment of the subject matter of the main claim by way of the features of the respective dependent claim; they should not be understood as dispensing with obtaining independent protection of the subject matter for the combinations of features in the referred-back dependent claims. Furthermore, with regard to interpreting the claims, where a feature is concretized in more specific detail in a subordinate claim, it should be assumed that such a restriction is not present in the respective preceding claims. Since the subject matter of the dependent claims in relation to the prior art on the priority date may form separate and independent inventions, the applicant reserves the right to make them the subject matter of independent claims or divisional declarations. They may furthermore also contain independent inventions which have a configuration that is independent of the subject matters of the preceding dependent claims. Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
|
047864656 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates a sectional view of a typical pressurized water reactor 10. In reactor 10, coolant flows thereinto through inlet nozzle 12, downward through annulus 14, upward through core region 16, and then out of reactor 10 through outlet nozzle 18. In the original design of some reactors as described above some of the coolant flows through horizontally positioned coolant flow holes 20 adjacent the upper end of core barrel 22 as best seen in FIG. 2. As indicated by the arrows, this bypass coolant flows downwardly through vertically positioned coolant flow holes 24 in former plates 26 and then upward through core region 16 with the main coolant flow. As seen in FIG. 2, the bypass coolant flows between core barrel 22 and baffle plate 28. The method presented for converting the vertically downward flow of bypass coolant through the core barrel and former plates to a vertically upward flow is best understood by reference to FIGS. 3-5. In FIG. 3, it is seen that one of the steps in making the conversion comprises providing holes 24A in top former plate 26A which are substantially in coaxial alignment with existing holes 24 in the intermediate and lower former plates 26. Another step is plugged horizontal coolant flow holes 20 in core barrel 22 adjacent top former plate 26A. A final step comprises plugging of selected holes in lower former plate 26B. FIG. 4 illustrates a typical expander tool 30 and plug 32 which may be used for the plugging procedure. Expander tool 30 is comprised of roll expander 34, first and second tubes 36, 38, and torque shaft 40. Plug 32 is removably attached to expander tool 30 by means of left handed threads 42. First and second tubes 36, 38 form the body of expander tool 30 which serves to position and hold plug 32 and also to encase torque shaft 40. Torque shaft 40 is attached to roll expander 34 so as to cause expansion of plug 32 in response to rotation of torque shaft 40. The roll expansion process produces a tight joint between plug 32 and lower former plate 26B. Naturally, the tooling is designed for remote operation in plugging the core barrel and former plate and the tooling shown is intended only as an illustration of the type of tooling which should be acceptable for this type of operation. FIG. 5 illustrates a typical octant of lower former plate 26B with the preferred plugging pattern of coolant flow holes 24 being illustrated. Coolant flow holes which remain unplugged according to the preferred pattern are designated by the numeral 24. It is seen that the preferred plugging pattern comprises plugging alternate coolant flow holes. Coolant flow holes which are fully plugged are designated by the numeral 24B. Coolant flow holes which are partially plugged are designated by the numeral 24C. As seen in FIG. 5 a typical octant of lower former plate 26B is provided with ten (10) coolant flow holes 24, four of which are fully plugged and one of which is partially plugged. Every fifth coolant flow hole is partially plugged. Coolant flow hole 24C has forty-four (44) percent of its flow area plugged according to the preferred embodiment. It can then be seen that according to the preferred plugging pattern forty (40) percent of coolant flow holes 24 in lower former plate 26B are fully plugged and ten (10) percent are partially plugged. In operation the conversion method of the present invention is practiced as follows. Top former plate 26A is provided with coolant flow holes 24A substantially in coaxial alignment with existing coolant flow holes 24 in intermediate and lower former plates 26, 26B. Any suitable means such as drilling with remotely operated tools known in the art may be used. Coolant flow holes 20 in core barrel 22 are fully plugged using plugging techniques and equipment known in the art. Selected coolant flow holes 24B in lower former plate 26B are fully plugged while selected coolant flow holes 24C are partially plugged using techniques and equipment known in the art such as expander tool 30 described above. It is preferable to use an expander tool which can accommodate a certain minimum amount of offset between coolant flow holes 26 in adjacent former plates 26 which are not in perfect coaxial alignment. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense. |
description | 1. Field of the Invention The invention is related to the field of metrology, and in particular, to an x-ray analysis system capable of efficient measurements on semiconductor wafers. 2. Related Art As semiconductor devices continue to shrink to enable greater device density in integrated circuits (ICs), accurately and efficiently measuring the characteristics of the structures that form those devices becomes increasingly difficult. In the realm of thin film composition and thickness measurements, x-ray analysis metrology systems (i.e., metrology systems that measure x-ray emissions from a thin film) are becoming increasingly important for ensuring that semiconductor wafers have been properly processed. For example, modern gate dielectrics are typically silicon dioxide (SiO2). A small amount of nitrogen is sometimes added to improve the electrical characteristics of the gate dielectric. By directly measuring nitrogen x-ray emissions from a gate dielectric layer, an x-ray analysis metrology system can determine if the oxidation process is providing the proper nitrogen concentration in a thin (e.g., 20 A or less) gate dielectric. The two main x-ray analysis metrology techniques are electron probe microanalysis (EPMA) and x-ray fluorescence (XRF). EPMA is a metrology technique in which an electron beam (e-beam) is directed at a thin film to cause the thin film to emit x-rays. Those emitted x-rays can then be analyzed to determine the composition and/or thickness of the thin film. In XRF, an x-ray beam is used instead of an e-beam to generate x-ray emissions from the thin film. Both techniques can provide the type of high-precision compositional analysis capabilities required to evaluate modern semiconductor device structures. FIG. 1A shows a conventional EPMA system 100 that includes an e-beam source 110, a stage 140 for supporting a test sample 120, a cylindrical crystal (or multilayer) diffractor 130, and an x-ray detector 150. E-beam source 110 directs an e-beam 111 at an analysis spot 125 on test sample 120, thereby causing test sample 120 to emit output x-rays 121. Note that for clarity, only a portion of output x-rays 121 emitted from test sample 120 are depicted. The actual x-ray emission from test sample 120 in response to e-beam 111 will occur in all directions from analysis spot 125. A portion of those output x-rays 121 are reflected and focused onto x-ray detector 150 by diffractor 130 so that the characteristics (e.g., elemental origin and quantity/ratio) of those output x-rays 121 can be measured. The measurements taken by x-ray detector 150 can then be used to determine the composition and/or thickness of a thin film on test sample 120. Diffractor 130 and x-ray detector 150 form what is sometimes referred to as a wavelength-dispersive x-ray (WDX) detector. Diffractor 130 is tuned to only reflect a particular x-ray wavelength, which allows x-ray detector to precisely measure the level of a particular element (i.e., the element that generates the x-ray wavelength for which diffractor 130 is tuned) within test sample 120. High performance XRF systems also sometimes incorporate WDX detectors to provide high-precision measurement capabilities. An XRF system incorporating a WDX detector would operate in substantially the same manner as described above with respect to EPMA system 100, except that e-beam source 110 would be replaced with an x-ray generator for directing a focused x-ray beam (rather than e-beam 111) at analysis spot 125. Collection and measurement of the resulting output x-rays 121 would be performed by diffractor 130 and x-ray detector 150 in the same manner as described above with respect to EPMA system 100. The speed at which measurements can be taken by EPMA system 100 (or a comparable XRF system) is dependent on the x-ray flux at x-ray detector. Therefore, the larger the amount of x-ray emission that can be reflected and focused by diffractor 130 (onto x-ray detector 150), the more quickly EPMA system 100 can complete a measurement on test sample 120. Unfortunately, diffractor 130 is not well suited for intercepting a large portion of the total x-ray emission from test sample 120. Diffractor 130 is formed from multiple layers of parallel crystal planes. Incoming x-rays that exhibit incident angles that are very near the Bragg angle are partially diffracted by the multiple crystal planes. X-rays having wavelengths that are integer multiples of the distance between the crystal planes experience constructive interference at diffractor 130, and therefore provide a strong response at x-ray detector 150. Diffractor 130 can only reflect x-rays that exhibit incident angles with the diffractor that are very near the Bragg angle (the Bragg angle is determined by the x-ray energy and the spacing between crystal planes in the diffractor). Therefore, diffractor 130 can only span a very small arc of the Rowland circle before it can no longer reflect the desired x-ray wavelengths. As a result, the x-ray flux at x-ray detector 150 is relatively low, and metrology operations using EPMA system 100 (and similar XRF systems) can be very time consuming. This throughput problem is exacerbated for thin films that generate relatively low concentrations of the x-ray wavelength of interest (e.g., the low-concentration nitrogen x-rays emitted from a thin gate dielectric layer). The time consuming nature of conventional x-ray metrology tools has mandated that such tools be used as “off-line” tools in production environments. For example, FIG. 1B shows an exemplary flow diagram for a conventional EPMA tool in a production environment. In a “PERFORM FIRST PROCESS” step 181, a batch (e.g., a cassette) of wafers is processed (e.g., gate oxides are formed on the wafers). A monitor wafer is then selected from the processed batch in a “SELECT MONITOR WAFER” step 182 to begin the metrology operation. An e-beam (111) is then directed at the wafer in a “DIRECT E-BEAM AT MONITOR WAFER” step 183, and the resulting x-rays (121) are focused by a diffractor (130) at an x-ray detector (150) in a “FOCUS X-RAYS W/DIFFRACTOR” step 184. The focused x-rays (131) are then measured by the x-ray detector (150) in a “MEASURE FOCUSED X-RAYS” step 185, and the desired characteristics of the test sample are then determined in a “DETERMINE MONITOR WAFER PROPERTIES” step 186. If additional monitor wafers from the batch of processed wafers are to be evaluated, the process then loops back to step 182. The results of the EPMA measurement(s) on the monitor wafer(s) can then be used to determine if the first process is performing within specification in a “QUALIFY FIRST PROCESS” step 187. Note that because the EPMA operation(s) of steps 182 through 187 is relatively time consuming (for the reasons described above with respect to FIG. 1A), processing of the batch of wafers from which the monitor wafer(s) being examined in steps 182 through 187 has been selected continues in parallel with that analysis in a “PERFORM SECOND PROCESS” step 190. Therefore, the EPMA analysis performed in steps 182 through 187 is described as an “offline analysis”. Unfortunately, offline analysis is generally an undesirable technique, because by the time a problem is discovered by the offline analysis, significant additional (costly) processing may have been performed on the problematic batch of wafers. Furthermore, the additional processing can make subsequent tracing of the root cause of the problem impossible. Accordingly, it is desirable to provide a system and method for efficiently performing x-ray analysis metrology. Conventional wavelength-dispersive x-ray (WDX) detectors for electron probe microanalysis (EPMA) and x-ray fluorescence (XRF) tools incorporate a diffractor for focusing output x-rays onto a x-ray detector. Due to the limited curvature range providing effective Bragg reflection in those diffractors, EPMA and XRF tools are limited to use as offline analysis tools. By incorporating a graded multilayer diffractor into a WDX detector for an EPMA or XRF system, a significantly larger portion of output x-rays can be focused onto the x-ray detector, thereby allowing the EPMA or XRF measurement, respectively, to be made much more quickly than with conventional tools. This increased measurement speed can allow such EPMA or XRF systems to be integrated into the wafer production process (i.e., the EPMA or XRF tool can be used to perform in-line monitoring of production wafers). Therefore, an x-ray analysis metrology system for analyzing a test sample can include a probe beam source, a graded multilayer diffractor, and an x-ray detector. The probe beam source can direct a probe beam (e.g. an e-beam or an x-ray beam) onto the test sample. The graded multilayer diffractor can advantageously focus the output x-rays from the test sample. The x-ray detector can capture those focused output x-rays. In one embodiment, the x-ray analysis metrology system can include a set of graded multilayer diffractors and a set of x-ray detectors, thereby allowing simultaneous measurement of different elements within the test sample. For example, a first graded multilayer diffractor and a first x-ray detector could be configured to measure oxygen x-rays, whereas a second graded multilayer diffractor and a second x-ray detector could be configured to measure nitrogen x-rays. Note that the graded multilayer diffractor can be symmetrical, asymmetrical, cylindrical, spherical, paraboloidal, toroidal, or ellipsoidal in shape. A method for processing a set of wafers can include performing a first process on the set of wafers to create a processed set of wafers. An inline analysis can then be performed on at least one wafer of the processed set of wafers. This inline analysis can be performed by focusing output x-rays from the wafer onto an x-ray detector using a graded multilayer diffractor. Advantageously, a second manufacturing process can be performed on the processed set of wafers after performing the inline analysis. In one embodiment, performing the inline analysis can include focusing different sets of output x-rays with different wavelengths using a set of graded multilayer diffractors. In this embodiment, each graded multilayer diffractor can be configured to measure a predetermined element x-ray. The invention will be more fully understood in view of the following description and drawings. Conventional wavelength-dispersive x-ray (WDX) detectors for electron probe microanalysis (EPMA) and x-ray fluorescence (XRF) tools incorporate a cylindrical crystal diffractor for focusing output x-rays onto a x-ray detector. Due to the limited curvature range providing effective Bragg reflection in those crystal diffractors, EPMA and XRF tools are limited to use as offline analysis tools. By incorporating a graded multilayer diffractor into a WDX detector for an EPMA or XRF system, a significantly larger portion of output x-rays can be focused onto the x-ray detector, thereby allowing the EPMA or XRF measurement, respectively, to be made much more quickly than with conventional tools. This increased measurement speed can allow such EPMA or XRF systems to be integrated into the wafer production process (i.e., the EPMA or XRF tool can be used to perform in-line monitoring of production wafers). FIG. 2A shows an embodiment of an x-ray analysis metrology system 200 that incorporates a graded multilayer diffractor 230 to improve measurement efficiency. Metrology system 200 includes a probe beam source 210, a graded multilayer diffractor 230, a stage 240, and an x-ray detector 250. Stage 240 supports and positions a test sample 220 that includes a thin film or other semiconductor structure to be measured by x-ray analysis metrology system 200. During a measurement operation, probe beam source 210 directs a probe beam 211 at an analysis spot 225 on test sample 200. In one embodiment, metrology system 200 could be an EPMA system, in which case probe beam 211 would be an e-beam generated by an e-beam source 210. In another embodiment, metrology system 200 could be an XRF system, in which case probe beam 211 would be an x-ray beam generated by x-ray beam source 210. In either case, probe beam 211 causes test sample 220 to emit output x-rays 221 from analysis spot 225. A portion of those output x-rays 221 are then reflected and focused by graded multilayer diffractor 230 onto x-ray detector 250. Note that while test sample 220 will generally emit output x-rays 221 in all directions from analysis spot 225, only those output x-rays 221 that are intercepted and reflected by graded multilayer diffractor 230 are depicted for clarity. Like diffractor 130 shown in FIG. 1A, graded multilayer diffractor 230 is designed to diffract and focus only a small range of x-ray wavelengths. Therefore, graded multilayer diffractor 230 and x-ray detector 250 form a WDX detector that can measure a particular element in test sample 220. Note that in various embodiments, metrology system 200 can include any number of graded multilayer diffractors 230 (indicated by the dotted outline of graded multilayer diffractor 230(n)) and any number of corresponding x-ray detectors (indicated by the dotted outline of x-ray detector 250(n)), thereby allowing metrology system 200 to include multiple WDX detectors for simultaneous measurement of different elements within test sample 220. For example, graded multilayer diffractor 230 and x-ray detector 250 could be configured to measure oxygen x-rays, while graded multilayer diffractor 230(n) and x-ray detector 250(n) could be configured to measure nitrogen x-rays (e.g., to allow metrology system to evaluate nitrogen-doped gate oxides). Unlike cylindrical crystal diffractor 130, which is formed from parallel crystal planes, graded multilayer diffractor 230 includes layers of varying thickness that allow Bragg reflections to be generated across a much larger diffractor area than would be possible with a conventional crystal diffractor. Graded multilayer diffractors, such as the Max-Flux™ optics produced by Osmic Inc., have seen limited use in the realm of optical x-ray metrology (i.e., systems where x-ray reflections from a test sample are measured to determine material characteristics, such as x-ray diffraction (XRD) and x-ray reflectometry (XRR)) for monochromatization of x-rays incident on the test sample. However, in the realm of x-ray analysis metrology systems, graded multilayer diffractors have never been used. A graded multi-layer diffractor (such as diffractor 230) is formed from a series of alternating layers of high Z (high reflectivity) and low Z (low reflectivity) materials. The materials are selected and sized such that only raw x-rays 221 of a particular wavelength (energy) are reflected. X-rays incident on a surface of one of the high Z layers are partially reflected and partially transmitted. Bragg's law of reflection states an incident set of x-rays is reflected with maximum intensity if the Bragg condition is fulfilled, as indicated by the following:n*λ=2*d*sin(θ) [Eqn. 1]where n is the order of the reflection, λ is the wavelength of the incoming x-rays, d is the distance between reflecting surfaces (i.e., the thickness of a high Z/low Z layer pair, sometimes referred to as the period of the multilayer structure), and θ is the angle of incidence between the incoming x-ray beams and the reflecting surface. When the Bragg condition is satisfied, the distance an x-ray travels before being reflected is a multiple of one half its wavelength, so that reflected x-rays are all in phase, and therefore produce a strong reflected x-ray flux. As noted above, diffractors (e.g., diffractor 130 in FIG. 1) used in conventional x-ray analysis metrology systems are essentially “parallel layer” structures, in which the parallel crystal layers forming the diffractor act as reflecting surfaces for incoming x-rays. Because those crystalline layers are all parallel, a crystal diffractor is only effective across a relatively small range of incident x-ray angles. Therefore, a crystalline diffractor can only exhibit a small amount of curvature before the Bragg condition is no longer satisfied for incoming x-rays, which results in those x-rays not being reflected. This size limitation is exacerbated by the non-parallel nature of the output x-rays generated from a test sample in response to a probe beam (e.g., output x-rays 121 in FIG. 1A and output x-rays 221 in FIG. 2A all effectively originate and diverge from a point source (i.e., analysis spots 125 and 225, respectively)). Consequently, only a small percentage of raw x-rays 121 can be intercepted by cylindrical crystal diffractor 139, resulting in a relatively low x-ray flux at x-ray detector 150 in conventional EPMA system 100, and hence, a relatively slow measurement speed. In contrast, the layers in diffractor 230 are “graded”, i.e., the thicknesses of the high Z and low Z layers vary across the diffractor to change the distance d between reflecting surfaces across diffractor 230. This layer grading enables efficient reflection of output x-rays 221 that are incident on diffractor 230 across a wide range of incident angles. Therefore, graded multilayer diffractor 230 compensates for the incident angle variation between output x-rays 221 and diffractor 230. The multiple layers making up diffractor 230 are configured such that by properly orienting diffractor 230, x-rays emanating from a particular location (in this case, analysis spot 225 on test sample 220) all satisfy the Bragg condition at diffractor 230. In this manner, the graded multilayer construction of diffractor 230 allows a large portion of output x-rays 221 to be intercepted and focused onto x-ray detector 250, thereby providing a high flux set of focused x-rays 231 that enable high throughput EPMA or XRF metrology. Note that the actual shape of graded multilayer diffractor 230 can comprise any type of focusing arrangement. In various embodiments, diffractor 230 can comprise a single diffractor surface (“singly curved”), and in various other embodiments, diffractor 230 can comprises multiple diffractor surfaces (“doubly curved”). In various embodiments, graded multilayer diffractor 230 can comprise a symmetrical shape to reduce manufacturing complexity. In various other embodiments, graded multilayer diffractor 230 can comprise an asymmetrical shape to enable alternative positionings relative to test sample 220. In one embodiment, graded multilayer diffractor 230 can comprise a cylindrical or spherical diffractor. However, in another embodiment, graded multilayer diffractor 230 can comprise a paraboloidal, toroidal, or ellipsoidal diffractor to provide improved focusing capabilities. Typically, an ellipsoidal diffractor will provide the best focusing capabilities. The use of an ellipsoidal diffractor allows either magnification or demagnification to be performed on output x-rays 221, so that measurement spot 255 at x-ray detector 250 can be either larger or smaller than analysis spot 225 on test sample 220. This focusing/defocusing capability can provide flexibility when selecting the sensor system for x-ray detector 250. In any case, graded multilayer diffractor 230 improves output x-ray collection, thereby significantly improving the throughput capabilities of metrology system 200 over conventional EPMA or XRF tools. As a result, metrology system 200 allows EPMA or XRF to be used as an inline analysis technique (even for difficult gate dielectric nitrogen and oxygen measurements), thereby eliminating the above-described problems associated with offline analysis, while still providing the high precision measurements associated with WDX detectors. FIG. 2B shows a flow diagram of an inline analysis operation that can be performed using metrology system 200 (described above with respect to FIG. 2A). A batch of wafers is processed using a first process in a “PERFORM FIRST PROCESS” step 281. One of the processed wafers is then selected in a “SELECT PRODUCTION WAFER” step 282, and a probe beam (e.g., probe beam 211 in FIG. 2A) is directed at the wafer (e.g., test sample 220 in FIG. 2A) in a “DIRECT PROBE BEAM AT PRODUCTION WAFER” step 282. For EPMA, the probe beam would be an e-beam, and for XRF, the probe beam would be an x-ray beam. In either case, the resulting output x-rays (e.g., output x-rays 221 in FIG. 2A) emitted by the wafer are reflected onto an x-ray detector (e.g., x-ray detector 250 in FIG. 2A) by a graded multilayer diffractor (e.g., graded multilayer diffractor 230 in FIG. 2A) in a “FOCUS X-RAYS W/GRADED MULTILAYER DIFFRACTOR” step 284. The x-rays are then measured by the x-ray detector in a “MEASURE FOCUSED X-RAYS” step 285 to determine the desired properties of the wafer in a “DETERMINE PRODUCTION WAFER PROPERTIES” step 286. Note that different sets of output x-rays with different wavelengths may be focused and measured by multiple sets of graded multilayer diffractors and x-ray detectors (e.g., graded multilayer diffractor 230(n) and x-ray detector 250(n) in FIG. 2A) during steps 284-286. After step 286, if analysis of multiple wafers is desired, the process can loop back to step 282. Otherwise, the results of the analysis can be used to determine whether the processed wafers meet the specified requirements in a “QUALIFY FIRST PROCESS” step 287. If the results of step 287 are satisfactory, next manufacturing process step can be performed in a “PERFORM SECOND PROCESS” step 290. By performing the EPMA or XRF analysis between the first and second manufacturing process steps (i.e., between steps 281 and 290), the wastage and troubleshooting issues associated with conventional offline techniques can be avoided. Meanwhile, the high measurement speed enabled by the use of graded multilayer diffractor 230 in metrology system 200 minimizes any throughput degradation on the overall manufacturing process. In this manner, the use of graded multilayer diffractor 230 beneficially allows inline analysis to be performed using EPMA and XRF tools. Although the invention has been described in connection with several embodiments, it is understood that the invention is not limited to the embodiments disclosed, but is capable of various modifications that would be apparent to one of ordinary skill in the art. Thus, the invention is limited only by the following claims and their equivalents. |
|
abstract | Disclosed herein is an aerosol generating and mixing system operating at a high temperature and a high pressure which includes an aerosol generating device; and an aerosol mixing device, wherein the aerosol generating device includes a pre-mixing tank and a mixing tank, and the mixing tank and the pre-mixing tank include a wing configured to rotate about a central shaft of the tank so as to agitate an inside aerosol, and an agitating motor configured to rotate the wing, and a filling nozzle of the mixing tank and the pre-mixing tank is configured to inject any of an aerosol aqueous solution and an aerosol particle. |
|
abstract | Heat exchangers for use in heavy liquid metal coolant mediums that ensure reliable fixation and spacing of heat exchanger tubes. A first embodiment includes one supporting spacer grid having a cylindrical shell and two or more tiers of plates spaced apart at a preset gap, while the width of each plate is parallel to the shell axis. Ends of all plates are fixed to the shell such that plates of any tier are parallel to each other and located at the preset gap. Plates of different tiers are criss-crossed at an angle of 60 degrees along the shell axles and fastened together at the crossing points. Another embodiment includes three dividers which run through the cylinder axis; their ends are connected to the shell and are spaced at an angle of 60 degrees. |
|
summary | ||
claims | 1. A tool that is structured to be received into an interior region of a core shroud of a boiling water reactor and that is structured to carry a device thereon into the interior region, the tool comprising:a frame, the frame being elongated along an axis of elongation and having a receptacle formed therein that is elongated along the axis of elongation;an elevator apparatus situated on the frame;a manipulator apparatus situated on the elevator apparatus, at least a portion of the manipulator apparatus being situated in the receptacle;a reciprocation apparatus comprising a support that is elongated and that is situated on the manipulator apparatus, the reciprocation apparatus further comprising a mount that is situated on the support and that is structured to carry the device;the elevator apparatus being operable to move the manipulator apparatus between a first position and a second position along the longitudinal extent of the frame;the manipulator apparatus being operable to move the reciprocation apparatus between a first position wherein the support is disposed at least in part in the receptacle and a second position wherein the support and the mount are removed from the receptacle; anda foot apparatus situated on the frame and comprising a number of feet and a pivot mechanism, the number of feet being situated at an end of the frame and being structured to be received on at least one of a fuel support, a control rod guide tube, and a core plate of the boiling water reactor, the pivot mechanism being structured to pivot the frame about the axis of elongation with respect to the number of feet when the number of feet are received on the at least one of the fuel support, the control rod guide tube, and the core plate. 2. The tool of claim 1 wherein the frame includes a head that is situated at another end of the frame and that is elongated along the axis of elongation, the head being of a circular profile in a plane transverse to the axis of elongation. 3. The tool of claim 2 wherein the head has formed therein an access port that is structured to receive therein another device. 4. The tool of claim 1 wherein the manipulator apparatus comprises an extension apparatus situated on the elevator apparatus and a rotation apparatus situated on the extension apparatus, the extension apparatus being operable to move the reciprocation apparatus between the first position and second positions, the rotation apparatus being operable to rotate the support with respect to the extension apparatus. 5. The tool of claim 4 wherein the extension apparatus comprises a four bar linkage, and wherein the rotation apparatus is situated on a bar of the four bar linkage. 6. The tool of claim 5 wherein the rotation apparatus comprises a pair of actuators extending between the bar and the support, each actuator of the pair of actuators comprising:a stationary portion;an effector that telescopes with respect to the stationary portion along a telescoping direction; andone of the stationary portion and the effector being situated on the bar, the other of the stationary portion and the effector being connected with the support. 7. The tool of claim 6 wherein the telescoping direction of each actuator of the pair of actuators is oriented substantially parallel with the telescoping direction of the other actuator of the pair of actuators. 8. The tool of claim 7 wherein the support comprises a crank, the other of the stationary portion and the effector of each actuator of the pair of actuators being operatively connected with the crank, the crank being situated between the effectors. 9. The tool of claim 7 wherein the stationary portions are situated side-by-side. 10. The tool of claim 4 wherein the support is elongated along an arcuate path that is of a fixed radius. 11. The tool of claim 4 wherein the manipulator apparatus is mountable on the elevator apparatus in either of a pair of configurations:in a first configuration of the pair of configurations, the extension apparatus in the first position extends from the elevator apparatus in a direction generally toward the foot apparatus; andin a second configuration of the pair of configurations, the extension apparatus in the first position extends from the elevator apparatus in a direction generally away from the foot apparatus. 12. The tool of claim 1 wherein the frame has at least one of a number of chamfers and a number of radii that are formed on an exterior surface thereof and that extend along the axis of elongation. |
|
abstract | A shielding device (20) for optical and/or electronic apparatuses (16) is described, wherein said apparatuses may cooperate with incident electromagnetic radiation (X1, X2), in particular for space telescopes, the shielding device including: at least a filter (24, 26) provided for interacting with said incident electromagnetic radiation (X1, X2), for selectively filtering said radiation; and a support structure (22) for the filter. |
|
claims | 1. A neutron detection apparatus configured to detect a neutron flux distribution inside of a pressurized water reactor, the neutron detection apparatus comprising:a neutron detector configured to detect the neutron flux distribution inside of the reactor;a thimble guide tube configured to be inserted into the reactor from the outside of the reactor, for inserting the neutron detector inside of the reactor;a drive apparatus which is connected to the thimble guide tube and which inserts the neutron detector into the thimble guide tube or extracts the neutron detector out of the thimble guide tube;a vacuum unit which controls a vacuum state in the thimble guide tube;a supply unit which supplies carbon dioxide gas;a gas purge unit which is connected to the supply unit and conducts gas purge in the thimble guide tube via the flow of carbon dioxide gas into the thimble guide tube;a gate valve which is provided between the thimble guide tube and the drive apparatus and opens or closes to allow or prevent communication between the thimble guide tube and the drive apparatus; anda control apparatus which controls the gate valve, the drive apparatus, the vacuum unit, the supply unit, and the gas purge unit, so that when the gate valve is closed, first flow of carbon dioxide gas flows inside the thimble guide tube, and when the gate valve is opened, a second flow of carbon dioxide gas, smaller than the first flow, flows inside the thimble guide tube. 2. The neutron detection apparatus according to claim 1, whereinthe control apparatus is configured to close the gate valve and control the vacuum unit to make the inside of the thimble guide tube have a vacuum atmosphere. 3. The neutron detection apparatus according to claim 2, whereinthe control apparatus is configured to, after controlling the vacuum unit to make the inside of the thimble guide tube have a vacuum atmosphere, adjust carbon dioxide gas flowing from the gas purge unit to perform gas purge in the thimble guide tube. 4. The neutron detection apparatus according to claim 3, further comprising an exhaust pipe configured to discharge gas from the inside of the drive apparatus, whereinthe control apparatus is configured to, after the gas purge in the thimble guide tube, open the gate valve, and adjust carbon dioxide gas flowing from the gas purge unit to perform gas purge in the thimble guide tube and in the drive apparatus, andthe exhaust pipe discharges carbon dioxide gas to outside of the drive apparatus. 5. The neutron detection apparatus according to claim 2, whereinthe control apparatus is configured to open the gate valve and insert the neutron detector into the thimble guide tube via the drive apparatus. 6. The neutron detection apparatus according to claim 2, whereinthe control apparatus is configured to open the gate valve and insert the neutron detector into the thimble guide tube via the drive apparatus. 7. The neutron detection apparatus according to claim 4, whereinthe control apparatus is configured to, after the gas purge in the thimble guide tube and in the drive apparatus, insert the neutron detector into the thimble guide tube via the drive apparatus. 8. The neutron detection apparatus according to claim 1, wherein the position of the gate valve is configured to be higher than a top portion of the reactor. |
|
047327057 | abstract | Before or during their solidification in a matrix, the radioactive ion exchange resin particles, which can be anion and/or cation resins, treated with an additive, which has inorganic or organic anions or cations or organically anion active or cation active components and is chosen in such a manner that the treatment has the effect to reduce the swelling behavior of the resin particles and preferably produces a permanent shrinkage of the resin particles. This change of the resin particles can also be attained or supported by a thermal treatment.. A matrix contains ion exchange resin particles which are treated in such a manner shows an improved water resistance which, contrary to the current state of the art, will also remain assured when the matrix is dried and then again stored in water. In addition, it is possible to accommodate a larger amount of treated resin particles in a volume, as compared to untreated resin particles. In this manner, the disposal and final storage of radioactive ion exchange resins is also made easier. |
abstract | In order to provide an aperture position adjusting mechanism in an X-ray CT system with low cost and high accuracy to enable stable reconstruction of X-ray tomographic images, a first shaft (23) is provided with a bore (23a) at a position offset from a center axis, and is rotatably supported by a base plate (20) orthogonally to a pair of rails (21a, 21b). A second shaft (25) is received and is rotatably supported within the bore (23a) through the first shaft (23). The aperture (6) is moved along the rails (21a, 21b) as the second shaft (25) is eccentrically rotated by a motor (7) and, following the eccentric rotation and in a direction opposite to that of the rotation, the first shaft (23) is eccentrically rotated around the center axis of the bore (23a). |
|
abstract | Methods and apparatus are provided for producing and extracting Mo-99 and other radioisotopes from fission products that overcome the drawbacks of previously-known systems, especially the excessive generation of radioactive wastes, by providing gas-phase extraction of fission product radioisotopes from a nuclear fuel target using a mixture including halide and an oxygen-containing species with heat to convert the fission product radioisotopes to gas (e.g., Mo-99 to MoO2Cl2 gas). The gaseous species are evacuated to a recovery chamber where the radioisotopes solidify for subsequent processing, while the substantially intact uranium target made available for further irradiation and extraction cycles. |
|
description | This invention was made with government support under Contract Number DE-AC07-05ID14517 awarded by the United States Department of Energy. The government has certain rights in the invention. This application is related to U.S. patent application Ser. No. 12/901,309 to Gamier et al., entitled “METHODS OF PRODUCING SILICON CARBIDE FIBERS, SILICON CARBIDE FIBERS, AND ARTICLES INCLUDING SAME,” assigned to the Assignee of the present application and filed on even date herewith, the disclosure of which is incorporated by reference herein in its entirety. The invention, in various embodiments, relates generally to cladding material for use in nuclear reactors, tubes formed from such cladding material, and to methods of forming such tubes. More particularly, embodiments of the invention relate to tubes including an inner metallic material surrounded by fiber reinforced ceramic matrix composite and, optionally, an outer metallic material, that may be used as a fuel containment barrier. Nuclear reactor fuel designs, such as pressurized water reactor and boiling water reactor fuel designs, impose significantly increased demands nuclear fuel cladding tubes. Such components are conventionally fabricated from the zirconium-based metal alloys, such as zircaloy-2 and zircaloy-4. Increased demands on such components are in the form of longer required residence times, thinner structural members and increased power output per area, which cause corrosion. Resistance to radiation damage, such as dimensional change and metal embrittlement, is one of the most important considerations in selecting cladding materials for a fuel cladding tube. Zirconium alloys are currently used as the primary cladding material for nuclear fuel in nuclear power plants because of their low capture cross-section for thermal neutrons and good mechanical and corrosion resistance properties, high thermal conductivity and high melting point. While zirconium and other metal alloys have excellent corrosion resistance and mechanical strength in a nuclear reactor environment under normal and accident conditions where the heat fluxes are relatively low, they encounter mechanical stability problems during conditions such as a departure from nucleate boiling (“DNB”) incident that might occur during accidental conditions. Any action tending to increase the heat flux of the core in order to raise the plant output will aggravate these problems. A significant in-reactor life limiting use with currently available fuel cladding tubes formed from zirconium-based alloys is corrosion, especially in the presence of water and increased operating temperatures of newer generations of nuclear reactors, such as light water reactors (LWRs) and supercritical water cooled reactors (SCWRs). For example, buildup of oxide material on the fuel cladding tubes caused by oxidation of zirconium during reactor operation may lead to adverse effects on thermal conduction. Hydrogen generated by oxidation of the zirconium in the fuel cladding tubes causes embrittlement of the zirconium and formation of precipitates in the fuel cladding tube which is under an internal gas pressure. The presence of the precipitates may reduce mechanical strength of the fuel cladding tube causing cracks in walls and end caps. Fuel cladding tubes formed from zirconium and zirconium alloys are also susceptible to stress corrosion cracking during operation due to joint action of fission precuts and mechanical stress resulting from radiation-induced swelling of fuels. The interaction between the fuel and the cladding results in nucleation and propagation of cracks and depressurization of the fuel cladding tube. Such cracks propagate from an internal surface of the fuel cladding tube to an external surface and, thus, may rupture the cladding wall. Depressurization of the fuel cladding tube due to stress corrosion cracking significantly reduces the life of the fuel cladding tube and, in addition, reduces the output and safety of the nuclear reactor. Moreover, the fuel cladding tube may be circumferentially loaded in tension due to expansion of the contents, such as fuel pellets, within the fuel cladding tube. Deformation of the fuel cladding tube resulting from such tension increases susceptibility of the fuel cladding tube to stress corrosion failure. Silicon carbide has also been used to form fuel cladding tubes for use in nuclear reactors. The silicon carbide fuel cladding tubes are porous structures that are difficult to achieve reliable hermetic sealed around the nuclear fuel. Thus, ceramic material debris dislodged from the silicon carbide fuel cladding tubes during use may reside between the fuel and the ceramic cladding and may be a source of local stress concentration during normal fuel swelling. The release of such ceramic material debris causes localized thermal and mechanical damage in the silicon carbide fuel cladding tubes, eventually causing failure thereof. Given the resurgence of nuclear energy development worldwide there is a significant need today for both safety and economical performance enhancements to power plant or other reactor operations. Improved fuel cladding tubes that reduce operation costs and increase safety during reactor accidents are desirable. In one embodiment, the present disclosure includes a cladding material. The cladding material may include a metallic material comprising at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof and a ceramic matrix composite overlying the metallic material and comprising reinforcing fibers within a silicon carbide matrix. For example, the metallic material may comprises zircaloy-4. In another embodiment, the present disclosure includes a tube having an inner metal liner and a ceramic matrix composite disposed over the inner liner. The inner liner may include at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof. The ceramic matrix composite may include reinforcing fibers within a silicon carbide matrix. The reinforcing fibers may include at least one of silicon carbide, carbon and fibers thereof. The inner liner may include exposed distal ends protruding from the ceramic matrix composite, the exposed distal ends having an increased thickness. The tube may additionally include an outer liner formed from at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof. The outer liner may be interconnected with the inner liner through voids or pores in the ceramic matrix composite. In another embodiment of the present disclosure includes a method forming a tube that includes forming an inner metallic liner and forming a ceramic matrix composite over the inner metallic liner, the ceramic matrix composite comprising reinforcing fibers within a silicon carbide matrix. The inner metallic liner may be formed from at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof. The ceramic matrix composite may be formed over the inner metallic liner by forming a preform comprising the reinforcing fibers over the inner metallic liner, infiltrating the preform with a pre-ceramic polymer material and heating the pre-ceramic polymer material to a first temperature to form the ceramic matrix composite. The inner metallic liner may be fused to the outer ceramic matrix through a plurality of pores formed by the weave of the fibers. Yet another embodiment of the present disclosure includes a method forming a multi-layered tube that includes forming an elongated cylinder surrounding a hollow compartment from a ceramic matrix composite, the ceramic matrix composite comprising a reinforcing fiber within a silicon carbide matrix and forming a metallic material over surfaces of the ceramic matrix composite. Embodiments of the present disclosure related to a cladding material that may be used in a containment vessel, such as a fuel tube, for nuclear fuel (i.e., fissile material), used in a nuclear power plant or other reactor or used in an industrial process. The cladding material may have a multi-layered structure including a metallic material that includes a zirconium alloy and a ceramic matrix composite (CMC) layer that includes continuous silicon carbide fibers and a matrix comprising a silicon carbide ceramic. The cladding material may be used to form a multi-layered tube that includes the metallic material as an inner liner and the ceramic matrix composite as an outer support. The multi-layered tube may be used, for example, as a fuel cladding tube for a nuclear reactor, a chemical processing heat exchanger, a steam generator, a gas phase cooling system, a radiator or a combustion chamber liner. The multi-layered tube may further include an outer metallic liner that may, optionally, be fused with the inner liner to encapsulate the ceramic matrix composite. The metallic material at the ends of the fuel tube may have a greater thickness to provide area for end cap welding of the fuel tube. The cladding material of the present disclosure provides a combination of thermal and mechanical features as a result of the combination of metallic and ceramic layers. Specifically, the metallic material provides hermetic sealing and containment of gases and fuel within a chamber of the fuel cladding tube and enables end cap sealing. The ceramic matrix composite layer imparts additional mechanical strength, stiffness, thermal shock resistance and high temperature load carrying capability to the fuel cladding tube. Thus, the presently disclosed fuel tube increases the lifetime and significantly increases safety margins as compared to conventional fuel tubes. As used herein, the terms “comprising,” “including,” “containing,” “characterized by,” and grammatical equivalents thereof are inclusive or open-ended terms that do not exclude additional, unrecited elements or method steps, but also include the more restrictive terms “consisting of” and “consisting essentially of” and grammatical equivalents thereof. As used herein, the term “may” with respect to a material, structure, feature or method act indicates that such is contemplated for use in implementation of an embodiment of the invention and such term is used in preference to the more restrictive term “is” so as to avoid any implication that other, compatible materials, structures, features and methods usable in combination therewith should or must be, excluded. As used herein, the term “ductile” means and includes materials, such as a metal or metal alloy, with sufficient strength under tension that may be stretched or elongated before fracturing. As used herein, the term “axial” means and includes a direction substantially parallel to a defined axis of, for example, the fuel cladding tube. As used herein, the term “radial” means and includes a direction substantially perpendicular to the central axis of, for example, the fuel cladding tube. As used herein, the term “axial force” means and includes a force exerted in a direction substantially parallel to the defined axis, while the term “radial force,” as used herein, means and includes a force exerted in a direction in a plane substantially perpendicular to the defined axis. Neither term is limited to forces exerted in directions that intersect the defined axis. As used herein, the term “thermal expansion” means and includes dimensional changes of a solid material in response to an internal temperature increase. The terms “coefficient of thermal expansion” and “CTE,” as used herein, mean and include a parameter characterizing a change in dimension of a material relative to a change in temperature. As used herein, the term “thermal expansion material” means and includes a material that expands in response to a temperature change. As used herein, the term “hermetic” means and includes preventing undesirable ingress or egress of chemicals into or out of the multi-layered tube over the useful life of the device using a seal that is essentially impermeable to chemicals. As used herein, the term “off-normal event” means and includes any event that may cause mechanical damage to a conventional fuel rod, devices or structures, or thermal mechanical damage caused by external fuel rod coolant loss during operation. As used herein, the terms “seeding” and “seeded” mean and include introduction of one or more crystals or particles of a material as a seed or nucleus for crystallization. Referring to FIG. 1A, a cladding material 100 may be formed that includes a metallic material 102 and a ceramic matrix composite 104. The metallic material 102 may be formed from a monolithic material that comprises one single, unbroken unit without joints or seams and may be formed from a ductile metal or metal alloy. For example, the metallic material 102 may be formed from at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof. As a non-limiting example, the metallic material 102 may be formed from a zirconium alloy, such as zircaloy-2, zircaloy-4, and other low tin zirconium-tin alloys. Zircaloy-4 includes about 98.23 wt % zirconium, about 1.45 wt % tin, about 0.21 wt % iron, about 0.1 wt % chromium, and about 0.01 wt % hafnium. Zircaloy-2 includes about 98.25 wt % zirconium, between about 1.2 wt % and about 1.7 wt % tin, between about 0.5 wt % and about 0.15 wt % chromium, between about 0.07 wt % and about 0.135 wt % iron, between about 0.03 and about 0.08 wt % nickel and 0.01 wt % hafnium. A thickness d1 of the metallic material 102 may be less than or equal to between about 0.05 mm and about 1 mm, and more particularly 0.25 mm. The ceramic matrix composite 104 may have a thickness d2 of between about 0.25 mm and about 2.5 mm, and more particularly, about 1.27 mm. The ceramic matrix composite 104 may comprise a ceramic matrix interspersed with reinforcing fibers. As a non-limiting example, the ceramic matrix composite 104 may comprise a silicon carbide reinforced composite, examples of which are known in the art. The ceramic matrix may include, for example, a silicon carbide material, such as an amorphous or nano-crystalline beta silicon carbide material or an alpha silicon carbide material. The ceramic matrix may optionally include a metal particulate, such as zirconium, dispersed in the silicon carbide material. Other metal particulate having a high melting point and compatibility with silicon carbide, such as titanium, niobium, vanadium, hafnium, molybdenum and tantalum, may be also be used. Addition of the metal particulate to the ceramic matrix substantially increases the coefficient of thermal expansion (CTE) of the ceramic matrix composite 104 to be closer with that of the metallic material 102. For example, the ceramic matrix composite may have a CTE of about 3.4.times.10.sup.−6 and the zirconium metal may have a CTE of about 6.times.10.sup.−6. Adding the metal particulate to the ceramic matrix composite may, therefore, increase the CTE to between about 4.5.times.10.sup.−6 to about 5.times.10.sup.−6 metal. In addition, addition of the metal particulate to the ceramic matrix composite may impart oxidation resistance. Accordingly, addition of the transition metal to the ceramic matrix enables a thickness of the metallic material 102 to be increased. The reinforcing fibers may be formed from alpha or beta carbon, alpha or beta silicon carbide, silicon nitride, boron carbide and basalt. As a non-limiting example, the reinforcing fibers may include NICALON®. Type S beta ceramic fiber, which is commercially available from Nippon Carbon Company (Tokyo, Japan), Tyranno beta ceramic fiber from UBE Industries (Tokyo, Japan) or alpha silicon carbide fibers formed using methods described in, for example, in the aforementioned U.S. patent application Ser. No. 12/901,309, filed on even date herewith. As an example, the ceramic matrix composite 104 may include reinforcing fibers formed from alpha silicon carbide disposed in a matrix formed from alpha silicon carbide. As another non-limiting example, the ceramic matrix composite 104 may include reinforcing fibers formed from beta silicon carbide disposed in a matrix formed from beta silicon carbide. In some embodiments, the metallic material 102 may be disposed over or in contact including through the wall with the ceramic matrix composite 104 without the metallic material 102 and the ceramic matrix composite 104 being physically bonded to one another. In other embodiments, the metallic material 102 and the ceramic matrix composite 104 may be bonded to one another via an intermediate material 106 at an interface between the metallic material 102 and the ceramic matrix composite 104. The intermediate material 106 may be formed by a chemical interaction between the metallic material 102 and the ceramic matrix composite 104, as will be discussed. For example, if the metallic material 102 includes a zirconium alloy and the ceramic matrix composite 104 includes silicon carbide, the intermediate material 106 may include a zirconium silicate (ZrxSiy). The intermediate material 106 may have a thickness d3 of between about 0.02 mm and about 1 mm, and more particularly about 0.02 mm. The intermediate material 106 may also function as a thermal expansion material in the cladding material 100 and may enhance thermal transport from the metallic material 102 into the ceramic matrix composite 104. The cladding material 100 may be used in a variety of high-temperature applications involving exposure to oxidative and corrosive materials. As a non-limiting example, the cladding material 100 may be used as in a chemical processing apparatus, as a reactor seal, as a fuel cladding tube, as a chemical processing heat exchanger, as a steam generator, as a gas phase cooling system, as a radiator or as a combustion chamber liner, as will be described. Referring to FIG. 1B, the metallic material 102 may be formed on opposite surfaces of the ceramic matrix composite 104. The metallic material 102 may infiltrate voids within the ceramic matrix composite 104 such that the ceramic matrix composite 104 is encapsulated within the metallic material 102. The additional metallic material 102 may provide increased mechanical strength and may protect the ceramic matrix composite 104 from oxidation. As shown in FIGS. 2A and 2B, a tube 200 may be formed from the cladding material 100 described with respect to FIGS. 1A-1B and may be used with a fuel rod for a reactor such as in a nuclear power plant or other power plant. The tube 200 may be used, for example, as a containment tube for one or more fuels in the reactor. For example, the tube 200 may be used to contain nuclear fuel in a variety of nuclear reactor designs, such as, light water reactors (LWR), pressurized water reactors (PWR), liquid metal fast reactors (LMFR), high temperature gas-cooled reactors (HTGR) and steam cooled reactor boiling-water reactors (SCBWR). For simplicity, the tube 200 is shown as having an elongated cylinder shape surrounding a hollow compartment 208. The tube 200 may, however, be formed in any number of cross-sectional shapes, such as a triangular shape, a square shape, a rectangular shape or a trapezoidal shape. The tube 200 may include the ceramic matrix composite 104 overlying the metallic material 104, the metallic material 104 forming a liner over inner surfaces of the ceramic matrix composite 104. The combination of the ceramic matrix composite 104 over the metallic material 102 in the tube 200 provides advantageous properties, as will be described. For example, the tube 200 may have a substantially increased lifetime and improved safety margins in comparison to conventional zirconium fuel tubes and conventional silicon carbide fuel tubes. The ability to maintain strength and structure during an off-normal event results in an increased margin between where the fuel would fail and where it can operate even in an accident. The increased margin makes for an inherently safer fuel. The safety margin could be traded for a greater operating flexibility while maintaining adequate safety margins. The metallic material 102 may encompass the compartment 208, which is sized and configured to house the fuel. For example, the fuel tube 200 may have an outer diameter D1 of from about 7 mm to about 12 mm and, more particularly, about 9.5 mm. The ceramic matrix composite 104 may provide mechanical support for the metallic material 102 as well as mechanical strength in the axial and radial directions and protection from environmental elements, such high temperatures, oxidation and hydrating. The tube 200 may be exposed to high temperatures from heater water and in an off-normal event super heated water which will dissociate into oxidizing and hydrating elements. The ceramic matrix composite 104 and the metallic material 102 may be bonded to one another by an intermediate material 106, as described with respect to FIG. 1A. For example, the ceramic matrix composite 104 may comprise silicon carbide, the metallic material 102 may comprise a zirconium alloy, and the intermediate material 106 at the interface of the ceramic matrix composite 104 and the metallic material 102 may comprise a zirconium silicate material. The zirconium silicate material may be formed, for example, by a reaction between silicon in the ceramic matrix composite 104 and zirconium in the metallic material 102, as will be described. During off-normal events the metallic material 102 may react fully with dissociated oxygen to form a brittle non-supportive ceramic zirconium dioxide material. The ceramic matrix composite 104 is substantially non-reactive with the dissociated oxygen and, thus, retains strength and stability for containing fissile materials. The non-exothermic reaction of silicon carbide with oxygen may form a passivating material comprising silicon dioxide (SiO2) that inhibits further reaction with the underlying silicon carbide. Metallic elements such as zirconium, niobium, hafnium, tantalum and tungsten or carbides thereof may be added to the matrix to enhance temperature resistance to oxidation. Table 1 provides examples of particles that may be added to a ceramic matrix comprising silicon carbide to increase resistance of the ceramic matrix composite 104 to oxidation at increased temperatures. TABLE 1ThermalSilicate GlassUpperCTECTE ChangeMeltingNeutronformed withTemp(10-6with MaterialTempDensityAdsorbingSiC in presenceRangeMaterialK-1)addition to SiC(° C.)(gm/cc)StructureBehaviorof oxygen(° C.)TiB27increase3,1404.93Hexagonalmedium toTitania1,600highborosilicateZrC6.7increase3,5326.73cubiclowZirconia silicate2,100NbC6.6increase3,5007.8cubiclowNiobium silicate2,100B4C1.7decrease2,9733.48alpha-highBorosilicate1,400rhombohedralSiC2.4no change2,7303.21beta - cubiclowSilicate (SiO2)2,000alpha-hexagonalHfC7.3increase3,89012.2cubiclowHafnium silicate2,300TiC5.5increase4,8204.93cubicmediumTitanium1,800silicateTaC6.4increase3,88013.9cubicmediumTantalum2,400silicateWC5.5increase2,87015.8hexagonalmediumTungsten2,400silicate As shown in FIG. 2B, the tube 200 may have a length L1 of from about 0.3 m to about 4 m, and more particularly, about 3.6576 m (i.e., 3657.6 mm). The metallic material 102 may include thickened regions 210 extending beyond the ceramic matrix composite 104 at distal ends of the tube 200 for the purpose of providing a sufficiently thick metallic region for welding of end caps 212 to contain the nuclear fuel and starting helium and fission by-product gases generated during fuel operation (not shown), The thickened regions 210 may have a substantially increased wall thickness d4 of between about 0.4 mm to about 1.2 mm and, more particularly, between about 0.5 mm to about 1 mm. As a non-limiting example, a length L2 of the thickened regions 210 may be between about 0.5 mm and about 1.5 mm. The thickened regions 210 may provide increased surface area and material for sealing the ends of the tube 200 by, for example, attaching the thickened regions 210 at each of the ends to an end cap 212. The end cap 212 may include any metal, metal alloy or other material suitable for attachment to the thickened regions 210 using a conventional process, such as a welding process. For example, the end caps 212 and the thickened regions 210 may each comprise a zirconium alloy, such as zircaloy-4, and the ends of the tube 200 may be sealed by attaching the ends caps 212 to the thickened regions 210 using a conventional welding process or other process. The thickened regions 210 of the metallic material 102, therefore, enable hermetic sealing of the tube 200 containing nuclear fuel and pressurized starting life gas (helium) and fission gas products formed during the useful life of the fuel. The ceramic matrix composite 104 may include reinforcing fibers within a ceramic matrix. The reinforcing fibers may be in the form of a continuous fiber or may be woven or otherwise interlaced to form a multi-axial fabric. The form (i.e., woven using continuous fiber) of the reinforcing fibers of the ceramic matrix composite 104 may be selected to provide both axial and radial strength tailored to a specific nuclear reactor or a location within the nuclear reactor. For example, the reinforcing fibers may be provided as a woven structure, such as an open or closed tri-axial weave, a harness satin weave or an three dimensional X, Y, Z weave, in which the reinforcing fibers are interlaced with one another to tailor the reinforcing fibers of the ceramic composite for thermal expansion, modulus, conductivity and drapability. The reinforcing fibers having a tri-axial weave include axial and radial fibers and, thus, may provide substantially increased stiffness and mechanical and thermal load capacity when incorporated into the ceramic matrix composite 104 of the tube 200. As a non limiting example, the reinforcing fibers may be formed from silicon carbide ceramic fibers having a tri-axial weave, and a volume fraction of the reinforcing fibers in the ceramic matrix composite 104 may be between about 30% and about 45%. Variations in axial and radial orientation of the reinforcing fibers within the ceramic matrix composite 104 may result from changes in braid angle (e.g., between about 30 and about 60 degrees) of the reinforcing fibers, a percentage of the reinforcing fibers oriented in the axial direction (e.g., between about 20% and about 40%) and percentage of reinforcing fibers oriented in the radial directions (e.g., between about 40% and about 80%). A fiber denier (i.e., tow count or filament size) of the reinforcing fibers within the ceramic matrix composite 104 may be selected to tailor a texture of an outer surface 214 of the ceramic matrix composite 104. For example, the fiber denier of the reinforcing fibers may be reduced so that the outer surface 214 of the ceramic matrix composite 104 is finer and less textured (i.e., exhibits increased smoothness). The difference between a coefficient of thermal expansion of the ceramic matrix composite 104 and the metallic material 102 provide a substantial reduction in overall thermally induced stresses. As the tube 200 is exposed to increased temperatures, the metallic material 102 may expand forcing the metallic material 102 into compression. In addition, the metallic material 102 may expand in a radial direction as the tube 200 is exposed to increased temperatures placing the ceramic matrix composite 104 into radial tension. The radial tension on the ceramic matrix composite 104 may relieve tensile stresses on the metallic material 102. The radial tension of the ceramic matrix composite 104 may be substantially similar or equal to a net internal gas pressure within the tube 200 (e.g., 2,000 psi (13790 kPa) to 3,000 psi (20685 kPa)), and may be well below a pressure at which the ceramic matrix composite 104 may yield leading to failure. Since the compressive stresses on the metallic material 102 are substantially reduced by the ceramic matrix composite 104, the tube 200 exhibits increased resistance to cracking and provides a substantially increased lifetime in comparison to conventional fuel cladding tubes. The ceramic matrix composite 104 may, optionally, include at least one oxygen inhibitor, such as an oxygen getter and/or a glass former. Examples of suitable oxygen inhibitors are shown in Table 2. For example, at least one of a glass forming metallic species including at least one of calcium (Ca), ytterbium (Y), zirconium (Zr), and tantalum (Ta) may be included in the ceramic matrix of the ceramic matrix composite 104. TABLE 2Material Types as added to theMaterialOxygen InhibitorsSiC MatrixFormOxygen GettersSilicon (Si), Zirconium (Zr),powderM(s) + O2(g)--> MO2(g)Molybdenum (Mo), Titanium (Ti),(micron)Tantalum (Ta), Niobium (Nb),Yttrium (Y), Tungsten (W)Glass formersSilicon (Si), Silicon carbidepowder2MC(s) + 3O2(g) -->(SiC), Zirconium carbide (ZrC),(micron)2MO2(solid) + 2CO(g)Tantalum carbide (TaC), Titaniumcarbide (TiC), Tungsten carbide(WC)Getter + Glass:Zirconium silicate (ZrSi3, ZrSi2),powderMetallic SilicatesTitanium silicate (Ti5Si3),(micron)MxSiy(s) + O2(g)-->Titanium silicate (TiSi)MxSiyO2(s) In embodiments in which the metallic material 102 includes zirconium or a zirconium alloy and the ceramic matrix composite 104 includes silicon carbide, the oxygen inhibitor may include, for example, silicon powder, silicon carbide powder, zirconium powder or a zirconium silicate. For non-nuclear applications, boron carbide (B4C) powder may be added to a ceramic matrix composite 104 comprising silicon. In embodiments in which the reinforcing fibers of the ceramic matrix composite 104 comprise silicon carbide coated carbon fibers, boron oxide (B2O3) may be added to the silicon carbide matrix to wet the carbon. Oxygen released by dissociation of water may contact the ceramic material (i.e., silicon carbide) causing oxidation of the ceramic matrix followed by oxidation of the ceramic fibers. The glass forming metallic species may act as an oxygen getter by trapping and/or chemisorbing the oxygen also the metallic species can function to increase the viscosity of the now formed silicon dioxide (SiO2) at elevated temperatures to provide further increased oxidation resistance and longer high temperature utility. The glass forming species may also react with metal particulates or additives in the ceramic matrix composite 104 or other metals, such as the metallic material 102. For example, zirconium dioxide (ZrO2) may be formed from zirconium and, in turn, the combination of the zirconium dioxide and the silicon dioxide may form zircon (ZrSiO4), which is a stable glass with a melting point of about 2750° C. (about 4980° F.). Other compounds that act as glass formers with silicon dioxide include, but are not limited to, tungsten oxide (WO2), which has a melting point of about 2870° C. (about 5200° F.) and tantalum pentoxide (Ta2O5), which has a melting point of about 2996° C. (about 5425° F.). The increased viscosity of the silicon dioxide in the ceramic matrix also reduces oxygen transport through the ceramic matrix to the metallic material 102. The ceramic matrix composite 104 of the tube 200 may further provide a substantially reduced rate of material oxidation in comparison to conventional fuel cladding tubes. During later stages of an off-normal event, the tube 200 may be heated to temperatures in excess of about 800° C. (about 1475° F.) and, more particularly, between about 900° C. (about 1650° F.) and about 1200° C. (about 2200° F.), causing water used as a coolant in the reactor to dissociate on contact with the outer fuel rod and into hydrogen and oxygen (H2O→H2+O). The oxygen may directly react in an exothermic manner with the metal of the metallic material 102 leading to surface temperatures of greater than about 1650° C. (about 3000° F.). The metallic material 102 may lose much of its strength at temperatures greater than about 537.8° C. (about 1000° F.), thus, compromising the mechanical strength of the tube 200. At temperatures of greater than about 815.6° C. (1500° F.), the metallic material 102 may exothermically react with the oxygen formed by dissociation of the water. For example, the metallic material 102 may comprises a zirconium alloy and the zirconium may reaction with the oxygen to form crystalline zirconium oxide (e.g., Zr+2O→ZrO2) on a surface of the metallic material 102. Because the zirconium oxide reaction product does not adhere to the metallic material 102, cracks may form in ceramic matrix composite 104 of the tube 200 that enable additional oxygen ingress leading to breaching of the tube 200. For example, the ceramic matrix composite 104 may comprise silicon carbide and the metallic material 102 may comprise zircaloy-4. As the tube 200 is exposed to increased temperatures, the silicon carbide of the ceramic matrix composite 104 may react with oxygen resulting in formation of an adherent amorphous glass material comprising silicon dioxide (e.g., 2SiC+3O2→2SiO2 (glass)+2CO (gas)) on surfaces of the ceramic matrix composite 104. The presence of the amorphous glass material on the ceramic matrix composite 104 may substantially reduce or eliminate the ingress of oxygen such that oxygen enters the tube 200 only by way of diffusion through the amorphous glass material. In addition, the reaction of the silicon carbide of the ceramic matrix composite 104 with the oxygen inherently consumes additional undesired oxygen from the tube 200. Accordingly, an amount of the oxygen available for reaction with the metal (i.e., zirconium) of the metallic material 102 is substantially reduced by the ceramic matrix composite 104. Thus, the presence of the ceramic matrix composite 104 overlying the metallic material 102 of the tube 200 provides a significantly increased lifetime and improved safety margins in comparison to conventional zirconium metal multi-layered tubes. Additional embodiments of the invention include methods of forming cladding material, such as the tube 200 shown in FIGS. 2A and 2B. In some embodiments, the metallic material 102 may be formed before forming the ceramic matrix composite 104 and the ceramic matrix composite 104 may be formed around the metallic material 102. In such an embodiment, a portion of the metallic material 102 and the ceramic matrix composite 104 may react to form the intermediate material 106, as will be described. For example, the metallic material 102 may be formed using a conventional process, such as a machining process, a molding process or an extrusion process. FIG. 3 illustrates an embodiment of a method of forming the metallic material 102. A metallic tube with walls having at least the thickness d4 of the thickened regions 210 may be mounted on a support structure 300, such as a solid metal rod (e.g., an aluminum rod or a brass rod). As a non-limiting example, the metallic tube may be immobilized on the support structure 300 using an adhesive material (not shown), such as a wax. Material may be removed from proximal regions of an outer wall of the metallic tube until the thickness d1 of the metallic material 102 is achieved. In some embodiments, the material may be removed from the metallic tube using a conventional machining process performed with a mandrel. A relief polish may be performed such that a transition 216 between a thinned portion of the metallic material 102 and the thickened regions 210 is beveled and substantially free of burrs. The support structure 300 provides structural support for the metallic material 102 during the machining process and handling of the metallic liner after processing. In embodiments in which the wax is used as the adhesive material, the metallic material 102 may be released from the support structure 300 by heating the wax to a temperature sufficient to at least partially melt the wax. The ceramic matrix composite 104 may be formed using a conventional liquid phase infiltration process such as, a polymer infiltration and pyrolysis process (PIP), a slurry infiltration process (SIP), and a reactive metal infiltration (RMI) process. In some embodiments, the ceramic matrix composite 104 may be formed around the metallic material 102 by forming a fiber preform from the reinforcing fibers and disposing the fiber preform over a circumference of the metallic material 102. As previously discussed, the reinforcing fibers may comprise beta silicon carbide fibers, types of which are known in the art and are commercially available, or alpha silicon carbide fibers formed using methods described in, for example, in the aforementioned U.S. patent application Ser. No. 12/901,309. The reinforcing fibers of the fiber preform may be infiltrated with a pre-ceramic polymer and silicon to form a precursor structure. Examples of pre-ceramic polymers include, but are not limited to, allyhydridopolycarbosilane (AHPCS), CERASET® polysilazane and polyureasilazane ceramic precursor resins (commercially available from Kion Corporation a Clariant Corporation, Charlotte, N.C.), and STARFIRE® SMP-10 polycarbosilane/siloxane silicon carbide precursor polymer (commercially available from Starfire Systems, Inc., Schenectady, N.Y.). Optionally, a silicon powder may be mixed with the pre-ceramic polymer. The pre-ceramic polymer may be cured to form the precursor structure by exposing the pre-ceramic polymer to a temperature of about 200° C. (about 400° F.). In some embodiments, the fiber preform may be infiltrated with the pre-ceramic polymer to form a precursor structure and the precursor structure may be disposed over or molded around the circumference of metallic material 102. The metallic material 102 may, optionally, be bonded to the ceramic matrix material of the ceramic matrix composite 104 by exposing the precursor structure to a temperature sufficient to initiate a chemical reaction between the material of the metallic material 102 and the pre-ceramic polymer. The chemical reaction may result in formation of the intermediate material 106 bonding the metallic material 102 to the ceramic matrix composite 104. For example, the metallic material 102 may be formed from zircaloy-4 and the pre-ceramic polymer may be formed from CERASET® polysilazane 20 ceramic precursor resin and precursor structure may, optionally, be heated to a temperature of about 1420° C. (about 2590° F.) to form a zirconium silicate material. As the zirconium silicate forms, it acts as a barrier to the silicon, slowing diffusion of the silicon into the zircaloy-4 and the reaction between the silicon and zirconium. Thus, the thickness d3 of the zirconium silicate material may be dependent on an amount of free silicon in the pre-ceramic polymer available to react with the zircaloy-4 material. For example, the ceramic matrix composite 104 may be formed by depositing the preform over the metallic material 102 or, if present, the intermediate material 106 and exposing the pre-ceramic polymer to a temperature sufficient to obtain the ceramic matrix material. As a non-limiting example, the pre-ceramic polymer may be formed from CERASET® polysilazane 20 ceramic precursor resin. The pre-ceramic polymer may additionally include particles of beta silicon carbide (e.g., beta silicon carbide powder), or the pre-ceramic polymer may be seeded with particles of alpha silicon carbide (e.g., alpha silicon carbide powder). In embodiments in which the reinforcing fibers comprise beta silicon carbide, beta silicon carbide powder may be added to the pre-ceramic polymer. In embodiments in which the reinforcing fibers include alpha silicon carbide, the pre-ceramic polymer may be seeded with particles of silicon carbide. The pre-ceramic polymer may, optionally, be cured by exposing the pre-ceramic polymer to a temperature of about 200° C. (about 400° F.). The pre-ceramic polymer may be exposed to a temperature sufficient to convert the pre-ceramic polymer to the ceramic matrix material in the presence of an inert gas (i.e., argon, nitrogen, neon, xenon, etc.) to form the ceramic matrix composite 104. The pre-ceramic polymer may be exposed to a temperature of less than a crystallization temperature thereof to form an amorphous silicon carbide. For example, the pre-ceramic material may include amorphous beta silicon carbide, and the ceramic matrix composite 104 may be formed by exposing the cured pre-ceramic polymer to a temperature of between about 600° C. (about 1110° F.) and about 1200° C. (about 2200° F.) in the inert gas. The ceramic matrix composite 104 may be re-infiltrated with the pre-ceramic polymer and heated as previously described, any number of times to form additional ceramic material and increase a density of the ceramic matrix material. Heating the ceramic matrix composite to a temperature between about 1550° C. (about 2820° F.) and about 1600° C. (about 2910° F.) will form the silicon carbide in the crystalline beta phase. To form the silicon carbide in the crystalline alpha phase (“alpha silicon carbide”) when using alpha silicon carbide fibers, the pre-ceramic polymer may be seeded with particles of alpha silicon carbide (e.g., alpha silicon carbide powder) to provide nucleation sites for formation at desired locations of the alpha silicon carbide. The pre-ceramic polymer and the particles of alpha silicon carbide may be heated to a temperature at which formation of the alpha silicon carbide is thermodynamically favored, such as a temperature from about 600° C. (about 2910° F.) to about 750° C. (about 3180° F.) to form the alpha silicon carbide matrix of the ceramic matrix composite 104. After forming the ceramic matrix composite 104, a crystallization cycle may optionally be performed to crystallize the ceramic matrix material. For example, the ceramic matrix material may comprise beta silicon carbide and may be exposed to a temperature less than or equal to about 1650° C. (about 3000° F.) to crystallize the ceramic matrix material of the ceramic matrix composite 104. In embodiments where the matrix material of the ceramic matrix composite 104 is bonded to the metallic material 102, the zirconium dioxide may react with zirconium oxide to form Zr5Si4. In other embodiments, the ceramic matrix composite 104 may be formed using the methods previously described and, thereafter, the metallic material 102 may be formed on inner walls of the ceramic matrix composite. The metallic material 102 may be deposited using conventional metal deposition techniques, such as sputtering, or by applying molten metal to the inner surfaces of the ceramic matrix composite 104. The tube 200 may be sealed by fusing the thickened regions 210 to one of the end caps 212 using a conventional welding process. Sealing the thickened regions 210 of the tube 200 substantially reduces or eliminates permeation of gases through the tube 200. In some embodiments, a coating 218 may be formed over the ceramic matrix material 104 to provide a smooth outer surface to the tube 200. For example, to form the coating 218 a final pre-ceramic polymer material may be applied to outer surfaces of the tube 200 and may then be converted to beta or alpha silicon carbide using processes previously described. FIG. 4 illustrates another embodiment of a tube 400 that may be formed from the cladding material 100 described with respect to FIGS. 1A-1B. The tube 400 may, however, be formed in any of a number of cross-sectional shapes, such as, a triangular shape, a square shape, a rectangular shape or a trapezoidal shape. The tube 400 may additionally include an outer metallic material 402 formed from at least one of zirconium, iron, nickel, chromium, molybdenum, niobium, bismuth, and alloys thereof. The ceramic matrix composite 104 may include a plurality of voids, such as pores or holes 404, each of which provides a channel in which the inner metallic material 102 and outer metallic material 402 may be co joined or fused, as will be described. The tube 400, therefore, includes inner and outer metallic materials 102 and 402 bonded to one another through ceramic matrix composite 104. The ceramic matrix composite 104 may be contained internally within the bonded inner and outer metallic materials 102 and 402. The ceramic matrix composite carries the mechanical loads and is located along the fuel rod length where fuel pellets reside. The tube 400 enables fissile materials, such as fuel pellets 406, to be hermetically sealed therein and provides substantially increased mechanical support under normal and off-normal conditions. In addition, since the ceramic matrix composite 104 is encapsulated within the metallic material of the inner and outer liners 102 and 402, ceramic material debris that may be dislodged from the silicon carbide composite is prevented from entering the fuel-clad gap or being displaced into the external coolant, thus providing enhanced through wall thermal conductance. In some embodiments, the inner metallic, material 102 may be pre-fabricated and may be fused to the ceramic matrix composite 104 prior to forming the outer metallic liner 402 over the ceramic matrix composite 104 using the methods previously described. In such an embodiment, the outer metallic liner 402 may be formed by applying a metallic material to the ceramic matrix composite 104 in a molten state such that the molten metallic material infiltrates the holes 404, contacting and bonding with the inner metallic material 102. Alternatively, the metallic material of the outer metallic liner 402 may be disposed about the ceramic matrix composite, for example, in the form of a sheet (not shown), and the tube 400 may be heated such that the inner and outer metallic materials 102 and 402 melt, filling the holes 404 therebetween. In other embodiments, the ceramic matrix composite 104 may be formed over a temporary tool to maintain a shape of an inner diameter of the tube 400 using the methods previously described to form a stand alone, partially infiltrated ceramic matrix composite 104. In such an embodiment, the inner and outer metallic materials 102 and 402 may be formed over the ceramic matrix composite 104 by applying a molten metallic material to the ceramic matrix composite 104 such that the metallic material is deposited on inner and outer surfaces of the ceramic matrix composite 104 and infiltrates the holes 404 therein. The tubes 200 and 400 each provide thermal and mechanical features that uniquely result from the combination of the metallic material 102 and the ceramic matrix composite 104. The metallic material 102 enables hermetic sealing and, thus, containment of gases and fuel within the tubes 200 and 400, and provide for conventional end cap sealing. The fiber-reinforced ceramic matrix composite 104 imparts additional mechanical strength, stiffness, thermal shock resistance and high temperature load carrying capability exceeding these properties of the metallic material 102 alone. The tubes 200 and 400 may provide substantially increased operational lifetime and improved safety margins in comparisons to conventional fuel cladding tubes, thus reducing nuclear power plant capital and operating costs. While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following appended claims and their legal equivalents. |
|
059490837 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1: (1) denotes the cylindrical metal body of the container with a non-circular section; PA1 (2) denotes the inner cavity of the container; PA1 (3) denotes the initial thick shell, on the outer wall (4) of which flat surfaces (5) have been formed by grinding; PA1 (6) denotes the inner wall of the shell onto which crescent-shaped sections (7) have been mounted whose cross-sectional perimeter essentially comprises an arc of a circle (8), with the same diameter as that of the inner cavity (2) bounded by the inner wall (6), the arc of the circle (8) being subtended by a chord (9) which thus represents a flat surface of the inner cavity (2). It can therefore be seen that the cylindrical body of the container comprising the flat surfaces (5) and the crescents (7) subtended by their chords (9) which are parallel to the flat surfaces (5), clearly has a non-circular cross-section. The dimensions of the flat surfaces and of the crescents can vary and can be adapted to the assemblies to be arranged in the cavity 2, always ensuring, however, that the thickness of the cylindrical body 1 satisfies shielding and mechanical strength standards. FIG. 2 denotes the body of the shell (3) and the crescent (7) mounted to the inner wall 6 of the shell by means of a screw (10). FIG. 3 shows a container similar to the container of FIG. 1, but in which the container is a hexagon with rounded corners. |
052531864 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic blocks in a process facility monitoring system to which the present invention could be applied are illustrated in FIG. 1. As illustrated in FIG. 1, a processor 10 which may be included in a workstation, such as a SPARCstation 2 from SUN Microsystems, Inc. of Mountain View, Calif., receives data from sensors (not shown) in the process facility via a data acquisition system 12 while operating under the control of a program stored in a storage unit 14. The data acquisition system 12 may be any conventional system adequate for the number of sensors required and connectable to the processor 10, while the storage unit 14 may be any of a variety of mass storage devices, used individually or in combination. Since the purpose of the system illustrated in FIG. 1 is to provide information to an operator of the process facility, an operator display 16, such as a cathode ray tube display is provided. An operator input unit 18, such as a mouse, touch screen, light-pen, keyboard, etc., permits the operator to control what is displayed. As illustrated in FIG. 2, like the conventional process facility monitoring system disclosed in U.S. Pat. Nos. 4,803,039 and 4,815,014, it is necessary to store 20 initial, sequential and constraining conditions for a procedure to be monitored. In addition, the text of the procedure and other related information also may be stored in the storage unit 14. The conditions and related information may be stored in many different forms. As noted above, the two referenced patents disclose a system which has been implemented by encoding all of the conditions in a FORTRAN program, while other systems which monitor process facilities in a different manner utilize expert systems. It is also possible to use external files, accessed by a program, to store much of the information. In the preferred embodiment, an external file may be used for ease of updating. One of the files may contain transform flags which may be set 22 to designate transformable sequential conditions prior to beginning 24 execution of the procedure. The purpose of monitoring systems of the type to which the present invention is applied is to aid an operator in executing the steps of a procedure. For a complex process facility, such as a nuclear power plant, the procedures are not the simple execution of one step after another, but may contain branches, steps which may be skipped or performed in any order or simultaneously, etc. Since the present invention is not directed to the order of execution of steps per se, FIG. 2 indicates the execution of multiple steps by loop block 26. However this should not be taken as a literal description of how the steps must be executed, but rather as a recognition that a procedure includes many steps and involves progressing from one step to another with a defined relationship between the steps, even though the relationship may not be so simple that steps change by incrementing an iteration value. Regardless of how the order of execution of the steps is defined, at least one step is executed at a time. Each step may have several sequential conditions corresponding to the step. According to the defined procedure, all of these sequential conditions should be met to complete a step. In a computer task for checking sequential conditions, a sequential condition loop block 28 may be used to control repeated checks of the sequential conditions associated with a corresponding step I. An iterative value J is initialized and incremented by the loop block 28 so that each sequential condition can be compared with sensor readings in the process facility to determine 30 whether the condition is met. When a condition has been met, the transform flag is checked 32 and if the transform flag is set, an enable flag for sequential condition J is set 34. In addition to predefined transformable sequential conditions, in the preferred embodiment the operator is given the ability to select sequential conditions to be tracked as transformed conditions in the same manner as constraining conditions are tracked. This may be accomplished in several ways. The operator display 16 could be used to display the sequential conditions and the process facility status corresponding to these conditions. Associated with the display of this information could be a box which the operator may check using the operator input device 18. In this case, all or a selected set of the sequential conditions for the current executing step may have such a box. In most applications, it is expected that an operator will rarely select a sequential condition to be transformed into a constraining condition. Therefore, in the preferred embodiment, a display screen like that illustrated in FIG. 3 is displayed on the operator display 16. At the bottom of the screen is a command menu 36 which may include command buttons 37-40 for selecting auxiliary screens. These screens permit selection of items, such as user reports, print log, access to other procedures, etc. As indicated by command button 40, one of the options which may be provided in the command menu 36 is to modify settings. When a request to modify settings is detected 42 (FIG. 2) by an operator selecting the area of command button 40 using a touch screen, light pen, mouse, etc. in the input unit 18, a menu is displayed 44 permitting the operator to set the transform flag of a sequential condition. The display may be limited to the sequential conditions for the currently executing step I, or the program executing in the processor 10 may permit the operator to scan through the sequential conditions for a number of steps, such as all of the previously executed steps, in addition to the currently executing step and set the transform flag for any sequential condition corresponding to these steps. When all of the sequential conditions for the currently executing step I have been tested, a determination is made as to whether step I has ended 46. This determination may be made in several ways. The process facility monitoring method disclosed in U.S. Pat. Nos. 4,803,039 and 4,815,014 include action buttons 48, 49 which permit the operator to indicate when an action has been completed 48 or if an action is to be overridden 49. When all of the actions within a step have been indicated as completed or overridden, a determination will be made 46 that step I has ended. Alternatively, the process facility monitoring system may be computer paced, whereby the sensor readings must indicate that all of the sequential conditions have been met in order for the determination 46 to be made that step I has ended. Regardless of how the determination 46 is made, according to the present invention the enable flag for all transformable sequential conditions in step I are set 50 when the determination 46 is made that step I has ended. Thus, if a transformable sequential condition is overridden in a step, the enable flag corresponding to that condition will be set 50 so that the sequential condition will continue to be checked as a constraining condition in the subsequent steps. In an alternative embodiment, the check for a transform flag and setting of an enable flag as each condition is met which is indicated in blocks 30, 32, 34, may be eliminated and the setting 50 of enable flags at the end of each step may be relied upon. As described above, in addition to moving sequentially through a procedure, a process facility monitoring system like that disclosed in U.S. Pat. Nos. 4,803,039 and 4,815,014 continually checks constraining conditions. When transformable sequential conditions are included according to the present invention, the program steps illustrated in FIG. 4 will be executed in checking constraining conditions. As in the case of FIG. 2, the flowchart in FIG. 4 is representative of the computer operations which must be performed. These steps can be implemented in many ways. If the processor 10 is capable of multi-tasking operation, the sequential condition iteration loop controlled by block 26 of FIG. 2 may be located in one or more tasks, while the computer program code represented by the flowchart in FIG. 4 is in a separate task. In this manner, the multi-tasking operating system will control the simultaneous execution of the program flow in FIGS. 2 and 4. Alternatively, a single application program may be written encompassing both FIGS. 2 and 4 and the program code corresponding to the blocks illustrated in FIG. 4 may be inserted in place of one of the ellipses 52, 54 in FIG. 2, or some other timing mechanism may be used to determine when the constraints loop illustrated in FIG. 4 is performed. Regardless of exactly how it is determined to execute the constraints loop in FIG. 4, each of the constraining conditions must be checked in some manner at appropriate times during execution of a procedure. In FIG. 4, a constraints loop block 56 is illustrated as one example of how to control checking all of the constraining conditions. However, the present invention may be implemented in an expert system or using other software which does not support iteration loops, but has other known mechanisms for repeatedly checking a large number of conditions. Regardless of how the constraining conditions are checked, a determination is made 58 whether a constraining condition is violated and a warning is displayed 60 for those constraining conditions which are found to be violated. In addition, an iteration loop block 62 or other means for checking transformable sequential conditions is provided. For each sequential condition, determinations must be made regarding whether the sequential condition is transformable 64 and if so whether it has been enabled 66. If these determinations are made in the affirmative, the condition is a transformed condition which will be treated like a constraining condition and checked to determine 68 whether the condition has been violated. A warning will be displayed 70 in a manner similar to that for constraining conditions when a transformed condition is violated. As noted above, the present invention may be implemented in many ways. In the case of complex procedures, it is common to have a computer-based procedure maintaining support system for defining the procedures. The system used for computer-based support may provide means for automatically generating the control codes to create transformable sequential conditions. In a case where a FORTRAN program is used to provide a process facility monitoring system, instead of having transform flags, the procedure maintaining support system may copy FORTRAN code from a sequential condition group of statements to a constraining condition group of statements. This copying of course could be performed manually, although as noted above the benefits of ensuring consistency and accuracy of the conditions being checked is not as easily maintained when the copying is performed manually. The many features and advantages of the present invention are apparent from the detailed specification, and thus it is intended by the appended claims to cover all such features and advantages of the system which fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art from the disclosure of this invention, it is not desired to limit the invention to the exact construction and operation illustrated and described, accordingly, suitable modifications and equivalents may be resorted to, as falling within the scope and spirit of the invention. |
044629559 | abstract | An anti-earthquake support device arranged between an element of large mass and a fixed support, comprising roller elements arranged between support parts forming roller tracks inclined with respect to the horizontal plane. The roller elements are cylindrical rollers (14,15,17) arranged horizontally in two superposed sets of rollers with perpendicular axes. The support parts (4,10 and 11) are entirely independent of one another and are arranged above one of the sets of roller for the first (4), between the two sets of rollers for the second (10) and beneath the second set of rollers for the third (11). The corresponding roller tracks (9, 20, 21 and 24) are formed on either the lower, or the lower and upper, or the upper surfaces of the three support parts (4, 10 and 11), respectively. The invention is used for the support of a fuel assembly rack for a nuclear reactor on the bottom of the storage pool of such reactor. |
056446152 | summary | The invention relates to an X-ray analysis apparatus comprising an X-ray collimator which comprises a plurality of plates of a radiation absorbing material which are provided with openings and which are arranged so as to extend parallel and offset relative to one another in the propagation direction of the radiation, each plate comprising a pattern of holes with a given period p.sub.1 in a direction perpendicular to one of the sides of the holes, said period having a given opening fraction t.sub.1. The invention also relates to a collimator for use in such an X-ray analysis apparatus. A collimator of the described kind is known from U.S. patent specification Ser. No. 4,465,540. The collimator described therein, notably with reference to FIG. 5, consists of a number of collimator plates which are arranged consecutively in parallel (in the direction of the X-rays to be collimated). The plates shown in the cited document comprise a pattern of square holes arranged in mutually parallel rows. The rows are situated at equal distances from one another, so that they occur with a period p.sub.1, being the distance between, for example the upper sides of the holes in two successive rows. This period thus consists of two parts, i.e. a part which is formed by the hole and which amounts to the fraction t.sub.1 (the opening fraction), so that the dimension of the hole in this direction equals t.sub.1 p.sub.1, and a pan which is formed by the intermediate absorbing material and which amounts to the fraction (1-t.sub.1), so that the dimension of the intermediate absorbing material in this direction equals (1-t.sub.1)p.sub.1. The plates in this known collimator are arranged at equal distances from one another. The distance between these plates is determined by thin plate-shaped spacers which are clamped between the collimator plates and which are made of a material which transmits the relevant X-rays. Collimators of this kind are comparatively heavy because a substantial fraction of their volume is filled with plates of an absorbing material. Moreover, this material, for example lead, tin or molybdenum, is heavy. The intermediate spacers also absorb a given amount of X-rays which is undesirable for some applications, notably in analysis equipment. It is an object of the invention to provide a collimator of the kind set forth which has a lower weight and a negligibly low absorption of X-rays in the desired transmission direction. To this end, the collimator in accordance with the invention is characterized in that the holes have a rectangular shape and that the collimator is provided with a first series of plates in which the ratio of two successive distances (d.sub.i, d.sub.i+1) between the plates of the series is equal to the given opening fraction t.sub.1 of the period p.sub.1. It can be geometrically demonstrated that said arrangement of collimator plates suffices for all X-rays which do not extend in the desired transmission direction to be intercepted by at least one plate. Moreover, this results in a collimator whose weight is much lower weight and in which a large clearance exists between the collimator plates, which clearance can be used to accommodate a variety of elements for influencing or manipulating the X-ray beam. In an attractive embodiment of the invention, the X-ray analysis apparatus is characterized in that the holes furthermore have a given second period p.sub.2 in a second direction in the plane of the plates, perpendicular to the first direction, said second period having a given second opening fraction t.sub.2, the collimator being provided with a second series of plates in which the ratio of two successive distances between the plates of the second series equals the given second opening fraction t.sub.2 of the second period p.sub.2. These steps result in a collimator whereby collimation can be performed in two mutually perpendicular directions, the degree of collimation in one direction being independent of that in the other direction. This is achieved in that the length/width ratio of the rectangular holes is decisive in this respect. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. |
