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description | This application claims the benefit of U.S. Provisional Application No. 62/039,361, filed Aug. 19, 2014, the disclosure of which is hereby expressly incorporated by reference in its entirety herein. In a previously designed system and process described in U.S. Pat. No. 4,780,269 (as seen in FIGS. 1-4), a spent fuel storage system 10 uses a dry shielded canister 12. The canister assembly 12 is inserted into a transfer cask 14. The transfer cask 14 and canister assembly 12 can be placed by a crane 16 into an irradiated fuel storage pool 18 filled with water (see FIG. 1). Irradiated fuel contained in fuel assemblies (see, e.g., fuel assembly 20) can be stored in the pool 18. To remove the irradiated fuel from the pool 18, the fuel is placed in the canister assembly 12, and appropriate seals and covers (as described below) are affixed to the canister assembly 12 before the transfer cask 14 is removed from the pool 18. Referring to FIG. 2, upon removal from the pool 18, water can be forced out of both the canister assembly 12 and the transfer cask 14 with a pressurized gas being applied through selected ports of the canister assembly and cask. The canister assembly 12 can further be dried by using a vacuum pump to evacuate the residual water from the canister assembly 12. After evacuation of the canister assembly 12, helium or another gas may be pumped into the canister assembly 12. As the transfer cask 14 (containing the canister assembly 12 and irradiation fuel assemblies 20) is removed from the pool 18, appropriate radiation shielding is provided for the contained irradiated fuel assemblies by the shielded end plugs of the canister assembly 12 and the transfer cask 14. Referring now to FIG. 3, the transfer cask 14 can be loaded into a horizontal position onto a transfer trailer 22 having a specially designed skid 24. The skid 24 allows the transfer cask 14 to be moved in three dimensions to permit alignment of the cask 14 with a horizontal storage module (HSM) 26, which can be seen in FIG. 4, for dry storage of the canister assembly 12. Referring to FIG. 4, the cask 14 is aligned with a port 28 in the HSM 26 to extract the canister assembly 12 from the transfer cask 14 for storage in the horizontal storage module 26. In the illustrated embodiment, a hydraulic ram 30 is at least partially insertable through a second port 32 at the opposite end of the dry storage module 26 to extract the canister assembly 12 from the transfer cask 14 for storage in the horizontal storage module 26. Alternatively, a winch (not shown) or another extraction device could be used in place of ram 30 to extract the canister assembly 12 from the transfer cask 14. It should further be appreciated that the reverse operation of pushing the canister assembly 12 into the dry storage module 26 can also be accomplished. There exists a need for improvements to the previously designed storage system and method. Embodiments of the present disclosure aim to improve these and other systems and methods. This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. In accordance with one embodiment of the present disclosure, a transport conveyance for a canister containing radioactive material is provided. The conveyance includes means for lateral movement; walls defining an interior compartment for holding a canister and a support structure; and actuation means for moving the canister and the support structure horizontally from the compartment. In accordance with another embodiment of the present disclosure, a transport conveyance for a canister containing radioactive material is provided. The conveyance includes one or more transport conveyance devices for lateral movement of the transport conveyance; outer walls defining an interior compartment for holding a canister and a support structure; and a transfer assembly for moving the canister and the support structure horizontally from the compartment. In accordance with another embodiment of the present disclosure, a method of transferring radioactive material in a canister to a storage module is provided. The method includes acquiring radioactive material in a canister; placing the canister on a support structure in a transport conveyance; and moving the support structure and the canister into the storage module using a transfer assembly. In accordance with another embodiment of the present disclosure, a method of transferring radioactive material in a canister to a storage module is provided. The method includes acquiring radioactive material in a canister; placing the canister on a support structure; and moving the support structure and the canister into the storage module. In accordance with another embodiment of the present disclosure, a system for transferring a canister containing radioactive material from a cask to a horizontal storage module is provided. The system includes a transfer station for transferring the canister from the cask to a support structure; and a transport conveyance for conveying the canister and the support structure in a horizontal orientation to a horizontal storage module and loading the canister and the support structure into the horizontal storage module. In accordance with another embodiment of the present disclosure, a horizontal storage module for a canister containing radioactive material is provided. The module includes a housing having an interior space for receiving a cylindrical canister disposed on a support structure; and a closure. In accordance with another embodiment of the present disclosure, a transport conveyance for a canister containing radioactive material is provided. The conveyance includes means for lateral movement; walls defining an interior compartment for holding a canister and a support structure; and actuation means for moving the canister and the support structure horizontally from the compartment. In accordance with another embodiment of the present disclosure, a transport conveyance for a canister containing radioactive material is provided. The conveyance includes one or more transport conveyance devices for lateral movement of the transport conveyance; outer walls defining an interior compartment for holding a canister and a support structure; and a transfer assembly for moving the canister and the support structure horizontally from the compartment. In any of the embodiments described herein, the transport conveyance may be a transfer wagon. In any of the embodiments described herein, the one or more transport conveyance devices may be selected from the group consisting of wheels, tracks, rollers, bearing pads, bearing surfaces, air skids, and combinations thereof. In any of the embodiments described herein, the outer walls may include shielding material for radiation containment. In any of the embodiments