summary | ||
claims | 1. A system for processing spent nuclear fuel from fuel assemblies having fuel tubes into fast molten salt reactor fuel, the system comprising components including at least:means for chlorinating and processing the spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the spent fuel with anhydrous hydrogen chloride (AHCl);a fluidized bed configured to receive spent fuel gasses and to convert the spent fuel gases to chlorinated fuel salts; andmeans for chlorinating the spent fuel salt to yield molten chloride fuel salt for a fast molten salt reactor. 2. The system of claim 1, further comprising:at least one of a first mill, configured to granulate the spent fuel in an atmosphere that is at least semi-voided, and a second mill, configured to mill the molten chloride fuel salt to predetermined specifications for the fast molten salt reactor. 3. The system of claim 1, further comprising:at least one tray configured to receive the molten chloride fuel salt and to allow the molten chloride fuel salt to cool to solidify. 4. The system of claim 3, wherein the tray is configured to receive the molten chloride fuel salt and to allow the molten chloride fuel salt to cool to solidify in the form of bars, sticks, or canisters. 5. The system of claim 1, further comprising means for enriching the spent fuel salt. 6. The system of claim 5, wherein the means for chlorinating and processing the spent fuel into chloride salt includes reacting the enriched spent fuel salt with AHCl. 7. The system of claim 1, further comprising means for enriching the spent fuel salt with one or more of uranium-235 (U235), plutonium-239 (Pu239), or mixed oxide (MOX). 8. The system of claim 1, further comprising a rod puller disassembly table configured for receiving the fuel assemblies and for removing the spent fuel from the fuel assemblies. 9. The system of claim 1, further comprising a laser configured for slitting or slicing the fuel tubes for allowing removal of the spent fuel. 10. The system of claim 1, further comprising an oxide reduction tank configured for enriching the spent fuel salt. 11. The system of claim 1, wherein the means for chlorinating includes a molten chloride salt bath, and wherein the chlorinating step occurs by immersion in the molten chloride salt bath. 12. The system of claim 1, further comprising means for enriching the spent fuel salt with enriched uranium. 13. The system of claim 1, further comprising:a site within a secured perimeter;a limited-access facility on the site;the components of the system being located within the limited-access facility;a spent nuclear fuel storage facility located on the site; anda molten salt reactor located on the site. 14. The system of claim 1, wherein the means for chlorinating and processing the spent fuel into chloride salt by ultimate reduction and chlorination produces hydrogen and further comprises converting the hydrogen to water and continuously removing the water. 15. A system for processing spent nuclear fuel from fuel assemblies having fuel tubes into fast molten salt reactor fuel, the system comprising:means for removing spent fuel from the fuel assemblies;a first mill configured for granulating, in an atmosphere that is at least semi-voided, the removed spent fuel into granular spent fuel suitable for chlorination;means for processing the granular spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the granular spent fuel with anhydrous hydrogen chloride (AHCl);means for chlorinating the granular spent fuel salt to yield molten chloride fuel salt by reacting the granular spent fuel salt with AHCl;a fluidized bed configured to receive spent fuel gasses and to convert the spent fuel gases to chlorinated fuel salts; anda second mill configured for milling the molten chloride fuel salt to predetermined specifications. 16. The system of claim 15, further comprising a disassembly table configured for receiving the fuel assemblies and for removing the spent fuel from the fuel assemblies. 17. The system of claim 15, further comprising a laser configured for slitting or slicing the fuel tubes for allowing removal of the spent fuel. 18. The system of claim 15, further comprising an oxide reduction tank configured for enriching the granular fuel salt. 19. A system for processing spent nuclear fuel from fuel assemblies having fuel tubes into fast molten salt reactor fuel, the system comprising:a first mill configured for granulating, in an atmosphere that is at least semi-voided, the removed spent fuel into granular spent fuel suitable for chlorination;means for processing the granular spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the granular spent fuel with anhydrous hydrogen chloride (AHCl);an oxide reduction tank configured for enriching the granular fuel salt;means for chlorinating the enriched granular spent fuel salt to yield molten chloride fuel salt by reacting the enriched granular spent fuel salt with AHCl;a fluidized bed configured to receive spent fuel gasses and to convert the spent fuel gases to chlorinated fuel salts; anda second mill configured for milling the molten chloride fuel salt to predetermined specifications. 20. A system for processing spent nuclear fuel from fuel assemblies having fuel tubes into fast molten salt reactor fuel, the system comprising components including at least:means for chlorinating and processing the spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the spent fuel with anhydrous hydrogen chloride (AHCl) wherein hydrogen is produced, converting the hydrogen to water, and continuously removing the water; andmeans for chlorinating the spent fuel salt to yield molten chloride fuel salt for a fast molten salt reactor. |
|
description | FIG. 1 shows diagrammatically an embodiment of a step-and-scan lithographic projection apparatus 1 in which an EUV radiation source according to the invention may be used and with which the method according to the invention may be performed. The apparatus comprises an illumination system for illuminating a mask MA and a mirror projection system for imaging a mask pattern, present in the mask, on a substrate W, for example, a semiconductor substrate which is provided with an EUV radiation-sensitive photoresist WR. The illumination system 10 shown in the left-hand part of FIG. 1 is designed in known manner in such a way that the illumination beam IB supplied by the system at the area of the mask MA has a cross-section in the form of an annular segment or a rectangle, and has a uniform intensity. The illumination system comprises, for example, three mirrors 11, 12 and 13 which are maximally reflecting for EUV radiation at, for example, a wavelength of the order of 13 nm because they have a multilayer structure of, for example, silicon layers alternating with molybdenum layers. The mask MA is arranged in a mask holder MH which forms part of a mask table MT. By means of this table, the mask can be moved in the scanning direction SD and possibly in a second direction perpendicular to the plane of the drawing, such that all areas of the mask pattern can be introduced under the illumination spot formed by the illumination beam IB. the mask table and the mask holder are shown only diagrammatically and may be constructed in different ways. The substrate W to be illuminated is arranged in a substrate holder WH which is supported by a substrate table WT, also referred to as stage. This table can move the substrate in the scanning direction SD but also in a direction perpendicular to the plane of the drawing. The substrate table is supported, for example, by a table bearing ST. For further details of a step-and-scan apparatus, reference is made by way of example to PCT patent application WO 97/33204 (PHQ 96004). For imaging the mask pattern on the substrate with a reduction of, for example, 4x, a mirror projection system 20 comprising, for example, four mirrors 21, 22, 23 and 24 is arranged between the mask and the substrate. For the sake of simplicity, the mirrors are shown as plane mirrors but actually these mirrors, as well as those of the illumination system 10, are concave and convex mirrors and the mirror projection system 20 is designed in such a way that the desired sharp image is realized at a reduction of, for example 4x. The design of the mirror projection system does not form part of the present patent application. Analogously as the mirrors of the illumination system, each mirror 21, 22, 23 and 24 is provided with a multilayer structure of first layers having a first refractive index, alternating with second layers having a second refractive index. Instead of four mirrors, the mirror projection system may alternatively comprise a different number of mirrors, for example, three, five or six. Generally, the accuracy of the image will be greater as the number of mirrors is larger, but there will be more radiation loss. Thus, a compromise will have to be found between the quality of the image and the radiation intensity on the substrate, which intensity also determines the velocity at which the substrates are illuminated and can be passed through the apparatus. Mirror projection systems having four, five or six mirrors for lithographic apparatuses are known per se. For example, a six-mirror system is described in EP-A 0 779 528. Since EUV radiation is absorbed by air, the space in which this radiation propagates must be a highly vacuum-exhausted space. Minimally, both the illumination system, from the radiation source to the mask, and the projection system, from the mask to the substrate, must be arranged in a vacuum-tight space, which is denoted by means of the envelope 16 in FIG. 1. Instead of being accommodated in the same envelope, the illumination system and the projection system may be alternatively accommodated in separate envelopes. The mask MA and the substrate W may be juxtaposed, as shown in FIG. 2, instead of opposite each other. In this Figure, the components corresponding to those in FIG. 1 have the same reference numerals or symbols. The separate mirrors of the illumination system are not shown in FIG. 2 but form part of the block 10 representing the illumination system, with which the illumination beam is given the desired shape and the uniform intensity. FIG. 2 is a plan view of a mask with a mask pattern C and a plan view of a substrate W with substrate fields, with an image of the mask pattern C being formed on each field. The mask and the substrate comprise two or more alignment marks M1 and M2, and P1 and P2, respectively, each, which are used for aligning the mask pattern with respect to the substrate or with respect to each substrate field separately before the mask pattern is projected. For checking the movements of the mask and the substrate, the lithographic projection apparatus comprises very accurate measuring systems, preferably in the form of interferometer systems IF 1 and IF2. The block denoted by reference numeral 2 in FIGS. 1 and 2 comprises an EUV radiation source unit in which EUV radiation is generated by irradiating water droplets or xenon clusters with a high-intensity laser beam. FIG. 3 is a cross-section of an embodiment of such a radiation source unit. This unit comprises a capillary tube 31, one end of which is connected to, for example, a water inlet, for example a water tank 32, and the other end projects into a vacuum space 33. Water is transported at a high pressure through this tube to the vacuum space, which is denoted by arrow 35. The space 33 is connected to a pump 34, for example, a turbo pump having a power of, for example, 1000 dm3/sec, with which the space 33 can be pumped to a vacuum of 10xe2x88x924 mbar. The capillary tube 31 is caused to vibrate, for example, by means of a piezoelectric driver 37. At a given vibration frequency, for example 0.3 MHz, the tube supplies a continuous flow of individual water droplets 39. The droplet formation is based on the principle which is comparable with that used in various ink jet printers for forming ink droplets. The water droplets may not only be formed by means of piezoelectric pulses but also by thermal pulses or by ultrasonic means. At a water flow 35 of, for example, 5.4 ml/hour, the water droplets have a diameter of the order of 20 xcexcm. The radiation source unit further comprises a high-power laser 40, for example, an Nd-YAG laser which supplies laser pulses at a frequency of, for example, 10 Hz and at a pulse duration of, for example, 8 ns and with an energy content of 0.45 Joule. The optical frequency of the laser radiation may be doubled in known manner so that laser radiation with a wavelength of the order of 530 nm is obtained. An excimer laser, for example a Kr-F laser emitting at a wavelength of 248 nm, may be alternatively used as a laser source. The beam 41 emitted by the laser 40 enters, through a window 43, into the wall of the space 33. This beam is focused by a lens system 42, illustrated by a single lens element, to a radiation spot 45 in a position 46 in a plane which is aligned with the centerline of the tube 31 along which the water droplets pass. An absorbing element 55 is arranged behind a second window 44 in the wall of the vacuum space 33, which absorbing element ensures that radiation of the laser beam exiting from the space 33 cannot enter the apparatus of which the radiation source unit forms part. The beam 42 is each time substantially focused on a water droplet which is instantaneously present at the position 46. The radiation spot 45 has a diameter of, for example, 30 xcexcm so that a water droplet is completely irradiated. The driver 37 is synchronized with the laser driver via an electronic circuit 48 comprising a delay element, so that a laser pulse is generated at the instant when a water droplet arrives at the position 46. Due to the laser energy supplied to the water droplet, a plasma 47 in which oxygen ions are present is produced at the location of this droplet. As a result of the extremely high energy density, for example, of the order of 1021 W/m3 of the laser beam at the location of the droplet, this plasma reaches a temperature which corresponds to an energy of the order of 30 eV. At this high temperature, the dominant ionization state of oxygen O is VI. Then, EUV radiation is generated at wavelengths around 11.6 nm and 13 nm. For further details about the way and circumstances in which EUV radiation is formed, reference is made to the article xe2x80x9cLaser produced oxygen plasmasxe2x80x9d in Proceedings of the 2nd Int. Symp. on Heat and Mass Transfer under Plasma conditions, 1999. One or more mirrors 49 for collecting, concentrating and directing the generated EUV radiation may be arranged in the space 33. Alternatively, such mirrors may be arranged outside the space so as yet to concentrate and direct the EUV radiation exiting from this space. The number of mirrors required is dependent on the percentage of the EUV radiation which must be collected and used and is emitted by the plasma in all directions. In the EUV generation process, not all water droplets are converted into a plasma. On their way through the source space, the droplets give off water vapor. Since the vapor pressure of water at room temperature is approximately 23 mbar, the water vapor and the water droplets which have not been converted must be removed from the source space 33 so as to comply with the vacuum requirement in connection with a free passage of the generated EUV radiation. As described in the article mentioned above, excess water droplets may be drained by introducing them into a second vacuum space 50 via a narrow aperture 51. In the space 50, a relatively low vacuum of, for example, 0.5 mbar is maintained by means of a further vacuum pump 53 having a power of, for example, 70 dm3/sec. By means of this special embodiment of the principle of differential pumping, i.e. separate pumping of two communicating spaces to different degrees of vacuum, a relatively satisfactory vacuum, of the order of 2xc3x9710xe2x88x924 mbar, can in principle be maintained in the source space 33. Moreover, the pumps may be chosen to be such that the remaining water droplets are drained as water vapor. Consequently, the radiation source can be operated continuously and at a constant, rest, pressure level. This pressure level is determined by the vapor pressure of the water droplets moving from the tube to the space 50. However, this vapor pressure is 23 mbar at room temperature so that, without further measures, still so many water molecules are present in the space 33 that EUV radiation coming from the plasma 47 may be absorbed in this space and the intensity of this radiation is reduced. The wall of the vacuum space 33 must be further provided with at least one aperture through which the generated EUV radiation can leave the space 33 so as to enable it to enter the space in which the mirrors of the illumination system, 10, 12 and 14 in FIG. 3, are present. This aperture may be located at the position where the window 43 is situated in FIG. 3. It has been found that, due to the presence of such an aperture, the problem not mentioned in the above-mentioned article xe2x80x9cLaser produced oxygen plasmaxe2x80x9d may occur that water emerging from this aperture may drip on the mirrors of the illumination system and on those of the projection system and may attack these mirrors, thus reducing their reflection. This is an important problem in lithographic projection apparatuses because a reduced reflection of the mirrors, whereby less radiation can reach the mask and notably the substrate, has a direct influence on an important performance parameter of such an apparatus, namely the velocity at which substrates can be illuminated. This problem can be eliminated, or at least sufficiently reduced, by making use of a radiation source unit in accordance with the concept of the invention. FIG. 4 shows a cross-section of an embodiment of this radiation source unit. In this Figure, the elements corresponding to those in FIG. 3 are denoted by the same reference numerals. Furthermore, the components of the radiation source unit which are not important for the present invention are no longer shown in this Figure and subsequent Figures. In FIG. 4, the reference numeral 61 denotes the wall of a source space 60 which has the shape of, for example, a cylinder and in which the water flow 35 is introduced through the tube 31 and in which the water droplets (not shown) propagate. This wall is provided with, for example, narrow apertures 63, 64 having a diameter of, for example, 2.5 mm, via which the pulsed laser beam 41 can enter (63) the space 60, or can leave (64) this space. The generated EUV radiation can leave the source space 60, for example, via these apertures or other apertures (not shown) and enter a space 65. In this space, which is only shown diagrammatically and in which a high vacuum of, e.g.,10xe2x88x924 mbar is maintained by means of the vacuum pump denoted by the reference numeral 34 in FIG. 3, the EUV radiation is guided towards the mask via the mirrors of the illumination system. The space 65 may also be filled with a rare gas such as helium, or with hydrogen at a low pressure of, for example 10xe2x88x921 mbar. According to the invention, not only a flow of water droplets but also a flow 77, 78 of rare gas, for example helium, is introduced into the source space 60 so that the helium flow is parallel to the flow of individual water droplets leaving the tube 31. To this end, the source space has a tube 70 which communicates with a helium outlet, for example, in the form of a tank 73. This tube has a diameter of, for example, 5 mm. A vacuum pump 75 connected to the source space ensures that a continuous helium flow is maintained and that the helium pressure in the source space will not exceed, for example, 10xe2x88x921 mbar. At this low helium pressure, the generated EUV radiation is not absorbed. The water droplets are now encapsulated in a tubular and viscous flow of helium which has a sufficient suction power. As a result, water vapor from the droplets remains enclosed within the helium column and is taken along by the helium flow and transported to the vacuum pump 75. This also applies to water droplets which have not been converted into plasma. The tube 70 ensures that the helium flow is a laminar flow so that the helium gas and the elements of the water present therein cannot flow back. Due to the interaction of the flow of water droplets with the helium flow, the desired flow profile of the helium flow may be disturbed. To prevent this, a second tube 71 connected to the helium tank 73 is preferably arranged in the source space 60, so that a second helium flow 78 is established coaxially with the first flow 77. The flow profile can be restored again by means of the second flow. Instead of helium, another rare gas may be used for draining water vapor and excess water droplets from the source space. An example of another gas is argon having larger molecules than helium so that an argon flow has a better suction power than helium. However, argon is more absorbing than helium. In the choice of the gas, a compromise must be made between the minimal absorption and the maximal suction power. By suitable choice of the diameter of the tube 70 and the tube 71, if any, and of the pump speed, it can be ensured that the quantity of rare gas which may leak through the apertures 63, 64 into the space 65 is sufficiently small to maintain a helium pressure of at most 0.1 mbar in the space by means of a suitable pump for this space. FIG. 5 is a cross-section of a part of a second embodiment of the radiation source unit according to the invention. This embodiment differs from that in FIG. 4, inter alia, in that the source space 60 has a smaller diameter, for example 5 mm, and consists of three parts. The lower part is surrounded by a wall 81. The upper part is closed by the wall 82 of the tube 88 surrounding the inlet tube 31 for the supply of the rare gas. The central part 85 of the source space, at the area of the radiation path of the laser beam 41, communicates with the ambience. At the area of this central part, the walls 81 and 82 are slightly bent outwards so that a so-called ejector configuration, or geometry, is obtained. The combination of the vacuum pump 75 and its specific wall shape at the area of the central part of the source space operates as a so-called ejector pump or jet pump. Such a pump prevents helium or other particles from leaking to the ambience of the source space because it also sucks up possible medium present in this ambience and removes it. The open central part 85 of the source space 60 only needs to have such a height that the converging laser beam 41 can enter the source space in an unhindered way. Helium gas or another rare gas is supplied from a helium inlet 63 between the tube 31 and the wall 82. This helium gas is sucked downwards by the vacuum pump 75 in the form of a laminar flow and takes along the water vapor and water droplets, if any. Due to the jet pump configuration of the source space, diffusion of water vapor and loss of helium gas to the high-vacuum space 65 is prevented, and this to a stronger extent than is the case in the embodiment of FIG. 4. In this way, the helium gas pressure in the space 65 may be further reduced. To be able to operate as a jet pump, the straight part of the source space 60 must have a small diameter, for example, 5 mm. Then, the laser beam must be focused substantially on the position where the water droplets pass. Then there is a greater risk that the beam radiation does not impinge upon a desired water droplet, as compared with the case where the laser beam is focused at some distance from said position and hence this beam has a larger diameter at this position. Moreover, when focusing the laser beam on said position, the laser radiation has a large energy density at that position. When irradiating a water droplet and forming a plasma, matter particles, such as highly energetic ions and radicals, may be released, while the number of these particles increases with an increasing density of the laser energy. These particles may also get into the high-vacuum space 65 and reach the mirrors of the illumination system and of the projection system, where they attack the mirror coatings and reduce their reflection. These possible problems are mitigated by the embodiment shown in FIG. 6. This embodiment also comprises a jet pump. However, the inlet tube 90 now has an annular cross-section, with the width of the ring, for example 1 mm, being considerably smaller than its internal diameter which is, for example, 10 mm. The wall portions 92 and the upper parts of the wall 81 again constitute an ejector configuration. The gas curtain supplied through the tube 90 ensures that both the water vapor of the water droplets and the water droplets which have not been converted into a plasma as well as the energy-rich ions and radicals from a plasma remain enclosed and are drained to the pump 75. The jet pump configuration ensures that the gas curtain moves downwards at a great velocity and prevents rare gas particles from leaking to the high-vacuum space 65. Since the jet tube has an annular cross-section, the source space 60 may have a relatively large diameter so that the laser beam can be focused at some distance from the position where the water droplets pass so that the risk of missing a droplet will thus become smaller. Moreover, the energy density of the laser radiation in a droplet is considerably smaller in the embodiment of FIG. 5, so that the number of energy-rich ions and radicals repelled by the plasma is smaller. The embodiment of FIG. 6 thus combines the advantages of the embodiment of FIG. 5 with those of the embodiment of FIG. 4. For the theoretical background and details about ejector pumps, reference is made to the article xe2x80x9cExit Flow Properties of Annular Jet-Diffuser Ejectorsxe2x80x9d in Journal of the Chinese Society of Mechanical Engineers, Vol. 18, No. 2, pp. 1113-125, 1997. The fact that water droplets are used as a medium for forming the plasma in the embodiment described hereinbefore does not mean that the invention is limited thereto. As has been described in the article xe2x80x9cDebris elimination in a droplet target laser plasma soft X-ray sourcexe2x80x9d in Rev., Sci. Instruments 66 (10), October 1995, pp. 4916-4920, ethanol droplets may be alternatively used as a medium for forming a plasma emitting EUV radiation. Similar problems as with water droplets occur, which problems can be solved by using the invention. Water and ethanol are only two examples of possible liquid media which, if irradiated with a high-power pulsed laser, form an EUV radiation emitting plasma and can be used in a laser-generated plasma EUV radiation source. Generally, the invention can be used in all EUV radiation sources in which a liquid medium is converted by a high-power pulsed laser into an EUV radiation-emitting plasma and in which the problems occur that the medium raises the (vapor) pressure in the source space and the plasma formed repels contaminating particles which may penetrate the high-vacuum space and reduce the reflection of the mirrors which are present in this space. Gaseous media instead of liquid media may be alternatively used in an EUV radiation source. For several years, theories have been developed about and experiments have been carried out on the interaction between high laser and xenon clusters for creating a plasma which emits EUV radiation to a sufficient extent, as was recently reported from different research centers at the OSA conference on applications of high field and short-wavelength sources VIII (1999). However, xenon gas absorbs EUV radiation to a great extent so that, without further measures, the EUV radiation output of a xenon plasma source would be too small to operate projection lithography with such a source. By enclosing the xenon gas and draining it with a flow or a curtain of rare gas such as helium according to the invention, it can be achieved that absorption of the generated EUV radiation is reduced considerably. The embodiments shown in FIGS. 4, 5 and 6 may be used, in which xenon clusters are supplied via a tube which is similar to the tube 31 in the Figures, which tube is then not caused to vibrate. As regards their physical state, xenon clusters occupy a position between molecules and a solid material. Such clusters can be injected into a source space by means of a pulsed valve having an aperture diameter of, for example, 2 mm. If such a cluster in this space is excited by laser pulses of, for example, a Kr-F excimer laser, which laser pulses have a very short pulse duration of, for example, 0.35 p/sec and a power of, for example, 20 mjoule, then there will be a strong ionization of the cluster and it will emit EUV radiation at a wavelength of the order of 11 nm. The strong absorption of the EUV radiation formed can be prevented and the collection and drainage of energy-rich ions can be ensured by making use of the present invention and the various embodiments described. The invention may also be used in an EUV radiation source unit in which a tape or wire of a metal is used as a medium. The problem when using a metal medium is that, when it is impinged upon by a laser beam to obtain the desired plasma, the metal is locally caused to explode so that metal particles are released. If these particles get outside the source space, they will have a destructive effect on the optical components of the apparatus incorporating the radiation source unit. The present invention and its various embodiments provide an eminent possibility of preventing this. EUV radiation sources may not only be used in lithographic projection apparatuses but also in EUV microscopes having a very high resolving power. The radiation path of the EUV radiation in such a microscope must be in a high vacuum. To prevent the vacuum from being attacked from the radiation source and from contaminating the optical components, the invention and its various described embodiments may be used to great advantage. It has been noted hereinbefore that EUV radiation is also known as soft X-ray radiation because its wavelength is close to that of real X-ray radiation having a wavelength of the order of 1 nm or less. It has also been noted that the wavelength of the radiation generated with the described radiation sources is dependent on, inter alia, the medium used. For generating X-ray radiation, similar radiation sources, with similar problems as for generating EUV radiation may therefore be used. For this reason, the present invention may also be used to great advantage in X-ray sources and this invention also relates to these sources and apparatuses such as an X-ray microscope or an X-ray analysis apparatus, hence the use in the claims of the term extremely short-wave radiation which is understood to be EUV radiation and X-ray radiation. |
|
claims | 1. A process for the electrochemical dissolution of a metallic structure having a plurality of electrically conducting components, the process comprising utilising the structure as a sacrificial electrode in an electrochemical cell so as to dissolve at least a part of the structure, characterised in that, prior to use of the structure as a sacrificial electrode, molten metal is allowed to solidify about the structure so as electrically to connect together said components. 2. A process according to claim 1 in which the metallic structure is a spent nuclear fuel assembly. claim 1 3. A process according to claim 2 in which the molten metal is allowed to solidify about one end of the assembly and the assembly is then used as a sacrificial electrode with that end positioned uppermost and the other end extending into the cell electrolyte. claim 2 4. A process according to claim 2 in which the fuel assembly includes a plurality of pins each being coated with an oxide film. claim 2 5. A process according to claim 2 in which the fuel assembly includes a plurality of Zircaloy clad pins. claim 2 6. A process according to claim 1 in which the molten metal is stainless steel. claim 1 7. A process according to claim 6 in which the molten metal is at a temperature between 1350xc2x0 and 1420xc2x0 C. claim 6 8. A process according to claim 7 in which the molten metal is a temperature between 1375xc2x0 and 1395xc2x0 C. claim 7 9. A process according to claim 7 in which the molten metal is a temperature of the order of 1385xc2x0 C. claim 7 10. A process according to claim 1 in which the metallic structure is substantially fully immersed into the molten metal prior to solidification thereof. claim 1 11. A process according to claim 10 in which, after said full immersion, the molten metal is cooled at a rate of at least 100xc2x0 C. min xe2x88x921 . claim 10 |
|
description | The present invention relates to a method in processing, such as pharmaceutical processing. The invention also relates to a processing device, such as a pharmaceutical processing device, and to a use of a processing vessel, such as a pharmaceutical processing vessel, or of a pipe connected to such a vessel. The use of production lines with long pipe or piping structures is common in many industries, such as the pharmaceutical industry, the chemical industry, the food industry, etc. These pipe structures are generally used to convey materials to or from a vessel, or to convey materials between two vessels. For instance, in the production of pharmaceutical dosage forms, such as tablets or capsules, the ingredients are processed or conveyed in different processing structures. One processing structure may be a granulation vessel, another processing structure may be a drying vessel, yet another processing structure may be a pipe for leading materials or substances from the granulation vessel to the drying vessel. Also a system of several processing vessels and/or pipes can be regarded as a processing structure. In the production of pharmaceuticals it is desirable to reduce the risk of mixing materials from different batches or reduce the risk of leaving high-risk substances, such as high-potency drugs or chemically or microbiologically reactive materials, inside the processing structure. It is also desirable to detect any geometrical changes on the interior of the processing structure, such as damaged or disconnected portions of the processing structure, so that the personnel may take appropriate actions at an early stage. Apart from changes on the actual processing structure or its components, a geometrical change may also be a change in the amount of material inside the processing structure. In the present situation, the manufacturing personnel have to gain access to the interior of the processing structure in order to perform manual cleanness tests or a damage check. In some cases such tests may be difficult to execute, e.g. depending on the dimensions of the processing structure, the location of the processing structure, or even the location to be cleaned or inspected inside the processing structure. Also, by not knowing whether or not the processing structure is free from material remains, or if other geometrical changes have occurred, the personnel will tend to check the processing structure more often than necessary, resulting in unnecessary time loss and additional production costs. Thus, it would be desirable to detect any material remains from processes from different batches, or to detect other changes in the internal geometry of processing structures, in an easy and reliable manner. It would also be desirable to reduce possible time loss and production costs. An object of the present invention is to alleviate the drawbacks of the prevailing manual tests. This and other objects, which will become apparent in the following, are accomplished by the methods, the devices and the uses defined in the independent claims. The present invention is based on the insight that use may be made of an existing structure for determining the presence of material remains inside the structure or other changes in the internal geometry of the structure. By allowing an existing processing structure to act as part of a detection arrangement which conveys information which can be related to the geometry or environment inside the structure, the personnel does not have to open the structure to gain access to the inside in order to obtain the information. Thus, by using the existing processing structure as an information carrier the detection of any material remains or other geometrical changes may be performed substantially non-invasively and/or non-destructively. It should be noted that, in this application, the term “processing structure” includes not only vessels, dryers, mixers or the like in which a material is treated, but also includes any pipe or other tubular structure or container in a production line through which the material is transported or contained without being subjected to any particular treatment. Furthermore the term “processing structure” is not limited to mean only a single pipe or a single vessel, but can also be construed as a combination of pipes or vessels, or any other combination of these items. In other words, the term “processing structure” is herein used to include either a single item, such as a vessel or a pipe, or any combination of such items in a system configuration. The present invention is applicable in various types of industries, some non-exhaustive examples being the pharmaceutical industry, the chemical industry, the food industry, the metallurgical industry and the agricultural industry, however other alternative types of industries are also possible. Thus, it should be understood that the present invention is not limited to any particular field of processing or any particular processing device, however, for explanatory purposes and ease of understanding, the following description will mainly be related to the pharmaceutical industry. The terms “material”, “pharmaceutical material” or “pharmaceutical substance” are herein to be interpreted as including at least any one of the items from the group consisting of powders, powders in combination with water or other liquid, solids, solids in combination with water or other liquid, slurries, liquids and suspensions. It may also be a combination of said items. It should also be understood that pharmaceutical materials and is substances are not limited to meaning only one or more active components, but it may also mean one or more non-active components, generally referred to as excipients, or a combination of active and non-active components. The information related to the geometry inside the structure is suitably conveyed by means of a signal introduced into the processing structure, the signal being any detectable physical quantity or impulse by which information can be transmitted. Depending on the interior geometry of the structure, the presence or absence of objects, and the like, the signal may be affected in different ways. By analysing how signals are affected it is possible to determine whether or not the interior conditions of the processing structure has changed from one time to another. Thus, according to one aspect of the invention a method in processing, such as pharmaceutical processing is provided. The method comprises: providing materials, such as pharmaceutical materials, in a processing structure, such as a vessel or a pipe, or any combination of one or more vessels and/or pipes; removing materials from said processing structure; and thereafter transmitting at least one signal to be propagated in said processing structure, and, suitably, also guided by said processing structure; receiving the thus propagated signal; and comparing at least one parameter value of the received signal with a reference value to evaluate if there is any remaining material in the processing structure or any geometrical change in the processing structure. Similarly, according to a second aspect of the invention a processing device, such as a pharmaceutical processing device is provided. The device comprises a processing structure, such as a vessel or a pipe, or any combination of one or more vessels and/or pipes, for processing or transporting materials (e.g. pharmaceutical materials) in or through said processing structure; at least one transmitter for transmitting at least one signal to be propagated in said processing structure; at least one receiver for receiving the thus propagated signal; and an analysing unit, such as a computer or microprocessor, operatively connected to the receiver for determining a parameter related to the received signal. Suitably, the analysing unit may also be operatively connected to the transmitter. The information carrying signal may have different parameters. For instance, if the signal comprises a wave, it may be described by parameters such as phase, amplitude, power and frequency. The wave may be an electromagnetic wave or an acoustic wave which is propagated through the processing structure, wherein the phase, amplitude, power and/or the frequency of the wave will be differently affected depending on the presence or absence of pharmaceutical material or other geometrical changes inside the processing structure. Alternatively, the signal may comprise a combination of an electromagnetic wave and an acoustic wave. It should be noted that an acoustic wave (also referred to as pressure wave) does not necessarily mean that it constitutes an audible sound, but rather that it is a wave in which the propagated disturbance is a variation of pressure in a medium. Alternatively, the signal may be an electric current which may be affected by a changed resistance, capacitance, etc. due to changes in the interior of the processing structure. In such case, the processing structure may suitably be insulated. As mentioned previously, an electromagnetic wave may be used for conveying information related to the interior condition of the processing structure. Therefore, according to at least one embodiment of the invention said processing structure is used as a waveguide. Consequently, the embodiment comprises transmitting at least one electromagnetic wave to be propagated in said processing structure, receiving the thus propagated electromagnetic wave, and comparing at least one parameter value of the received electromagnetic wave with said reference value. According to at least one embodiment, the processing structure is made of metal or any other material which is suitable for guiding an electromagnetic wave. As previously, explained the parameter may e.g. be the amplitude, the power, the phase or the frequency of the wave. For instance, information regarding the interior condition of the processing structure may be obtained by comparing the detected value of the amplitude of the received signal with a reference or set amplitude value. Suitably, if the difference between the detected value and the reference value exceeds a predetermined difference it is considered indicative of a changed condition inside the processing structure. Said predetermined difference may either be zero or a non-zero value. In this context a changed condition means that the condition inside the processing structure at the time the signal was received is different from a condition at an earlier occasion. The changed condition may thus be a change in the amount of pharmaceutical material present in the processing structure, or a geometrical change in the wall due to damage. The changed condition may suitably be detected based on a changed dielectric constant or at least a change in either of its real part or imaginary part. For instance, if the processing structure is empty the dielectric constant for air is known, and if some pharmaceutical or other foreign material remains are present inside the processing structure the dielectric constant may be different, affecting the amplitude and/or the phase of the propagating signal. If it is established that there is a changed condition, the personnel may take appropriate measures, e.g. cleaning or repairing the processing structure, before it is brought into use again. If it is established that there is no changed condition, the personnel does not need to spend time on accessing the interior of the processing structure. Any interruption of the process or other general control of the process, e.g. if a changed condition has been detected which calls for some kind of action being taken, may be performed manually or automatically. Therefore, in general terms at least one embodiment of the invention comprises controlling the process on basis, at least partly, of the detected parameter or parameter value. The act of controlling the process may e.g. comprise at least the act of stopping the process. However, if the obtained parameter or parameter value does not require any action to be taken, the act of controlling the process may e.g. comprise at least the act of continuing the process or provide new material to be treated, etc. This control is suitably performed automatically, for instance by an analysing and control unit mentioned below. The controlling may follow a flow chart having a feedback-loop or some other general type of controlling scheme. The controlled process may be a batch process, wherein one batch of material at a time is processed, or a continuous process wherein material is processed continuously. Suitably, in connection with a continuous process, the acts of transmitting a signal, receiving the signal and evaluating the information are performed continuously for monitoring the progress of the process. However, these acts may also be performed continuously within one batch process. Note that the term “continuously”, may include measurements at several discrete moments, however at substantially steady intervals or a certain repetition frequency rather than at random. An integrated parameter value of the signal over time may be used as a reference value in a continuous measurement. Apart from the above mentioned acts of controlling, an act of controlling the process may include performing repair work. The reference parameter value is suitably determined before pharmaceutical material is introduced into the processing structure, i.e. in a clean condition or state of the processing structure. Transmission and reception of one or more signals is performed in such a clean state in a corresponding manner to the subsequent transmission and reception when establishing any changed condition of the processing structure. Thus, by transmitting into the “clean” processing structure a signal having one or more specified parameter values and receiving the thus propagated signal and determining the value of the parameter or parameters, an initial response is obtained and a calibration is achieved. When pharmaceutical materials are later introduced and removed, a change from the calibrated state may be detected, suitably by transmitting a signal having the same parameter values as signal transmitted at the time of calibration. If the received signal differs from the initial response it is indicative of a change inside the processing structure, such as remaining pharmaceutical particles or alternatively some other geometrical change such as a damaged wall. An alternative for setting the reference value, is to make theoretical mathematical calculations. Another alternative is to perform simulations, e.g. computer simulations, in order to determine a reference value for a “clean” processing structure. Yet another alternative, as will be described below, is the case wherein it is desired to calibrate for a non-zero amount, such as a predetermined filling level. Thus, in a general sense, the calibration may be expressed as determining the reference value by transmitting at least one signal to be propagated in said processing structure when a known amount, such as a zero or non-zero amount, of pharmaceutical material is present in processing structure, receiving the thus propagated signal, and determining the value of at least one parameter related to the received signal. The information conveyed by the existing processing structure may be contained in an applied microwave radiation. According to at least one embodiment of the invention said signal comprises at least one electromagnetic wave, wherein said electromagnetic wave has a frequency in the range of 100 MHz to 3 THz, e.g. in the form of a microwave frequency in the range of 300 MHz to 300 GHz. In a pharmaceutical production line, the dimensions of the tubular structures and vessels are generally in the order of microwave wavelengths, is the microwave region being known to use components comparable in size to their wavelengths. Microwave radiation has a good penetrating capacity compared to other types of radiation, e.g. NIR. Even though microwaves penetrate pharmaceutical powder, they are affected and become distorted, e.g. changed amplitude or phase, thereby making detection possible. Microwaves can be controlled to fill out the entire cavity into which they are introduced, i.e. the microwaves are able to reach corners and other small spaces. It should be noted that the use of microwaves functions for processing structures having circular profile or cross-section, as well as for processing structures having rectangular profile or cross-section. If the entire processing structure does not have a single continuous cross-section, the processing structure may for calculations be considered as consisting of several sections of different profiles or cross-sections. For a processing structure in the form of a pipe having a circular profile with diameter d the wavelength λ of the microwave signal used may suitably be selected in the region of approximately 1.3d≦λ≦1.7d in order to obtain a single mode electromagnetic propagation. The single mode propagation provides predictability and repeatability of the measurements in the system. The system could utilise higher order propagation modes, generated when using λ<1.3d, even though this may decrease the sensitivity to system changes and reduce the performance predictability, due to the mutual interference of the coexisting propagation modes. In the case of rectangular pipe profiles having dimensions a·b the wavelength suitably used will lie in the interval a≦λ≦2a, where we assume that a>b. The hereby obtainable single mode propagation will again provide a good sensitivity and measurement repeatability. In the case of a=b (wherein a≦λ≦2a) or λ<a higher order propagation modes will appear having similar consequences as in the circular case with higher order propagation modes. If the processing structure is in the form of a production vessel, the selection of which frequency or frequencies to be used could be performed using simulations, since the more complex electromagnetic environment may require a more specific and situation adjusted selection of frequency or frequencies. In summary the applicability of the suggested approach is not limited by which frequency or frequencies (wavelength(s)) will be selected, but could be improved in terms of performance and predictability if such adjustments/considerations taking into account the is particular system set-up are used. It should be noted that even though the application mainly describes using a signal of at least one wavelength, the invention and its aspects and embodiments are not limited to using only a single wavelength or frequency. Thus, the invention also encompasses transmitting signals to be propagated in the processing structure in the form of a plurality of electromagnetic waves of a plurality of frequencies. In other words several information carrier signals may be used within the scope of the invention. According to at least one embodiment of the invention a transmission mode or a reflection mode of operation is used, or even a combination of said modes of operation. In the transmission mode the signal, suitably in the form of an electromagnetic wave, travels from a first location of the processing structure where it was transmitted to a second location of the processing structure. For instance, the two locations may be at two opposite sides of the processing structure. However, other alternatives are also possible. During its propagation from the first location to the second location, the signal may become affected by the geometry or the presence of any material inside the processing structure. This may result in a distortion of the signal which may be detected at the second location. In the reflectance mode, the propagated signal is reflected when reaching an inner surface of the processing structure before being received. The reflected signal is suitably received at the same location as the one from which it was transmitted. This may be realised by first using an antenna for transmitting the signal and then using the same antenna for receiving the reflected signal. Alternatively, or as a complement, another antenna at another location may receive the reflected signal. According to at least one embodiment of the invention said at least one transmitted signal, suitably comprising at least one electromagnetic wave, is received at two or more locations, advantageously by means of two or more receivers, such as receiving antennas, at their respective location. The signal or signals may either be transmitted from a single transmitter, such as a transmitting antenna, or alternatively by at least two transmitters. If several transmitters are used, each one of them may have an associated receiver. By arranging the transmitter/receiver pairs at different designated locations and studying their respective responses, it may be possible to detect in which area inside the processing structure pharmaceutical material remains are present. Another advantage of using several transmitters and receivers is that it becomes easier to detect smaller objects, e.g. small particles, in particular if the measurements are to be performed over a long distance. Therefore, depending on the area or areas in which it is desired to make measurements, and the desired detectable object size, it may be decided how many transmitters and receivers should be used. Instead of covering irrelevant areas where it is known that material does not generally remain, the sensors (transmitters/receivers) may be placed at areas which are more likely to present detectable material remains. If desired, the sensors may be identifiable or differentiated by different methods, e.g. a unique frequency being associated with each transmitter or each transmitter using a unique signal encoding, or any other suitable multiple access method. It is also conceivable to use only one transmitter which emits signals in a decided frequency band, e.g. comprising the microwave frequency region, and several receivers arranged to detect a respective frequency sub-band. Alternatively, or as a complement to having transmitters and receivers at different locations, an array of receivers and/or transmitters may be provided on a common module. Such transmitter/receiver arrays may be provided in one-dimensional format, wherein the transmitters and/or receivers are arranged along a line, or in a two-dimensional format, wherein the transmitters and/or receivers are arranged in a rectangular matrix. Other formats are also possible. This type of array provided as a module may either be regarded as a large antenna made up of several sub-antennas, or each transmitter and/or receiver on the module may be regarded as a plurality of stand-alone antennas. Said plurality of antennas may therefore be regarded as located at essentially the same location relative to the processing structure or possibly as located at “different” locations but only separated by a relatively short distance. It should also be understood that several arrays may be used simultaneously for measurement on a processing structure. According to at least one embodiment of the invention one or more reflectors may be located in the propagation path of the transmitted signal in order to at least partially block the propagation of the transmitted signal and at least partially reflect the transmitted signal. The use of reflectors may enable a larger amount of different measurements to be made. For instance, by positioning a reflector in the signal propagation path inside the processing structure the signal will be partially reflected and suitably received at the same side of the reflector, thereby obtaining one possible measurement mode, and by removing the reflector allowing the signal to be propagated along its path and received at a location further away another measurement mode is made possible. Also, if the reflector is at least partially transparent to the signal, the reflected part of the signal may be received on one side of the reflector while the transmitted part of the signal may be received on the other side of the reflector. It is also conceivable to use a reflector for which it is possible to vary how much of the signal is to be reflected, for instance by varying the effective blocking area of the reflector. The person skilled in the art will understand that by varying the number of reflectors used or the location of the one or more reflectors further information regarding e.g. material remains may be obtained. In particular, by using reflectors it may facilitate the finding of the approximate location of such material remains. The reflectors may be used for at least partially closing or sealing off at least one portion of the processing structure. Thus, according to at least one embodiment of the invention the reflectors may be in the form of one or more closure or sealing elements, such as valves, sliding gates or the like. By closing off the processing structure a limited space may be obtained for measurements. This may for example be used for determining the approximate location of material remains or damages in the processing structure. Thus, by sealing off different portions and performing measurements therein, it can be determined in which sub-space or sub-spaces of the processing structure any change has occurred when compared to a reference state of the sub-space or sub-spaces. However, as previously mentioned, the reflector does not necessarily have to completely block the propagation of the signals, the same principle with sub-spaces being applicable also with partly transparent reflectors. The reflectors in the form of closure or sealing elements may be already existing valves in the processing structure. The valves may be open when material is transported therethrough and may be closed before performing a measurement for checking whether there is any material remains left. Alternatively, it is contemplated that additional reflectors may be applied to existing processing structures, e.g. if it is desirable to obtain more or smaller sub-spaces for facilitating the locating of the intrusion in the form of e.g. material remains or other interior geometrical changes. Furthermore, the use of reflectors allows a single unit or a small number of transmitters and receivers to be used for the measurements in a processing structure. For instance, if a unit which is located at one end of a processing structure is used as both transmitter and receiver, reflectors may be activated in a certain order for performing reflectance mode measurements in different sub-spaces. Thus, a signal may be transmitted towards a first reflector which reflects the signal at least partially, and the received reflected signal being compared with a reference. Afterwards, that reflector is opened or inactivated and another reflector further away or nearer to the transmitter/receiver unit is activated before performing a new measurement, etc. In this way it is possible to find an approximate location of e.g. material remains by checking which measurement indicated possible presence of material remains and which measurement did not indicate presence. Also, a first processing structure in the form of a pipe, could be used to couple electromagnetic energy into a second processing structure, such as a bigger processing vessel. An advantage of this is that probes already present on the first processing structure may be used for obtaining information about the state inside the second processing structure. Thus, the first processing structure may be regarded as a transmitter and/or receiver antenna per se. It should be noted that even though the description has been focused on measurements performed on one processing structure in a production line, the inventive methods may be used at several processing structures. Thus, there may be a pair of or an array of transmitters and receivers arranged e.g. at a granulation vessel, another pair or array at a drying vessel, and yet another pair or array at a pipe connecting the two vessels. Alternatively, there may be a pair of one transmitter in a first processing structure and one receiver in a second processing structure. The receivers, and suitably also the transmitters, at each processing structure may be operatively connected to a single common analysing unit, such as a computer or microprocessor. Alternatively, each processing structure may have its own designated analysing unit. Thus, from the above it should be clear that the present invention contemplates the use of a transmitter and receiver placed at different locations or at the same location (e.g. as one unit). The invention also contemplates the use of a single or multiple transmitters and receivers, with a possibility to set them in an array along the production system. For implementing at least one embodiment of the invention, the one or more transmitters and receivers may be arranged exteriorly of the processing structure. In such case, the processing structure may suitably be provided with a window or some other wall portion which is at least partly transparent to the transmitted signal, thereby enabling the transmitted signal to be entered into the processing structure, and also enabling the propagated signal to exit the processing structure for detection by the one or more receivers. Alternatively, a portion of the wall may be openable for enabling one or more transmitters and/or receivers to be introduced as probes into the processing structure. The probes may suitably be introduced automatically e.g. after pharmaceutical material has been removed from the processing structure. It has been described above to use a processing structure as a waveguide for implementing the invention. The processing structure may e.g. be an already existing part of a processing system. However, it is also conceivable to do it the other way around, i.e. to incorporate a waveguide into the processing system, even though the waveguide in some cases is obtainable from other suppliers than the other parts of the system. Once incorporated, the waveguide may be used as a processing structure for receiving, containing, transporting and/or treating pharmaceutical materials. This implementation is encompassed by a third aspect of the invention. Thus, according to the third aspect of the invention a method in processing, such as pharmaceutical processing is provided. The method comprises providing a waveguide configured and dimensioned for directing the propagation of electromagnetic waves, such as microwaves; providing materials in said waveguide; processing or transporting the materials in or through said waveguide; removing materials from said waveguide; transmitting at least one signal, in the form of an electromagnetic wave, to be propagated in said waveguide; receiving the thus propagated electromagnetic wave; and using at least one parameter related to the received electromagnetic wave to evaluate if there is any remaining material in the waveguide or any geometrical change in the waveguide. Corresponding to the method according to the third aspect of the invention, a processing device, such as a pharmaceutical processing device is provided in accordance with a fourth aspect of the invention. Said device comprises a waveguide configured and dimensioned for directing the propagation of electromagnetic waves, such as microwaves, wherein the waveguide, comprises an inlet for introducing materials into the waveguide and an outlet, preferably separate from the inlet, for removing materials from the waveguide. Even though the inlet will generally be separate from the outlet, it is also conceivable that the same port is used as both inlet and outlet. Said device further comprises at least one transmitter for transmitting at least one signal, in the form of an electromagnetic wave, to be propagated in said waveguide and at least one receiver for receiving the thus propagated electromagnetic wave, and said device also comprises an analysing unit, such as a computer or microprocessor, operatively connected to the receiver for determining a parameter related to the received electromagnetic wave. The analysing unit may either provide visual or audible information to the personnel, so that a decision may be made whether any action should be taken in the processing structure, e.g. for repairing the processing structure or for cleaning the processing structure from material, or on the contrary for adding more material as will be described below. Some actions may be taken automatically without necessarily informing the personnel, e.g. if after a batch has been removed and no material remains are detected a valve controlled by the analysing unit may be opened for allowing a new batch to enter the processing structure. It should be understood that the third and fourth aspects of the invention encompass any embodiments or any features described in connection with the first and second aspects of the invention, as long as those embodiments or features are compatible with the use of the waveguide of the third and fourth aspects. It should be understood that a waveguide controls the propagation of an electromagnetic wave so that the wave is forced to follow a path defined by the physical structure of the guide. A waveguide of a given dimension will not propagate electromagnetic waves lower than a certain frequency (the cutoff frequency). At least some of the aspects and embodiments of the present invention utilises the processing structure as a guiding means for guiding the electromagnetic wave along the processing structure. The above described aspects of the invention and the different embodiments thereof have mainly been described in relation to detecting material remains, such as pharmaceutical material remains, after removal of material from the processing structure, or detecting other interior geometrical changes such as a damaged, loose or disconnected portion of the processing structure. However, an internal geometrical change may also be a change in the amount of material from one time to another. For instance, when it comes to detecting material remains, the amount is zero before any material is introduced into the processing structure. After the material is attempted to be removed, any remains will be a non-zero amount. In another situation it may be desirable to fill the processing structure with material up to a predetermined level, i.e. a predetermined amount. After some filling, the measurements may indicate that the level has not yet been reached, i.e. the measured amount is not equal to the predetermined amount. Therefore, further filling, suitably automatically, may be performed by means of the analysing unit which may be operatively connected to a material supply source for controlling the adding of more material. A new measurement is then made to detect if there has been an interior geometrical change, i.e. if the desired predetermined amount has been reached. Thus, the detection of this type of internal geometrical change, which not only relates to structural changes, but also to a change in contents or amount, is also encompassed by the previously mentioned aspects of the invention. Furthermore, all the above types of detection are encompassed by a fifth aspect of the invention. In accordance with the fifth aspect of the invention a method in processing, such as pharmaceutical processing is provided. The method comprises providing a processing structure, such as a vessel, a pipe or a combination thereof such as a combination of one or more vessels and/or pipes, which is adapted to receive materials (e.g. pharmaceutical materials). The processing structure is used as a waveguide by transmitting at least one signal in the form of at least one electromagnetic wave to be propagated along and guided by the processing structure. The thus propagated electromagnetic wave is received, wherein at least one parameter value of the received electromagnetic wave is compared with a reference value related to a reference state of the interior of the processing structure. Based on the comparison of said values, it is evaluated whether the present state of the interior of the processing structure is different from said reference state. It should be noted that the term “present state” is meant to be interpreted as the state at the point of time when the propagated signal was received and measured. It should therefore not be limited to the state of the processing structure at the exact time when the evaluation or interpretation of the signal is performed which could be at a later stage. As described above it may be desirable to detect a change in the amount of material inside the processing structure. Thus, according to at least one embodiment of the invention the reference state and the present state may be related to material content in the processing structure, wherein the processing structure contains a first amount of materials in the reference state and a second amount of materials in the present state. Therefore, said at least one embodiment comprises evaluating whether said second amount is different from said first amount. As mentioned above the first amount may be a zero (empty processing structure) or non-zero amount, and likewise the second amount may be a zero or non-zero amount (in the non-zero cases it is assumed that any material property changes are negligible). If the reference state is a state in which a predetermined non-zero amount of material is present in the processing structure, the personnel may measure the present state e.g. to ensure that the actual amount stays below the predetermined amount, or to ensure that it reaches the predetermined amount, or to ensure that it exceeds the predetermined amount. This could be achieved by using several additional predetermined reference states apart from a desired reference state. The additional reference states will indicate the presence of higher or lower levels of material compared to the desired reference state. Thus, according to at least one embodiment of the invention, the method further comprises changing, such as by adding or removing, the amount of material inside the processing structure, based on the evaluation of whether the second amount is different from the first amount. This may suitably be accomplished automatically, by means of a feedback or control system. It should be noted that apart from what has been described above, the fifth aspect of the invention encompasses any embodiments or any features described in connection with the previously described aspects of the invention, as long as those embodiments or features are compatible with the use of the processing structure as a waveguide. Furthermore, the insight of using an existing processing structure as a waveguide is set forth in accordance with a sixth aspect of the invention, which provides a use of a processing vessel (e.g. a pharmaceutical processing vessel), or a pipe connected to such a vessel, as a waveguide for detecting the presence of material (e.g. pharmaceutical material). Similarly in accordance with a seventh aspect of the invention there is provided a use of a processing vessel (e.g. a pharmaceutical processing vessel), or a pipe connected to such a vessel, as a waveguide for detecting a change over time in the amount of material (e.g. pharmaceutical material) therein. Thus, by using the processing structure as waveguide it is possible to make a measurement at a first point of time, suitably in accordance with the above described methods, and another measurement at a second point in time, and comparing the responses in order to determine whether the amount has changed between the measurements. An additional way of using a processing structure (e.g. pipe or vessel) as a microwave guiding device is by employing a resonance mode of operation. A microwave resonator can be defined as section of a transmission line bound by impedance discontinuities (impedance transition borders). In the case of pipe structure, the discontinuities could be formed at both ends of the pipe. They could be open circuit—transition from a waveguide structure to air (e.g. open valves) or a short-circuit—transition in a waveguide structure closed by metal plate (e.g. closed valves). In the case of vessel structure the whole structure itself can be regarded as a hollow resonator. The field inside the resonator is excited by coupling of a transmitter/receiver system in ways similar to the above or below discussed cases. Resonance will occur if the excited field is in-phase with the one reflected at the impedance transition borders. The conditions for that are varying depending on the discontinuities types (air, metal etc.), on the type of resonance structure used (waveguide, coaxial etc.), its dimensions and on the frequency used, but generally speaking the phase difference between the input and the reflected energy should be n×2π for the effective wavelength of the propagated energy (n is an integer number). The parameters associated with resonances are the resonant frequency and/or the Q-factor (the ratio of the energy stored in the resonator to the energy dissipated during 1 cycle). In accordance with the applications of the invention, the frequency used for a resonance to occur is adjusted. Measurements of the change of the resonant frequency and/or the Q-factor with respect to the initially established reference state may be used to indicate presence of material remains or changes of other character. For example, in the cases of material remains determination, reaching the predetermined reference value of the resonance frequency and/or the Q-factor will indicate that the predetermined state (empty structure) has been reached. Similarly, when a presence of certain amount of material is the reference state, reaching the predetermined resonance frequency/Q-factor will indicate its achievement. An advantage of using a resonance mode of operation is that it may be performed by using a single transmitter/receiving unit. Another advantage is the high sensitivity to changes in the environment in the measured structure. However, if desired the use of several units is a possible alternative. Apart from enabling detection of e.g. material remains after a process has been performed in a processing structure, the invention may also be implemented for continuous monitoring of a process. Thus, according to an eighth aspect of the present invention there is provided a method of monitoring a process of transporting an amount of material through a processing structure (e.g. a pharmaceutical processing structure) such as a vessel, a pipe or a combination thereof such as a combination of one or more pipes and/or vessels. This method of monitoring transportation of an amount of material comprises using the processing structure as a waveguide by repeatedly or continuously transmitting signals in the form of electromagnetic waves to be propagated along and guided by the processing structure, receiving the thus propagated electromagnetic waves, and comparing at least one parameter value of the received electromagnetic waves with a reference value that is indicative of a reference state of the interior of the processing structure before said amount of material has been introduced into the processing structure. When said amount of material is introduced into the processing structure said parameter value will become different from said reference value and when said amount of material has been transported through and out of the processing structure said parameter value will return to substantially correspond to said reference value. Thus, by noticing how the response changes during the monitoring it is possible to see when material has been, or is being, added to the processing structure as well as when material has been, or is being, removed from the processing structure. Even though it may be practical to use an empty processing structure as a reference level, a partly filled processing structure could also be conceivable. The latter case may be used e.g. for monitoring whether a substantially even amount of material is flowing through the processing structure, wherein a change in the response indicates if there has been an increase or a decrease in the material flow. It should be noted that apart from what has been described above, the eighth aspect of the invention encompasses any embodiments or any features described in connection with the previously described aspects of the invention, as long as those embodiments or features are compatible with the use of the processing structure as a waveguide. In the following a number of non-limiting embodiments of the present invention will be given with reference to the accompanying drawings. FIG. 1a and FIG. 1b illustrate schematically an underlying principle of at least one embodiment of the invention, wherein it is illustrated how different dielectric constants affect an electromagnetic power flow through a processing structure (pipe) or waveguide 10. The waveguide 10 has a rectangular profile in these figures, however, the corresponding principle applies also to other profiles. The waveguide 10 illustrated in FIG. 1a is empty, i.e. the only dielectric medium inside the waveguide 10 is air. Electromagnetic energy, e.g. microwave energy, is transmitted into the waveguide 10 through an input end 12 thereof. We assume ideal coupling of the electromagnetic energy at the input end 12 and a single mode of propagation. The distribution of the electromagnetic power flow through the waveguide 10 is indicated by the different shades of a grey scale representative of the power intensity, wherein white is high intensity and black is low or no intensity. As can be seen from FIG. 1a, the propagated electromagnetic wave has not lost any power when it reaches the other end 14 of the waveguide, seen from the figure by the same power intensity. The power flow distribution is almost constant throughout the waveguide 10. In FIG. 1b the illustrated waveguide 10 contains a small amount of pharmaceutical material 16, such as e.g. powder, that has a dielectric constant which is different from that of air. The pharmaceutical material 16 is located near the input end of the waveguide 10 as indicated by the contour on the side of the waveguide 10. Due to the dielectric constant of the pharmaceutical material 16 an electromagnetic wave transmitted through the input end will be affected differently than if only air would have been present inside the waveguide 10. As illustrated in FIG. 1b there is a substantial power loss as the electromagnetic wave propagates through the pharmaceutical material 16 (illustrated by the bright shade quickly transforming into a darker shade along the pharmaceutical material 16), and there is a clear difference between the electromagnetic power flow in the waveguides of FIG. 1a and FIG. 1b. This detectable difference at the output 14 or anywhere along the waveguide may be used for detecting the presence of material remains. Also, it should be understood that this principle of detectable difference may also be used e.g. for establishing the amount of material present in a processing structure, such as a vessel. The attenuation of the propagating electromagnetic energy may be regarded as substantially proportional to the amount of material that it propagates through. Therefore, let us assume that a processing structure, such as a vessel, e.g. a granulation vessel, is to be filled with a certain amount of material, wherein said amount is expected to attenuate 50% of the power of the electromagnetic energy that is propagated through the material (here, for simplicity, field distribution effects are neglected). If, after an initial supply of material into the processing structure, it is detected that the power of the electromagnetic energy that has propagated through the material is higher than 50% of the transmitted power, the interpretation would be that said certain amount of material has not yet been reached. Thus, it should be clear from above that even though FIG. 1a and FIG. 1b show a waveguide 10 or a processing structure in the form of a pipe, the principle is also usable in other processing structures, such as vessels or portions thereof. Also, an acoustic wave or any other signal which is differently affected by air and other materials may be used for detecting the presence of material remains or the amount of material. Furthermore, any damage or disconnected portion of a processing structure may also cause a different attenuation to the electromagnetic energy power compared with an intact processing structure. In this connection it should be understood that the invention may also be used for detecting whether two processing structures have become at least partly disconnected. FIG. 2 illustrates schematically parts of a pharmaceutical processing system 20 in which at least one embodiment of the present invention has been implemented. One of the shown parts of the pharmaceutical processing system 20 is a granulation vessel 22 in which an active ingredient is mixed with a filler and a binding substance, such as water. Another part is a drying vessel 24 in which the mixed pharmaceutical materials are dried to obtain a desired low water content. A connecting part in the form of a pipe 26 allows the mixed material in the granulation vessel 22 to be transferred to the drying vessel 24. The granulation vessel 22 has one or more inlets (not shown) for receiving the material to be mixed, and has also an outlet 28 from which the mixed material may enter into the pipe 26. Similarly, the drying vessel 24 has an inlet 30 connected to the pipe 26 for receiving the mixed materials, and one or more outlets (not shown) for outputting the sufficiently dried materials for further processing. The outlet 28 of the granulation vessel 22 is arranged on a vertically higher level than the inlet 30 of the drying vessel 24, thereby allowing the gravitation to act on the mixed materials for transporting it through the inclined pipe 26, however other arrangements for promoting transport through the pipe may also be provided. There are two sensors or probes 32, 34 provided on the pipe 26, in this embodiment comprising antennas for transmitting and/or receiving electromagnetic radiation, suitably in the form of microwaves. However, in other embodiments they could be acoustic probes. The antennas 32, 34 may be insertable through the wall of the pipe 26 or be arranged to transmit and receive electromagnetic radiation outside the pipe 26 through a window which is at least partly transparent to electromagnetic radiation. A first valve 36 is provided at the outlet 28 of the granulation vessel 22 and a second valve 38 is provided at the inlet 30 of the drying vessel 24. One function of the valves 36, 38 is to control the material flow. For instance, before the materials in the granulation vessel 22 have been mixed to a desired degree at least the first valve 36 is closed so as to prevent material from leaving the granulation vessel 22. Another function of the valves 36, 38 is to delimit a space for facilitating electromagnetic radiation measurements and to act as a reflector which reflects the propagating electromagnetic waves. The use of the valves as reflectors allows a single unit to function as both transmitter and receiver. Also if the system is suitably adjusted and there is a disturbance (e.g. material remains), the signal will be more attenuated since it will pass the disturbance twice or more and there will therefore be a greater detectable difference to a reference signal. Furthermore, a resonance mode may be used, as has been described previously herein. Also, in accordance with at least one embodiment of the invention an analysing unit 40 is connected at least to one of the antennas 32, 34 which receives the propagated electromagnetic wave. A parameter value, such as amplitude or phase is compared with a reference value of that parameter in order to determine the state of the pipe 26, e.g. whether there are any material remains after material has been allowed to flow into the drying vessel 24 from the pipe 26. However, as illustrated in FIG. 2, the analysing unit 40 may also be operatively connected to the other components, i.e. the other antenna and the valves 36, 38, and will in the following therefore be generally referred to as an analysing and control unit 40. The analysing and control unit 40 is herein illustrated with wires 42 connected to the different components. However, the control unit 40 may also be operatively connected to said components by other means, e.g. radio control or coaxial lines wherein the microwaves are conducted all the way to the analysing and control unit 40. In at least one mode of operation, the sufficiently mixed materials are passed from the granulation vessel 22 through the pipe 26 and into the drying vessel 24. Thereafter, a command signal may be sent from the analysing and control unit 40 to close the valves 36, 38, or the valves 36, 38 may be manually closed. Next, the analysing and control unit 40 activates one of the antennas 32, 34 to transmit electromagnetic radiation in the form of one or more electromagnetic waves which will propagate inside the pipe 26 and will be received by the other antenna. The analysing and control unit 40 will analyse the contents of the received electromagnetic wave, e.g. by comparing the amplitude of the wave with the expected amplitude response for an empty pipe 26. If there is a difference which is indicative of there being remaining pharmaceutical material in the pipe 26 or that the pipe 26 has been damaged or disconnected, the analysing and control unit 40 will alert the personnel so that appropriate action may be taken (e.g. cleaning or repairing). However, if the evaluation performed by the analysing and control unit 40 indicates that the pipe is sufficiently clean, the analysing and control unit 40 may open the valves 36, 38 once new materials have been satisfactorily mixed in the granulation vessel 22. It should be noted that the valves 36, 38 in FIG. 2 do not necessarily have to be closed when transmitting the electromagnetic radiation. The measurements may still provide satisfactorily distinguishable information. Thus, during the propagation of the electromagnetic wave inside the pipe both valves 36, 38 could be open, or one of the valves could be open while the other one is closed. It should also be noted that either one of the two antennas 32, 34 may act as a receiving and/or transmitting antenna. Thus, it need not necessarily be the case that one transmits and the other one receives. It could very well be the case that only one antenna is used, e.g. antenna 32, and that said antenna both transmits and receives the electromagnetic wave. Alternatively, both antennas 32, 34 could transmit simultaneously and also receive the electromagnetic waves. Another alternative is that one of the antennas, e.g. antenna 32, acts as a transmitting and receiving antenna while the other antenna 34 acts only as a transmitting antenna or only as a receiving antenna. The locations of the antennas 32, 34 may be chosen from general electromagnetic considerations for constructive interference. For taking advantage of the reflecting function of the valves or similar reflectors, it has e.g. been found suitable to locate the antennas at a distance of nλ/4 from the valves, wherein n is an odd positive number (n=1, 3, 5, . . . ). The frequency or frequencies used may be chosen depending on the geometry of the pipe 26. It should also be noted that even though FIG. 2 illustrates only two antennas 32, 34, another number of antennas may be provided. For instance, there may be provided a single antenna working in reflection mode (the valves suitably being closed), or there may be provided more than two antennas, e.g. in several groups or arrays. FIG. 3 illustrates schematically a processing structure in which at least another embodiment of the present invention has been implemented. The processing structure is in the form of a long pipe 50 or a system of several pipes connected together. If several pipes are connected together, they may include a pipe having a larger diameter connected to a pipe having a smaller diameter, or the pipes may have equal diameters. The pipe 50 may be some type of connecting pipe similar to the one shown in FIG. 2 or some other type of supply or discharge pipe in a pharmaceutical processing system. Even though no analysing or control unit is illustrated in FIG. 3, such a unit may suitably be provided. Due to the length of the winding pipe 50 several antennas may be provided. In the illustrated embodiment there are provided four antennas 52, 54, 56, 58. The antennas may act as transmitters and/or receivers in any combination. There is also provided a first valve 60 at one end of the pipe 50, a second valve 62 at the other end of the pipe 50 and a third valve 64 halfway along the pipe 50. The valves 60, 62, 64, which may be opened and closed, act as reflectors in their closed position, wherein an incident electromagnetic wave will be at least partly reflected by the closed valve (some transmission may be allowed). The measurements may be performed with all the valves 60, 62, 64 closed, or all open, or with one or two open. By combining measurements at the different antennas 52, 54, 56, 58, it is possible to approximate the location of where remaining pharmaceutical material or a damage may be present. By closing the third valve 64, it would be possible to determine on which side of the valve 64 remaining material may be present. It would also be possible to use only one of the antennas, e.g. antenna 52, as a transmitter and receiver and while the illustrated valves 60, 62, 64 or more valves are closed sequentially so that measurements in several sub-spaces of the pipe 50 may be performed in order to find the approximate location of an intrusion in the form of remaining material or other geometrical change in the pipe 50 such as a damaged wall portion. The person skilled in the art will realize that there are several other ways and variations of using the antennas 52, 54, 56, 58 and valves 60, 62, 64 for finding the approximate location of any remaining material. Also, it would be conceivable to arrange a vessel instead of a pipe portion between e.g. valves 62 and 64 with all previously described combination of measurement possibilities. Thus, e.g. antenna 52 could be used as a transmitter and an antenna (corresponding to 56 or 58) on a vessel arranged after valve 64 could be used as a receiver. FIG. 4 illustrates another processing structure 70 in which at least yet another embodiment of the present invention has been implemented. The processing structure 70 defines a contained space. The below described conducted measurements could be applicable to any type of pharmaceutical production vessel, but in this figure it is intended to illustrate measurements in a granulation vessel 70. On the wall of the vessel 70 there are provided two probes comprising antennas 72, 74, however, there may be another number. One of the antennas, e.g. antenna 72, may be a transmitter while the other antenna 74 may be a receiver, or alternatively one or both of the antennas 72, 74 may act both as transmitter and receiver. The choice of frequency and antenna location is determined by employing general electromagnetic theory. FIG. 4 also illustrates two supply sources 76, 78 from which different pharmaceutical materials may be feed into the production vessel through respective supply lines 80, 82. An analysing and control unit 84 is operatively connected, e.g. by means of wires 86 or radio control, to both the supply sources 76, 78 and the antennas 72, 74. Based on the information contained in the received electromagnetic wave(s), the analysing and control unit 84 may control the supply sources to feed more material into the vessel 70 until the received electromagnetic wave has appropriate parameter value(s) when compared to one or more corresponding reference values. The analysing and control unit 84 may also be used in an operating mode for detecting whether there is any material left in the vessel 70 after material has been discharged therefrom. It should be noted that the set-ups in FIG. 2, FIG. 3 and FIG. 4 may be used in any combination with each other or with other set-ups. For instance, in the illustrated set-up of the system parts in FIG. 2 the granulation vessel 22 could also be provided with probes 72, 74 as illustrated in FIG. 4, wherein those probes could be operatively connected to a specific analysing and control unit 84 or to the same unit 40 as the probes 32, 34 in FIG. 2. Furthermore, the drying vessel 24 in FIG. 2 may also be fitted with probes so as to enable the detection of any remaining pharmaceutical material after discharge, the detection of whether a filling level has been achieved or whether any damage has occurred on the drying vessel 24, etc. Thus, probes may be present on both a production vessel and a on pipe to such a vessel. Furthermore, the invention may be implemented on other types of pharmaceutical processing devices than those illustrated in the figures. It should also be understood that the invention may be implemented in different types of pharmaceutical processes. For instance, the invention may be implemented in both a batch process and/or a continuous process. |
|
abstract | The invention relates to a beam allocation apparatus (21) for medical particle accelerators and also to a beam allocation method. This beam allocation apparatus (21) should manage a plurality of control rooms (8-12) for different treatment rooms and for quality assurance rooms and control rooms for the particle accelerator (1) and co-ordinate the assignment of beam sovereignty. For the purpose, the beam allocation apparatus (21) has an arbitration unit (26) having switching logic (27) and monitoring unit (28) and also a sequence control (29). The latter are provided, by way of signal lines (30), with a spill abort system (31) for aborting ion beam irradiation within micro-seconds. For the purpose, the spill abort system (31) has at least one spill abort magnet (32). For the purpose, the beam allocation apparatus (21) provides direct access from one of the control room (8-12) of the irradiation-active treatment room for aborting the particle beam within micro-seconds. |
|
summary | ||
047568526 | summary | BACKGROUND OF THE INVENTION This invention relates to systems for storing nuclear waste material and, more particularly, to apparatus for venting nuclear waste storage containers in a manner that allows gases generated by the stored waste material to escape, while simultaneously minimizing the intrusion of water. One of the pressing problems currently facing society is the storage and disposal of nuclear waste. Given the magnitude and prolonged duration of the dangers inherent in storing nuclear waste, storage systems must satisfy exacting criteria over long periods of time. Thus, nuclear waste is generally stored in an impervious system specially designed for the application. A typical constraint on the design of such a system is that the waste must be contained, without leakage, for a period of 300 years. Development of a suitable storage system is further complicated by the variety of potential storage locations employed. For example, is frequently stored at the generation site initially. During this time, the storage container is accessible to personnel working at the site, making it susceptible to tampering or accidental damage. The container eventually may be buried at an underground site selected for its geological stability. Burial storage minimizes the likelihood of human interference with the stored waste. In most cases, clay, sand, rock, or salt burial sites are selected to provide a relatively dry storage environment for the container and to minimize the possibility of groundwater contamination. From the preceding discussion, it can be seen that successful storage of nuclear waste requires the system to be resistant to the effects of radiation, erosion, vibration, biodegradation, thermal cycling, burial loading forces, impact forces sustained by the container, and chemical action of the waste and environment on the container. As noted, the specific problem of nuclear waste storage addressed by this invention is the venting of gas generated within the container. Should these gases cause the internal pressure of the container to become too great, the container structure could become overpressurized, allowing the stored waste to contaminate the environment. Three sources of gas generation within the container must be considered in order to realize a satisfactory venting system. First, the container material itself may generate gas when exposed to the radiation of its contents. Second, ion-exchange resins, which are used to reduce the radioactivity of fluids in nuclear power systems, may undergo radiolytic gas generation when stored in the container. Third, gas may be generated by the biodegradation of organic waste stored in the container (e.g., contaminated grease, solvents, oils, or organic materials attached to the ion-exchange resins). The rate at which gas is generated depends, among other things, on the total radiation dose exposure of the container and contents, the container and ion-exchange resin materials, the amount of organic waste present in the stored material, and the amount of oxygen within the container. From the preceding discussion, it is clear that a precise determination of the amount of gas will be generated within the container would be difficult at best. Thus, given the need to ensure the structural integrity of the storage container under any set of conditions, a means for venting the interior of the container to the environment must be provided. In that manner, pressure differences between the interior of the container and the environment will be minimized, preventing the container from becoming overpressurized. It is extremely doubtful that conventional venting devices can meet the design constraints for venting nuclear waste storage containers. For example, the natural venting characteristics of high-density polyethylene, as a container material, are generally incapable of producing the degree of venting required. Small check valves have good water restriction characteristics, but uncertainty exists as to their operation and ability to reseal over the 300-year design life of the container. Filters made of a porous metallic material would appear to have a number of drawbacks. First, their water restriction characteristics appear to be insufficient for nuclear waste storage container applications. Second, the material has a tendency to become wetted and trap water, greatly increasing the pressure required to pass gases through the material. Finally, the use of a metallic material can establish a galvanic couple between the container and the filter and lead to corrosive failure. Activated charcoal filters, while noncorrosive, resistant to gamma radiation, and readily available, generally have a low resistance to the ingress of water. SUMMARY OF THE INVENTION In accordance with the invention, there is provided a passive vent having as its primary component a reversibly porous, air-diffusible, water-restrictive, polymer plug secured in a port provided in the wall of the container. The air-diffusible nature of the material allows gases to flow through the plug in both directions. Thus, variations in pressure between the inside of the container and the container environment may be relieved. In the presence of water, water flow through the plug is restricted by a swelling of the plug material, minimizing the possibility of groundwater contamination from the waste stored in the container. The degree of waterflow restriction exhibited by the plug is directly proportional to the amount of water retained by the plug. Airflow through the plug is also inhibited in direct proportion to the amount of water retained in the plug. Even with the plug material saturated with water, however, some venting takes place. In addition, the reversible porosity of the material allows the reduction in air-diffusibility of the material attendant liquid saturation to be reversed by allowing the material to dry. The characteristics of the plug material selected also include a high resistance to the effects of radiation, chemicals, corrosion, biodegradation, and thermal cycling. A means for securing the plug in the wall of the housing is provided that will ensure plug retention in the wall over the life of the system even when subject to environmental effects, such as vibration. Finally, in the currently preferred embodiments, a sealing means, impervious to the flow of both gas and liquid, is placed between the wall of the port, and the plug. In these currently preferred embodiments the plug material is a low-density, linear porous polyethylene having an average pore diameter of less than 5 microns. Threads provided on the sides of the plug for engagement with similar threads provided in the container wall port constitute the means for securing the plug in the container wall. A thread sealant is applied to the threads. In the preferred embodiments, the plug has a cross-sectional area of less than 0.5 square inch (approximately 3.2 square centimeters), limiting the size of the port required to be made in the wall of the housing. Thus, even if the vent should fail, the constrictive effect of the relatively small port cross section will minimize the ingress and egress of liquids, protecting the environment. The plug also has an outer portion that includes means (such as a screwdriver slot) for receiving a tool capable of driving the plug into the port until the plug is properly seated. This outer portion of the plug constitutes an excess region that protrudes from the outer wall of the container when the plug is inserted. After insertion, this excess region is removed, minimizing the possibility that the plug will be tampered with or subject to forces incurred by the container wall from the environment. Additionally, with the portion of the plug containing the means for receiving the insertion tool removed, there are no depressions on the plug surface to collect water. A slight protrusion of material may also be left to minimize the collection of groundwater around the vent. According to the invention, a process for installing the plug in the wall of the housing is revealed. The process consists of applying a sealant to the threads of the plug, inserting the plug a predetermined distance in a port provided in the wall of the housing, and removing the excess portion of the plug protruding from the wall of the housing. |
053032730 | summary | BACKGROUND ART This application claims the priority of Japanese Patent Application No. 3-357763 filed Dec. 26, 1991, which is incorporated herein by reference. The present invention pertains to an apparatus for assembling a nuclear fuel assembly. FIG. 6 depicts a known nuclear fuel assembly which is mounted on a nuclear reactor such as a pressurized water reactor. The assembly, generally designated at 1, includes a pair of top and bottom nozzles 2 and 3 arranged in a facing relation to each other and in a vertically spaced relation to each other. A plurality of guide pipes 4 such as control-rod guide pipes or instrument pipes are disposed so as to extend between the top and bottom nozzles 2 and 3, and fixedly secured thereto. A plurality of grids 4 are secured to the intermediate portions of the guide pipes 5 so as to be vertically spaced from one another, and a plurality of fuel rods 6 are inserted through and supported by the grids 4 so as to extend parallel to the guide pipes 5. As shown in FIGS. 7 and 8, each grid 5 is formed as follows. A plurality of straps 11, each in the form of a thin strip sheet, are assembled perpendicularly to each other into a grid 5 to define a number of grid cells 13. Springs 15 and dimples 16 for supporting a respective fuel rod 6 are formed on the walls of each grid cell in opposed relation to each other. More specifically, as shown in FIG. 8, a single spring 15 is formed on one side of each wall of the grid cell 13, while a pair of dimples 16 are formed on the other side of the same wall defining adjacent grid cell so as to sandwich the aforesaid spring 15, and a spring 15 and a pair of dimples 16 are opposed to each other and protrude into the same grid cell 13. Each fuel rod 6, which is inserted into the grid cell 13, is supported by being urged to the dimples 16 by the spring 15 opposing thereto. Furthermore, rectangular cut-outs 14 or openings are formed at the intersections of the straps 11. Those wall portions which sandwich the spring 15 therebetween and are spaced apart from each other in the longitudinal direction of the strap serve as ribs 23 with which hook portions 22 of a key member 21 are held in engagement. A conventional method for inserting the fuel rods 6 in the grid 5 thus constructed will now be described. First, a deflecting jig 24 as shown in FIG. 9 is inserted through the grid cell 13. The deflecting jig 24 comprises a cylindrical jig body 25 divided at its forward portion into four pieces, and a tapered pin 26 inserted in the jig body 25 for sliding movement therealong. When the tapered pin 26 is withdrawn or retracted in its axial direction while holding the deflecting jig 24 in the grid cell 13, the jig body 25 is enlarged to deflect the springs 15 as shown in FIG. 10. Subsequently, an elongated key member 21 of a generally rectangular cross-section is inserted into the cut-outs 14 from the lateral side of the grid 12, to bring the hooks 22 of the key member 21 into engagement with the ribs 23 to keep the springs deflected. Then, the deflecting jig 24 is removed from the grid. Thereafter, the fuel rod 6 is inserted in the grid cell 13, and the key member 21 is removed from the grids to release constriction of the spring. Thus, the fuel rod 6 is secured by being resiliently urged by the springs 15 toward the dimple 16 opposing thereto. However, inasmuch as the aforesaid tasks of deflecting the springs 15 and inserting the key member 21 are carried out manually, they are labor-intensive and time-consuming, resulting in low operational efficiency. Furthermore, the task of deflecting the springs 15 using the aforesaid deflecting jig 24 must be carried out carefully so as not to cause any twisting or shifting to the springs 15, without exerting any force thereon in a direction other than the acting direction of the spring 15. Therefore, the deflecting task requires a high level of skill, so that it has been desired to improve this task and achieve standardization of the operating procedure. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide an apparatus for assembling a nuclear fuel assembly which solves the aforesaid problems and achieves substantial reduction in working time and cost. According to the present invention, there is provided an apparatus for assembling a nuclear fuel assembly which includes a grid for supporting a plurality of fuel rods, the grid having a plurality of straps intersecting each other to define a plurality of grid cells therein, and a plurality of pairs of dimples and springs provided on the straps for supporting the fuel rods, the dimple and the spring being disposed in facing relation to each other, on wall portions of the straps, which cooperate with each other to define the grid cells, the dimple and the spring projecting into the grid cell, the apparatus comprising: deflecting means disposed adjacent to the grid for deflecting the spring away from the dimple opposing thereto; the deflecting means including a tubular member defining a plurality of circumferentially divided sleeve pieces, a rod member releasably inserted in the tubular member for sliding movement therealong, and drive means drivingly connected to the rod member for moving the rod member in the tubular member in a longitudinal direction thereof to bring the rod member into urging engagement with the sleeve pieces of the tubular member, whereby the sleeve pieces are deflected to be urged against the spring to deflect the same. In the foregoing apparatus, when the drive means is actuated, the rod member which is inserted in advance in the tubular member is moved by the drive means in a longitudinal direction thereof, and the rod member is brought into urging engagement with the sleeve pieces of the tubular member, so that the sleeve pieces are deflected to be urged against the spring to deflect the same. Thus, the deflecting operation of the spring on the strap of the grid can be mechanically carried out very efficiently by operating the apparatus, thereby achieving substantial reduction in working time and cost. |
description | This application relies on and claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/787,667, filed 31 Mar. 2006, the entire disclosure of which is hereby incorporated herein by reference. 1. Field of the Invention This invention relates to the field of firearms. More specifically, the invention relates to articles of manufacture for use as identifiers of objects using infrared light. In exemplary embodiments, the invention finds use in targeting and sight calibration for firearms equipped with infrared sighting scopes. The present invention thus generally relates to signage visible to those using infrared imaging techniques, and particularly to a method of calibrating infrared weapons sights. 2. Description of Related Art Users of infrared cameras for operations such as the military and police have the advantage of being able to view heat sources, such as people, in complete darkness. However, they are unable while using infrared imaging techniques to differentiate words or symbols. In order to convey information they can utilize heated objects, such as exothermic chemical heaters. However, these and similar technologies only create a point in the imaging system. Therefore, the ability to convey complex information is very limited. The invention addresses this and demonstrates a method of making more complex signage that is visible to people using infrared imaging. In particular, users of weapons with infrared sights such as the TWS (Thermal Weapon Sight) from BAE, DRS Technologies, or Raytheon must calibrate their sight to their weapon to ensure they will hit their target. This is very important whenever the sight is disturbed in any way. Using traditional iron sights, the user fires at the center of a target similar to the target shown in FIG. 1. The group of shots should land a predefined distance away from the target center depending on the weapon and sight characteristics. If the shots do not hit the target where expected, the sights must be adjusted so they will hit the target where they should. However, the soldier using a thermal weapon sight is unable to see the target to perform this calibration. Migliorini (U.S. Pat. No. 6,337,475) proposes using a small electrically heated silhouette placed on the front of a standard 25 meter zeroing target. This appears to be a valid solution, but lacks in the following: a battery is required for operation, which poses logistical problems due to the greater weight of the 25 meter zeroing target. Additionally, battery disposal can create logistical problems; the addition of a battery and wiring poses significant cost increases in the 25 meter zeroing target relative to those used with iron sights; and the heat from the silhouette can bleed off from it and begin to warm the target, thereby increasing the size of the target for the user. This could result in lower accuracy. Others have also proposed articles of manufacture, methods, and means for sighting of infrared optical devices. Among these are U.S. Pat. No. 6,767,015, which discloses a thermal target; U.S. Pat. No. 6,051,840, which discloses an infrared heat emitting device; U.S. Pat. No. 6,020,040, which discloses a thermal pack having a plurality of individual heat cells; and U.S. Pat. No. 5,918,590, which discloses heat cells. Although each of these solutions has advantages, each also has drawbacks and limitations. Therefore a new method of creating signage is required that will address needs in the art. The invention in general comprises a physical object that can be used as a sign for, among other things, calibrating an infrared targeting scope. It also provides a method of making such an object, and a method of calibrating an infrared imaging device, such as a thermal camera, using such an object. The invention thus provides an article of manufacture, which is an infrared sign or target for calibrating devices that detect infrared radiation, as well as methods of making and using the article of manufacture. In embodiments, the object is a sign that comprises a laminar member with a first and second surface. The first surface can comprise any one or more of a multitude of materials. It typically has the characteristic of interfacing properly with any materials adhered to it. The second surface has the characteristic of having low emissivity (emissivity value of about 0.4 or less). A design consisting of words, graphics, or any other creation can be printed on the second surface. The printing has the characteristic of being the proper thickness and type such that the printed locations on the second surface are of high emissivity (emissivity value of about 0.7 or more). When viewed through an infrared imaging device, the design will be readily apparent. Using this invention, any conceivable design can be created using traditional printing means, such as a silk screening. It should be understood that any technology used to print and any design falls within the scope of this patent. Additionally removing sections of the film will typically create regions of higher emissivity where the background is able to show through the film. In embodiments, the method of making the object, such as a marker or sign, comprises making an object that is visible using an infrared optical device, such as an infrared camera or infrared optical sighting device for a weapon. The method of making the marker or sign provides an object that contains characters and/or images that can be detected with an infrared detector, but may or may not be detectable by the naked eye. In general, the method comprises providing an object with a surface and depositing on the surface one or more substances that can be detected with a device sensitive to infrared electromagnetic radiation. In embodiments, the method of calibrating an infrared imaging device, such as an infrared detector, comprises viewing an object according to the invention through such a device, and determining whether the device is calibrated to correctly locate an image or character on the object. Where the determining step identifies a mis-calibration, the method typically further comprises adjusting the location, angle, or other parameter of the imaging device to more accurately calibrate the device. Often, the method will be practiced under controlled conditions, such as at a shooting range on a military facility or police facility. For additional clarity in the infrared imaging device, the laminar member can be completely or partially warmed. In the area where warmth is applied the difference in infrared energy emitted from the non-printed second surface relative to the printed second surface will increase. As this difference increases the clarity in the infrared imaging device will increase. In a preferred embodiment, the heat is applied to the first surface of the laminar member. In one embodiment, the heat is applied utilizing a chemical heater, which begins to warm when exposed to oxygen in the air (e.g., “Tosti Toes” from Heatmax). The chemical heater can be completely biodegradable, which minimizes the cost and logistics of disposal. In another embodiment, the heat is applied utilizing an electric heater, which begins to warm when an electric voltage is applied to it. It should be understood that any technology used to heat falls within the scope of this patent. The heater shape does not have to assume a specific shape for the invention because the infrared image is created on the front surface and is a function of the printing not the geometry of the heater. For yet other additional or alternative clarity, the low emissivity sections of the signage can be insulated from the heater. This further improves the contrast between the regions of the target in the thermal viewer. For improved use, in embodiments, the assembly can be built on a cardboard platform, such as a corrugated cardboard platform, that maintains the proper shape and/or position of the target relative to where it is mounted. In another preferred embodiment the infrared pattern can be created by altering the insulation value of the article rather than the emissivity value. Another preferred embodiment of the invention comprises a laminar member (9), such as C flute cardboard without low emissivity film, as shown in FIG. 6. This is a less expensive, though possibly less effective, article of manufacture. All surfaces of the laminar member (9) have the characteristic of having high emissivity. Removing sections of laminar member (9) modifies its insulation value in those areas. The removed section or sections create a pattern of higher and lower thermal insulation that can be used to generate a pattern of higher and lower infrared emissions. To generate the infrared pattern in the thermal weapons sight, the laminar member can be completely or partially warmed using laminar members. In the area where the laminar member is cut away, insulation is negligible and infrared energy is emitted from the emitting surface of the heat generator; in areas without cutouts, the cardboard acts as an insulator and there is less infrared emitted from that surface. The heater can comprise a heat generator and a heated surface, such as solid bleached sulfate (SBS) board, which may provide thermal dissipation and/or mechanical stability. In a preferred embodiment, the heat is applied utilizing a chemical heater that begins to warm when exposed to oxygen in the air. The entire target or just the heater is packaged in an airtight package to prevent the heater from operating before its intended use. In embodiments, the chemical heater is completely biodegradable, which minimizes the cost and logistics of disposal. In another embodiment, the heat is applied utilizing an electric heater, which begins to warm when an electric voltage is applied to it. In an embodiment, there is an electrical power source, such as a battery with a part such as a pull-tab, which prevents current from flowing until the tab is pulled. When the tab is removed, the circuit is connected and current flows heating the heater. It should be understood that any method of preventing current flow until the target is ready for use is contemplated by the present invention. It should also be understood that any technology used to heat is contemplated by the invention. It also should be noted that Migliorini (U.S. Pat. No. 6,337,475) proposes placing an electric heater on the second surface of a paper target, which has high or normal emissivity. The effectiveness of this is dependent on the effectiveness of the thermal insulating layer. If not completely effective, the silhouette shape will become distorted. On the other hand, the heater shape does not have to assume a specific shape for the present invention because the infrared image is created on the front surface and is a function of the insulator geometry, not the geometry of the heater. The pattern created by the insulator cutouts creates a 25 Meter Zeroing Target or any other object or pattern of interest to the practitioner. When viewed through an infrared imaging device, the target will be readily apparent. Using the article of manufacture of the present invention, any conceivable sign, target, etc. can be created by altering the shape of the insulator. The present invention will now be described with detailed reference to exemplary embodiments of the invention. The following detailed description should not be considered as a limitation on the invention, but rather should be considered as a detailed description of certain embodiments, which is presented to give those of skill in the art a better understanding of various features of the invention. One preferred embodiment of the invention comprises a laminar member (1) with a first (3) and second (2) surface, as shown in FIG. 2. Painted Mylar film, commonly referred to as “no power material” or “reverse polarity material”, can be used for this purpose. The first surface (3) can comprise a multitude of materials. It has the characteristic of interfacing properly with any materials adhered to it. The second surface (2) has the characteristic of having low emissivity. On the second surface (2) is printed a 25 Meter Zeroing Target or any other object or pattern of interest (4) to the practitioner. An exemplary sample target appears in FIG. 1. The printing (4) has the characteristic of being the proper thickness and type such that the printed locations on the second surface are of high emissivity. When viewed through an infrared imaging device, the target will be readily apparent. Using the article of manufacture of the present invention, any conceivable sign, target, etc. can be created using traditional printing means, such as a silk screening. It should be understood that any technology used to print and any target design is contemplated by the present invention. For additional clarity in the thermal weapons sight, the laminar member can be completely or partially warmed, as depicted in FIG. 3 and FIG. 4. In the area where warmth is applied, the difference in infrared energy emitted from the non-printed second surface (3) relative to the printed second surface (4) will increase. As this difference increases, the clarity in the thermal weapons sight will increase. The practitioner may need to adjust the detector gain and contrast for optimum clarity. In a preferred embodiment, the heat is applied to the first surface (3) of the laminar member. The heater comprises a heat generator (7) and a heated surface (8), which may provide thermal dissipation and/or mechanical stability. Elements (7) and (8) may comprise a single object or multiple objects. In a preferred embodiment, the heat is applied utilizing a chemical heater (3), such as a “Toasti Toes” from Heatmax which begins to warm when exposed to oxygen in the air. The entire target or just the heater is packaged in an air-tight package to prevent the heater from operating before use. In embodiments, the chemical heater is completely biodegradable, which minimizes the cost and logistics of disposal. In another embodiment, the heat is applied utilizing an electric heater (6), which begins to warm when an electric voltage is applied to it. In an embodiment, there is an electrical power source such as a battery with a part such as a pull tab, which prevents current from flowing until the tab is pulled. When the tab is removed, the circuit is connected and current flows heating the heater. It should be understood that any method of preventing current flow until the target is ready for use is contemplated by the present invention. It should also be understood that any technology used to heat is contemplated by the invention. It also should be noted that Migliorini (U.S. Pat. No. 6,337,475) proposes placing an electric heater on the second surface of a paper target, which has high or normal emissivity. The effectiveness of this is dependent on the effectiveness of the thermal insulating layer. If not completely effective, the silhouette shape will become distorted. On the other hand, the heater shape does not have to assume a specific shape for the present invention because the infrared image is created on the front surface and is a function of the printing, not the geometry of the heater. In some embodiments, for improved clarity, an insulating laminar member (9) is placed between the heater and the first laminar layer. This further minimizes the temperature of the low-emissive surface (3). Additionally or alternatively, cutouts are placed in the first layer (6) and the insulating laminar layer (10), which selectively exposes portions of the emitting surface of the heater. This further increases the difference between the amount of energy emitted from the high and low emissivity areas of the target. This can improve the image in the thermal imaging device. Another preferred embodiment of the invention comprises a laminar member (9) such as C flute cardboard without low emissivity film, as shown in FIG. 6. This is a less expensive though potentially less effective article of manufacture. All surfaces of the laminar member (9) have the characteristic of having high emissivity. Removing sections of laminar member (9) modifies its insulation value in those areas. The removed section or sections create a pattern of higher and lower thermal insulation that can be used to generate a pattern of higher and lower infrared emissions. To generate the infrared pattern in the thermal weapons sight, the laminar member can be completely or partially warmed using laminar members (7,8), as depicted in FIG. 6. In the area where the laminar member is cut away, insulation is negligible and infrared energy is emitted from the surface (11); in areas without cutouts, the cardboard acts as an insulator and there is less infrared emitted from that surface (12). The heater comprises a heat generator (7) and a heated surface (8) such as solid bleached sulfate (SBS) board, which may provide thermal dissipation and/or mechanical stability. Elements (7) and (8) may comprise a single object or multiple objects. In a preferred embodiment, the heat is applied utilizing a chemical heater (7), such as a “Toasti Toes” from Heatmax that begins to warm when exposed to oxygen in the air. The entire target or just the heater is packaged in an airtight package to prevent the heater from operating before its intended use. In embodiments, the chemical heater is completely biodegradable, which minimizes the cost and logistics of disposal. In another embodiment, the heat is applied utilizing an electric heater (7), which begins to warm when an electric voltage is applied to it. In an embodiment, there is an electrical power source such as a battery with a part such as a pull tab, which prevents current from flowing until the tab is pulled. When the tab is removed, the circuit is connected and current flows heating the heater. It should be understood that any method of preventing current flow until the target is ready for use is contemplated by the present invention. It should also be understood that any technology used to heat is contemplated by the invention. It also should be noted that Migliorini (U.S. Pat. No. 6,337,475) proposes placing an electric heater on the second surface of a paper target, which has high or normal emissivity. The effectiveness of this is dependent on the effectiveness of the thermal insulating layer. If not completely effective, the silhouette shape will become distorted. On the other hand, the heater shape does not have to assume a specific shape for the present invention because the infrared image is created on the front surface and is a function of the insulator geometry, not the geometry of the heater. The pattern created by the insulator cutouts creates a 25 Meter Zeroing Target or any other object or pattern of interest to the practitioner. When viewed through an infrared imaging device, the target will be readily apparent. Using the article of manufacture of the present invention, any conceivable sign, target, etc. can be created by altering the shape of the insulator. In embodiments, the entire assembly is built on a foldable frame that provides rigidity and holds the target at a predetermined angle relative to the target-mounting surface. In the practice of one embodiment of the invention relating to a 25 m target, the weapons user will remove the target and/or heater from its air-tight package. If not already affixed to the rear of the target, the heater is affixed there and the assembly is placed on a fixture. The weapons user, or shooter, returns to the shoot position twenty-five meters from the target. The chemical heater will begin to react, warming the target. When viewed through the thermal weapon sight, the aim point will be visible. The shooter will shoot at the aim point in the center of the target. After shooting, the shooter will note the location of the rounds relative to the point of aim and, if needed, adjust his sights to bring the rounds to their correct location. |
|
abstract | A pattern density distribution and a dose distribution calculated using the pattern density distribution are multiplied by each other to calculate an exposure distribution. A fogging electron amount distribution is calculated using the exposure distribution and a function descriptive of a fogging spread distribution. Charge amount distributions in irradiation and non-irradiation regions are calculated using the exposure distribution and the fogging electron amount distribution. A position displacement amount distribution is calculated using the charge amount distributions and a response function for converting a charge amount to a position displacement error. |
|
062367005 | summary | BACKGROUND OF THE INVENTION This invention relates generally to nuclear reactors and more particularly, to apparatus and methods for coupling piping within reactor pressure vessels of such reactors. A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spray spargers inside the RPV. The core spray piping and spargers deliver water flow to the reactor core. Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC. Reactor internal piping, such as T-boxes and core spray line downcommers, occasionally require replacement as a result of SCC. Replacing the core spray piping often requires removing and replacing the core spray line downcommer. The core spray line downcommer attachment to the shroud, however, typically is installed during original reactor construction and is difficult to access. In addition, replacing the core spray line downcommer is complicated by the limited available working space. The core spray line downcommer includes a lower elbow secured to a shroud core spray sparger T-box. Installing a replacement downcommer pipe into the reactor requires that the replacement lower elbow be welded to the shroud. However, as explained above, it is difficult to access this area of the reactor. It would be desirable to provide an apparatus which facilitates replacing a core spray line downcommer attached to the shroud core spray sparger T-box. It would also be desirable to provide such an apparatus which is installed without the necessity of field welding. BRIEF SUMMARY OF THE INVENTION Replacement of a lower elbow section of a downcommer pipe without field welding may be attained by a downcommer pipe coupling apparatus which, in one embodiment, includes a wedge, a wedge flange, and a wedge housing. The wedge is a split tapered sleeve having a plurality of flexible thinned segments extending lengthwise. The separate wedge flange is configured to be located over the wedge and includes two openings sized for wedge flange bolts with each opening having a square recess to mate with a bolt locking collar. The wedge housing is substantially frustro-conical shaped and has a wedge housing flange at a larger diameter end, a tapered bore matching the wedge, and two opposing threaded dowel bolt openings threaded to receive dowel bolts. Each dowel bolt opening has a square recess to mate to a bolt locking collar. The downcommer pipe is coupled to the apparatus using two wedge flange bolts and two dowel bolts. Particularly, the wedge flange bolts extend through the wedge flange and into the wedge housing so that as the wedge flange bolts are secured, the wedge clamps the downcommer pipe tightly to the wedge housing. The dowel bolts extend through the dowel bolt openings and the downcommer pipe, forming a shear connection between the wedge housing and the downcommer pipe. The tightened wedge, wedge housing and downcommer pipe form a rigid connection which is aligned to the downcommer pipe and the dowel bolt openings. The apparatus further includes a substantially cylindrical pipe connected to the smaller diameter end of the wedge housing, an elbow connected to the second end of the cylindrical pipe, and a substantially circular shaped lower flange connected to the second end of the elbow. The lower flange includes a T-box opening having an inner diameter sized to receive a portion of a T-box extending from the shroud, and a circular lip on the lower flange face is configured to engage the shroud spot face to transmit applied piping shear loads and the joint preload forces. The lower flange also includes eight lower flange bolt openings sized to receive lower flange bolts. Each lower flange bolt opening has a square recess to mate to a bolt locking collar. Lower flange bolts are installed in three of the eight possible locations, depending on the available access. Additionally, the coupling apparatus includes a nutbar and a substantially L-shaped clamp having a bolt opening sized to receive one of the lower flange bolts. The nutbar is sized to receive two lower flange bolts using the connection of the two nuts to act as an anti-rotational mechanism. The clamp is sized to axially restrain the T-box to the shroud so that the T-box does not move inward toward the reactor core. The two connecting ends of the coupling apparatus are provided with seals to minimize leakage. Both the pipe seal and T-box seal are double diaphragm type seals which are self-energizing so that the pressure difference tending to cause leakage also increases the seal surface contact force, tightening the seal. This flexible type of seal minimizes the added joint load required to accomplish sealing, so the sizing of the required bolts and bolt openings is minimized to fit in the available access. In particular, access on the inside of the shroud is limited by numerous existing core spray sparger nozzles. The coupling apparatus is mechanically joined to the shroud and downcommer pipe with sufficient strength and stiffness to react the originally specified piping loads from seismic, weight, thermal expansion and hydraulic conditions without significantly changing the piping system loads. The wedge and wedge housing grip the downcommer pipe tightly over a sufficient length to develop the full bending strength and stiffness of a continuous pipe. The dowel bolts are sized to react the axial twisting and vertical loads. The bolted lower flange connection to the shroud is a similarly stiff connection, with the bolt preload sufficient to prevent separation of the lower flange from the shroud. Placement of the lower flange bolts outside the downcommer pipe minimizes the preload change due to temperature transients in the fluid inside the downcommer pipe. The coupling apparatus is constructed, typically, of materials matching the thermal properties of the attached downcommer pipe and shroud, for example, 316 stainless steel. Components of the coupling apparatus are fabricated to ease assembly, provide strength, and provide optimum corrosion resistance. To install the coupling apparatus, a lower portion of the existing downcommer pipe is removed, for example, by cutting-off a portion of the downcommer pipe near the lower elbow and removing the lower elbow from the shroud. Two dowel bolt openings are then machined in the downcommer pipe, aligned with the shroud outside diameter and downcommer pipe end. A circular groove surrounding the T-box in the shroud outside diameter and the cut end of the T-box are then spot face machined to the correct depth. Three lower flange bolt openings are then machined through the shroud at accessible locations. After inserting the pipe seals into the wedge housing and lower flange groove, the replacement coupling apparatus, wedge flange, wedge, and wedge housing are installed over the end of the downcommer pipe, until the downcommer pipe is seated against the seal inside the bottom of the wedge housing. The two dowel bolts are then engaged through the wedge housing into the downcommer pipe openings, aligning the coupling apparatus to the shroud outside diameter and applying a controlled compression to the pipe seal. The coupling apparatus is then coupled to the shroud. The lower flange is placed adjacent to the shroud so that the lower flange lip engages the shroud spotface and the T-box extends into the lower flange opening seating against the T-box seal. Two lower flange bolts are then extended through the lower flange and shroud bolt openings and the nutbar. The third lower flange bolt is extended through the lower flange, shroud, and clamp bolt openings and a nut. The lower flange bolts secure the coupling apparatus lower flange to the shroud. The downcommer pipe is then secured to the coupling apparatus by tightening the two wedge flange bolts through the wedge flange into the wedge housing to compress the wedge. As the wedge flange bolts are tightened, the wedge is clamped between the wedge flange and the wedge housing. As a result, the wedge is inserted into the wedge housing, compressing against the downcommer pipe and tightly connecting the downcommer pipe to the coupling apparatus. After final torquing, the wedge flange, dowel, and lower flange bolts are locked against rotation by crimping locking collars into grooves provided in the bolt heads. The above-described apparatus facilitates replacing a lower portion of a downcommer pipe. The coupling apparatus is mechanically joined to the shroud and the downcommer pipe therefore avoiding field welding in the limited space surrounding the downcommer pipe on material which has evidenced cracking from the original attachment welds. Additionally, the resulting connection between the downcommer pipe and the shroud T-box is a permanent replacement. |
claims | 1. A charged particle beam application device comprising:a specimen stage on which a specimen is mounted;an irradiation optical system to scan said specimen mounted on said specimen stage with a primary charged particle beam;a detector to detect secondary charged particles generated by the scanning with said charged particle beam; anda display means to display the output signals from said detector in the form of images,wherein said irradiation optical system comprises:an aberration corrector to correct the aberration of said incoming primary charged particle beam; anda means for dividing an optical path of either said primary charged particle beam entering said aberration corrector or said primary charged particle beam having passed through said aberration corrector into plural optical paths. 2. A charged particle beam application device according to claim 1, wherein said means for dividing the optical path of said primary charged particle beam into plural optical paths is a stop having plural openings. 3. A charged particle beam application device according to claim 1,wherein said stop has a first aperture group having plural openings through which said primary charged particle beam divided into said plural optical paths passes, andwherein said first aperture group has a first opening, and plural second openings disposed symetrically around a center axis of said first opening. 4. A charged particle beam application device according to claim 3, wherein said irradiation optical system has a high-voltage wobbler function. 5. A charged particle beam application device according to claim 3, wherein said plural second openings include at least two openings disposed at the positions twofold rotationally symmetrical around the center of said first opening. 6. A charged particle beam application device according to claim 3, wherein said plural second openings include at least two openings disposed at the positions either fourfold rotationally symmetrical or eightfold rotationally symmetrical around the center of said first opening. 7. A charged particle beam application device according to claim 3, wherein said stop has a third opening disposed in addition to said first aperture group. 8. A charged particle beam application device according to claim 7, including a stop moving means of retracting either said first aperture group or said third opening from the optical axis of said primary charged particle beam. 9. A charged particle beam application device according to claim 8, including a control means for controlling said stop moving means,wherein said display means is connected to said control means, andwherein an icon to select any of said first aperture group, said second aperture group, and said third opening is displayed on said display means. 10. A charged particle beam application device according to claim 8, including:a control means for controlling said stop moving means; andan input means for selecting any of said first aperture group, said second aperture group, and said third opening. 11. A charged particle beam application device comprising:a specimen stage on which a specimen is mounted;an irradiation optical system to scan said specimen mounted on said specimen stage with a primary charged particle beam;a detector to detect secondary charged particles generated by the scanning with said charged particle beam; anda display means to display the output signals from said detector in the form of images,wherein said irradiation optical system comprises:a charged particle beam source;an aberration corrector to correct the aberration of said incoming primary charged particle beam; anda stop disposed between said charged particle beam source and said aberration corrector, andwherein said stop has a first opening disposed on an optical axis of the primary charged particles emitted from said charged particle beam source, and plural second openings disposed symmetrically around a center axis of said first opening. 12. A charged particle beam application device according to claim 11, wherein said charged particle beam source is an electron source. 13. A wafer inspection device using a charged particle beam application device according to any one of the claims 1 to 8 and 9 to 12, said wafer inspection device comprising a means for judging existence or nonexistence of defect in said specimen on the basis of the output signals of said detector. 14. A critical-dimension-measurement device using a charged particle beam application device according to any one of the claims 1 to 8 and 9 to 12, said critical-dimension-measurement device comprising a means for measuring the dimension of a pattern formed on said specimen on the basis of the output signals of said detector. 15. A charged particle beam application device comprising:a specimen stage on which a specimen is mounted;an irradiation optical system to scan said specimen mounted on said specimen stage with a primary charged particle beam;a detector to detect secondary charged particles generated by the scanning with said primary charged particle beam; anda display means to display the output signals from said detector in the form of images,wherein said irradiation optical system comprises:an aberration corrector to correct the aberration of said incoming primary charged particle beam; anda first stop for dividing an optical path of either said primary charged particle beam entering said aberration corrector or said primary charged particle beam having passed through said aberration corrector into plural optical paths. 16. A charged particle beam application device according to claim 15 further comprising a second stop having an orbicular zone aperture and a shield from the primary charged particle beam arranged in the center of the orbicular zone. 17. A charged particle beam application device according to claim 16, further comprising a means for switching said first stop and said second stop. 18. A charged particle beam application device according to claim 16, wherein the orbicular zone aperture comprises a plurality of round apertures. 19. A wafer inspection device using a charged particle beam application device according to any one of the claims 15 and 16 to 18, said wafer inspection device comprising a means for judging existence or nonexistence of defect in said specimen on the basis of the output signals of said detector. 20. A critical-dimension-measurement device using a charged particle beam application device according to any one of the claims 15 and 16 to 18, said critical-dimension-measurement device comprising a means for measuring the dimension of a pattern formed on said specimen on the basis of the output signals of said detector. |
|
claims | 1. A device for generating compressed fluids, the device comprising:a first process chamber A for containing and treating a first reaction material, the first process chamber A having an inlet that receives the first reaction material into the first process chamber A;a second process chamber B for containing and treating a second reaction material the second process chamber B having an inlet that receives the second reaction material into the second process chamber B;a third process chamber C, for containing and treating of a fluid designed to be compressed,wherein the first process chamber A, the second process chamber B, and the third process chamber C are each distinct sealed chambers separate from each other,wherein the first process chamber A is adjacent the third process chamber C and the second process chamber B is embedded within the third process chamber C;a nebulization pump (N) operatively connected to the first process chamber and to the second process chamber B, the nebulization pump (N) configured for nebulization of the first reaction material taken from the first process chamber and consequent entry of nebulized first reaction material into the second process chamber B; anda magnetron (M) arranged adjacent the third process chamber C, the magnetron (M) configured to provide an emission of radio waves with variable frequencies in a direction into said second process chamber B,wherein said radio waves, emitted by said magnetron (M) into the second process chamber B, interact with said nebulized first reaction material and the second reaction material, in solid form, contained in said second process chamber B, to thereby produce a high energy plasma that creates a temperature increase in the fluid contained in the third process chamber C to thereby warm-up and by being warmed-up compresses the fluid contained in the third process chamber C. 2. The device according to claim 1,further comprising the first reaction material in the first process chamber A, wherein the first reaction material contained and treated in the first process chamber A is in liquid or gaseous form and is selected from the group consisting of water, fossil hydrocarbons, biologic hydrocarbons, and mixtures or emulsions comprising said water, fossil hydrocarbons, and biologic hydrocarbons. 3. The device according to claim 1, further comprising the second reaction material in the second process chamber B, wherein the second reaction material contained and treated in the second process chamber B comprises solid cluster material selected from the group consisting of copper, nickel, titanium, tungsten, iron, carbon, and compounds containing copper, nickel, titanium, tungsten, iron, or carbon. 4. The device according to claim 1, further comprising the fluid in the third process chamber C, wherein the fluid contained and treated is in the third process chamber C in gaseous form and is selected from the group consisting of atmospheric air, carbon dioxide, helium, nitrogen, and mixtures of atmospheric air, carbon dioxide, helium, and nitrogen. 5. The device according to claim 1, further comprising adjusting valves located at the inlet of the first process chamber A and at the inlet of the second process chamber B, said adjusting valves being operable to control entry of the first process material and the second process material respectively into the first process chamber A and the second process chamber B. 6. The device according to claim 1, further comprising an adjusting valve located at an outlet of the third process chamber, said adjusting valve being operable to control ejection of the compressed fluid from the outlet of the third process chamber C. 7. The device according to claim 1, further comprising: a fourth process chamber D for pre-heating the first process chamber A and the third process chamber C, the first process chamber A and the third process chamber C being enclosed in the fourth process chamber D. 8. The device according to claim 7, further comprising: adjusting valves at an inlet and an outlet of the fourth process chamber, the adjusting valves operable to control entry of a warming-up fluid into the fourth process chamber D and for ejection of said warming-up fluid from said chamber. 9. The device according to claim 8, wherein the warming-up fluid contained in the fourth process chamber D comprises fluids for thermal recovery in liquid or gaseous form. 10. The device according to claim 1, further comprising a balancing valve operatively connected to the first process chamber A and to the third process chamber C, the balancing valve being operable for balancing pressure between the first process chamber A and the third process chamber C for controlling overpressure of the first reaction material in the first process chamber A and controlling overpressure of the fluid in the third process chamber. 11. The device according to claim 1, further comprising an electronic control unit (S) for the coordinated management of the single elements of the device. 12. The device according to claim 1, further comprising the second reaction material in the second process chamber B, wherein the second reaction material contained and treated in the second process chamber B comprises solid powder material selected from the group consisting of copper, nickel, titanium, tungsten, iron, carbon, and powered compounds containing copper, nickel, titanium, tungsten, iron, or carbon. 13. The device according to claim 1, further comprising:the first reaction material in the first process chamber A,the second reaction material in the second process chamber B, andthe fluid in the third process chamber C,wherein the first reaction material is in liquid or gaseous form and is selected from the group consisting of water, fossil hydrocarbons, biologic hydrocarbons, and mixtures or emulsions comprising said water, fossil hydrocarbons, and biologic hydrocarbons,wherein the second reaction material comprises solid cluster or powder material selected from the group consisting of copper, nickel, titanium, tungsten, iron, carbon, and compounds containing copper, nickel, titanium, tungsten, iron, or carbon, andwherein the fluid is in gaseous form and is selected from the group consisting of atmospheric air, carbon dioxide, helium, nitrogen, and mixtures of atmospheric air, carbon dioxide, helium, and nitrogen. 14. The device according to claim 13, wherein the second reaction material is in tablet form. 15. The device according to claim 13, further comprising:first adjusting valves located at the inlet of the first process chamber A and at the inlet of the second process chamber B, said first adjusting valves being operable to control entry of the first process material and the second process material respectively into the first process chamber A and the second process chamber B;a second adjusting valve located at an outlet of the third process chamber, said second adjusting valve being operable to control ejection of the compressed fluid from the outlet of the third process chamber C;a fourth process chamber D for pre-heating the first process chamber A and the third process chamber C, the first process chamber A and the third process chamber C being enclosed in the fourth process chamber D;third adjusting valves at an inlet and an outlet of the fourth process chamber, the third adjusting valves operable to control entry of a warming-up fluid into the fourth process chamber D and for ejection of said warming-up fluid from said chamber,wherein the warming-up fluid contained in the fourth process chamber D comprises fluids for thermal recovery in liquid or gaseous form;a balancing valve operatively connected to the first process chamber A and to the third process chamber C, the balancing valve being operable for balancing pressure between the first process chamber A and the third process chamber C for controlling overpressure of the first reaction material in the first process chamber A and controlling overpressure of the fluid in the third process chamber; andan electronic control unit (S) operative connect to the first adjusting valves, the second adjusting valve, the third adjusting valves, and the balancing valve. |
|
046655417 | description | Referring more particularly to the drawing, there is shown a frequency tripled Nd:glass laser system using a Nd:glass laser 10. The laser is operated as a mode locked laser by a Pockels cell controller 12 to produce a single pulse of infrared laser light one ns in duration. The wavelength of this light is about 1.05 microns (.mu.m). The light emanates from the laser in a beam which passes through a tripler 14 to produce a pulse of output light of approximately 0.35 .mu.m in wavelength. The tripler may suitably be of the type described in Pat. No. 4,346,314, issued Aug. 24, 1982 to R. S. Craxton. The one ns pulse of ultraviolet light exits from the tripler 14 in a beam which is focused by a lens 16 to a spot on a flat target 18. In the event that lasers which produce sufficient power in short wavelengths (e.g., the ultraviolet) become available, they may also be used. The light is transmitted through a port in a vacuum chamber 20, which includes the target 14, a mask 22 which defines the pattern, a silicon substrate 24 having a coating 26 of x-ray resist, and a shield 28, suitably of beryllium. The chamber 20 may suitably be evacuated to a pressure of about 10.sup.-6 Torr. The target is suitably of pure iron. Other metals of high atomic number materials may be used. The target may also be a microballoon containing the target material; for example, a material having a strong emission which matches the sensitivity of the photoresist when converted into a plasma by the laser pulse. The microballoon may be supported on a stalk as in laser fusion apparatus. Then the laser beam may be divided into a plurality (two or more) of beams which can implode the target and produce an intense and very small x-ray source. The target material is heated by the laser pulse to x-ray emitting temperatures. A small mass of the target, for example, 50 nanograms is converted into a plasma. Most of the absorbed laser energy goes into kinetic energy of the plasma (for example, seventy-three percent). The rest of the energy is converted into the x-ray flux. Suitably, the Nd:glass laser produces a one nanosecond, 35 Joule (J) laser pulse, after frequency tripling. The total x-ray energy emitted by the iron target 18 is then approximately 5.7 J. The remainder of the energy is converted into the heated plasma. The x-rays radiate as radial rays from the focal spot on the target onto which the laser pulse is focused by the lens 16. This spot may be approximately 100 .mu.m in diameter. The x-rays project towards the shield 28, the pattern 22 and the resist 26. The shield 28, pattern 22 and resist 26 assembly may be positioned at an angle closer to the axis of the laser beam than shown. The inclination of the target 18 may be closer to normal to the laser beam. This alternate arrangement may increase the x-ray flux effective on the resist 26. The plasma or target debris also is projected towards this assembly of shield, pattern and resist. The x-rays are indicated by the lines made up of longer dashes while the plasma/target debris is indicated by the lines made up of short dashes. Consider the arrangement of the shield 28, mask 22, resist 26 and substrate 24. The resist and the substrate may be supported on a heat-sink, for example, of aluminum. It is not believed that the resist is heated by absorbed x-rays, since the weak exposure can only raise the resist temperature by a few degrees. The resist may be any conventional resist such as PBS (poly butyl sulfide), PMMA (poly methyl methacrylate) or COP (poly glyclycidyl methacrylate-co-ethyl acrylate). After exposure, the resist may be developed by known methods, for example, as described in U.S. Pat. No. 4,215,192 issued July 29, 1980, in the case of COP. The resist properties and development techniques are also discussed in L. F. Thompson, et al., J. Electrochem. Soc.: Solid State Sci. Techn., 121, 1500 (1974) and P. D. Lenzo, et al., Appl. Phys. Lett. 24, 289 (1974). The mask is suitably a gold grating which is supported along its edges in a frame. The width of the grating lines and their separations may be approximately 0.45 .mu.m. The mask 22 is suitably spaced in close proximity to the surface of the resist 26; a 25 .mu.m spacing being suitable. The shield 28 is also in close proximity to the resist 26 so as to be thermally coupled thereto. For example, the resist may be 5 mm from the mask 22. The hot plasma/target debris is blocked by the shield 28 and causes heating thereof. Because the shield is in close proximity and thermally coupled to the resist, the resist is heated. Thermal coupling may occur by radiational coupling and conductive coupling, as through the frame or other support structure for the assembly, which is used but not shown to simplify the drawing. The resist may reach a temperature approximately equal to the glass transition temperature of the polymer constituting the resist 26; for example, a temperature of about 100.degree. C. Heating of the resist occurs soon after the exposure of the resist by the x-rays. This is because the target debris arrives at the shield 28 with a delay of approximately one microsecond, which is long after the exposure has taken place; the x-rays travelling at the speed of light and both the x-rays and the plasma being produced essentially simultaneously at the surface of the target. Other shields may be used, depending upon the transmissivity to x-rays which is desired. The shield 28 passes x-rays above about 1 keV. While other materials, such as Mylar also have x-ray transmissive and plasma blocking properties, beryllium is preferred, since it transmits more x-rays for a given plasma blocking capability. As mentioned above, approximately 27% of the laser energy which is absorbed in the target 18, is converted into x-rays. The efficiency of x-ray production by a UV laser light is high, even though some of the laser energy is lost in the tripler 14. The beryllium shield 22, which is suitably 18 .mu.m thick, acts as a filter of the total x-ray energy (5.7 J), and approximately 0.72 J is transmitted through the beryllium shield 28. The x-ray energy density incident on the resist 26, which is located 10 cm from the target 20 is approximately 0.57 mJ per cm.sup.2. The total x-ray energy per unit volume absorbed at the surface of the resist is 0.9 J per cm.sup.3. With conventional x-ray lithography as reported in the above referenced Thompson, et al. and Lenzo, et al. articles, approximately 14 J per cm.sup.3 of laser energy must be absorbed in the same resist in order to obtain an exposure equivalent to that obtained with the 0.9 J per cm.sup.3 energy absorbed in the exemplary apparatus described herein. This is an order of magnitude less x-ray flux (energy) than has heretofore been needed for obtaining a complete exposure. The system is therefore more sensitive by an order of magnitude than systems of x-ray lithography heretofore proposed. Variations and modifications in the herein described method and apparatus, will undoubtedly suggest themselves to those skilled in the art. In particular, heating of the resist upon or following exposure can be applied by any other method of heating, to any other resist and relating to any other radiation source or particles source used for registering a pattern. Accordingly, the foregoing description should be taken as illustrative and not in a limiting sense. |
051620944 | summary | BACKGROUND OF INVENTION The present invention relates to an apparatus and method of achieving a fusion propulsion engine as could be used by a starship that is both highly efficient and is capable of achieving very high fuel specific impulse. The invention also relates to the use of said basic engine as a generator for supplying very large amount of power in the form of heat that can then be converted to electrical energy by use of conventional steam turbogenerators. The search for controlled fusion has been a major scientific effort for many years. The major thrust has been directed at the brute force approach of heating a gaseous mixture (usually deuterium and tritium) in the form of a plasma (ionized gas) to sufficient temperature and pressure and then holding this state for sufficient time to allow the nuclei of the mixture to collide and thus fuse with the liberation of energy. Despite the expenditures of vast sums of money and effort, this approach has yet to achieve a "breakeven" condition as defined by the point at which the amount of energy being produced is equal to the amount of input energy. The "breakeven" condition, assuming it can eventually be achieved by the plasma "ohmic heating approach" would represent only about 1% of the available fusion energy being realized and with 99% being lost. The major difficulty with the plasma heating approach has been that the only way to contain the plasma during the heating phase is with magnetic fields. The plasma has, so far, always been able to exhibit some form of instability that has prevented the magnetic fields from being able to contain the heated, ionized gas for sufficient time to even reach the breakeven point in energy production. The present prediction is that it will be at least 40 years before this approach can be expected to produce useful energy. The production of useful energy is estimated to require a fusion energy output at least 10 times the breakeven point. It may also be true that this approach will never work in terms of producing useful energy from a fusion process. In the late '60s another approach was given serious consideration in an attempt to solve the controlled fusion problem. This approach involved the creation of a potential well through which ionized particles (again notably deuterium and tritium, the D-T reaction) were made to osillate at high relative energies and thus occasionally experience a head-on collision that resulted in fusion. The best example of this approach is contained in a paper by Dr. R. L. Hirsch (Inertial-Electrostatic Confinement of Ionized Fusion Gases, J. Appl. Phys. 38, No. 11, 4522-4534, 1967) in which it was reported that significant neutrons (the product of a D-T fusion reaction) were detected from the apparatus as described in the article. It is believed that the approach was abandoned, however, as it did not appear that it could lead to the generation of useful amounts of energy. Its major problem was that the maximum relative ion energy occurring at the center of the potential well was also the point of minimum density. The low density at the well's center prevented appreciable fusion reactions from occurring. SUMMARY OF THE INVENTION The present invention is a form of the potential well approach to fusion. In this approach gaseous, positive ionized molecules are injected into a potential well (in a vacuum) as formed by an electrostatically negative, ring electrode that is constructed to first accelerate the ions through a potential as determined by the magnitude of voltage of the negative electrode and then decelerate them as they attempt to leave the vicinity of the electrode. The ions are thus captured in the potential well and will repeatedly oscillate through the well as the ion energy is continually exchanged between kinetic and potential. This is basically the approach as described in the Hirsch paper as previously cited. A departure from previous efforts is accomplished in the present invention by allowing the potential well to exist in a uniform magnetic field and by the further innovation of using two accelerating ring electrodes of the same negative potential and thus create a constant potential drift region in the magnetic field between the two rings. After an initial ion acceleration to high velocity by the first electrode, the ions are caused to move across the drift region at essentially constant high velocity until they reach the second electrode. After passing through the second electrode they will then experience a deceleration force until finally reversing their direction and with the second electrode accelerating them again though the potential well. In this manner the ions are made to repeatedly oscillate though the drift region, potential well of the device as they are caused to move between the two electrodes. In addition, the action of the uniform magnetic field acting on the ions though their entire flight causes the individual paths to be brought to a focus within the drift region that can be designed to be the region's midpoint. After passing through the magnetic convergent point in the drift region, the ions diverge before reaching the second electrode and are then decelerated to be refocused to a virtual anode before reversing direction to repeat the oscillating process. The ions at the drift region focus point are thus in a concentrated form and possess high energies. As new ions can be continually added to the potential well from the ion source (or sources) the ion concentration at the convergent point can continually be made to increase. In addition, on the average, the convergent point will always contain equal numbers of ions moving in opposite directions. If the ions being used are the two heavy isotopes of hydrogen, deuterium and tritium, and the accelerating potential for the ions is in the range of 100 Kev, then head-on collisions will result in fusion occurring. Collisions between deuterium and tritium can be used by the application of this invention to achieve a fusion condition and thus the creation of very high energy fusion byproducts. The equation for this reaction can be expressed as .sub.1 D.sup.2 +.sub.1 T.sup.3 .fwdarw..sub.2 He.sup.4 +.sub.o n.sup.1 +17.6 Mev where the subscripts denote the number of protons while the superscripts provide the number of both protons and neutrons and thus the atomic mass. The D-T fusion reaction is the most easily accomplished as only a single proton exists in the nuclei of the two input gases, D and T, that presents an electrostatic barrier needing to be overcome by the relative energy of the two colliding nuclei. As shown by the equation, the neutron and helium byproducts of the reaction share in the resultant fusion energy of 17.6 Mev in proportion to their mass with approximately 1/5 the total energy being contained by the kinetic energy of the neutron. While the D-T fusion reaction requires the least amount of input energy to overcome the repulsive potential barrier caused by the two protons in the nuclei, a problem exists in that an appreciable amount of the resultant fusion energy released is contained by the kinetic energy imparted to the neutron that is not ionized and thus its flight path cannot be controlled by either electrostatic or magnetic fields. For some fusion applications, such as a fusion propulsion engine for a spacecraft, it is very desirable that all resultant fusion particles can be controlled to prevent them from impacting spacecraft structure. Impacts would cause the kinetic energy of the collision particle to be transformed into heat that would have to be rejected by the vehicle to prevent it from being vaporized by its own waste heat, assuming even a modest size propulsion unit. Calculations show that if a D-T fusion reaction is used for spacecraft propulsion, the neutron from the reaction will cause insurmountable waste heat problems for engines that have in excess of about 1000 pounds thrust. A more favorable fusion reaction for use in a spacecraft that could also be employed by the present invention is the deuterium-helium.sup.3 reaction (.sub.1 D.sup.2 +.sub.2 He.sup.3 .fwdarw..sub.2 He.sup.4 +.sub.1 H.sup.1 +18.3 Mev). As both fusion byproducts (.sub.2 He.sup.4 and .sub.1 H.sup.1) are ionized, their paths can be controlled by a sufficiently strong magnetic field to prevent the particles from contacting spacecraft structure including the electrical conducting coils (that could be superconductors) as used to generate the magnetic field. It can be shown that if a magnetic field in the range of 10,000 gauss is generated by a 14 foot minimum diameter solenoid, fusion particles from a D-he.sup.3 reaction generated along the major axis of the solenoid will be forced by the magnetic field into spirals having diameters less than the radius of the solenoid and thus prevented from reaching the solenoid structure. The particles instead will spiral to the two ends of the solenoid and then leave the magnetic field as its field strength diminishes to a point insufficient to further contain the particles. In addition, by altering the form of the solenoid from a simple cylinder to a U-shaped configuration, the ionized, high energy particles can be made to exit the magnetic field from the ends in essentially the same direction and thus impart a net momentum transfer of thrust to the spacecraft by virtual of the solenoid's magnetic field forcing the particles to experience a 90.degree. change in direction. By use of the D-He.sup.3 fusion reaction, all resultant fusion particles can be deflected by the magnetic field and can thus result in useful thrust in addition to avoiding waste heat collisions with the spacecraft structure. The D-He.sup.3 reaction has, however, two problems that need to be addressed. First, the light isotope of helium, He.sup.3, does not exist in nature and thus must be manufactured. One method for accomplishing this goal is to create a supply of tritium by bombarding the relative abundant light lithium isotope, Li.sup.6, with neutrons: EQU .sub.o n.sup.1 +.sub.3 Li.sup.6 .fwdarw..sub.2 He.sup.4 +.sub.1 T.sup.3 The tritium so produced can then be stored allowing radioactive decay to proceed with a half life of 12.3 years and thus generate the desired light helium isotope: EQU .sub.1 T.sup.3 .fwdarw..sub.2 He.sup.3 +beta A second method that will result in the direct production of helium.sup.3 is to use the present invention to cause deuterium ions to collide in a fusion reaction by use of the present invention: EQU .sub.1 D.sup.2 +.sub.1 D.sup.2 .fwdarw..sub.2 He.sup.3 +.sub.o n.sup.1 Of equal probability, however, when two deuterium nuclei collide is the fusion reaction: EQU .sub.1 D.sup.2 +.sub.1 D.sup.2 .fwdarw..sub.1 T.sup.3 +.sub.1 H.sup.1 The tritium so produced can be stored to generate an additional amount of helium.sup.3 by allowing radioactive decay to proceed as with the neutron-lithium.sup.6 reaction. A second problem with the D-He.sup.3 reaction is that more initial energy is required to overcome the nuclei potential barrier than for the D-T reaction. The optimum input energy allowing two nuclei to fuse for the D-T reaction is about 100 Kev and therefore giving a relative energy of 200 Kev during head-on collisions. Because the helium nucleus has two protons, it can be shown that the optimum input energy for fusion of the input particles must be doubled to about 200 Kev and thereby achieving a relative energy of 400 Kev during head-on fusion collisions. However, as the resultant energy from the D-He.sup.3 reaction is 18.3 Mev as compared to 17.6 Mev for the D-T reaction, the net gain in energy favors the deuterium-helium.sup.3 reaction. Achieving sustained fusion conditions allowing essentially 100% utilization of fuel with either the D-T or D-He.sup.3 reaction at the magnetic convergent point in the drift region of the present invention will require a high density of ions in addition to high relative energy between particles. As the geometry of the magnetic focus, fusion region of the present invention is a mirror image of the ion source geometry, it is, of course, important that the ion source geometry have as small dimensions as possible to produce the highest concentration of input nuclei at the magnetic convergent point. One method of achieving this goal is to use a modification of an invention by the American inventor, Nicola Tesla (U.S. Pat. No. 493,776, Incandescent Electric Light, 1892). In this invention Tesla showed how a small button of refractory material such as diamond could be heated to incandescent temperatures by allowing the material to be bombarded by ions as caused by the application of a high voltage, high frequency excitation to the refractory material. One embodiment of the present invention makes use of Tesla's Incandescent Electric Light by adding a few thousands of an inch diameter hole through the refractory material button. The added hole allows the passage of the input gases as required for the fusion reaction. As the gases are passing though the hole in the center of the button, they are heated to a high temperature that can be in the range of 5,000.degree. F. as they make contact with the inner walls of the refractory material (diamond, for example). Upon leaving the hole exit, the already thermally excited molecules of gas are then totally ionized by the high intensity, RF field in combination with the concentrated ion bombardment created by the RF field. The net result is a highly concentrated ion source insuring that the ion concentration at the magnetic focused point of the present invention will be sufficient for a high probability of fusion reactions occurring. With either the D-T or the D-He.sup.3 fusion reaction two problems are encountered in using the potential well approach that need to be addressed. The first is the mutual repulsion force acting between the positively charged ions trapped in the potential well. This force will act to defocus the particles as they are made to magnetically converge within the drift region of the device. As the amount of defocusing as caused by the mutual repulsion force is proportional to the number of ions present, adding ions to the potential well in order to increase the density at the convergent point will tend to be nullified by the increased repulsive force. Offsetting this effect, however, is the fact that free electrons will always be present in the ion stream that will act to shield the individual ions from each other. Electron shielding will therefore permit high nuclei density in the oscillating beams at their convergent points. A second potential cause of defocusing of the ion beam at the convergent points is the problem of ion scattering as caused by near misses of two approaching nuclei. Most ions, in fact, will experience many scattering collisions before encountering a fusion collision. After a scattering collision the near miss of the two ions can cause an alteration of trajectories approaching 90.degree. and without corrective action there would be little hope of achieving an appreciable number of fusion reactions at the magnetic focus region as the particles would be scattered before a fusion reaction could occur. The corrective action is achieved by the fact that the initial ion scattering occurs in a magnetic field that controls the flight of the two particles after scattering happens. The magnetic field forces the nuclei to return to the exact spot where the initial scattering occurred during the next oscillation of the particles through the potential well of the apparatus. The ion density at the magnetic focus region is thereby allowed to increase as new ions are added to the well despite scattering. An ion trajectory moving exactly perpendicular to the axial magnetic field of the encompassing solenoid after scattering (the 90.degree. scattering angle) will always cause the trajectory to be a circle and in one revolution the ion will return to the precise site in the magnetic focus region at which the initial scattering occurred. It can be shown that the maximum radius of curvature will be about 9 centimeters for a 90.degree. scattered, 200 Kev deuterium ion and a little over 11 centimeters for a 200 Kev helium.sup.3 ion when the scattering happens in a 10,000 gauss magnetic field. The general case scattering angle will be less than 90.degree.. Scattered ions normally will then have two components of velocity, one parallel to the magnetic field and the second perpendicular to the field at a radius of curvature less than the 90.degree. case. The general case trajectory of an ion experiencing a near miss at the site of the magnetic focus region will, therefore, be a helix of diameter, D, less than 2.times.11 or 22 centimeters and having an axial velocity bringing it to one or the other of the accelerating rings of the potential well generator. If the ring diameter is at least 2D (44 centimeters) the ion will pass through and then experience deceleration as it leaves the ring's vicinity. When the electrode has brought the ion's velocity and thus its helix diameter to zero, the ion will then exactly retrace its path through the accelerating electrode and converge with other ions to the spot in the magnetic focus region where the near miss scattering collision had previously occurred. Therefore, even if the ion scattering occurs within the magnetic focus region, the action of the axial magnetic field will always bring the scattered ions back to a convergent point. By continually feeding new ions into the stream, the nuclei density at the magnetic focus/fusion point will continue to increase until fusion reactions are occurring at the same rate as new ions are being introduced and thus, essentially 100% fuel utilization and thus 100% fusion energy production is the result. One embodiment of the present invention would be for a spacecraft propulsion engine in which a U-shaped configuration of the magnetic containment field solenoid would be used to direct the ions produced from the fusion reaction in essentially the same direction when exiting the two solenoid and thus produce a net thrust to the craft. A second embodiment of the present invention would be for the generation of output power by placing two heat exchangers at the exit ends of the solenoid to intercept the resultant fusion ions and thus convert their kinetic energy to heat. In the latter power generating configuration a straight solenoid could be used as net thrust would not be required to be produced. In the power generating configuration the two heat exchangers could then be used to produce superheated steam allowing the generation of electrical energy from conventional turbogenerator power generating plants. It can be shown that a modest size, 10,000 pound thrust, spacecraft propulsion unit, when equipped with the necessary heat exchangers for the conversion of the kinetic energy of the fusion particles to heat, would have an output capacity of over 500,000 megawatts (0.5.times.10.sup.12 watts) in the kinetic energy of its exhaust. This is a prodigious amount of power and can be compared to the total power level of the 15.times.10.sup.12 watts presently used by the world including all forms of fossil fuel combustion in addition to the world's total electrical production. One 10,000 pound thrust engine as described is therefore capable of generating approximately 1/25 the power requirements of the world. Of course, a larger number of smaller capacity units could also be constructed allowing both more manageable size power generating stations and greater flexibility of energy distribution. Converting some electrical energy produced at the output of the turbogenerators into hydrogen (electrolysis of water to hydrogen can be accomplished at an 83% energy efficiency conversion level), could also be employed as a means of further increasing the ease of energy distribution and use. Hydrogen as a gas could be used as a direct replacement for all present low pressure burning of fossil fuels such as space heating and gas/oil/coal driven electrical power generating plants. By this means roughly 75% of the present world's CO.sub.2 production and thus the Greenhouse Effect would be eliminated. The remaining 25% of the present world's CO.sub.2 production is caused by the use of internal combustion engines required primarily for transportation. Electrical energy produced from the fusion engine could first be converted to hydrogen, and the hydrogen could then be combined with carbon monoxide in a catalytic convertor to result in methanol. Methanol is a liquid at room temperatures and can thus become the direct replacement for gasoline while allowing the use of existing internal combustion engines with only minor fuel mixture modification. |
description | In general, the present invention relates to a method and apparatus which enable high resolution particle beam profile measurement. There is no admission that the background art disclosed in this section constitutes prior art. To be able to use a particle beam, such as an electron beam, by way of example and not by way of limitation, to create a pattern on a substrate, it is important to know the profile of the beam. The profile of the beam refers to the intensity of the beam as a function of position/location on the beam. Knowledge of the profile of the beam is innately valuable, because it shows how the particles, electrons for example, are being put down on the substrate, which determines how the pattern is formed. Since formation of the pattern on the substrate is carried out by making one little shape, and then another right next to it, and another little shape next to that, understanding at the very edges of the shapes how those shapes combine is important. For example, when a the pattern being formed is an image in a photoresist, whether for direct production of a semiconductor device, or in the fabrication of a photomask/resist, the pattern is being created “blind”, where the actual pattern being created is not visible. Knowledge of the profile of the beam enables the technologist to be able to predict the pattern image which is being created in the photoresist. In fact, knowledge of the profile of the beam enables the technologist to “tune” the beam profile in order to obtain a desired pattern image in the photoresist. The general shape of the beam may be a rectangle, a triangle, or a square, for example, and the beam profile will be different for each general shape. Typically, a particle beam profile such as an e-beam profile has been determined by scanning the beam relative to edges in two orthogonal directions and measuring the beam current that is not obscured by the grid with a detector. Most simply, the edge is held stationary, and the particle beam is scanned (position is changed via deflection as a function of time) over the edge while the number of particles (e.g. current) that pass the grid striking a detector is monitored as a function of time. Because both the position of the particle beam and the current are known as related to time, the current is also known as a function of position. The current striking the detector is the integral of the particle-beam current density that is not obscured by the edge. To re-obtain the particle-beam current density profile, software may be used to take the derivative of the current versus position function. One of skill in the field of particle beams will recognize that there are several shortcomings in the simple method of measuring a beam current-density profile; particularly if the beam is blanked (rapidly turned on and off) or scanned during normal use, as these actions may distort the dose deposited on the target as compared to the beam profile. In this sense, the dose is the time integral of the particle-beam current-density profile as it strikes the target. For example, instead of continuously scanning the beam over the edge, the beam may be stepped over the edge. In stepping, the beam is moved in small increments and then held steady while the current is measured in each position for a longer time. The longer time period at each beam position relative to the edge allows for a more accurate measurement of the current at each position. Typically 100 to 1000 unique positions would be measured, and particle beams may range in extent from 25 nanometers to 2000 nanometers. The exact relationship between the number of unique positions and the size of the particle beam will depend on the spatial resolution required by the application and the time allowed to take the measurement. For maximum resolution, the distance between unique steps must be less than ½ the width of the point spread function (PSF) of the metrology array edges, which, for the invention described herein would be less than about 1.5 nanometers(nm). Additional complexity may be added to the measurement to obtain more accurate information. For example, the particle beam may be blanked on and off repeatedly at each unique measurement position to account for blanking affects. If the particle beam is scanned during normal operation, the blanking may be combined with scanning the beam where the beam is unblanked at the position of the scan corresponding to the unique measurement position. A metrology array is used to measure beam profile. The metrology array most commonly used has been a square lattice. The openings in the array are typically such that the ratio of opening to bar is about 1:1. A limiting factor of this design is the heat conduction from along the bar, due to interaction of the beam with the bar. The limited availability of heat conduction changes the temperature at the measurement point, and thermal expansion at the measurement point causes the grid to drift. When the grid drifts with respect to the particle beam, the measurement changes, making the measurements inaccurate. A critical figure of merit for a metrology array is the width of the point-spread function (PSF). The PSF is the effect of convolution between the metrology array and the particle beam. To convincingly measure the profile of an electron beam, without relying on deconvolving the metrology array, for example, the PSF of the array should be at least 3 times smaller than the intrinsic blur of the electron beam. The blur of the electron beam as used herein means the width of the profile edges. For example, one metric of the blur is the Y direction or X direction distance between 20% and 80% of the maximum current density on a plot of the kind shown in FIGS. 4-6 of the present disclosure. To measure the profile of an electron with intrinsic blur of 10 nm, the PSF of the metrology array should be in the range of 3 nm. The current state of the art for a metrology array is approximately 30 nm, although isolated edges with the required PSF exist. In an effort to reduce the PSF of the metrology array, efforts have been made to increase the effective opaqueness of the material on the surface of the array. The scattering of electrons passing through the array material is analogous to the opaqueness of the material. Since the scattering probability of a material is proportional to Z2, high-Z materials are often deposited on silicon metrology arrays after fabrication of the array. This not only requires additional processing of the array, but also roughens the edges of apertures in the array, further increasing the PSF of the aperture. Another important factor in determination of the PSF of the metrology array is the kind of edge present at the edges of the apertures in the array. Silicon metrology arrays typically are created using an etch process that creates sidewalls which are at about a 55 degree angle with respect to a horizontal surface beneath the sidewalls. This angle causes an increase in the PSF due to the limited material thickness near the edge of the aperture, making opaqueness a function of distance from the edge. To emulate a step function in opaqueness of the aperture, those skilled in the art have created high-angle edges (knife edges) by cleaving a crystal of indium phosphide, for example. This method of creating edges creates only a single edge and is not reliable in terms of a manufacturable, reliable means of edge creation. There is currently a need in the industry to reduce the PSF of a metrology array, so that better resolution of a particle beam profile measurement can be achieved. The PSF for a metrology array for high resolution particle beam profile measurement has been improved by improving five major elements of the metrology array which impact the PSF of the array. While improvement in each of the five elements provides and improved PSF, a combination of all five of the elements provides an unexpected synergistic effect. The individual element improvements are as follows. 1) The metrology array comprises a plurality of slots rather than the previously-used square openings of the kind described above. The use of slotted openings in the metrology array reduces thermal effects because the thermal resistance away from the measurement point is lower. The lower thermal resistance is achieved because a lower percentage of the array substrate is removed than in a 1:1 square grid design, for example. 2) At least the upper 0.25 μm of thickness of the metrology array is comprised of a high-Z (high atomic number) material. Typically the upper 1 μm of thickness is essentially the high-Z material. In some instances, the entire substrate may be a high-Z material. A high-Z material is one in which the atomic number of the material is at least 45. The use of a high-Z material improves the opaqueness of the material to the particle beam, improves the scattering probability at the solid surfaces of the metrology array substrate, and provides better resolution in the backscattered image used to produce the beam shape profile. 3) The sidewalls on the slotted opening area of the metrology array substrate form an angle with a horizontal surface at the base of the metrology array substrate which is at least 75°, and which typically ranges from about 83° to about 89°. The steeper sidewall angles of the slotted opening in the metrology array substrate provide better contrast along the edge of the slot, because the edge transitions from 100% transmitting to 100% opaque is less distance. 4) The radius at the upper corner (knife edge) of a slotted opening ranges from about 1 nm to about 5 nm. The high Z material is applied to the substrate at an appropriate time in the manufacturing process, with respect to before or after slot formation, to minimize the radius. 5) The edge roughness at the upper corner (the knife edge) of each slot is less than 5 nm RMS, and typically ranges from about 1 nm RMS to about 3 nm RMS. The reduction in edge roughness from that typically present prior to the present invention also improves the contrast along the edge of the slot, so that there is less blur of the edge in the backscattered image used to produce the beam shape profile. As previously discussed, a critical element for a metrology array is the width of the point-spread function (PSF). To accurately measure the profile of a particle beam, such as an electron beam, for example and not by way of limitation, the PSF should be at least three times smaller than the intrinsic blur of the electron beam. A typical particle beam blur for current day device feature sizes is in the range of 10 nm. The current apparatus (metrology arrays meeting the elemental requirements of the present invention) is capable of providing a PSF of about 3 nm or less. As a preface to the detailed description, it should be noted that, as used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents, unless the context clearly dictates otherwise. Use of the term “about” herein indicates that the named variable may vary to ±10%. A substantial improvement in the measurement of a particle beam profile has been achieved using an improved metrology array over which the particle beam is scanned to obtain the beam profile. The point-spread function (PSF) of the a metrology array has been improved to provide better resolution of the particle beam profile. Although the embodiments described herein are with respect to an electron beam profile, one skilled in the art will see that the principles applied in the improvement of the metrology array are applicable to the improvement in measurement of beam profile with respect to any particle beam. The metrology array has been improved by improving five major elements of the metrology array which impact the PSF of the array. While improvement in each of the five elements provides and improved PSF, a combination of all five of the elements provides an unexpected synergistic effect. By creating a metrology array which includes improvement of all five elements in the manner described, the PSF of the metrology array has been reduced to less than 3 nm. FIG. 1 shows a simulated plot 100 of the measured current on axis 102 as a function of beam position with respect to the grid, including noise, on axis 104. The simulated plot is for a square beam which is 200 nm in extent with 20 nm wide tails, where the beam is scanned over a theoretical metrology array with step-function contrast to produce a plot. Upon reviewing the plot 100, it becomes readily apparent that measuring the width of the tails of the beam at the low current region will provide a more accurate measurement at the edge of the beam. The low current portion of the plot where the magnitude of the noise is less should be considered, because the noise level will not increase the apparent PSF of the metrology array beyond the desired PSF, which is in the range of 3 nm or less. FIG. 2A shows a top view schematic 200 of one embodiment of a slotted metrology array of the kind which may be used in the present invention. The slots 202 are placed in a grid, where four slots make up a square 203 and, and where a portion of the slots 202 are shared between sidewalls for two squares. The length of the sidewall 204 of a square is designated as “a”, which can be a nominal distance determined by the measurement application. When the particle beam profile which is being measured is an electron beam, the nominal value “A” ranges between about 25 μm and about 2.5 μm. The length 206 of the slot 202 in this particular embodiment is 0.6 times a. The width 208 of the slot 202 is 0.1 times a. The end distance 210 of solid array substrate at each end of the slot 202 is 0.2 times a, so that the slot 202 plus two times the end distance 210 equals a total sidewall 204 length, a, of each square. The aspect ratio of a slot, the height of a sidewall (not shown) divided the width 208 of a sidewall may be varied depending on the application. The length and width of a slot relative to the sidewall length for a square is a trade off between heat conductivity and the ability to use the slot to find a location on a substrate. Typically the ratio of the length of the slot to the width of the slot ranges from about 3:1 to about 6:1. The pattern shown on FIG. 2A continues arbitrarily off toward the edges of that which is shown. FIG. 2B shows a top view schematic 220 for a second embodiment of a slotted metrology array of the kind which may be used in the present invention. The slots 222 are placed in a grid, where four slots make up a square 223 and, and where a portion of the slots 222 are shared between sidewalls for two squares 223. The length of the sidewall 224 of a square is designated as “a”, which can be a nominal distance determined by the measurement application. When the particle beam profile which is being measured is an electron beam, the nominal value of “a” ranges between about 25 μm and about 2.5 μm. The length 226 of the slot 222 in this particular embodiment is 0.6 times a. The width 228 of the slot 222 is 0.05 times a. The end distance 230 of solid array substrate at each end of the slot 222 is 0.2 times a, so that the slot 222 plus two times the end distance 230 equals a total sidewall 224 length, a, of each square 223. The slots 232 which are interior to square sidewalls 224 have a length 234 of about 0.25 times a. The interior slots 232 have a width 236 of 0.1 times a. A centerline through interior slots 232 forms an angle θ of 45° with sidewall 222. The center distance 240 between interior slots 232 is 0.2 times a. The metrology array shown in FIG. 2B may be used to look at beams that are not rectangular in shape, for example, beams which are triangular in shape. Although the two embodiment metrology arrays shown in FIGS. 2A and 2B are four-fold designs, one skilled in the art can envision additional shapes and patterns which can be used in the array and still take advantage of the elements of the invention described herein. It is not intended that the invention bel limited to these grid designs. In any case, a design similar to the four-fold pattern shown in FIG. 2A offers the advantage that 88% of the high-Z substrate used as the substrate for the array surface remains after patterning. This increases the thermal mass of the structure, limiting the temperature rise which occurs on the array surface during profiling of the beam. Additionally, the gaps between bars are designed to optimize thermal conductivity away from the slots used as the metrology site. Since a lower temperature means less thermal drift takes place on the substrate surface during beam profiling, the beam position with respect to the edge is better known, and the measurement is more accurate. FIG. 3A shows a side view schematic of a slot 300 of the kind used in FIG. 2A. The slot 300 has a width 302 having a nominal value 303, a length 306 having a nominal value 307, and a depth 304, having a nominal value 305. The bottom 308 of slot 300 is open. The bottom 308 of slot 300 is a horizontal surface. Sidewalls 304a and 304b are at an angle α with respect to bottom 308 of slot 300, as shown in FIG. 3B. The aspect ratio of the slot 300 is the depth of the slot D divided by the width of the slow W. Typically, the aspect ratio for a slot 300 used to form a grid in a matrix array of the kind described with respect to the present invention ranges from about 1:10 to about 10:1. More typically, the aspect ratio ranges from about 4:1 to about 10:1. The angle α typically ranges from about 80° to about 89°. More typically, the angle α ranges from about 85° to about 88°. FIG. 3B also shows the corner 312 at the upper surface 301 of the slot 300. The corner 312 at upper surface 301 forms a radius R between sidewall 304a and surface 301, and between sidewall 304b and surface 301. This radius R typically ranges from about 1 nm to about 5 nm. Further, corner 312 has a surface finish which is designed to provide contrast at the edge provided by corner 312. Typically the surface finish ranges from about 1 nm RMS to about 3 nm RMS, and frequently is in the range of about 2.5 nm. With respect to the high Z materials which need to comprise the metrology array substrate, at least in the upper portion of the slotted apertures, materials such as tungsten or tantalum work well. Other materials such as indium phosphide, gold, platinum, which have an atomic number of at least 45 may also be used. When it is desired to have only an upper portion of the matrix array formed from the high Z material, due to difficulty in forming the slots in the high Z material, it is possible to use a thin layer of the high Z material which is bonded to a surface of the matrix array. For example, and not by way of limitation, a thin foil of tungsten having slots formed therein using a technique such as FIB cutting may be applied over another substrate surface which is used for support. The tungsten foil thickness must be sufficient to absorb or back scatter nearly all of the electrons that strike the foil. In practice, about 1 μm of tungsten thickness is more than adequate. However, tungsten foil is generally available commercially in thicknesses down to 10 μm. While 10 μm surpasses the requirement and may be used, this additional thickness in the foil makes formation of the slots in the foil more difficult. With this in mind, thinner foils should be used if they are available. Alternatively, thin films of tungsten or platinum or other high Z material may be deposited on a carrier material such as silicon, by way of example and not by way of limitation. FIG. 4 shows an exemplary simulated beam profile for a square shaped beam, scanned over a perfect metrology edge (having no blur caused by the metrology edge). The simulated beam profile was created using software known in the art, with the assumptions of a 100 nm square beam exhibiting a 10 nm blur on the beam tales, measured with an array exhibiting a 0 nm PSF. Plot 403 shows the beam current density in nA on axis 402, as a function of the beam position in X nm on axis 404. Plot 407 shows the beam current density in nA on axis 406, as a function of the beam position in Y nm on axis 408. Simulated beam profile 400 shows the beam current density in pA/nm2 on axis 410 as a function of the beam position in X nm on axis 412 and the beam position in Y nm on axis 414. FIG. 5 is for comparative purposes, and shows an exemplary simulated beam profile for a square shaped beam scanned over a square-shaped opening metrology array of the kind typically used in the industry prior to the present invention. The assumptions were a 100 nm square beam, exhibiting a 10 nm blur on the beam tales, measured with an with an array exhibiting a 30 nm PSF. Plot 503 shows the beam current density in nA on axis 502, as a function of the beam position in X nm on axis 504. Plot 507 shows the beam current density in nA on axis 506, as a function of the beam position in Y nm on axis 508. Simulated beam profile 500 shows the beam current density in pA/nm2 on axis 510 as a function of the beam position in X nm on axis 512 and the beam position in Y nm on axis 514. FIG. 6 shows an exemplary beam profile for a square shaped beam, scanned over a metrology edge which meets the requirements of the present invention. The assumptions were a 100 nm square beam, exhibiting a 10 nm blur on the beam tales, measured with an with an array exhibiting a 3 nm PSF. Plot 603 shows the beam current density in nA on axis 602, as a function of the beam position in X nm on axis 604. Plot 607 shows the beam current density in nA on axis 606, as a function of the beam position in Y nm on axis 608. Simulated beam profile 600 shows the beam current density in pA/nm2 on axis 610 as a function of the beam position in X m on axis 612 and the beam position in Y nm on axis 614. Clearly the array of the present invention enables one skilled in the art to have a more accurate understanding of the shape of the beam, which enables the creation of a pattern of smaller feature size, the alignment of patterns during manufacturing with greater accuracy, and the determination of whether a semiconductor device meets specification when the feature sizes are in the ranges discussed herein, for example. One skilled in the art will recognize the myriad of applications for the present invention. While the invention has been described in detail above with reference to particular schematics and drawings, various modifications within the scope and spirit of the invention will be apparent to those of working skill in this technological field. One skilled in the art, upon reading applicants' disclosure, can make use of metrology arrays which utilize slotted openings as apertures in the array; aperture sidewalls where the sidewalls form an angle with a horizontal base which is at least 75°, and typically range between about 80° and 89°; knife edges at the upper corners of the array surface, where the corner radius included within the knife edge ranges between about 1 nm and about 5 nm; a finish on the knife edge upper surface of the apertures which ranges between about 1 nm RMS and about 3 nm RMS; and a high-Z material as the substrate material in which the array apertures are formed. Various combinations of these advantageous array features may be used to reduce the blur produced as a result of the metrology array design. By optimizing each of these advantageous array features for a given particle beam, the blur produced can be substantially reduced, permitting one skilled in the art to take advantage of the invention disclosed. Accordingly, the scope of the invention should be measured by the appended claims. |
|