described herein, the transfer assembly may include a jack assembly. In any of the embodiments described herein, the transfer assembly may include one or more transfer conveyance devices. In any of the embodiments described herein, the transfer assembly may include a lateral extender. In any of the embodiments described herein, the one or more transfer conveyance devices may be selected from the group consisting of wheels, tracks, rollers, bearing pads, bearing surfaces, air skids, and combinations thereof. In any of the embodiments described herein, the transfer assembly may be hydraulically or electromechanically operated In any of the embodiments described herein, the canister may be placed on the support structure in a conveyance. In any of the embodiments described herein, the conveyance may move the support structure and the canister to the storage module. In any of the embodiments described herein, the storage module may be a horizontal storage module. In any of the embodiments described herein, the support structure may be supported by a transfer wagon configured to move the canister. In any of the embodiments described herein, the transfer wagon may include one or more outer walls. In any of the embodiments described herein, the one or more outer walls may include shielding material for radiation containment. In any of the embodiments described herein, the canister may be acquired in a horizontal orientation. In any of the embodiments described herein, the canister may be acquired in a vertical orientation, further comprising transferring the material from the vertical orientation to a horizontal orientation before moving the support structure and the canister into the horizontal storage module. In any of the embodiments described herein, transferring the material from the vertical orientation to the horizontal orientation may include up-ending the conveyance to a vertical orientation to receive the canister, then righting the conveyance to a horizontal orientation. In any of the embodiments described herein, a method may include further comprising transferring the canister from a cask. In any of the embodiments described herein, the transfer station may be a vertical to horizontal transfer station. In any of the embodiments described herein, the transfer station may include an up-ender platform to move the transport conveyance to a vertical orientation for receiving the canister. In any of the embodiments described herein, the transfer station may include a securement device for securing the transport conveyance on the up-ender platform. In any of the embodiments described herein, the transfer station may include a gantry platform for mating with the transport conveyance when in the vertical orientation. In any of the embodiments described herein, the gantry platform may guide a canister into the conveyance in the vertical orientation. In any of the embodiments described herein, the gantry platform may include an aperture through which the canister is delivered. In any of the embodiments described herein, the gantry platform may include a device for removing a lid on the cask to allow delivery of the canister from the cask. In any of the embodiments described herein, the gantry platform may include a device for removing a door on the transport conveyance to allow insertion of the canister in the transport conveyance. In any of the embodiments described herein, the up-ender platform may be configured to move the transport conveyance from a vertical orientation back to a horizontal orientation. In any of the embodiments described herein, the transfer station may be a horizontal to horizontal transfer station. In any of the embodiments described herein, the transfer station may include a roller stand. In any of the embodiments described herein, the transfer station may include a lift assembly. In any of the embodiments described herein, the lift assembly may be a sling lift assembly. In any of the embodiments described herein, the conveyance may include an actuation assembly for moving the canister and the support structure into the horizontal storage module. In any of the embodiments described herein, the transport conveyance may include one or more transport conveyance devices. In any of the embodiments described herein, the one or more transport conveyance devices may be selected from the group consisting of wheels, tracks, rollers, bearing pads, bearing surfaces, air skids, and combinations thereof. In any of the embodiments described herein, the transport conveyance may include a transfer assembly for loading the canister and the support structure into the horizontal storage module. In any of the embodiments described herein, the transfer assembly may include a jack assembly, one or more transfer conveyance devices, and a lateral extender. In any of the embodiments described herein, the one or more transfer conveyance devices may be selected from the group consisting of wheels, tracks, rollers, bearing pads, bearing surfaces, air skids, and combinations thereof. In any of the embodiments described herein, the interior space of the HSM may have a rectangular cross-section. In any of the embodiments described herein, the interior space of the HSM may not have a circular cross-section. In any of the embodiments described herein, the housing may not include rails for receiving a canister. In any of the embodiments described herein, the housing may not include heat shields. In any of the embodiments described herein, the housing may not include dissipation fins. In any of the embodiments described herein, the housing may be made from a high temperature concrete. In any of the embodiments described herein, the housing may be made from a non-porous concrete. In any of the embodiments described herein, a storage facility may include a plurality of adjacent horizontal storage modules as described herein. The detailed description set forth below in connection with the appended drawings in which like numerals reference like elements is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result. In the following description, numerous specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that many embodiments of the present disclosure may be practiced without some or all of the specific details. In some instances, well-known process steps have not been described in detail so as not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein. Embodiments of the present disclosure are directed to systems, components, and methods for transferring canisters containing radioactive material, for example, from a container assembly using a transfer assembly to a horizontal storage module (HSM). Systems in accordance with various embodiments of the present disclosure include, for example, a vertical to horizontal (VTH) transfer station for a