description | The method and apparatus for a neutron based portable system for detection of specific elements is described herein. There are three separate elements which comprise the method and apparatus of the present invention. They include: (i) the portable probe and control equipment; (ii) data de-convolution; and (iii) object identification. Each will be dealt with individually herein. I. Probe Construction The apparatus is shown schematically in FIG. 1 wherein each of the separate elements of the portable apparatus 10 are shown. The portable pulsed neutron detection system 10 is comprised of multiple elements including the probe 10, low voltage power supply 32, portable computer 30, data and power lines 25 and 26. The entire apparatus is lightweight and easily movable which allows the apparatus 10 to be used in many different environments without the need of a heavy, permanently placed stand alone apparatus. The probe 20 is constructed of multiple elements. The probe 20 is encased in a stainless steel cylindrical housing 27 and has a diameter of less than 5 cm. The probe has a length of around 2 meters and weighs around 36-45 kg. Inside the housing 27 is found the electronics and other apparatus for emitting, detecting and controlling the probe. At the distal end of the probe housing are found gamma ray detectors 21 for detection of the gamma rays emitted from the interrogated object after subjecting it to pulsed neutrons. Next in line within the probe 20 is found shielding material 22 which separates the neutron emitter 23 from the detectors 21. The pulsed neutron generator is found adjacent to the shielding material and emits pulses of neutrons at 14 MeV. Finally there is found within the probe housing 27 the electronics which generate the low and high voltage power supplies and electronics which control the gamma ray detectors. The gamma ray detectors 21 found at the distal end of the probe 20 are high efficiency detectors made of Bismuth Germanate or Gadolinium Orthosilicate. The gamma ray detectors 21 are organized in linear geometry. The materials which constitute these gamma ray detectors are important in the operation of the present apparatus and should therefore be able to detect low intensities of the gamma rays. The orientation of the actual detectors within the probe does not particularly affect the efficiency of detection of levels corresponding to carbon, nitrogen and oxygen and a linear orientation is set forth herein for explanatory purposes. Many different orientations are possible as long as the probe calibration is adjusted appropriately. These detectors are temperature stabilized to avoid any changes in the light collection efficiency. Thus, the analog amplitude of the signal generated from the gamma ray detectors 21 does not deviate for a given gamma ray detected. The temperature stabilization is accomplished through a thermo-electrically controlled jacket which surrounds each detector. Each detector is connected to a photomultiplier which changes the optical or light output of the detector to a voltage signal. A resistor chain and preamplifier provide high voltage to the photomultiplier and shape and pre-amplify the analog photomultiplier output. The resistor chain is connected to the base of the photomultiplier tube. After pre-amplification, each gamma ray signal detected by the detectors 21 is sent through the data link 25 to the data acquisition system or computer 30. The data acquisition system 30 is comprised of multiple parts consisting of an amplifier, an analog to digital converter, voltage stabilizers and live-time correction. The live-time correction of the gamma-ray detection signals acts to correct for the delay in which the analog to digital converter is busy analyzing and converting data. Within computer 30, the analog signals provided by the photomultiplier representing the counts of gamma photons detected by detectors 21 during a specified time period are amplified and converted to representative digital values by an analog to digital converter. The amplitudes of the signals received by the computer 30 fluctuate within a range of 0-10 Volts and correspond to the energy channel or level of each gamma ray detected by the gamma ray detectors 21. The analog to digital converter utilized in the data acquisition system converts these amplitude values to digital values for use in the data deconvolution and object identification steps detailed herein. The digital value converted from this amplitude signal represents the number of detected gamma rays. These digital values are then stored in a database on the computer 30. The neutron generator 23 is a sealed tube deuterium tritium neutron generator and provides pulsed neutrons at 14 MeV. Each pulse is several microseconds wide and has a frequency of between 10 kHz and 14 kHz. The pulse separation, depending on the pulse width and pulse frequency, varies between 85 and 90 microseconds. These pulsed neutrons initiate the fast neutron reactions described above within the object being interrogated. Outgoing gamma rays emitted by the object are detected by the gamma ray detectors 21 for a specified time period. The gamma rays are measured and recorded as a single spectrum of data during that time period in the data acquisition system 30. At the end of the neutron pulse, the fast neutrons are thermalized at which point they initiate neutron capture reactions with the object. The gamma rays from these reactions are detected again by the detectors 21 and they are stored similarly as with the prior spectrum data. However, this spectrum data is offset within the computer systems 30 memory so as to have two distinct spectrum data from separate time periods. The ability to measure two separate gamma ray spectra created by these reactions and store said data utilizing the same equipment provides a significant advantage over prior art devices. Previously, detecting and storing two distinct gamma ray spectra has required separate electronic components. Further, the present apparatus and method utilizes data collected from a third spectrum from the activation analysis. To detect elements through activation analysis, the neutron generator bombards the object under interrogation for a few minutes or a few seconds, depending on the material being detected. For example, phosphorus must be bombarded for proper detection for about 5 minutes while sodium only requires about 30 seconds. The generator is then turned off and the activation gamma rays are acquired for a time equal to the bombardment time. The activation data is then further utilized to determine the material contained within the object under interrogation. Radiation shielding 22 and 29 is provided and comprised of a high atomic number material such as lead or bismuth. The shielding 22 separates the gamma ray detectors within the probe from the neutron generator 23. Additional shielding 29 is also provided concentrically around each of the detectors 21, surrounding it through at least 125 degrees, and preferably around 235 degrees. This shielding prevents detection of gamma rays emitted from the generator tube 23 and from materials in the background. The concentric shielding 29 provided on the detectors 21 allows the probe to differentiate the contents of two objects when the probe 20 is placed between them. One spectrum of data may be taken with the concentrical shielding 29 towards one of the objects and another is measured with the shielding towards another object. The preferred embodiment of the probe construction contains shielding about 235 degrees of the detector as is shown in FIG. 8. Voltage supply 24 provides 6 V, 12 V and 24 V low voltage for the detectors electronics and the neutron generator electronics. The voltage supply 24 also provides 900 V to 1300 V high voltage for the detectors 21. Differing values of the supplied voltage may be required due to varying requirements from the specific type of detector utilized. Three thousand volts (3,000 V) are provided for the pulsing of the neutron beam and 110,000 V high voltage is provided for the deuterium acceleration within the neutron generator. The probe 20 can also operate with a high voltage power supply residing external of the cylindrical probe 20 thereby reducing the size of probe 20. Such external connection to a high voltage supply would require a high voltage connector between the probe and supply. Neutron generator controller 32 controls the pulsing of the neutron generator 23 and is designed according to the specific design requirements of the particular application. The controller 32 additionally provides controlling logic for the low voltage supplied by voltage supply 24. Additionally, controller 32 can contain diagnostic electronics for the operation of probe 20. Computer 30 is powered by the low voltage power supply 24 and is connected to the probe via data link 25. Computer 30 conducts the appropriate amplification and conversion of the analog data signals generated by the gamma ray detectors 21. Computer 30 also produces the appropriate offset of the gamma ray spectra so that the same analog to digital converter can be used for the separate acquisition of gamma rays produced from both fast and thermal neutrons on the same detector. The computer 30 additionally contains the appropriate software for data reduction and elemental characterization which allow real time analysis of the data. The relationship of the spectra of data collected by each detector and the manner in which computer 30 stores said data are shown in FIG. 9 wherein the detector 21 is shown as well as memory 40 such that when a signal is provided by the detector 21 through cables 25, the data is typically stored in a single memory space due to the fast detection and storage requirements inherent in these types of detection systems. However, due to the requirement of storing two sets of data generated at two different time periods, said periods being within microseconds of each other, the computer offsets the write portion in memory where the data is stored. The fast neutron signals typically last 14 Fs and are represented as signal 1 in FIG. 9 as 48. This signal is stored in the upper portion of the memory storage area for that particular detector 21. After 14 Fs, the thermal neutron signal 49 is generated. Without the offsetting of the write portion of the computer for saving these data, the second set of data would overwrite the first set of data detected representing fast neutrons. Thus, in this short time period, computer 30 offsets the write pointers in order to properly store the data for multiple sets of signals detected by detectors 21. This cycle is repeated for several seconds or minutes, depending on the investigation carried out. For the neutron activation data, since no cycling is involved and the neutron generator is turned off, the output from detector 21 in FIG. 9 is stored as signal 3 in a separate part of the computer memory. Upon completion of the data acquisition, the acquired files are transferred to the de-convolution computer code residing within computer 30 for analysis. Data link cables 25 and 26 are coaxial shielded cables that provide the probe with the necessary voltages and carry to the controller 32 and computer 30 the detector signals and diagnostic signals. The cables can have a length of up to 17 m allowing the operation of the probe from varying distances. II. Data De-Convolution Shown in FIGS. 2, 3 and 4 are gamma ray spectra from fast neutron, thermal neutron and neutron activation reactions. Each spectrum contains several gamma-rays produced from chemical elements contained in the interrogated object. The peaks in the spectrum, of FIGS. 2-6, represent particular elements present in the sample while the numbers associated with the peaks represent the energy, in kiloelectron volts, of the respective gamma rays. Data is collected for the specific probe geometry or detector configuration utilized in probe 20. Each probe is required to be properly calibrated based upon actual physical configuration of detectors 21, size of detectors, shielding geometry and position of the generator relative to the detectors. For a given detector and a given detection geometry, geometry meaning the probe configuration, each chemical element produces a characteristic gamma ray spectrum which is called a response spectrum. FIG. 5 shows a response spectrum produced from a carbon sample placed in front of the gamma ray detector bombarded with fast neutrons from the neutron generator 23. A gamma ray spectrum from any innocuous material or from a suspect drug or explosive will contain several chemical elements including hydrogen, carbon, nitrogen and oxygen. Depending on the packaging and surrounding materials, it can also contain elements such as silicon, chlorine, iron, lead or other elements. In the absence of any sample placed in front of the detector, the detector 21 will record gamma rays emanating from the materials surrounding the detector as well as from the materials inside and around the neutron generator 23. This spectrum is called the background spectrum. The de-convolution computer code used for the reduction of the data represents the counts or incidences of gamma rays in each energy channel of the spectrum by the equation: f [ i ] = ∑ k c k * m k [ i ] + a * bg [ i ] ( 1 ) where f[i] is the number of counts in the i-th energy channel of the fitted spectrum, ck is the multiplication coefficient for the response spectrum of the k-th element, mk[i] is the number of counts in the i-th energy channel of the response spectrum of the k-th element, a is the multiplication coefficient of the background, and bg[i] is the number of counts in the i-th energy channel of the background. The mk[i]""s are determined by measuring the spectrum of a sample containing only one chemical element (the response spectrum). The coefficients ck and a are determined by the least squares method, minimizing the general c2 expression: c 2 = ∑ i ( y i - f [ i ] ) 2 / s i 2 ( 2 ) where yi and si are the measured counts in the i-th energy channel and the statistical error respectively. For a given probe configuration (position of detectors 21 relative to the neutron generator, size of each detector, which as previously indicated are cylindrical and 2.5 to 5 cm in diameter and 5 cm in length, collimation of each detector, etc.), response functions are measured for all the major and minor chemical elements (hydrogen, oxygen, chlorine, etc.) that are expected to be detected. To measure a response function, a sample containing primarily the chemical element of interest is placed in front of the detector. The neutron generator is turned on and a spectrum is accumulated. For some elements, such as chlorine, the response spectrum is due primarily to thermal energy neutrons. In this case the response spectrum will be used for the analysis of data from this particular neutron energy. In other cases such as earbon, a gamma ray response spectrum can be formed from both fast neutron arid thermal neutron reactions. Finally, the gamma ray response from thermal, fast neutron and activation reactions may all be utilized. All these response spectra are stored as a library in the computer. As long as the probe configuration is not altered, these spectra can be used irrespective of the locality where the probe is used and the type of object being interrogated. When the probe is to be used for specific interrogation, the probe is placed at the position where the measurement is to take place. Without placing in front of the detector the object to be interrogated, the probe is turned on and a spectrum is taken under the exact same conditions (pulsing frequency, time interval of data accumulation) as it would be used for the measurement of the object under interrogation. In the case of an object that cannot be removed, a spectrum is taken at a distance from the object but in its vicinity. This spectrum is called the background spectrum. Since separate spectra are accumulated for fast neutron and thermal neutron induced reactions, these are two distinct background spectra recorded. While the response spectra remain the same for a given probe configuration, irrespective of where the probe is used, the background spectrum is specific to the measurement. Prior to the initiation of the measurement, the background spectrum is examined, the major and minor chemical elements present in it are recognized and recorded. When a spectrum is accumulated, it is displayed and all major and minor chemical elements which were not observed in the background spectrum are also recorded. The de-convolution software is started and the major and minor chemical elements present in the background and the actual spectrum are listed. The software uses this list of elements for accessing from the library the response spectra of the elements of interest. The computer 30 additionally displays the specific background spectra. The data de-convolution software, using the information generated, utilizes equations (1) and (2) and provides a best fit to the data. To generate the best fit data shown in FIG. 6, multiple spectra are produced based upon assumptions in the content of the object being examined. The de-convolution code assumes certain amounts of each element of interest in the sample being interrogated. These assumed amounts are then utilized to generate a fitted spectrum utilizing the above referenced equations. Multiple iterations of adjusting the amounts of the assumed elements are then attempted by the de-convolution code until a best fit of the experimental spectrum is produced. This process is represented in the schematic of FIG. 10. The results of the best fit can be displayed as shown in FIG. 6. The figure contains the experimental spectrum, the fitted spectrum and the background spectrum. Below the spectra the difference at each energy channel between the experimental and fitted spectrum is displayed. The two horizontal lines above and below the difference spectrum are the 3s lines indicating 99% confidence limit. A table is also provided with the number of counts (in the form of counts per second or any other time unit desired) for each major and minor element detected above the background, along with the error for this measurement. III. Object Identification The de-convolution software provides information on the chemical elements contained in the interrogated object. This information is utilized in several ways depending on the environment of the object under interrogation. If the investigation is of same size objects under standard geometry conditions, the probe 20 can be calibrated absolutely so that the gamma ray counts for each element would correspond to a specific elemental content. This interrogation would correspond to a fixed probe configuration for interrogation of same-sized objects placed at a fixed position relative to the probe. To calibrate the probe for each element, samples with specific elemental composition are analyzed, and measured gamma ray counts versus elemental concentrations are established. An example of such analysis would be the examination of projectiles of similar size containing the same amount of explosives of differing composition. If the probe cannot be calibrated absolutely because the contents of the same sized objects vary in composition and density, the elemental composition of each object with differing content is established under the same geometry conditions. To differentiate and identify each object, a decision tree is made that depends on the elemental content of certain elements as well as elemental ratios of other elements. Such a decision tree is shown in FIG. 7. When interrogating objects under random conditions, if the elemental content cannot be uniquely determined from the number of counts for each element, elemental ratios can be uniquely determined. Ratios such as carbon to oxygen and carbon to nitrogen can be measured irrespective of the size of the object and position of the probe relative to the object. As an example, drugs hidden within innocuous materials such as coffee or sugar can be found by placing the probe close to the material and measuring the carbon to oxygen ratio. For sugar, the carbon to oxygen ratio is 1.1, for coffee it is 1.8, while for heroin and cocaine, it is 4.2. If the calculated number differs from the ratio expected for coffee or sugar by an amount larger than 3s, one can say with 99% confidence that the material contains something different than coffee or sugar. The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention or the scope of the appended claims. |
|
047524383 | claims | 1. In a nuclear reactor having upper internals comprising a lower plate with openings for flow of coolant out of fuel assemblies, an upper plate, support columns connecting the plates together and tubular guides for slidably receiving vertically movable control clusters, said guides being fixed individually to the upper plate, a device for individually guiding and centering the lower part of each of said guides in the lower core plate, comprising: a plurality of rigid blades carried by the lower part of the guide, spaced apart angularly about a vertical axis of the guide and engaged in said opening with a predetermined radial clearance, and a plurality of flexible blades located between said rigid blades and fixed to the lower part, having a shape at rest such that they resiliently bear on an edge defining the opening and exert a radial force thereon. a device for individually guiding and centering the lower part of each of said guides in the lower core plate, comprising: at least three rigid blades distributed at equal angular intervals about an axis of said guide, fast with said guide and projecting downwardly from said guide into an opening of said lowere core plate dimensioned to provide a radial clearance to said rigid blades; and at least three flexible blades interleaved with said rigid blades, fast with said guide and projecting downwardly from said guide into said opening, said flexible blades being so dimensioned when in released condition that they are resiliently bent inwardly by a surface of said lower core plate defining said opening when inserted in said opening. 2. Device according to claim 1, wherein the opening and the pluralities of blades have a rotational symmetry about the axis of the guide. 3. Device according to claim 2, wherein the opening is cylindrical in shape. 4. Device according to claim 2, wherein the opening is polygonal in shape, each angle of the polygon receiving one of the rigid blades. 5. Device according to claim 1, wherein said guide has a body and a base fixed to said body and wherein the pluralities of blades are fast with said base. 6. Device according to claim 5, wherein the blades are integral with the base. 7. Device according to claim 5, wherein contacting surfaces of the body and of the base have circular cross-sections and the base is provided with means for securing it to the body in an adjustable orientation. 8. Device according to claim 1, wherein the lower plate comprises means for retaining the flexible blades upon breakage thereof and preventing them from getting loose. 9. Device according to claim 8, wherein said means comprise a plurality or bridges each associated with a flexible blade and each fixed to the edge of the opening. 10. Device according to claim 1, wherein said radial clearance is of about 1 mm. 11. In a nuclear reactor having upper internals comprising a lower plate with openings for flow of coolant out of fuel assemblies, an upper plate, support columns connecting the plates together and tubular guides for slidably receiving vertically movable control clusters, said guides being fixed individually to the upper plate, |
claims | 1. A method of adjusting an X-ray optical apparatus, said X-ray optical apparatus including:an X-ray source; anda reflective structure in whichat least three reflective substrates are arranged with an interval, andX-rays which are incident into a plurality of passages, both sides of each passage being put between the reflective substrates, are reflected and parallelized by the reflective substrate at both sides of each passage to be emitted from the passage,wherein when one edge of the reflective structure is an inlet of the X-ray and the other edge is an outlet of the X-ray, a pitch of the reflective substrates at the outlet side is larger than a pitch at the inlet side,the method comprising adjusting the relative positions of the X-ray source and the reflective structure so as to reduce a penumbra amount formed by the X-ray emitted from each passage. 2. The method of adjusting an X-ray optical apparatus according to claim 1, wherein the penumbra amount is a penumbra amount formed by an object when the X-ray emitted from the passage is irradiated onto the object. 3. The method of adjusting an X-ray optical apparatus according to claim 1, wherein the penumbra amount is a penumbra amount formed by a one-dimensional grating when the X-ray emitted from the passage is irradiated onto the one-dimensional grating. 4. The method of adjusting an X-ray optical apparatus according to claim 1, wherein when the X-ray emitted from the passage is irradiated onto a first one-dimensional grating and a second one-dimensional grating which are disposed in order from the outlet side of the reflective structure, the penumbra amount is estimated based on an interval of moiré stripes of the X-ray formed by the two one-dimensional gratings. 5. The method of adjusting an X-ray optical apparatus according to claim 1, wherein when the X-ray emitted from the passage is irradiated onto a solar slit, the penumbra amount is estimated based on an intensity of the X-ray which passes through the solar slit. 6. The method of adjusting an X-ray optical apparatus according to claim 1, wherein in a state where a one-dimensional grating that allows the X-ray to be incident into only a specific passage is disposed between the X-ray source and the reflective structure, the penumbra amount is estimated based on a size of the X-ray emitted from the specific passage. 7. An X-ray optical apparatus, comprising:an X-ray source; anda reflective structure in whichat least three reflective substrates are arranged with an interval, andX-rays which are incident into a plurality of passages, both sides of each passage being put between the reflective substrates, are reflected and parallelized by the reflective substrate at both sides of each passage to be emitted from the passage,wherein when one edge of the reflective structure is an inlet of the X-ray and the other edge is an outlet of the X-ray, a pitch of the reflective substrates at the outlet side is larger than a pitch at the inlet side,wherein the X-ray source and the reflective structure are disposed so as to reduce a penumbra amount formed by the X-ray emitted from each of the passages. 8. The X-ray optical apparatus according to claim 7, wherein the penumbra amount is a penumbra amount formed by an object when the X-ray emitted from the passage is irradiated onto the object. 9. The X-ray optical apparatus according to claim 7, wherein the penumbra amount is a penumbra amount formed by a one-dimensional grating when the X-ray emitted from the passage is irradiated onto the one-dimensional grating. 10. The X-ray optical apparatus according to claim 7, wherein when the X-ray emitted from the passage is irradiated onto a first one-dimensional grating and a second one-dimensional grating which are disposed in order from the outlet side of the reflective structure, the penumbra amount is a value estimated based on an interval of moiré stripes of the X-ray formed by the two one-dimensional gratings. 11. The X-ray optical apparatus according to claim 7, wherein the penumbra amount is a value estimated based on an intensity of the X-ray which passes through a solar slit when the X-ray emitted from the passage is irradiated onto the solar slit. 12. The X-ray optical apparatus according to claim 7, wherein in a state where a one-dimensional grating that allows the X-ray to be incident into only a specific passage is disposed between the X-ray source and the reflective structure, the penumbra amount is a value estimated based on a size of the X-ray emitted from the specific passage. |
|
039717321 | summary | BACKGROUND OF THE INVENTION This invention relates to an apparatus for fixing radioactive and/or toxic waste materials obtained, for example, from nuclear installations. The apparatus is particularly designed for embedding aqueous concentrates, sludges and resins in a plasticizeable carrier material, such as hot bitumen. The apparatus has an extruder, as well as devices for the preparation, storage and the continuous, separated charging of carrier material and waste material into the extruder for mixing the materials. The extruder usually has two parallel-spaced horizontal shafts each carrying a screw conveyor passing through heating zones. Each heating zone has a vapor outlet device (vapor exhaust coupling) and a condenser, and after the condensers there is connected a common distillate accumulator. Each exhaust coupling is, at its upper end oriented away from the screw conveyors, closed by a window. With the extruder there are associated storage and/or transporting containers positioned, for example, on a rotatable disc for advancing the containers between the discharge spout of the extruder and the work zone of a conveying mechanism. The production of nuclear energy is expected to sharply increase in the years ahead and thus necessarily one has to expect a substantial increase in the quantities of radioactive waste. These wastes have to be prepared in such a manner that the threat to the environment by residual radioactivities is excluded. It is noted that the quantities of liquid radioactive waste in a nuclear energy station are substantially greater than the quantities of solid wastes. Thus, the coolant circuit of a reactor is continuously contaminated by fission products and activated corrosion products so that a continuous purification is necessary. In addition, there is obtained radioactive waste water from the storage of fuel elements in water-filled containers and during the decontamination of reactor components and building structures. Further sources of radioactive waste water are leakages, laboratories and sanitary installations. The total waste water quantity in boiling water reactors is between 30,000 and 50,000 m.sup.3 a year and in case of pressure water reactors, between 15,000 and 20,000 m.sup.3 a year. For decontaminating radioactive waste water in nuclear power installations several processes are used. Waste water having a relatively constant composition and small activity concentrations is treated by filtering through alluvial filters or by chemical precipitation. Empirical data show that this process yields 15 to 20 tons of residuals yearly. This volume, however, is substantially increased by the addition of inactive materials, such as filtering agents and precipitation reactants. The purification of salt-poor waste water obtained from the reactor circuits and fuel element storage containers is effected almost exclusively by means of ion exchangers. The yield of ion exchange resin wastes is, dependent upon the type of reactor, between 10 and 20 m.sup.3 annually, with a specific activity in the order of magnitude of 10 to 500 Ci/m.sup.3. The most universal and most effective process for the decontamination of radioactive waste water is vaporization. It finds application where larger quantities of waste water may be found which have a high activity in ion form bound to solid material. This process makes possible to increase the salt concentration of radioactive raw water up to approximately 30%. The purpose of conditioning radioactive concentrates from the waste water preparation is to convert the final product into a storable, that is, a water-insoluble form. Besides a mixing with cement up to a salt content of approximately 10 to 15% per weight, as a fixing method the substantially more advantageous embedding of aqueous concentrates or sludges or resins in hot bitumen is used. Here the fixation may be up to 60% by weight salt so that a 200 liter barrel may receive approximately 168 kg salt as opposed to 20 kg salt per barrel when the cementing process is used. According to a known bitumenization process, the sludges or concentrates are introduced into the bitumen at a temperature of more than 140.degree.C by means of a dual-shaft extruder, whereby the water is evaporated and the radioactive salts are mixed with bitumen. The above-outlined bituminization apparatus has a number of disadvantages which substantially increase the likelihood of malfunctioning and may require extensive maintenance work on heavily contaminated devices. Thus, for example, in the zone of the vapor exhaust device adjacent the screw conveyors of the extruder there are formed, during operation, deposits of radioactive salts which adversely affect the operation or even render it impossible because the resulting radiation limits the operational freedom of the maintenance or servicing personnel. The observation window at the upper end of the vapor exhaust device becomes obstructed after a relatively short period as a result of soiling by tar sprayers. The distillate produced in the condensers adjoining the vapor exhaust devices still carries bitumen particles which may adversely affect the operation of the evaporator unit. These particles must be removed in any event. from the distillate before its further processing to prevent organic material from entering the after-connected devices. Further, the loading of the mixture formed of bitumen and radioactive salts can be effected in the known apparatuses only by complex mechanisms which are thus prone to malfunctioning. In these known devices several containers are arranged on two rotary discs and to the discharge spout of the extruder there is attached a hose-like switchable device so that the mixed material emerging from the extruder can be, after filling one container on the first rotary disc, introduced without interruption into an empty container positioned on the second rotary disc. SUMMARY OF THE INVENTION It is an object of the invention to provide an improved apparatus for fixing radioactive and/or toxic wastes from which the above-discussed drawbacks are eliminated thus creating conditions for a disturbance-free operation for long periods without the necessity of external interference involving long inoperative periods and further, which insures superior operational safety. This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the apparatus for fixing radioactive or toxic waste has an extruder including a mixing mechanism for intermingling and advancing the waste and a carrier material introduced into the extruder. The extruder has a heating zone with which there communicates a vapor outlet device having an observation window. Within the vapor outlet device there is disposed an arrangement for cleaning the window and an arrangement for removing deposits from those locations of the vapor outlet device that are adjacent the mixing mechanism. The condenser is coupled to a distillate accumulator with the interposition of two alternatingly operating filters for removing particles from the condensate obtained from the condenser. To the outlet of the extruder there is coupled a loading device in which containers are successively filled with the material discharged by the extruder. The loading device includes an interrupter bowl which receives the material discharged by the extruder during an exchange of an empty container for a filled container below the extruder outlet. The advantages accomplished by the invention reside particularly in that the utilization factor of an apparatus for fixing radioactive and/or toxic waste is significantly increased with the aid of simple means which effect a substantial reduction in the soiling of components with radioactive materials. Thus, the supplemental work necessary in conventional apparatus for removing such soiling material and the operational pauses involved, are substantially or entirely eliminated. By practicing the invention, the radioactive waste fixing apparatus associated, for example, with a nuclear installation of known waste yield may be of reduced capacity compared to conventional apparatus. In this manner, better efficiency is ensured, involving economy of space and capital investment. A further important advantage resides in the substantially reduced radiation exposure of personnel, due to significantly reduced periods of maintenance. |
claims | 1. A tritium radioactive contaminated water decontamination method of reducing or removing tritium radiation from radioactive contaminated water, the method comprising the steps of:a first step of performing an addition treatment in an addition treatment tank, the addition treatment including adding 0.5-6 parts by weight of a mineral powder obtained by pulverizing a mineral comprising one or more selected from silicon dioxide ore, old shellfish fossil and radium ore, and 0.5-6 parts by weight of a nano-level carbon liquid to 100 parts by weight of tritium radioactive contaminated water heated to 30-80° C.;a second step of pumping the addition treated water from the addition treatment tank to a mineral solid filled tank by a hydraulic pump of 1 to 7 atmosphere pressure, the mineral solid filled tank being filled with a mineral solid in which the mineral is crushed to a predetermined size;a third step of passing the pumped addition treated water through the mineral solid filled tank, while the pumped addition treated water is colliding with the mineral solid;a fourth step of returning the treated water passed through the mineral solid filled tank to the addition treatment tank by the hydraulic pump; and,a fifth step of performing a circulation process of repeating the second to fourth steps for 20 to 80 minutes. 2. The tritium radioactive contaminated water decontamination method according to claim 1, whereinthe first to fifth steps are performed for 10-60 minutes, andthereafter, the mineral powder and nano-level carbon liquid addition treatment in the first step of adding 0.5-6 parts by weight of the mineral powder and 0.5-6 parts by weight of the nano-level carbon liquid to 100 parts by weight of the tritium radioactive contaminated water is further performed, andthereafter, the second to fifth steps are performed for 10-60 minutes. 3. The tritium radioactive contaminated water decontamination method according to claim 1, wherein a series of the first to fifth steps are repeated until a desired tritium radioactive concentration is obtained. 4. The tritium radioactive contaminated water decontamination method according to claim 1, further comprising:a sixth step of introducing a predetermined amount of a decontamination treatment water to which a series of the first to fifth steps are executed into an electrolytic cell in which 2-30 rod-like or plate-like electrodes are arranged and performing electrolytic treatment for 10-30 hours. 5. The tritium radioactive contaminated water decontamination method according to claim 4, wherein the electrolytic treatment is carried out until electrolytic treatment water in the electrolytic cell reaches a non-conducting state. 6. The tritium radioactive contaminated water decontamination method according to claim 4, wherein the electrodes arranged in the electrolytic cell are two or three selected from iron electrodes, stainless steel electrodes and platinum electrodes. 7. The tritium radioactive contaminated water decontamination method according to claim 4, wherein the electrolytic treatment is carried out by applying an alternating current of 100 to 500 V to the electrodes. 8. The tritium radioactive contaminated water decontamination method according to claim 4, wherein the electrolytic treatment is repeatedly performed until a desired tritium radioactive concentration is obtained. 9. The tritium radioactive contaminated water decontamination method according to claim 1, wherein the mineral powder is agitated by a stirring device and extruded into the addition treatment tank. 10. The tritium radioactive contaminated water decontamination method according to claim 2, wherein a series of the first to fifth steps are repeated until a desired tritium radioactive concentration is obtained. 11. The tritium radioactive contaminated water decontamination method according to claim 2, wherein the mineral powder is agitated by a stirring device and extruded into the addition treatment tank. 12. The tritium radioactive contaminated water decontamination method according to claim 2, further comprising:a sixth step of introducing a predetermined amount of a decontamination treatment water to which a series of the first to fifth steps are executed into an electrolytic cell in which 2-30 rod-like or plate-like electrodes are arranged and performing electrolytic treatment for 10-30 hours. 13. The tritium radioactive contaminated water decontamination method according to claim 12, wherein the electrolytic treatment is carried out until electrolytic treatment water in the electrolytic cell reaches a non-conducting state. 14. The tritium radioactive contaminated water decontamination method according to claim 12, wherein the electrodes arranged in the electrolytic cell are two or three selected from iron electrodes, stainless steel electrodes and platinum electrodes. 15. The tritium radioactive contaminated water decontamination method according to claim 12, wherein the electrolytic treatment is carried out by applying an alternating current of 100 to 500 V to the electrodes. 16. The tritium radioactive contaminated water decontamination method according to claim 12, wherein the electrolytic treatment is repeatedly performed until a desired tritium radioactive concentration is obtained. |
|
059995858 | summary | FIELD OF THE INVENTION The present invention relates to nuclear fuels based on UO, ThO.sub.2 and/or PuO having improved fission product retention properties. BACKGROUND OF THE INVENTION In the use of nuclear fuels based on oxide, particularly uranium oxide, one of the problems caused is due to the release of fission gases in the fuel element during the operation of the reactor, because these fission products must be kept in the fuel element, particularly in the actual fuel pellets, so as to limit the internal pressure of the sheaths or cans and the interaction of the fission products with the latter. Therefore, at present, the burn-up of nuclear elements is limited to 50 GWj/t of U in order not to exceed the threshold beyond which the release of fission gases becomes significant. However, operators of electronuclear reactors, particularly pressurized water reactors (PWR), wish to optimize control of the nuclear fuel by increasing burn-up of the uranium dioxide pellets contained in the rods in order to achieve minimum values of 60 to 70 GWj/tU. Research carried out up to now for obtaining such an improvement has used procedures for increasing the size of the uranium dioxide grains, because it has been found that the gas quantity released by an irradiated large grain fuel is less than that released by an irradiated small grain fuel. Use has also been made of procedures for forming precipitates in the nuclear fuel in order to anchor the fission gases on such precipitates. In order to obtain an increase in the size of the uranium dioxide grains, it is possible to add additives such as iO, NbO, CrO, AlO, VO and MgO to the uranium dioxide powder subject to fritting or sintering in order to activate its crystal growth, provided that the sintering takes place under a wet hydrogen atmosphere so that the added oxide quantity remains in solution in the uranium dioxide and is not reduced to a metallic element. The use of such additives for obtaining a large grain microstructure is, e.g., described by Killeen in Journal of Nuclear Materials, 88, 1980, pp 177-184, Sawbridge et al in Report CEGB RD/B/N 4866, July 1980 and Radford et al in Scientific Paper 81-7D2-PTFOR-P2, 1981. However, the use of certain additives of this type can lead to an increase in the diffusion coefficients of cations and fission gases in the uranium dioxide, which is unfavorable for the retention of the fission products and does not make it possible to take full advantage of the large grain microstructure. Another procedure for improving the retention rate of nuclear fuels consists of dispersing in the uranium dioxide grains nanoprecipitates of a second phase for ensuring the anchoring of the fission products on such second phase. Nanoprecipitates of this type can consist of magnesium oxide inclusions, as described by Sawbridge et al. in Journal of Nuclear Materials, 95, 1980, pp. 119-128, and in FR-A-2 026 251. SUMMARY OF THE INVENTION The present invention makes use of a method different from that described hereinbefore for improving the retention rate of fission products in a nuclear fuel. This method consists of trapping the oxygen atoms released by the fission of the uranium and/or plutonium atoms, so as to maintain the O/U (Th, Pu) or O/M stoichiometry with M=U+Pu or U+Th or U+Pu+Th of the fuel at 2 and thus prevent a rise in the diffusion coefficients in the fuel and a reduction of its thermal conductivity. Thus, the increase in the diffusion coefficients is a mechanism leading to the accumulation of fission products at the grain boundaries, followed by release of these fission products. In the same way, a reduction of the thermal conductivity of the fuel is prejudicial, because it has the effect of increasing the temperature of the fuel for the same linear power and consequently both reducing the solubility of the fission products and favoring their diffusion. The invention also relates to a process for improving the retention of fission products within a ceramic nuclear fuel based on UO.sub.2, ThO.sub.2 and/or PuO.sub.2, which consists of including in the ceramic nuclear fuel at least one metal able to trap oxygen by forming an oxide having a free formation enthalpy at the operating temperature T of the nuclear reactor below the free formation enthalpy at the same temperature T of the superstoichiometric oxide or oxides of formulas (U, Th)O.sub.2+x and/or (U, Pu)O.sub.2+x, in which x is such that 0<x.ltoreq.0.01. The use of such a metallic additive consequently makes it possible to maintain the O/U (Th or Pu) or O/M ratio defined hereinbefore of the nuclear fuel at a value of 2 and in this way to avoid an increase in the diffusion coefficients, which remain at a low value, and a reduction in the thermal conductivity of the fuel. Thus, a high fission product retention rate is obtained. This procedure can be combined with known methods of increasing the size of the UO.sub.2 and/or PuO.sub.2 and/or ThO.sub.2 grains and forming precipitates for anchoring the fission gases, which is very interesting and makes it possible to improve the performance characteristics of the fuel. In the case of uranium dioxide-based fuels, the free formation enthalpy of the superstoichiometric oxide UO.sub.2+x with 0<x.ltoreq.0.01 can be expressed in oxygen potential and calculated on the basis of the law of Lindemer and Besmann, as described in Journal of Nuclear Materials, 130, 1985, pp. 473-488. In this case, and as is indicated on p. 480 thereof, the oxygen potential .DELTA.G(O.sub.2) of the above-defined superstoichiometric oxide can be expressed in J/mole according to the following formula: EQU -360 000+214 T+4 RTLn[2x(1-2x)/(1-4x).sup.2 ] in which R is the molar constant of the gases, T is the temperature in Kelvins and x is as defined hereinbefore. Moreover, for uranium dioxide-based fuels, the metal included in the fuel must be able to form an oxide having an oxygen potential defined by the formula: .DELTA.G(O.sub.2)=RT Ln (pO.sub.2) in which R is the molar constant of the gases, T the reactor operating temperature and p(O.sub.2) the partial oxygen pressure, equal to or below the above-estimated value for UO.sub.2+x in accordance with the Lindemer and Besmann law. Examples of suitable metals are Cr, Mo, Ti, Nb and U. The invention also relates to a fuel for nuclear reactors comprising a ceramic material based on UO.sub.2, ThO.sub.2 and/or PuO.sub.2 in which is dispersed at least one metal able to trap oxygen and having the characteristics given hereinbefore. According to the invention, the oxide-based ceramic material can be constituted by UO.sub.2, ThO.sub.2 PuO.sub.2 or mixtures thereof, the mixed oxide UO.sub.2 --PuO.sub.2 or UO.sub.2 --ThO.sub.2, mixed oxides based on UO.sub.2 and other oxides such as oxides of rare earths or mixed oxides based on PuO.sub.2. Preferably, the ceramic material is based on UO.sub.2 and the dispersed metal is able to form an oxide having an oxygen potential below the oxygen potential of UO.sub.2+x, as described hereinbefore. In general, to obtain a burn-up of 60 GWj/t.sup.-1, the dispersed metal represents 0.1 to 2% by weight of the fuel material. Preferably, the metal is chromium and represents 0.1 to 1 or better still 0.2 to 0.5% by weight of the fuel material. Moreover, the fuel material can also comprise additives such as TiO.sub.2, Nb.sub.2 O.sub.5, Cr.sub.2 O.sub.3, Al.sub.2 O.sub.3, V.sub.2 O.sub.5 and MgO, in order to increase the size of the fuel grains and/or aid the anchoring of the fission products, as well as other additives, e.g., SiO.sub.2, in order to improve other properties. The fuel material according to the invention can be prepared by conventional sintering or fritting processes by adding to the ceramic material powder to be sintered the metal, either in metallic form, or in the form of an oxide or oxygenated compound. In the first case, after shaping the powder by cold compression, sintering is carried out in a dry hydrogen atmosphere, e.g., having a water content below 0.05 volume % so as not to oxidize the metal. In the second case, if it is wished to simultaneously obtain a size increase of the UO.sub.2, ThO.sub.2 and/or PuO.sub.2 grains, use is made of an oxide or oxygenated compound quantity which may or may not exceed the solubility limit of the oxide or oxygenated compound in UO.sub.2, ThO.sub.2 and/or PuO.sub.2 at the sintering temperature. After shaping the powder by cold compression, sintering takes place under wet or humidified hydrogen, e.g., having a water content above 1 volume %, in order to preserve the oxide during sintering and activate crystal growth. After sintering, the sintered material undergoes a reduction treatment under dry hydrogen, e.g., having a water content below 0.05 volume %, in order to reduce the oxide or oxygenated compound to metal. In the second case, this manner of operating makes it possible to obtain a large grain microstructure (diameter>40 .mu.m) with: either intragranular, nanometric metallic precipitates (diameter<100 nm) if the added oxide or oxygenated compound quantity is below the solubility limit, PA1 or intragranular, nanometric metallic precipitates (diameter<100 nm) and micrometric, metallic precipitates (diameter>0.3 .mu.m) if the added oxide or oxygenated compound quantity exceeds the solubility limit. However, if in the second case it is not wished to simultaneously obtain a large grain structure following the shaping of the powder by cold compression, sintering takes place under a dry hydrogen atmosphere, e.g., having a water content below 0.05 volume %, in order to simultaneously reduce the oxide or oxygenated compound to metal. In this case, intragranular, micrometric, metallic precipitates are obtained (diameter>0.3 .mu.m). In all these cases, the shaping of the powder by cold compression, e.g., in order to form pellets, can be carried out in a conventional manner by uniaxial compression, e.g., under pressures of 200 to 700 MPa. A temperature of 1600 to 1750.degree. C. is normally used for sintering. When there is a supplementary reduction heat treatment, the latter can be carried out at temperatures of 1300 to 1750.degree. C. The ceramic material powder including the metallic additive in the form of an oxide or oxygenated compound can be prepared by mixing powders of the constituents or by atomization-drying processes using a slip containing the additive in the form of salt in solution, or by coprecipitation of a uranium salt and a salt of the additive. Therefore the process of the invention makes it possible to take advantage not only of the oxygen trapping capacity of the added metal, but also of the properties of the metallic oxides in order to activate the UO.sub.2 crystal growth and improve the retention of fission products within the fuel. |
051538989 | summary | FIELD OF THE INVENTION AND RELATED ART The present invention relates to a projection exposure apparatus, more particularly to an X-ray reduction projection exposure system of the reflection type and an X-ray reduction imaging system particularly usable for effecting high resolution printing. In the field of semiconductor circuit manufacturing, exposure apparatuses such as mask aligners and steppers are widely used to print a circuit pattern from a mask or reticle onto a wafer. The recent trend to the high density of the semiconductor chips such as IC and LSI increases the need for an exposure apparatus capable of very high resolution printing. Various researches and developments are being made to provide an exposure apparatus which can replace the recently used deep UV light. In general, in the exposure apparatuses of this type, more particularly to projection exposure apparatuses such as steppers, the minimum line width which is printable by the apparatus, represented by resolution power, is determined by wavelength of light used and a numerical aperture of the projection optical system. As regards the numerical aperture, the resolution increases with increase of the numerical aperture, but the increase of the numerical aperture leads to shorter depth of focus, with the result that the image to be printed or transferred is blurred due to very small defocusing. For this reason, it is considered from the standpoint of optical design that obtaining high resolution by changing the numerical aperture is difficult. In view of this, efforts have been made to accomplish high resolution by using as the projection energy ray, a beam produced by an excimer laser or the like and X-rays which are relatively short in wavelength. Particularly, the X-ray exposure apparatus is expected as an exposure apparatus of the next generation, and an X-ray exposure apparatus in a proximity type has been proposed. However, the currently proposed proximity type X-ray exposure is still not satisfactory in that the resolution is not enough for an ultra LSI such as 64 mega bit DRAM or higher density requiring very high resolution on the order of submicrons. Another problem is that a highly accurate pattern must be formed on a mask. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide an X-ray reduction projection exposure system of reflection type and an X-ray reduction projection imaging system of reflection type, not the conventional proximity type. It is another object of the present invention to provide an X-ray reduction projection exposure system of reflection type capable of printing images in high resolution on the order of submicrons. It is a further object of the present invention to provide an X-ray reduction projection exposure system of reflection type capable of effecting printing in very high resolution. According to an embodiment of the present invention, there is provided a system comprising means for directing X-rays to a mask and a projection imaging system for forming an image of a mask pattern in a predetermined reduced magnification or scale. Therefore, the pattern of the mask can be transferred in a reduced scale onto a wafer disposed at an imaging position by way of a projection exposure system. These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. |
description | This application claims the benefit of priority to U.S. Provisional Patent Application 61/242,237, filed Sep. 14, 2009, and incorporated herein in its entirety. The United States government has rights in this invention pursuant to Contract No. DE-AC52-06NA25396 between the United States Department of Energy and Los Alamos National Security, LLC for the operation of Los Alamos National Laboratory. The present invention relates to composites comprising BeO and AmBe13, in an excess of Be metal, having reduced dispersion characteristics and which are suitable for use in neutron sources, and methods of making thereof. Neutron sources are used in a variety of applications, including oil and natural gas exploration. Currently available commercial neutron sources contain finely divided powders comprising a radioactive material, e.g., 241AmO2, and beryllium metal, which are mixed together to provide intimate contact between the materials. In natural gas and oil exploration, “logging” wells (i.e., determining characteristics such as density, porosity, and attenuation, among others) is an important step in predicting production potential. Logging may be performed by “wire line,” in which the neutron source is placed in an open or cased hole, or alternatively logging may be performed while drilling, in which case the neutron source and detector(s) are placed on a special section of the drilling stem. In some instances, neutron sources may be lost or damaged during the process. In order to prevent accidental dispersion, the powdered material is encased in multiple welded capsules, however, the capsules are not always strong enough to prevent accidental dispersion. In addition, in recent years, concerns about intentional dispersion have increased. Whether accidental or intentional, once a powdered substance is dispersed, containment and cleanup become difficult (if not impossible) and expensive. A need exists, therefore, for neutron sources which comprise an AnBe material which is less dispersible, and which provides a steady, reliable source of neutrons. The present invention meets the aforementioned needs by providing a neutron source comprising a Be/BeO/AmBe13 composite. The composite comprises crystals comprising BeO and AmBe13, in an excess of Be metal. The composite is a solid monolith engineered for strength rather than a mixture of powders, and thus exhibits decreased dispersibility. The crystals have a size of less than 2 μm, and are monodisperse, meaning that the size distribution is narrow. These characteristics impart desirable qualities to the composite, including hardness and tensile strength which allow for more robust sources. The composite is obtained by a novel process which utilizes induction heating to perform rapid heating and cooling. The composite of the present invention is not easily dispersed, and allows for more efficient and complete cleanup in the event of an accident. The source of the present invention further is more efficient than currently available sources, which means that less 241Am is required to achieve the same neutron output. AmBe neutron sources provide a portable, tough, continuous, and reliable source of neutrons independent of a reactor or a neutron generator. 241AmO2 and Be mixtures create a neutron source via an “alpha-N” reaction (shorthand representation 9Be(α,N)12C). 241Am has a half-life of 432 years, and this relatively high specific activity provides good neutron source efficiency, useful neutron flux ranges, and steady neutron output for years in an AmBe source. Be has the highest neutron yield from (α,N) reaction of any element, although even Be does require many thousands of alpha particles to produce one neutron. The following describe some non-limiting embodiments of the present invention. According to one embodiment of the present invention, a neutron source comprising a composite is provided, said composite comprising crystals comprising BeO and AmBe13, and an excess of beryllium, wherein the crystals have an average size of less than 2 microns; the size distribution of the crystals is less than 2 microns; and the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe13. According to another embodiment of the present invention, a neutron source comprising a composite is provided, said composite comprising crystals comprising BeO and AmBe13 and an excess of beryllium, wherein the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe13, and wherein the composite has a tensile strength of greater than 20,000 psi. According to yet another embodiment of the present invention, a method of producing a composite is provided, said composite comprising crystals comprising BeO and AmBe13 and an excess of beryllium, comprising providing Am metal and Be metal powder in a sealed capsule, wherein the weight ratio of the Be metal to the AmO2 powder is from about 10:1 to about 100:1; heating the mixed Am metal and Be metal powder in an induction furnace to a temperature of from about 1400° C. to about 1600° C. for a period of about 5 minutes; and lowering the temperature below the freezing point of the composite within about 5 minutes. “AmBe,” as used herein, refers to a generic term encompassing any material comprising 241americium and beryllium. “AmBe source,” as used herein, means a neutron source comprising 241americium and beryllium. “AnBe,” as used herein, refers to a generic term encompassing any material comprising an actinide and beryllium. “241AmBe13” or “AmBe13,” as used herein, mean an intermetallic compound comprising 241americium and beryllium. “Be/BeO/AmBe13,” as used herein, means the composite material of the present invention, which comprises crystals comprising BeO and AmBe13, and an excess of beryllium. The present invention relates to an AmBe neutron source comprising a solid, metallic composite comprising small BeO and AmBe13 crystals, which are uniformly dispersed in an excess of Be metal. Alpha particles (+2 charge) are emitted from the 241Am nucleus with high energy, but travel only a very short distance through the electron clouds of neighboring atoms. The range of 5.5 MeV alpha particles in water is about 40 microns. The range of alpha particles in materials with greater electron cloud density is significantly less (e.g., about 20 microns in 241AmO2). The alpha particle must retain enough energy to initiate the 9Be(α,N)12C reaction when striking the Be nucleus to effect the nuclear reaction. Thus, smaller 241AmO2 crystals result in more efficient utilization of alpha particles in AmBe sources. The intermetallic compound AmBe13 is very hard but also very brittle, and has a tensile strength limited to a few psi. Cast beryllium metal is light and far stronger than any of the intermetallic compounds or pressed powders found in existing source designs, with a typical tensile strength of about 15,000-20,000 psi. However, beryllium metal cast by traditional methods is a bit weaker, more brittle and less ductile than Be made from hot pressed powders, extrusion, or by utilizing vacuum chill cast methods. For example, smaller Be crystals made from hot pressed powders typically have a tensile strength of 30,000 to 40,000 psi. Higher tensile strength and more ductile Be metal composites are made by including small percentage of BeO (or other dispersed compounds) to create a cermet. The present invention utilizes unique methods of assembly, chemistry, and an excess of Be metal, to produce Be/BeO/AmBe13 composite materials having useful properties such as good tensile strengths, toughness, resistance to oxidation, and which are monolithic and thus far less dispersible than current AmBe sources. The present invention comprises a Be/BeO/AmBe13 composite. However, Be/BeO/AnBe13 composites also may be used, where An is understood to mean any element selected from the group of actinides. Other suitable alpha emitting actinide isotopes include, but are not limited to, 238Pu and 244Cm. It is noted, however, that 239Pu isotopic mixtures have a significantly lower alpha specific activity, which requires much larger sources to achieve a similar output. The Be/BeO/AmBe13 composite comprises crystals comprising BeO and AmBe13 and an excess of beryllium. The weight ratio of Be:Am-containing reagent materials (AmO2 or Am metal) materials is about 1:10 to about 1:100. In one embodiment, the crystals have a size (average diameter) of less than 2 μm, alternatively of less than 0.01 μm, and alternatively of from about 0.01 μm to about 2 μm. The crystals have a size distribution of about 2 μm, understood to mean that the size variation between individual crystals does not exceed about 2 μm. In theory, the crystals may approach the theoretical limit of a solid solution of AmBe13 in the Be/BeO matrix, meaning that the AmBe13 crystals approach the size of a single molecule, which increases neutron output efficiency compared to crystal sizes of 20 μm or more. One method of forming the AmBe13 intermetallic is from the two pure metals: The above reaction is performed with induction heating and in a crucible. In one embodiment, the crucible is made of tantalum (Ta). One drawback of the above reaction is that 241Am metal is more difficult to purify and to handle than other actinide metals such as Pu, thus is not readily available. Unlike Pu, Am has both a high melting point and high vapor pressure. Another drawback is that 241Am metal is extremely reactive, and the finely divided material would be difficult to fabricate and pyrophoric. Pure metal source fabrication methods would utilize bulk Am metal, and the molten metals mixed in the induction furnace. An alternative method of formation of 241AmBe13 is by using AmO2 and Be metal as starting materials: The above reaction also is performed with heating and in a crucible, preferably comprised of Ta. Thermodynamically, molten Be metal reacts with any metal oxide except BeO, ThO2 and CaO. This reaction with 241AmO2 is known to occur above the melting point of Be metal. One advantage of the above reaction is that 241AmO2 and Be metal are more readily available in pure form. Fabrication from 241AmO2 as a reagent produces BeO as a by-product, which may phase-separate from the Be metal, particularly after long time periods at high temperature and slow cool down periods. BeO has been utilized to strengthen Be metal composites in specific applications, thus it may prove advantageous in product source properties. A rapid cool down minimizes 241AmBe13 crystal growth, Be metal crystal growth and phase separation. Other refractory materials like W, ZIRCALOY, or Pt30% Rh metal offer unique properties, and may be utilized instead of Ta to contain the high T melt. Method of Making The present invention further comprises a method of making a Be/BeO/AmBe13 composite. In one embodiment, the Be/BeO/AmBe13 composite may be made by casting. Products may be prepared from heating mixtures of varying ratios of 241AmO2 (or bulk Am metal) and Be metal to a temperature ranging of from about 1400° C. to about 1600° C.). In one embodiment, the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe13 Alternatively, the weight ratio of the Be metal to the AmO2 powder or Am metal starting materials is from about 10:1 to about 100:1. Byproduct BeO (if 241AmO2 is used) is generated by chemical reaction in the mixture. BeO in significant quantities has been shown to strengthen Be metal, and may prove advantageous in product source properties. The AmBe13 would become insoluble and crystallize as molten bulk Be metal cools. Brief heating times and rapid cool down are believed to be important parameters to keep AmBe13 crystals small and to minimize migration of Be and Am metals. Induction heating of the mixtures may be used to achieve brief heating, sufficient mixing, and rapid cool down. Alternatively, methods of imparting ultrasonic or acoustic energy for mixing may be used. Alternatively, the mixture may be quenched to provide rapid cool down. One non-limiting example of a method of making the Be/BeO/AmBe13 composite of the present invention comprises the following steps. 1. Place dry AmO2 powder and Be metal powder in Ta capsule. For example, for a 10 Ci source at a 10:1 weight ratio of Be to 241AmO2 add 33 g Be and 3.3 g 241AmO2. 2. Seal the Ta capsule by welding, optionally under vacuum. 3. Optionally, mix the powders in a shaker, an example being a high energy “ball mill” apparatus. In an alternative embodiment, Am metal may be used instead of AmO2 powder, in which case mixing is not required. 4. Place the Ta capsule in an induction furnace. 5. Heat to a temperature of from about 1400° C. to about 1600° C. to initiate the chemical reaction to form AmBe13 and BeO. 6. Hold at the above temperature for about 5 minutes, optionally monitoring neutron flux increase as verification of reaction progress. 7. Cool the temperature below the freezing point of the composite within about 5 minutes, optionally with external mixing during cool down. The cooling may occur in the induction furnace (minutes), or alternatively by a rapid quench method (cools in seconds).8. The Ta capsule is then encased in additional layers of stainless steel and sealed by welding. The above reaction should initiate at around the melting point of Be (1287° C.). An exothermic temperature spike associated with the formation of AmBe13 has been observed raising the temperature to about 1800° C. (depending upon mass of excess Be). The length of time is important and should be brief (5 minutes) for the reaction to reach completion, followed by rapid cooling. Short reaction times and rapid cool down will minimize volatile migration of Am metal, improve neutron efficiency by keeping AmBe13 crystals small, and improve composite strength properties by keeping Be and BeO crystals small. The method of the present invention results in a Be/BeO/AmBe13 composite having excellent tensile strength. “Tensile strength,” as used herein, means the maximum stress a material can withstand without shearing, i.e. without exhibiting a break along a face of the crystalline material, and herein is expressed in units of psi (pounds per square inch). For the purposes of the present invention, the tensile strength may be determined as described in ASTM E8/E8M-08 Standard Test Methods for Tension Testing of Metallic Materials. The Be/BeO/AmBe13 composites of the present invention have a tensile strength of at least 20,000 psi. Method of Source Fabrication The Be/BeO/AmBe13 composite of the present invention may form part of a neutron source. One method of making a neutron source of the present invention is to place an amount of the desired reagent mixture of the present invention in a right circular cylinder of surface-oxidized tantalum as a crucible during the heating and cool down cycles as described above. In this manner, the source composite material may be formed in situ in a refractory metal crucible (nonlimiting examples of which include, Ta, W, ZIRCALOY, and Pt30% Rh), which would become the innermost sealed capsule for the neutron source. In one embodiment, the crucible comprises Ta. A lid may be welded on this metal crucible either before or after heating to create an innermost sealed capsule for the neutron source. The neutron source additionally may comprise one or more outer layers of welded stainless steel encasements which surround and enclose the innermost sealed capsule. In all embodiments of the present invention, all percentages are by weight of the total composition, unless specifically stated otherwise. All ratios are weight ratios, unless specifically stated otherwise. All ranges are inclusive and combinable. All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. Whereas particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. |
|
051005867 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides novel cementitious containers for storage of solid hazardous waste. In general, the cementitious hazardous waste containers within the scope of the present invention include an inner layer of substantially unhydrated powdered hydraulic cement in contact with and compressed around the hazardous waste. An outer layer of hydrated cement is preferably included to add strength to the container. Referring now to FIG. 1, one possible hazardous waste container within the scope of the present invention is illustrated. Hazardous waste container 10 is prepared by compressing substantially unhydrated powdered hydraulic cement 12 around solid hazardous waste 14, followed by hydrating outer surface layer 16 of the powdered hydraulic cement. The average thickness of outer surface layer 16 may vary from as little as 0.001 inches to as much as 100 inches. In most cases, the thickness will range from about 0.25 inches to about 3 inches. Desired strength characteristics often dictate the thickness of the hydrated outer surface layer. In some cases, natural water vapor in the atmosphere may hydrate a thin outer surface layer prior to depositing the waste container in an underground storage site. More complete hydration would then occur over the years as ground water contacts the waste container. Although the hazardous waste container shown in FIG. 1 is generally spherical in shape, it will be appreciated that the waste containers within the scope of the present invention may be prepared in a variety of different shapes. For instance, triangular, rectangular, hexagonal, and many other geometric cross-sectional configurations may be used. These cross-sectional configurations enable completed waste containers to be packed together more efficiently than cylindrical waste containers for tranportation and final storage of the waste containers. Waste containers within the scope of the present invention may also be prepared by compressing powdered hydraulic cement around the solid hazardous waste and thereafter applying a layer of cement paste over the compressed powdered hydraulic cement. Aggregates may be added to the powdered hydraulic cement or to the cement paste to provide desired mechanical properties. It is also within the scope of the present invention to compress a first layer of powdered hydraulic cement around a quantity of solid hazardous waste, hydrate the outer cement surface, compress another layer of the powdered hydraulic cement around the first layer, and then hydrate the outer cement surface. Any number of cement layers can be prepared in this manner. It is also possible to incorporate aggregates into one or more layers to obtain desired structural or mechanical characteristics. Because the powdered hydraulic cement is compressed around the hazardous waste materials, the void space within the hazardous waste container is substantially reduced. The hazardous waste materials are essentially "precrushed" inside the container walls. In this pre-stabilized condition, the waste containers are much closer to equilibrium with the ground without the need for further compaction, grouting, or sealing. In the case where the hazardous waste containers are buried in underground vaults, the fewer number of void spaces within the waste containers enables the ground to reach equilibrium high pressure faster when the underground storage room collapses. In addition, the problems with ground water seeping into void spaces are reduced. Many of the general principles regarding pressure compaction of powdered hydraulic cement as well as various techniques for hydrating packed hydraulic cement are discussed in copending patent application Ser. No. 07/526,231, filed May 18, 1990, in the names of Hamlin M. Jennings and Simon K. Hodson and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and Use," which is incorporated herein by specific reference. The family of cements known as hydraulic cements used in the present invention is characterized by the hydration products that form upon reaction with water. It is to be distinguished from other cements such as polymeric organic cements. The term powdered hydraulic cement, as used herein, includes clinker, crushed, ground, and milled clinker in various stages of pulverizing and in various particle sizes. The term powdered hydraulic cement also includes cement particles which may have water associated with the cement; however, the water content of the powdered hydraulic cement is preferably sufficiently low that the cement particles are not fluid. The water to cement ratio is typically less than about 0.20. Examples of typical hydraulic cements known in the art include: the broad family of Portland cements (including ordinary Portland cement without gypsum), calcium aluminate cements (including calcium aluminate cements without set regulators, e.g., gypsum), plasters, silicate cements (including .beta. dicalcium silicates, tricalcium silicates, and mixtures thereof), gypsum cements, phosphate cements, and magnesium oxychloride cements. Hydraulic cements generally have particle sizes ranging from 0.1 .mu.m to 100 .mu.m. The cement particles may be gap-graded and recombined to form bimodal, trimodal, or other polymodal systems to improve packing efficiency. For example, a trimodal system having a size ratio of 1:5:25 and a mass ratio of 21.6:9.2:69.2 (meaning that 21.6% of the particles, by weight, are of size 1 unit and 6.9% of the particles, by weight, are of size 5 units and 69.2% of the particles, by weight are of size 25 units) can theoretioally result in 85% of the space filled with particles after packing. Another trimodal system having a size ratio of 1:7:49 and a mass ratio of 13.2:12.7:66.1 can result in 88% of the space filled with particles after packing. In yet another trimodal system having the same size ratio of 1:7:49 but a different mass ratio of 11:14:75 can result in 95% of the space filled with particles after packing. It will be appreciated that other particle size distributions may be utilized to obtain desired packing densities. A bimodal system having a size ratio of 0.2:1 and a mass ratio of 30:70 (meaning that 30% of the particles, by weight, are of size0.2 units and 70% of the particles, by weight, are of size 1 unit) can theoretically result in 72% of the space filled with particles after packing. Another bimodal system having a size ratio of 0.15:1 and a mass ratio of 30:70 can result in 77% of the space filled with particles after packing. The compressing of powdered hydraulic cement within the scope of the present invention is not to be confused with prior art processes which mold and shape cement pastes. As used herein, the term "cement paste" includes cement mixed with water such that the hydration reaction has commenced in the cement paste. 1. Pressure Compaction Processes Pressure compaction processes, such as dry pressing and isostatic pressing, may be used to compress the powdered hydraulic cement around the nuclear waste according to the teachings of the present invention. Dry pressing consists of compacting powders between die faces in an enclosed cavity. Pressures can range from about 500 psi to greater than 100,000 psi in normal practice. Such pressures generally result in materials having void fractions between 2% and 50%, with a void fraction between about 5% and 30%, and a most preferred void fraction between about 5% and 30%, and a most preferred void fraction in the range from about 10% to about 25%. In some cases, additives are mixed with the powdered hydraulic cement to make molding easier and to provide sufficient strength so that the article does not crumble upon removal from the press. Suitable additives preferably neither initiate hydration nor inhibit hydration of the hydraulic cement Grading the cement particles, as discussed above, may also provide a certain fluidity of the cement powder during compressing. In addition, it may be useful to lubricate the cement powder with an oil emulsion, according to techniques known in the art, to facilitate the lateral movement among the particles. Suitable emulsions may be prepared using nonaqueous, volatile solvents, such as acetone, methanol, and isopropyl alcohol. Because cement particles are formed by crushing and grinding larger cement clinker pieces, the individual particles have rough edges. It has also been found that rounding the edges of the cement particles enhances their ability to slide over each other, thereby improving the packing efficiency of the cement particles. Techniques for rounding cement particles known in the art may be used. Some of the air enclosed in the pores of the loose powder has to be displaced during pressing. The finer the mix and the higher the pressing rate, the more difficult the escape of air. The air may then remain compressed in the mix. Upon rapid release of the pressure, the pressed piece can be damaged by cracks approximately perpendicular to the direction of pressing. This pressure lamination, even though almost imperceptible, may weaken the resulting product. This problem is usually solved by repeated application of pressure or by releasing the pressure more slowly. Isostatic pressing is another powder pressing technique in which pressure is exerted uniformly on all surfaces of the cement article. The method is particularly suitable in forming of symmetric shapes, and is similarly employed in the shaping of large articles which could not be pressed by other methods. In practice, the powdered mix is encased in a pliable rubber or polymer mold. The mold is then preferably sealed, evacuated to a pressure between 0.1 atm and 0.01 atm, placed in a high-pressure vessel, and gradually pressed to the desired pressure. An essentially noncompressible fluid such as high-pressure oil or water is preferably used. Pressures may range from 100 psi to 100,000 psi. The forming pressure is preferably gradually reduced before the part is removed from the mold. Vibrational compaction techniques, as described more fully in copending patent application Ser. No. 07/526,231, may be used to help pack the mix into the mold cavity. In vibrational compaction processes, the powdered hydraulic cement particles are typically compacted by low-amplitude vibrations. rticle friction is overcome by vibrations. Inter-particle friction is overcome by application of vibrational energy, causing the particles to pack to a density consistent with the geometric and material characteristics of the system and with the conditions of vibration imposed. Packed densities as high as 100% of theoretical are possible using vibration packing processes. As used herein, the term "theoretical packing density" is defined as the highest conceivable packing density achievable with a given powder size distribution. Hence, the theoretical packing density is a function of the particle size distribution. Vibration packing processes may also be combined with pressure compaction processes to more rapidly obtain the desired packing densities or even higher packing densities. Typical vibration frequencies may range from 1 Hz to 20,000 Hz, with frequencies from about 100 Hz to about 1000 Hz being preferred and frequencies from about 200 Hz to about 300 Hz being most preferred. Typical amplitudes may range from about one half the diameter of the largest cement particle to be packed to about 3 mm, with amplitudes in the range from about one half the diameter of the largest cement particle to about 1 mm. If the amplitude is too large, sufficient packing will not occur. Once the amplitude is determined, the frequency may be varied as necessary to control the speed and rate of packing. For particle sizes in the range from 0.1 .mu.m to 50 .mu.m, the vibration amplitude is preferably in the range from about 10 .mu.m to about 500 .mu.m. Although it is not necessary to have a specific particle size distribution in order to successfully use vibrational compaction processes, carefully grading the particle size distribution usually improves compaction. 2. Aggregates and Composite Materials It is within the scope of the present invention to include aggregates commonly used in the cement industry with the powdered hydraulic cement prior to hydration. Examples of such aggregates include sand, gravel, pumice, perlite, and vermiculite. One skilled in the art would know which aggregates to use to achieve desired characteristics in the final cementitious waste container. For many uses it is preferable to include a plurality of differently sized aggregates capable of filling interstices between the aggregates and the powdered hydraulic cement so that greater density can be achieved. In such cases, the differently sized aggregates have particle sizes in the range from about 0.01 .mu.m to about 2 cm. In addition to conventional aggregates used in the cement industry, a wide variety of other fillers, fibers, and strengtheners, including balls, filings, pellets, powders, and fibers such as graphite, silica, alumina, fiberglass, polymeric fibers, and such other fibers typically used to prepare composites, may be combined with the powdered hydraulic cement prior to hydration. When the waste container is to be stored in a salt mine, salt may be included as an aggregate material with the powdered hydraulic cement to enhance the thermodynamic compatibility of the container with its storage environment. One overriding goal in developing suitable waste storage containers is to design a container which will be as thermodynamically compatible with the storage environment as possible so that the container will quickly reach thermodynamic equilibrium with its environment. For example, the more chemically compatible the storage container is to its storage environment, the closer the container is to thermodynamic equilibrium with its environment and the lower the driving force for chemical change. 3. Cement Hydration Techniques a. Cement Hvdration in General The term hydration as used herein is intended to describe water. The chemistry of hydration is extremely complex and can only be approximated by studying the hydration of pure cement compounds. For simplicity in describing cement hydration, it is often assumed that the hydration of each compound takes place independently of the others that are present in the cement mixture. In reality, cement hydration involves complex interrelated reactions of the each compound int he cement mixture. With respect to Portlaned cement, the principal cement components are dicalcium silicate and tricalcium silicate. Portland cement generally contains smaller amounts of tricalcium aluminate (3CaO.Al.sub.2 O.sub.3) and tetracalcium aluminum ferrite (4CaO.Al.sub.2 O.sub.3.FeO). The hydration reactions of the principal components of Portland cement are abbreviated as follows: ##STR1## where dicalcium silicate is 2CaO.SiO.sub.2, tricalcium silicate is 3CaO.SiO.sub.2, calcium hydroxide is Ca(OH).sub.2, water is H.sub.2 O, S is sulfate, and C--S--H ("calcium silicate hydrate") is the principal hydration product. (The formula C.sub.2 S.sub.2 H.sub.2 for calcium silicate hydrate is only approximate because the composition of this hydrate is actually variable over a wide range (0.9<C:S<3.0)). It is a poorly crystalline material which forms extremely small particles in the size of colloidal matter less than 0.1 .mu.m in any dimension.) It will be appreciated that there are many other possible hydration reactions that occur with respect to other hydraulic cements and even with respect to Portland cement. On first contact with water, C and S dissolve from the surface of each C.sub.3 S grain, and the concentration of calcium and hydroxide ions rapidly increases. The pH rises to over 12 in a few minutes. The rate of this hydrolysis slows down quickly but continues throughout a dormant period. After several hours under normal conditions, the hydration products, CH and C--S--H, start to form rapidly, and the reaction again proceeds rapidly. Dicalcium silicate hydrates in a similar manner, but is much slower because it is a less reactive compound than C.sub.3 S. For additional information about the hydration reactions, reference is made to F. M. Lea, Chemistry of Cement and Concrete, 3rd edition, pp. 177-310 (1970). It has been observed that the better the contact between individual cement particles both before and during hydration, the better the hydration product and the better the strength of the bond between the particles. Hence, the positioning of cement particles in close proximity one to another before and during hydration plays an important role in the strength and quality of the final cementitious waste container. b. Hydration With Gaseous and Liquid Water It is within the scope of the present invention to hydrate the powdered hydraulic cement after the cement particles have been compressed into a hazardous waste container. Hydration is accomplished without mechanical mixing of the cement and water. Thus, diffusion of water (both gaseous and liquid) into the compressed hazardous waste container is an important hydration technique within the scope of the present invention. In most cases, hydration occurs immediately after the container is compressed. In other cases, initial hydration occur from water vapor in the atmosphere, with a more complete hydration occurring from ground water exposure after the container is placed in underground storage. When hydration is achieved by contacting the cementitious waste container with gaseous water, the gas may be at atmospheric pressure; however, diffusion of the water into the article, and subsequent hydration, may be increased if the gaseous water is under pressure. The pressure may range from 0.001 torr to about 2000 torr, with pressures from about 0.1 torr to 1000 torr being preferred, and pressures from about 1 torr to about 50 torr being most preferred. Even though water vapor is introduced into the cement compact, it is possible that the water vapor may immediately condense into liquid water within the pores of the cement compact. If this happens, then gaseous water and liquid water may be functional equivalents. Atomized liquid water may, in some cases, be used in place of gaseous water vapor. As used herein, atomized water is characterized by very small water droplets, whereas gaseous water is characterized by individual water molecules. Gaseous water is currently preferred over atomized water under most conditions because it can permeate the pore structure of the compressed cementitious container better than atomized water. The temperature during hydration can affect the physical properties of the hydrated cement container. Therefore, it is important to be able to control and monitor the temperature during hydration. Cooling the cement container during hydration may be desirable to control the reaction rate. The gaseous water may also be combined with a carrier gas. The carrier gas may be reactive, such as carbon dioxide or carbon monoxide, or the carrier gas may be inert, such as argon, helium, or nitrogen. Reactive carrier gases are useful in controlling the morphology and chemical composition of the final cementitious container. Reactive carrier gases may be used to treat the hazardous waste container before, during, and after hydration. The partial pressure of the water vapor in the carrier gas may vary from about 0.001 torr to about 2000 torr, with 0.1 torr to about 1000 torr being preferred, and 1 torr to about 50 torr being most preferred. An autoclave may be conveniently used to control the gaseous environment during hydration. It is also possible to initially expose the cement container to water vapor for a period of time and then complete the hydration with liquid water. In addition, the cement container may be initially exposed to water vapor and then to carbon dioxide. Heating the gaseous water will increase the rate of hydration. Temperatures may range from about 25.degree. C. to about 200.degree. C. It should be noted that the temperature at which hydration occurs affects certain physical characteristics of the final cement container, especially if an additional silica source is added. For example, when hydration temperature is greater than 50.degree. C., the formation of a hydrogarnet crystalline phase is observed, and when the hydration temperature is greater than 85.degree. C. other crystalline phases are observed. These crystalline phases, which often weaken the cement structure, are not always desirable. However, in some cases, the pure crystalline phases may be desired. In order to form the pure crystalline phase, it is important to use pure starting materials and to accurately control the hydration temperature. It should be remembered that obtaining a container with high chemical and structural stability may be more important than obtaining mechanical strength when hydrating the powdered hydraulic cement. c The Effect of Carbon Dioxide on Hydration The inventors have found that when carbon dioxide is introduced during the stages of hydration, significant structural benefits can be realized, such as high strength and reduced shrinkage on drying. These concepts are disclosed in copending patent application Ser. No. 07/418,027, filed Oct. 10, 1989, entitled Process for Producing Improved Building Material and Product Thereof, which is incorporated herein by specific reference. More specifically, as applied to the cementitious hazardous waste containers within the scope of the present invention, it has been found that CO.sub.2 can be used to prepare cement containers having improved water resistance, surface toughness, and dimensional stability. These results may be obtained by exposing the cement container to an enriched CO.sub.2 atmosphere while rapidly desiccating the cement container. For best results, the CO.sub.2 is preferably at a partial pressure greater than its partial pressure in normal air. d. Control of the Aqueous Solution Aqueous solutions may also be used to hydrate the cementitious hazardous waste containers within the scope of the present invention. As used herein, the term aqueous solution refers to a water solvent having one or more solutes or ions dissolved therein which modify the hydration of hydraulic cement in a manner different than deionized water. For instance, it is possible to simply immerse the unhydrated cement container in lime water to achieve adequate hydration. Lime water is an aqueous solution containing Ca.sup.2+ and OH.sup.- ions formed during the hydration reactions. Because of the presence of hydroxide ions, lime water typically has a pH in the range from about 9 to about 13. Other aqueous solutions, such as extracts from cement paste, silica gel, or synthetic solutions may be used to hydrate the cement containers of the present invention. Other ions in addition to Ca.sup.2+ and OH.sup.-, such as carbonates, silica, sulfates, sodium, potassium, iron, and aluminum, may also be included in aqueous phase solutions. In addition, solutes such as sugars, polymers, water reducers, and superplasticizer may be used to prepare aqueous solutions within the scope of the present invention. A typical aqueous solution within the scope of the present invention may contain one or more of the following components within the following ranges: ______________________________________ Most Preferred Component Concentration (ppm) Concentration (ppm) ______________________________________ calcium 50-3000 400-1500 silicon 0-25 0.25-5 carbon 0-5000 5-250 iron 0.001-10 0.01-0.2 aluminum 0.001-10 0.01-0.2 sulfur 0-5000 200-2000 sodium 0-2000 400-1500 potassium 0-4000 800-2000 sugars sdr sdr polymers sdr sdr water reducers sdr sdr superplasticizer sdr sdr ______________________________________ Where the term "sdr" refers to the standard dosage rate in the concrete industry, and where the term "ppm" means the number of component atoms or molecules containing the component compound per million molecules of water. Apparatus capable of monitoring the concentrations of ions in the aqueous solution include pH meters and spectrometers which analyze absorbed and emitted light. EXAMPLES Various cementitious hazardous waste containers and their method of manufacture within the scope of the present invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the use of the invention and should not be viewed as a limitation on any claimed embodiment. EXAMPLE 1 In this example, a hazardous waste container is prepared by isostatically compressing powdered hydraulic cement surrounding solid hazardous waste materials. The solid hazardous waste and the ordinary Portland cement are positioned within a pliable polymer mold such that from 5 to 10 inches of powdered cement surrounds the solid waste. The Portland cement also fills irregularities around the exterior surface of the solid hazardous waste materials. The container is then compressed at a pressure of 35,000 psi. After compression, the cement container has a green density of 2.6 g/cm.sup.3. The hazardous waste container is hydrated by immersing the container in saturated lime water having a pH of about 12 for about 24 hours. The saturated lime water is prepared by dissolving CaO in water. The lime water is maintained at a temperature between 22.degree. C. and 25.degree. C. at atmospheric pressure during hydration. EXAMPLE 2 In this example a hazardous waste container is prepared according to the procedure of Example 1, except that a layer of powdered high alumina cement is positioned adjacent the solid hazardous waste and a layer of ordinary Portland cement is positioned around the high alumina cement prior to isostatic compression. The high alumina cement also fills irregularities around the exterior surface of the solid waste materials. The thickness of the high alumina cement layer is maintained between 2 to 8 inches, and the thickness of the Portland cement layer is maintained between 2 to 8 inches. EXAMPLE 3 In this example a hazardous waste container is prepared according to the procedure of Example 1, except that the compressed cement container is hydrated by immersing the container in a 10% aqueous phase solution for about 24 hours. The 10% aqueous phase solution is prepared by making a cement paste having a 0.4 water to cement ratio and mixing the cement paste for 5 minutes. The aqueous phase is extracted from the paste and diluted with water to form the 10% aqueous phase solution. EXAMPLE 4 In this example a hazardous waste container is prepared according to the procedure of Example 1, except that after isostatic compression, the hazardous waste container is hydrated by immersing the container in water for about 24. EXAMPLE 5 In this example a hazardous waste container is prepared according to the procedure of Example 1, except that after isostatic compression, the hazardous waste container is hydrated by immersing the container in water for about 24 hours and thereafter exposing the hazardous waste container to CO.sub.2 while in a desiccating environment. EXAMPLE 6 In this example a hazardous waste container is prepared according to the procedure of Example 1, except that after isostatic compression, the hazardous waste container is carbonated under autoclaving conditions at 100% relative EXAMPLE 7 In this example a hazardous waste container for high level nuclear waste is prepared according to the procedure of Example 1, except that the relative thickness of the cement compared to the quantity of waste materials is increased. EXAMPLE 8 In this example, a hazardous waste container is prepared by isostatically compressing powdered hydraulic cement surrounding solid hazardous waste materials. The solid hazardous waste and ordinary Portland cement are positioned within a pliable polymer mold such that from 5 to 10 inches of powdered cement surrounds the solid waste. The Portland cement also fills irregularities around the exterior surface of the solid hazardous waste materials. The container is then compressed at a pressure of 35,000 psi. After compression, the cement container has a green density of 2.6 g/cm.sup.3. A layer of cement paste approximately 3 inches thick is then placed around the compressed waste container. Upon curing, the hazardous waste container includes an inner layer of substantially unhydrated cement compressed about and in contact with the hazardous waste and a hydrated cement outer layer. EXAMPLE 9 In this example, a multi-layered hazardous waste container is prepared by isostatically compressing powdered hydraulic cement surrounding solid hazardous waste materials. The solid hazardous waste and high alumina cement are positioned within a pliable polymer mold such that from 5 to 10 inches of powdered cement surrounds the solid waste. The powdered cement also fills irregularities around the exterior surface of the solid hazardous waste materials. The container is then compressed at a pressure of 35,000 psi. After compression, the cement container has a green density of 2.6 g/cm.sup.3. The outer surface of the compressed high alumina cement is carbonated under autoclaving conditions at 100% relative humidity. An outer layer of Portland cement is then positioned around the compressed high alumina cement and compressed at a pressure of 35,000 psi as described above. The outer layer of compressed Portland cement is hydrated by immersing the waste container in saturated lime water having a pH of about 12 for about 24 hours. The saturated lime water is prepared by dissolving CaO in water. The lime water is maintained at a temperature between 22.degree. C. and 25.degree. C. at atmospheric pressure during hydration. The resulting hazardous waste container has a quantity of substantially unhydrated powdered hydraulic cement in contact with the solid hazardous waste material. EXAMPLE 10 In this example, a multi-layered hazardous waste container is prepared according to the procedure of Example 9, except that the outer layer of Portland Cement also contains a plurality of fibers wrapped around the compressed high alumina cement to improve the mechanical properties of the final hazardous waste container. EXAMPLE 11 In this example, a multi-layered hazardous waste container is prepared according to the procedure of Example 9, except that the outer layer of Portland Cement also contains electrical and thermal conducting aggregates dispersed therein to improve the mechanical properties of the final hazardous waste container. SUMMARY From the foregoing, it will be appreciated that the present invention provides novel containers for storing solid hazardous waste which are constructed of strong nonmetal materials which do not intrinsically corrode to produce a gas. The present invention also provides novel containers for storing solid hazardous waste which are H.sub.2 O and CO.sub.2 getters. In addition, the present invention provides novel containers for storing solid hazardous waste constructed of materials which expand upon contact with aqueous solution to inhibit further aqueous solution penetration into the container. Finally, it will be further appreciated that the present invention provides novel hazardous waste containers which are inexpensive. The present invention may be embodied in other specific forms without departing from its spirit or essential charac teristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. |
description | Embodiments of the invention will now be described by the following examples. Arsenic Sodium Arsenite 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filer (ashxe2x80x94to soak up excesss water), and 160 gm of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 2.1 ppm which was much less than the allowed limit of 5.0 ppm. Powdered arsenic 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was less than the allowed limit of 5.0 ppm. Arsenic Trioxide 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was much less than the allowed limit of 5.0 ppm. Arsenic Pentoxide 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was much less than the allowed limit of 5.0 ppm. Powdered Arsenic 100 g, aluminium sulphate 50 g, calcium carbonate 20 g and water 150 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 200 g of calcium carbonate and caustic magnesium oxide, 400 g of a filer (ashxe2x80x94to soak up excess water), and 10 g of a mixture of 30 g aluminium sulphate, 60 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 1.0 ppm which was much less than the allowed limited of 5.0 ppm. Mercury Mercury from a mercury-containing brine sludge is encapsulated: in the following manner. The brine sludge contains between 100-200 mg of mercuric per kilogram of sludge. The sludge additionally contains 10-29% calcium carbonate, 1-9% magnesium hydroxide, 10-29% sodium chloride, 1-9% soil/dust and 30-60% water. The sludge is a waste produce from brine purification. The sludge is an odourless brown sludge insoluble in water. The sludge has a pH of 11.6 and a specific gravity of 1.29. 1 kg of the brine sludge, 900 g of settable composition, 270 g of water, 50 g of aluminium sulphate and 50 g of citric acid were mixed in a mixer. If desired, water is added to form a mouldable composition. The mixture is poured into moulds and set. A leach rate analysis showed a mercury leach of less than 0.01 parts p/million making the encapsulated composition safe for unlined tip storage. Nickel and Chromium 150 ml of an undiluted fully concentrated nickel and chromium containing residue (containing 360 mg p/litre chromium and 28,000 mg p/litre nickel), 400 ml water, 150 g calcium carbonate and 40 g of aluminium sulphate are mixed together to form a slurry. To the slurry is added 300 g of calcium carbonate and caustic magnesium oxide, 60 g of aluminium sulphate, 34 g of citric acid, 6 g of soda ash, 1 kg of filler (powerhouse ash) and an additional 50 ml of water. The thickness of the total mixture can be adjusted with water to form a mouldable composition. The mixture is poured into moulds and left to cure for T.C.L.P. tests (Toxic Characteristic Leachate Procedures). After 30 days of testing, a leach rate of below 0.2 parts p/million was established showing that the encapsulated product is suitable for storage in an unlined tip. 150 ml of an undiluted fully concentrated nickel and chromium containing residue (containing 3.1 mg p/litre chromium and 1,100 mg p/litre nickel), 400 ml water, 150 g calcium carbonate and 40 g of aluminium sulphate are mixed together to form a slurry. To the slurry is added 300 g of calcium carbonate and caustic magnesium oxide, 60 g of aluminium sulphate, 34 g of citric acid and 6 g of soda ash, 1 kg of filler (powerhouse ash) and an additional 50 ml of water. The thickness of the total mixture can be adjusted with water to form a mouldable composition. The mixture is poured into moulds and lets to cure for T.C.L.P. tests (Toxic Characteristic Leachate Procedures). After 30 days of testing, a leach rate of below 0.2 parts p/million was established showing that the encapsulated product is suitable for storage in an unlined tip. Radioactive Monazite Tests were conducted using a powdered sample of the mineral monazite. Monazite is a monoclinic phosphate of the rare earth elements containing the cerium groups (Ce, La, Y, Th) PO4, as well as some uranium and thorium. Monazite is relatively abundant in beach sands, and is one of the principal sources of rare earth minerals and thorium. Thorium is used as a radioactive source in scientific instruments. Rare earth compounds are used in various manufacturing processes, including the manufacturing of glass and certain metals. Analysis of the monazite material employed in the tests found that it contained 246 Becquerels per gram (Bq/gm) of thorium-232 and 28 Bq/gm of uranium-238. The half life of the thorium contained in the monazite is approximately 4.5 billion years (4.5xc3x97109). The monazite particle size can be from dust (approx. 0.1 xcexcm) up to particles of approximately 1.0 mm, ideally. The lead tailings, caustic magnesium oxide and calcium carbonate were all preground to approximately 110 xcexcm, ie. 90% passed through a 150 xcexcm sieve. 300 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 400 grams of caustic magnesium oxide and a mixture of 480 grams of lead tailings (ex Mt. Isa) and 320 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 300 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 44.60xc2x10.20 becquerels per gram thorium and 5.06xc2x10.21 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was less than 0.05 micrograms per litre and the leachable thorium was 0.25 micrograms per litre. At 28 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.45-0.50 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 part per million and the leachable thorium radioactivity was 0.034xc2x10.007 becquerels per gram. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 per million and the leachable thorium radioactivity was below detectable levels or equivalent to less than 2 parts per million. 500 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 450 grams of caustic magnesium oxide and a mixture of 360 grams of lead tailings (ex Mt. Isa) and 240 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 310 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 70.20xc2x10.30 becquerels per gram thorium and 8.01xc2x10.31 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was less than 0.05 micrograms per litre and the leachable thorium was 0.15 micrograms per litre. At 28 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.15-0.45 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 part per million and the leachable thorium radioactivity was below detectable levels or equivalent to less than 2 parts per million. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 part per million and the leachable thorium radioactivity was 0.038xc2x10.007 becquerels per gram. 800 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 400 grams of caustic magnesium oxide and a mixture of 300 grams of lead tailings (ex Mt. Isa) and 200 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 400 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 104.0xc2x10.41 becquerels per gram thorium and 12.0xc2x10.42 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.25 micrograms per litre. At 28 days the leachable uranium was 0.10 micrograms per litre and the leachable thorium was 1.10-1.40 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 part per million and the leachable thorium radioactivity was below detectable levels or equivalent to less than 2 parts per million. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to less than 1 part per million and the leachable thorium radioactivity was 0.038xc2x10.007 becquerels per gram. In each of the above examples 9 to 11 the leach rate solutions were all less than 10 parts per million (ppm) for thorium and uranium, indicating successful encapsulation of the radioactive material. It should be appreciated that various other changes and modifications can be made to the embodiments without departing from the spirit and scope of the invention, the nature of which is to be determined from the foregoing description and the appended claims. Furthermore, the preceding examples are provided for illustrative purposes only, and are not intended to limit the scope of the process of the invention. |