canister and method of transfer (see FIGS. 10-27), a horizontal to horizontal (HTH) transfer station for a canister and methods of transfer (see FIGS. 28-33), a transport wagon system for transporting a canister to a horizontal storage module (HSM) (see e.g., FIGS. 5, 25, and 28), and an HSM system for long-term storage of a canister (see FIG. 5-8). Horizontal Storage Module (HSM) With reference to FIG. 5-8, a horizontal storage modular (HSM) 120 for the dry storage of irradiated (e.g., spent) fuel will now be described. The horizontal dry storage module 120 includes a housing 140. The housing 140 is in block or rectilinear form and is preferably constructed from reinforced concrete, which may be positioned on a load-bearing foundation 142 (see, e.g., FIG. 6). In previously designed HSMs, the housing was typically formed from concrete reinforced with rebar. However, in the improved design described herein, the housing 140 is reinforced with metal fiber, for example, steel fiber, to increase blast, missile, and earthquake resistance and provide long-term durability and crack resistance. The metal fiber also reduces shrinkage and cracking of the concrete in the short term, thereby decreasing water incursion and also increasing spalling resistance in the long term. In sum, the use of steel or other comparable fibers to reinforce the concrete increases the toughness, tensile strength, density, and dynamic strength of the concrete. Vertical storage modules or other storage modules (not shown), having housings reinforced with metal fiber, for example, steel fiber, are also within the scope of the present disclosure. Also, it is to be appreciated that the use of metal fiber to reinforce the concrete can be used in lieu of or in addition to primary and secondary rebar used in standard concrete construction. Further, other high-strength fibers can be used in place of or in addition to metal fibers, such as fiberglass fibers, glass fibers, or carbon fibers. In addition to metal fiber reinforcement, the housing 140 may be formed using a high temperature concrete, for example, CERATECH brand concrete. High temperature properties reduce the need for a heat dissipation assembly (such as a heat shield assembly) in the housing 140 by being more resistant to high temperatures and able to more readily dissipate heat. In previously designed HSMs, heat shields are used in the interior space of the HSM by enhancing the overall heat rejection capability of canister assembly 12 by increasing the surface area for heat rejection. In that regard, the heat shields were designed to be heated both by radiation and by air flowing from the canister to the near surface of the shield by natural convection. A heat shield configuration directly increases the surface area available for transferring heat away from the canister 12. Also, a shielding surface facing the concrete wall increases the ability of the shield to serve as a heat barrier and protecting the concrete walls of the housing from being overheated. As a non-limiting example of a previous design, a heat dissipation assembly 60 including heat dissipation fins 62 from a previously designed HSM can be seen in FIG. 8. The fins 62 were used to enhance convective heat transfer from the canister surface to the air flowing through the module 26. In addition to being high temperature, the concrete used in HSMs designed in accordance with embodiments of the present disclosure may be substantially non-porous. Non-porous properties improve the long-term durability of the housing 140 and help reduce or prevent water permeation. The housing 140 includes an inlet 144 at one end and an interior volume 146 designed for receiving and containing a canister assembly 12. Embedded in housing 140 is an underlying support bed 148 to support the canister assembly 12 when it is fully inserted into housing 140. The support bed 148 may be positioned on an optional raised base-mat (not shown) to raise the height of the inlet 144 into the HSM 120, but to reduce the amount of concrete requirement for the housing 140. In accordance with embodiments of the present disclosure, the canister 12 rests on a support structure or skid 160 transferred from a wagon 170 into the HSM together with the storage canister 12. In contrast, in previously designed systems, the canister 12 was moved along rails into the HSM (see FIG. 8). One advantageous effect of the support structure 160 transferring into the HSM 120 is that it eliminates the need for highly accurate alignment that was required to slide the canister 12 onto the rails fixed in the previously designed HSM. In addition, the transfer of the support structure 160 reduces the chance of scratches to the canister 12, which may provide a weakness in the canister or opportunity for corrosion. In addition, the cradle effect of the support structure 160 also contributes to improved convective air cooling of the canister 12 as compared to the previously designed longitudinal rail support as seen in FIG. 9. In that regard, the rectangular cross-section of the HSM has increased inner volume as compared to the circular cross-section of the previously designed HSM, allowing for more air circulation and heat dissipation. As will be discussed in greater detail below, wagon 170 delivers the canister 12 on the support structure 160. Referring to FIG. 5, a temporary shielding structure 190 can be installed at the inlet 144 to the HSM 120. The support structure 160 and the wagon 170 include an actuation means, such as transfer assembly 180, for transferring the support structure 160 from the wagon 170 to the HSM 120 (see FIG. 6). The housing 140 includes a closure device 150 to cover the inlet 144. The closure device 150 may be constructed from steel and/or concrete and/or other appropriate radiation protection media. As seen in FIG. 9, a closure device 50 from a previously developed system includes an inner, round-shaped cover plug 54 and an outer hat plate 52 that is sized to overlap the front wall of the housing surrounding the inlet 44. The plug 54 closely fits within inlet 44. In embodiments of the present disclosure, the closure device 150 is a wall-type structure that mates with the housing 140 (see FIG. 5), which provides for more structural integrity in the closure. Referring to FIG. 5, the housing 140 may be designed and configured to allow similar housings 140 to be placed adjacent other housings, which may be interlocked therewith. Therefore, several housings 140 can be affixed next to each other and stacked together in series to provide additional shielding to minimize radiation leakage. Multiple HSMs 120 may be arranged in a centralized interim storage facility having infrastructure to support the dry storage of spent nuclear fuel. As discussed in greater detail below, transfer systems are capable of placing