|
summary | ||
abstract | Thermal neutron irradiation of superconducting body compositions into which Li or B has been incorporated as a unit cell external or internal dopant introduces by the nuclear reaction of the dopant pinning centers which substantially improve the critical current density of the body. |
|
053348478 | claims | 1. A shield for ionizing radiation, said shield comprising: a body made of uranium and having an exterior; and a bismuth coating adhered to said exterior of said body, said coating being made of a corrosion-resistant material and adhering to said exterior by forming an intermetallic compound. heating said first material to approximately 300.degree. C.; heating said bismuth until said bismuth is molten; and pouring said bismuth over said first material. a body made of uranium, said body having a first surface and a cavity with an interior surface and an opening, said cavity dimensioned to receive said source; a lid dimensioned to cover said opening, said lid made of uranium and having a second surface; a first bismuth coating adhering to said first surface, said first coating made of a corrosion-resistant material, said first coating forming an intermetallic compound with said first material; a second bismuth coating adhering to said second surface, said second coating made of a corrosion-resistant material, said second coating forming an intermetallic compound with said second surface; and a third coating adhering to said interior surface, said third coating made of a corrosion-resistant material, said third coating forming an intermetallic compound with said interior surface. heating said uranium body to approximately 300.degree. C.; heating said bismuth until said bismuth is molten; and pouring said bismuth over said uranium body. coating said uranium with a layer of gadolinium; heating said bismuth until said bismuth is molten; and then pouring said bismuth over said first material, said bismuth adhering to said layer of gadolinium. 2. The shield as recited in claim 1, further comprising a layer made of gadolinium being adhered to said exterior of said body, said bismuth coating being adhered to said gadolinium layer. 3. The shield as recited in claim 1, wherein said bismuth coating is applied to said exterior of said body by a method comprising the steps of: 4. The shield as recited in claim 1, wherein said shield is for use with a source of ionizing radiation, and wherein said body is a container for storing said source. 5. The shield as recited in claim 1, wherein said bismuth coating is applied to said exterior of said body by heating said bismuth until said bismuth is molten and then dipping said first material into said molten bismuth. 6. Apparatus for storing a source of ionizing radiation, said apparatus comprising: 7. The apparatus as recited in claim 6, wherein said first surface further comprises a first external layer of gadolinium, said second surface further comprises a second external layer of gadolinium and said interior surface further comprises a third external layer of gadolinium, said first coating being adhered to said first external layer, said second coating being adhered to said second external layer, and said third coating being adhered to said third external layer. 8. The apparatus as recited in claim 6, wherein said bismuth is applied to said first surface and said interior surface by a method comprising the steps of: 9. The apparatus as recited in claim 6, wherein said second bismuth coating is applied to said second surface by heating said bismuth until said bismuth is molten and then dipping said lid into said molten bismuth. 10. A method for making a shield for ionizing radiation, said method comprising the step of applying a bismuth coating to a first material so that said coating adheres to said first material and forms an intermetallic compound with said first material, said first material absorbing gamma radiation. 11. The method as recited in claim 10, wherein said first material is made of uranium, further comprising the step of coating said uranium with a layer of gadolinium. 12. The method as recited in claim 10, wherein said applying step further comprises the steps of heating said bismuth until said bismuth is molten and then pouring said bismuth over said first material. 13. (Amended) The method as recited in claim 10, wherein said applying step further comprises the steps of heating said bismuth until said bismuth is molten and then dipping said first material into said molten bismuth. 14. The method as recited in claim 10, wherein said first material is uranium, further comprising the steps of: |
053751531 | description | DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS The present invention provides a coolant vent structure to be used alone in a bundle, in conjunction with a lower water rod, or in conjunction with a combination rod of water and fuel elements, or in conjunction with a part length fuel rod. In the latter case, the arrangement is particularly advantageous for improving CHF performance while retaining the benefits of a part-length fuel rod. The coolant vent duct is thus located above a part-length fuel rod. The duct can include a hollow tube extension that has one or more inlet openings at a bottom thereof and one or more outlet openings at a top thereof. Accordingly, some of the reactor coolant, that is a two phase mixture, passes inside the hollow tube extension. Due to the structure of the coolant vent fuel rod, at least a partial separation of the steam and liquid of the two phase coolant that surrounds the tube is achieved by the hollow tube extension. This allows coolant with a higher steam content to bypass the upper active portions of the fuel assembly. The structure of the present invention reduces the enthalpy rise maldistribution problem by providing active flow subchannels outside of and adjacent to the coolant vent duct that are much smaller than in the case of a part-length fuel rod without a duct. The coolant vent duct also provides an isolated inactive flow path inside of the duct so as to retain a significant part of the pressure drop reduction that occurs with a part-length rod. The coolant vent duct achieves a significant part of the part length rod pressure drop reduction because it provides most of the flow area gain that one achieves with a part-length fuel rod. The coolant vent duct can function as a steam extraction device. Specifically, the geometry of the inlet region of the coolant vent duct can be configured to achieve significant separation of steam from water such that the coolant with the increased steam content flows inside the hollow duct while the remaining coolant with increased liquid water content continues up the active flow channels. This coolant with increased liquid water content enables generally better cooling of the nuclear fuel rods and thus enables improved CHF performance. With either a part-length rod alone or with the coolant vent duct of the present invention, the improvement in pressure drop relative to having full length fuel rods is controllable via the number of such rods and the length of the fuel section of the rods. The trade off on whether to adjust the number or the length is made so as to yield favorable neutronics performance. The coolant vent duct of the present invention allows for fine tuning the pressure drop by using the flow holes in the coolant vent duct to meter the amount of flow that will go inside the coolant vent duct. Referring now to the Figures, and specifically to FIGS. 1 and 2, an embodiment of a combination coolant vent duct and part length fuel rod 10 of the present invention is illustrated. As illustrated, a part-length fuel rod 12 is provided that includes a fuel portion 14 that is located within the cladding 16 of the rod. The upper end of the part-length fuel rod 12 includes an insulator disk 18 that can be preferably constructed from Al.sub.2 O.sub.3. Additionally, the part-length fuel rod 12 and includes a connector member 20 that is received by and extends from an end 22 of the part-length fuel rod 12. The connector member 20 allows a coolant vent duct 23 having an extension tube 24 to be coupled to the part-length fuel rod 12 and disposed axially thereto. In the preferred embodiment illustrated, a horizontal pin 25 is provided for proper rotational alignment. The duct 23 extends vertically to the vicinity of the upper spacer 22 shown in FIG. 1, or to some point above the upper spacer (see FIG. 8). The duct could extend all the way up to the upper tie plate (not shown) in which case there would be a means for fixing the upper end such as an upper end cap 41 and locating pin 42 (see FIG. 8). The connector member 20 may be an assemblage of smaller pieces. Among other functions the connector member 20 can serve as an upper end cap to the part length fuel rod 12 below and as a mechanical connection between the part length fuel rod 12 and the coolant vent duct 23. The extension tube 24 includes a hollow interior 26 that provides a coolant flow path. The duct 23 also includes a transition portion 28 and an upper portion 30 formed together or bonded together. The upper portion 30 has an outer perimeter, or diameter, that is greater than the outer perimeter of the part-length fuel rod 12. Because the outer perimeter of the upper portion 30 and the tube 24 is greater than the outer perimeter of the part-length fuel rod 12, a more radial uniform enthalpy distribution among the active flow channels is achieved. The transition portion 28 has a lower section 32 that has a substantially constant outer perimeter, and has a tapered section 34 thereabove. The tapered section 34 and lower section 32 are formed together or attached together. The lower section 32 has an outer perimeter approximately equal to the outer perimeter of the part-length fuel rod 12. The outer perimeter of the transition portion 28 increases in the tapered section 34 to a point where the upper portion 30 begins. Preferably, at the end of the transition portion 28, there is a sharp break 36 that functions to assist in stripping liquid film off the outside surface of the coolant vent fuel rod 10. As illustrated in FIG. 2, the duct 23 can include a plurality of inlet openings 38 located in the transition portion 28. The inlet openings 38 allow a fluid to enter into the interior 26 of the extension tube 24. In a preferred embodiment, four inlet openings 38 are provided; one inlet opening 38 being aligned with each of the four subchannels that surround the combination coolant vent fuel rod 10. At an upper portion of the extension tube 24, outlet openings 40 are provided. These outlet openings can be a grouping of openings around the tube circumference as shown in FIG. 8. The outlet openings 40 allow fluid to exit the enclosed area 26 defined by the extension tube 24. The principle section of the extension tube 24 could be round, square, or some other shape that provides an open interior. The extension tube surface can have a local distortion 45 at certain elevations to facilitate mechanical interfacing with the spacers 22, 25 and mating with the upper portion 30 or upper end cap 41 if any. This invention has inlet openings 38 either in the extension tube 24 or the transition portion 28 and outlet openings 40 to enable upwards flow of the reactor coolant inside of the duct 23. There may be additional openings over the length of the duct either to admit flow into or exhaust flow from the interior 26 of the duct. The openings could also be simply open end or ends of the duct such as at the top 48 of extension tube 24 shown in FIG. 1. The mechanical connection of the lower part length fuel rod 12 and the upper tube 24 is a desirable feature but not a mandatory feature of this invention. When there is no connection the hollow tube 24 is located above a part length rod and has some means for admitting flow into the region inside the tube at the bottom and for exhausting flow at the top. The spacers provide lateral restraint when this invention is either connected or unconnected to the part length rod. When not connected to the part length rod below, vertical restraint of this invention would be provided by either the spacers or the upper tie plate. For example, locking tabs could be added to the outside surface of the tube or the tube could be distorted locally at one or more spacer elevations in such a way that if the tube is rotated 45.degree. it would lock into place and could not be removed vertically unless rotated again. In simple form, a hollow tube is placed axially above a part length fuel rod, and serves to add hydraulic resistance in a region that would otherwise be a large open subchannel. The addition of hydraulic resistance reduces subchannel flow and thereby provides a means to correct the enthalpy rise maldistribution problem of the prior art (i.e., fuel bundles with part length fuel rods). With a simple hollow tube form of this invention either the top or bottom (or both) ends of the tube might be deformed in such a way as to exert control over the amounts of liquid water and steam flows entering the tube. A transition piece and holes in the sides of the tube may or may not be present. In the embodiment illustrated in FIG. 2, a liquid diversion structure 50 is provided. In FIG. 2, the liquid diversion structures 50 extends outwardly from the transition portion 28, in juxtaposition to the inlet opening 38. In the embodiment illustrated, the liquid diversion structure 50 has a "V" shaped fence. Of course, other shapes and structures can be used to create a liquid diversion. The liquid diversion structure 50, as illustrated, is so constructed and arranged that liquid, such as droplets 52 in the two phase mixture, that are near the surface as well as the liquid film on the surface, are diverted away from the inlet opening 38 while steam 54 is allowed to enter the inlet opening 38. The V-shaped fence 50 diverts the liquid film flowing up the surface of the part length rod 12 below around and away from the inlet opening 38. It also provides an obstacle for steam and liquid drop flow near the surface of the combination coolant vent fuel rod 10 that is headed for the inlet opening. This obstacle is more easily negotiated by the steam than drops. This maximizes the steam quality of the fluid flowing into the interior 26 of the extension tube 24. By causing steam to enter the extension tube 24, and therefore, exit at the outlet openings 40 or 48 of the extension tube 24, one is able to maximize the liquid available for cooling the active fuel rods while maintaining sufficient flow inside the extension tube 24 to achieve the desired reduction and bundle pressure drop. The liquid diversion structures 50 provide at least some separation of vapor from liquid at the inlet opening 38 of the extension tube 24. This allows one to achieve a separation of the two phases as soon as practical after the fuel section of the part-length fuel rod 12. The increased diameter or size of the upper portion 30 of the extension tube 24, with respect to the transition portion 28, also facilitates flow separating inlet designs by allowing the liquid diverting structure 50, or other protrusion, to be located in the vicinity of flow inlet openings 38 without compromising fuel loadability into the bundle. For example, as illustrated in FIG. 2, the V-shaped fence 50 does not protrude beyond the outer circumference of the extension tube 24. Hence, coolant vent duct loading is not compromised. As set forth above, pursuant to the present invention, the transition portion 28 preferably has increasing diameter as one moves upwards and ends with a sharp break 36 to help strip off the liquid film on the outside surface of the rod. Additional film stripping means could be included over the length of the hollow tube 24 to minimize the liquid flow on the surface. The tube extension 24 could be truncated at the top spacer or it could be continued up to the upper tie plate with multiple outlet holes above the last spacer to minimize the hydraulic resistance of the flow leaving the coolant vent duct 10 (see FIG. 8). Referring now to FIG. 3, an embodiment of the coolant vent fuel rod 110 of the present invention is illustrated. In this embodiment, inlet openings 138 are located in a transition portion 128 of this invention. In this embodiment, the openings 138 are located in a lower section 132 below a tapered section 134 of the transition portion 128. As illustrated, in this embodiment, several inlet openings 138 are located one after the other. Each opening 138 includes a liquid diversion structure 150 located in juxtaposition to the opening. Again, the structure 150 limits the liquid that enters the openings 138. In all other aspects, the coolant vent duct 110 is similar to the embodiment illustrated in FIGS. 1 and 2. By having several inlet openings 138 one after the other, the openings provide a larger total inlet flow hole area if this is necessary to achieve sufficient flow inside the coolant vent fuel rod to achieve the necessary reduction and bundle pressure drop. Referring now to FIGS. 4 and 5, a further embodiment of a coolant vent duct 210 of the present invention is illustrated. In this embodiment, within an enclosed interior 226 defined by an extension tube 224, a structure 227 is located for separating water droplets from steam in the two phase mixture. Once separated, at least a portion of the separated water can be transferred to the surface of adjacent fuel rods increasing the critical heat flux (CHF) capability. To this end, openings 240 are provided along the length of the extension tube 224 to facilitate the transfer of the water that is separated to adjacent fuel rods. The structure 227 for separating the water from the steam can be, as illustrated in FIG. 5, a device for imparting centrifugal force to the two phase mixture. In the embodiment illustrated in FIG. 5, the device includes a louver 227 that is formed into the wall of the extension tube. Referring now to FIGS. 6 and 7, a further embodiment of the coolant vent fuel rod 310 is illustrated. In this embodiment, a structure 327 for separating steam from liquid is a twisted ribbon 327 located within an interior 326 defined by an extension tube 324. As in FIG. 4, separated water exits through one or more vent holes facilitating its transfer to adjacent fuel rods. In addition to the internal devices for imparting centrifugal force illustrated in FIGS. 4-7, other devices and surfaces for causing agglomeration of water droplets can be used. For example, a spacer can be used. Surfaces that cause a rapid change in direction or configurations can also facilitate separation through gravity, surface tension, and other natural forces. Referring now to FIGS. 8 and 9, there is another embodiment of the coolant vent duct. In this embodiment a connector/transition piece 414 is provided having a central flared section 415. A part length fuel rod 412 mounts axially thereon a coolant vent duct 416. Inlet holes 427 are located at the bottom end of the extension tube 416. The connector/transition piece 414 provides separation of the liquid water and steam. A liquid film 462 is shown moving up the part length rod 412 surface and onto the surface of the connector/transition piece 414. Once on the transition piece 414, this film is brought in inward direction 464 by a reduction in transition piece diameter 464a and then is rapidly redirected in radially outward direction 465. A sharp break 466 in the surface contour causes the film to separate and to continue to flow in a radially outwards direction as a thin sheet of liquid water 468. The liquid sheet of water 468 and approaching liquid drops 470 collide and outwards radial momentum is imparted to the liquid drops such that downstream of the separator device, liquid 481 is moving radially outwards while steam vapor 482 is moving inward towards the inlet holes 427. Above the outwardly flared section 415 of the transition piece 414 the diameter is again reduced 474 so that a naturally forming eddy flow 476 behind the separating sheet of liquid 468 intersects the separating sheet 468 in a more parallel fashion as opposed to a more perpendicular fashion, at the film separation point, the break 466. A second flared portion 478 of the transition connector piece 414 repeats the process for any residual liquid. If the initial flared portion 415 is not present, the second flared portion 478 becomes the primary means of directing liquid outward and away from the inlet holes 427. The initial diameter reduction 464a at the bottom end of the transition connector piece is done smoothly so that the liquid film remains attached to the surface until it reaches the intended separation point, the break 466. The diameter is reduced ahead of the flared section so that the flared section presents a greater frontal area to the main flow stream and therefore has a greater interaction with it. The flared surfaces are rounded or curved as opposed to being straight conical or tapered surfaces so as not to impede the flowing film by trapping it in any sharp concave corners, upstream of the intended separation point 466. As shown in FIG. 9, the transition connector piece is a surface of revolution about a vertical axis down the vents. While this is easy to fabricate, sections other than round sections, for example square sections, would likely function in a satisfactory manner. Also the flared section might be sectioned into several pieces that are displaced axially from one another. In the embodiments shown in FIGS. 8 and 9, connector/transition piece 414 which functions to separate liquid water and steam is mounted at one end to a part length fuel rod 412 and at its other end is connected to the coolant vent duct 416. As contrasted to functioning, in part, as a mechanical connection between the part length fuel rod and the coolant vent duct, the connector/transition piece can instead serve as an upper end cap of the part length fuel rod. In a further embodiment of the present invention, a reflex upper end cap or fitting 2201, is connected to the part length fuel rod and is shown in FIG. 16. The reflex upper end fitting is shown connected to a part length fuel rod without using either a connector/transition piece and/or a coolant vent duct. The reflex upper end fitting has a flared section which is truncated at a sharp break. As coolant/moderator flows through the fuel assembly and along the part length fuel rod, a liquid film is formed on the surface of the part length fuel rod. The liquid film moves up the part length fuel rod and onto the reflex upper end fitting and is then directed towards surrounding fuel rods. In the case of light water reactors, upwards flowing liquid water drops in the two phase flow collide with the continuous liquid film sheet as it is moving towards the surrounding fuel rods and is imparted with an outwards radial momentum, and together with the liquid film sheet impinge upon the surrounding fuel rods. The reflex upper end fitting thus increases the amount of liquid coolant/moderator on and near the surface of the surrounding fuel rods while steam vapor flows into the large open subchannel above the top of the part length fuel rod. Reflex upper end fitting 2201 shown in FIG. 16 is the portion of connector/transition 414 shown in FIG. 9 from and including sharp break 466 upstream to the part length fuel rod 412. FIG. 16 shows reflex upper end fitting 2201 in which corresponding elements in each of FIGS. 9 and 16 have the same reference numbers. Reflex upper end fitting 2201 is connected to part length fuel rod 412 and in the present embodiment is shown without a coolant vent duct. As shown in FIG. 16, a single flared section 415 is truncated at sharp break 466 and liquid film 462 is shown moving up the surface of part length fuel rod 412 onto the surface of the reflex upper end cap 2201. Once on the reflex upper end cap, liquid film 462 is brought in inward direction 464 by a reduction in diameter 464a and then is rapidly redirected in radially outward direction 465. Sharp break 466 in the surface contour causes liquid film 462 to separate from the reflex upper end fitting 2201 and to continue to flow in a radially outwards direction towards the surrounding subchannels and fuel rods as a thin sheet of liquid water 468. Liquid sheet of water 468 and approaching liquid drops 470 collide in the flow stream and outwards radial momentum is imparted to liquid drops 470 such that downstream of the reflex upper end fitting 2201, liquid 481 is moving radially outwards towards the surrounding fuel rods 2220 and surrounding subchannels while steam vapor 482 concentrates in the large open subchannel above the reflex upper end fitting. After impact with water drops, sheet 468 is no longer continuous and begins to break up thereby enabling vapor to pass through it to the large open subchannel above the reflex upper end fitting. Eddy flow 2210 is formed behind sheet 468 and intersects the sheet 468 in a parallel fashion at sharp break 466. The movement of liquid onto and around the surrounding fuel rods 2220, and the concentration of vapor in the large open subchannel above the part length fuel rod and away from surfaces of the surrounding fuel rods, results in an enthalpy reduction for the flow on and near the surface of the surrounding fuel rods. In order to facilitate the insertion and/or removal of a part length fuel rod having a reflex upper end fitting into a fuel assembly as well as to facilitate fuel assembly fabrication, it may be desirable that the maximum outside diameter of the reflex upper end fitting not exceed that of the part length fuel rod to which it is connected. As discussed previously, in order for liquid film 462 which flows upwards on the surface of part length fuel rod 412 to separate from the surface of the end fitting as a thin continuous sheet, the reflex upper end fitting has an outwardly flared section 415 which ends in sharp break 466. In order to both facilitate fuel rod loading into a fuel assembly as well as to have the liquid film separate as a thin continuous sheet from the surface of the end fitting, the shape of the reflex upper end fitting includes a reduction in diameter 464a, upstream of outwardly flared section 415 and sharp break 466. As a practical matter, with respect to the embodiments illustrated in FIGS. 1-3, 8 and 9, the separation of steam from water at the coolant vent duct inlet openings may be less than 100%, i.e., 100% steam may not be flowing into the interior of the coolant vent duct. Therefore, if desirable, the concepts illustrated in FIGS. 1-3, 8 and 9 and 4-7 can be combined. Accordingly, even though liquid diversion means are located on an outer wall of the extension tube, additional flow separation means can be enclosed inside the coolant vent ducts as set forth in the embodiments illustrated in FIGS. 4-7. Further embodiments of connector/transition pieces are shown in FIGS. 10-15. These embodiments can be used alone to mount beneath a coolant vent duct or can be used such as shown in FIG. 8 to mount a coolant vent duct 416 to a part length fuel rod 12. All these embodiments can be used to mount a coolant vent duct 416 to a water rod or a water/fuel rod or the like. FIG. 10 shows a transition/connector 500 having a hollow perforated tube portion 504 mounted axially above a substantially solid connector portion 506. The hollow tube portion 504 can be fashioned having a top socket portion 510 which interfits inside the coolant vent duct 416. The socket portion 510 has a top open end 512. The connector section 506 has a bottom socket portion 516 for mechanical insertion and connection to a rod therebelow. The transition section 506 has a taper 520 in upward direction, an elongate neck portion 522 terminating in a sharp expansion 524 with a sharp break 526 at the intersection with the hollow tube portion 504. The connector 506 would behave similarly as the lower one half of the connector 414 as shown in FIG. 9. FIG. 10 shows the hollow tube portion 504 having a plurality of holes 530 thereinto. The holes 530 can merely be openings around a circumference of the cylindrical tube wall. Optionally, the holes can have a cylindrical protruding rim 534 or a beveled protruding rim 536. These protruding rims 534, 536 or variations thereof could be applied to any of the embodiments if desired. The transition connector 600 shown in FIG. 11 is substantially the same as the transition connector 500 shown in FIG. 10 except that a helical fin is attached to and wound around a connector section 604. The connector section 604 provides a first taper 608, a neck section 610 and a sharp expansion 612 terminating in a sharp break 614 at an intersection between the connector section 604 and a hollow perforate tubular section 620 thereabove. The transition/connector 600 provides a open top socket 622 similar to the socket 510 in FIG. 10. A bottom socket portion 626 can be provided for connection to a rod below. Another embodiment of the transition/connector is shown as transition/connector 700 in FIG. 12. This embodiment is similar to FIGS. 10 and 11 and can provide an open top socket 704 at a top end thereof and a mechanical connection socket 706 at a bottom end thereof. The transition connector is substantially hollow. A helical pad 708 is formed or wrapped around an elongate neck 710 of the transition/connector 700. Arranged along the helical pad 708 are openings 712. The elongate neck section 710 terminates at an upper end in a sharp expansion 720 and at a lower end in a taper 722. The opening 712 communicate into the hollow neck section 710 where steam vapor can be carried upward through the elongate neck section 710 and out of the open top socket 704 into a coolant vent duct 416 arranged thereabove (not shown). Another embodiment of a transition/connector 800 is shown in FIG. 13. In this embodiment a substantially hollow neck section 802 has an open top socket portion 804 for interfitting into a coolant vent duct 416 thereabove (not shown). A bottom socket 806 is provided for mechanical interconnection with a rod below. Adjacent the socket 806 is a sharp expansion 808 and a sharp break 810 into the hollow neck section 802. A plurality of openings 816, in this embodiment shown as square, are provided. Above each opening is a cone-shaped depression 820 which tapers down in upward direction to the surface of the elongate neck section 802. Another embodiment of a transition/connector 900 is shown in FIG. 14. In this embodiment, a perforated hollow tube section 902 having a top socket with an open top 904 thereabove is mounted axially above a connecting portion 906 having a plurality of helical veins 908 arranged protruding from a tapered neck section 910. The tapered neck section tapers inwardly from its bottom to a central area and outwardly thereafter up into hollow tube portion 902. An attachment socket 914 is provided below the neck section 910. The hollow tube portion 902 is provided with openings 920 for inlet of steam to progress upwardly inside the tube portion 902, out of the top socket 904 into a coolant vent duct 416 mounted thereabove (not shown). Another embodiment of a connection portion 950 is shown in FIG. 15. In this embodiment, the connector 414 of FIG. 9 is elongated and means for separating the upwards flowing liquid surface film is a ridge 952. The embodiments for the connector/transition pieces shown in FIGS. 10-15 could also be used in combination with the embodiments of FIGS. 4-7, thus providing liquid diversion means on both an outside and on an inside of the transition/connection piece or the coolant vent duct. The present inventive coolant vent duct need not be associated with a part-length fuel rod. It could be used in conjunction with a water rod or some combination of water and fuel elements. A bundle containing one or more coolant vent ducts can use these ducts in conjunction with water rods, water channels, and the like. The inlet elevation of the coolant vent duct can be at any elevation along the active length of the bundle where there is available steam to be separated from liquid coolant. A coolant vent duct bundle can contain one or more individual coolant vent ducts whose design need not all be identical. For example, each coolant vent duct in the bundle might have a different inlet elevation. The shape of inlet and outlet openings can be various. Examples of inlets are round holes, rectangular holes, or openings of some other regular or irregular shape. The surface of the duct can be distorted in the vicinity of the inlets to enhance separation of steam from liquid, or to reduce pressure drops. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims. |
summary | ||
description | This Patent Application is a continuation-in-part of U.S. patent application Ser. No. 14/634,834, entitled X-RAY SURFACE ANALYSIS AND MEASUREMENT APPARATUS and filed Mar. 1, 2015, which is incorporated herein by reference in its entirety, and which claimed the benefit of U.S. Provisional Patent Application Nos. 61/946,475 and 61/946,527, both filed on Feb. 28, 2014; 62/008,856, filed Jun. 6, 2014; 62/086,132, filed Dec. 1, 2014, and 62/117,062, filed Feb. 17, 2015, all of which are also incorporated herein by reference in their entirety; and further claims the benefit of U.S. Provisional Patent Application No. 62/127,781, entitled X-RAY DIFFRACTION AND SMALL ANGLE SCATTERING APPARATUS USING A LINEAR ACCUMULATION X-RAY SOURCE filed Mar. 3, 2015, and U.S. Provisional Patent Application No. 62/195,746 filed on Jul. 22, 2015, both of which are incorporated herein by reference in their entirety. The present Application presents an x-ray analysis and measurement apparatus for analysis, quantification of chemical composition, structural determination, measurements and metrology of a specimen with a flat surface or for specimens such as fine particles or liquid that are deposited on a flat surface of a substrate. The x-ray techniques may include x-ray diffraction (XRD), grazing incidence x-ray diffraction (GIXRD), grazing incidence diffraction (GID), grazing incidence x-ray small angle scattering (GISAXS), total reflection x-ray fluorescence analysis (TXRF), and x-ray reflectivity (XRR), singularly or in combination. X-ray diffraction (XRD), grazing incidence x-ray diffraction (GIXRD), grazing incidence diffraction (GID), grazing incidence small angle x-ray scattering (GISAXS), x-ray fluorescence (XRF), total reflection x-ray fluorescence (TXRF) analysis and x-ray reflectometry (XRR) are well-established x-ray surface analysis and measurement techniques [see, for example, R. Klockenkämper and A. von Bohlen, Total Reflection X-ray Fluorescence Analysis and Related Methods 2nd Ed. (J. Wiley and Sons, 2015); R. Fernández-Ruiz, “TXRF Spectrometry as a Powerful Tool for the Study of Metallic Traces in Biological Systems” Development in Analytical Chemistry vol. 1 2014; Jeremy Karl Cockcroft & Andrew N. Fitch, “Chapter 2: Experimental Setups”, in Powder Diffraction: Theory and Practice, R. E. Dinnebier and S. J. L. Billinge, eds. (Royal Society of Chemistry Publishing, London, UK, 2008); M. Birkholz, “Chapter 4: Grazing Incidence Configurations”, in Thin Film Analysis by X-ray Scattering (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2005); J. Levine Parrill et al., in “GISAXS—Glancing Incidence Small Angle X-ray Scattering,” Journal de Physique IV vol. 3 (December, 1993), pp. 411-417; and G. Renaud et al., “Probing surface and interface morphology with Grazing Incidence Small Angle X-ray Scattering” Surface Science Reports vol. 64:8 (2009), pp. 255-380]. The grazing incidence techniques utilize an x-ray beam incident upon a specimen with an incidence angle smaller than the critical angle for total reflection of the surface material at the incident x-ray energy. Under this condition, the incident x-rays penetrate only a short distance into the surface, typically less than 20 nm, resulting in the surface sensitivity of the techniques. X-ray diffraction (XRD) is useful for crystalline structural determination of a specimen by measuring diffraction patterns resulting from an x-ray beam impinging on the specimen. This is a common technique to determine crystal structures of compounds and materials. GIXRD is useful for crystalline structural determination of a thin surface layer of a specimen with a flat surface by measuring diffraction patterns resulting from an x-ray beam incident on the specimen at a grazing incidence angle. This is typically used with flat surfaces. GID records the diffraction pattern at a grazing exit angle. GISAXS is useful to characterize structures (typically with dimensions on a nanometer scale) of a thin surface layer of a specimen as well as inner electron density fluctuations of the deposited material by measuring the scattering signal that results from an x-ray beam of grazing incidence. TXRF provides highly sensitive chemical composition and concentration analysis and quantification of a thin surface layer (<20 nm) of a specimen with a flat surface or a specimen (e.g. liquid or fine particles) on top of an optically flat substrate by measuring the x-rays produced by the specimen under x-ray excitation. It may also be used to determine the thickness of a thin film on top of an optically flat substrate. XRR measures the intensity of x-rays undergoing specular reflection from a surface at various angles of incidence to obtain density, thickness, and roughness profiles of surface layers and thin films. For scientific studies of materials that need high brightness x-rays, high brightness synchrotrons or free-electron lasers have been used with great success. However, these facilities are large, often occupying acres of land, and expensive to operate, and obtaining beamtime can take months of waiting. They are impractical for conventional laboratory use. Until now, the laboratory application of the grazing incidence x-ray techniques described above have relied on conventional laboratory x-ray sources that use an extended solid metal anode (such as copper) and have relatively low brightness and limited choice of x-ray spectra of the incident x-ray beam. This is due to the limitation of using x-ray target anode materials with suitable thermal, mechanical, and chemical properties to ensure continuous operation of the x-ray target, typically preventing the anode target from melting, as disclosed in U.S. Pat. Nos. 5,249,216, 7,551,719, and 7,680,243, whose disclosures are incorporated herein by reference in their entirety. U.S. Pat. No. 7,929,667, also incorporated herein by reference in its entirety, describes the use of an x-ray source using a liquid metal jet anode to circumvent the thermal limitations of conventional x-ray sources for x-ray metrology applications. However, to achieve the desired benefit, the metal jet needs to be in liquid form and have sufficiently high speed and low vapor pressure, among other challenging requirements. The major limitation of this type of x-ray source is that only an extremely limited number of metals are in liquid form at reasonable temperatures, i.e., below 200 centigrade. Consequently, the choice of x-ray characteristic lines for monochromatic x-ray beam illumination is extremely limited. To make substantial performance improvements to grazing incidence x-ray techniques, singularly or in combination, there is need of an x-ray apparatus comprising a high brightness laboratory x-ray source, preferably providing flexibility in choice of anode material to produce a range of x-ray energies. Additionally, among these techniques, there is also continued demand for reducing (improving) absolute and/or relative trace element detection limit in liquids and solutions, especially for low atomic number elements (e.g. boron (B), carbon (C), oxygen (O), fluorine (F), sodium (Na), aluminum (Al), and sulfur (S)), improving throughput, quantitative elemental composition analysis accuracy, higher spatial resolution for small spot analysis or mapping/imaging of elemental composition as well as higher sensitivity and performance in determining crystallographic phases and/or texture, measurement of thin film thickness, semiconductor metrology, and measurement of impurities and contamination on silicon surfaces in semiconductor manufacturing. The present invention discloses an x-ray surface analysis and characterization apparatus that comprises an x-ray source using the linear accumulation of x-rays that provides high x-ray brightness and a wide choice of x-ray energy. The linear accumulation x-ray source compromises two or more sub-sources of x-rays, with each sub-source having predetermined x-ray spectral characteristics, with the sub-sources separated physically from each other by predetermined spatial intervals and aligned with each other along a predetermined axis to allow accumulation of x-rays along that axis, thereby increasing brightness. The x-ray sub-sources produce x-rays by electron bombardment of a target, and the linear accumulation of x-rays from the multiple origins leads to greater x-ray brightness. In some embodiments, the x-ray sub-sources may be a single microstructure, or comprise of one or more embedded multi-microstructures, each of which comprise an x-ray generating material selected for x-ray generating properties, such as spectral characteristic and x-ray production efficiency. The microstructures of x-ray generating material may have at least one dimension less than 10 micrometers, embedded in a substrate of low Z material with high thermal conductivity. A significant advantage to some embodiments is that the high x-ray brightness from the linearly accumulating source results in greatly improved throughput and higher sensitivity for the above mentioned grazing incidence x-ray techniques, which is particularly important for industrial applications such as semiconductor metrology. Furthermore, the higher brightness combined with a wider range of characteristic x-rays can extend the analytical performance capabilities of XRR, TXRF, GIXRD, GID, and GISAXS. Some embodiments additionally comprise an x-ray optical train that is configured to collect and collimate or focus x-rays along the predetermined axis to produce an x-ray beam with predetermined beam properties, such as the beam profile, intensity cross section, or angular composition, as well as predetermined spectral properties. In some embodiments, the x-ray optical train comprises at least one x-ray mirror optic with an axially symmetric reflecting surface of a predetermined surface profile, selected from paraboloids, ellipsoids, or type I Wolter optics. Additionally, it may include one or more spectral filter(s) or monochromator(s) to narrow the spectral band of the x-ray beam. Furthermore, some embodiments comprise at least one absorbing x-ray collimator, such as an aperture or slit, to collimate the angular convergence of the x-ray beam or the incident x-ray spot upon the specimen. The x-ray optic is positioned such that the x-ray beam is directed to be incident at a grazing angle upon the flat surface of a specimen to be analyzed. Additional advantages may be provided in some embodiments of the invention by using an axially symmetric x-ray optic with a large numerical aperture, producing a higher brightness x-ray beam incident upon the specimen. Additional advantages may be provided in some embodiments of the invention by using optics of small point spread function and using a flat crystal monochromators within the optical train to provide higher spatial resolution and analytical sensitivity. At least one detector receives x-rays from the specimen in response to the interaction of the incident x-ray beam with the specimen, and produces signals indicative of properties of the specimen. The x-ray signals from the specimen might include diffracted x-rays, scattered x-rays, and/or reflected x-rays. An electromechanical system controls the source, the components of the optical train, positioning the specimen with respect to the incident x-ray beam, and the detector, acquires data, and determines the properties of the specimen based on the x-ray signals at least in part, singularly or in combination. In various embodiments, the x-ray surface analysis and measurement apparatus is configured to perform TXRF, XRR, GIXRD, GID, and GISAXS, singularly, sequentially, or simultaneously in combination of a subset or all of the above techniques. Example applications include analysis of material contamination of semiconductor wafers, elemental composition analysis and thin film thickness measurement during semiconductor device manufacturing processes, such as dielectric materials, copper diffusion barriers, composition analysis and size and size distribution characterization of nanoparticles deposited on a flat surface, trace element detection and analysis in solutions and solid (with digestion) in forensics, pharmaceuticals, food, environmental samples, and biological tissue. Note: The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. For all of the surface x-ray techniques mentioned above, the x-ray flux F of the x-ray beam incident on the specimen surface is an important parameter and is equal to the product of the x-ray beam brightness Bs at the specimen (defined as number of x-rays per unit area and per unit solid angle illuminating the specimen), the cross sectional area A′ of the incident beam at the sample point, and the convergence angles: Δθ in the scattering plane which contains incident and reflected x-ray beam, and ω in the out-plane which is perpendicular to the reflection plane:F=BsA′Δθ*ω [Eqn. 1] The x-ray beam brightness Bs at the specimen is typically smaller than the x-ray source brightness (B) because the inherent low focusing efficiency and aberrations of the x-ray optical train lead to blurring and therefore an increase in the effective x-ray source size. Bs and B are approximately related by: B s = B ρ s 2 s 2 + [ M δ / ( M + 1 ) ] 2 [ Eqn . 2 ] where ρ is the total focusing efficiency of the all the optical components of the x-ray optical train from the source to the specimen, s is the diameter of the source size (assumed to be of a circular shape), δ the full width half maximum (FWHM) of the point spread function (PSF) of the x-ray optical train, and M the image magnification of the x-ray optical train. Note that M is equal to infinity when the source is located at a focus of the x-ray optical train. Eqns. 1 and 2 show that for given incident beam cross sectional area A′ and beam angular convergence Δθ, to increase F, it is desirable to have a high brightness x-ray source B, an x-ray optical train with high efficiency p, and a FWHM of the PSF optical train δ smaller than the source size s, and a large out-of-plane angle ω which is enabled by using an optic that has a large solid angle of collection along the out-of-plane direction. Various embodiments of the present invention obtain a large F by increasing B with a bright linear accumulation x-ray source, and enable large Bs, ρ, and ω values with a high performance x-ray optical train comprising an x-ray mirror optic. The value of Δθ must be constrained to be what is suitable for the grazing incidence surface x-ray techniques (less than the critical angle of reflection of the specimen or substrate at the incident x-ray energy of interest) and can be achieved by using additional x-ray aperture(s) or slit(s). The maximum value of Δθ is set to be less than the critical angle of reflection of the substrate at the x-ray energy of the incident x-ray beam, which is inversely proportional to the x-ray energy E and the square root of the mass density of the specimen or substrate, which are well-known values, some of which may be found through websites and references such as the X-ray Optics Calculator at [www.ipmt-hpm.ac.ru/xcalc/xcalc/ref_index.php]. By using a two dimensional X-Y Cartesian coordinate system in the specimen surface, with the X axis defined as being parallel to the x-ray beam and the scattering plane (containing the incident and reflected x-ray beam axis) and the Y axis perpendicular to the X axis, the area A=A′/sin(θ) of the beam footprint on the specimen placed at the focus of the focused x-ray beam can be expressed by: A = L y L x sin θ [ Eqn . 3 ] where Lx and Ly are the cross sectional beam size in the X and Y directions, respectively, and θ the mean grazing incidence angle. Lx and Ly are in turn given by L i = ( MS i M + 1 ) 2 + δ 2 [ Eqn . 4 ] where i may correspond to either X or Y, M is the magnification of the x-ray optical train, Si the full width half maximum (FWHM) size of the linear accumulation x-ray source in the respective direction, and δ the full width half maximum (FWHM) of the point spread function (PSF) of the x-ray optical train. For many applications, a small area A is required to obtain small spot analysis or perform high resolution spatial mapping over a large area, such as mapping surface contaminants over a wafer in semiconductor manufacturing. Various embodiments of the present invention obtains a small A by using a linear accumulation x-ray source with a small source size Si, an x-ray optical train with a small FWHM point spread function δ, and/or a small magnification factor M. Additionally, in some embodiments it is preferred to use x-rays of lower incident x-ray energies, as it can increase the critical angle θ and thus the convergence angles Δθ and ω to obtain a small footprint dimension A on the specimen in the scattering plane (due to the 1/sin(θ) factor) and to increase F. Moreover, the x-ray optical trains disclosed in embodiments of the present invention typically have higher solid angle of collection for low energy x-rays than higher energy x-rays. For most embodiments, it is preferred to achieve a combination of a large F and a small A in order to obtain low (better) absolute detection sensitivity. X-Ray System. FIG. 1A schematically illustrates one exemplary embodiment of the invention. The system comprises an x-ray source apparatus 80 that comprises an x-ray generator 08 that produces x-rays 888 with high brightness and a variety of x-ray energy spectra, an x-ray optical train 840 that collects a portion of x-rays 888 from the source and produces an x-ray beam 887 collimated in the scattering plane (as shown) to be incident at an angle on the specimen 240 to be investigated, and a variety of x-ray data collection systems, discussed further below. The x-ray generator 08 comprises a vacuum environment (typically 10−6 torr or better) commonly maintained by a sealed vacuum chamber 20 or using active pumping, and manufactured with sealed electrical leads 21 and 22 that pass from the negative and positive terminals of a high voltage source 10 outside the vacuum chamber 20 to the various elements inside the vacuum chamber 20. The x-ray source 80 will typically comprise mounts 30 which secure elements of the x-ray generator 08 such as the vacuum chamber 20 to a housing 50, and the housing 50 may additionally comprise shielding material, such as lead, to prevent x-rays from being radiated by the source apparatus 80 in unwanted directions. Inside the vacuum chamber 20, an emitter 11 connected through the lead 21 to the negative terminal of a high voltage source 10, which serves as a cathode and generates a beam of electrons 111, often by running a current through a filament. Any number of prior art techniques for electron beam generation may be used for the embodiments of the invention disclosed herein. A target 1100 comprising a target substrate 1000 and regions of x-ray generating material (shown in FIG. 1A as a set of embedded microstructures 700) is electrically connected to the opposite high voltage lead 22 and target support 32 to be at ground or positive voltage relative to the electron emitter 11, thus serving as an anode. The electrons 111 accelerate towards the target 1100 and collide with it at high energy, with the energy of the electrons determined by the magnitude of the accelerating voltage. The collision of the electrons 111 into the target 1100 induces several effects, including the emission of x-rays 888, some of which exit the vacuum chamber 20 and are transmitted through a window 40 that is transparent to x-rays. The target 1100, as will be further described below, is configured to have multiple sub-sources of x-rays generated from points that are generally aligned with each other such that they produce x-rays that may have linear accumulation, leading to higher brightness. Microstructured targets such as those that may be used in embodiments of the invention disclosed herein have been described in detail in the co-pending US Patent Application entitled STRUCTURED TARGETS FOR X-RAY GENERATION (U.S. patent application Ser. No. 14/465,816, filed Aug. 21, 2014), which is hereby incorporated by reference in its entirety, along with the provisional Applications to which it claims benefit. Furthermore, sources using these targets that have a linear accumulation of x-ray sources as are described more fully in the co-pending U.S. Patent Application entitled X-RAY SOURCES USING LINEAR ACCUMULATION by the inventors of the present invention (U.S. patent application Ser. No. 14/490,672 filed Sep. 19, 2014), which is also hereby incorporated by reference in its entirety, along with the provisional Applications to which it claims benefit. Any of the target and source designs and configurations disclosed in the above referenced co-pending Applications may be considered as alternative components and designs in any or all of the embodiments of the x-ray measurement systems according to the invention disclosed herein. In some embodiments of the invention, there may also be an electron control mechanism 70 such as an electrostatic lens system or other system of electron optics that is controlled and coordinated with the electron dose and voltage provided by the emitter 11 by a controller 10-1 through a lead 27. The electron beam 111 may therefore be scanned, focused, de-focused, or otherwise directed onto a target 1100 comprising one or more microstructures 700 fabricated to be in close thermal contact with the substrate 1000. In addition to providing one or more electron beam(s) with predetermined properties (e.g. electron energy, current, and focal spot size), such a control mechanism 70 may also direct the respective electron beams to its desired position on one or more x-ray target(s) to generate x-rays at the positions of sub-sources along a predetermined direction. The system will typically comprise an optical train 840 to collect the x-rays from the source and direct them towards the specimen 240 to be investigated. The combined x-ray source apparatus 80 and optical train 840 may be considered together to be an x-ray illuminator 800. The x-ray beam 887 may be adjusted to be a beam of varying properties depending on the specific measurement desired, but for x-ray diffraction measurements, and in particular grazing-incidence angle small angle x-ray scattering, the x-ray beam 887 will generally be formed to be a collimated beam. The specimen 240 is typically held in a mount 244, which may have motion controls for x-, y- and z-translation, along with controls for rotation about these and axes as well. The data collection system may comprise an x-ray detector or spectrometer 2900-D that collects reflected x-rays 2887 as well as scattered and/or diffracted x-rays 2888 resulting from the interaction of the incident x-ray beam 887 with the specimen 240. Depending on the measurement technique being employed, the spectrometer 2900-D may comprise x-ray optical elements and sensors designed to detect x-ray intensity and discriminate between x-ray energies. It may also in some embodiments be an x-ray detecting array designed to determine position dependent intensity for the x-rays emerging from the specimen 240. The spectrometer 2900-D may comprise a photon counter, an energy dispersive detector such as a silicon drift detector or Si(Li) detector that can discriminate between the energies of the x-ray photons detected, a wavelength dispersive spectrometer, a micro-calorimeter, or an apparatus that comprises of a combination of one or more crystal or multilayer spectrometers and detectors to generate an electronic signal representing the number of counts for the x-rays at various energies, or some other set of elements that converts x-ray intensity into an electronic signal. The detector 2900-D may also be an array x-ray detector that converts spatially dependent x-ray intensity to an electronic signal, including linear detectors, position-sensitive array detectors, pin diodes, proportional counters, spectrometers, etc. These electronic signals may be further processed by signal processing electronics 292 and passed to an analysis system 295 and presented to the user using a display 298. The specimen 240 may be mounted in a holder 244. Such a specimen holder 244 may be a simple tray, or comprise a complex mount, having controls 246 for translation of the specimen in x, y and z directions, and may also include x-, y-, and/or z-axis rotation mechanisms, such as a goniometer. Other detector geometries and arrangements may be known to those skilled in the art. For more on x-ray detectors, see Albert C. Thompson, “X-Ray Detectors”, Section 4.5 of the X-ray Data Booklet [xdb.lbl.gov/Section4/Sec_4-5.pdf]. FIG. 1B illustrates the interactions of the x-rays and the specimen as shown in FIG. 1A in more detail. The collimated incident x-ray beam 887 falls on the specimen at an angle θ relative to the plane of the specimen. For most materials, the majority of the incident x-rays will be transmitted through the specimen, resulting in a transmitted x-ray beam 1887. This beam may be absorbed by a beam stop 580. In some embodiments, the detector 2900-D will be placed to detect all the x-rays that emerge from the specimen, both reflected x-rays 2887 as well as diffracted/scattered x-rays 2888. In some embodiments, a beam stop 590 may be placed between the specimen 240 and the detector 2900-D to block the x-rays that are reflected from the specimen, allowing only diffracted/scattered x-rays 2888 (usually much lower in intensity) to fall on the detector. FIG. 2A illustrates a portion of another embodiment of the invention, in which an additional set of x-ray optical elements 845 is placed between the specimen and an x-ray detector 2900-F. In this embodiment, the diverging diffracted/scattered x-rays 2888 encounter the surface of an x-ray focusing optic in the set of x-ray optical elements 845 and form focused x-rays 2889 onto the x-ray detector 2900-F, while the reflected x-rays 2887 encounter a beam stop 588 and are blocked. This may allow a smaller detector to be used. For embodiments using the configuration of FIG. 2A, the point where the incident x-ray beam 887 falls on the specimen 240 may be designated as the center of a virtual circle, in which the incident x-ray beam 887 makes an angle θ relative to the plane of the specimen. The additional set of x-ray optics 845 and the detector 2900-F may be positioned as shown to collect diffracted/scattered x-rays emerging from the specimen at an angle of 2θ relative to the incident x-ray beam. In some embodiments, the rotation of the mount 244 holding the specimen 240 is controlled to rotate about this point at which the incident x-ray beam 887 falls on the specimen 240, thereby varying the angle θ. This is illustrated in FIG. 2B. An x-ray detector 2900-M is then mounted on a track 2905 that allows motion of the detector 2900-M such that, as the incidence angle θ varies, the angle between the detector 2900-M and the incident x-ray beam 887 is controlled to be 2θ, while the distance from the detector 2900-M to the specimen 240 is kept constant. In this manner, the well known “theta−2 theta” diffraction plots for the specimen may be obtained. FIG. 2C illustrates another variation to “theta−2theta” embodiments, in which the detector is an extended, curved detector 2900-C with an array of position sensitive x-ray sensors. The detector therefore need not move along the track 2905 (or need not move as much) as the incidence angle θ changes as long as the x-ray output as a function of position in the array has been calibrated to the corresponding angle 20. For such an embodiment, focusing optics or beam blocks may not be necessary, although configurations in which they are also used may also be implemented in some embodiments of the invention. Additional x-ray optical elements may be placed to adjust and adapt the properties of the incident x-ray beam 887. These additional optical elements may comprise x-ray optics (preferably axially symmetric grazing incidence x-ray optics), absorbing collimators (pinholes, apertures, slits, etc.), monochromators (e.g. double crystal or channel-cut monochromators), filters (including foil filters), anti-scatter slits and pinholes. Such pinholes may include the SCATEX pinhole (Incoatec) or MolemeX Scientific pinholes and slits. Likewise, additional x-ray optical elements may be placed to adjust and adapt the properties of the diffracted/scattered x-ray beam 2888. These additional optical elements may comprise x-ray optics (preferably axially symmetric grazing incidence x-ray optics), absorbing collimators (pinholes, apertures, slits, etc.), monochromators (e.g. double crystal or channel-cut monochromators), filters (including foil filters), anti-scatter slits and pinholes. Such pinholes may include the SCATEX pinhole (Incoatec) or MolemeX Scientific pinholes and slits. FIG. 3 illustrates details from another embodiment of the invention, in which the specimen 240 is probed in transmission mode instead of at a grazing incidence. The x-ray beam 887 impinges on the specimen 240 at normal incidence or near normal incidence. The transmitted x-rays 1887 may be blocked using a beam stop 584, while diffracted x-rays 2898 may be detected by a detector 2900-D. The detector may be any position sensitive detector, such as CCD detectors and other known position sensitive detector arrangements, as well as those discussed above. WAXS (wide angle x-ray scattering) embodiments are similar to the SAXS embodiments shown, except measuring the x-rays scattered at wide angles by placing the detector at larger angles or moving the detector larger angles. In all of these embodiments, the detectors used may be any combination of detectors capable of position-sensitive measurements. This may include point detection systems that are moved spatially, linear detectors, or 2D array detectors (e.g. curved area detectors or CCD detectors). Electromechanical systems may be used to move the detectors to collect over a wide angular range or to be used at a fixed scattering. As before, additional x-ray optical elements may be placed to adjust and adapt the properties of the incident x-ray beam 887. These additional optical elements may comprise x-ray optics (preferably axially symmetric grazing incidence x-ray optics), absorbing collimators (pinholes, apertures, slits, etc.), monochromators (e.g. double crystal or channel-cut monochromators), filters (including foil filters), anti-scatter slits and pinholes. Such pinholes may include the SCATEX pinhole (Incoatec) or MolemeX Scientific pinholes and slits. In any of the embodiments presented here, the electronic signals generated by the detector may be further processed by signal processing electronics 292 and passed to an analysis system 295 and presented to the user using a display 298. In general, the analysis system 295 may also function as a controller for the system, directing the motion of the stage and the detector to generate the appropriate dataset for the desired protocol. X-Ray Source. FIG. 4 schematically illustrates a portion of a linear accumulation x-ray source as may be used in some embodiments of the present invention that provides high x-ray brightness. In most embodiments, the linear accumulation x-ray source is preferred to have a focal spot of less than 1 micron to 300 microns. In this source, six discrete microstructures 2701, 2702, 2703, 2704, 2705, 2706 comprising x-ray generating materials selected for x-ray generating properties are embedded or buried in a substrate 2000 and configured at or near a recessed edge 2003 of the substrate 2000 by a shelf 2002, where the material of the substrate is of low average atomic number, high thermal conductivity and high melting point. The x-ray generating microstructures 2701, 2702, 2703, 2704, 2705, 2706 are arranged in a linear array along a predetermined axis 3000, and emit x-rays 888 when bombarded with electrons 111. Along the direction within an angle ψ of the axis 3000, x-rays generated in the six sub-sources accumulate and appear to be generated from a single sub-source. The angle range is approximately limited to smaller value of D and W divided by total length of the x-ray generating region 6*(l+d). The thickness of the bar D (along the surface normal of the target) is selected to be between one-third and two-thirds of the depth of the incident electron penetrating into the substrate for optimal thermal performance, but it can be bigger or smaller. It may also be selected to obtain a desired x-ray source size in that direction which is approximately equal in combination with selecting sufficiently large acceleration energy of the incident electron beam as the penetration depth of the incident electron beam is approximately proportional to the energy of the electrons. The width of the bar W is selected to obtain a desired source size in the corresponding direction. Though W≈1.5 D is illustrated in FIG. 4, it could also be substantially smaller or larger, depending on the size of the source spot desired. In FIG. 4, each of the discrete microstructures 2701, 2702, 2703, 2704, 2705, 2706 shown to have equal a length l along the axis 3000. The total length of all the six discrete microstructures 6l will commonly be set to be ˜2L, where L is the x-ray linear attenuation length of the materials of the discrete microstructures for the x-ray energy of interest, but a value of 0.5L to 4L may be selected. The thickness of the substrate material between two adjacent discrete microstructures is may a value between 0.5l to 3l, optimized by considering the relative thermal conductivity and mass density of the materials of the substrate and the discrete microstructures, and the x-ray linear attenuation length of the substrate at the x-ray energy of interest, and the desired convergence angle ψ. The selection of the materials of the linear accumulation source target used in some embodiments is such that the substrate (the first material) is of low Z material with high thermal conductivity, such as diamond or beryllium, and the material of the sub-sources (the second material) are selected for x-ray generating properties such as spectral characteristics and x-ray production efficiency and may include (but are not limited to) copper, molybdenum, and tungsten. In some embodiments, the thermal conductivity of the targets is mainly determined by the thermal conductivity of the substrate material, which allows the use of x-ray generating materials with lower thermal conductivity otherwise not suitable as x-ray target materials in a contiguous single material target employed in prior art, such as germanium and lead, consequently allow more choice of elements to produce characteristic x-ray lines. In one embodiment of the linear accumulation x-ray source of the present invention, the incident electron beam uniformly illuminates the area of the substrate containing the discrete microstructures (as shown in FIG. 4). Because electron energy deposition rate in a material is proportional to the mass density, the ratio of the energy deposited in the substrate between two adjacent discrete microstructures and the discrete microstructures is approximately equal to the ratio of the their mass relative mass density. In some embodiments of the invention, the incident electron beam is spatially modulated so that a large fraction of the electron beam is incident on the discrete microstructures. This makes efficient use of the incident electron energy for x-ray production and reduces the electron energy deposition in the substrate and improves thermal dissipation of the discrete microstructures. Because each of the discrete microstructures has five faces transferring heat into the substrate, increasing the heat transfer away from the discrete microstructures 2701-2706 and into the substrate. As illustrated, the separation between the sub-bars is a distance d≈l, although larger or smaller dimensions may also be used, as discussed above. The distance between the edge of the shelf and the edge of the x-ray generating material p as illustrated is p≈W, but may be selected to be any value, from flush with the edge 2003 (p=0) to as much as 5 mm, depending on the x-ray reabsorption properties of the substrate material for the x-ray energy of interest, the relative thermal properties of the materials of the substrate and the discrete microstructures, and the amount of heat expected to be generated when bombarded with electrons. For example, in some embodiments it may be generally preferred that the x-ray transmission through the edge of the shelf and the edge of the x-ray generating material p as illustrated is greater than 50%. X-rays that are generated are collected from the side of the anode, most preferably at near-zero take-off angles. Although the microstructures shown in FIG. 4 are of rectangular prisms of equal size, other any number of shapes and sizes can be used to achieve high x-ray source brightness using the linear accumulation design principle from plural of sub-sources and the use of the discrete microstructures embedded or buried in a substrate to improve the thermal dissipation property of the x-ray generating material of each sub-source, such as cubes, rectangular blocks, regular prisms, right rectangular prisms, trapezoidal prisms, spheres, ovoids, barrel shaped objects, cylinders, triangular prisms, pyramids, tetrahedra, or other particularly designed shapes, including those with surface textures or structures that enhance surface area, to best generate x-rays of high brightness and that also efficiently disperse heat. Furthermore, the x-ray generating material in each of the sub-sources may not be of single uniform material but comprise additional finer structures of x-ray generating material. FIG. 5 schematically illustrates a portion of an embodiment of the present invention comprising a single microstructure 2700 instead of the discrete microstructures of FIG. 4. In this illustration, the width W and depth D into the substrate of the microstructure 2700 are the same as in FIG. 4, while the accumulated length L of the microstructure 2700 is equal to 6l. In other words, the volume of the x-ray generating material in FIGS. 4 and 5 are the same, and similar volume of x-rays may be produced by similar excitation by an electron beam 111. Similar design considerations on D, W, L, and p for FIG. 4 apply here. In FIG. 6, a variation of the source target used in some embodiments is shown in which a two-dimensional array of microstructures is embedded in a substrate, and works in a similar principle to the one-dimensional array of microstructures described in FIG. 4. Each of the microstructures 700-R acts as a sub-source of x-rays when bombarded by an electron beam 111. The combination of the high thermal conductivity of the substrate and the small dimension of the discrete microstructures allows heat to be efficiently drawn out of the x-ray generating material, in turn allows bombardment of the discrete microstructures with higher electron density and/or higher energy electrons, which leads to greater x-ray brightness and flux. It should also be noted here that, when the word “discrete microstructure” is used herein, it is specifically referring to microstructures comprising x-ray generating material. Likewise, it should be noted that, although the word “discrete microstructure” is used, x-ray generating structures with dimensions smaller than 1 micron, or even as small as nano-scale dimensions (i.e. greater than 10 nm) may also be described by the word “discrete microstructures” as used herein as long as the properties are consistent with the geometric factors for sub-source size and pitches set forth in the various embodiments. It should also be noted that here that, when the word “sub-source” is used it may refer to a single discrete microstructure of x-ray generating material, or an ensemble of smaller microstructures of x-ray generating materials, illuminated by a single electron beam. The x-ray generating material used in the target should have good thermal properties, such as a high melting point and high thermal conductivity, in order to allow higher electron power loading on the source to increase x-ray production. The x-ray generating material should additionally be selected for good x-ray production properties, which includes x-ray production efficiency (proportional to its atomic number) and in some cases, it may be desirable to produce a specific spectra of interest, such as a characteristic x-ray spectral line. For example, targets are often fabricated using tungsten, with an atomic number Z=74, due to its efficient x-ray production and its high thermal conductivity. Additionally, in FIG. 6, the target 1100-R comprises a substrate 1000-R with a recessed shelf 1002-R. This allows the region 1001-R comprising an array of microstructures 700-R to be positioned flush with, or close to, a recessed edge 1003-R of the substrate, and emit x-rays at or near zero angle without being reabsorbed by the substrate 1000-R, yet provides a more symmetric heat sink for the heat generated when exposed to electrons 111. The two-dimensional array enables a line source when viewed at a zero degree take-off angle. FIG. 7 schematically illustrates a portion of an embodiment of the linear accumulation x-ray source employed in various x-ray source embodiments of the present invention that comprises two sub-sources with targets sharing a common substrate 2230. The substrate may be a first material of low atomic number, low mass density, high thermal conductivity and high melting point, aligned to increase linear accumulation of x-rays along an axis 3001 connecting the two sub-sources. In this embodiment, the source will have two electron beams 1231 and 1232 that are controlled to bombard the respective x-ray generating materials 2231 and 2232 coated on the common substrate 2230 and generate x-rays 831 and 832, respectively. The x-ray generating materials are sufficiently thick for efficient generation of x-rays of desired spectra but sufficiently thin for high transmission of the desired x-rays. The underlying principle is that the electron penetration depth is typically much smaller than the x-ray linear attenuation length, especially for higher energy x-rays. The thickness of the x-ray generating materials 2231 and 2232 is typically selected to be less than or comparable to the depth of the incident electron beam penetrating into the x-ray generating materials 2231 and 2232, a larger value may be used. If the bombardment occurs at an angle to the surface normal, as illustrated, the angle of incidence can also affect the selection of the coating thickness. Although the tilt of the targets 2203 and 2204 relative to the electron beams 1231, 1232 and 1222 is shown as ˜45°, any angle from 0° to 90° that allows x-rays to be generated may be used. The material of the common substrate 2230 is typically selected from a material of low Z material with high thermal conductivity, such as diamond, diamond like material, and beryllium, and silicon carbide. The thickness of the common substrate is selected to have high x-ray transmission for the x-ray energy of interest, often greater than 50%. The distance between the two sub-sources is generally greater than the incident electron beam size. It is possible that one or more of the anodes of the sub-sources has a very thin substrate or even zero thickness in the impact region of the electron beam(s). It is typical that the anodes (with or without the substrate) of the sub-sources are supported on a support frame with an opening reasonably larger than the incident electron beam or x-ray source size. The support frame will typically have high thermal conductivity and may be cooled using techniques well known to those skilled in the art. In some embodiments, the frame will be cooled to a temperature of minus 90 centigrade when the substrate or the frame is made of diamond to make use of the increased thermal conductivity of diamond with decreasing temperature. Though the x-ray sub-sources 2231 and 2232 in FIG. 7 are shown as extended targets comprising a layer of single material, in other embodiments at least one of the single material layer target may be replaced with a region comprising a plurality of discrete microstructures of x-ray generating materials embedded or buried in the common substrate 2230, such as those illustrated in FIG. 8. In this figure, each of the discrete microstructures in the sets of microstructures 2151 and 2152 acts a sub-source x-ray source when illuminated by an electron beam. When aligned with each other along axes 3002-3005, these also produce a higher brightness x-ray beam with an extended beam profile that operates on the same principle the source as illustrated in FIG. 7. FIG. 9 schematically illustrates yet another embodiment of the linear accumulation x-ray source employed in various embodiments of the present invention that comprises a plurality of sub-sources 2801, 2802, and 2803 with x-ray targets fabricated on at least two separate substrates, aligned along a predetermined axis. At least one x-ray imaging optic (2821 or 2831) that collects and image x-rays from one sub-source, for example, 2886, to another sub-source on, for example, 2885, on a different substrate so that x-rays from the two sub-sources appear to originate from a single sub-source viewed along the axis, achieving linear accumulation of x-rays from the two sub-sources to achieve high brightness. Each of the sub-sources comprises a corresponding electron beam (1181, 1182, 1183, 1184, 1185, and 1186) and an x-ray target containing an x-ray generating material. The x-ray target may be a layer of the x-ray generating material deposited on its respective substrate, as illustrated, or comprise plural of the discrete microstructures fabricated in close thermal contact with (such as embedded in or buried in) with its respective substrate, as was illustrated in FIG. 8. To preserve the brightness of the sub-sources, the x-ray imaging optic that collects the generated x-rays is may have a point spread function less than the effective source size of the two sub-sources, the smaller one if two sub-sources have different source sizes. The focusing efficiency of the x-ray imaging optic 2831 and/or 2831 is may be designed to be greater than 50%. Variations of the optics 2831 and/or 2831 may include focusing optics illustrated in FIGS. 12, 13, and 14. Characteristics of the substrate may be similar to those presented in FIG. 7. The anode targets shown in FIGS. 1A through 9 may be cooled using methods known in the art, such as water cooling, thermoelectric cooling, and/or heat pipes, which may also be employed to increase the thermal performance of the anode and thus the brightness of the x-ray source. A second objective of the invention is to enable x-ray sources that produce sufficiently bright characteristic x-rays of desired spectra from element(s) whose materials are of poor thermal property, including low thermal conductivity, low melting point, or both. In one example, the element is titanium (Ti) and the material is a Ti metal or a Ti compound, whose Kα x-rays have significantly larger fluorescence cross sections for many biologically important elements including phosphorus, sulfur, chlorine, selenium, and low Z elements like oxygen, nitrogen, and fluorine, than those at 8 keV or higher energy x-rays. Despite the need for characteristic x-rays of several of these elements in TXRF applications (to increase fluorescence of particular element(s), or to suppress background signal from x-ray scattering and fluorescence from the other element(s) within the specimen or material of the substrate), many elements like Ti have largely excluded them from use in conventional x-ray sources because of inferior thermal property. The structured anode design overcomes this limitation. Any number of prior art techniques for generating electron beam may be used for the embodiments of the linear accumulation x-ray source disclosed herein. Additional known techniques used for electron beam generation include heating for thermionic emission, Schottky emission (a combination of heating and field emission), emitters comprising nanostructures such as carbon nanotubes), and by use of ferroelectric materials. [For more on electron emission options for electron beam generation, see Shigehiko Yamamoto, “Fundamental physics of vacuum electron sources”, Reports on Progress in Physics vol. 69, pp. 181-232 (2006)]. It is preferred that the size of the electron beam is optimized according to the x-ray source size desired. Some embodiments use x-ray generating material (the second material) comprised of predetermined characteristic spectral lines to enable optimal fluorescent x-ray generation for a group of elements of interest or to suppress characteristic fluorescence x-rays from a major matrix element in the specimen to reduce signal background in TXRF, or optimize scattering cross in GISAXS, or optimize refractive index contrast between layers in XRR. In some embodiments of the invention, there may also be one or more electron optical systems that, in addition to providing electron beam(s) with predetermined property (electron energy, current, and focal spot size), can control and direct the respective electron beams to its desired position on the respective x-ray target to incident on the respective x-ray generating material and/or align the sub-sources along a predetermined direction. X-Ray Optical Train. Various embodiments of the x-ray surface analysis and measurement apparatus comprise an x-ray optical train to collect a portion of x-rays from the linear accumulation x-ray source, subsequently spectrally filter, collimate or focus the x-rays to produce an x-ray beam to be incident on the specimen to be analyzed, depending on the desired performance of the x-ray surface analysis and measurement system in terms of desired measurement parameters, such as spatial resolution, throughput, and element analysis sensitivity and accuracy. It should be noted that in the variations of optical trains illustrated as cross-sections in the following figures that the optics may be axially symmetric and also have either an absorbing beam stop, slit, or aperture that absorbs X-rays that are not reflected. In some embodiments, the optics may furthermore be nested (concentric within each other) to allow greater collection of x-rays, as is typical with the non-axial symmetric mirrors used commonly in x-ray astronomy. Optical trains such as those that may be used in embodiments of the invention disclosed herein have been described in detail in the co-pending US Patent Application entitled X-RAY ILLUMINATORS WITH HIGH FLUX AND HIGH FLUX DENSITY (U.S. patent application Ser. No. 14/544,191, filed Dec. 5, 2014), which is hereby incorporated by reference in its entirety, along with the provisional Applications to which it claims benefit. To improve the numerical aperture of the optical elements of the optical train, some embodiments of the invention may use coatings on the reflective surface. These coatings are preferably high density materials (greater than 2.5 g/cm3) such as platinum, iridium, or gold and are typically around a few angstroms to a few nanometers in thickness. Such high density coatings provide a larger critical angle for reflection, enabling the collection of more x-rays. Alternatively, multilayer coatings that reflect x-rays using alternating periodic layers of two or more materials that provide constructive interference in reflection for certain wavelengths may be used. The reflection efficiency depends on the wavelength and angle of incidence of the x-rays, as well as the thickness of the alternating layers, so this has limited use as a broadband reflector, but may be used if specific wavelengths are desired. Combinations that may be used for multilayer reflectors may be tungsten/carbon (W/C), tungsten/tungsten silicide (W/WSi2), molybdenum/silicon (Mo/Si), nickel/carbon (Ni/C), chromium/scandium (Cr/Sc), and lanthanum/boron carbide (La/B4C), and tantalum/silicon (Ta/Si), among others. The surface may also be a compound coating comprising an alloy or mixture of several materials. In some embodiments, the optics may furthermore be nested (concentric within each other) to allow greater collection of x-rays, as is typical with the non-axial symmetric mirrors used commonly in x-ray astronomy. FIGS. 10 and 11 schematically illustrate variations of optical train components to produce a collimated high brightness x-ray beam. FIG. 10 illustrates a cross-section of an x-ray mirror 3020 of which the interior reflecting surface is of portion of a paraboloid 3010. It is configured that its focus 3050 will be positioned with the center of the linear accumulation x-ray source and its axis is aligned along the axis of the linear accumulation x-ray source, such as was illustrated by the axis 3000 in FIG. 4. The x-ray mirror 3020 collects x-rays from the source and generates a collimated x-ray beam. As the source will not be a perfect point source, the angular convergence of the collimated beam is approximately equal to the apparent linear accumulation x-ray source divided by the distance between the source and the entrance of the x-ray mirror 3020. In some embodiments, the angular convergence of the collimated beam in the scattering plane to be smaller than the critical angle for total reflection of the specimen. Otherwise, additional slit(s) may be used in the optical train to obtain the desired angular collimation in the scattering plane. The surface profile of the x-ray mirror may be designed such that the x-rays with the desired x-ray energy incident on the x-ray mirror surface at a grazing angle smaller than or equal to the critical angle for total reflection of the mirror surface material at the desired x-ray energy. The mirror surface material may be glass, or coated either with a high mass density material to increase the critical angle for total reflection to collect more x-rays from the linear accumulation x-ray source. The mirror surface may also be coated with a multilayer of appropriate material composition, d-spacing gradient, and appropriate d-spacing gradient along the optical axis, to increase solid angle of x-ray collection from the linear accumulation x-ray source and obtain an x-ray beam with narrow spectra. FIG. 11 schematically illustrates a cross-section of another optical train that may be used in embodiments of the presentation invention to produce a collimated high brightness x-ray beam. The optical train in this example comprises a type I Wolter mirror optic having an ellipsoid and a hyperboloid, both aligned so one of the foci of the ellipse Fe1 corresponds to one of the foci of the hyperbola Fh1. The type I Wolter mirror is typically configured such that the focus Fh1 will be positioned at the center of the linear accumulation x-ray source and its optical axis is aligned to correspond to the axis of the linear accumulation x-ray source, such as was illustrated by the axis 3000 in FIG. 4. Similar to the parabolic optic of FIG. 10, it is preferred that the angular convergence of the collimated beam in the scattering plane is smaller than the critical angle of the specimen. The slopes and surface profiles of the x-ray optics are designed such that the x-rays with the desired x-ray energy are incident on the x-ray mirror surface at a grazing angles that are smaller than or equal to the critical angle of the mirror surface material for total at the desired x-ray energy. The surface material of one or both mirror components may be glass, or coated either with a high mass density material to increase the critical angle for total reflection, which is proportional to the square root of the density of the material. The mirror surface may also be coated with a multilayer of appropriate material composition, d-spacing gradient, and appropriate d-spacing gradient along the optical axis, to increase solid angle of x-ray collection from the linear accumulation x-ray source and obtain an x-ray beam with narrow spectra. Compared with the single paraboloid mirror illustrated in FIG. 10, the type I Wolter mirror illustrated in FIG. 11 can have up to 4× the solid angle of collection of x-rays from the linear accumulation x-ray source, resulting in a collimated x-ray beam with a larger x-ray flux. The x-ray optical train illustrated in FIGS. 10 and 11 may further comprises a spectral filtering component to narrow the energy spectra of the collimated x-ray known in the prior art, such as a thin foil spectral filter, or multilayer or crystal monochromator. Additionally, it may also compromise aperture(s) or slit(s) to obtain a desired beam shape and size, as will be known by those skilled in the art. In addition to collimating optics, variations of optics for the optical train of embodiments may use focusing optics such as are shown in FIGS. 12, 13, and 14. It should be noted that like the collimating optics, all optical mirror surface materials may be glass, or coated either with a high mass density material. The mirror surface may also be coated with a multilayer of appropriate material composition, d-spacing gradient, and appropriate d-spacing gradient along the optical axis, to increase solid angle of x-ray collection from the linear accumulation x-ray source and obtain an x-ray beam with narrow spectra. FIG. 12 schematically illustrates an embodiment of the presentation invention to produce a high brightness focused x-ray beam for increasing x-ray flux density on the specimen, or for small spot analysis or measurement spatially resolved mapping with TXRF, GIXRD, and/or GISAXS, or for increasing x-ray flux density. The optical train comprises an x-ray mirror 3010 of which the reflecting surface corresponds to a portion of an ellipsoid. It is configured that one of its foci F1 is positioned with the center of the linear accumulation x-ray source and its axis is aligned to the axis of the linear accumulation x-ray source, such as was illustrated by the axis 3000 in FIG. 4). This configuration generates a bright, focused x-ray beam. The surface profiles of the x-ray mirrors are designed such that the x-rays with the desired x-ray energy incident on the x-ray mirror surface at a grazing angle smaller than or equal to the critical angle for total reflection of the mirror surface material at the desired x-ray energy. FIG. 13 schematically illustrates another focusing optic that may be used in the optical train of some embodiments of the invention comprising a first x-ray mirror 3020 of which the reflecting surface corresponds to a portion of a paraboloid. It is configured that one of its focus is positioned with the closest edge of the last of the sub-sources 1700 in the linear accumulation x-ray source 1100 and its axis is aligned to the axis 3008 of the linear accumulation x-ray source 1100. The x-ray mirror 3020 collects x-rays from the source 1100 and generates a collimated x-ray beam 889. A central beam stop 1854 that blocks non-reflected x-rays passing through the center of the x-ray optic 3020 is also shown. A second x-ray mirror 3022, of which the reflecting surface corresponds to a portion of a paraboloid, is aligned with the first x-ray mirror 3020 so that they are symmetric with their axes are aligned, such that the collimated x-rays 889 are focused to produce a focused x-ray beam 887. The surface profiles of the x-ray mirrors are designed such that the x-rays with the desired x-ray energy incident on the x-ray mirror surface at a grazing angle smaller than or equal to the critical angle for total reflection of the mirror surface material at the desired x-ray energy. Compared with the single ellipsoid x-ray mirror illustrated in FIG. 12, the current configuration provides more x-rays collected from the linear accumulation x-ray source, resulting in a focused x-ray beam with a larger x-ray flux. Although FIG. 13 shows a second paraboloidal optical element 3022 of the same size and shape as the initial paraboloidal optical element 3020, these need not be the same dimensions, but may have paraboloid surfaces with different geometric parameters. By selecting appropriate parameters, the x-ray optical train can be designed to demagnify the x-ray source to produce a small focused x-ray beam on to the specimen or magnify the x-ray source to produce a large focused beam on to the specimen. It should be noted that, although only certain embodiments of a linear accumulation x-ray source have been illustrated, other embodiments of linear accumulation x-ray sources can be used as well. FIG. 14 schematically illustrates another embodiment of the presentation invention to produce a high brightness focused x-ray beam. The x-ray optical train comprises two type I Wolter mirrors: the first one comprising an ellipsoidal mirror 3030 and a hyperboloidal mirror 3040, is configured such that its focus is positioned at the center of the linear accumulation x-ray source and its optical axis is aligned the axis 3009 of the linear accumulation x-ray source 1100; and the second one comprising a hyperboloidal mirror 3042 and an ellipsoidal mirror 3032, is aligned such that its optical axis is aligned with that of the first Wolter mirror to receive x-rays reflected by the first Wolter mirror and produce a bright, focused x-ray beam. This configuration allows more x-rays to be collected from the linear accumulation x-ray source, resulting in a focused x-ray beam with a larger x-ray flux. Although FIG. 14 shows two Wolter mirrors of the same size and shape, these need not be the same dimensions, but may have different focal lengths. By selecting appropriate focal length, the x-ray optical train can be designed to demagnify the x-ray source to produce a small focused x-ray beam onto the specimen or magnify the x-ray source to produce a large focused beam on to the specimen. Likewise, although only certain embodiments of a linear accumulation x-ray source have been illustrated, other embodiments of the linear accumulation x-ray sources can be used as well. In many embodiments, the optical train additionally comprises at least one absorbing beam collimator, such as a beam stop, aperture, or slit, used in conjunction with one or more of the optical elements as previously described. These collimators are typically made using materials that are highly absorbing to the bandwidth of x-ray energies of interest. This is to meet the requirements of certain embodiments that the angular convergence of the focused beam in the scattering plane to be less than the critical angle for total reflection for surface sensitivity. FIG. 15A illustrates a cross-section of an optical train taken along the scattering plane, showing a central beam stop 1854 that blocks non-reflected x-rays passing through the center of the optic 3010. Additionally or alternatively, a collimating slit or aperture 1851 may be used to remove the unreflected x-rays. Furthermore, a slit 1850 may be positioned behind the x-ray mirror 3010 and configured to block portion of the x-rays reflected by the x-ray mirror 3010. The slit opening width is selected to obtain a predetermined angular convergence of the focused x-ray beam in the scattering plane, which should be smaller than the critical angle for total reflection for a given experiment. FIG. 15B illustrates a top-down view of the optical train of FIG. 15A in the plane parallel to the specimen surface. FIG. 15C illustrates a cross-section of the exit of the axially symmetric optic 3310, indicating the region 887 where reflected x-rays are uncollimated and regions 1850 at the top and bottom in which the x-ray are collimated. The opening width of the slit or aperture 1850 that determines the region 887 is selected to achieve a predetermined angular convergence angle. In FIG. 15B, the center of the aperture or slit is positioned at the center of the x-ray mirror 3010 and its long opening is aligned to perpendicular to the scattering plane. In some embodiments, the aperture or slit 1850 may not be positioned at the center and may either be or act as a knife edge, as the primary goal of the aperture or slit 1850 is to set an upper limit of the angular incidence of the x-rays. Note that although FIG. 15B illustrates an embodiment using an ellipsoidal mirror, mirrors with any reflecting surface profile may be used in embodiments of the invention. FIG. 16 illustrates a perspective view of an x-ray source 1100 with sub-sources 1700 providing x-rays that are aligned to produce an x-ray beam with linear accumulation, along with a focusing optical train 3100 comprising a first optical component comprising a collimating Wolter type I mirror with mirror surfaces 3030 and 3040, and a second optical element comprising a focusing Wolter type I mirror with a mirror surfaces 3042 and 3043. A beam stop 1854 is placed to remove the non-reflected X-rays. The slit 1850 limits the angle of convergence of the focused beam 887 incident upon the specimen. FIG. 17 schematically illustrate portion of an embodiment of the present invention that may be used to obtain a bright, focused x-ray beam with a narrow energy spectrum, comprising a linear accumulation x-ray source 1100 generating bright x-rays along a predetermined axis, a first paraboloidal x-ray mirror 3026 which is properly positioned and aligned with x-ray source 1100 to collect x-rays from the source 1100 and produce a collimated x-ray beam 889; a central beam stop 1854 that blocks non-reflected x-rays passing through the center of the optic 3026; a double crystal monochromator comprising a first crystal 3054 and second crystal 3056 is configured to monochromatize the incident x-ray beam 889 to obtain a monochromatized x-ray beam 889-2 with predetermined x-ray energy, and a second paraboloidal x-ray mirror 3021 which is configured in reverse orientation with the first paraboloidal x-ray mirror 3026 to receive the monochromatized x-ray beam 889-2 and produce a focused x-ray beam that is incident on the specimen. The crystal monochromator may be of any type known to the art, such as common U-shaped (channel-cut) crystals comprised of silicon (Si) or germanium (Ge) single crystal or parallel semiconductor crystal plates. The double crystal monochromator is rotated to change the incidence angle of the collimated x-ray beam, which enables selection of x-ray energies of interest by changing angle of diffraction. The surface material of one or both mirror components may be glass, or coated either with a high mass density material to increase the critical angle for total reflection to collect more x-rays from the linear accumulation x-ray source. It should be noted that although a second focusing optic is shown, in some embodiments, there is only a single collimating optic and a double crystal monochromator. The monochromatized and collimated beam is then incident upon the specimen without passing through an additional optical element. In various embodiments of the x-ray surface analysis and measurement apparatus, the x-ray optical train may additionally comprise a spectral filter such as a thin foil made from a material containing a large atomic fraction of element with an absorption edge slightly above the predetermined x-ray energy of the x-ray beam, such as a thin nickel (Ni) foil for copper (Cu) Ka characteristic lines. In various preferred embodiments of the presentation invention, the x-ray optical train has a point spread function that is smaller than or comparable to the effective source size of the linear accumulation x-ray source to preserve the source brightness. Alternatively, the x-ray optical train may comprise a doubly curved crystal optic (for example, the Doubly-Bent Focusing Crystal Optic produced by XOS Inc. of Albany, N.Y.). Additionally or alternatively, the x-ray optical train may comprise multiple elements to focus and monochromatize the beam, such as the combination of a coated cylindrical mirror and a double multilayer monochromator [see, for example, Pianetta et al. “Application of synchrotron radiation to TXRF analysis of metal contamination on silicon wafer surfaces” Thin Solid Films vol. 373, pp. 222-226 (2000)]. The x-ray beam after the x-ray optical train impinges upon a specimen 240 (as was illustrated in FIG. 1A) at a grazing angle less than the critical angle of the substrate at the incident x-ray energy. The specimen is optionally placed upon a specimen stage capable of moving in three orthogonal directions (X, Y, and Z) for locating a single analysis and/or measurement point or for mapping over a large area. Preferably, the stage accommodates large flat planar shapes, such as wafers and other reflective media (e.g. quartz glass for liquid specimens to be prepared as a thin film or for microparticles located upon the flat substrate). Optionally, specimen preparation and loading systems known to the art can be added, including robotic or automated specimen loading and transfer systems or vapor phase deposition. In some embodiments, additional or alternative electromechanical systems are implemented to move the source, optical train, and detector either independently or simultaneously. Example applications include analysis of material contamination of semiconductor wafers, elemental composition analysis and thin film thickness measurement during semiconductor device manufacturing processes, such as dielectric materials, copper diffusion barriers, composition analysis and size and size distribution characterization of nanoparticles deposited on a flat surface, trace element detection and analysis in solutions and solid (with digestion and deposition on a flat and smooth surface) in forensics, pharmaceuticals, food, environmental samples, nanoparticles, and biological tissue In various embodiments, the x-ray surface analysis and measurement apparatus is configured to perform XRR, TXRF, GIXRD, GID, and GISAXS, singularly, sequentially, or simultaneously in combination all or a subset of all. The brighter sources and the various embodiments of optical train also described herein, as well as in the other co-pending Applications cited by reference herein, may be combined with any number of these established techniques, including those cited herein, to produce a surface analysis and measurement system that is faster, and with a stronger signal and therefore a better signal/noise ratio, due to the additional flux of x-rays available from a source using linear accumulation. Those skilled in the art will recognize that these combinations of techniques will, along with the source using linear accumulation and an optical train that can collect the x-rays so generated efficiently, will therefore constitute a new system for use in performing XRR, TXRF, GIXRD, GID, and/or GISAXS, singularly, sequentially, or simultaneously in combination all or a subset of all. Various embodiments of the present invention comprises at least one detector to receive x-rays from the specimen in response to the interaction of the incident x-ray beam with the specimen, and produces signals indicative of properties of the specimen. The x-ray signals from the specimen may include diffracted, scattered, and reflected x-rays. In various embodiments, when the x-ray surface analysis and measurement apparatus is configured for TXRF, the x-ray detector 2900 as was shown in FIG. 1A may include one or more of various x-ray detectors known in the art, such as solid state energy dispersive detectors (including lithium drift silicon detector (Si(Li)), silicon drift detector (SSD) and variants, silicon PIN diodes, microcalorimeters, and wavelength dispersive spectrometer comprising a wavelength dispersive component based on Bragg reflection in combination with any detector capable of detecting x-rays. For low energy x-ray detection, a detector with a highly transmissive window or a windowless detector for low energy x-rays is preferred. Qualitative/quantitative analysis is performed based on the intensity of the x-rays measured by the spectrometer, specimen preparation, and parameters of the incident x-ray beam. Data acquisition procedures known to the art are used including aligning the specimen relative to the incident x-ray beam in position and angle. Data analysis methods known to the art including absolute and relative quantification are used. For example, qualitative/quantitative analysis is performed based on the intensity of the x-rays measured by the spectrometer, specimen preparation, and parameters of the incident x-ray beam. Many analysis examples and specimen preparation techniques have been well established and published, including the qualitative/quantitative analysis of a specimen placed on a wafer surface. In some preferred embodiments, the signal obtained is then analyzed by established techniques or software packages similar to common XRF and TXRF analysis packages, such as WinAxil (Canberra Eurisys Benelux, Zellik, Belgium) or Rigaku TXRF Software (Rigaku Corp., Tokyo, Japan). In various embodiments, when the surface analysis and measurement apparatus is configured for XRR, GIXRD, GID, and/or GISAXS, the x-ray detector 2900-R of FIG. 1A may include one or more position sensitive array detectors known in the art, including line and 2D array detectors. Such examples of position-sensitive detectors include photodiode detectors, scintillator-type and gas-filled array detectors. In some embodiments, the detector includes one or more detector elements of any type that detects x-rays, including proportional and avalanche detectors or energy-dispersive elements. In various embodiments enabling TXRF analysis, use of an x-ray imaging optic between the detector and the specimen to define a small analysis volume. A preferred embodiment is to use an x-ray imaging optic with a small aperture or slit to obtain even smaller analysis volume. Furthermore, by selecting an appropriate E, making use of the wider choice of x-ray energies afforded by the new x-ray source, the cross-section of element(s) of interest is optimized. Additionally or alternatively, the incident x-ray energy can be purposely selected to reduce x-ray fluorescence signal from other element(s) in the specimen and/or the substrate. Alternatively, a thin film spectra filter to obtain a desired x-ray spectra know in the art can also be used. In some embodiments that enable XRR analysis, it is preferred that a double crystal monochromator is added and collimating elements are removed from the optical train such that the incident beam is focused at a large angles of incidence, including ones that are greater than the critical angle. This allows the processor to interpret the signals from a position-sensitive detector corresponding to the intensity and angle of reflection of the monochromatic x-rays sensed to determine, based on well-established methods, various properties of the surface layer(s), including thickness, density, and smoothness. In some embodiments that enable GIXRD analysis, it is preferred that the radiation source and detector array are positioned so that the array senses x-rays that are diffracted from the surface in a vicinity of the Bragg angle of the specimen. A motion assembly system may be employed to move the source, specimen, and detector, singularly or in combination. It is preferred in some embodiments to have a focusing optical train with a monochromator to enable high resolution XRD with the incident x-ray beam exceeding the critical angle of the specimen. In other embodiments, it is preferred that the optical train is collimating and placed at a high angle. In the most preferred embodiments, it is preferred to have a collimating optical train for GIXRD placed at a low grazing incidence angle. In some embodiments that enable GISAXS measurements, the detector is preferably placed within the specimen plane of the surface to enable measurement of scattering as a function of azimuth and the source and optical train are positioned such that the specimen is illuminated with a collimated beam of incident x-rays at low angles. Rotating Anode. While some embodiments of the invention may have a target anode in a fixed and static position relative to the optical train, other embodiments may make use a moving or rotating anode to further dissipate the heat that is generated within the target generating x-rays under electron beam bombardment. Rotating anodes have been applied to x-ray sources for many decades, and various designs may be well known to those skilled in the art. FIG. 18 illustrates an example of a portion of an embodiment of the invention employing a rotating anode. In this embodiment, the optical train 3100 is an optical train as may be used in other embodiments of the invention, for example as presented in the description of FIG. 14. However, the target 1010 in the embodiment as illustrated comprises a core circular cylinder 1019 on a rotating spindle 1033 with an outer coating 1018 of thermally conducting material such as diamond or diamond-like carbon (DLC), and, embedded in this coating/substrate 1018, stripes 2709 of material selected for its x-ray generating properties, (such as tungsten, gold, molybdenum, copper, or others as described above) have been formed. When these x-ray generating stripes 2709 are bombarded by electrons 111, x-rays 888 are generated, and subsequently collected and directed by the optical train 3100. These stripes 2709 may have similar dimensions of depth D into the substrate and “length” L along/parallel to the optical axis of the optical train that are comparable to the dimensions discussed previously for the targets comprising microstructures, such as the microstructures 2701-2706 illustrated in FIG. 4 (e.g. a depth on the order or micrometers, and/or related to the electron penetration depth into the selected x-ray generating material, and “lengths” on a micrometer scale). However, the “width” W of the microstructures stripes 2709 as illustrated in FIG. 18 may be considered to be infinite, or at least as large as the circumference of the cylinder, as the “width” of the structures completely encircles the cylinder. The illustration of FIG. 18 shows only 4 contiguous microstructure “stripes” 2709 for illustration purposes, however any number of “stripes” may be used. Similarly, the “stripes” may actually comprise broken lines, and therefore also comprise microstructures of a finite, predetermined “width”. Likewise, other rotating x-ray target patterns such as a checkerboard structure for the x-ray generating material may also be used. As illustrated, the rotating anode target 1010 comprises a core circular cylinder 1019 of a solid material, preferably one that is lightweight to minimize the energy required to spin the target, and is also thermally conducting, to draw heat away from the coating substrate 1018. Materials such as aluminum or copper may therefore be used. However, this core may also be designed to encompass further means of cooling the target, such as thermoelectric coolers, water cooling channels, heat pipes, or other known means to accelerate heat transfer. Furthermore, although illustrated as a right circular cylinder, other shapes, such as a cone-shaped target, may be used as a structure upon which the x-ray generating material is formed. Rotating target structures comprising topography steps may also be employed. Likewise, although the x-ray generating material as illustrated has the “stripes” 2709 embedded into the coating/substrate 1018, embodiments of the invention in which the x-ray generating material is buried into the coating/substrate 1018, or is deposited on top of the coating/substrate 1018, may also be effective. Embodiments with additional coatings may also be used, such as those in which an additional overcoating of electrically conducting material is employed to provide a path to ground for the electrons, or an additional coating of thermally conducting material to further draw heat away from the x-ray generating material may also be used. Embodiments of the invention using rotating anodes may be used in conjunction with any of the optical trains and x-ray optical elements, such as x-ray filters and monochromators, as described above as well. Limitations and Extensions. With this application, several embodiments of the invention, including the best mode contemplated by the inventors, have been disclosed. It will be recognized that, while specific embodiments may be presented, elements discussed in detail only for some embodiments may also be applied to others. Elements in the co-pending Applications incorporated by reference into this Application, such as, for example, polycapillary optics, may also be incorporated into embodiments of the invention disclosed herein. While specific materials, designs, configurations have been set forth to describe this invention and the preferred embodiments, such descriptions are not intended to be limiting. Modifications and changes may be apparent to those skilled in the art, and it is intended that this invention be limited only by the scope of the appended claims. |