into horizontal storage a canister 12 designed to be handled either horizontally or vertically. In addition, other configurations of placing a canister into vertical storage (not shown) from either horizontal or vertical transport are also within the scope of the present disclosure. Transport Wagon Referring to FIGS. 5 and 28, the transport conveyance or wagon 170 for transporting the canister 12 to the HSM 120 will now be described in detail. The wagon 170 is a configured to move and may include conveyance devices 176, including but not limited to wheels, tracks, rollers, bearing pads or surfaces, such as Teflon pads, air skids, or suitable other conveyance means or devices for movement, and combinations thereof. In addition, the wagon has outer walls 174 for receiving and containing a canister 12 supported on a support structure 160. The outer walls 174 may include shielding material for radiation containment. The wagon 170 is sized and configured to support a support structure 160 for the canister 12. In the illustrated embodiment of FIG. 28, the support structure 160 is a pallet or skid upon which the canister 12 is received. In the illustrated embodiment, the support structure 160 includes two supports 178 for holding the canister 12. As can be seen in FIGS. 6 and 7, the canister 12 is transferred to the HSM 120 by transferring the entire support structure 160 upon which the canister 12 is supported from the wagon 170 and into the HSM 120. In the illustrated embodiment of FIG. 8, transfer is achieved by a transfer assembly 180 that includes a jack assembly 186, rollers or tracks 182, and a lateral extender 184. The transfer assembly 180 is shown in FIG. 8 in a cut-away view of the undercarriage of the support structure 170. When in the transport wagon 170, the jacks that make up the jack assembly 180 are extended such that the support structure 160 is lifted off tracks 182 and therefore not capable of lateral movement. When the wagon 170 is aligned with the inlet of the HSM 120, the jack assembly 180 can be retracted, such that the support structure 160 rests on the transfer conveyance devices 182. In the illustrated embodiment, the transfer conveyance devices are show as rollers. Other transfer conveyance devices include but are not limited to wheels, tracks, rollers, bearing pads or surfaces, such as Teflon pads, air skids, or suitable other conveyance means or devices for movement, and combinations thereof. When enabled for lateral movement, a lateral extender 184 can telescope to push against a wall of the wagon 170 to push the support structure 160 and the canister 12 into the interior 146 of the HSM 120. The transfer assembly 180 may be hydraulically or electromechanically operated. As described in greater detail below with respect to FIGS. 10-33, the transport wagon 170 is designed and configured for either vertical or horizontal receipt of a canister 12. Vertical to Horizontal Transfer Station Referring to FIG. 10-27, a vertical to horizontal (VTH) transfer station 200 and methods of using the same will now be described. Referring to FIG. 10, the VTH transfer station 200 includes up-ender platform 210 for receiving the transport wagon 170, and a gantry platform 220 to guide the insertion of a canister 12 into the up-ended transport wagon 170. Now referring to FIGS. 11-15, a method of transferring a canister 12 into the transport wagon 170 using the VTH transfer station 200 will be described. Referring to FIG. 12, the transport wagon 170 rolls onto and is received on the up-ender platform 210 and abuts a stop 214 that prevents the transport wagon 170 from traveling off the up-ender platform 210. When on the platform 210, a frame 216 surrounds the wagon. A securement device 212 on the frame can be used to secure the wagon 170 on the platform 210. In the illustrated embodiment of FIGS. 16-18, the securement device 212 is a clamping mechanism that is spaced from the top of the transport wagon 170. When the wagon 170 is received on the up-ender platform 210, the clamping mechanism engages the top of the wagon 170 to secure the wagon on the platform 210. Referring to FIGS. 12-14, the up-ender platform 210 is then tilted from its normal horizontal position (see FIG. 12) to an intermediate position (see FIG. 13), and to an upright vertical position (see FIG. 14). In the illustrated embodiment, a lifting device 222 located beneath one end of the platform 210 lifts the platform such that the platform pivots 90 degrees around pivot hinge 218. The lifting device 222 may be a hydraulic device or other type of lifting device. Comparing FIGS. 14 and 15, after the wagon 170 is up-ended to the vertical position, a gantry platform 220 moves to align with the transport wagon 170 in an engaged position. When in the upright vertical position and engaged with the gantry platform 220, a vertically oriented canister 12 can be lowered into the up-ended wagon 170 (as further described below with reference to FIGS. 19-27). Referring now to FIGS. 19-21, the mechanism for opening the wagon door 232 to allow access for the canister is shown and described. When the gantry platform 220 is engaged with the up-ender platform 210, a sliding platform 230 on the gantry platform 220 can be used to slidingly open the wagon door 232. In that regard, the sliding platform 230 slides from a first unengaged position (see FIG. 19) to a second engaged position (see FIG. 20), in the direction of arrow A1 in FIG. 20. When engaged, extensions 234 extend upwardly to engage with the door 232 in the direction of arrow A2 in FIG. 20. When the extensions 234 are engaged with the door 232, they are used to pull the door 232 in the direction of arrow A3 in FIG. 21 from a closed position (see FIG. 20) to an open position (see FIG. 21). Referring now to FIG. 22, the vertically oriented transport cask 14 holding a canister 12 can be lowered to meet the gantry platform 220 in the direction of arrow A4 and be deposited into the up-ended wagon 170. In that regard, the gantry platform 220 includes a top aperture 240 for receiving a canister 12 therethrough. Referring now to FIG. 23, when the cask 14 abuts the gantry platform 220, a lid 34 on the cask 14 can be slidingly removed from the cask 14 using sliding platform 242 which is configured to move in the direction of arrow A5. As can be seen in FIG. 24, the canister 12 is lowered from the cask 14 into the wagon 170 in the direction of arrow A6. After the vertically oriented canister 12 has been received by the up-ended wagon 170, the wagon door 232 is returned to its closed position in the direction of arrow A7 (see FIG. 25), the sliding platform 242 is returned to its closed position in the direction of arrow A8 (see FIG. 26), and the cask 14 is vertically lifted away from the gantry platform 220 in the direction of arrow A9 (see FIG. 