|
claims | 1. A method of treating the surface of a steel package, in order to reduce contamination by radioactive cesium, the method comprising the steps of:a) providing a steel package;b) prior to exposing the package to radioactive cesium, pre-washing the package with a cation-containing pre-wash solution having a pH greater then about 6 and less than about 8, the pre-wash cation being selected from one or more of the group consisting of Na+, Li+, Cs+, Rb+, Ag+, Tl+, K+, and NH4+;c) exposing the package to radioactive cesium; andd) after exposing the package to radioactive cesium, post-washing the package with a cation-containing post-wash solution having a pH greater than about 6 and less than about 8, the post-wash cation being selected from one or more of the group consisting of Na+, Li+, Rb+, Ag+, Tl+, K+, and NH4+;wherein the pre-wash solution comprises a cesium salt selected from the group consisting of cesium sulfate, cesium chloride, cesium nitrate, and cesium acetate. 2. The method of claim 1 wherein the concentration of Cs+ in the pre-wash solution is greater than approximately 0.1 molar. 3. The method of claim 1 wherein the cation in the post-wash solution is selected from the group consisting of K+ and NH4+−. 4. The method of claim 3 wherein the concentration of K+ in the post-wash solution is greater than approximately 0.1 molar. 5. The method of claim 3 wherein the concentration of NH4+ in the post-wash solution is greater than approximately 0.1 molar. 6. The method of claim 1 wherein the cation used in the pre-wash solution is different that the cation used in the post-wash solution. 7. The method of claim 1 wherein the post-wash solution additionally comprises one or more complexing agents selected from the group consisting of ammonium fluorosilicate, oxalic acid, disodium chromotropic acid, glutamic acid, and sodium salicylate. 8. The method of claim 1, wherein the pre-wash solution additionally comprises one or more complexing agents selected from the group consisting of ammonium fluorosilicate, oxalic acid, disodium chromotropic acid, glutamic acid, and sodium salicylate. 9. The method of claim 1, wherein the steel package comprises a spent fuel shipping cask. 10. The method of claim 1, wherein the cation in the post-wash solution is K+. 11. The method of claim 1, wherein the surface of the steel package is contaminated with clay. |
|
053496183 | description | DETAILED DESCRIPTION According to the principles of this invention, a boiling water nuclear reactor, preferably used for the generation of electricity, includes novel fuel rods and novel assemblies of these fuel rods that improve the reactor performance in comparison to conventional BWRs that are in use for electric power generation. In particular, as described more completely below, hydride fuel pellets are included at selected axial and radial positions within the core so as to improve the neutron moderation while increasing the total length of fuel rods in the core. Herein "hydride fuel" refers to a material which includes hydrogen and at least one fissionable material among its constituents. The fissionable material includes at least one of the fissile isotopes uranium-233, uranium-235, plutonium-239 and plutonium-241. The hydride fuel functions simultaneously as a fuel and as a moderator. The location and concentration of the hydride fuel is adjusted within a fuel rod and within a fuel assembly, as described more completely below, to achieve a more uniform power density. When the hydride fuel is substituted for oxide fuel in undermoderated regions of the core, the fuel itself provides additional moderation. Herein, "oxide fuel" refers to the composition of fuel that is made of the oxide of at least one fissionable material, such as uranium and plutonium. In the presently operating BWRs, the oxide fuel is, typically, uranium oxide (UO.sub.2). Neutrons are moderated better in the core regions where the hydride fuel is substituted for the oxide fuel and the multiplication constant increases in these regions. Therefore, more fissions occur so that enhanced power production is achieved in these regions of the core. Consequently, the moderation provided by the hydride fuel in undermoderated regions flattens the power distribution across the core. This more uniform power distribution permits reduction of the use of burnable poisons and of control rods for power shaping, as used in the prior art BWRs, which in turn improves the fuel utilization, the reactor availability, and the reactor safety. Additional improvement in the fuel utilization, reactor availability and reactor safety is obtained by substituting hydride fuel rods for water rods in the interior of the BWR fuel assemblies, thus increasing the overall length of fuel pellets in the assembly without compromising the moderation capability. According to the principles of this invention, the basic geometry of the BWR core including the fuel rods and fuel assemblies is not changed. Rather, the fuel pellets used in the fuel rods and the axial and radial composition of the fuel within a fuel assembly are modified to provide enhanced performance. While axial and radial dimensions are referred to herein with respect to a BWR core, these dimensional references are illustrative only of the principles of this invention and are not intended to limit the invention to the particular dimensions described. More generally, the axial dimension is a dimension in a first direction and the radial dimension is a dimension in a second direction where the second direction is orthogonal to the first direction. In view of this disclosure, those skilled in the art can implement the invention in a wide variety of geometries. In a preferred embodiment, the BWR uranium oxide fuel pellets of the prior art are utilized within the novel fuel rods of this invention along with uranium-zirconium hydride pellets. The uranium oxide is slightly enriched in the fissile isotope uranium-235 (.sup.235 U). However, as is known to those skilled in the art, a mixed uranium-plutonium oxide may also be utilized in place of uranium oxide. As described above, a novel fuel rod of this invention includes hydride fuel pellets which in the preferred embodiment are made of uranium-zirconium hydride (U-ZrH.sub.x). The number of hydrogen atom per zirconium atom in the uranium-zirconium hydride fuel, denoted above by the x subscript, ranges from zero to about two, and is preferably about 1.6 to 1.7. The weight percent (wt %) of the uranium in the uranium-zirconium hydride fuel ranges from about 30 wt % to about 60 wt %, and is preferably about 45 wt % uranium. The uranium used for the uranium-zirconium hydride fuel is low-enriched uranium (LEU). The enrichment of the uranium ranges from about 2% to about 6%. In the preferred embodiment of this invention, all the hydride fuel pellets used in a given BWR core use the same weight percent uranium and the same ratio of hydrogen to zirconium atoms. In other embodiments of this invention, the uranium weight percent and the hydrogen-to-zirconium atom ratio vary with the location of the hydride fuel within the fuel rod, with the location of the fuel rod within the assembly, as well as with the location of the fuel assembly within the core. Such variations provide an optimal match between the hydride fuel, the oxide fuel, and the variation in the void fraction in the coolant. The enrichment of the uranium in the hydride fuel typically varies with the location of the hydride fuel in the core. The number of enrichment levels used within one core ranges from one to about ten, and is preferably between 2 and 4. This is similar to the number of enrichment levels of the oxide fuel used in state-of-the-art BWRs. The selection of the optimal location for placement of hydride fuel pellets within the core, of the hydrogen-to-zirconium atom ratio, of the weight percent uranium, and of the uranium enrichment for each hydride fuel pellet can be determined by those skilled in the art by using state-of-the-art computer codes for core design and optimization. (Herein, state-of-the-art computer codes refers to those codes in common use by nuclear engineers for design of the prior art BWR fuel described above.) Accordingly, the following examples are illustrative of the principles of this invention, but the examples are not intended to limit the invention to the specific embodiments disclosed herein. In a first embodiment, a first plurality of fuel rods in a fuel assembly includes both oxide and hydride fuel pellets and a second plurality of fuel rods in the fuel assembly include only hydride fuel pellets. For example, BWR fuel assembly 300 (FIG. 3A) includes a total of 81 fuel rods in a 9.times.9 array. Seventy-two of fuel rods 328, the first plurality, contain both oxide fuel pellets and hydride fuel pellets (mixed hydride-oxide fuel rods) while nine of fuel rods 330, the second plurality, contain only hydride fuel pellets (all-hydride fuel rods). All-hydride fuel rods 330 are arranged within a 3.times.3 array in which a mixed hydride-oxide rod 328 is used to separate all-hydride rods 330. FIG. 3B is another conceptual view of fuel assembly 300. Fuel assembly 300 contains 81 fuel rods in channel 326. The coolant, i.e., water, enters at bottom 320 of channel 326 and flows through space 332 between the fuel rods in axial direction 340 and exits at top 310. As the water flows up through fuel assembly 300, the water is heated and begins to boil at about the location shown by dotted line 350. The steam volume fraction, i.e., the void fraction increases as the water flows upward of dotted line 350 in axial direction 340 and reaches about seventy percent at top 310. Thus, upper region 346 of fuel assembly 300 contains steam, which for neutron moderation acts like a void. In mixed hydride-oxide rods 328, the oxide fuel pellets are, in this embodiment, located below line 360 and the hydride fuel pellets are located above line 360, where line 360 is between onset of boiling line 350 and assembly top 310. The exact preferred location for line 360 can be determined by those skilled in the art by using the state-of-the-art computer codes for core design and optimization. The void fraction in the vicinity of line 360 ranges between 0% to 70%, and is preferably between about 30% to 50%. Thus, fuel rod 328 has a total fueled length in a first direction. A first fueled length is occupied by the oxide fuel pellets. A second fueled length is occupied by the hydride fuel pellets. The second fueled length is smaller than the portion of the fueled length of fuel rod 328 surrounded by a coolant with a non-zero void fraction, i.e, portion 346 of fuel rod 328 above line 350. The compensation in neutron moderation achieved by using the hydride fuel pellets in the region of the core having a void fraction is described more completely below. There are various possibilities for arranging mixed hydride-oxide fuel rods 328 and all-hydride fuel rods 330 within fuel assembly 326. In 9.times.9 fuel assembly 400A (FIG. 4A) the nine innermost fuel rods are all-hydride fuel rods 330, whereas the rest of the fuel rods are mixed hydride-oxide fuel rods 328. Notice that fuel rods 330 are in the interior of fuel assembly 400A and fuel rods 328 surround fuel rods 330. In 9.times.9 fuel assembly 400B (FIG. 4B), only five fuel rods are all-hydride fuel rods 330, whereas the rest of the fuel rods are mixed hydride-oxide fuel rods 328. The innermost fuel rod is an all-hydride fuel rod 330 and in the eight rods surrounding the innermost fuel rod that form a square, the corner fuel rods of the square are also all-hydride fuel rods 330. Notice again that fuel rods 330 are in the interior of fuel assembly 400B and fuel rods 328 surround fuel rods 330. In 8.times.8 BWR fuel assembly 400C (FIG. 4C), eight of the fuel rods are all-hydride fuel rods 330 and the rest of the fuel rods are mixed hydride-oxide fuel rods 328. In a second embodiment, a first plurality of fuel rods in a fuel assembly are mixed hydride-oxide fuel rods, a second plurality of fuel rods in the fuel assembly are all-hydride fuel rods, and a third plurality of fuel rods in the fuel assembly are all-oxide fuel rods. For example, BWR fuel assembly 500 (FIG. 5) includes a total of 81 fuel rods in a 9.times.9 array. Fifty-two fuel rods 328, the first plurality, contain both oxide and hydride fuel pellets (mixed hydride-oxide fuel rods) while nine fuel rods 330, the second plurality, contain only hydride fuel pellets (all-hydride fuel rods). Twenty fuel rods 574 contain only oxide fuel pellets (all-oxide fuel rods). All-hydride fuel rods 330 are arranged within a 3.times.3 array in which a mixed hydride-oxide fuel rod 328 is used to separate all-hydride fuel rods 330. Many other embodiments are possible using the novel fuel rods of this invention. One embodiment uses all-hydride fuel rods located at the inner region of the fuel assembly with the rest of the fuel rods being all-oxide fuel rods. Such fuel assemblies are identical to those illustrated in FIGS. 4A, 4B, 4C, and 5 except that mixed hydride-oxide fuel rods 328 are replaced by all-oxide fuel rods 574. Another embodiment uses mixed hydride-oxide fuel rods 328 throughout the assembly. Yet another embodiment uses only mixed hydride-oxide fuel rods 328 and all-oxide fuel rods 574. In this embodiment, the hydride-oxide fuel rods are preferably surrounded by the all-oxide fuel rods. Of course, any of the fuel assemblies of this invention may contain one or more water rods or rods containing solid moderators, as proposed for BWRs which do not use hydride fuel. Also, the all-hydride and mixed hydride-oxide fuel rods may contain burnable poisons, such as the burnable poisons used in state-of-the-art BWRs. As is known to those skilled in the art, the onset of boiling in a BWR fuel assembly and the volume fraction occupied by voids at different locations along the assembly first direction vary with the reactor power level, coolant flow rate, coolant inlet temperature, control-rods position, location of burnable poisons, level of fuel burnup, as well as other core design and operating conditions. Typically, multi-dimensional coupled neutronic and thermal hydraulic computer codes are used to determine the optimal composition of a particular fuel rod in a particular fuel assembly during a particular cycle of the reactor. In this embodiment, the fuel rod contains hydride fuel from or above the point of onset of boiling for that particular fuel rod to the top of the fueled region of the fuel rod, and typically from a point where the void fraction is in the range of 30% to 50% to the top of the fueled region. Alternatively, as described above, the entire fuel rod may contain only hydride fuel. Thus, the hydride fuel may occupy from zero to one hundred percent of the fueled length in a fuel rod. An important aspect of the invention is that, unlike prior art designs that traded moderation for fuel volume, the fuel rods of this invention provide improved moderation in regions of the core that are undermoderated and simultaneously maintain the fuel volume. Several alternative embodiments for the axial distribution of the oxide fuel and hydride fuel within a fuel rod are illustrated in FIGS. 6A through 6G. Fuel rod 574 (FIG. 6A) contains only oxide fuel 636 while fuel rod 330 (FIG. 6F) contains only hydride fuel 634. Fuel rods 328A (FIG. 6B), 328B (FIG. 6C), 328C (FIG. 6D) and 328D (FIG. 6E) contain differing amounts of oxide fuel 636 and hydride fuel 634. The point of transition from oxide fuel 636 to hydride fuel 634 is determined for each BWR design and operating plan using coupled neutronic and thermal-hydraulic computer codes in use by those skilled in the art of BWR core design. Note that FIGS. 6A to 6G refer to the fueled region of the fuel rods. As is known to those skilled in the art, a fuel rod includes a plenum above the fuel pellets, and end caps. Fuel rod 328D (FIG. 6E) is referred to as a "predominantly-hydride fuel rod". Fuel rod 328D may be substituted in fuel assembly locations otherwise occupied by all-hydride fuel rods 330 (FIG. 6F). Oxide fuel pellets 636 are used at the lower part of the fuel rod where the neutron density and, therefore, power density tend to decline due to neutron leakage from the bottom of the core. The use of oxide fuel pellets 636 instead of hydride fuel pellets 634 in this relatively low neutron density lower core region will increase the power generated in this region relative to the power generated in the same region when using all-hydride fuel rods. In predominantly-hydride fuel rod 328D, the hydride fuel occupies at least the upper two thirds of the fueled length of the fuel rod. In a typical embodiment, the oxide fuel in fuel rod 328D is confined to the lower one eighth to one sixth of the rod where the neutron density is lower than in the upper core regions and where the steam volume fraction is negligible. Fuel rod 328E (FIG. 6G) is another embodiment of mixed hydride-oxide fuel rod. It uses oxide pellets 636 at its far top, in addition to oxide pellets 636 at its lower part. Typically, the volume of oxide pellets 636 at the top of fuel rod 328E is small, so that the use of oxide fuel at this highly voided core region will not significantly reduce the average multiplication constant of the upper part of the core. Solid moderator can be placed in the reflector right above the upper oxide fuel pellets to compensate for the lack of hydrogen in the oxide fuel. The purpose of placing the oxide fuel at the top is to increase the power density in the upper core region where the neutron density declines due to leakage. The fuel in all the fuel rods of this invention is contained within a cladding 638 (FIGS. 6A to 6G) made of, for example, the zirconium alloy "zircaloy". The mechanical design of the fuel rods for the innovative mixed hydride-oxide fuel rods 328 and all-hydride fuel rods 330 and the fuel assemblies containing these fuel rods are similar to the mechanical design of the all-oxide fuel rods and fuel assemblies used for typical prior art BWRs. Examples of such typical nuclear fuel assemblies were depicted and described in the above-identified patents of Venier et al., Lass, and Fritz et al. The fuel rods of this invention differ from the typical BWR fuel rods in their fuel composition and their cladding design. In any of the fuel rods of this invention containing a hydride fuel, gaseous hydrogen fills the small gap between the pellets and the fuel rod cladding, as well as the volume of the plenum above the pellets. The free hydrogen gas may hydrogenize the cladding material, or diffuse out through it. Hydrogenization of the cladding material may impair its mechanical integrity and is preferably prevented. If hydrogen gas permeates through the cladding, the hydrogen gas pressure inside the cladding drops, and part of the hydrogen dissociates from the hydride fuel pellets and become free hydrogen. Thus, if the hydrogen permeation rate is large, the dissociation of the hydride fuel may impair its neutron moderation ability. To avoid impairment of the mechanical integrity of the fuel rod cladding and lose of an unacceptably large fraction of the hydrogen of the hydride fuel, the hydride fuel pellets are surrounded by a sealed hydrogen permeation barrier. Several different embodiments are available for designing this hydrogen permeation barrier. In the preferred embodiment, the hydrogen permeation barrier design is the design proposed by Weitzberg for zirconium hydride moderator containing fuel rods in his above identified patent. FIGS. 7A, 7B, 7C, 7D and 7E illustrate a partial elevation view cross-section of fuel rods for a number of embodiments. In the embodiment illustrated in FIG. 7A, oxide fuel pellets 736, which are indicated by the capital letter "O", fill the lower part of fuel rod 328 while hydride fuel pellets 734, which are indicated by the capital letter "H", fill the upper part of fuel rod 328. There is no barrier between oxide fuel pellets 736 and hydride fuel pellets 734. Between fuel rod cladding 738 and pellets 734, 736 there is a barrier 744 to inhibit the permeation of hydrogen through cladding 738 to the water which surrounds this cladding. Barrier 744 is either a coating on internal side 738A of cladding 738 or a cylindrical sleeve with an inner surface adjacent pellets 734, 736 and an outer surface adjacent internal side 738A of cladding 738. The coating or sleeve is made of a material having (i) no hydrogenization, (ii) a high resistance to hydrogen permeation, and (iii) preferably a relatively low probability for neutron absorption. As used herein, "a high resistance to hydrogen permeation" is a resistance that prevents the loss of more than 50% and, preferably, of more than 10% of the hydrogen content of the hydride pellets during the residence time of these pellets in the core. Also as used herein, "a relatively low probability for neutron absorption" is measured relative to the probability for a neutron absorption in the fuel. As is known to those skilled in the art, the fission neutrons are preferably moderated and absorbed in the fuel. Different materials and material thicknesses are possible for hydrogen permeation barrier 744. One preferred embodiment is a layer of stainless steel, typically 0.05 to 0.1 mm in thickness. Such a barrier is proposed by Gylfe in his above-identified patent. Preferably, the stainless steel is oxidized to further improve its hydrogen retention capability. In another embodiment, hydrogen permeation barrier 744 is an oxidation layer on internal side 738A of zircaloy cladding 738. In still another embodiment, internal side 738A of zircaloy cladding 738 is a glass-enamel coating, as suggested in the above-identified Weitzberg patent. According to Weitzberg, glass-enamel coating metal cladding, about 0.08 mm thick, has been successfully utilized in SNAP reactors at temperatures up to 700.degree. C. Of course, cladding 738 may be made from a material, such as stainless steel, Which does not interact with hydrogen and which has a high resistance to hydrogen permeation. Such a cladding is used in TRIGA reactors. Although the simplest to implement, the latter approach is the most wasteful on neutrons, as the stainless steel has a higher neutron absorption probability than zirconium. In the embodiment illustrated in FIG. 7B, oxide fuel pellets 736 again fill the lower part of the fuel rod while hydride fuel pellets 734 are in the upper part. Hydrogen permeation cladding barrier 742 is a special material layer which encloses, i.e., clads, all hydride pellets 734 and is contained within fuel rod cladding 738. Hydrogen permeation barrier cladding 742 for hydride fuel pellets 734 extends, in one embodiment, above the upper most hydride fuel pellet to provide a plenum for accumulating gaseous fission products that are emitted from hydride fuel pellets 734. Hydrogen permeation barrier cladding 742 is one of stainless steel, a glass-enamel coated metal cladding, and any other material having high resistance to hydrogen permeation and low neutron absorption probability. In the embodiment of FIG. 7C, oxide fuel pellets 736 and hydride fuel pellets 734 are oriented as described above in the two previous embodiments. Each hydride fuel pellet 734 is surrounded by a hydrogen permeation barrier 746 in the form of a cladding or coating and the cladded (coated) hydride fuel pellet is contained within fuel rod cladding 738. In the embodiment of FIG. 7D, there is not a single boundary between hydride fuel pellets 734 and oxide fuel pellets 736. The transition from the completely oxide fuel region to completely hydride fuel region within the fuel rod is done gradually. Hydrogen permeation barrier 744, as described above for FIG. 7A, is utilized and that description is incorporated herein by reference. Alternatively, each hydride fuel pellet 734 is individually encased as illustrated in FIG. 7C. Of course, another alternative is to individually encase each hydride fuel pellet 734 in any transition regions, and each group of hydride fuel pellets 734 in fuel rod 728 are to use hydrogen permeation barrier 742 (FIG. 7B). This embodiment is a combination of embodiments 746 and 742. In fuel rod 330 (FIG. 7E) with all-hydride fuel pellets 734, any one of the embodiments 744, 742 and 746 may be used. In FIG. 7E, hydrogen permeation barrier 744 is illustrated. The density of hydrogen atoms per unit volume of U-ZrH.sub.1.6, the preferred fuel, is approximately 4.7.times.10.sup.22 hydrogen atoms per cubic centimeter of fuel. This is very close to the hydrogen density of 4.8.times.10.sup.22 in liquid water at the BWR operating temperature of about 280.degree. C. As in a typical BWR the volume of fuel in a fuel rod is nearly 62% of the volume of water which surrounds the fuel rod, the hydride fuel significantly increases the hydrogen content in the fuel assembly. Table 1 compares the relative amounts of hydrogen in selected elevations in the fuel assembly, when the preferred hydride fuel is used instead of the regular oxide fuel. The elevations considered feature the steam volume fractions given in Table 1. In the fuel assembly regions in which the void fraction is less than 60%, the use of the hydride fuel increases the hydrogen content to above its value in the reference BWR assembly lower section which does not experience boiling. At the outlet from the fuel assembly, where the void fraction is nearly 70%, the replacement of oxide fuel by the hydride fuel increases the hydrogen content by nearly three fold, bringing the hydrogen content to 90% of its value at the bottom of the reference BWR core. The effect of the improved moderation provided by the hydride fuel on the axial power profile is described more completely below. TABLE 1 ______________________________________ Assembly Hydrogen Content With The Hydride Fuel Void fraction (%) 0 40 50 60 70 ______________________________________ Relative to liquid water 1.6 1.2 1.1 1.0 0.9 Relative to oxide fuel 1.6 2.0 2.2 2.5 3.0 ______________________________________ When the preferred hydride fuel rod is used to replace the water rods or water rod segments within a prior art BWR fuel assembly, the hydrogen density in these rods and rod segments changes insignificantly. Thus, the hydride fuel provides practically the same improvement in moderation as provided by the special water rods, while adding nuclear fuel to these rods. The fuel addition converts these rods and rod segments to power producing, thus making a better utilization of the fuel assembly volume. In the above embodiment, a hydride fuel has been used to offset the problems that result from undermoderation associated with boiling or with uneven moderation resulting from the existence of water-gaps in-between the fuel assemblies in a BWR. The uranium-zirconium hydride fuel is illustrative only of the principles of this invention and is not intended to limit the invention to the particular fuel described. In view of this disclosure those skilled in the art will be able to use a variety of fissile isotopes containing fissionable materials and hydride materials to form a hydride fuel suitable for use in the fuel rod. Other hydride fuel materials include, but are not limited to, uranium and plutonium containing hydrides of thorium, titanium, cerium and yttrium. In another promising embodiment of this invention, the hydride fuel used in undermoderated regions of the core is uranium-thorium hydride (U-ThH.sub.x). The number of hydrogen atoms per thorium atom in this fuel material can range from about one to about three and is preferably about 2. Details about the properties and fabrication of the uranium-thorium hydride fuel U-ThH.sub.x can be found in U.S. Pat. No. 4,493,809 by Simnad (1/85). The uranium-thorium hydride fuel U-ThH.sub.x is incorporated in the BWR fuel rods as pellets, just as the uranium-zirconium hydride fuel U-ZrH.sub.x described above was incorporated. Relative to uranium-zirconium hydride, the uranium-thorium hydride fuel offers a better neutron economy, as the neutrons captured in thorium convert it to the fissile isotope uranium-233. The longer the uranium-thorium hydride fuel is irradiated in the BWR, the higher will be the U-233 concentration and the larger will be the contribution of this U-233 to the chain reaction, or reactivity of the core. So far there is only little experience in the fabrication of uranium-thorium hydride. Little is known also on the behavior of the uranium-thorium hydride fuel in BWR operating conditions. While the advantages of this invention have been demonstrated with respect to BWRs where the problems of undermoderation are most profound, the principles of this invention are applicable to undermoderation in other type of nuclear reactors. For example, in pressurized water reactors (PWRs) hydride fuel rods would replace control rod thimbles in those fuel assemblies which do not house control rods. The power attainable from the fuel assemblies of the present invention can be higher by nearly 10% than the power attainable from conventional PWR fuel assemblies. Alternatively, for the same power output, the PWR fuel assemblies of the present invention can reside longer in the PWR core and generate more energy than conventional PWR fuel assemblies. In above described embodiments of this invention, the hydride fuel pellet is homogenous in the sense that the fissionable material and the hydride are highly mixed. In another embodiment, the hydride fuel pellet is heterogeneous. One illustration of such an heterogenous fuel is a fuel made of zirconium hydride ZrH.sub.x into which small grains of uranium oxide UO.sub.2 are imbedded. A more extreme heterogeneity is illustrated in FIGS. 8 and 9 which show two-zone fuel pellets 850 having a cylindrical hydride inner zone 854 and a uranium oxide outer zone 852. Outer zone 852 is an annulus surrounding inner zone 854. Except for the specifics of the design of pellet 850, fuel rod 828A (FIG. 8) is the same as fuel rod 328 of FIG. 7A. Hydride materials suitable for inner zone 854 of two-zone pellet 850 includes but are not limited to zirconium hydride ZrH.sub.x. The volume fraction of inner hydride zone 854 is adjusted in accordance with the design requirements for fuel rod 828A. Outer region 852 of the two-zone pellet 850 may include any fissionable material. The replacement of the oxide fuel with hydride fuel in the upper part of fuel rods adds a significant amount of hydrogen to the BWR core regions in which the water substantially boils which in turn eliminates or, at least, highly reduces the undermoderation. Moreover, the addition of hydrogen to the otherwise undermoderated core regions is done along with the inclusion of fissile fuel with the solid moderator thus maximizing the weight of fuel and the total length of fuel rods which can be loaded into the BWR core while using BWR fuel assemblies that have a mechanical design similar to that of existing BWRs. Other prior art designs for alleviating the undermoderation compromised fuel volume for increased moderation. The improvement in the performance of a BWR made possible by the present invention is illustrated by considering an infinite array of BWR hydride fuel rods surrounded by water, to be referred to as the hydride fuel lattices, in comparison to an infinite array of BWR oxide fuel rods. The dimensions and composition of the oxide fuel lattices in the array of BWR oxide fuel rods are of a typical BWR design. The fuel pellet outside diameter is 1.0566 cm. The zircaloy cladding inside diameter is 1.0795 cm. The fuel rod outside diameter is 1.2522 cm. The distance between fuel rod centers is 1.6256 cm. The dimensions and composition of the hydride fuel lattices in the array of BWR hydride fuel rods are identical in all respects to the oxide fuel lattices with the exception to the fuel composition, which is U-ZrH.sub.1.6 having 45 wt. % uranium. The barrier to hydrogen permeation in the hydride fuel is taken to be a 0.1 mm layer of zirconium oxide. The oxide fuel has a characteristic beginning-of-life enrichment of 2.07%, whereas the uranium enrichment of the hydride fuel is taken as 2.07% in one embodiment and 3.0% in another embodiment. The characteristics of the three fuel rod lattices as a function of the void fraction in the water moderator surrounding the fuel rods in the lattice were determined using the WIMS lattice code using 69 energy groups of the WIMS cross-section library. The WIMS lattice code and the WIMS cross-section library is available from the Radiation Shielding Information Center of the Oak Ridge National Laboratory having Post Office Box 2008 Oak Ridge, Tenn., 37831-6362. Curve 1076 (FIG. 10) is multiplication constant K for the lattice of hydride fuel rods with 3.0% uranium enrichment. Curve 1080 is multiplication constant K for the lattice of hydride fuel rods with 2.07% uranium enrichment. Curve 1078 is multiplication constant K for the lattice of oxide fuel rods with 2.07% uranium enrichment. The curves in FIG. 10 represent the multiplication constant at different axial elevations in that part of the BWR core where boiling occurs. In the high void fraction regions of the core, the multiplication constant of the hydride fuel lattices, curves 1076 and 1080, exceeds that of the oxide fuel lattice, curve 1078. The higher the void volume fraction, the larger is the reactivity improvement offered by the hydride fuel. The multiplication constant of the hydride fuel lattices vary only slightly with the change in the steam volume fraction in comparison to the variation of the multiplication constant with the void fraction in the oxide fuel lattices. In view of the large amount of zirconium present in the hydride fuel lattices relative to the amount of zirconium in the oxide fuel lattices, it was surprising to find that the multiplication constant of U-ZrH.sub.1.6 fuelled lattices can be comparable and even higher than the multiplication constant of similar UO.sub.2 fueled lattices, when both the oxide and hydride fueled lattices use LEU of the same enrichment. As described above, only MEU and HEU was used so far for uranium-zirconium hydride fuel. This unexpected finding is due to the fact that in the high void fraction lattices, the improvement in the neutron moderation provided by the hydrogen of the hydride fuel more than compensates for the increase in the probability for neutron absorption in the zirconium. Table 2 compares the multiplication constant of a lattice of identical BWR fuel rods with and without hydride fuel. Six lattice compositions are considered for this comparison; they represent the fuel composition and steam volume fraction found in six elevations, or axial locations, in the core. The fuel design is as described in connection with FIG. 10. In a first embodiment, "all-oxide", the array contained uranium oxide fuel UO.sub.2 having an enrichment of 2.07%. In a second embodiment, "mixed hydride-oxide", the uranium oxide in the upper half of the fuel rod is replaced by the hydride fuel (U-ZrH.sub.1.6) in which the uranium is enriched to 3.0%. Table 2 shows that whereas with the all-oxide fuel the multiplication constant strongly declines towards the top of the fuel rod (or core), the use of hydride fuel brings the multiplication constant at the upper part of the core to practically its value at the bottom of the core. The improved moderation and increased reactivity resulting from the substitution of hydride fuel for oxide fuel in the upper region of the core make the axial power distribution more uniform without the use of either burnable poisons or control rods. One benefit of the flatter axial power distribution is an improved fuel utilization. Another benefit of the flatter axial power distribution is a larger safety margin against fuel meltdown in case of accidents. Yet another benefit of the flatter axial power distribution is a higher effectiveness of the BWR control rods TABLE 2 ______________________________________ Axial Distribution of the Multipication Constant With and Without Hydride Fuel Axial core zone (from Bottom) 1/6 2/6 3/6 4/6 5/6 6/6 ______________________________________ All-oxide 1.21 1.18 1.11 1.07 1.04 1.02 Mixed hydride-oxide 1.21 1.18 1.11 1.21 1.20 1.19 ______________________________________ towards the end of the irradiation cycle and, hence, a smaller period of time for scramming the reactor. Moreover, the reactivity swing associated with the transition from full power operation to low or zero power operation is substantially smaller with hydride fuel rather than oxide fuel occupying the high void fraction part of the core, i.e., the most undermoderated region of the core. This behavior is demonstrated by curves 1076 and 1080 of FIG. 10 which show that the void fraction dependence of the hydride fuel lattice multiplication constant is significantly flatter than the corresponding dependence for the oxide fuel lattice, curve 1078 of FIG. 10. The smaller the reactivity swing, the larger the cold shutdown reactivity margin which is a positive safety feature. Another improvement in the BWR economics and safety is derived from the increase in the total length of fuel rods in the BWR core made possible by using hydride fuel in place of the water rods used in the prior art BWR fuel assemblies. (Note: any particular fuel rod is not being increased in length, but as fuel rods substitute for water rods, the total length of fuel pellets in the assembly and, therefore, in the core, is increased.) The increase in the total length of fuel in the core lowers the maximum power density the reactor needs to operate at if the reactor is to deliver a given total power output. One benefit of the increase in the total length and mass of fuel is an increase in the amount of electricity which the BWR can generate in between refuellings. Another benefit of the increase in the total length and mass of fuel in the assembly is an increase in the fuel residence time in the core. The increased fuel residence time in the core increases the reactor operation time between refueling outages thereby increasing the reactor availability and reducing the cost of generating electricity. Yet another benefit of the increase in the total length of fuel in the assembly is lowering of the maximum power density and linear-heat-rate, thus increasing the safety margin against fuel meltdown accidents. Finally another advantage of the present invention is that the leakage of energetic neutrons out of the upper part of the core is reduced relative to the neutron leakage from oxide fuel in the prior art BWR fuel assemblies. The reduced leakage of energetic neutrons increases the core reactivity and reduces the neutron induced damage to structural components located in the vicinity of the core. In another embodiment of the present invention, rather than operating the BWR at a reduced peak power density, the BWR with the novel fuel rods of this invention is operated with the same maximum power density as in the prior art and thereby benefit from the flatter power distribution and larger accumulated fuel rod length by running the hydride fueled core at a higher power level. This may not be achievable in certain of the existing BWRs in which the heat transport and energy conversion system are not capable of accommodating an increase in the power output. However, the design of new BWRs could take full benefit from this feature. That is, the hydride fuel makes it possible to design more compact BWRs than existing BWRs, i.e., the same total power output is obtained from a smaller size core, making the reactor more economical. The maximum linear-heat-rate BWR oxide fuel rods are designed to deliver is, typically, 450 watts per cm. When operating at such a linear-heat-rate, the temperature at the center of the oxide fuel is in the vicinity of 1800.degree. C. The thermal conductivity of the uranium-zirconium hydride fuel, 17.6 watts/m.degree. K., is significantly higher than that of an oxide fuel, which is typically about 2.8 watts/m.degree. K. As a result, if the hydride fuel is to operate at 450 watts per cm, its central temperature will be only about 700.degree. C. Part of the improvements and benefits described above can be achieved by replacing only water rods in the central part of conventional all-oxide BWR fuel assemblies by all-hydride, or predominantly hydride fuel rods. By using hydride rods instead of the water rods, the improved moderation and power flattening across the fuel assembly are achieved without a reduction in the overall length of fuel rods in the assembly. Consequently, the optimal number of all-hydride fuel rods in the BWR fuel assembly that is designed in accordance with the present invention is likely to be larger than the number of water rods in conventional designs of BWR fuel assemblies. Thus, hydride fuel rods can flatten the power density distribution across the BWR fuel assembly better than water rods or than rods containing fuel free solid moderator. The consequences are improved fuel utilization, longer fuel residence time, improved safety or, alternatively, increased power output per assembly. The inclusion of fissionable material with the hydride of the hydride fuel reduces the probability that moderated neutrons will be absorbed in the hydride and in the cladding relative to the absorption probability in fuel assembly designs which have the same hydride moderator but without fissionable material. For example, relative to the zirconium hydride moderator sections proposed in the above-identified Weitzberg patent, the probability of neutron loses through absorption in the zirconium of the solid moderator is reduced by two orders of magnitude. The reduction in the neutron absorption in the zirconium of the solid moderator increases the reactivity of the core and improves the fuel utilization relative to that achievable with solid moderators. Accordingly, the use of hydride fuel in combination with oxide fuel according to the principles of this invention improves the moderation of BWR cores while maximizing the total length of fuel rods in these cores. As a result, BWR cores can be designed to have a flatter power distribution; a smaller amount of burnable poisons; a reduced neutron absorption in control rods; and a reduced leakage of neutrons from the core. The benefits from these improvements in BWR cores include a better fuel utilization; a longer fuel residence time and a larger amount of energy generation between refuelling periods, and, therefore, an increased availability; or a higher total power output from a core of a given size. These advantages improve the economics of generating electricity from BWRs. Additional improvements of the present invention include a larger cold shutdown reactivity margin, a shorter time for scramming the reactor, and a larger safety factor against fuel meltdown accidents. These advantages improve the safety of BWRs. In addition, the reduced leakage of energetic neutrons out of the upper part of the core reduces the damage rate to structural components. Although the description is illustrative of the principles of this invention, the description should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. In view of this disclosure, it will be apparent to those skilled in the art that the hydride fuel can be included in the fuel rod in different combinations with oxide fuel and with segments of water or of solid moderators; the uranium in the hydride and oxide fuel can be of different enrichment; the hydride fuel can be made of thorium hydride rather than of zirconium hydride; the hydride fuel can contain different number of hydrogen atoms per zirconium or thorium atom; the cladding of the fuel rod which contains hydride pellets can be made of a material different than zirconium or its alloy, such as stainless steel, or of stainless steel or glass enamel coated zircaloy; the hydride fuel can be made of small fuel particles imbedded in the solid moderating material; and the fuel rod and fuel assembly can be of different dimensions and different designs. Accordingly, the scope of this invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents. |
description | The first to third embodiments of the present invention will be described below with reference to the several views of the accompanying drawing. First Embodiment The first embodiment of the present invention will be described below with reference to the several views of the accompanying drawing. In the following description, the same reference numerals denote the same functions and parts throughout the drawing, and a repetitive description thereof will be omitted. The schematic arrangement of an X-ray flat panel detector according to the first embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 is a diagram for explaining the schematic arrangement of an X-ray flat panel detector 12 according to the first embodiment. The X-ray flat panel detector 12 comprises X-ray sensor elements 16 for detecting incident X-rays, a gate scanning line driving circuit 18, an integrating amplifier circuit 20, a multiplexer 22, and an A/D converter 24. The X-ray sensor elements 16 have a plurality of photoelectric conversion films (not shown) which are arrayed in a matrix and convert incident X-rays into charge information, pixel electrodes which are arranged in respective pixels and acquire charges from the photoelectric conversion films, a plurality of capacitors in which the charges acquired by the pixel electrodes are accumulated, and switching elements (e.g., TFTs: Thin Film Transistors) which read out the charges accumulated in the capacitors as electrical signals on the basis of a control signal from the gate scanning line driving circuit 18. The plurality of X-ray sensor elements 16 are arrayed in a two-dimensional matrix to form a sensor element array. As will be described later, the X-ray sensor elements 16 are classified into effective pixels, dummy pixels A (to be referred to as xe2x80x9cDAsxe2x80x9d hereinafter), and dummy pixels B (to be referred to as xe2x80x9cDBsxe2x80x9d hereinafter) (see FIG. 2). The gate scanning line driving circuit 18 is electrically connected to the gate terminal of the switching element of each X-ray sensor element 16 via a corresponding gate scanning line 27. The gate scanning line driving circuit 18 supplies a control signal to the gate terminal of each switching element to ON/OFF-control switching elements on each gate scanning line 27. The gate scanning line driving circuit 18 may have a scanning line driving IC which is connected to each scanning line and has a function of supplying a potential to a protective electrode. In FIG. 1, the gate scanning line driving circuit 18 is formed on only one side. Alternatively, the gate scanning line driving circuits 18 may be arranged on two sides via the sensor element array to supply driving signals to the switching elements from the two sides. The integrating amplifier circuit 20 amplifies the electrical signals of pixels on the same column that are read out from the X-ray sensor elements 16 via a corresponding signal line 26 every column at a predetermined timing. The multiplexer 22 sequentially selects signals amplified by the integrating amplifier 20, and sends them to the subsequent A/D converter 24. The A/D converter 24 converts an analog signal input from the multiplexer 22 into a digital signal. In FIG. 1, the integrating amplifier circuit 20 and multiplexer 22 are arranged on only one side. Alternatively, the integrating amplifier circuits 20 and multiplexers 22 may be arranged on two sides via the sensor element array to read out the detection signals of the sensor elements from the two sides. The effective pixel, dummy pixel A (DA), and dummy pixel B (DB) of the X-ray flat panel detector 12 will be explained with reference to FIG. 2. FIG. 2 is a plan view showing pixel areas formed by respective pixels when the X-ray sensor elements 16 are classified into effective pixels, dummy pixels A (DA), and dummy pixels B (DB). Areas where the respective pixels are distributed will be called an effective pixel area, dummy pixel A area, and dummy pixel B area. As described above, pixels which constitute each pixel area are formed from the sensor elements 16. The effective pixels are pixels for detecting incident X-rays. An X-ray diagnostic image is generated based on X-rays detected by these pixels. DAs are pixels arranged above and below the effective pixel area in the column direction (direction parallel to the signal line), as shown in FIG. 2, in order to cancel noise (NA) which flows into the signal line 26 and is superposed on the detection signals of the effective pixels when the gate scanning line driving circuit 18 changes the potential of the scanning line 27. A DA has a structure in which no charge information based on X-rays is accumulated (e.g., a photoelectric conversion film and capacitor are not electrically connected, the surface (X-ray incident side) is covered with a shield, or the like). Charges detected from the DA when TFT is changed from the OFF state to the ON state are only extracted noise (NA). Removal of noise (NA) from the effective pixel by using the DA is executed as follows. That is, in driving the scanning line of the effective pixel, the scanning line of the DA is driven with a phase opposite to that of the scanning line of the effective pixel. Then, noise (NA) with an opposite sign as that of the effective pixel is generated to cancel noise (NA) superposed on the detection signal. DBs are pixels arranged on the right and left sides of the effective pixel area in the row direction (direction parallel to the scanning line), as shown in FIG. 2, in order to remove noise (NB) which is generated by fluctuations in the potential of the scanning line 27 in a steady state and is superposed on the detection signal of the effective pixel. A DB has a structure in which no charge information based on X-rays is accumulated (e.g., a photoelectric conversion film and capacitor are not electrically connected, the surface (X-ray incident side) is covered with a shield, or the like). According to a method of removing noise (NB) by the DB, the output value of the dummy pixel (DB) is subtracted from the output value of the effective pixel on the same gate line after irradiation of X-rays to remove the fluctuation component of the scanning line potential. The dummy pixel (DB) is so designed as to to have the same output value as that in the absence of X-rays incident on the effective pixel. Function of Preventing Dielectric Breakdown Caused by Application of High Electric Field The function of the X-ray flat panel detector 12 for preventing dielectric breakdown caused by application of a high electric field will be explained. Generally in X-ray diagnosis, a high electric field is applied to the X-ray flat panel detector in order to acquire charges generated in the photoelectric conversion film to the pixel electrode. The applied high electric field may cause dielectric breakdown in the effective pixel area and peripheral areas (dummy pixel A area, dummy pixel B area, scanning line area around the effective pixels, and signal line area around the effective pixels). A measure against dielectric breakdown is adopted in each area. In the effective pixel area, a high electric field is applied within the photoelectric conversion film. If a large number of X-rays are incident on the photoelectric conversion film, a transient large current is generated to excessively increase the pixel potential. At this time, dielectric breakdown may occur between the effective pixel and a common electrode (capacitance is formed between them) or in the TFT. To prevent dielectric breakdown in the effective pixel area, the pixel is equipped with a function of externally removing charges when charges are excessively accumulated in the pixel. This function can be realized by, e.g., giving the TFT a diode function within the pixel. Also in the peripheral area, a high electric field is so applied as to sufficiently enhance the characteristics of the photoelectric conversion film. Application of the high electric field may cause dielectric breakdown between a high-electric-field applying electrode, the dummy pixel, the scanning line, and the signal line. To prevent dielectric breakdown in the peripheral area, a protective electrode (potential: GND) for shielding charging by an insulating film is formed between the scanning line, the signal line, and the high-electric-field applying electrode in the X-ray flat panel detector. The protective electrode is made of a material having an electrical resistance. FIGS. 3A and 3B are views for explaining a protective electrode 30 of the X-ray flat panel detector 12, and are sectional views taken along the line Dxe2x80x94D in FIG. 2. FIG. 4 is an enlarged view showing the inside of the circle in FIG. 3B. As shown in FIGS. 3A, 3B, and 4, the protective electrode 30 is formed between a high-voltage electrode 32 and a signal line layer 33. The protective electrode 30 is formed in correspondence with the dummy pixel A or B, as described above. Thus, the protective electrode 30 exists around the effective pixel area. The protective electrode 30 is electrically divided between the effective pixel area and the dummy pixel A area, and between the effective pixel area and the dummy pixel B area (see FIGS. 3A, 3B, and 4). Further, the protective electrode 30 is also divided at G, H, I, and J between the dummy pixel A area and the dummy pixel B area. The purpose of this structure is not to transmit potential variations generated upon driving DA to the signal line 26 connected to the DB. More specifically, the protective electrode 30 forms capacitances together with all the signal lines 26 connected to DAs or DBs due to the structure of the X-ray flat panel detector. All the scanning lines 27 connected to DAs or DBs form capacitances together with the protective electrode 30. If a DA is driven by the gate scanning line driving circuit 18, the protective electrode 30 flows a transient current which depends on potential changes. Since the protective electrode 30 is made of a material having a resistance component, the potential of the protective electrode 30 becomes unstable. Especially when the protective electrode 30 is not divided between the dummy pixel A area and the dummy pixel B area, the unstable potential of the protective electrode 30 transfers to the signal line of the DB and is superposed as a noise component on the signal line. On the other hand, the effective pixel area is not influenced by driving of the DA because the protective electrode covers only the dummy pixels. As a result, the output values of the effective pixel and dummy pixel differ from each other in dark imaging. This difference acts as an offset within the output range of the A/D converter, and generates noise in an X-ray diagnostic image. To the contrary, the protective electrode 30 of the X-ray flat panel detector is divided between the dummy pixel A area and the dummy pixel B area, and can prevent noise from flowing. This is because a transient current flowing through the protective electrode 30 which covers the DA upon driving the gate scanning line is not superposed on the signal line via the protective electrode 30 which covers the DB. Each divided protective electrode must receive a stable potential such as GND potential. As for supply of a potential to the protective electrode 30, four examples will be described below. Note that each example can also be applied to an X-ray flat panel detector according to any one of the following embodiments. An X-ray flat panel detector according to Example 1-1 will be explained. FIG. 5 is a plan view for explaining an X-ray flat panel detector 121 according to Example 1-1. In the X-ray flat panel detector 121 shown in FIG. 5, switching elements are driven from the two sides, and signals are read out from pixels from two, upper and lower sides. A scanning line extending from each sensor element of the sensor element array is extracted on the right or left side of the sensor element array. A signal line extending from each sensor element of the sensor element array is extracted on the upper or lower side of the sensor element array. The gate scanning line driving circuits 18 arranged on the two, right and left sides of the sensor element array have ICs which are connected to the scanning lines and drive the switching elements. In the X-ray flat panel detector 121, the ICs have a function of supplying potentials to the protective electrode, and supply GND potential at several points from respective sides. The arrangement of potential supply to the protective electrode is not limited to this. A contact portion for supplying GND potential at several points may be arranged separately from the ICs. The integrating amplifier circuits 20 arranged on the upper and lower sides of the sensor element array in the row direction have amplifier ICs connected to the respective signal lines. In the X-ray flat panel detector 121, these ICs have a function of supplying potentials to the protective electrode, and supply potentials at several points from respective sides. Similar to the gate scanning line driving circuit 18, potential supply to the protective electrode may be achieved by supplying GND potential at several points, separately from the ICs. FIG. 6 is a plan view for explaining an X-ray flat panel detector 122 according to Example 1-2. In the X-ray flat panel detector 122 shown in FIG. 6, switching elements are driven from the right or left side of the sensor element array, and signals are read out from pixels from the upper and lower sides of the sensor element array. The X-ray flat panel detector 122 comprises the gate scanning line driving circuit 18 arranged on either one of the right and left sides of the sensor element array, and the integrating amplifier circuits 20 and A/D converters which are arranged on the upper and lower sides of the sensor element array. The gate scanning line driving circuit 18 arranged on either one of the right and left sides of the sensor element array has a scanning line driving IC which is connected to each scanning line and has a function of supplying a potential to the protective electrode. The arrangement of potential supply to the protective electrode is not limited to this. An arrangement for supplying GND potential by supply line 200 at several points may be arranged separately from the IC. A side not connected to the scanning line driving IC receives GND potential at one or two points from the signal line side. In this case, the protective electrode has a resistance component, the GND stability degrades, and an output difference occurs between the right and left sides of the dummy pixel (DB). To prevent generation of the output difference, a low-resistance material is preferably applied below the protective electrode and brought into contact with the protective electrode at several points, thereby enhancing GND. FIG. 7 is a sectional view taken along the line Exe2x80x94E in FIG. 6. As shown in FIG. 7, the low-resistance material 202 may also be applied below the protective electrode on a side connected to the scanning line driving IC in order to eliminate the output difference between the right and left sides of the dummy pixel (DB). Alternatively, a portion 31 where GND potential can be supplied may be set on a side not connected to the scanning line driving IC so as to supply GND potential. On the signal line side, GND potential can be supplied to the protective electrode by the potential supply function described in Example 1-1. FIG. 8 is a plan view for explaining an X-ray flat panel detector 124 according to Example 1-3. In the X-ray flat panel detector 124 shown in FIG. 8, switching elements are driven from the right and left sides of the sensor element array, and signals are read out from pixels from the upper or lower side of the sensor element array. The X-ray flat panel detector 124 comprises the gate scanning line driving circuits 18 arranged on the two, right and left sides of the sensor element array, and the integrating amplifier circuit 20 and A/D converter which are arranged on the upper or lower side of the sensor element array. On the scanning line side, GND potential can be supplied to the protective electrode by the potential supply function described in Example 1-1. On the signal line side, similar to Example 1-1, the amplifier IC within the integrating amplifier circuit 20 connected to the respective signal lines 26 has a function of supplying a potential to the protective electrode, and supplies potentials at several points from respective sides. A signal line side not connected to the amplifier IC receives GND potential at one or two points from the scanning line side. Similar to the gate scanning line driving circuit 18, potential supply to the protective electrode may be accomplished by supplying GND potential at several points, separately from the IC. Alternatively, a contact portion (e.g., pads) capable of supplying GND potential from a signal line side not connected to the amplifier IC to a signal line side not connected to the amplifier IC may be employed. FIG. 9 is a plan view for explaining an X-ray flat panel detector 126 according to Example 1-4. In the X-ray flat panel detector 126 shown in FIG. 9, switching elements are driven from the right or left sides of the sensor element array, and signals are read out from pixels from the upper or lower side of the sensor element array. The X-ray flat panel detector 126 comprises the gate scanning line driving circuit 18 arranged on the right or left side of the sensor element array, and the integrating amplifier circuit 20 and A/D converter which are arranged on the upper or lower side of the sensor element array. On the scanning line side, GND potential can be supplied to the protective electrode by the potential supply function described in Example 1-2. On the signal line side, GND potential can be supplied to the protective electrode by the potential supply function described in Example 1-3. In the above-described arrangements, the protective electrode 30 is divided between the dummy pixel A area and the dummy pixel B area. The signal line 26 connected to the DB is not influenced by potential variations caused by DA driving. Hence, noise can be properly corrected by the DB, and a low-noise, high-quality X-ray diagnostic image can be acquired. An LC wiring line 291 is also divided between the dummy pixel A area and the dummy pixel B area. The output of the effective pixel is not influenced by fluctuations in the scanning line potential of the DA in a steady state. The noise generation cause (conductive path) itself can be eliminated, and a low-noise, high-quality X-ray diagnostic image can be obtained. The LC wiring line 291 has an auxiliary wiring line 295 which is to be disconnected between the dummy pixel A area and the dummy pixel B area. This disconnection can be easily executed even upon the completion of the X-ray flat panel detector 12. Second Embodiment The second embodiment will describe an X-ray flat panel detector having an arrangement in which a protective electrode 30 does not form any capacitance together with a signal line 26 or scanning line 27. FIG. 10 is a plan view for explaining the arrangement of an X-ray flat panel detector 12 according to the second embodiment. FIG. 11 is a sectional view taken along the line Pxe2x80x94P in FIG. 10. As shown in FIGS. 10 and 11, the X-ray flat panel detector 12 does not exist on a DA or DB. With this arrangement, the protective electrode 30 does not form capacitances together with the signal line 26 and scanning line 27. Even if a gate scanning line driving circuit 18 drives the DA and the potential of the protective electrode 30 becomes unstable, the unstable potential of the protective electrode 30 is not transferred to the signal line of the DB. For example, even in dark imaging, the output values of the effective pixel and dummy pixel do not differ from each other, and generation of noise can be prevented. Two modifications of the X-ray flat panel detector 12 according to the second embodiment will be explained. The X-ray flat panel detector according to each modification has a protective electrode 30 disconnected at at least one portion in terms of removal of a loop current flowing through the protective electrode 30. FIG. 12 is a plan view showing an X-ray flat panel detector 12 having a C type protective electrode 30 disconnected at a position Q. In the X-ray flat panel detector 12 according to this modification, the protective electrode 30 does not form any circuit. The protective electrode 30 can disconnect the path of a loop current generated upon, e.g., driving the detector 12. FIG. 13 is a plan view showing an X-ray flat panel detector 12 having a protective electrode 30 disconnected at positions Q and R. Particularly in the modification of FIG. 13, the protective electrode 30 is axially symmetrical about the central axis of the X-ray flat panel detector 12. This protective electrode 30 copes with an array of X-ray sensor elements 16 which are arranged axially symmetrical about the central axis of the X-ray flat panel detector 12. If the protective electrode 30 is axially symmetrical about the central axis of the X-ray flat panel detector 12, similar to an array of the X-ray sensor elements 16, noise superposed on an image can be efficiently canceled using this symmetry. Third Embodiment Generally in the TFT array manufacturing step and detector assembly step in the manufacture of an X-ray flat panel detector, scanning lines and signal lines are electrostatically charged. If the electrostatic charging amount increases, dielectric breakdown may occur between the scanning line, the signal line, and a conductor on the same layer as that of the scanning line or the like or on another layer. The third embodiment will exemplify an X-ray flat panel detector which has a function of preventing dielectric breakdown caused by static electricity, and even if a dummy pixel is driven, does not influence the potential of the scanning line of each effective pixel. An X-ray flat panel detector 12 according to the third embodiment prevents such dielectric breakdown by a dielectric breakdown preventing section 29 as shown in FIG. 1. The dielectric breakdown preventing section 29 is constituted by bidirectional diodes 290 connected to scanning lines 27 and signal lines 26 outside all the pixel areas (effective pixel area, dummy pixel A area, and dummy pixel B area), and LC wiring lines 291 which are combined into one line and laid out around the pixel area while one of the electrodes of each LC wiring line 291 is connected to a corresponding diode 290. When scanning lines irrelevant to driving of switching elements or signal lines irrelevant to read of a signal from each pixel exist, these scanning lines or signal lines are also preferably connected to the diodes 290. The LC wiring line 291 of the X-ray flat panel detector 12 according to the third embodiment is disconnected at a predetermined position and separated from the scanning line side and signal line side. As for disconnection of the LC wiring line 291, the following five examples will be described. Note that each example can also be applied to an X-ray flat panel detector according to any one of the above-described embodiments. FIG. 14 is a plan view for explaining disconnection of the LC wiring line 291 of the X-ray flat panel detector 12 according to Example 3-1. As shown in FIG. 14, the X-ray flat panel detector 12 has a second DA 296 for removing noise of a DB, and the LC wiring line 291 disconnected between the scanning line side and signal line side at positions K. Each cutoff LC wiring line 291 receives a potential (e.g., OFF potential of the scanning line or signal line potential) which does not influence the array function. In the dielectric breakdown preventing section 29, charges accumulated in the scanning line or signal line are distributed by the diode 290 to the LC wiring line 291. This can prevent dielectric breakdown caused by static electricity in the manufacturing process. The LC wiring line 291 is disconnected between the scanning line side and signal line side at the positions K. FIG. 15 is a plan view for explaining disconnection of the LC wiring line 291 of the X-ray flat panel detector 12 according to Example 3-2. As shown in FIG. 15, the X-ray flat panel detector 12 has the LC wiring line 291 which is disconnected at positions K serving as the boundaries between the scanning line sides and the signal line sides and at positions L serving as the boundaries between the dummy pixel A areas and the dummy pixel B areas. In this way, the LC wiring line 291 is also disconnected at the positions L in order to completely separate the LC wiring line 291 connected to the DA from the LC wiring line 291 connected to the effective pixel, and to prevent the influence of fluctuations in the scanning line potential of the DA in a steady state on the output of the effective pixel. When the DA is actually driven using the X-ray flat panel detector 12, potential fluctuations by this driving are considered to influence the scanning line potential of the effective pixel through a path: scanning line (dummy pixel (DA))xe2x86x92the dummy pixel (DA)xe2x86x92wiring line (LC)xe2x86x92the effective pixelxe2x86x92scanning line (effective pixel). The fluctuation component of the DA is superposed on the potential of each scanning line, increasing noise (NB). However, the X-ray flat panel detector 12 has divided LC wiring lines, so potential fluctuations in a scanning line connected to the DA do not influence the potential of a scanning line connected to the effective pixel. This can reduce the noise component superposed on the scanning line connected to the effective pixel. To easily disconnect the LC wiring line 291 at the position L, the LC wiring line 291 preferably has an auxiliary wiring line 295 for disconnection, as shown in FIG. 16. This arrangement facilitates disconnecting the LC wiring line 291 between the dummy pixel A area and the dummy pixel B area. To easily disconnect the LC wiring line 291 at the position K, the LC wiring line 291 may have an auxiliary wiring line 295 for disconnection, similar to the position L. FIG. 17 is a plan view for explaining the LC wiring structure of the X-ray flat panel detector 12 according to Example 3-3. As shown in FIG. 17, the X-ray flat panel detector 12 comprises a first LC wiring line 292, second LC wiring line 293, and third LC wiring line 294. The first LC wiring line 292 is connected to scanning lines connected to a DA and the second DA 296. The second LC wiring line 293 is connected to a signal line connected to a DB. The third LC wiring line 294 is connected to the signal line of the second DA 296. The first, second, and third LC wiring lines 292, 293, and 294 are electrically separated from each other. Since the current path is disconnected, potential fluctuations by driving of the DA do not influence the potential of a scanning line connected to the effective pixel. As a result, the noise component superposed on the scanning line connected to the effective pixel can be reduced. Note that each LC wiring line may be disconnected at positions serving as the boundaries between the scanning line sides and the signal line sides, i.e., positions K1, K2, and K3. The LC wiring line may also be disconnected at the positions L, as shown in FIG. 15. This also applies to the following Examples 3-4 and 3-5. FIG. 18 is a plan view for explaining the structure of the LC wiring line 291 of the X-ray flat panel detector 12 according to Example 3-4. The X-ray flat panel detector 12 shown in FIG. 18 has resistors 300 which connect the respective LC wiring lines, in addition to the first, second, and third LC wiring lines 292, 293, and 294. Each resistor 300 has a resistance value enough to prevent dielectric breakdown caused by static electricity. The first, second, and third LC wiring lines 292, 293, and 294 are connected to each other via the resistors 300. This arrangement can further improve the dielectric breakdown preventing function in the manufacturing process or the like, compared to a case wherein the respective wiring lines are electrically disconnected completely. Since the respective LC wiring lines are connected via the resistors 300, the influence of driving of a DA on the potential of a scanning line connected to the effective pixel can be reduced. Consequently, the noise component superposed on the scanning line connected to the effective pixel can be reduced. FIG. 19 is a plan view for explaining the structure of the LC wiring line 291 of the X-ray flat panel detector 12 according to Example 3-5. The X-ray flat panel detector 12 shown in FIG. 19 has auxiliary wiring lines 301 for disconnection that are connected to the respective LC wiring lines, in addition to the first, second, and third LC wiring lines 292, 293, and 294. The first, second, and third LC wiring lines 292, 293, and 294 are connected to each other via the auxiliary wiring lines 301. The dielectric breakdown preventing function can be further improved in the manufacturing process or the like, compared to a case wherein the respective wiring lines are electrically disconnected completely. In actual use of the X-ray flat panel detector 12, the auxiliary wiring lines 301 are disconnected. Therefore, the current path is disconnected, and the respective LC wiring lines are electrically independent of each other. Potential fluctuations by driving of a DA do not propagate to a scanning line connected to the effective pixel. The noise component superposed on the scanning line connected to the effective pixel can be reduced. The above-described embodiments can implement an X-ray flat panel detector capable of preventing dielectric breakdown and providing a high-quality X-ray diagnostic image free from any noise. The present invention has been explained on the basis of the above embodiments. However, various changes and modifications will readily be made by those skilled in the art within the spirit and scope of the present invention. These changes and modifications are also incorporated in the present invention, and the present invention can be variously changed without departing from the spirit and scope of the present invention. The embodiments include inventions on various stages, and various inventions can be extracted by an appropriate combination of building components disclosed. For example, even if several building components are omitted from all the building components described in the embodiments, the problems disclosed in xe2x80x9cBACKGROUND OF THE INVENTIONxe2x80x9d may be solved, and at least one of the above-described effects may be obtained. In this case, an arrangement from which the building components are omitted can be extracted as an invention. |
|
summary | ||
claims | 1. An emergency core cooling system of a boiling water nuclear plant, comprising:four active safety divisions exclusively used for an active emergency core cooling system, each of the active safety divisions including only one motor-driven low pressure core cooling system so as to reduce a volume of a building housing the low pressure core cooling system; andone or more passive safety divisions including a passive safety system that does not require motor drive, whereina number of the active safety divisions is larger by two or more than a number required upon occurrence of a design basis accident,each of the active safety divisions includes an emergency power source for supplying electric power to the motor-driven low pressure core cooling system, andthe passive safety system is configured to cool a core of the boiling water nuclear plant for at least 8 hours during an accident without being replenished with cooling water from outside. 2. The emergency core cooling system according to claim 1, whereina number of the passive safety divisions is one,the only one motor-driven low pressure core cooling system of each of the active safety divisions exclusively used for the active emergency core cooling system is a low pressure core cooling system that is also used as a residual heat removal system,the low pressure core cooling system has at least 100% of an injection capacity required for cooling the core upon occurrence of at least the design basis accident in a state where a reactor pressure is low,the residual heat removal system has at least 50% of a heat removal capacity required for cooling the core and a containment vessel upon occurrence of the design basis accident, andthe passive safety division includes at least an isolation condenser. 3. The emergency core cooling system according to claim 1, whereinthe emergency power source of each of the active safety divisions is an emergency diesel generator. 4. The emergency core cooling system according to claim 1, further comprisingat least one auxiliary power source configured to selectively supply power to any one of the active safety divisions. 5. The emergency core cooling system according to claim 4, whereinthe auxiliary power source is a gas turbine generator. 6. The emergency core cooling system according to claim 1, further comprising:an auxiliary feed water system including one or more turbine-driven reactor core isolation cooling systems driven by main steam supplied from the boiling water reactor. 7. The emergency core cooling system according to claim 1, whereinthe passive safety division includes a passive containment cooling system. 8. The emergency core cooling system according to claim 7, whereinthe passive safety division includes a gravity-driven cooling system. 9. The emergency core cooling system according to claim 7, whereinat least one of the active safety divisions includes a direct current power source and an equalized pressure flooder system driven by the direct current power source. 10. The emergency core cooling system according to claim 1, whereinthe passive safety system includes at least one isolation condenser that holds a predetermined volume of cooling water, the predetermined volume configured to cool the core of the boiling water nuclear plant for at least 8 hours during the accident without being replenished with cooling water from outside. 11. A boiling water nuclear plant provided with an emergency core cooling system, the emergency core cooling system including:four active safety divisions exclusively used for an active emergency core cooling system, each of the active safety divisions including only one motor-driven low pressure core cooling system so as to reduce a volume of a building housing the low pressure core cooling system; andone or more passive safety divisions including a passive safety system that does not require motor drive, whereina number of the active safety divisions is larger by two or more than a number required upon occurrence of a design basis accident,each of the active safety divisions includes an emergency power source for supplying electric power to the motor-driven low pressure active safety system, andthe passive safety system is configured to cool a core of the boiling water nuclear plant for at least 8 hours during an accident without being replenished with cooling water from outside. |
|
summary | ||
claims | 1. A Fuel element comprising:a cladding tube having upper and lower sections and a middle section having a smaller diameter than the upper and lower sections;a gas plenum region in the upper section and an upper portion of the middle section;a metal fuel contained in the lower section;a fuel swelling absorption region in the lower section above the metal fuel; anda coolant disposed between sides of the metal fuel and the cladding tube in the lower section, in the fuel swelling absorption region, and in a lower portion of the middle section, whereina coolant density reactivity coefficient in the lower section has a negative value, anda coolant density reactivity coefficient in the upper portion of the middle section has a positive value. 2. The fuel element according to claim 1, wherein a length in a vertical direction of the upper portion of the middle section having the positive value of the coolant density reactivity coefficient is (100/Lf)2×Lf×40/100 where Lf is an effective fuel length of the metal fuel. 3. A fuel assembly comprising:a plurality of fuel elements;a wrapper tube surrounding the plurality of fuel elements;a coolant material passage formed between the plurality of fuel elements; each fuel element of the plurality of fuel elements including:a cladding tube having upper and lower sections and a middle section having a smaller diameter than the upper and lower sections, a gas plenum region in the upper section and an upper portion of the middle section, a metal fuel contained in the lower section, a fuel swelling absorption region in the lower section above the metal fuel, and a coolant disposed between sides of the metal fuel and the cladding tube in the lower section, in the fuel swelling absorption regions, and in a lower portion of the middle section, whereina coolant density reactivity coefficient in the lower section has a negative value, anda coolant density reactivity coefficient in the upper portion of the middle section has a positive value. 4. A core comprising: an inner core fuel region loaded with the fuel assembly according to claim 3; and an outer core fuel region loaded with the fuel assembly according to claim 3. 5. A core comprising: a plurality of fuel elements, each including a cladding tube having upper and lower sections and a middle section having a smaller diameter than the upper and lower sections, a gas plenum region in the upper section and an upper portion of the middle section, a metal fuel contained in the lower section, a fuel swelling absorption region in the lower section above the metal fuel, and a coolant disposed between sides of the metal fuel and the cladding tube in the lower section, in the fuel swelling absorption regions, and in a lower portion of the middle section; whereina coolant density reactivity coefficient in the lower section has a negative value, anda coolant density reactivity coefficient in the upper portion of the middle section has a positive value,the plurality of fuel elements is divided between an outer core fuel assembly and an inner core fuel assembly;the metal fuel is a ternary alloy of U—Pu—Zr, anda Pu content of the metal fuel in the fuel elements of the outer core fuel assembly is higher than a Pu content of the metal fuel in the fuel elements of the inner core fuel assembly. 6. The core according to claim 5, wherein an effective fuel length of the fuel elements in the inner core fuel assembly is shorter than an effective fuel length of the fuel elements in the outer core fuel assembly. 7. The core according to claim 5, wherein a length in a vertical direction of the middle section of the fuel elements in the outer core fuel assembly is shorter than a length in the vertical direction of the middle section of the fuel elements in the inner core fuel assembly. |
|
047987006 | description | DETAILED DESCRIPTION OF THE PRESENT INVENTION The invention, together with advantageous examples of the embodiments and improvements, will become more apparent and are described in more detail below, with references to the figures in which two different embodiments are illustrated. FIG. 1 shows a cross-section through a core 14, enclosed by circular cylindrical reactor pressure vessel 10, against the inner wall 11 whereof ceramic installations, in particular graphite blocks built up in the shape of a wall, are set as the side reflector 12, and into which four projections 13 are radially projecting in mutually opposing pairs. The projections consist of individual nose stones 20, 30 set upon each other and positively joined to the side reflector 12. The nose stones 20, 30, which are made of graphite, as is the side reflector 12, comprise in their free frontal side 17 projecting into the core 14, a vertically arranged cavity with an elongated cross-section extending parallel to the external surfaces facing the core 14. In the area of its frontal side 17 a vertically oriented continuous gap or opening 23, 33 is formed in each nose stone 20, 30, said gap connecting the cavity 18 with the core 14. While the core is intended to receive the fuel elements 15, the vertical cavity 18 is to receive the absorber elements 16. FIG. 2 shows an individual nose stone in a lateral or side elevation. The surface 21 of the nose stone 20 projecting into the core 14 is provided with a plurality of vertical grooves 22 close to the horizontal surface and laid out in a grid-like pattern, intended for the division of the external surfaced exposed to neutron radiation into small surface units to make possible the equalization of neutron-induced volume changes. From the slit lateral surface 21 of the nose stone 20, into which the continuous gap 23 connecting the core 14 with the cavity 18 extends, the support surface 24 is offset by means of a step 25, whereby the nose stone 20 is joined both upward and downward with the next nose stone or the bottom or roof reflector respectively. The height of the step 25 corresponds to one-half the width of a surface gap 22, so that a gap 22 is again formed in case of nose stones set upon each other in the area of the adjacent surfaces 24. The rear part of the nose stone 20, which is attached into the side reflector 12, comprises a groove 27 formed in the lateral surface 26 for anchoring purposes, with the side reflector 12 entering the said groove to form a positive joint. The surface 26, which is otherwise without gaps, joins the slit surface 21 in alignment. With the exception of the lateral layout of the gap 23, which establishes the connection of the cavity 18 with the core 14, the lateral view of a nose stone 20 shown in FIG. 2 is identical with that of a nose stone 30 comprising a frontal gap opening. Therefore, no separate figure is shown to display this difference. FIG. 3 shows a nose stone 20 in a top view. In a supplementation of the view in FIG. 2, the configuration of the gap 22 close to the surface 21 facing the core 14 and of the support surface 24 offset by the center step 25 may be seen, together with the smooth surface 26 in the rear part of the nose stone 20, interrupted only by a groove 27 arranged vertically on each of the two sides. The groove 27 is rectangular, but according to the present invention a groove with a cylindrical profile may be provided in order to reduce stresses in the bottom of the groove, particularly in the corners. The cavity 18 has a longitudinal cross-section and is connected at its narrow frontal side 19 through a gap 23 with the core 14. The gap 23 is thereby extended as a continuation of the narrow frontal side 19 of the cavity 18 through one of the two longitudinal sides of the nose stone 20 to the outside and expands at an angle from inside to the outside, with the gap surfaces being straight. However, according to the invention, the gap surfaces may also be curved away from the center portion of the core in an involute manner. FIG. 4 shows a top view of a nose stone 30 with a gap 33 on its frontal side, i.e., the gap 33 centrally passes through the narrow frontal side 19 of the elongated cavity 18. The nose stone 30 is thereby divided by the vertically continuous gap 33, the gap surfaces of which define the grooves 38 to receive a graphite blocking element 39, into two equal halves, which laterally surround the cavity 18 in the form of cheeks. The lateral surface 31 projecting into the core 14 is provided in the manner shown in FIG. 3 with slit-like recesses 32 close to the surface. The support surface 34 is similarly offset from the slit area by a step 35. The rear area of the nose stone again has a smooth surface 36, into which on both sides a vertical groove 37 is set, said groove 37 being intended for anchoring in the side reflector 14. |
044407149 | claims | 1. A method for extracting useful radiation in a controlled manner from target pellets imploded by an energy beam in an inertial confinement fusion reactor such that components of said reactor are subjected to an approximately linear source radiation fluence, which comprises (A) injecting a first target pellet into the reactor causing said pellet to follow a trajectory which is a linear path; (B) directing an energy beam at a first site along said linear path timed to intersect and strike said pellet thereby inducing fusion through inertial confinement; (C) injecting a second target pellet into the reactor along said linear path; (D) directing said energy beam at a second site along said linear path, said second site being displaced from said first site by a first distance in one dimension along said linear path, said energy beam timed to intersect and introduce inertial confinement fusion in said second pellet at said second site; (E) repeating the above steps C and D with third, fourth and subsequent pellets and third, fourth and subsequent sites, and second, third, and subsequent distances such that all fusion events occur along a line being said linear path and reactor components are exposed to an approximately linear source radiation fluence. 2. The method of claim 1 wherein the beam is laser light. |
054066115 | abstract | A gating device for a radiation apparatus has at least one diaphragm plate adjustable in the beam path of a radiation transmitter, the plate having at least one guide aligned obliquely relative to the longitudinal axis of the diaphragm plate and an adjustment mechanism is attached to the diaphragm plate for moving the diaphragm plate in a manner defined by its guide to adjust the position of the plate in the beam path. |
claims | 1. A method of treating metal using an apparatus having sensors and a controller for selectively monitoring the sensors and controlling output actuators of a multi-staged metal treatment process to more accurately and reliably administer treatment, the method comprising: cleaning a metal workpiece with an alkaline solution in a first stage; applying an ionic conditioner to the workpiece in a second stage; applying a phosphate solution to the workpiece in a third stage; applying a finishing overcoat in an ionic aqueous sealing agent to the workpiece in a fourth stage; monitoring temperature and conductivity of the alkaline solution in the first stage, conductivity and pH of the conditioner in the second stage, temperature, conductivity and pH of the solution in the third stage, and conductivity and pH of the agent in the fourth stage; and generating an alarm if any of the monitored parameters vary from desired parameters for a predetermined amount of time; and actuating output actuators if an alarm is generated to maintain the desired parameters for the metal treatment process. 2. A method according to claim 1 , wherein the method further comprises: claim 1 providing remote access, monitoring and controlling features which allow individuals who are removed from the immediate vicinity of the treatment controlling apparatus to access, monitor, control the treatment control apparatus. |
|