27). Thereafter, the gantry platform 220 is returned to its unengaged position (see FIG. 14), and the wagon 170 can then returned to its horizontal position (see reverse process in series of FIG. 14, 13, 12). In the horizontal position, the canister 12 rests on the transfer skid 160 in the wagon 170, and the wagon 170 can be used to convey the canister 12 to the HSM 120 (see FIG. 5). Horizontal to Horizontal Transfer Station Referring now to FIGS. 28-33, a horizontal to horizontal (HTH) transfer station 300 will now be described. The HTH transfer station 300 includes a roller stand 310 for receiving a canister 12 from a horizontally oriented transport cask 14. The HTH transfer station 300 further includes a lift assembly 320 for lifting the canister 12 from the roller stand 310 onto the support structure 160 in the transfer wagon 170. A ram 324 may be used to move the canister 12 from the horizontally oriented transport cask 14 to the roller stand 310. In previously designed system, rails were used to receive a canister 12. The advantageous effect of a roller stand 310 is that is reduces the chance of scratches to the canister 12, which may provide a weakness in the canister or opportunity for corrosion. In the illustrated embodiment, the lift assembly 320 is a sling lift. In that regard, lifting straps 322 can be used to lift and move the canister 12. However, other lifts are also within the scope of the present disclosure. Referring to FIG. 29, canister 12 is received from the cask 14 onto the roller stand 310. Lifting straps 322 are placed around the canister 12 and the canister is lifted using canister lifting device 320. Referring to the sequence of FIGS. 30 and 31, the canister 12 is moved using the canister lifting device 320 from the roller stand 310 to the support structure 160 (or transfer skid) in the transport wagon 170. Referring to the sequence of FIGS. 32 and 33, after being placed in the transport wagon 170, lifting straps 322 disengage and are retracted to a position above the roller stand 310. As seen in FIG. 33, lid 250 from the transport wagon 170, which is shown retracted by lid lift assembly 252 in FIG. 29, is replaced on the transport wagon 170. While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure. |
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claims | 1. A gamma radiation source comprising: 75Selenium or a precursor thereof, wherein the 75Selenium is provided in the form of one or more thermally stable compounds or mixtures, and with one or more nonmetals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of 75Selenium. 2. A gamma radiation source as defined in claim 1, wherein the one or more nonmetals comprise a natural isotopic composition, an enriched isotopic composition, or a depleted isotopic composition. 3. A gamma radiation source comprising: 75Selenium or a precursor thereof, wherein the 75Selenium is provided in the form of one or more thermally stable compounds, or mixtures with one or more nonmetals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of 75Selenium, wherein the one or more nonmetals may comprise a natural isotopic composition, an enriched isotopic composition, or a depleted isotopic composition; wherein the gamma radiation peaks of the composition may be adjusted in relative frequency. 4. A gamma radiation source comprising: 75Selenium or a precursor thereof, wherein the 75Selenium is provided in the form of one or more thermally stable compounds, or mixtures, and with one or more nonmetals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of 75Selenium, wherein said one or more nonmetals comprises Germanium or Silicon. 5. A gamma radiation source comprising: 75Selenium or a precursor thereof, wherein the 75Selenium is provided in the form of one or more thermally stable compounds, or mixtures with one or more nonmetals the neutron irradiation of which does not produce products capable of sustained emission of radiation which would unacceptably interfere with the gamma radiation of 75Selenium, wherein the one or more nonmetals may comprise a natural isotopic composition, an enriched isotopic composition, or a depleted isotopic composition, wherein said one or more nonmetals comprises Ge or Si, wherein the gamma radiation peaks of the composition may be adjusted in relative frequency. |
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044540930 | claims | 1. A fuel assembly for a nuclear power reactor, comprising: a plurality of groups of vertical fuel rods; a plurality of wall systems, each wall system substantially surrounding one of said groups of fuel rods and extending along a greater part of the length of said fuel rods; an annular fuel channel portion extending above said plurality of wall systems, a horizontal projection of said annular fuel channel portion surrounding all of the fuel rods of said fuel assembly, said annular fuel channel portion having an inner circumference; a substantially horizontal water distribution channel extending above said groups of fuel rods as well as along and adjacent to most of said inner circumference, said water distribution channel being upwardly open and comprising means for receiving emergency cooling water supplied from a location above at least one of said groups of fuel rods and for distributing water so received to at least one of the remaining groups of fuel rods. 2. A fuel assembly according to claim 1, wherein said annular fuel channel portion has a substantially quadratic cross-section; each of said groups of fuel rods is arranged below a corresponding quadrant of said annular fuel channel portion; and said water distribution channel extends along the inner side of said annular fuel channel portion above a plurality of said quadrants, said water distribution channel in at least one quadrant comprising at least one water outflow for water to the corresponding group of fuel rods. 3. A fuel assembly according to claim 1, wherein said water distribution channel comprises a radially inner channel wall, a portion of which is inwardly-bent in such a way that the radial width of said water distribution channel at the upper edge of said inwardly-bent portion is at least 15% larger than the average channel width at the upper edge of the channel. 4. A fuel assembly according to claim 1, wherein said fuel assembly comprises a top plate arranged above said groups of fuel rods and said water distribution channel comprises a bottom portion at least a part of which comprises a peripheral portion of said top plate. 5. A fuel assembly according to claim 1, wherein said distribution channel comprises a wall portion which in use of said fuel assembly faces a control rod gap, said wall portion comprising a radially outwardly extended portion, the horizontal projection of said radially outwardly extended portion protruding substantially outside said horizontal projection of said annular fuel channel portion. |
055043445 | abstract | In a radiation shield between joinder surfaces to preclude a radiation path therethrough, a series of alternating complemental ridges and valleys on each surface. The ridges and valleys on each surface are in turn interdigitated with the complementary ridges and valleys on the second surface and of a height and depth sufficient to preclude the lateral free movement of radiation flux. |
summary | ||
claims | 1. A method for determining power limit criteria for a nuclear reactor based on operational thermal-mechanical limits of fuel rods in the nuclear reactor core, comprising the steps, executed by a computer, of: a) constructing individual fuel rod power histories for each nuclear fuel rod in the reactor core based on information acquired during previous fuel cycles and a projected operation of the reactor in an upcoming fuel cycle; b) computing internal pressure data for each fuel rod in the core for an upcoming fuel cycle based on the power histories constructed in step (a); c) identifying a fuel rod as having a greatest computed internal pressure as computed in step (b); and d) establishing an operational thermal-mechanical limit based on the power history of the identified fuel rod. 2. The method of claim 1 wherein step (b) includes computing thermal and mechanical overpower limits for fuel rods in the core. claim 1 3. The method of claim 1 wherein steps (b) through (d) are repeated for each fuel cycle. claim 1 4. A method for establishing power limit criteria of a nuclear reactor based on operational thermal-mechanical limits of fuel rods in the nuclear reactor core, comprising the steps of: a) computing power history data for each fuel rod in the reactor based on historical operating data of the reactor; b) computing fuel rod internal pressure data for each fuel rod in the reactor core based on a computed power history data of a fuel rod and a projected operation of the reactor in an upcoming fuel cycle; c) identifying a maximum fuel rod internal pressure for the upcoming fuel cycle based on the fuel rod internal pressure data computed in step (b); and d) confirming that the identified maximum is less than fundamental criteria established by the applicable licensing authority. 5. The method of claim 4 , further including: claim 4 repeating steps (b) and (c) for each fuel cycle of the reactor. 6. A system for establishing power limit criteria for a nuclear reactor based on operational thermal-mechanical limits of fuel rods in the nuclear reactor core, said system comprising a computer including a data storage memory and one or more I/O or display devices, said computer programmed to: (i) construct individual fuel rod power histories for each nuclear fuel rod in the reactor core based on empirical information acquired during previous fuel cycles and the projected operation of the reactor in an upcoming fuel cycle; (ii) compute internal pressure data for each fuel rod in the core for an upcoming fuel cycle based on the individual power histories; and (iii) identify a fuel rod having a maximum internal pressure; wherein an operational power limit criteria is established based on thermal-mechanical limit data associated with the identified fuel rod. 7. The system of claim 6 wherein the computer is further programmed to compute thermal overpower and mechanical overpower limit data for each fuel rod in the reactor core. claim 6 8. The system of claim 6 wherein the computer provides, via an I/O or display device, output data identifying at least peak internal pressure and exposure information for one or more fuel rods in the reactor core. claim 6 9. A computer program product embodied on a computer-readable medium for distribution and/or storage on a computer system for execution to establish power limit criteria for a nuclear reactor based on operational thermal-mechanical limits of fuel rods in the nuclear reactor core, comprising: means for constructing individual fuel rod power histories for each nuclear fuel rod in the reactor core based on empirical information acquired during previous fuel cycles and the projected operation of the reactor in an upcoming fuel cycle; and means for computing internal pressure data for each fuel rod in the core for an upcoming fuel cycle based on individual fuel rod power histories and for identifying a fuel rod having a maximum internal pressure. 10. The computer program product of claim 9 further including means for computing thermal-mechanical limit data for each fuel rod in the core and for establishing an operational thermal-mechanical limit based on thermal-mechanical limit data associated with the identified fuel rod. claim 9 11. A method for demonstrating compliance of a nuclear reactor with fundamental licensing criteria for nuclear fuel rod internal pressure during nuclear reactor operation, comprising the steps of: a) constructing individual fuel rod power histories for each nuclear fuel rod in the reactor core based on empirical information acquired during previous fuel cycles and the projected operation of the reactor in an upcoming fuel cycle; b) computing internal pressure data for each fuel rod in the core for an upcoming fuel cycle based on the power histories constructed in step (a); c) identifying a fuel rod having a maximum internal pressure; and d) confirming that the identified maximum is less than an established licensing limit criteria, wherein the established power limit criteria is based on thermal-mechanical limit data associated with the identified fuel rod. |
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description | Intensifying screens are often used in conventional radiography procedures for exposing X-ray films. For example, X-ray films utilizing intensifying screens are used for a variety of diagnosis and treatment procedures in the fields of dentistry and medicine. A conventional intensifying screen may include a polymer backing sheet coated with a phosphor material. The phosphor material converts radiation energy into visible light. An X-ray film used with an intensifying screen typically includes a photographic film that is coated with an emulsion layer that is sensitive to light. Exposure of the X-ray film to visible light results in darkening of the film in areas struck by light rays, thereby producing an image on the film. While conventional X-ray films utilizing intensifying screens may reduce exposure of patients and medical workers to radiation in comparison with techniques that don't utilize intensifying screens, such as X-ray procedures utilizing direct-exposure X-ray films, further reductions in radiation generation during X-ray procedures are desirable. Continued exposure to doses of radiation over time may lead health problems in patients and medical