052001172 | summary | FIELD OF THE INVENTION This invention relates to compositions which are effective for solubilizing and removing scale, particularly strontium and barium sulfate scale, from surfaces with scale deposits on them. It is particularly useful for the removal of such scale from oilfield equipment including downhole pipe, tubing and casing as well as subterranean formations. It is also applicable to the removal of these scale deposits from other equipment such as boilers and heat exchangers. BACKGROUND OF THE INVENTION Many waters contain alkaline earth metal cations, such as barium, strontium, calcium and magnesium, and anions, such as sulfate, bicarbonate, carbonate, phosphate, and fluoride. When combinations of these anions and cations are present in concentrations which exceed the solubility product of the various species which may be formed, precipitates form until the respective solubility products are no longer exceeded. For example, when the concentrations of the barium and sulfate ions exceed the solubility product of barium sulfate, a solid phase of barium sulfate will form as a precipitate. Solubility products are exceeded for various reasons, such as evaporation of the water phase, change in pH, pressure or temperature and the introduction of additional ions which .can form insoluble compounds with the ions already present in the solution. As these reaction products precipitate on the surfaces of the water-carrying or water-containing system, they form adherent deposits or scale. Scale may prevent effective heat transfer, interfere with fluid flow facilitate corrosive processes, or harbor bacteria. Scale is an expensive problem in many industrial water systems, in production systems for oil and gas, in pulp and paper mill systems, and in other systems, causing delays and shutdowns for cleaning and removal. Barium and strontium sulfate scale deposits present a unique and particularly intractable problem. Under most conditions, these sulfates are considerably less soluble in all solvents than any of the other commonly encountered scale-forming compounds, as shown by the comparative solubilities given in Table 1 below. TABLE 1 ______________________________________ Comparative Solubilities, 25.degree. C. in Water. Scale Solubility, mg./l. ______________________________________ Gypsum 2080.0 Strontium sulfate 140.0 Calcium Carbonate 14.0 Barium sulfate 2.3 ______________________________________ It is generally acknowledged that barium sulfate scale is extremely difficult to remove chemically, especially within reasonably short periods of time: the solvents which have been found to work generally take a long time to reach an equilibrium concentration of dissolved barium sulfate, which itself is usually of a relatively low order. Consequently, barium sulfate must be removed mechanically or the equipment, e.g. pipes, etc., containing the deposit must be discarded. The incidence of barium sulfate scale is worldwide, and it occurs principally in systems handling subsurface waters. Because of this, the barium sulfate scale problem is of particular concern to the petroleum industry as water is generally produced with petroleum and as time goes on, more petroleum is produced by the waterflooding method of secondary recovery, implying even greater volumes of produced water. The scale may occur in many different places, including production tubing, well bore perforations, the area near the well bore, gathering lines, meters, valves and in other production equipment. Barium sulfate scale may also form within subterranean formations such as in disposal wells. Scales and deposits can be formed to such an extent that the permeability of the formation is impaired resulting in lower flow rates, higher pump pressures, and ultimately abandonment of the well. Barium sulfate scale is particularly troublesome when sulphate-rich seawater is used as an injection fluid in oil wells whose formation water is rich in barium ions. This particular aspect of the barium scale problem is severe in some U.S. oil fields as well as some older North Sea oil fields. Scaling of this nature is also expected to occur during advanced production stages in other North Sea fields particularly after seawater breakthrough has taken place. Another problem associated with the formation of barium and strontium sulfate scales is that radium, another member of the alkaline earth group of metals tends to be deposited at the same time so that the equipment becomes radioactive, and may eventually have to become unusable for safety reasons alone. At present, a considerable amount of oilfield tubular goods are in this condition and cannot be readily restored to usable condition because of the difficulty of removing the radioactive scale. Various proposals have been made in the past for removing barium sulfate scale chemically. Most of these processes have utilised chelating or complexing agents, principally the polyaminopolycarboxylic acids such as ethylenediaminetetraacetic acid(EDTA) or diethylenetriaminepentaacetic acid(DTPA). U.S. Pat. No. 2,877,848 (Case) discloses the use of EDTA in combination with various surfactants for this purpose. U.S. Pat. No. 3,660,287 (Quattrini) discloses the use of EDTA and DTPA in the presence of carbonate ion at relatively neutral pH (6.5-9.5) and U.S. Pat. No. 4,708,805 (D'Muhala) discloses a process for the removal of barium sulfate scale by sequestration using an aqueous solution of citric acid, a polycarboxylic acid such as carbazic acid, and an alkylene-polyaminopolycarboxylic acid such as EDTA or DTPA. The preferred aqueous sequestering solutions have a pH in the range of about 9.5 to about 14, provided by a base such as potassium hydroxide or potassium carbonate. Another approach which has recently been made is to use a polyether in combination with the aminopolycarboxylic acid. U.S. Pat. No. 4,190,462 (deJong) discloses that barium sulfate scale can be removed from remote locations extending into a subterranean earth formation by contacting the scale with an aqueous solution consisting essentially of water, a monovalent cation salt of a monocyclic macroyclic polyether containing at least two nitrogen-linked carboxymethyl groups and enough monovalent basic compound to provide a solution pH of about 8. Similar disclosures are to be found in U.S. Pat. Nos. 4,215,000 and 4,288,333. These polyether materials have, however, the disadvantage of being costly which is a severe drawback for oilfield use where cost is a major factor. Although many of these known compositions will remove scale, the rate of dissolution is slow and the amount of scale dissolved is small. SUMMARY OF THE INVENTION We have now found a way of removing barium sulfate scale using various novel combinations of scale-removing agents. These combinations are capable of removing scale at markedly higher speeds than prior scale-removing compositions and are also capable of removing relatively more scale for a given quantity of solvent. They are, moreover, relatively cheap and are therefore well suited to use in oilfield operations. According to the present invention, barium sulfate and other sulfate scales are removed by a chemical process using a combination of a polyaminopolycarboxylic acid such as EDTA or DTPA together with an anion of a monocarboxylic acid such a acetic acid, hydroxyacetic acid, mercaptoacetic acid or salicylic acid as a synergist or catalyst for the dissolution. The scale is removed under alkaline conditions, preferably at pH values of at least 10, usually 10-14, with best results being achieved at about pH 12. The concentration of synergist or catalyst is usually about 0.01M to about 1.0M, preferably about 0.5M, with similar concentrations being appropriate for the primary chelant (the polyaminopolycarboxylic acid). Substantially improved scale dissolution rates are obtained when the aqueous solution containing the composition is at a temperature of about 25.degree. C. to about 100.degree. C. but higher temperatures are obtainable downhole because at greater formation depths higher existing pressures will raise the boiling point of the aqueous solution, and consequently greater scale removal rates may be attained. The composition is particularly useful for more efficiently removing barium or strontium sulfate scale from wells, wellstream processing equipment, pipelines and tubular goods used to produce oil from a subterranean formation. |
abstract | A process automation system for determining, monitoring and/or influencing different process variables and/or state variables in at least one manufacturing or analytical process. Included is: at least one control station; and a plurality of field devices; wherein in each field device at least one sensor is provided for ascertaining a measured value of a process variable and/or state variable and/or an actuator is provided for influencing a process variable and/or state variable by means of an actuating value. Each field device makes available its cyclically or acyclically ascertained, measuring-device-specific, measured values and/or actuating values of the process variable and/or state variable to every other field device of the process automation system as information, and the current information of all ascertained measured values and/or actuating values of the process variables and/or state variables is available to each field device as a current process-state-vector. |
|
042788900 | claims | 1. An apparatus for implanting ions in an electrically insulating target comprising: a support for holding the target in a vacuum region; an ion gun to direct a beam of ions at the target; means for maintaining the vacuum in the vacuum region; a filament disposed to emit electrons in a direction to reach the target; a controllable electrical source connected to the filament for heating the filament; means for measuring the flow of electrical current between the filament and the target; means for measuring the net electrical current flowing between the target support and electrical ground; a voltage source for establishing an electrical bias between the target support and electrical ground; and a current integrator for integrating the current between the filament and the target as a function of time. |
abstract | A method and a system for catalytic recombination of hydrogen, which is carried in a gas flow, with oxygen, has the gas flow passed through a reaction zone with a number of catalytic converter elements, with steam being added to the gas flow before it enters the reaction zone. The method and system ensure a particularly high operational reliability of the recombination device, even in varying operating conditions or with varying operating methods, in particular with regard to a hydrogen feed, which is provided as required, in the steam/feed water circuit of the installation. For this purpose, the feed rate of the steam to be added is adjusted in dependence on a measured value which is characteristic of a current actual temperature in the reaction zone. |
|
abstract | A boiling water reactor has a reactor pressure vessel and a through piping. The reactor pressure vessel includes a main body trunk and an openable upper lid covering an upper open end of the main body trunk from above. The through piping penetrates lateral side of the main body trunk and has an opening section at a same level with or higher than the upper open end of the main body trunk in the reactor pressure vessel. The through piping may be connected to the sump arranged outside the reactor pressure vessel in the dry well. The through piping may be further connected to the suppression pool in the wet well and/or to the water level gauge in the dry well. |
|
044118597 | claims | 1. For use with a gamma sensor positioned within a tubular guide of a fuel assembly in a nuclear reactor, said sensor having an elongated gamma heated body provided with relatively hot and cold regions and an outer sheath in thermal contact with said body along the cold region thereof to establish axially symmetrical heat distribution therein in response to uniform external cooling of the outer sheath within an annular gap between said outer sheath and the tubular guide, the improvement residing in thermal bridge means engageable with the tubular guide within the annular gap for establishing a thermally conductive path between the outer sheath and the tubular guide, and means restrictively mounting the thermal bridge means on the outer sheath in axially spaced adjacency to the hot region of the body for preventing disturbance of said symmetrical heat distribution. 2. The improvement as defined in claim 1 wherein said thermal bridge means includes a centering element in sliding contact with the tubular guide. 3. The improvement as defined in claim 2 wherein said thermal bridge means further includes at least two separable ring sections on which the centering element is supported. 4. The improvement as defined in claim 3 wherein said centering element is a helical spring. 5. The improvement as defined in claim 4 wherein said mounting means includes an annular groove formed in the outer sheath within which the ring sections are seated. 6. The improvement as defined in claim 2 wherein said mounting means includes an annular groove formed in the outer sheath within which the centering element is seated. 7. The improvement as defined in claim 6 wherein said centering element is a split, undulating ribbon spring. 8. The improvement as defined in claim 2 wherein said centering element is a metal wire fabric. 9. In combination with a gamma sensor positioned within a tubular guide of a fuel assembly in a nuclear reactor, said sensor having an elongated gamma radiation heated body provided with relatively hot and cold regions and an outer sheath in thermal contact with said body along the cold regions thereof to establish axially symmetrical heat distribution therein in response to uniform external cooling of the outer sheath within an annular gap between said outer sheath and the tubular guide, the improvement residing in thermal bridge means engageable with the tubular guide within the annular gap for establishing a thermally conductive path between the outer sheath and the tubular guide, said thermal bridge means being formed by portions of the outer sheath radially deformed into thermal contact with the tubular guide at a location in axially spaced adjacency to the hot region of the body for preventing disturbance of said symmetrical heat distribution. 10. For use with a gamma sensor positioned within a tubular guide of a fuel assembly in a nuclear reactor, said sensor having an elongated gamma radiation heated body provided with relatively hot and cold regions and an outer sheath in thermal contact with said body along the cold region thereof to establish axially symmetrical heat distribution therein in response to uniform external cooling of the outer sheath within an annular gap between said outer sheath and the tubular guide, the improvement residing in thermally conductive centering means projecting from the outer sheath through the gap into sliding contact with the tubular guide only at an axial location on the body in spaced adjacency to the hot region. |
052271307 | summary | BACKGROUND OF THE INVENTION The present invention relates to a fuel assembly for a nuclear reactor of pressurized-water type. Such a fuel assembly of a known design comprises a plurality of fuel rods held together into a bundle by means of spacers arranged along the fuel rods as well as guide tubes arranged between the fuel rods and fixed to the spacers. The bundle is arranged between a top nozzle and a bottom nozzle. These are provided with a plurality of openings for the coolant flow which is to pass through the fuel assembly. The fuel assembly has no surrounding casing at all, a so-called fuel box, with which the fuel assemblies in a boiling-type nuclear reactor are provided. It is further known to throttle the coolant flow to the most burnt-up fuel assemblies in a nuclear reactor to be able, in the case of an unchanged total coolant flow through the reactor core, to increase the coolant flow to the less burnt-up fuel assemblies and hence to be able to absorb more power from these. The throttling normally takes place at the openings of the bottom and/or top nozzle, either manually during refuelling or by some form of automatic means. This type of control is effective for fuel assemblies provided with fuel boxes but less effective in the case of boxless fuel assemblies for a pressurized-water reactor. This is due to the fact that the coolant flow may divert in the lateral direction over to adjacently positioned fuel assemblies. Since particularly in highly loaded fuel assemblies there is a tendency for steam formation on the fuel rods and thus higher resistance to the passage of the coolant flow than in fuel assemblies subjected to lower load, the coolant flow has a tendency to pass from fuel assemblies subjected to higher load to those subjected to lower load even at a relatively short distance from the bottom nozzles of the assemblies when throttling the coolant flow in the fuel assemblies subjected to lower load. SUMMARY OF THE INVENTION According to the invention, now at least the lower part of the fuel assembly is provided with a partial fuel box which surrounds the bundle and extends from the bottom nozzle and at least up past the lowermost, ordinary spacer of the bundle. The box should have a length which is smaller than the length of the bundle and preferably smaller than half the length of the bundle. The partial fuel box means that the control of the coolant flow to low-load fuel assemblies may be performed with a considerably improved effect. At the same time, the reactivity load of the box is small, particularly if the box is made shorter than half the length of the bundle. An even better result is obtained if also the upper part of the fuel assembly is provided with a partial fuel box. A suitable length of the two fuel boxes may then be for them to extend from a top or bottom nozzle and covering two of the adjacent ordinary spacers of the bundle. A control of the coolant flow by throttling of the opening in the top or bottom nozzle will now be considerably more effective than when there are no fuel boxes at all. |
claims | 1. An image processing device for making a comparison between an optical microscope image acquired by an optical microscope, and an elemental mapping image acquired by a charged-particle beam device, comprising:a comparing unit for making said comparison between said optical microscope image of a specimen stained for an observation made by said optical microscope and said elemental mapping image, said optical microscope image being acquired by said optical microscope, said elemental mapping image being based on detection of X-rays by said charged-particle beam device, andan outputting unit which outputs, as a location or locations that a charged-particle beam image is acquired by said charged-particle beam device, position information of a location or locations in the specimen such that coincidence degrees between said optical microscope image and said elemental mapping image exceeds a predetermined value specified by a user, or obtain a highest value. 2. The image processing device according to claim 1, whereinsaid locations on said specimen are ranked in a descending order of said coincidence degrees. 3. The image processing device according to claim 1, whereinsaid optical microscope image or said elemental mapping image, and the position information outputted by the outputting unit or a charged-particle beam image at the location or locations corresponding to said position information are recorded as a single file. 4. An image processing device for making a comparison between an optical microscope image acquired by an optical microscope, and an elemental mapping image acquired by a charged-particle beam device, comprising:a comparing unit for making said comparison between said optical microscope image of a specimen for an observation made by said optical microscope and said elemental mapping image, said optical microscope image being acquired by said optical microscope, said elemental mapping image being based on detection of X-rays by said charged-particle beam device, anda storing unit for storing a secondary-electron image or reflection-electron image of a location or locations in the specimen such that coincidence degrees between said optical microscope image and said elemental mapping image exceed a predetermined value specified by a user, or obtain a highest value. 5. The image processing device according to claim 4, whereinsaid locations on said specimen are ranked in a descending order of said coincidence degrees. 6. The image processing device according to claim 4, whereinsaid optical microscope image or said elemental mapping image, and the position information outputted by the outputting unit or a charged-particle beam image at the location or locations corresponding to said position information are recorded as a single file. |
|
summary | ||
054223830 | summary | BACKGROUND OF THE INVENTION This invention relates to a resin composition affording a hardened surface on which a clear mark, sign, letter or the like pattern can be marked with a laser beam. The present invention is also directed to a coloring material for use in preparing the above composition and to a laser beam marking method. There is a known marking method in which a laser beam is irradiated on a surface of a shaped body containing a laser marking material, so that the irradiated portions are colored or discolored to form a desired, discriminative pattern on the surface of the shaped body. Such a laser marking material, e.g. a lead compound, is mixed in a resin matrix material and the resulting composition is shaped into a desired form. The known composition, however, has a problem because a clear, high contrast pattern is not obtainable even if the irradiation is sufficiently carried out. To cope with this problem, JP-A-4-28758 and JP-A-4-183743 propose a laser beam absorbing resin composition including a colorant capable of discoloring upon being irradiated with a laser beam, a laser bean absorbing substance selected from calcium pyrophosphate, triphenyl phosphine, calcium hexafluorosilicate and zirconium silicate, and an epoxy resin. Because of the presence of the laser beam absorbing substance, the absorption of the laser beam is enhanced so that the coloring reaction of the colorant is accelerated. The known technique is, however, still unsatisfactory in forming a clear, high contrast pattern. SUMMARY OF THE INVENTION It is, therefore, the prime object of the present invention to provide a laser beam absorbing resin composition which can give a shaped body whose surface affords a clear, high contrast pattern by irradiation with a laser beam. Another object of the present invention is to provide a coloring material useful for forming the above composition. It is a further object of the present invention to provide a method for forming desired letters or patterns on a surface of a shaped body using a laser beam. In accomplishing the foregoing objects, there is provided in accordance with the present invention a laser beam absorbing resin composition, comprising 100 parts by weight of a laser beam absorbing resin composition, comprising 100 parts by weight of a resin, and 1-100 parts by weight of composite particles having an average particle diameter of 0.1-50 .mu.m and each including a particulate, laser beam absorbing inorganic substance, and a colorant physically bonded substantially directly to said inorganic substance and capable of discoloring upon being heated at a temperature of 250.degree. C. or more, the weight ratio of said colorant to said inorganic substance being in the range of 1:99 to 50:50. In a further aspect, the present invention provides a coloring material comprising composite particles which have an average particle diameter of 0.1-50 .mu.m and each of which is composed of (a) a particulate, laser beam absorbing inorganic substance selected from the group consisting of cordierite, zeolite, zirconium silicate and calcium silicate and (b) a colorant physically bonded substantially directly to said inorganic substance and capable of discoloring upon being heated at a temperature of 250.degree. C. or more, the weight ratio of said colorant to said inorganic substance being in the range of 1:99 to 50:50. In a further aspect, the present invention provides a marking method comprising the steps of forming a shaped body of the above composition, hardening said shaped body to form a hardened body having a first color, and irradiating a surface of said hardened body with a laser beam to discolor said colorant, so that the irradiated surface has a second color discriminative from said first color. Other objects, features and advantages of the present invention will become apparent from the detailed description of the invention to follow. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Laser beam absorbing, thermosetting resin composition according to the present invention contains a resin, and composite particles having an average particle diameter of 0.1-50 .mu.m, preferably 0.5-30 .mu.m, dispersed in the resin. Each of the composite particles includes a particulate, laser beam absorbing inorganic substance (herein after referred to as LB absorber), and a colorant physically bonded substantially directly to the LB absorber and capable of discoloring upon being heated at a temperature of 250.degree. C. or more. The weight ratio of the colorant to the LB absorber should be in the range of 1:99 to 50:50, preferably 5:95 to 40:60. The shape of the composite particles is not specifically limited and may be spherical or any other forms. Any inorganic substance may be used as the LB absorber as long as it can absorb a laser beam and can emanate a heat upon absorption of the laser beam without changing the color thereof. Illustrative of suitable LB absorbers are cordierite, zeolite, zirconium silicate and calcium silicate. Cordierite is a mineral expressed by the formula: 2MgO 2Al.sub.2 O.sub.3 5SiO.sub.2. Natural cordierite which generally contains water and impurity metals such as Fe substituted for part of Mg may be used for the purpose of the present invention. High purity synthetic cordierite obtained from talc-alumina- kaolin is preferably used. Both natural and synthetic zeolite may be suitably used in the present invention. Examples of suitable zeolite include silicalite, crystalline aluminosilicate, crystalline aluminometalo-silicate (e.g. aluminogallosilicate or aluminoborosilicate), faujasite and mordenite. Physical properties, such as pore characteristics, of zeolite are not specifically limited. Generally, zeolite having a pore diameter of at least 2 A (angstrom), preferably 2-10 A, is used. The LB absorber generally has an average particle diameter of 0.1-50 .mu.m, preferably 0.5-30 .mu.m. A colorant capable of being discolored upon being irradiated with a laser beam is composited with the LB absorber. A substance which undergoes a chemical change (generally thermal decomposition and/or oxidation) and discolors when heated at a temperature of 250.degree. C. or more, preferably 250.degree.-2,000.degree. C., is suitably used as the colorant. The term "discolor" used herein is intended to refer a phenomenon which is caused by irradiation of a laser beam and by which a surface of the laser beam absorbing resin composition irradiated with the laser beam is visually discriminative from non-irradiated surfaces. Thus, the colorant may be, for example, (a) a substance which has a first color (such as white, black or blue) at room temperature but shows a second color different from the first color upon laser beam irradiation and (b) a substance which has a color (such as white, black or blue) at room temperature but becomes colorless upon laser beam irradiation. The colorant generally has an average particle diameter of 0.01-10 .mu.m, preferably 0.02-5 .mu.m. Examples of the colorant include ferric hydroxide, cuprous oxide, stannous oxide (IV), niobium oxide (V), chromium oxide (III), tungsten oxide (VI), copper hydroxide, copper gluconate, copper carbonate, silver acetate, nickel hydroxide, chromium hydroxide, indium hydroxide, nickel formate, copper oxalate, cobalt oxalate, aluminum acetylacetone, bismuth oxalate, silver acetate, titanium dioxide, metal titanates, basic nickel carbonate, basic copper carbonate, bismuth oxide (III), ammonium vanadate, red lead (Pb.sub.3 O.sub.4), titanium yellow, basic lead phosphite, basic lead sulfite, basic lead phosphite sulfite, lead phosphite and lead sulfite. Semiconductor metal oxides such as disclosed in JP-A-49-82340 (e.g. zinc oxide semiconductors and titanium dioxide semiconductors) may also be used. The composite particles may be prepared by the following methods. (1) Dry mixing method: The LB absorber and the colorant each in the form of powder or particle are mixed using a suitable mixer such as a ball mill, an automatic mortar, a hybridizer or a mechano-fusion system. During the mixing, the two kinds of the particles are contacted under pressure or at a high speed with each other so that the colorant particles deposit on or are bound to respective LB absorber particles. If desired, a liquid binder such as a silicone may be incorporated into the admixture of the LB absorber and the colorant to strengthen the bonding between therebetween. In this case, the amount of the binder is not greater than 10% by weight based on the weight of the LB absorber. (2) Wet mixing method: The LB absorber in the form of particles is mixed with a dispersion or solution of the colorant in a suitable solvent or a medium. After thorough mixing, the mixture is dried by evaporation of the liquid medium. If desired a binder may be incorporated into the solution or dispersion in an amount of not greater than 10% by weight based on the weight of the LB absorber. (3) Precipitation method: A solution of a precursor of the colorant is reacted in the presence of the LB absorber in the form of particles to precipitate the resulting colorant and to allow the precipitates to deposit on respective LB absorber particles. The reaction of the precursor may be, for example, neutralization, hydrolysis or decomposition. (4) Coprecipitation method: The LB absorber and the colorant are co-precipitated and the resulting precipitates are dried and, if necessary, calcined and pulverized. (5) Sintering method: A mixture of the LB absorber and the colorant each in the form of powder or particles is sintered at such a temperature that the colorant is not discolored. The resulting sintered mass is then pulverized. The sintering is generally performed at a temperature of 1,100.degree.-1,300.degree. C. for 1-3 hours. Preferably the temperature is gradually increased to the sintering temperature at a rate of 5.degree.-10.degree. C./minute. This method is preferably adopted when the colorant used is not discolored at the sintering temperature. (6) Spray-drying method: The LB absorber in the form of particles is dispersed in a solvent solution of the colorant. The dispersion is sprayed in a hot atmosphere to rapidly evaporate the solvent so that the colorant deposit on the particles of the LB absorber. The above composite particles are used as a coloring material to be mixed with the resin for the formation of the laser beam absorbing resin composition according to the present invention. The resin may be a thermoplastic resin or a thermosetting resin. Examples of suitable thermoplastic resins include polyolefin resins, polyvinyl chloride resins, styrene resins, polyamide resins, polyester resins, polycarbonate resins, acrylic resins, polyimide resins and polysulfone resins. Examples of suitable thermosetting resins include epoxy resins, phenol resins, bismaleimide resins, unsaturated polyester resins and urethane resins. A light sensitive resin such as of a photo decomposition type, a photo dimerization type, a photo polymerization type, or a photo curing type may also be used. The composite particles are used in an amount of 1-100 parts by weight, preferably 2-50 parts by weight, more preferably 5-30 parts by weight, per 100 parts by weight of the resin. The laser beam absorbing resin composition of this invention is in the form of powder or liquid (dispersion) and is used for forming a shaped body. The term shaped body used herein is intended to refer to a plate, a film, a pipe, a block, a coating or the like molded article or a composite article using these materials. Coatings, casings or packages for electric or electronic parts, such as condensers, resistors, diodes, IC, are typical examples of the shaped bodies. Various known methods may be used for the preparation of the shaped bodies, such as transfer molding, injection molding, press molding, casting, dipping, fluidized powder coating, electrostatic spray coating, spray coating and brush coating. The coating may be applied onto any desired surface such as of a metal, a ceramic, a plastic material, paper or wood. Various additives may be incorporated into the laser beam absorbing resin composition. Examples of such additives include an auxiliary colorant which may be inert to a laser beam (e.g. ferric oxide) or may be discolored by irradiation with a laser beam; a filler which may be an inorganic or organic one; a thixotropic agent; a flame retardant such as hexabromobenzene, antimony trioxide or tetrabromobisphenol A; a coupling agent such as of a zirocoaluminum type, a silane type or a titanium type; a leveling agent such as an acrylic acid ester oligomer; a rubber such as carboxy-terminated butadiene acrylonitrile copolymer rubbers and nitrile-butadiene rubbers; a curing agent; a curing accelerator; a photopolykerization initiator; and a photopolymerization catalyst. The auxiliary colorant is generally used in an amount of 0.01-100 parts by weight, preferably 0.1-50 parts by weight, per 100 parts by weight of the resin. Examples of fillers include alumina, silica, magnesia, antimony trioxide, calcium carbonate, magnesium carbonate, mica, clay and sepiolite. The filler is generally used in an amount of 1-500 parts by weight, preferably 50-300 parts by weight, per 100 parts by weight of the resin. Examples of thixotropic agents include (a) silica or alumina having an average particle size of 0.1 .mu.m or less or (b) aluminum hydroxide, fibrous magnesium oxysulfate, fibrous silica, fibrous potassium titanate, flake mica or montmorillonite-organic base double salt (bentonite) having an average particle size of 3 .mu.m or less. The thixotropic agent is generally used in an amount of 0.1-100 parts by weight, preferably 1-20 parts by weight, per 100 parts by weight of the resin. The resin to be blended with the composite particles is preferably an epoxy resin such as a diglycidyl ether of bisphenol A, a diglycidyl ether of bisphenol F, a cresol novolak epoxy resin, a phenol novolak epoxy resin, an alkylphenol novolak epoxy resin, an alicyclic epoxy resin, a hydrogenated diglycidyl ether of bisphenol A, a hydrogenated diglycidyl ether of bisphenol AD, a diglycidyl ether of a polyol such as propylene glycol or pentaerythrytol, an epoxy resin obtained by reaction of an aliphatic or aromatic carboxylic acid with epichlorohydrin, an epoxy resin obtained by reaction of an aliphatic or aromatic amine with epichlorohydrin, a heterocyclic epoxy resin, a spiro-ring containing epoxy resin and a resin modified with an epoxy group. These epoxy resins may be used singly or as a mixture of two or more thereof. If desired the above epoxy resin may be used in conjunction with a thermoplastic resin. As a curing agent for the epoxy resin, there may be used, for example, a carboxylic acid, an acid anhydride, an amine, a mercaptane, a polyamide, a boron compound, dicyandiamide or its derivative, a hydrazide, an imidazole compound, a phenol compound, a phenol novolak resin or an amineimide. The curing agent is generally used in an amount of 0.5-1.5 equivalents, preferably 0.7-1.2 equivalents, per one equivalent of epoxy groups of the epoxy resin. The curing agent may be used in combination with a curing accelerator, if desired. Examples of curing accelerators include tertiary amines such as triethylamine, N,N- dimethylbenzylamine, 2,4,6-tris(dimethylaminomethyl)-phenol and N,N-dimethylaniline; imidzole compounds such as 2-methylimidazole and 2-phenylimidazole; triazine salts, cyanoethyl salts and cyanoethyltrimellitic acid salts of imidazole compounds; amides such as dicyandiamide; peroxides; triphenylphosphine; amine adducts; and phenol novolak salt of DBU (1,8-diazabicyclo(5,4,0)undecene-7). The curing accelerator is used in an amount of 0.05-10 parts by weight, preferably 0.1-5 parts by weight per 100 parts by weight of the epoxy resin. Desired marks or patterns such as bar codes or letters having a color clearly discriminative from the background can be marked on the surface of the shaped body formed from the laser beam absorbing resin composition with a laser beam. Suitable laser beam used for marking is that which has a wavelength in an infrared or near infrared radiation region. Carbon dioxide laser beam, helium-neon laser beam, argon laser beam and YAG (yttrium-aluminum-garnet) laser beam are illustrative of suitable laser beams. The use of carbon dioxide laser beam is particularly preferred. Commercially available laser beam generating devices may be suitably used. Such laser beam generating devices generally produces a laser beam with a radiation energy of 2-10 J/cm.sup.2. The irradiation of laser beam is performed for a period of time sufficient to discolor the irradiated surface of the shaped body and is preferably less than 10.sup.-5 second. More particularly, when a surface of a shaped body formed from the laser beam absorbing resin composition is irradiated with a laser beam, the irradiated portion only is heated to a high temperature to cause not only the thermal decomposition of the resin but also the discoloration of the colorant. The thermal decomposition of the resin generally results in the formation of gaseous products so that the resin disappears from the irradiated surfaces. When the laser beam discoloring colorant used is of the above-mentioned type (a) in which discoloration from a first color to a second color is caused by laser beam irradiation, the color of the irradiated surface generally turns from a first, mixed color of the first color and the other ingredients to a second, mixed color of the second color and the other ingredients. When the discoloring colorant is of the type (b) which becomes colorless upon being heated, the color of the laser beam-irradiated surface shows a mixed color of the ingredients other than that colorant. Since the colorant is in contact with the LB absorber, the irradiation with the laser beam cause the colorant to be discolored with a high sensitivity so that clear, high density marks may be instantaneously formed on the irradiated surface. If desired, the composite particles composed of the LB absorber and the colorant may be used for incorporation into an inorganic paint such as a water glass composition. Namely, the composite particles of the present invention may be used with an inorganic binder to form inorganic molded bodies, such as ceramic bodies, whose surface can be marked with a laser beam. |
claims | 1. A shipping container for nuclear fuel assembly, comprising:a base frame;a lid frame includinga plurality of clamps separated from each other and rotatably hinged to the base frame, anda plurality of supports installed apart from each other and coupled perpendicularly to the plurality of clamps. 2. A shipping container for nuclear fuel assembly, the shipping container comprising:a lower container including a cradle;an upper container detachably coupled to the lower container;a base frame coupled to the cradle; anda pair of lid frames installed on opposite long sides of the base frame,wherein each of the lid frames includes,a plurality of clamps separated from each other and rotatably hinged to the base frame; anda plurality of supports installed apart from each other and coupled perpendicularly to the plurality of clamps. 3. The shipping container according to claim 2, further comprising buffers interposed between the lower container and the cradle in order to absorb shocks. 4. The shipping container according to claim 2, further comprising:hinge couplers located at one end of the cradle;hinge pieces located on the base frame so as to correspond to the hinge couplers; andhinge bolts, each of the hinge bolts being configured to couple a corresponding hinge coupler and hinge piece. 5. The shipping container according to claim 2, further comprising press members installed on inner surfaces of the plurality of clamps. 6. The shipping container according to claim 5, wherein each of the press members includes,at least one press plate facing an inner surface of a corresponding clamp, andan adjustment screw coupling the at least one press plate to the corresponding clamp,wherein the plurality of clamps includes a first clamp and a second clamp, and the first clamp has a narrower width than that of the second clamp. 7. The shipping container according to claim 6, further comprising:a first press plate holding recess located in an inner surface of the first clamp and configured to hold the at least one press plate; andat least one second press plate holding recess located in an inner surface of the second clamp and configured to hold the at least one press plate. |
|
046708960 | claims | 1. A radiological installation, comprising: an x-ray source for projecting a short pulsed x-ray beam; a support for an object placed within said beam; at least one adjustable compensating filter, normally placed within said x-ray beam, between said source and said support; said compensating filter partially absorbing both x-rays and visible light; means for receiving x-rays that have passed through said filter and said object and for converting the resulting x-ray image into an electrical television signal; means for storing said television signal; means for displaying said television signal as a visible image; and means for projecting a beam of said visible image through said filter and onto said object so that the visible image of the object precisely overlaps the object. 2. A radiological installation according to claim 1, wherein at any point of said filter, the visible image attenuation is substantially proportional to the attenuation of the X-rays. 3. A radiological installation according to claim 1, further comprising: a means for deflecting the beam of the visible image disposed such that a portion of the volume in which said deflected beam of said visible image is inscribed substantially coincides with a portion of the volume in which the said X-ray beam is inscribed, the filter being situated within this common portion of the volume. 4. A radiological installation according to claim 1, wherein said filter is mounted on a support which is movable between two predetermined positions, wherein the two positions are respectively an adjustment position where the said filter is situated in the eam of the said image and a utilization position where the said filter is situated in the X-ray beam. 5. A radiological installation according to claim 4, wherein said support is integral with a movable patient table, on which said object is placed, and wherein the two predetermined position are defined by a given displacement of the said table. 6. A radiological installation according to claim 4, further comprising: means to output a series of digital data from said receiver; an image memory connected to said receiver; to memorize the series of digital data outputted by said receiver which is representative of a radiological image, wherein said memory is cyclical and of the autonomous reading type and wherein said memory is connected to said visible projection means. 7. A radiological installation according to claim 3, further comprising: means to output a series of digital data, which is representative of a radiological image, an image memory connected to said receiver so as to memorize the series of digital data outputted by said receiver that is representative of a radiological image wherein said memory is of the cyclical and autonomous reading type, and further wherein a video projector having its signal input connected to the output of the said memory is disposed such that the axis of optical projection of said projector is substantially perpendicular to the axis of the X-ray beam; and a mirror interposed, in the volume within which said X-ray beam is inscribed, at 45.degree. with respect to said optical projection axis. 8. A radiological installation according to claim 7, wherein said mirror is fixed in position and is essentially radiotransparent. 9. A radiological installation according to claim 7, wherein said mirror is movably mounted so as to be removable from the volume within which said X-ray beam is inscribed. 10. A radiological installation according to claim 1, wherein said compensating filter is made of a partially visible light absorbing plastic material. 11. A radiological installation according to claim 10, wherein said compensating filter is made of colored plastic material containing lead. 12. A radiological installation according to claim 2, further comprising for deflecting the beam of the image, these means being disposed so that a portion of the volume in which said beam of said image is inscribed, substantially coincides with a portion of the volume in which the said X-ray beam is inscribed, the filter being situated within this common portion of the volume. 13. A radiological installation according to claim 2, wherein said filter is mounted on a support which is movable between two predetermined positions, wherein the two positions are respectively an adjustment position where said filter is situated in the beam of the said visible image and a utilization position where said filter is situated in the X-ray beam. |
claims | 1. A control rod for a pressurized water nuclear reactor, comprising:an absorber rod disposed in a sheathing tube, said sheathing tube surrounding said absorber rod in a gas-sealed manner, said absorber rod having a lower section with a circumferential surface;said absorber rod being formed with at least one recess in said lower section occupying at most only a part of said circumferential surface, to define a free space within said sheathing tube, said at least one recess being a longitudinal groove running on an outer peripheral surface in an axial direction of said absorber rod, said circumferential surface having a surface area adjoining said groove, said surface area of said circumferential surface being spaced from said sheathing tube for defining a gap between said surface area and said sheathing tube. 2. The control rod according to claim 1, which further comprises a noble gas filling the control rod with a filling pressure, measured at room temperature, greater than 1.5 bar. |
|
054811171 | abstract | A shipping container is provided for a hexagonal nuclear fuel assembly including a top nozzle having a top end, an outer barrel, an external shoulder, and an inner barrel; a plurality of grids which support fuel rods; and a bottom nozzle having an internal shoulder within a recess, a spherical taper, and a bottom end. The container may include a housing, a support for the fuel assembly, a top nozzle holder secured to the support, plural grid supports secured to the support, plural clamping frames for clamping the grids, plural guide plates for guiding the fuel assembly between adjacent grid supports, and a bottom nozzle holder secured to the support. The top nozzle holder may include a shoulder holder for holding the external shoulder, an end holder for enclosing and holding the top end, and a shoulder clamp for clamping the shoulder holder to the support. The shoulder holder may include a resilient split ring for positioning around the inner barrel and a resilient split support for encasing the resilient split ring. The grid supports may each include two wedges for supporting two sides of the grid, a base plate for fixedly supporting the two wedges thereto, a bearing pad fixedly mounted to the support for slidably supporting the base plate, and shoulder screws for limiting a sliding motion of the base plate on the bearing pad. The guide plates may have a guide side and two surfaces for guiding the two sides of the grids. |
048200581 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also, in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown an overall combination of a fuel assembly, generally designated by the numeral 10, an upper core support plate 12 disposed above and extending across the top of fuel assembly 10, and a spider assembly 14 disposed above the upper core support plate. Each of these components will be described and discussed separately. The fuel assembly 10, being shown in a vertically foreshortened form in FIG. 1, basically includes a lower end structure or bottom nozzle 16 for supporting the assembly on a lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 18 which project upwardly from the bottom nozzle 16. The assembly 10 further includes a plurality of transverse grids 20 axially spaced along the guide thimbles 18 and an organized array of elongated fuel rods 22 transversely spaced and supported by the grids 20. Finally, the assembly 10 has an instrumentation tube 24 located in the center thereof and an upper end structure or top nozzle 26 attached to the upper ends of the guide thimbles 18. With such arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. Since the fuel assembly 10 does not form a part of the present invention and is merely for illustrational purposes, any further description thereof is unnecessary and thus will not be given. For a more detailed description of the fuel assembly 10, reference should be made to the pending patent application of Robert K. Gjertsen et al, entitled "Nuclear Reactor Fuel Assembly with Improved Top Nozzle and Hold Down Means"; filed Oct. 17, 1983; and assigned U.S. Ser. No. 542,625. The upper core support plate 12, being conventional, extends across the top of the fuel assembly 10 as well as across the top of other identical fuel assemblies (not shown) arranged within the core. For the sake of brevity, it should suffice to say that the core plate 12 has a multiplicity of flow openings 28 (only one of which is seen in FIG. 1) to allow coolant to pass upwardly through the core, and that at least some of these openings are aligned over the guide thimbles 18 such that control rods 30 can pass down through the core plate 12 and be inserted into the guide thimbles 18 of the fuel assembly 10. Connected to the upper ends of the control rods 30 is the spider assembly 14 which supports the rods for vertical movement within the guide thimbles 18 by a conventional drive mechanism (not shown). In the illustrated embodiment, the spider assembly 14 is disposed above the core plate 12 and is restably supported thereon when the control rods 30 are fully inserted in the guide thimbles 18 as seen in FIG. 1. In other arrangements, the spider assembly is located between the bottom of the upper core plate and the top of the fuel assembly. As best seen in FIGS. 2 and 3, the spider assembly 14 basically includes a central hub 32, a plurality of vanes 34 radially extending outwardly from the hub 32, and a plurality of fingers 36 associated with the vanes 34 for connection with the upper ends of the control rods 30. The central hub 32 is preferably in the form of an elongated cylindrical tube having on its upper end an internally threaded segment 40 for connection with the drive mechanism (not shown) which vertically raises and lowers the spider assembly 14 and the control rods 30 therewith in a conventional manner. The tubular hub 32 houses a common load absorbing mechanism which includes a coil spring 42 held in a state of compression and a nipple 44 which seats in a shallow cavity (not shown) provided in the top surface of the core plate 12 to assist in proper alignment of the control rods 30 within the core plate openings 28 and the guide thimbles 18. As is well known, the primary purpose of such a load absorbing mechanism is to prevent shock loading of the core plate 12, as well as the fuel assembly 10, as the spider assembly 14 abuts the top of the core plate 12 when the control rods 30 are fully inserted in the guide thimbles 18. As seen in FIG. 3, each control rod 30 is supported by one of the elongated fingers 36 of the spider assembly 14. The lower end 46 of each finger 36 is drilled and internally threaded for connection with the upper end 48 of one control rod 30. Each control rod 30 includes an elongated tubular cladding member 50 and an end plug 52 having the stabilizing configuration of the present invention attached to the lower end of the cladding member. The end plug 52 of the control rod 30 is solid and imperforate to coolant flow through the end plug and into the cladding member 50. In some control rod designs, a plurality of pellets of neutron absorbing material are arranged in an end-to-end stack within the cladding member 50. In other control rod designs, the pellets are of a material which does not absorb neutrons (water displacer rods) and the control of the reactor is achieved by the displacement of the water moderator as described in the above-mentioned U.S. Pat. No. 4,432,934. As mentioned earlier, the power level of the reactor is usually regulated by the insertion and withdrawal of the control rods 30 into and from the guide thimbles 18. The control rods 30 are fully inserted during reactor shutdown, and some are withdrawn when the reactor is operating at full power. However, even in their withdrawn positions such as seen in FIG. 5, the control rods 30 still extend into the upper ends of the guide thimbles 18 a short distance, such as six inches or so. When the control rods 30 are fully inserted into the guide thimbles 18, and thus within the reactor core (not shown), they will generate heat. Provision is made for cooling the control rods to prevent the pellets therein from melting. Typically, the lower portions of the guide thimbles have openings (not shown) whereby some of the pumped coolant entering the bottom of the fuel assembly 10 is diverted into the thimbles 18 and flows upwardly therein over the control rods 30. As previously mentioned, particularly when the control rods 30 are in their withdrawn positions the flow of water upwardly through the thimbles 18 past the partially inserted control rods induces vibratory motion in the lower ends of the rods which, absent the stabilizing configuration of the present invention, produces vibratory contact of their end plugs 52 with the internal walls 58 of the thimbles 18. Control Rod End Plug With Stabilizing Configuration Referring now to FIGS. 4 and 6 to 8, there is shown a variety of different stabilizing configurations or shapes of a control rod end plug which interact with the coolant to cause it to flow at non-symmetric velocities past the end plug. Such different shapes are all designed to produce generally similar non-symmetric flow velocity patterns which impose a lateral steady-state force against the control rod at its end plug that reduces vibratory motion and contact of the control rods with the internal walls 58 of the respective guide thimbles 18. Instead, the force F presses or biases the control rod 30 against the internal wall 58 of the thimble 18, as seen in FIG. 5. As mentioned above, several asymmetric end plug designs can be used to achieve a desired pattern of non-symmetric coolant flow velocities around the tip of the end plug. These alternate designs will now be described. FIG. 4 depicts a first asymmetric design of the end plug 52. The end plug 52 has the normal, generally conical or tapered outer surface 60, except for a flat 62 formed, such as by machining, on one side of the otherwise axially symmetrical outer surface. The original profile of the surface which the flat 62 replaces is shown in broken line form in FIG. 4. The flat 62 begins in the cylindrical body 64 of the end plug 52 adjacent the beginning of the lower tip 66 and extends down the tip 66, crossing the central axis 68 of the end plug 52 and forming a terminal end 70 on the opposite side of the axis 68. FIGS. 4a to 4c provide comparative cross sectional views of the end plug 52 which allow one to form a more complete three-dimensional mental image of the stabilizing configuration of the end plug. The end plugs 52 of FIGS. 3 and 5 have the stabilizing configuration of FIG. 4. FIG. 6 illustrates a second asymmetrical design of an end plug 72 wherein a pair of flats 74,76 are formed on opposite edges of the tapered outer surface 78. Again, the original configuration of the lower tip 80 of the plug 72 is shown in broken line form. The left flat 74 is substantially identical to the flat 62 of the FIG. 4 design in that it crosses the axis 82 with the other flat 76 on the opposite side of the axis. The right flat 76 begins higher on the end plug cylindrical body 86 than the left flat 74 and thus forms a shallower angle with the axis 82 than the angle formed therewith by the left flat 74. Again, FIGS. 6a to 6c provide a sequence of cross sectional views of the end plug 72 which enhances one's ability to form a three-dimensional image of the plug. FIG. 7 represents a third asymmetrical design of an end plug 88 wherein the original symmetrically tapered configuration of the plug tip, as shown in dash line form, has been reduced down, such as by machining, into a tip 90 having a steeper and more pointed conical configuration. The tip 90 has an axis 92 which intersects the central axis 94 of the end plug 88 and forms a terminal end 96 offset to one side of the axis 94. The cross sectional views in FIGS. 7a to 7c clearly depict the conical form of the tip 90. Finally, FIG. 8 illustrates a fourth asymmetrical design of an end plug 98 having a concave surface 100 formed on a side of the tapered outer surface 102 of the plug. The concave surface 100 begins in the cylindrical body 104, crosses the central axis 106 of the end plug 98 and forms a lower terminal end 108 on the tip 110 on the opposite side of the axis 106. A clear understanding of the three-dimensional configuration of the end plug 88 may be gained from a review of the cross sectional sequence of views in FIGS. 8a to 8c. A common feature of each of these asymmetrical tip designs of FIGS. 4 and 6 to 8 is that the terminal tip ends 70, 84, 96 and 108 thereof are all offset to the right of the respective central axes 68, 82, 94 and 106 of the end plugs 52, 72, 88 and 98. This ensures that the lateral force imposed on each of the end plugs by the non-symmetric coolant flow velocity patterns is imparted from the left side of the axis. Also, each of the asymmetrical end plug shapes reduces the possibility of flow-induced vibration such as caused by vortex shedding in the symmetrical designs heretofore. Thus, all of the asymmetrical end plug stabilizing configurations perform the same functions in an advantageous manner; however, some of the geometric arrangements may be more suitable from a manufacturing standpoint than others. It is thought that the end plug stabilizing configurations of the present invention and many of their attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of their material advantages, the forms hereinbefore described being merely a preferred or exemplary embodiments thereof. |
claims | 1. A nuclear fuel assembly including:a plurality of elongated nuclear fuel rods having an extended axial length;at least a lowermost grid supporting said fuel rods in an organized array and having unoccupied spaces defined therein adapted to allow flow of fluid coolant therethrough and past said fuel rods when said fuel assembly is installed in a nuclear reactor;a plurality of guide thimbles extending along said fuel rods through and supporting said grid;a bottom nozzle disposed below said grid, below lower ends of said fuel rods, supporting said guide thimbles and having openings therethrough to allow the flow of fluid coolant into said fuel assembly, the bottom nozzle comprising:a substantially horizontal plate, orthogonal to the axis of the fuel rods, having an upper face directed substantially toward the lowermost grid and a lower face on an underside of said horizontal plate with said openings extending therethrough for the flow of coolant, at least some of said openings in at least one of either the upper face or the lower face having a funnel-like first appendage respectively extending above the upper face or below the lower face, as the case may be, around at least some of the openings in the one of the upper face or the lower face with an opening at the first appendage's substantially highest extent, in the case of the upper face or lowest extent, in the case of the lower face, having a larger diameter than a diameter of the opening in the one of the upper face or the lower face, an internal wall of the first appendage substantially gradually decreasing in diameter from the opening at the first appendage's substantially highest extent in the case of the upper face or substantially lowest extent in the case of the lower face, until the wall of the first appendage transitions to the opening in the upper face or lower face, as the case may be and wherein a lip of at least some of the openings at the first appendage's substantially highest extent in the case of the upper face or lowest extent in the case of the lower face, has a scalloped contour. 2. The nuclear fuel assembly of claim 1 wherein the scalloped lip has four substantially equally spaced depressions, resembling the contour of an egg receptacle in an egg carton. 3. The nuclear fuel assembly of claim 1 wherein the substantially horizontal plate has a plurality of such openings extending therethrough and substantially all of the lips of the openings at the first appendages' substantially highest extents in the case of the upper face or lowest extents in the case of the lower face, have a scalloped contour. 4. The nuclear fuel assembly of claim 1 including a funnel-like second appendage extending outwardly from at least some of the openings in another of the upper face or the lower face with an opening at the second appendages' substantially highest extent in the case of the upper face or lowest extent in the case of the lower face, having a larger diameter than a diameter of the opening in the another of the upper face or the lower face, an internal wall of the second appendage substantially gradually decreases in diameter from the opening at the second appendages' substantially highest extent in the case of the upper face or lowest extent in the case of the lower face until the wall of the second appendage transitions to the opening in the another of the upper face or the lower face. 5. The nuclear fuel assembly of claim 4 wherein a lip of at least some of the openings at the second appendages' substantially highest extent in the case of the upper face or lowest extent in the case of the lower face, has a scalloped contour. 6. The nuclear fuel assembly of claim 5 wherein the scalloped lip has four substantially equally spaced depressions resembling the contour of an egg receptacle in an egg carton. 7. The nuclear fuel assembly of claim 6 wherein the appendage to the upper face is at least partially recessed within a corresponding one of the openings in the upper face. 8. The nuclear fuel assembly of claim 4 wherein substantially all of the lips of the appendages' substantially highest extent, on the upper face have a scalloped contour. 9. The nuclear fuel assembly of claim 4 wherein the appendages to the upper face terminate below the lower ends of the fuel rods. 10. The nuclear fuel assembly of claim 9 wherein the highest extent of the appendages to the upper face is smaller than the lowest extent of the appendages to the lower face. 11. The nuclear fuel assembly of claim 1 wherein at least some of the openings in the bottom nozzle substantially align with the unoccupied spaces in the lowermost grid. 12. A nuclear fuel assembly including:a plurality of elongated nuclear fuel rods having an extended axial length;at least a lowermost grid supporting said fuel rods in an organized array and having unoccupied spaces defined therein adapted to allow flow of fluid coolant therethrough and past said fuel rods when said fuel assembly is installed in a nuclear reactor;a plurality of guide thimbles extending along said fuel rods through and supporting said grid;a bottom nozzle disposed below said grid, below lower ends of said fuel rods, supporting said guide thimbles and having openings therethrough to allow the flow of fluid coolant into said fuel assembly, the bottom nozzle comprising:a substantially horizontal plate, orthogonal to the axis of the fuel rods, having an upper face directed substantially toward the lower most grid and a lower face on an underside of said horizontal plate with said openings extending therethrough for the flow of coolant, at least some of said openings in at least one of either the upper face or the lower face having a funnel-like first appendage respectively extending above the upper face or below the lower face, as the case may be, around at least some of the openings in the at least one of the upper face or the lower face with an opening at the first appendage's substantially highest extent, in the case of the upper face or lowest extent, in the case of the lower face, having a larger diameter than a diameter of the opening in the at least one of the upper face the lower face, an internal wall of the first appendage substantially gradually decreasing the lateral flow area axially through the first appendage as the first appendage transitions from the opening at the first appendage's substantially highest extent, in the case of the upper face or lowest extent, in the case of the lower face, to the opening in upper face or the lower face, as the case may be, wherein a lip of at least some of the openings at the first appendage's substantially highest extent in the case of the upper face or lowest extent in the case of the lower face, has a scalloped contour. 13. The nuclear fuel assembly of claim 12 including a funnel-like second appendage extending up from at least some of the openings in another of the upper face or the lower face with an opening at the second appendage's substantially highest extent, in the case of the upper face, or lowest extent, in the case of the lower face, having a larger diameter than a diameter of the opening in the another of the upper face or the lower face, an internal wall of the second appendage substantially gradually decreases the lateral flow area axially through the second appendage as the second appendage transitions from the opening at the second appendage's substantially highest extent in the case of the upper face or lowest extent in the case of the lower face to the opening in the another of the upper face or the lower face, as the case may be. 14. The nuclear fuel assembly of claim 13 wherein the appendage to the upper face is at least partially recessed within a corresponding one of the openings in the upper face. 15. The nuclear fuel assembly of claim 1 wherein the openings for the flow of coolant include both first openings that are aligned with the unoccupied spaces in the lowermost grid and additional openings that are aligned with the fuel rods. 16. The nuclear fuel assembly of claim 15 wherein at least some of the additional openings have appendages substantially the same in general design as the first appendage. 17. The nuclear fuel assembly of claim 16 wherein the additional openings respectively have a standoff at a coolant flow exit, with the standoff configured to prevent the fuel rod from closing off the coolant flow exit. 18. The nuclear fuel assembly of claim 17 wherein the highest extend of the appendages to additional openings on the upper face have a scalloped lip forming peaks and valleys wherein the peaks form the standoff. 19. The nuclear fuel assembly of claim 15 wherein the additional openings are smaller in diameter than the openings aligned with the unoccupied spaces. 20. A nuclear fuel assembly including:a plurality of elongated nuclear fuel rods having an extended axial length;at least a lowermost grid supporting said fuel rods in an organized array and having unoccupied spaces defined therein adapted to allow flow of fluid coolant therethrough and past said fuel rods when said fuel assembly is installed in a nuclear reactor;a plurality of guide thimbles extending along said fuel rods through and supporting said grid;a bottom nozzle disposed below said grid, below lower ends of said fuel rods, supporting said guide thimbles and having openings therethrough to allow the flow of fluid coolant into said fuel assembly, the bottom nozzle comprising:a substantially horizontal plate, orthogonal to the axis of the fuel rods, having an upper face directed substantially toward the lowermost grid and a lower face on an underside of said horizontal plate with said openings extending therethrough for the flow of coolant, at least some of said openings positioned in line with a corresponding one of the fuel rods and wherein a lip of at least some of the openings' substantially highest extent in the case of an upper face of the substantially horizontal plate or lowest extent in the case of the lower face of the horizontal plate, has a scalloped contour. 21. The nuclear fuel assembly of claim 20 wherein at least some of the openings are in line with the unoccupied spaces. 22. The nuclear fuel assembly of claim 21 wherein the openings in line with the unoccupied spaces are larger than the openings in line with the fuel rods. |
|
abstract | An x-ray imaging system uses particular emission lines that are optimized for imaging specific metallic structures in a semiconductor integrated circuit structures and optimized for the use with specific optical elements and scintillator materials. Such a system is distinguished from currently-existing x-ray imaging systems that primarily use the integral of all emission lines and the broad Bremstralung radiation. The disclosed system provides favorable imaging characteristics such as ability to enhance the contrast of certain materials in a sample, to use different contrast mechanisms in a single imaging system, and to increase the throughput of the system. |
|
summary | ||
abstract | Provided are an operation support device and an operation support method for a nuclear power plant which are capable of accurately grasping the condition of a nuclear power plant and capable of offering support for instantly performing a predetermined operation by an operator when an unusual situation occurs. The operation support device for a nuclear power plant is provided with an operation state check display unit (20) for displaying whether or not a system or equipment necessary for a safe operation of the entire nuclear power plant operates on the basis of a command signal to the system or equipment and a bypass and operation impossibility state display unit (21) for displaying whether the system or equipment is operable or not. |
|
052873919 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 4, a metering system 10 is shown and comprises a declivitous screen 12 provided by a parallel array of spaced bars 14. A nuclear transport container 16 in an inverted position is arranged to discharge on to the bars 14 relatively large nuclear fuel assembly appendages 20 (see FIG. 2) and relatively small hulls 22 in the form of sheared short lengths of nuclear fuel cladding tubes (see FIG. 3). The appendages 20 are wider than the spaces between the bars 14, and discharge into a receptacle provided by a tiltable trough 26. A deflector chute 28 below trough 26 guides the appendages 20 from the trough 26 in a lowered position (shown in broken line) into a secondary tiltable trough 30. In a lowered position (shown in broken line) the secondary trough 30 discharges into a delivery chute 32 which delivers the appendages 20 into a drum 34. The hulls 22 fall between the bars 14 into a hopper 40 having a lower discharge port 42. A discharge chute 44 from the discharge port 42 discharges hulls 22 from the hopper 40 through a maintenance shut-off valve 41. A feeder trough 46 of hemi-frusto-conical form having an included conical angle of about 12.degree. is disposed under the discharge chute 44, and is inclined downwardly at about 121/2.degree. towards its wider discharge end 48. The feeder trough 46 is capable of angularly oscillating around its longitudinal axis at an angle of about 30.degree. either side of a mean position and at a frequency of about 15 oscillations per minute. A positioning chute 50 is located below the discharge end 48 to direct and position hulls 22 from the feeder trough 46 through a flap valve 52 on to the delivery chute 32. Two ultrasonic probes 54a, 54b are positioned to detect levels of the appendages 20 and the hulls 22 at different positions in the drum 34, whilst two capacitance probes 56 (only one is shown) at the entry of the drum 34 monitor for overfilling of the drum 34. Two other ultrasonic probes 58a, 58b monitor the level of the hulls 22 at respective ends of the hopper 40. Operation of each element of the sytem 10 is initiated by an operator. Then whilst the feeder trough 46 is oscillating, the hulls 22 are gravity fed from the hopper 40 through the discharge chute 44 on to the feeder trough 46. A restricted number of hulls 22 fall from the discharge end 48 of the feeder trough 46 into the positioning chute 50 from which they are directed on to the delivery chute 32 and hence in to the drum 34. Initially a buffer layer of hulls 22 is fed into the drum 34. Subsequently a layer of appendages 20 is formed in the drum 34, the remaining space in the drum 34 then being filled with hulls 22. Although the system 10 has been shown as being fully under manual control, interlocks are provided (not shown) to ensure that the correct sequence of operation of the elements of the system 10 can only be initiated, and that overfilling of the drum 34 is prevented. Although the system 10 has been described as being manually initiated, it should be possible to interrelate the elements of the system 10 through a control unit so as to automate the operations of the system 10. It will be understood that although the invention has been described in relation to the separate metering of appendages and hulls, other components of nuclear fuel assemblies or the like may be similarly separated by the system and fed into a suitable container or receptacle. To assist maintenance and replacement of defective elements, the system 10 is desirably of modular form. |
abstract | In one embodiment, a charged particle beam writing method includes writing a first pattern statically in central part of a first substrate having Charge Dissipation Layer (CDL), calculating, based on a position of the written first pattern, a first correction coefficient, writing a second pattern statically applying with the first correction coefficient in central part of a second substrate having no CDL, calculating, based on a position of the written second pattern, a second correction coefficient, writing a third pattern continuously applying with the first correction coefficient in central part of a third substrate having CDL, calculating, based on a position of the written third pattern, a third correction coefficient, writing a fourth pattern statically applying with the first correction coefficient in wide range of a fourth substrate having CDL, and calculating, based on a position of the written fourth pattern, a fourth correction coefficient. |
|
051587416 | summary | FIELD OF THE INVENTION This invention relates to an improvement in passive cooling systems for a unique type of liquid metal cooled nuclear reactors having the heat producing core of fissionable fuel substantially submerged within a pool of the liquid metal. A typical liquid metal cooled nuclear reactor is disclosed in U.S. Letters Pat. No. 4,508,677, issued Apr. 2, 1985, and a typical passive cooling system for such liquid metal cooled nuclear reactors is disclosed in U.S. Letters Pat. No. 4,678,626, issued Dec. 2, 1985, and No. 4,959,193, issued Sept. 25, 1990. BACKGROUND OF THE INVENTION To deal with emergencies or perform maintenance service in the operation of liquid sodium or sodium-potassium metal cooled nuclear reactors for power generation it may be necessary to shut down the fission reaction of the fuel. Normally reactor shut down is achieved by inserting neutron absorbing controls into the core of fissioning fuel material to deprive the fuel material of neutrons needed to perpetuate the fission reaction. However decay of the fuel material in the shut down nuclear reactor continues to produce heat in substantial quantities which must be continuously dissipated from the reactor system. The heat capacity of the liquid metal coolant and adjacent structural material assist in dissipating the residual heat. Nevertheless, the structural material of the nuclear reactor may not have the capacity of safely withstanding prolonged high temperatures. For example, the concrete of the walls of the typical reactor silo and other structures may splay and crack when subjected to high or prolonged raised temperatures. Accordingly, auxiliary cooling means or systems are commonly utilized to safely remove heat from the nuclear reactor structure during periods of reactor shut down. Conventional nuclear reactors have employed a variety of complex energy driven cooling measures to dissipate heat from the fuel core and other components of the reactor system. Occasionally when a reactor shut down occurs, the energy source for actuating and/or operating such auxiliary cooling means may fail. For example, pumps and ventilation systems for performing supplementary fuel core cooling may malfunction or lack power. Moreover, when operator personnel intervention is needed, there are potential situations when an operator may not be responsive or be capable of performing the required action. Liquid metal cooled reactors utilizing sodium or sodium-potassium as the coolant provides numerous advantages. Water cooled reactors operate at or near the boiling point of water. Any significant rise in temperature results in the generation of steam and increased pressure. By contrast, sodium or sodium-potassium has an extremely high boiling point, in the range of 1800 degrees Fahrenheit at one atmosphere pressure. The normal operating temperature of the reactor is in the range of about 900 degrees Fahrenheit. Because of the high boiling point of the liquid metal, the pressure problems associated with water cooled reactors and the steam generated thereby are eliminated. The heat capacity of the liquid metal permits the sodium or sodiumpotassium to be heated several hundred degrees Fahrenheit without danger of materials failure in the reactor. The reactor vessels for pool-type liquid-metal cooled reactors are essentially open top cylindrical tanks without any perforations to interrupt the integrity of the vessel walls. Sealing of side and bottom walls is essential to prevent the leakage of liquid metal from the primary vessel. The vessel outer surfaces must also be accessible for the rigorous inspections required by safety considerations. Upon shutdown of the reactor by fully inserting the control rods, residual heat continues to be produced and dissipated according to the heat capacity of the plant. Assuming that the reactor has been at full power for a long period of time, during the first hour following shutdown, an average of about 2% of full power continues to be generated. The residual heat produced continues to decay with time. To maximize the power capacity in liquid metal cooled, pool type nuclear fission reactor plants, such as noted above and disclosed in the cited patents, it has been proposed to locate the reactor coolant circulating pump and primary heat exchanging units outside of the reactor vessel pool. This system enables the utilization of a larger heat producing fuel core within the reactor vessel, or a reduction in the size of the reactor vessel, which returns certain benefits. Liquid metal cooled pool nuclear reactors of this type comprise multiple component vessels, including the fuel containing reactor primary vessel, assembled with external satellites of one or more circulating pump units and heat exchanger units, operatively connected by top entry loops or conduits for coolant circulation in series between each separate component vessel. This top entry loop joined, "satellite" assembly reactor system comprises a reactor primary vessel containing a core of fissionable fuel submerged in liquid metal coolant and at least one primary heat transferring liquid metal coolant circuit or loop including a coolant circulating pump component housed within a separate vessel and a heat exchanger component housed within another separate vessel. Top entry loop conduits connect each component vessel in series to provide for liquid metal coolant circulation from the fuel core containing reactor vessel to the pump vessel, then to the heat exchanger vessel and finally back into the reactor vessel to repeat the cycle continuously during operation for transferring fuel core produced heat to the heat exchanges. This type of top entry loop, multiple component and vessel, satellite reactor system is illustrated in an article entitled "Cost Reduction Study Of A 1000MWe Loop-Type Demonstration Fast Breeder Reactor" by H. Nakagawa et al, published in the Proceedings of the International Conference On Fast Breeder Systems: Experience Gained and Path to Economic Power Generation. Sept. 13-17, 1987, pages 4.10-1 to 4.10-11. Liquid metal cooled pool reactors of such a satellite arrangement comprise open top unit vessels which are closed and protected by means of a shield deck which extends across the open upper end of the reactor vessel and any associated units contained in vessels. Commonly a single shield deck structure bridges the entire expanse of the upper end of the complete assembly of vessels of the satellite system, and may include extending over the open top of the concrete silo. The invention comprises an improvement in a passive cooling means for removing shutdown decay heat from top entry loop liquid metal coolant, pool nuclear reactor plants. The disclosed contents of the above noted U.S. Pat. Nos. 4,508,677, 4,678,626, and 4,959,193, and the cited article, all comprising background art, are incorporated herein by reference. SUMMARY OF THE INVENTION This invention comprises an improved shutdown, passive heat removal system for top entry loop, liquid metal cooled, pool nuclear reactors which transfers reactor fuel core decay and sensible heat from the reactor fuel core and liquid metal coolant by means of the inherent thermal energy transfer mechanisms of conduction, radiation, convection and material convection of fluids out to the ambient atmosphere. The improved system of the invention is entirely passive and operates continuously through the inherent phenomenon of natural convection in fluids, conduction, convection and thermal radiation. In the event of a reactor shutdown, after the control rods are fully inserted into the fuel core, the heat produced by the fuel core is transferred by the coolant to the primary reactor and adjoining satellite vessel walls and across the gas filled space between the reactor and containment vessels of each satellite component primarily by thermal radiation, with a small fraction of heat transferred by conduction and convection of the enclosed gas. Surfaces of high thermal emissivity provided on the outside of the reactor and satellite vessels and the interior of the containment vessels increased the efficiency of heat transfer. Heat is then removed from the outside surface of the containment vessels partly by thermal radiation and partly by direct convection to a flowing air passing over the containment vessel surface. The heat energy is then carried to the outside atmosphere by means of natural convection flow of the heated air. OBJECTS OF THE INVENTION It is a primary object of this invention to provide a passive cooling system for top entry loop, liquid metal cooled pool nuclear reactors for removal of decay and sensible heat. It is another object of this invention to provide a heat removing system for top entry loop, liquid metal cooled pool nuclear reactors which is entirely passive and operates continuously by the inherent phenomenon of natural convection is fluids, conduction, convection, and thermal radiation. It is a further object of this invention to provide an improved passive cooling system and structural means to operate the same for top entry loop, liquid metal cooled pool nuclear reactors having a covering deck for removing decay and sensible heat from the reactor core and providing support and reinforcement for the covering deck. It is also an object of this invention to provide a liquid metal cooled pool type nuclear fission reactor having a satellite assembly of component vessels connected in series with top entry loops with an inherently passive cooling system for removing decay produced heat from the fuel core of the reactor and related components. It is a still further object of this invention to provide a passive shutdown heat removal system comprising natural circulation of cooling air past and about the several separate component vessels of a satellite assembly liquid metal coolant loop type nuclear reactor having top entry loop connecting the component vessels. |
description | An example of a reflective illumination shaping device 10 is shown generally in FIG. 1. Although the illumination shaping device 10 is particularly well suited for off-axis step-and-scan microlithography, or the like, persons of ordinary skill in the art will readily appreciate that the teachings of the instant invention are not limited to any particular type of microlithography or microchip manufacturing illumination exposure process. On the contrary, the teachings of the invention can be employed with virtually any optical system where shaping the illumination pattern is desired. Thus, although the illumination shaping device 10 will be described below primarily in relation to off-axis lithographic microchip manufacturing using EUVL or deep ultraviolet lithography, persons of ordinary skill in the art will readily appreciate that the apparatus and method could likewise be used with any type of lithography methods, illumination system, exposure system, etc. Generally, the illumination shaping device 10 includes reflecting objectives 12, 14. In the illustrated example, the reflecting objectives 12, 14 are paraboloid sections depicted in FIG. 1 as finite half-parabola cross-sections having similar or identical curvatures. That is, the paraboloid sections of the reflecting objectives 12, 14 are the same, though, as discussed further below, the paraboloid sections of the reflecting objectives 12, 14 may differ depending on the desired illumination pattern. For the sake of clarity in explanation, the input reflecting objective 12 will be referred to herein as an input reflecting objective 12, and the output reflecting objective 14 will be referred to herein as an output reflecting objective 14. However, this terminology is merely for the sake of distinguishing each reflecting objective 12, 14, and is not intended to necessarily be descriptive of these reflecting objectives 12, 14 and should not be construed as a limitation on the scope of the claims. Furthermore, the depiction of the reflecting objectives 12, 14 as having a half-parabola cross-section is not necessarily reflective of all examples of the illumination shaping device 10, as will be seen further below, but nevertheless is helpful to illustrative of how the illumination shaping device 10 alters the illumination pattern of light, the principles of which hold true for all examples of the illumination shaping device 10. Each reflecting objective 12, 14 further includes a reflective surface 16, 18 respectively. The reflective surfaces 16, 18 are generally coated to optimally reflect illumination used with deep ultraviolet lithography or EUVL. In particular, the reflective surfaces 16, 18 are manufactured or coated so as to reflect wavelengths below 248 nanometers, and more particularly the reflective surfaces 16, 18 reflect wavelengths in the range of 8-248 nanometers, and even more particularly the reflective surfaces 16, 18 reflect wavelengths at 248 nanometers, 193 nanometers, 157 nanometers and/or 13 nanometers. While those of ordinary skill in the art will readily understand that the materials used to manufacture or coat the reflective surfaces 16, 18 may vary depending on the wavelength being utilized, examples of some coatings include fused silicon impregnated with fluorine, calcium fluoride and molybdenum. Further, those of ordinary skill in the art will appreciate that the coating of any reflective surfaces used in lithography, especially deep ultraviolet lithography and EUVL, may require several coatings and should be nearly perfect in order to achieve a proper image on the substrate wafer. The specific methods of manufacture for coating reflective surfaces 16, 18 used with deep ultraviolet lithography and EUVL are also well known to those of ordinary skill in the art and, thus, will not be described further herein. As with the reflecting objectives 12, 14, the reflective surface 16 will be referred to herein as the input reflective surface 16, and the reflective surface 18 will be referred to herein as the output reflective surface 18, though, as above, this is merely for the sake of clarity of explanation and should not be construed as a limitation. Each reflecting objective 12, 14 further includes a focal point 20 for each paraboloid section. While each reflecting objective 12, 14 has independent focal points, the focal points 20 are coaligned so as to occupy the same point in space. In other words, the corresponding paraboloid sections of the reflecting objectives 12, 14 can be considered to share the same focal point 20. The reflecting objectives 12, 14 also each have principal axes 22 passing through the focal points 20 that may run parallel to, though off the axis of, the optical axis 24 of the lithography system. In the example of FIG. 1, the principal axes 22 of both the reflecting objectives 12, 14 are coaxial, though this may not always be the case depending on the desired illumination pattern, as described further below. In operation, input light 26 is incident upon an input end 28 of the output reflecting objective 14. Generally, input light 26 for lithography will be collimated and on-axis with the optical axis 24. Further, the input light 26 generally has a conventional illumination mode centered on the optical axis 24. That is, the input illumination pattern is generally monopole in a circular or elliptical pattern. The input reflecting objective 12 is centered on the optical axis 24 so as to uniformly, evenly and symmetrically receive the input light 26 on the input reflective surface 16. Those of ordinary skill in the art will readily understand that the illumination pattern of the input light 26 may not be perfectly circular or elliptical considering optical alignment is one of degree and approximation. The input reflective surface 16 reflects the input light 26 to the output reflective surface 18 of the output reflecting objective 14. The output reflective surface 18, in turn, reflects the input light 26 through an output end 30 of the output reflecting objective 14 as output light 32. The output light 32 has an illumination pattern off the optical axis (i.e., off-axis) in an annular or multipole pattern depending on the configuration of the reflecting objectives 12, 14. The output reflecting objective 14 is also centered about the optical axis 24 thereby causing the illumination pattern of the output light 32 to be symmetrical about the optical axis In order to avoid stray reflections and maintain the cohesion of the illumination pattern of the output light 32 as it is incident on the design pattern, surfaces 34, 36 opposite the reflective surfaces 16, 18 may be non-reflective surfaces designed to absorb the illumination wavelength so as to avoid unintended scattering of the input light 26 and the output light 32. Coatings and techniques for absorbing light are well known to those of ordinary skill in the art, the choice of which may depend on the illumination wavelength. The formation of an off-axis, annular or multipole illumination pattern from an on-axis, monopole illumination pattern using the illumination shaping device 10 may be better understood via the ray diagram of FIG. 2. As shown in FIG. 2, the input light 26 from an illumination source (not shown) is reflected from the input reflective surface 16 of the input reflecting objective 12 onto the output reflective surface 18 of the output reflecting objective 14. The input light 26 reflects off the output reflective surface 18 of the output reflecting objective 14 and through the output end 30. It is a principle of geometric optics that incident light which is collimated and co-propagates parallel to the principal axis of a paraboloidal mirror will always pass through the focal point of the paraboloidal mirror. Therefore, all rays of the input light 26 incident on the reflecting surface 16 of a paraboloid section will pass through the focal point 20. It is also a principal of geometric optics that all incident light passing through the focal point of a paraboloidal mirror, regardless of direction, will be reflected as collimated light. Therefore, all rays of the input light 26 which are reflected off the input reflective surface 16, are further reflected off the output reflective surface 18 as collimated output light 32, because the focal points 20 are shared by both reflective surfaces 16, 18. This allows the output light 32 to have an illumination pattern that is off the axis of the optical axis 24. Assuming the input light 26 is centered on the optical axis 24, the illumination pattern of the output light 32 should have uniform intensity and radial symmetry about the optical axis 24. However, the intensity may be varied across the illumination pattern by variations in the coatings of the reflective surfaces 16, 18. For example, with a multipole illumination pattern, it may be desirable to increase or decrease the intensity in one of the poles in order to correct for any lens aberrations. Therefore, those portions of the reflective surfaces 16, 18 that reflect the light that will form the pole or section having a different intensity may be coated differently than other portions of the reflective surfaces 16, 18. Varying the coating and other methods of adjusting the intensity of light, including input light 26 having non-uniform intensity, are known to those of ordinary skill in the art. As seen in FIGS. 1 and 2, the reflecting objectives 12, 14 are symmetrical about the optical axis 24. However, this is only a cross-sectional view of the illumination shaping device 10. The degree of symmetry about the optical axis 24 is dependent on the desired illumination pattern of the output light 32. For example, it may be desirable to provide an illumination pattern that has a vertical axis larger than the horizontal axis. Therefore, those portions of the reflecting objectives that form the image of the vertical axis may be elongated according to the desired illumination pattern. Referring to FIGS. 3-5, an example of an illumination shaping device 100 for providing output light 32 having an annular illumination pattern is provided. A demonstrative drawing of how the illumination shaping device 100 changes a monopole, on-axis illumination pattern to an annular pattern is shown in FIG. 6. As seen best in FIGS. 3 and 4, the reflecting objectives 102, 104 correspond to the reflecting objectives 12, 14 of FIGS. 1 and 2. The reflecting objectives 102, 104 are radially and uniformly symmetrical about an axis, which would generally be the optical axis 24 or the axis of propagation for the input light 26. The input reflecting objective 102 may further be thought of as a finite half-parabola rotated about its asymptote. Likewise, the output reflecting objective 104 may be thought of as a finite half-parabola rotated about an axis positioned parallel to, but away from its asymptote at a distance of twice the half-parabola""s width from the asymptote. In either case, the reflecting objectives 102, 104 are essentially rotated about an axis that will be the optical axis 24. In this particular example, the starting half-parabola (i.e., the cross-section) of the reflecting objectives 102, 104 are identical, though inverted to one another. However, as mentioned above, it may be desirable to create an illumination pattern that is elongated along one axis. For example, rather than a perfectly annular illumination pattern, an oval illumination pattern may be desired. Therefore, rather than having the reflecting objectives 102, 104 being perfectly symmetrical about the optical axis 24, the reflecting objectives 102, 104 may be elongated in a direction perpendicular to the optical axis 24 so as to have an oval shape when viewed along the optical axis 24. The input light 26 would then be reflected to follow the shape of the reflecting objectives 102, 104 using the same principles described above to form an oval illumination pattern about the optical axis 24. The elongation of the reflecting objectives 102, 104 may cause variations in the intensity of the illumination pattern (e.g., greater intensity along the un-elongated portions and less intensity along the elongated portions) given the same amount of input light 26 is being spread over a larger reflective surface in some areas. One method of correcting for this is to vary the reflective coatings on the reflective surfaces to reflect more or less light as needed. Therefore, by varying the shape of the reflecting objectives 102, 104, the illumination pattern of the output light 32 may be manipulated to any desired illumination pattern. In the example of FIGS. 3-5, given the radial symmetry of the reflecting objectives 102, 104, the reflecting objectives 102, 104 may be thought of as being composed of an infinite number of paraboloid sections having reflective surfaces 106, 108, each paraboloid section having a focal point 20. This would mean that the reflecting objectives 102, 104 have a focal ring composed of each focal point 20 of the infinite number of paraboloid sections having reflective surfaces 106, 108. Therefore, the focal rings of reflecting objectives 102, 104 are coaligned and occupy the same space, similar to how the focal points 20 are aligned in FIGS. 1 and 2. Reflective surfaces 106, 108 correspond to reflective surfaces 16, 18, respectively. Referring to FIG. 3, an opening defined by an edge 110 in the rearward end of the output reflecting objective 104 exposes the input end 28. Input light 26 is permitted to enter through the opening 110 and reflect off of the input reflective surface 106 of the input reflecting objective 102. The reflected input light 26 is reflected through the focal rings of reflecting objectives 102, 104 and onto the output reflective surface 108 of the output reflecting objective 104. The output reflecting objective 104 then reflects the light as output light 32 through a second opening defined by an edge 112 in the forward-facing end of the output reflecting objective 104, corresponding to the output end 30, seen best in FIG. 4. Terminology regarding the orientation of the disclosed examples of an illumination shaping device, such as xe2x80x9cupperxe2x80x9d, xe2x80x9clowerxe2x80x9d, xe2x80x9crearward-facingxe2x80x9d, xe2x80x9cforward-facingxe2x80x9d, etc., are used herein for ease of explanation only and are not intended to limit the illumination shaping device to any particular orientation. Given the shape of the reflecting objectives 102, 104 any collimated input light 26 having a monopole, on-axis illumination pattern would be incident on the input reflective surface 106 and redirected out of the illumination shaping device 100 so as to have an off-axis, annular illumination pattern, as indicated in FIG. 6, based on the geometric principles outlined above. Even though the reflecting objectives 102, 104 may not seem to resemble the average paraboloidal mirror, the same geometrical optical principles apply. In other words, all collimated input light 26 is uniformly reflected by the input reflective surface 106 away from the optical axis 24 and through the focal ring. Because the focal ring of the input reflective surface 106 is shared with the focal ring of the output reflective surface 108, the reflected input light 26 is incident on the output reflective surface 108 through the focal ring, causing the output light 32 to be re-collimated, given the reflective surface 108 is theoretically composed of an infinite number of paraboloid-section reflective surfaces. Furthermore, because the input light 26 is uniformly and radially directed away from the optical axis 24 via the input reflective surface 106, the illumination pattern of the output light 32 is annular and symmetrical about the optical axis 24. It is noted that, as shown in FIG. 2, the input light 26 reflects off the input reflective surface 16 at several different angles, not all of which are perpendicular to the optical axis 24 or radial from a common point. However, for the purposes of explaining the reflection of the input light 26, the terms xe2x80x9cradialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d are used to reference the fact that all rays of the input light 26 reflect away from the optical axis 24. A view along the optical axis 24 would appear to be radial and symmetrical about the optical axis 24. Referring to FIGS. 7-9, an example of a multipole illumination shaping device 200 for shaping output light 32 having a dipole illumination pattern is provided. The illumination shaping device 200 includes reflecting objectives 202, 204, which correspond to the reflecting objectives 12, 14 of FIGS. 1 and 2, respectively. Though the dipole illumination shaping device 200 is described as corresponding to the illumination shaping device 10 of FIGS. 1 and 2, it can be seen in FIG. 9, and further in the representation of the dipole illumination shaping device 200 in FIG. 10, that the cross-section of the dipole illumination shaping device 200 is not identical to that of FIGS. 1 and 2. Rather, the upper and lower portions of the input reflecting objective 202 are depicted as two half-paraboloid sections, similar to the upper and lower portions of the output reflecting objective 204, that have been intersected, with the intersecting portions xe2x80x9ccut awayxe2x80x9d. The paraboloid sections are intersected to capture the majority of the input light 26. Otherwise, an input reflecting objective 202 having a cross-section identical to that for the illumination shaping device of FIGS. 1 and 2 would require two half-paraboloids joined only at a single point at the input end of the illumination shaping device 200. This would cause a significant portion of the input light 26 to miss the input reflecting objective 202 by passing between the half-paraboloids. By essentially having two half-paraboloids intersecting, preferably by equal amounts, with the intersecting portions removed, the input reflecting objective 202 accepts most or all of the input light 26. The reflecting objectives of multipole illumination shaping devices includes paraboloid sections, the inner surfaces of which are the reflective surfaces. The number of paraboloid sections for each reflecting objective is proportional to the number of desired poles. An output reflecting objective would generally include a paraboloid section to correspond with each paraboloid section for the input reflecting objective. In the case of the annular pattern, it can be assumed that an annular pattern is really an infinite number of poles, in which case the number of paraboloid sections is infinite. In the present example, the number of paraboloid sections for a dipole illumination shaping device is two. For example, input reflecting objective 202 has an upper paraboloid section 202a and a lower paraboloid section 202b. The inner surfaces of the paraboloid sections 202a, 202b correspond to an input reflective surface 206. The output reflecting objective 204 has an upper paraboloid section 204a and a lower paraboloid section 204b. The inner surfaces of paraboloid sections 204a, 204b correspond to an output reflective surface 208. As with the annular illumination shaping device 100, the principles regarding the operation of the dipole illumination shaping device 200 are similar to those described above. Input light 26 is incident upon the input reflective surface 206, preferably with equal distribution of the input light 26 on the upper paraboloid section 202a and the lower paraboloid section 202b. The paraboloidal shape of the input reflective surface 206 reflects all collimated light through a focal point. Because the input reflecting objective 202 is composed of two, preferably equal, paraboloid sections 202a, 202b, the input light 26 is redirected in two opposite directions away from the optical axis 24, one through the focal point of the upper paraboloid section 202a and the other through the focal point of the lower paraboloid section 202b. The reflected input light 26 is also through the focal point of the upper and lower paraboloid sections 204a, 204b of the output reflecting objective 204, thereby redirecting the light into two collimated beams of output light 32 having a dipole illumination pattern, as represented by FIG. 10. As with the annular illumination shaping device 100 above, the reflecting objectives 202, 204 may be modified to manipulate the illumination pattern. For example, if it is desired to have one of the poles larger than the other, upper paraboloid sections 202a, 204a may be made to have a larger curvature than the lower paraboloid sections 202b, 204b (e.g., viewing the illumination shaping device along the optical axis 24 would reveal the curvature of the upper paraboloid sections 202a, 204a as having greater radii perpendicular to the optical axis 24 than that of the lower paraboloid sections 202b, 204b). The intensity may be varied as necessary using techniques similar to those described above. Referring to FIGS. 11-13, a second example of a multipole illumination shaping device is shown. In particular, this is an example of a quadrapole illumination shaping device 300. Similar to the dipole illumination shaping device 200, the quadrapole illumination shaping device 300 includes an input reflecting objective 302 and an output reflecting objective 304. The input reflecting objective 302 is composed of four paraboloid sections 302a, 302b, 302c, 302d. The inner surfaces of the paraboloid sections 302a, 302b, 302c, 302d correspond to an input reflective surface 306. The output reflecting objective 304 is composed of four paraboloid sections 304a, 304b, 304c, 304d, the inner surfaces of which correspond to an output reflective surface 308. Each paraboloid section 302a, 302b, 302c, 302d of the input reflecting objective 302 has a focal point 20 that is shared with a focal point 20 of the paraboloid sections 304a, 304b, 304c, 304d of the output reflecting objective 304. Further, similar to the dipole illumination shaping device 200, the paraboloid sections 302a, 302b, 302c, 302d can be thought of as four intersecting half-paraboloids without the intersecting portions. Again, it is preferable that each half-paraboloid is intersected by equal amounts to create approximately equal-sized paraboloid sections 302a, 302b, 302c, 302d. As can be derived from the above examples, the number of paraboloid sections is proportional to the desired illumination pattern. For example, a tripole illumination pattern would utilize an input reflecting objective having three intersecting half-paraboloids without the intersecting portions to create three paraboloid sections; an octapole illumination pattern would utilize an input reflecting objective having eight intersecting half-paraboloids to create eight paraboloid sections, etc. The output reflecting objective, in turn, includes a corresponding paraboloid section for each paraboloid section in the input reflecting objective. Though not shown in the above examples, in some cases the paraboloid sections for the output reflecting objective may also intersect, in which case the intersecting portions are not included. Referring again to FIGS. 11-13, and further referring to FIG. 14, input light 26 is incident, preferably uniformly, upon each of the paraboloid sections 302a, 302b, 302c, 302d of the input reflecting objective 302. The input light 26 is reflected in four directions away from the optical axis 24 and through the focal point 20 of its corresponding paraboloid section 302a, 302b, 302c, 302d. Preferably each reflection direction is approximately orthogonal to the adjacent reflection direction. The reflected input light 26 is reflected again by each corresponding paraboloid section 304a, 304b, 304c, 304d of the output reflecting objective 304 as four beams of output light 32 having a quadrapole illumination pattern, as represented by FIG. 14. The beams of output light 32 are generally collimated given the reflected input light 26 passed through the focal point 20 of each paraboloid section 304a, 304b, 304c, 304d. As can be seen from these examples, the redirection of the input light 26 having been reflected off an input reflecting objective is proportional to the number of desired poles and is preferably radially symmetrical about the optical axis 24 to provide a radially symmetrical illumination pattern. This means each of the paraboloid sections of a reflecting objective have the same shape, curvature, reflective properties, etc. However, this may be varied, either by varying reflective coatings or non-uniformly distributing the input light 26 on the input reflecting objective 102, 202, 302, so as to create the illumination patterns with varying degrees of intensity throughout the pattern. The curvatures of the paraboloid sections may also be varied to manipulate the illumination pattern. In some of the above described examples, notably the annular illumination shaping device 100, the input reflecting objectives 12, 102 and the output reflecting objectives 14, 104 are shown as xe2x80x9cfloatingxe2x80x9d objects or otherwise completely detached from one another. However, many known techniques, which will not significantly degrade optical performance, are known by those of ordinary skill in the art and can be used to physically secure the xe2x80x9cfloatingxe2x80x9d reflecting objectives 12, 14, 102, 104 in their respective orientations. For example, structural supports may extend from an edge or surface of the input reflecting objective 12, 102 to an edge or surface of the output reflecting objective 14, 104. Such structural supports can be manufactured to a width and composed of materials that are unobtrusive to the illumination pattern and the illumination wavelength, as understood by those of ordinary skill in the art. Additionally, the supports may be positioned to avoid the more intense portions of the illumination pattern for the output light 32. While this may be more difficult for an annular illumination shaping device 100 as depicted in FIGS. 3-5, a quadrapole illumination shaping device 300 as depicted in FIGS. 11-13 may have supports extending from a forward-facing corner 310a, 310b, 310c, 310d of the output reflecting objective 304 to a forward-facing edge 312a, 312b, 312c, (312d not shown) of a paraboloid section 302a, 302b, 302c, 302d of the input reflecting objective 302 and/or an adjacent forward-facing corner 310a, 310b, 310c, 310d of the output reflecting objective 304. Alternatively, or in addition, the supports may extend from one or more forward-facing corners 310a, 310b, 310c, 310d of the output reflecting objective 304 to a corresponding rearward-facing corner 314a, 314b, 314c, 314d of the input reflecting objective 302. Similar support structures may be utilized with other multipole illumination shaping devices, such as the dipole illumination shaping device. While structural supports such as those described above may be beneficial to adding structural integrity to a multipole illumination shaping device 200, 300, other methods of securing the reflecting objectives 202, 204, 302, 304 may also be utilized in conjunction with or as an alternative to the structural supports. Adhesive may be introduced at the junctions where the input reflecting objective 202, 302 meets the output reflecting objective 204, 304 respectively. For example, referring to FIG. 11, the inside-facing edge of paraboloid section 304b meets the outside-facing edge of the paraboloid section 302b at two junctions 316, 318. A small amount of adhesive, the choice of which is within the knowledge of those of ordinary skill in the art, may be introduced at these junctions, either between the edges or alongside the edges. The location, type and amount of adhesive should not significantly interference with the optical properties of the illumination shaping device. Providing the adhesive alongside the edge may tend to avoid introducing a gap between the corresponding paraboloid sections 302b, 304b, whereby a gap may cause misalignment of the focal points 20. Alternatively, the edges of one or more of the paraboloid sections 302b, 304b may be cut down just enough to permit the introduction of some adhesive between the edges. Other methods, such as a structural member having adhesive on opposite sides may be introduced between the edges. Adhesives may further be introduced at the corners 310a, 310b, 310c, 310d of adjacent paraboloid sections 304a, 304b, 304c, 304d. As discussed above, the desired shape of the illumination pattern of the output light 32 may be varied by the number of paraboloid sections being used. However, other variations to the illumination pattern may be accomplished by varying the paraboloid sections themselves. For example, referring to FIG. 15, a cross-section of an annular illumination shaping device 400 is shown with a representation of the change in illumination pattern. By trimming the edge of the input reflecting objective, a portion of the input light 26 is allowed to pass through unimpeded. The remaining input light 26 is reflected as described above. The resulting illumination pattern of the output light 32 is an annular pattern having concentric rings. The desired width of the rings can be varied with the degree to which the edges are trimmed. The number of rings can further be varied by providing the appropriate openings in the reflecting objectives. Though delaying some of the input light 26 through reflection while allowing the remaining the input light 26 to pass through unimpeded causes the total output light 32 to be incoherent, this should not affect the use of the illumination device in lithography systems. Other variations in the paraboloid sections may also be used to vary the illumination pattern. For example, the curvature of each paraboloid section, and hence the focal length, may be varied, provided the focal point of each paraboloid section of the input reflecting objective is aligned with the focal point of the corresponding paraboloid section of the output reflecting objective. This means the curvatures may resembles sections of a spheroid or ellipsoid, if desired, or the paraboloid sections of the input reflecting objective may have different curvatures than the paraboloid sections of the output reflecting objective. Paraboloid sections of the same reflecting objective may also be different from one another if an asymmetrical illumination pattern is desired. Examples of differing paraboloid sections to manipulate the illumination pattern have been described in greater detail above. The paraboloid sections described above have generally been described as having coaxial principal axes (e.g., the reflecting objectives 12, 14 share a common principal axis). However, the paraboloid sections may be pitched forward or backward to cause the principal axis of the paraboloid sections to be at an angle to the optical axis 24, as shown in FIG. 16. The focal point of each paraboloid section is still aligned with the focal point of each corresponding paraboloid section. The illumination shaping device 500 of FIG. 16 is shown to be similar to the illumination shaping device 300 as shown in FIG. 14, though varying the pitch of the paraboloid sections is applicable to all examples of an illumination shaping device. In the present example, the paraboloid sections of the output reflecting objective are pitched backward. This causes the output light to diverge away from the optical axis, thereby expanding the illumination pattern. By pitching the paraboloid sections forward, the illumination pattern would be contracted. Referring to FIG. 17, a lithographic exposure system 600 for illuminating a substrate wafer using deep-ultraviolet or EULV with a reflective illumination shaping device is shown, though the claimed invention may be applicable to exposure systems utilizing other wavelengths. Input light 602 having a generally monopole, on-axis illumination pattern is incident on an illumination shaping device 604. In a manner similar to those described above, the illumination shaping device 604 reflects the input light 602 to create output light 606 having an off-axis, non-monopole illumination pattern, generally of the annular (single or concentric rings) or the multipole variety. A condenser system including a first series of mirrors 608 (collectively referred to as condenser mirrors 608) may be included to redirect the output light 606 to illuminate a design pattern on a reticle 610 at an angle to the optical axis. The condenser mirrors 608 are generally used instead of the lenses commonly used with other lithographic exposure systems, because of the drawbacks described above with respect to the use of lenses with EUVL. However, other ways of illuminating the reticle 610 at an angle to the optical axis may be used, in addition to or as an alternative to redirection reflectors 608. For example, as described above with respect to FIG. 16, the paraboloid sections of the reflecting objectives may be pitched forward or backward, while maintaining focal point alignment. By pitching the paraboloid sections of the output reflecting objective forward, the output light 606 is directed to converge towards the optical axis and illuminate the reticle 610 at an angle to the optical axis. Alternatively, the condenser system may include a condenser lens that may be used to direct the output light 606 onto the reticle 610 for some wavelengths in the deep ultraviolet spectrum without incurring the drawbacks associated with EUVL, though the condenser mirrors 608 may still be used with deep ultraviolet lithography. The reticle 610 generates diffraction images symmetrical about the optical axis from the illumination of the output light 606. A second series of mirrors 612 (collectively referred to as projection mirrors 612), or other reflective projection system, focus the diffracted image onto a substrate wafer 614. The projection mirrors 612 capture and focus the non-diffracted order (i.e., 0th order) and at least one of the higher diffraction orders (e.g., xc2x11st orders) from each diffracted beam of the output light 606 in order to resolve the image on the substrate wafer 614. In order to compensate for any shift in the image on the substrate wafer 614, the projection system captures and reflects diffraction orders that are symmetrical to each other about the optical axis. That is, for each non-diffracted order and a higher diffraction order of a particular beam (e.g., 0th and +1st orders), the non-diffracted order and a higher diffraction order of a beam (e.g., 0th and xe2x88x921 orders) symmetrical to the first beam are also captured and reflected by the projection mirrors 612. Other projection systems may be able to capture more than the first order of the higher diffraction orders. As with the condenser mirrors 608 above, the projection mirrors 612 are used to accommodate wavelengths used with EUVL. However, with deep ultraviolet lithography wavelengths, a projection lens may be used without the drawbacks associated with EUVL. Although certain apparatus constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the invention fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. |
|
abstract | In a radiation therapy and magnetic resonance unit, a magnetic resonance diagnosis part is provided. A radiation therapy part is provided for irradiation of an irradiation area within an interior of the diagnosis part. The radiation therapy part comprises a beam deflection enclosure for deflecting an electron beam toward an axis of the diagnosis part from an initial trajectory parallel to the axis. The beam deflection enclosure comprises a first magnetic field in a region of the beam deflection enclosure but of opposite direction and effective to cancel a main magnet field of the diagnosis part. A second magnet field is directed perpendicular to a trajectory of the electron beam to cause the electron beam to be deflected inward towards the axis. |
|
summary | ||
047864656 | abstract | A method for converting a vertically downward flow of bypass coolant through coolant flow holes in a core barrel and former plates in a nuclear reactor to a vertically upward flow. Coolant flow holes are provided in the normally solid top former plate by suitable means such as drilling. These new coolant flow holes are located so as to be substantially in coaxial alignment with the existing coolant flow holes in the intermediate and lower former plates. Existing coolant flow holes in the core barrel adajcent the top former plate are plugged. Existing coolant flow holes in the lower former plate are plugged in an alternating pattern with each fifth hole being plugged having only forty-four percent of its flow area plugged. |
059603682 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "wet" oxidation process for reducing the volume of hazardous, radioactive, and mixed wastes, and for converting said wastes into a form suitable for storage, particularly long-term storage in a repository. More particularly, the present invention relates to a process for treating waste containing both organic carbon compounds and radioactive or hazardous material to reduce the volume of the material by oxidizing the organic carbon compounds with a combination of nitric acid and phosphoric acid, and then converting the reduced volume waste material into an immobilized final form, such as a glass or ceramic, which can then be stored in a suitable repository. 2. Description of Background and Related Art The disposal of radioactive, hazardous, and mixed (radioactive and hazardous) waste has over the years become a growing environmental, political, and economic problem. Due to the limited number and capacity of suitable repositories and the political difficulties involved in establishing new repositories, the supply of disposal capacity has decreased. At the same time, increasing amounts of waste material must be disposed of due to nuclear disarmament, increasing awareness of existing waste in short term storage, and the production of new waste material in areas such as nuclear power plant operation and medical research. A particular area of concern is the disposal of low level radioactive and mixed wastes, such as job control waste (i.e., waste generated by everyday operations in nuclear facilities such as protective gloves, clothing, etc. worn by workers who handle or are possibly exposed to radioactive material), nuclear power plant operations (such as contaminated solutions and ion exchange resins used to remove corrosion from reactor secondary cooling systems), and operations involving treatment and purification of water used to cool stored nuclear material, such as fuel rods (e.g., ion exchange resins). At the present time, over 80% of this type of waste is sent for storage to a single site, which is at or near capacity. As a result of this lack of available storage capacity and the measures taken by political entities to limit the amount of waste storage, costs to store low level waste have increased significantly. In order to reduce these costs, attempts have been made to reduce the amount of waste that must be sent to repositories. One method proposed has been to eliminate some or all of the components of low level waste that are not hazardous or radioactive, and/or convert hazardous components to nonhazardous form. An additional concern with the storage of any radioactive or hazardous waste is the stability of the final storage form. Such waste must be safely stored for time periods that are often geological in scale, requiring that the material be stored in a form that is stable over time and also over exposure to a variety of conditions. The tendency of storage containers to break down or corrode over time and the resulting risk that the stored material will escape into the biosphere has led to the use of storage forms wherein the waste materials are immobilized in a solid form that is relatively stable toward the expected environments to which the stored material may be exposed. Immobilizing the waste material in a glass (vitrification) or ceramic that is stable over time to the conditions expected to be encountered in a repository are two examples of this approach. Prior attempts to reduce the volume of hazardous or radioactive waste have involved several different approaches, some of which also involve immobilizing the radioactive material in a solid form. U.S. Pat. No. 3,957,676 (Cooley et al.) describes treating combustible solid radioactive waste materials with concentrated sulfuric acid at a temperature within the range of 230.degree. C.-300.degree. C., and simultaneously and/or thereafter contacting the reacted mixture with concentrated nitric acid or nitrogen dioxide, in order to reduce the volume of combustible material and convert it into gaseous products. U.S. Pat. No. 4,039,468 (Humblet et al.) describes an approach of attempting to separate radioactive species using solvent extraction. An organic phosphate-containing solvent is contacted with the waste and then treated by contacting the stream with phosphoric acid, obtaining a light organic phase containing essentially no radioactive material, and heavy aqueous and organic phases which contain essentially all of the radioactive material. The light organic phase can then be combusted, and the concentrated radioactive material can be solidified by reaction on aluminum oxide and incorporation into a glass or resin matrix. U.S. Pat. No. 4,460,500 (Hultgren) describes reducing the volume of radioactive waste, such as ion exchange resins, by treatment with an aqueous complex forming acid, such as phosphoric acid, citric acid, tartaric acid, oxalic acid, or mixtures thereof to remove the radioactive species from the exchange resins and form a complex therewith. The radioactive species are then adsorbed onto an inorganic sorbent. The resulting material is then dried and calcined in the presence of air or oxygen, resulting in combustion of the organic material. The calcinated material is then collected into a refractory storage container, which is then heated to a temperature at which the material sinters or is fused to a stable product. U.S. Pat. No. 4,732,705 (Laske et al.) describes treating radioactive ion exchange resin particles with an additive containing anions or cations that reduce the swelling behavior of the resin particles and produces a permanent shrinkage of the resin particles. The additive may be a polysulfide or organic acid ester. The treated resin particles are then immobilized in a solid matrix, such as a cement. U.S. Pat. No. 4,770,783 (Gustavsson et al.) describes decomposing organic ion exchange resins containing radioactive materials by oxidation in a mixture of sulfuric acid and nitric acid in the presence of hydrogen peroxide or oxygen as an oxidant. Radioactive metals in the resulting liquid are precipitated with hydroxide and separated from the liquid, which contains other non-radioactive materials. The liquid is then released to the environment. The precipitated metal compounds are immobilized in cement. U.S. Pat. No. 4,904,416 (Sudo et al.) describes centrifuging wet radioactive ion exchange particles to remove water therefrom, then coating the particles with a small quantity of cement powder, and then adding water and cement, in order to increase the loading of resin in the cement. U.S. Pat. No. 5,424,042 (Mason et al.) also describes removing water from radioactive ion exchange resins prior to vitrification. U.S. Pat. No. 5,457,266 (Bege et al.) suggests dewatering radioactive ion exchange resins by mixing with a calcium compound and heating to a temperature over 120.degree. C. at a pressure of 120 hPa to 200 hPa. These attempts have not been completely successful because (1) the use of sulfuric acid and other acids to oxidize organic materials included in waste streams does not allow for efficient conversion of the resulting treated waste stream into a stable, immobilized final form, (2) processes involving one or more transfers of radioactive species between solvent or sorbent phases is complicated and inefficient, (3) dewatering and cementation processes do not result in sufficient volume reduction, and (4) processes using high temperatures are not viewed favorably by the nuclear industry for oxidation of materials containing organic compounds. Prior attempts to immobilize low level radioactive or mixed waste, such as ion exchange resins, have also been made. U.S. Pat. No. 4,483,789 (Kunze et al.) describes a method for encasing the radioactive ion exchange resin in blast furnace cement. The mixture of resin, cement, and water is disclosed to have a slow initial hardening and high sulfate resistance, and is allowed to harden at room temperature. U.S. Pat. No. 4,530,723 (Smeltzer et al.) describes a method for forming a solid monolith by mixing radioactive ion exchange resin and an aqueous mixture of boric acid or a nitrate or sulfate salt, a fouling agent, a basic accelerator, and cement, and allowing the cement to harden. U.S. Pat. No. 4,632,778 (Lehto et al.) describes a process for disposing of radioactive material by adsorbing the radioactive material on an inorganic ion exchanger, mixing the inorganic ion exchanger loaded with radioactive species with a ceramifying substance and baking this mixture to form a ceramic. U.S. Pat. No. 4,834,915 (Magnin et al.) describes immobilizing radioactive ion exchange resins by saturating them with a base, preferably sodium hydroxide and immobilizing them in a hydraulic binder. U.S. Pat. No. 4,892,685 (Magnin et al.) describes immobilizing radioactive ion exchange resins by first treating them with an aqueous solution containing NO.sub.3.sup.- and Na.sup.+ ions to ensure that all of the sites in the resin are saturated, and then adding a hydraulic binder, such as cement. U.S. Pat. No. 5,143,653 (Magnin et al.) describes treating borate containing radioactive ion exchange resins with calcium nitrate prior to incorporation into a hydraulic binder. These three patents are directed to attempting to resolve the problem of ion exchange of radioactive material between the immobilized resin material and the hydraulic binder. U.S. Pat. No. 5,288,435 (Sachse et al.) describes a process for the incineration and vitrification of radioactive waste materials, which may contain sulfur compounds, by contact of the waste materials with molten glass in a glass melter having an extended heated plenum to allow for sufficient combustion residence times. If sulfur-containing wastes are being processed, the off gases produced can be scrubbed of sulfur, which can then be converted into gypsum. U.S. Pat. No. 5,435,942 (Hsu) describes treating alkaline radioactive wastes with nitric acid to reduce pH and with formic acid to remove mercury compounds, in order to adjust the glass forming feedstock composition to achieve more efficient glass melter operation. The use of lead-iron phosphate glasses for the immobilization of radioactive waste is described in U.S. Pat. Nos. 4,847,008 and 4,847,219 (Boatner et al.). The use of glasses to immobilize radioactive waste is also described in U.S. Pat. No. 3,161,601 (Barton), U.S. Pat. No. 3,365,578 (Grover), U.S. Pat. No. 4,351,749 (Ropp), and U.S. Pat. No. 5,461,185 (Forsberg et al.). These methods of immobilizing radioactive materials are disadvantageous because the volume reduction of waste is inadequate, which results in increased costs for disposing of the organic, non-radioactive materials. In addition, removal of radioactive material is incomplete. Finally, any significant volume reduction that occurs is due to incineration, which creates the risk that radioactive species will be entrained in ash in the off gas. It is an object of the present invention to avoid the disadvantages of the prior procedures by providing a simple, efficient process for the wet oxidation of organic carbon-containing radioactive, hazardous, or mixed waste products. It is also an object of the present invention to provide a process that results in significant volume reduction of these waste materials, thereby significantly decreasing the costs associated with their long term disposal. It is also an object of the present invention to provide a process whereby the residual concentrated waste product produced by the wet oxidation process is conveniently and easily incorporated into a final form material without special intermediate treatment steps. Finally, it is also an object of the present invention to provide a process for immobilizing radioactive, hazardous, or mixed waste products in a final form that is stable to expected repository conditions over long periods of time. SUMMARY OF THE INVENTION The present invention achieves these and other objects of the invention and avoids the disadvantages of prior processes by providing a method whereby a combination of nitric acid and phosphoric acid is used to oxidize organic materials in a low level radioactive, hazardous, or mixed waste stream. The presence of phosphoric acid stabilizes the nitric acid in solution, and the combined acid mixture boils at a temperature that is considerably higher than that of nitric acid alone. This allows the oxidation reaction to be conducted at higher temperatures, resulting in more complete oxidation of the organic components of the waste stream, and resulting in the oxidation of some materials that otherwise cannot be oxidized in a "wet" process. The organic components are almost entirely converted to gaseous form, with a residual amount that is often on the order of less than 1000 ppm. This considerably reduces the volume of waste that must be placed in a repository, and substantially decreases the cost of waste disposal. In addition, the process according to the present invention avoids problems experienced with other acid systems, in particular with systems containing sulfuric acid and nitric acid, wherein sulfuric acid breaks down the nitric acid to such a degree that the usefulness of the nitric acid is adversely affected and the nitric acid cannot be recovered and recycled. Finally, phosphoric acid as used in the process of the present invention is not as corrosive or harsh on conventional metal process equipment as are other acids, such as sulfuric acid. The present invention also avoids the necessity of removing phosphorus-containing species from the remaining concentrated waste material prior to placing this material into final, stable form for disposal in a repository. Instead, the phosphorus-containing material is incorporated into the final form of the waste product. In its broad aspect, the present invention involves preparing radioactive, hazardous, or mixed waste for storage by first contacting the waste starting material, which contains at least one organic carbon-containing compound and at least one radioactive or hazardous waste component, with nitric acid and phosphoric acid simultaneously. This contacting is generally carried out at a contacting temperature in the range of about 140.degree. C. to about 210.degree. C. for a period of time sufficient to oxidize at least a portion, and preferably almost all, of the organic carbon-containing compound to gaseous products or off gas. This removal of the organic carbon-containing compounds produces a residual concentrated waste product containing substantially all of the radioactive or hazardous metal waste component. The residual concentrated waste product is then immobilized in a solid form suitable for disposal in a waste repository. Suitable solid forms include a glass or ceramic matrix containing the immobilized waste, in particular iron phosphate glasses, ferric phosphate ceramics, and magnesium phosphate ceramics. Other features and advantages of the present invention will be apparent to those skilled in the art from the above Summary, as well as from the following Detailed Description of the Specific Embodiments and the accompanying Drawing. |
summary | ||
041585992 | summary | CROSS REFERENCES TO RELATED APPLICATIONS This application relates to the following applications filed concurrently herewith or filed previously as indicated and, to the extent necessary or desirable, incorporated herein by reference: U.S. Pat. No. 3,836,429 entitled "Means for Rapidly Exposing The Core of A Nuclear Reactor For Refueling" by Erling Frisch and Harry N. Andrews. U.S. Pat. No. 3,836,430 entitled "Cable Support Structure For Enabling A Nuclear Reactor To Be Refueled Rapidly" by Erling Frisch and Harry N. Andrews. U.S. Pat. No. 3,766,006 entitled "Rapidly Refuelable Nuclear Reactor" by Erling Frisch and Harry N. Andrews. U.S. Pat. No. 3,752,737 entitled "Combination of Nuclear Reactor and Missile Shield" by Erling Frisch and Harry N. Andrews. U.S. Pat. No. 3,685,123 entitled "Means For Retaining and Handling Reactor O-Ring Seals" by Erling Frisch. U.S. Pat. No. 3,837,694 entitled "Hydraulic Head Closure Mechanism" by Erling Frisch and Harry N. Andrews. U.S. Pat. No. 3,607,629 entitled "Reactor Refueling Method" by Erling Frisch and Harry N. Andrews. BACKGROUND OF THE INVENTION This invention relates to the nuclear reactor art and has particular relationship to nuclear reactors which serve as primary sources for power-supply facilities. A demand which is imposed on such reactors is that they be refueled periodically. Refueling operations carried out in accordance with the teachings of the prior art consume about 3 to 6 weeks. While this invention is applicable to reactors of other types, it is uniquely applicable to the refueling of reactors of the pressurized water type, P.W.R. In the interest of concreteness this application, in its descriptive text, confines itself to P.W.R.'s assuming the pressure vessel to be vertical. Such nuclear reactor (U.S. Pat. No. 3,607,629 above) includes a pressure vessel having a body sealed by a head. The body is typically 40 feet long and 15 feet in diameter and includes the fuel core, which typically may include 193 fuel assemblies and the upper and lower internals. The head is typically 15 feet in diameter and in the past has been sealed by about 52 studs. The reactor includes control rods which are inserted in, or retracted from, the fuel for control purposes by control rod control mechanisms. The mechanisms operate in housings which are sealed pressure tight to the head and extend above the head. There are typically 60 such mechanisms each including drive or drives, typically a piston, a control rod drive shaft connected to the drive and extending from the mechanism housing through the head, each shaft engaging associated control rods. In refueling, in accordance with the teachings of the prior art, the studs are detensioned and removed from the vessel flange and the head and mechanism housing are lifted and removed exposing the control rod drive shaft and the control rods. The control rod drive shafts are then disconnected from the control rods and removed with the upper internals and the refueling is carried out with the control rods in the core. After refueling the above described process is reversed. The long shut down of several weeks which this method of refueling demands renders refueling at frequent intervals not practicable and the refueling in accordance with the teachings of the prior art takes place approximately annually. It has been discovered in arriving at this invention that this annular refueling imposes severe restrictions on the initial or replacement fuel. Typically, the initial enrichment in fissionable material of the fuel must be sufficient to maintain the reactivity of the reactor for at least a year. Typically, this enrichment is of the order of 3.2%. Because of this higher initial enrichment the medium in which the fuel is immersed must have a higher concentration of neutron absorber such as boron. These conditions are imposed not only on the initial fuel but also on each replacement. In addition, the number of fuel assemblies replaced is based on the annual refueling cycle and must be a substantial fraction of the assemblies in the core. Evaluation of the economic effects of refueling time reveals that there is large economic incentive in reducing materially the refueling time. Not only can the loss, resulting from the reactor being out of operation for long intervals, be reduced, but, in addition, because the refueling can take place at short intervals advantages are available in feasibility of using fuel of lower enrichment and in frequent replacement of a relatively small portion of the fuel assemblies during each refueling. In addition the concentration of neutron absorbing material in the medium in which the core is immersed, for example boron, in water, may be lower. Typically in a pressurized water reactor annual refueling, demanding enrichment in fissionable material of the order of 3.2% requires a concentration in the water of about 1200 parts per million of natural boron typically including by weight 20% B.sup.10 and 80% B.sup.11 at the beginning of life with a consequent build-up of a high concentration of tritium, H.sup.3, during life while the concentration of boron is being reduced to about 10 p.p.m. In a typical example, for a semiannual refueling cycle the initial enrichment is reduced and the concentration of boron at the start of life is reduced to 650 p.p.m. with consequent reduction in the H.sup.3 generated; and for a three-months refueling cycle the enrichment is only 2.7% and the boron concentration at the start of life is reduced to 350 p.p.m. It has been found that by refueling during an interval of three days about every three months a fuel saving amounting to about $14 per kilowatt can be realized. It is an object of this invention to improve the economy of operation of a nuclear reactor and to provide a method of refueling a nuclear reactor which can be carried out in a short interval of only a few days permitting a short time cycle, of the order of three or six months between refuelings of the reactor and consequent reduction of initial enrichment in fissionable material of the fuel and low concentration of neutron absorbers, and with minimized reactor downtime for refueling. SUMMARY OF THE INVENTION In accordance with this invention the number of separate tasks to be performed in refueling are substantially reduced so that access to the pressure vessel is obtained rapidly. In addition cross transportation of the old and new assemblies is simplified and speeded up and refueling techniques are simplified and automated. The possibility of delays from maloperation is reduced by improving the reliability of each step of the refueling. The result is that refueling can be carried out in a few days conceivably under minimum electrical utility system load conditions, and the refueling cycle can be only three to six months. Specifically, the studs are detensioned rapidly by hydraulically operated detensioners, as disclosed in U.S. Pat. No. 3,837,694. The missile shield, disclosed in U.S. Pat. No. 3,752,737 is then displaced locking the control rod control mechanisms in the retracted position in their housings without dependence upon electrical current flow, as disclosed in U.S. Pat. No. 3,766,006. The whole upper package including the missile shield, head of the pressure vessel, the control rod drive mechanisms and their drive shafts, the control rods and the upper internals, is then lifted and placed out of the way in a single lifting operation. The integral structure including the missile shield is disclosed in U.S. Pat. No. 3,836,429. The cables are on a pivoted cable tray, as disclosed in U.S. Pat. No. 3,836,430, and are sufficiently long so that they need not be, and are not, disconnected during the whole refueling operation. The removal of the control rods during refueling requires that the boron concentration be increased, during refueling. It is of interest that the increase is to 2500 p.p.m. for an annular refueling cycle. For a six-month refueling cycle the boron concentration during refueling is reduced to 1880 p.p.m. and for a three-month cycle it is correspondingly further reduced. The new replacement fuel assemblies are transferred in one operation into the containment where the open vessel is disposed and are in position for refueling. The spent fuel assemblies are likewise transferred out of the containment in one operation. A fuel transfer pit is provided in this containment where the spent assemblies may be retained temporarily. Typically, in refueling, at 6 month intervals, one-fifth of the spent assemblies in the core are replaced. In this practice assemblies are removed from the center of the core and are replaced by assemblies outside of the center. The peripheral assemblies are then replaced. Alternatively, a refueling technique may be adopted, wherein no fuel assembly rearrangement occurs. Typically where there are 193 assemblies in the core, 20 may be replaced directly during each refueling. The cycle is three-months. The replacements are in each case identified so that in about 21/2 years all assemblies are replaced. After the refueling the boron concentration is reduced to the required magnitude (for example 350 p.p.m. for a three month's cycle). |
summary | ||
050531913 | summary | BACKGROUND OF THE INVENTION The present invention relates to nuclear reactors, and more particularly, to holddown springs for nuclear reactor fuel assemblies. In most commercial nuclear power reactors, the space allocated to fuel assembly components is constrained by the other internal components of the reactor, so that only the type of fuel assembly holddown springs supplied by the original equipment manufacturer, can be used on replacement fuel assemblies. In the reactors of interest herein, each fuel assembly is vertically supported between an upper core plate and a lower core plate, and cantilever-type holddown springs are interposed between the upper core plate and the upper end fitting of the fuel assembly for biasing the assembly against the lower core plate. This bias accommodates differential thermal expansion between the assemblies and the reactor core and core plates, the upward forces imposed on the assemblies resulting from the flow of primary coolant through the core, and transient loads that can result from a variety of both normal and abnormal plant operating conditions. In nuclear reactors where the holddown springs are of the cantilever, rather than coil or leaf spring type, it is possible that certain transients can overload the cantilever springs, such that, upon the return of the reactor to normal operation, the performance of the springs has been permanently degraded. SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to modify the typical cantilever spring to improve its performance under peak loading, by increasing its spring rate as increased load is applied. In accordance with the present invention, the cantilevered spring has a secondary, or auxiliary loading point in the form of a dimple or thickened region projecting toward the upper core plate. The dimple contacts the core plate after the core plate has deflected the spring a predetermined amount via the primary loading point. The transferred, secondary loading effectively shortens and stiffens the spring against further movement of the core plate and upper end fitting toward each other. The cantilevered spring itself, in accordance with the invention, preferably comprises a unitary, elongated metal bar having a substantially straight, long legged portion with one end adapted to be mounted to the fuel assembly end fitting, and an arcuate transition portion at the other end of the long leg. A straight short legged portion extends from the transition portion at an acute included angle with the long legged portion and has an unrestrained free end. The load transfer projection is located on the long leg intermediate the transition portion, which is the spring loading point during normal operation, and the first end adapted for attachment of the long leg to the assembly. |
description | This application is a U.S. national stage application of a PCT application PCTRU2016/000320 filed on 27 May 2016, whose disclosure is incorporated herein in its entirety by reference, which PCT application claims priority of a Russian Federation application RU2015120422 filed on 29 May 2015. The invention is related to nuclear energy sector, particularly to low and ultra-low power reactors. In accordance with classification approved by IAEA (B. J. Csik Assessment of the world market for small and medium reactors. IAEA-TECDOC-999, Vienna, 1998), currently, low power nuclear reactors are reactors that do not exceed 300 MW. Medium power nuclear reactors are reactors in the range of 300-700 MW. Nuclear reactors exceeding 700 MW are high-powered reactors. Initially, low-power reactors were utilized in military in submarines. Civil nuclear energy sector borrowed a lot from military designs during the period of its development. However, a stake was made in 600-1000 MW NPP. Such development in nuclear energy sector perhaps is reasonable for industrially developed countries, who have developed electrical networks, qualified personnel, technologies, and growing energy absorption to implement expensive projects. However, the majority of developing countries do not have a sufficiently developed infrastructure, electrical transmission networks, sufficient population density and resources for large ambitious projects. To build a large power plant in those countries is not the best option in developing the energy sector at this stage. This will be even less effective if the nuclear energy would not be used to produce electricity, but, for example, for water desalination or heating. Therefore, it is more effective to utilize low power nuclear power plants with reactors, whose power does not exceed 25-40 MW. Low power and ultra-low power NPPs have good benefits due to unstable prices for organic fuel and its tendency to increase in price. Nuclear energy usage ensures a better stability. Besides significant advantages in fuel supply, environmental benefits for using ultra-low power NPPs was another motivation. Especially it is important to northern areas and island ecosystems, since they have weak capabilities for self-restoration. Another advantage of nuclear energy is its multi-purpose use of low and ultra-low power nuclear energy by combining productions of electricity, hot water and steam, water desalination, etc. A relative simplicity of fuel supply combined with a long-term fuel campaign (7-15 years) and low power of a single reactor unit make such type of energy affordable and cost-effective. In relation to abovementioned, reactors for such NPPs are actively developed in the world, while special attention is given to increasing the service life (up to 60 years) while performing overloads of the reactor's reactor core less frequently than once in 10 years. There is a known reactor with fast neutrons for a low-power power plant with a large (long) interval of fuel replacement (Small, fast neutron spectrum nuclear power plant with a long refueling interval, U.S. Pat. No. 8,767,902, G21 C1/02, 2014). This reactor is used as a coolant of liquid sodium and designed to produce energy in the range of 50 to 100 MW, while the fuel replacement interval is 20 years. Using liquid metal ensures a high power rating of the fuel, high conversion ratio, increased performance of thermodynamic cycle, and does not require high pressure, which improves the reactor's safety. A specific issue with fast reactors, first of all, with sodium coolants, is a large positive value of the sodium void reactivity effect, which negatively affects its safety in emergency situations by voiding the reactor core or boiling sodium. There is also a known 300 kW heat supply reactor with 60 years of service life without permanent operating personnel (Y. A. Kazansky, V. A. Levchenko, E. S. Matusevich, Y. S. Yuriev, et al. Ultra-low power self-adjusting heat supplying reactor “MASTER IATE”. “University news. Nuclear Energy”. No 3, p. 63, 2003). Disadvantages of this reactor are that it does not satisfy international requirements for non-proliferation of nuclear materials, since its operation requires approximately 40% enriched nuclear fuel, and low power of the reactor, consumed fuel, and reactor core materials yield a high-cost energy production. Furthermore, good technical and neutron-physical properties of the reactor became an insurmountable barrier for increasing power. There is a known pressure-tube reactor with fast neutrons with liquid metal coolant (patent RU 2088981, G21 C 1/02, 1997). The advantages of pressure-tube reactors with fast neutrons over tank reactors are that pressure-tube design allows to adjust the individual coolant absorption in fuel channels, ensuring an optimal temperature mode for fuel rods. The space between channels can be used to place control and protection systems (CPS). A significant positive moment is an independence of CPS from the first loop of reactor cooling—control rods cannot be expelled from the reactor core by the coolant flow, which ultimately increases the reliability of CPS and overall reactor safety. A lack of the reactor housing filled with a coolant gives an important advantage to a pressure-tube reactor from the point of view of seismic stability especially when using lead-bismuth coolant. If there is a damage to the reactor housing, the consequences from voiding the reactor core or from sodium burning will be more serious than a from a damage to a single channel. The housing service life is restricted by its radiation and thermal stability. Replacing a housing in the reactor is almost impossible, while channel covers can be periodically replaced with new ones, as needed, and thus the service life of the reactor can be prolonged significantly. Channel design relieves a problem of diverting remaining heat in case of stoppage of coolant circulation in the first loop, as well as significantly simplifies the problem solution of corium dispersion in case of reactor core meltdown to prevent a formation of a secondary critical mass. The proposed invention is a further development and improvement of low and ultra-low power pressure-tube reactor design, whose neutron spectrum is displaced into a space of intermediate and fast energies. A technical result of the invention is to expand options of technical resources of nuclear reactors by designing a nuclear reactor with heat capacity around 30 MW with an increased service life and improved mass-dimensional parameters of the reactor in general. Furthermore, the proposed reactor design ensures an improved heat exchange process due to an increase in evenness and effectiveness of heat removal by rated power of the reactor core of the nuclear reactor without increasing the coolant velocity. The mentioned technical result is achieved by having a nuclear reactor, consisting of a housing with a reflector, forming an reactor core, first (fuel) process channels located within an reactor core, designed for coolant circulation along them, and second (controlling) process channels located within an reactor core, designed for placement of CPS components, the reactor also contains coolant supply chamber from the first loop and discharge chamber of the coolant of the first loop, divided by a partition. First process channels are designed as Field tubes, whose external tubes are attached at the bottom of the coolant supply chamber of the first loop, while internal tubes are attached to the partition. Fuel rod arrays are installed within internal tubes and Field tubes on suspenders, attached to the upper part (lid) of the coolant discharge chamber of the first loop. Second process channels are isolated from coolant supply and discharge chambers of the first loop. The housing side of the reactor core is filled with medium or material, transparent for neutrons (or, in other words, having a small neutron absorption cross-section). In the case of the invention design, the reflector may consist of a side reflector, designed, for example, as a pack of rings, and upper and lower reflectors. In another case of invention design, zirconium alloy may be used as a housing side material, which has a small neutron absorption cross-section. In yet another case of invention design, CPS controls may be placed on the upper part (lid) of the heat carrying discharge chamber of the first loop. Also, emergency protection absorber rods, as well as compensating and control rods may be used as CPS components, placed within second process channels. Aside from that, it is preferable for the invention design to use B4C, enriched to 80% to 10B, as an absorber in shim rods. It is also preferable to use B4C, enriched to 20% to 10B as an absorber for control rods. In the case of invention design, a part of fuel rod arrays can be designed with Gd2O3 burnable absorber. Also, a part of fuel rod arrays can be designed with Er burnable absorber. The abovementioned is a summary of the invention and thus may contain simplifications, generalizations, inclusions and/or exclusions of details; therefore, technical specialists should take into consideration that this summary of the invention is only illustrative and does not mean any restrictions. While the invention may be susceptible to embodiment in different forms, there are described in detail herein, specific embodiments of the present invention, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as exemplified herein. The principal structural layout of the reactor is shown in FIG. 1. The reactor consists of a metal housing 1, within of which an reactor core 2 of the reactor is located, formed by reflector 3. First process channels 4, designed for the first loop coolant circulation, and second process channels 5, designed for the placement of CPS components are located within the reactor core. First loop coolant supply chamber 6 and discharge chamber 7, separated by partition 8 are located above reactor core 2. CPS controls 9 are located above the first loop coolant discharge chamber 7. Reflector 3 consists of a side reflector, designed as a pack of individual rings 10, lower reflector 11 and upper reflector 12. Al—Be alloy is used as a material for the reflector 3. As shown in FIG. 2, first loop coolant supply chamber 6 consists of lid 13 of housing 1 of the reactor, side wall (housing) 14 and partition 8. Ducts 15 (FIG. 3) are located on side wall 14, which feed the first loop het carrier to supply chamber 6 by circulating pumps. Water H2O is used as a first loop coolant. As shown on FIG. 3, the first loop coolant discharge chamber 7 is formed by partition 8, side wall 16 and upper lid 17. Ducts 18 are placed on side wall 16, which are used to carry the first loop coolant from chamber 7 to the heat exchanger, which can be designed as a steam generator. First (fuel) process channels 4 (FIG. 2) are designed as Field tubes, each containing external tube 19 and internal tube 20. External tube 19 is welded into lid 13 of the reactor housing 1, designed as a tube plate with holes placed along the triangular grid. Internal tube 20 is welded into partition 8 between supply chamber 6 and discharge chamber 7 of the first loop coolant, which (partition) is designed also as a tube plate with holes corresponding to holes of lid 13. Second (controlling) process channels 5 (FIG. 3) each containing tube 21, placed in the reactor core 2, and tube 22, passing through supply chamber 6 and discharge chamber 7 of the first loop coolant, and isolating second process channel from the coolant. The space 23 (FIG. 4) between process channels in the reactor core 2 is filled with zirconium alloy E-110, which has a small neutron absorption cross-section. The locations of first and second process channels in the reactor core 2 are shown in FIG. 5. Suspenders of fuel rod arrays 24 are installed on the upper lid 17 (FIG. 3) of the first loop coolant discharge chamber 7. Fuel rod array 24 consists of the central rod 25, at the lower end of which a bundle of 18 fuel rods 26 is attached. A special flange 27 is located at the upper end of the central rod 25 to tighten suspenders of fuel rod array 24 on the upper lid 17 and to grip fuel rods while installing and removing it from the reactor core 2. The coolant from circulating pumps through ducts 15 feeds into supply chamber 6 of the coolant to first process channels. Then, as shown in FIG. 2, along the space between external tube 19 and internal tube 20 of Field tubes, fed pre-heated into the reactor core 2. Further, as shown in FIG. 4, the coolant travels to internal tube 20, where fuel rod array 24 is located. Traveling through the fuel rod array, the coolant is completely heated to the required temperature and returns to coolant discharge chamber 7, and then, through ducts 18, fed to the heat exchanger. Such design of fuel channels allows to half linear dimensions of the reactor core, in our case, the height. Furthermore, an evenness and effectiveness of the heat removal due to a partial heat dissipation at the coolant outlet from internal tubes 20 to the coolant at the inlet to external tubes 19. Also, fuel rod heat load distribution along their lengths is improved. The reactor design is simple, which ensures a total compensation of temperature deformations. All of this allows to ensure a large consumption of the coolant through a reactor core, which increases rated power and gives a heat power capability of 20 MW at small dimensions. The described reactor's fuel rods are enriched uranium dioxide. Advantages include an optimal processing of this type of fuel, confirmed by its usage for thousands of reactor years. Uranium enrichment for nuclear fuel production is limited to 20% in accordance with IAEA requirements to prevent a proliferation of nuclear weapons. The chosen enrichment equals to 19% by uranium-235 content (enrichment, similar to production fuel for BN-800 reactors). A choice of the maximum allowed value of enrichment allows to reduce the size of the reactor core, reaching the required reactivity margin and high depth of burning. To ensure long operational life of the reactor without overloads, a large reactivity margin (around 22%) is required. A compensation of such margin at minimum number of absorbing rods in the reactor core and ensuring an internal self-defense are achieved by using fuel with burnable absorber. Erbium (Er) and Gadolinium (GdC) are used as burnable absorbers. The positions and content of fuel rods of the fuel rod array 24 are shown in FIG. 7. A fuel rod array contains three Er fuel rods 28, three Gd2O3 fuel rods, and twelve rods 30 that do not contain a burnable absorber. The reactor control is performed by thirteen regulating CPS controls (FIG. 2), each one of them is designed as a pack of seven absorbing rods 32 (FIG. 6). All packs of CPS absorbing rods are divided into the following groups, according to their purpose: four packs 33 of compensating rods, ensuring a compensation of the reactivity margin of the reactor, created by the loss of reactivity as a result of fuel burning; two packs 34 of control rods, ensuring control and support for the reactor power during its operation; seven packs 35 of emergency protection rods, ensuring a quick decrease in power and switching the reactor to sub-critical mode when there are normal operation failures and emergency situations. As shown in FIG. 5, twelve packs of absorbing rods are located along the hexagon perimeter and one pack (emergency protection) is located at the center of the reactor core. Packs 34 of control rods are symmetric to each other relative to the reactor core center. B4C, enriched to 80% to 10B, is used for compensating and emergency protection rods, and B4C, enriched to 20% to 10B, is used for absorbing and control rods. The proposed invention is not limited to the abovementioned options of its practical implementation. Thus, for example, we can assume that using internal designs, having the shape, quantity of components and locations differ from those described above. |
|
summary | ||
description | This is a division of application Ser. No. 09/598,656, filed Jun. 21, 2000, now abandoned. The present invention is directed to a probe used for a scanning probe microscope (hereinafter, referred to as SPM) and a method of fabricating the probe. More particularly, the present invention is directed to a probe for an SPM and a method of fabricating the probe in which a double side alignment process is not required to simplify the fabricating. The SPM is a microscope capable of observing various shapes on a surface of an object by nano meters that cannot be observed by an optical or electron microscope, and is used widely, now. In recent years, methods for realizing a highly integrated storage device using the SPM have been studied and much used in a photolithography for forming fine patterns. In the SPM, a probe is used to scan a surface of an object. A general structure of a probe is shown in FIG. 1. FIG. 1 is a photograph of a probe taken by a scanning electron microscope (SEM). The probe includes a cantilever 101, a body 102 supporting the cantilever 101 and a tip 103 formed at the end of the cantilever 101. The cantilever 101 includes two legs of which one ends are connected to a side of the body 102 and of which the other ends are connected to each other, so that the two legs form a triangle. A position where the other ends of the two legs are connected to each other is formed with the tip 103. The conventional probe is made of silicon dioxide, silicon nitride, metal, silicon and the like. Specifically, silicon is widely used as probe material because of its excellent mechanical characteristic. When the silicon is used as probe material, silicon on insulator (SOI) wafer is usually as a silicon substrate. An example of fabricating a probe of a AFM (Atomic Force Microscope) using the SOI wafer is described in a paper published with IEEE in 1991 by C. F. Quate et al., entitled “Atomic Force Microscope Using a Piezoresistive Cantilever”. According to this paper, a silicon cantilever is fabricated through a double side alignment process, using a silicon dioxide at the center of the SOI wafer as an etching-stopper layer. In this case, the cantilever is made of silicon with an excellent mechanical characteristic to obtain a sharp tip. However, because a complicate double side alignment process is used and a position of the silicon dioxide where etching is stopped is varied according to a thickness of the SOI wafer, a length of the cantilever is not constant. Also, because the SOI wafer is expensive, cost in mass production thereof increases. An example of fabricating a probe of a AFM (Atomic Force Microscope) using silicon dioxide, silicon nitride, metal and the like except for the silicon is described in U.S. Pat. No. 4,968,585, patented to T. R. Albrecht et. al, on Nov. 6th in 1990 and U.S. Pat. No. 5,021,364, patented to C. F. Quate et. al, on Jun. 4th in 1991. In these patents in which the probe of a AFM is made of silicon dioxide, silicon nitride, metal and the like, the mechanical characteristic of the cantilever is not as good as that of the silicon cantilever and a range in which a thickness of the cantilever can be adjusted is limited. In addition, deposition characteristic of deposited films make the tip not as sharp as the silicon tip. Therefore, a probe for an SPM and a method of fabricating the probe in which a probe with an excellent performance can be fabricated in simpler processes and in lower cost have been required. The present invention is made in order to solve the aforementioned problems. Therefore, An object of the present invention is to provide a method of fabricating a probe in which the probe can be fabricated with more ease and more simplification. Another object of the present invention is to provide a method of fabricating a probe in lower cost. Still another object of the present invention is to provide a probe with a more excellent performance. The above objects can be accomplished by a probe including a cantilever; a body supporting the cantilever; and a tip formed at an end of the cantilever, wherein the cantilever, the body and the tip are made of silicon, and boron is diffused into the cantilever and a predetermined area of the body. It is preferable that the silicon has a <110> directional crystal structure. It is more preferable that the boron is diffused into the tip. Also, the above objects can be accomplished by a method of fabricating a probe including a cantilever, a body supporting the cantilever and a tip formed at an end of the cantilever, the method comprising steps of: forming a first mask layer on an area of a silicon substrate to be formed with the body and the tip; etching the silicon substrate in a predetermined depth using the first mask layer to form the tip; removing the first mask and forming a second mask layer on an area of the silicon substrate except for an area to be formed with the body and the cantilever; forming a boron-diffused layer by diffusing boron into an area to be formed with the cantilever and a predetermined area of the body using the second mask; removing the second mask layer and forming a third mask layer on the boron-diffused layer; and etching the silicon substrate using the third mask layer to form the body and the cantilever. It is preferable that the silicon substrate has a <110> directional crystal structure. Also, it is preferable that the first, second and third mask layers are a silicon dioxide. According to the present invention, it is preferable that the step of etching the silicon substrate to form the tip is performed by an RIE (Reactive Ion Etching) process using SF6, He and O2 gases. A sharpness of the tip can be adjusted by varying a process condition of a constitution ratio of the gases, a power, a pressure and the like during the RIE process. It is still preferable that the step of forming the boron-diffused layer comprises steps of ion-implanting the boron and diffusing the boron by a heat treatment or a step of diffusing the boron by a heat treatment using a solid source containing the boron. Here, a thickness of the boron-diffused layer is determined by a temperature during the heat treatment and a time of diffusing the boron. Also, it is preferable that the step of etching the silicon substrate to form the body and the cantilever is performed by an anisotropic etching of the silicon substrate. Here, the boron-diffused layer can serve as an etching-stopper layer. It is preferable that the anisotropic etching of the silicon substrate is performed by using an etchant selected from the group consisting of EDP (Ethylene Diamine Pyrocathecol), TMAH and KOH. FIGS. 2a through 2f are cross-sectional views showing the results of various process steps for forming a silicon probe tip according to the present invention. First, as shown in FIG. 2a, a silicon substrate 201 is prepared. It is preferable that the silicon substrate has <110> directional crystal structure. Next, as shown in FIG. 2b, a first mask layer to be used as a mask during etching process for forming a silicon tip is formed on the silicon substrate. It is preferable that the first mask layer is silicon dioxide 202 and 203. The thickness of the silicon dioxide is determined by etching selectivity of the silicon substrate and the silicon dioxide. In the present embodiment, the silicon dioxide is formed 7000 Å thick. Subsequently, as shown in FIG. 2c, in order to selectively etch the silicon dioxide, photoresist 204 is coated and patterned so that the photoresist remains on a portion A of the silicon dioxide to be formed with a silicon tip and a portion B of the silicon dioxide to be formed with a body supporting the cantilever. Next, as shown in FIG. 2d, the exposed silicon dioxide is selectively etched using the remained photoresist as a mask. The selective etching is a wet etching using BOE (Buffered Oxide Etchant) as an etchant. At this time, the silicon dioxide 203 under the silicon substrate 201 is etched and removed. Subsequently, as shown in FIG. 2e, the remained photoresist is removed and the silicon substrate 201 is etched in a predetermined depth using the remained silicon dioxide as a mask to form a silicon tip 205. It is preferable that the etching is performed by RIE (Reactive Ion Etching) method using SF6, He and O2 gases. The etching is performed under such process condition as about 100 W of power and 150 mTorr of pressure. In the etching process, anisotropic etching and isotropic etching are performed at the same time. A sharpness of the silicon tip can be adjusted because if constituent ratio of the gases, the power and the pressure is varied, anisotropic and isotropic etching quantity will be adjusted. As shown in FIG. 2f, the remained silicon dioxide is removed. The silicon dioxide on the silicon tip can be previously removed by adjusting an etching time during the etching process in FIG. 2e. FIGS. 3a through 3e are cross-sectional views showing the results of various process steps for forming a boron-diffused layer in the probe according to the present invention. First, with reference to FIG. 3a, the silicon substrate with the silicon tip 205 formed as in FIG. 2f is formed thereon with a second mask layer to be used as a mask in selectively forming a boron-diffused layer. It is preferable that the second mask layer is silicon dioxide 302 and 303. In the present embodiment, it is preferable that a thickness of the silicon dioxide is 1 μm. In this case, the silicon dioxide is not formed on the end of the silicon tip as well as on the side of the silicon tip due to stress, and this enables the end of the silicon tip to become sharper. When formed at temperature not higher than about 950° C., the end of the silicon tip becomes sharpest. Also, the silicon dioxide makes the rough side of the silicon tip smooth. Here, reference number 301 indicates a silicon substrate having <110> directional crystal structure described above. Next, as shown in FIG. 3b, photoresist 304 is coated on the whole resultant surface and the photoresist on portions C to be formed with the probe body and the cantilever. On the other hand, FIG. 3c is a plan view of FIG. 3b, in which the silicon dioxide remains only on portions C to be formed with the probe body and the cantilever. On portions except for the remained silicon dioxide, photoresist 304 is formed. Successively, the silicon dioxide 302 is removed using the remained photoresist as a mask to expose the silicon substrate, and then boron is diffused. At this time, the silicon dioxide on the lower surface of the silicon substrate is removed. In the present embodiment, the boron can be diffused by ion-implantation of boron and heat treatment, or by heat treatment using a solid source containing boron. The heat treatment for diffusing boron is performed at temperature of about 850° C. through about 1200° C., most preferably at temperature of 1100° C., for 7 hours. A boron-diffused layer 305 as a result is shown in FIG. 3d. A thickness of the boron-diffused layer 305 can be easily adjusted by process temperature and diffusing time. As in the present embodiment, when the diffusion is performed at temperature of 1100 centigrade for 7 hours, a boron-diffused layer having a thickness of 4 μm is formed. On the other hand, FIG. 3e is a plan view of FIG. 3d, in which boron is diffused only into a portion C to be formed with a cantilever C and a portion A to be formed with a body supporting the cantilever, and the boron-diffused layer 305 serves as a etching-stopper layer in etching the silicon substrate to complete a probe. FIGS. 4a through 4e are cross-sectional views showing the results of various process steps for forming a cantilever of the probe according to the present invention. First, as shown in FIG. 4a, a third mask layer to be used as a mask in anisotropic etching to be performed later is formed on the silicon substrate formed with the boron-diffused layer 305 in FIG. 3e. It is preferable that the third mask layer is silicon dioxide 402 and 403. The silicon dioxide serves as protecting portions not etched in the anisotropic etching. In the present embodiment, it is preferable that a thickness of the silicon dioxide is 1 μm. As in forming the silicon dioxide 302 and 303 to selectively form the boron-diffused layer, the tip becomes sharper in forming the silicon dioxide used as an etching-mask to form the cantilever. As shown in FIG. 4b, photoresist 404 is coated on the whole resultant surface, and then the photoresist is patterned to cover only portion C to be formed with the cantilever and portion A to be formed with the body supporting the cantilever. On the other hand, FIG. 4c is a plan view of FIG. 4b, in which the photoresist remains only on portion C to be formed with the cantilever and portion A to be formed with the body supporting the cantilever and the silicon dioxide 402 to be etched is exposed. Successively, the exposed silicon dioxide 402 is etched using the remained photoresist 404. At that time, the silicon dioxide 403 on the lower surface of the silicon substrate is removed at the same time. Successively, the remained photoresist is removed to leave the silicon dioxide only on portion C to be formed with the cantilever and portion A to be formed with the body supporting the cantilever and to expose the rest portion. With reference to FIG. 4d, using the silicon dioxide remaining on portion C to be formed with the cantilever and portion A to be formed with the body supporting the cantilever as a mask, the exposed silicon substrate is etched. An EDP (Ethylene Diamine Pyrocathecol) solution which is an anisotropic etchant is used as an etchant, in which the EDP has etching ratio varied with crystal direction of silicon. In the other words, the etching ratio of <111> surface is much lower than that of <100> and <110> surfaces, so that etching is stopped on <111> surface 405. Namely, the silicon substrate is etched in a vertical direction from the surface. This is because unlike silicon having <100> crystal direction, silicon remains on the back surface of the cantilever. Therefore, the probe of a SPM can be fabricated without a double side alignment process. As other etchant, TMAH or KOH can be used for anisotropic etching of the silicon substrate. In another embodiment, as shown in FIG. 4e, gold(Au) 406 may be additionally formed on the back surface of the cantilever. This is for intensifying a reflecting effect of light, in which movement of the cantilever is detected by irradiating light to the back surface of the cantilever and measuring the phase of the reflected light. Also, before Au is deposited, Titanium(Ti)(not shown) may be deposited so as to increase the adhesion power between the silicon substrate and the boron-diffused layer. On the other hand, FIGS. 5a through 5c are cross-sectional views showing the shapes of probes formed by anisotropic etching with respect to the directions of silicon crystal structures, in which the present invention using a silicon substrate with <110> directional crystal structure and the conventional art are compared. First, in FIG. 5a illustrating the case in which the silicon substrate 501 having a <100> directional crystal structure is used, when the silicon substrate is anisotropically etched, a <111> surface of an etching-stopper surface on the back surface of the silicon cantilever 502 makes silicon remain. In this case, there is a problem that such cantilever cannot be used in the conventional SPM in which movement of the cantilever is detected by irradiating light to the back surface of the cantilever and measuring the phase of the reflected light. For solving the problem, it is required to pattern and anisotropically etch the back side of the wafer. However, such process makes the method complicated, and in addition, a position of the tip of the cantilever is varied with a thickness of the wafer to deteriorate characteristics of the cantilever. Next, FIG. 5b illustrates the case that the silicon substrate 504 having a <110> directional crystal structure is used, in which <111> surface of etching-stopper surface 505 is formed in a vertical direction from the end of the cantilever 502 by anisotropically etching the silicon substrate. Therefore, the problem that silicon remains on the back surface of the cantilever can be solved, and in addition, etching is stopped at the end of the cantilever. Also, FIG. 5c illustrates the case that the SOI wafer 506 is used as a substrate. In FIG. 5c, when the double side alignment process aligning the front and back surfaces of the wafer is used, the <111> surface of an etching-stopper surface is not formed on the back surface of the cantilever and the silicon dioxide layer 508 between silicon bulks serves as an etching-stopper layer. In this case, as in the present invention, silicon does not remain on the back surface of the cantilever. However, the double side alignment process is necessary to complicate the processes, and a length of the cantilever is varied with variation of a thickness of the wafer. Therefore, when using the silicon substrate with <110> directional crystal structure as in the present invention, a probe with an excellent performance can be easily fabricated without the complicated double side alignment process. On the other hand, the SPM of the present invention comprises an AFM (Atomic Force Microscope), an STM (Scanning Tunneling Microscope), an MFM (Magnetic Force Microscope), an EFM (Electrostatic Force Microscope), an SCM (Scanning Capacitance Microscope), an SNOM (Scanning Near-field Optical Microscope), and the like. The probe according to the present invention may be used for the aforementioned microscopes. As described above, advantages of a probe and a method of fabricating the probe according to the present invention are as follows. First, because silicon wafer having a <110> directional crystal structure is used as a probe material, the double side alignment process required in using the conventional SOI wafer is not necessary so as to simplify the processes. Second, in forming the silicon dioxide used as a mask after forming the tip, the silicon dioxide has functions sharpening the tip and smoothing the rough surface of the tip in addition to the function as a mask. The advantage of sharpening the tip is accomplished on the basis of a fact that a speed for forming the silicon dioxide is higher at the end of the tip than at the side surface of the tip. Third, because the cantilever is formed using the boron-diffused layer, the thickness of the cantilever can be adjusted with the diffusing temperature and time. Because the boron can be used as an etching-stopper layer, a silicon cantilever can be fabricated without the conventional SOI wafer used. Also, the fabrication cost can be decreased because the expensive SOI wafer is not used. Namely, according to the present invention described above in detail, the probe can be fabricated with more ease and more simplification, and in lower cost. In addition, a probe with a more excellent performance can be obtained. Although representative embodiments of a probe of a SPM and a method of fabricating the probe according to the present invention have been disclosed for illustrative purposes with reference to the appended drawings, the present invention should not be limited to the embodiments. Those who are skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the present invention as defined in the accompanying claims and the equivalents thereof. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. |
|
claims | 1. A method of cooling a suppression pool of a Boiling Water Reactor (BWR), comprising:removing heat from the suppression pool by running cooling water through a cooling pipe, the cooling water having a cooler temperature than water in the suppression pool;attaching a single inlet pipe and a single outlet pipe to the cooling pipe, the inlet and outlet pipe extending beyond the confines of the suppression pool;fluidly connecting the inlet pipe to a water source located at an elevation above a liquid level of the suppression pool; andfluidly connecting the outlet pipe to a water discharge location located at an elevation below the suppression pool,the running of the cooling water through the cooling pipe occurring via gravity draining. 2. The method of claim 1, further comprising:maintaining a pressure of the cooling water in the cooling pipe above the pressure of the suppression pool water. 3. The method of claim 1, further comprising:producing a natural convection within the suppression pool, by positioning portions of the cooling pipe above a bottom floor of the suppression pool and below a liquid level of the suppression pool. 4. The method of claim 1, further comprising:fluidly connecting the inlet pipe to a water source,connecting a pump to the inlet pipe, andelectrically connecting a back-up diesel generator to the pump. 5. The method of claim 4, further comprising:positioning the pump, and all controls for the pump, in a location that is remote from the suppression pool. 6. The method of claim 1, further comprising:providing branching and fins on portions of cooling pipe. 7. The method of claim 1, further comprising:anchoring portions of the cooling pipe to a wall of the suppression pool. 8. The method of claim 1, further comprising:inserting a second cooling pipe into the suppression pool, andremoving more heat from the suppression pool by running cooling water through the second cooling pipe, the cooling water having a cooler temperature than the suppression pool water. 9. A system of cooling a suppression pool of a Boiling Water Reactor (BWR), comprising:a cooling pipe, with portions of the cooling pipe being positioned below an expected liquid level of the suppression pool,a single inlet pipe attached to the cooling pipe,a single outlet pipe attached to the cooling pipe,the inlet and outlet pipe extending beyond the confines of the suppression pool,a water source fluidly coupled to the inlet pipe, the water source being located at an elevation above the expected liquid level of the suppression pool,a water discharge point located at an elevation below the suppression pool,the cooling pipe configured to provide a flow of cooling water through the cooling pipe via gravity draining, the cooling water being a higher pressure and cooler temperature than the suppression pool water. 10. The system of claim 9, further comprising:a pump connected to the inlet pipe, anda back-up diesel generator electrically connected to the pump. 11. The system of claim 10, further comprising:controls electrically connected to the pump,wherein the pump, and the controls for the pump, are positioned in a location that is remote from the suppression pool. 12. The system of claim 9, wherein the cooling pipe includes branches and fins. 13. The system of claim 9, further comprising:one or more anchors connected to a wall of the suppression pool, to support the cooling pipe. 14. The system of claim 9, further comprising:a second cooling pipe, with portions of the second cooling pipe being positioned below the liquid level of the suppression pool,the second cooling pipe configured to provide a flow of cooling water through the cooling pipe that is a higher pressure and cooler temperature than the suppression pool water. 15. A system of cooling a suppression pool of a Boiling Water Reactor (BWR), comprising:the suppression pool located in a reactor building,a spent fuel pool located in the reactor building, anda cooling pipe, with portions of the cooling pipe being positioned below an expected liquid level of the suppression pool,a single inlet pipe attached to the cooling pipe,a single outlet pipe attached to the cooling pipe,the inlet and outlet pipe extending beyond the confines of the suppression pool,a water source fluidly coupled to the inlet pipe, the water source being located at an elevation above the expected liquid level of the suppression pool,a water discharge point located at an elevation below the suppression pool,the cooling pipe configured to provide a flow of cooling water through the cooling pipe via gravity draining, the cooling water being a higher pressure and cooler temperature than the suppression pool water. |
|
052873927 | summary | FIELD OF THE INVENTION This invention relates to reducing the corrosion potential of components exposed to high-temperature water. As used herein, the term "high-temperature water" means water having a temperature of about 150.degree. C. or greater, steam, or the condensate thereof. High-temperature water can be found in a variety of known apparatus, such as water deaerators, nuclear reactors, and in steam-driven central station power generation. BACKGROUND OF THE INVENTION Nuclear reactors are used in central-station electric power generation, research and propulsion. A reactor pressure vessel contains the reactor coolant, i.e. water, which removes heat from the nuclear core. Respective piping circuits carry the heated water or steam to the steam generators or turbines and carry circulated water or feedwater back to the vessel. Operating pressures and temperatures for the reactor pressure vessel are about 7 MPa and 288.degree. C. for a boiling water reactor, and about 15 MPa and 320.degree. C. for a pressurized water reactor. The materials used in both boiling water and pressurized water reactors must withstand various loading, environmental and radiation conditions. Some of the materials exposed to high-temperature water include carbon steel, alloy steel, stainless steel, nickel-based alloys, and cobalt-based alloys. Despite the careful selection and treatment of these materials for use in water reactors, corrosion occurs on the materials exposed to the high-temperature water. Such corrosion contributes to a variety of problems, e.g., stress corrosion cracking, sticking of pressure relief valves, buildup of the gamma radiation emitting .sup.60 Co isotope and erosion corrosion. Stress corrosion cracking is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high-temperature water. As used herein, the term "stress corrosion cracking" (hereinafter "SCC") means cracking propagated by static or dynamic stressing in combination with corrosion at the crack tip. The reactor components are subject to a variety of stresses associated with, e.g., differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stress from welding, cold working and other asymmetric metal treatments. In addition, water chemistry, welding, heat treatment, and radiation can increase the susceptibility of metal in a component to SCC. It is well known that SCC occurs at higher rates when oxygen is present in the reactor water in concentrations of about 5 parts per billion (ppb) or greater. Stress corrosion cracking is further increased in a high radiation flux where oxidizing species, such as oxygen, hydrogen peroxide, and short-lived radicals are produced from radiolytic decomposition of the reactor water. Such oxidizing species increase the electrochemical corrosion potential of metals. Electrochemical corrosion is caused by a flow of electrons from anodic and cathodic areas on metallic surfaces. The corrosion potential is a measure of the thermodynamic tendency for corrosion phenomena to occur, and is a fundamental parameter in determining rates of, e.g., SCC, corrosion fatigue, corrosion film thickening, and general corrosion. Stress corrosion cracking in boiling water nuclear reactors and the associated water circulation piping has historically been reduced by injecting hydrogen in the water circulated therein. The injected hydrogen reduces oxidizing species in the water, such as dissolved oxygen, and as a result lowers the corrosion potential of metals in the water. However, factors such as variations in water flow rates and the time or intensity of exposure to neutron or gamma radiation result in the production of oxidizing species at different levels in different reactors. Thus, varying amounts of hydrogen have been required to reduce the level of oxidizing species sufficiently to maintain the corrosion potential below a critical potential required for protection from SCC in high-temperature water. As used herein, the term "critical potential" means a corrosion potential at or below a range of values of about -230 to -300 mV based on the standard hydrogen electrode (she) scale for the case of pure water. Stress corrosion cracking proceeds at an accelerated rate in systems in which the electrochemical potential is above the critical potential, and at a substantially lower rate in systems in which the electrochemical potential is below the critical potential. Water containing oxidizing species such as oxygen increases the corrosion potential of metals exposed to the water above the critical potential, whereas water with little or no oxidizing species present results in corrosion potentials below the critical potential. In a boiling water reactor (BWR), the radiolysis of the primary water coolant in the reactor core causes the net decomposition of a small fraction of the water to the chemical products H.sub.2, H.sub.2 O.sub.2 and O.sub.2. For steady-state operating conditions, equilibrium concentrations of O.sub.2, H.sub.2 O.sub.2, and H.sub.2 are established in both the water which is recirculated and the steam going to the turbine. This concentration of O.sub.2, H.sub.2 O.sub.2, and H.sub.2 is oxidizing and results in conditions that can promote SCC of susceptible materials of construction. One method employed to mitigate SCC of susceptible material is called hydrogen water chemistry, whereby the oxidizing nature of the BWR environment is modified to a more reducing condition. This effect is achieved by adding hydrogen gas to the reactor feedwater. When the hydrogen reaches the reactor vessel, it reacts with the radiolytically formed oxidizing species to reform water, thereby lowering the concentration of dissolved oxidizing species in the water. The rate of these recombination reactions is dependent on local radiation fields, flow rates and other variables. Corrosion potentials of stainless steels in contact with reactor water containing oxidizing species can be reduced below the critical potential by injection of hydrogen into the water in a concentration of about 50 to 100 ppb or greater. For adequate feedwater hydrogen addition rates, the conditions necessary to inhibit SCC can be established in certain locations of the reactor. These conditions are an electrochemical potential of less than -0.230 V.sub.she. Different locations in the reaction system require different levels of hydrogen addition, as shown in FIG. 2. Much higher hydrogen injection levels are necessary to reduce the corrosion potential within the high radiation flux of the reactor core, or when oxidizing cationic impurities, e.g., cupric ion, are present. However, feedwater hydrogen additions, e.g., of about 200 ppb or greater, that reduce the corrosion potential below the critical potential, can result in a higher radiation level in the steam-driven turbine section from incorporation of the short-lived .sup.16 N species, as shown in FIG. 3. For most BWRs, the amount of hydrogen addition required to provide mitigation of SCC of pressure vessel internal components results in an increase in the main steam line radiation monitor ("MSLRM") by a factor of greater than about four. This increase in main steam line radiation can cause high, even unacceptable, environmental dose rates that can require expensive investments in shielding and radiation exposure control. Accordingly, although the addition of hydrogen lowers the corrosion potential of reactor water, it is also desirable to limit the amount of hydrogen in reactor water, while maintaining the corrosion potential below the critical potential. The primary products of water radiolysis in the core are H.sub.2, H.sub.2 O.sub.2, OH, H and the hydrated electron. In irradiated water, O.sub.2 and H.sub.2 O.sub.2 are in a state of dynamic equilibrium. During HWC, the computed ratio of H.sub.2 O.sub.2 to O.sub.2 in the downcomer annulus is large. The reason reported by M. Ullberg et al., "Hydrogen Peroxide in BWRs", Water Chemistry for Nuclear Reactor Systems 4, BNES, London, 1987, pp. 67-73, is that the H.sub.2 added during HWC initially slows down the oxidation of H.sub.2 O.sub.2 to O.sub.2, speeds up the reduction of O.sub.2 to H.sub.2 O.sub.2 and has little effect on the reduction of H.sub.2 O.sub.2 to H.sub.2 O. Thus, hydrogen peroxide is relatively stable in the recirculation water of a BWR. It is further known from the Ullberg et al. article that H.sub.2 O.sub.2 in water will decompose on a heterogeneous solid surface at elevated temperatures by the reaction: EQU 2H.sub.2 O.sub.2 +Surface.fwdarw.2H.sub.2 O+O.sub.2 This decomposition of H.sub.2 O.sub.2 is referred to as heterogeneous decomposition. The rate of decomposition can be increased through the use of decomposition catalysts and will also be dependent on the temperature and the ratio of surface area to volume. SUMMARY OF THE INVENTION The present invention improves upon the conventional BWR operated in accordance with the HWC principle by incorporating a passive structure immediately downstream of the steam separator assembly which catalyzes the decomposition of hydrogen peroxide only or which catalyzes both the decomposition of hydrogen peroxide and the recombination of water. The only difference in the structure of the respective catalyzers is that the catalyzing structure which recombines water includes a water recombination catalyst, such as a noble metal, whereas the catalyzing structure which decomposes hydrogen peroxide without recombining water includes no water recombination catalyst. The present invention improves upon known HWC techniques by allowing the achievement of specified conditions at key locations in the reactor system by addition of relatively lower levels of hydrogen to the feedwater. Thus, he negative side effect of high main steam line radiation increase can be avoided. In addition, the amount of hydrogen required and associated costs will be reduced significantly. One preferred embodiment of the invention is a passive recombiner operating in the water phase of the BWR vessel immediately downstream of the steam/water separator location. This recombiner comprises a catalytic material arranged and situated in an open structure having a high surface area-to-volume ratio such that all (except perhaps a small leakage flow) water phase exiting the steam/water separator device flows over the surface of the catalytic material. The catalytic recombining surfaces react with the water radiolysis product species H.sub.2, O.sub.2 and H.sub.2 O.sub.2 in the liquid phase to reform water in accordance with reactions such as (but not limited to) the following: ##STR1## Reaction (3) is followed by reaction (1) to produce water. The passive catalytic recombiner of the invention is constructed to ensure that the pressure drop of the reactor water across the device is very small (less than 5 psi). In addition, the catalytic material must be corrosion resistant in pure water under BWR conditions and have structural strength at reactor temperatures. The recombiner includes a stainless steel flow-through housing packed with catalytic recombiner material, which could take the form of tangled wire or strips, crimped ribbon, porous sintered metal composite, a honeycomb structure or any other structure having a high surface area-to-volume ratio. The preferred catalytic recombiner material is stainless steel plated or alloyed with a noble metal. In accordance with another preferred embodiment of the invention, a passive catalytic decomposer is provided in a conventional BWR by installing the same flow-through structure as that used for the recombiner, except that the material making up the high surface area-to-volume structure does not incorporate a water recombination catalyst. The decomposer is made of a solid material having surfaces which cause heterogeneous decomposition of hydrogen peroxide, but which do not catalyze water recombination. The preferred catalytic decomposer material is stainless steel because of its predictable performance in a BWR environment. However, other solid materials which cause heterogeneous decomposition and which have structural strength and corrosion resistance suitable for the BWR environment can be used. The catalytic surfaces of the decomposer react with the water radiolysis product H.sub.2 O.sub.2 in the liquid phase to decompose H.sub.2 O.sub.2 in accordance with reaction (3). |
claims | 1. An apparatus for inserting or removing a string of tubulars from a subsea borehole, the apparatus comprising: a first, lower, gripping mechanism for use in a location subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars; a second, upper, gripping mechanism for use in a location subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars; wherein the first and second gripping mechanisms are moveable with respect to one another; a movement mechanism which, when actuated, moves one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms, such that the string of tubulars is inserted into or removed from the subsea borehole; a make up/break out mechanism configured to one of add a tubular to and remove a tubular from the string; and a compensation mechanism configured to keep the make up/breakout mechanism substantially stationary with respect to a subsea surface. 2. An apparatus as claimed in claim 1 wherein the first gripping mechanism is lower than the second gripping mechanism. claim 1 3. An apparatus as claimed in claim 2 wherein the first gripping mechanism is adapted to be substantially stationary with respect to the mouth of the subsea borehole, and the second upper gripping mechanism is moveable with respect to the first gripping mechanism. claim 2 4. An apparatus as claimed in claim 1 wherein the movement mechanism comprises a jacking mechanism including a piston cylinder and a piston located within the piston cylinder, and one of the first and second gripping mechanisms is secured to the piston and the other of the first and second gripping mechanisms is secured to the piston cylinder. claim 1 5. An apparatus as claimed in claim 4 wherein the jacking mechanism is operable by introducing fluid into, or removing fluid from, one side of the piston within the piston cylinder. claim 4 6. An apparatus as claimed in claim 5 further comprising a fluid reservoir to introduce fluid into, or remove fluid from, one side of the piston within the piston cylinder. claim 5 7. An apparatus as claimed in claim 6 wherein the fluid reservoir comprises a high pressure fluid reservoir. claim 6 8. An apparatus as claimed in claim 1 wherein the fluid reservoir is locatable subsea. claim 1 9. An apparatus as claimed in claim 8 wherein the fluid reservoir is disposed in close proximity to the jacking system. claim 8 10. An apparatus as claimed in claim 1 wherein the jacking mechanism and first and second gripping means are locatable vertically above a subsea equipment package. claim 1 11. An apparatus as claimed in claim 10 wherein the jacking mechanism and first and second gripping means are locatable in line with the subsea equipment package. claim 10 12. An apparatus as claimed in claim 1 further comprising a make up/break out mechanism which is capable of adding a tubular to or removing a tubular from the string. claim 1 13. An apparatus as claimed in claim 12 comprising a handling mechanism adapted to deliver a tubular into, or remove a tubular from, the make up/break out mechanism. claim 12 14. An apparatus as claimed in claim 1 further comprising a compensation mechanism to compensate the make up/break out mechanism for movement of a vessel in the sea. claim 1 15. An apparatus as claimed in claim 14 wherein the compensation mechanism is adapted to compensate for movement of the vessel in a direction parallel to the axial direction of the string, such that the string may be substantially continuously inserted into or removed from the borehole. claim 14 16. An apparatus for inserting or removing a string of tubulars from a subsea borehole, comprising: a first, lower, gripping mechanism for use in a location subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars; a second, upper, gripping/mechanism for use in a location subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars, wherein the first and second gripping mechanisms are moveable with respect to one another; a movement mechanism which, when actuated, moves one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms such that the string of tubulars is inserted into or removed from the subsea borehole; and a make up/breakout mechanism capable of adding a tubular to or removing a tubular from the string, wherein the make up/break out mechanism comprises a pair of vertically spaced tongs which are adapted to selectively grip the tubular. 17. An apparatus as claimed in claim 16 wherein an uppermost tong of the vertically spaced tongs is adapted to impart rotation to the tubular. claim 16 18. An apparatus for inserting or removing a string of tubulars from a subsea borehole, comprising: a first, lower, gripping mechanism for use in a location subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars; a second, upper, gripping mechanism for use in a location subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars, wherein the first and second gripping mechanisms are moveable with respect to one another; a movement mechanism which, when actuated, moves one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms such that the string of tubulars is inserted into or removed from the subsea borehole; and a riser into which an upper end of a string is insertable at a vessel. 19. An apparatus as claimed in claim 18 wherein the lower end of the riser is sealable with respect to the sea. claim 18 20. An apparatus as claimed in claim 1 further comprising a control system to control actuation of the first and second gripping mechanisms. claim 1 21. An apparatus as claimed in claim 20 wherein the control system is adapted to control the jacking mechanism. claim 20 22. An apparatus as claimed in claim 1 wherein the fluid reservoir is chargeable from a pump located on a vessel. claim 1 23. A method of inserting or removing a string of tubulars from a subsea borehole, the method comprising: providing a first gripping mechanism located subsea in the vicinity of the subsea borehole, the first gripping mechanism being capable of gripping a portion of the string of tubulars; providing a second gripping mechanism located subsea in the vicinity of the subsea borehole, the second gripping mechanism being capable of gripping a portion of the string of tubulars; wherein the first and second gripping mechanisms are moveable with respect to one another; providing a movement mechanism which is capable of moving one of the first and second gripping mechanisms with respect to the other of the first and second gripping mechanisms; actuating the movement mechanism such that the string of tubulars is inserted into, or removed from, the subsea borehole; providing a make up/breakout mechanism for one of adding a tubular to the string and removing the tubular from the string; and providing a compensation mechanism for keeping the make up/breakout mechanism substantially stationary with respect to a subsea surface. 24. A method as claimed in claim 23 wherein the first gripping mechanism is lower than the second gripping mechanism. claim 23 25. A method as claimed in claim 23 wherein the first gripping mechanism is substantially stationary with respect to the mouth of the subsea borehole, and the second, upper, gripping mechanism is moved with respect to the first gripping mechanism. claim 23 26. A method as claimed in claim 25 wherein the second, upper, gripping mechanism is operated to grip the string of tubulars whilst the movement mechanism is actuated. claim 25 27. A method as claimed in claim 26 wherein the first, lower, gripping mechanism is not actuated such that the first, lower, gripping mechanism does not grip the string of tubulars. claim 26 28. A method as claimed in claim 27 wherein the first, lower, gripping mechanism is operated to grip the string of tubulars when the second, upper, gripping mechanism is not operated to grip the string of tubulars. claim 27 |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.