workers. For example, patients and medical staff exposed to doses of radiation may be at risk of developing various medical conditions due to cumulative radiation exposure. Accordingly, reducing the exposure of patients and medical workers to harmful radiation even further is desirable so as to minimize any health risks associated with radiation exposure. Additionally, it is preferable to maintain high image quality while reducing the amount of radiation used, since reducing the amount the amount of radiation utilized in conventional X-ray technologies often results in a corresponding reductions in image sharpness, clarity, and detail. The instant disclosure is directed to exemplary intensifying screens for exposing X-ray film, as well as to X-ray film cassettes and X-ray film assemblies. According to at least one embodiment, an intensifying screen for exposing an X-ray film may comprise a screen support backing, a phosphor layer including a luminescent material that emits light in the presence of X-rays, and a reflective layer disposed between the luminescent layer and the screen support backing, the reflective layer including a plurality of micro-prisms that reflect light emitted by the luminescent material, thereby better utilizing available light to expose the film. Also, this may increase sharpness, clarity, and detail on the film. According to at least one embodiment, the reflective layer may be configured to reflect light emitted by the phosphor material toward an X-ray film disposed adjacent to the phosphor layer. For example, the reflective layer may reflect light in a direction toward the luminescent layer and/or in a direction generally perpendicular to a surface of the luminescent layer facing the reflective layer. In some embodiments, the luminescent layer may emit visible light in response to excitation by X-rays. For example, the luminescent material may comprise a phosphor material. The reflective layer may comprise any suitable material, including, for example, a polymer material and/or a crystalline material, such as a glass material. In some embodiments, the intensifying screen may include a light-absorbing layer on a side of the plurality of micro-prisms opposite the luminescent layer. The screen support backing may, for example, comprise a light-absorbing layer. According to various embodiments, an X-ray film cassette may be configured to accommodate an X-ray film. The cassette may include at least one intensifying screen and a housing surrounding the at least one intensifying screen. For example, the cassette may include a single intensifying screen disposed on an inner surface of the housing, or alternatively, two intensifying screens disposed on opposing inner surfaces of the housing. In at least one embodiment, an X-ray film assembly may comprise at least one intensifying screen and an X-ray film. The X-ray film may be positioned adjacent to the at least one intensifying screen and may include an emulsion layer. For example, the X-ray film may be disposed between two intensifying screens. Features from any of the disclosed embodiments may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features, and advantages will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings and claims. Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the exemplary embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the instant disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims. The instant disclosure is directed to exemplary X-ray intensifying screens for exposing X-ray film, as well as to X-ray film cassettes and X-ray film assemblies. Such X-ray intensifying screens may be used to facilitate exposure of X-ray films in the presence of X-rays for use in a variety of applications, including various medical and dental applications, without limitation. X-ray intensifying screens, as disclosed herein, may also be used in any suitable industrial applications, without limitation. FIGS. 1 and 2 illustrate an exemplary X-ray film assembly 100 that includes a first intensifying screen 101 and a second intensifying screen 111 disposed on opposite sides of an X-ray film 110 according to at least one embodiment. FIG. 2 shows a portion of FIG. 1 that is represented by a circular region labeled A in FIG. 1. As shown in FIGS. 1 and 2, first intensifying screen 101 may comprise a screen support backing 102, a reflective layer 104, and a luminescent layer 106. Second intensifying screen 111 may comprise a screen support backing 112, a reflective layer 114, and a luminescent layer 116. X-ray film 110 may comprise a film base 103 coated with an emulsion layer on one or two sides. For example, as illustrated in FIG. 1, opposite sides of film base 103 may be coated with a first emulsion layer 108 and a second emulsion layer 118. First emulsion layer 108 may be formed on a first side of film base 103 and second emulsion film 118 may be formed on a second side of film base 103. First and second emulsion layers 108 and 118 may comprise any film layer suitable for producing an image in the presence of light and/or X-rays. For example, first and second emulsion layers 108 and 118 may comprise materials that are sensitive to various wavelengths of light, such as visible light. In some examples, first emulsions layer 108 and/or second emulsion layer 118 may be primarily sensitive to light falling within a particular wavelength range. For example, first emulsions layer 108 and/or second emulsion layer 118 may have a greater sensitivity to light falling within a blue light and/or a green light spectrum. First and second emulsion films 108 and 118 may comprise any suitable material that darkens X-ray film 110 when exposed to visible light, without limitation. In at least one embodiment, emulsion films 108 and 118 may comprise silver halide crystals dispersed in a gelatin material. In various embodiments, first emulsion layer 108 and/or second emulsion layer 118 may be covered by an additional layer on a side opposite to film base 103, such as, for example, a protective coating. X-ray film 110 may be disposed adjacent to at least one intensifying screen prior to exposure to X-rays. For example, as shown in FIG. 1, X-ray film 110 may be sandwiched between first emulsion layer 108 and second emulsion layer 118 such that first intensifying screen 101 is disposed on a first side of X-ray film 110 adjacent to first emulsion layer 108 and second intensifying screen 111 is disposed on a second side of X-ray film 110 adjacent to second emulsion film 118. Alternatively, an X-ray film, such as an X-ray film having only a single emulsion layer, may be disposed adjacent to only a single intensifying screen. Each of first intensifying screen 108 and second intensifying screen 118 illustrated in FIG. 1 may comprise any suitable material which exhibits luminescence in response to excitation by X-rays. For example, first intensifying screen 108 and second intensifying screen 118 may each convert X-ray photons into visible light photons having a wavelength suitable for exposing first and second emulsion layers 108 and 118. Luminescent layers 106 and 116 may, for example, comprise a phosphor material. Examples of suitable phosphor materials include, without limitation, rare earth phosphors, such as gadolinium and/or lanthanum phosphors, calcium tungstate phosphors, silver-activated zinc sulfide, copper-activated zinc sulfide, and/or combinations of the foregoing. In various embodiments, luminescent layer 106 may be covered by an additional layer on a side opposite to reflective layer 104, such as a protective coating. Likewise, luminescent layer 116 may be covered by an additional layer, such as a protective coating, on a side opposite to reflective layer 114. In some embodiments, luminescent layer 106 and/or luminescent layer 116 may emit light falling within a certain wavelength range. For example, luminescent layer 106 and/or luminescent layer 116 may comprise phosphor materials that emit light within a certain portion of the visible light spectrum, such as, for example, blue light and/or green light. First emulsion layer 108 and/or second emulsion layer 118 may comprise materials that are sensitive to wavelengths of light emitted by luminescent layer 106 and/or luminescent layer 116, such as light falling within a blue light and/or a green light spectrum. Reflective layers 104 and 114 may comprise any suitable material that reflects visible light toward X-ray film 110. In at least one embodiment, reflective layers 104 and 114 may comprise at least one of a polymer material, a crystalline material, such as a glass material, a metallic material, and/or any other suitable material for reflecting light. In some examples, reflective layer 104 and/or reflective layer 114 may be coated with a reflective and/or semi-reflective material. Each of reflective layers 104 and 114 may comprise any suitable reflective surface configuration. For example, reflective layer 104 and/or reflective layer 114 may comprise an array of prisms, such as micro-prisms, configured to retroreflect light emitted by luminescent layer 106 and/or luminescent layer 116. Such micro-prisms may have any suitable configuration, without limitation. In some embodiments, the micro-prisms may be tinted to match the color sensitivity of X-ray film 110 so as to increase film exposure. FIG. 3 shows a cross-sectional side view of a portion of an exemplary intensifying screen 101 according to at least one embodiment. As illustrated in FIG. 3, intensifying screen 101 may include a luminescent layer 106 and a reflective layer 104 comprising an array of micro-prisms 120. Micro-prisms 120 may be sized, shaped, tinted, and arranged in any suitable manner, without limitation. For example, micro-prisms 120 may be formed in reflective layer 104 to include numerous geometric corners, such as corners defined by surfaces of micro-prisms 120 that are disposed at an angle α of approximately 90° relative to each other, so that light emitted by a luminescent layer in direction D2 strikes one micro-prism 120 surface defining a corner and is reflected toward another adjacent micro-prism 120 defining the corner; the light is then reflected (i.e., retroreflected) generally back toward the light emission source in direction D1. According to some embodiments, corners defined by surfaces of adjacent micro-prisms 120 may be disposed at an angle α of between approximately 80° and approximately 100° relative to each other. According to additional embodiments, corners defined by surfaces of adjacent micro-prisms 120 may be disposed at an angle α of between approximately 85° and approximately 95° relative to each other. Reflective layer 104 and/or reflective layer 114 may include, for example, a repeating pattern of micro-prisms, such as pyramidal prisms and/or any other suitably-shaped prisms. In some embodiments, reflective layer 104 and/or reflective layer 114 may additionally or alternatively include reflective beads or micro-spheres that retroreflect light back towards its source. Reflective layer 104 and/or reflective layer 114 may comprise a single material that is molded, etched, machined, and/or otherwise formed to have a surface region comprising the plurality of micro-prisms. In additional embodiments, the micro-prisms may be covered with one or more additional layers of material between the reflective layer and adjacent luminescent layer 106 and/or luminescent layer 116. Alternatively, the micro-prisms formed on reflective layer 104 and/or reflective layer 114 may be respectively disposed directly adjacent to luminescent layer 106 and/or luminescent layer 116 (see, e.g., micro-prisms 120 illustrated in FIG. 3) or may be directly adhered to luminescent layer 106 and/or luminescent layer 116 by an adhesive layer. In additional embodiments, micro-prisms and/or micro-spheres may be individually adhered to and/or embedded within reflective layer 104 and/or reflective layer 114. According to some embodiments, reflective layer 104 and/or reflective layer 114 may comprise a substantially opaque material that is substantially impermeable to light such that light incident upon reflective layer 104 and/or reflective layer 114 is either reflected or absorbed by reflective layer 104 and/or reflective layer 114. In additional embodiments, reflective layer 104 and/or reflective layer 114 may comprise a material that is semi-permeable or permeable to light. With such a configuration, light incident upon reflective layer 104 and/or reflective layer 114 is either reflected by or passes through reflective layer 104 and/or reflective layer 114. Reflective layer 104 and/or reflective layer 114 may either reflect or refract light based, for example, on the incident angle of light relative to the surface of reflective layer 104 and/or reflective layer 114, respectively. For example, as illustrated in FIG. 3, light traveling in direction D2 that is obliquely incident upon a micro-prism 120 surface of reflective layer 104 may be retroreflected in direction D1 if it impinges on the surface at an angle θ1 from the surface that is below a critical angle measured from the surface. Conversely, if the light traveling in direction D3 impinges upon a micro-prism 120 surface of reflective layer 104 at an angle θ2 from the surface that is above the critical angle measured from the surface, the light may be refracted in direction D4 and pass through at least a portion of reflective layer 104. Therefore, in reflective layer 104 comprising the array of micro-prisms 120 as illustrated in FIG. 3, light that is emitted from luminescent layer 106 may either be reflected or refracted based on the angle at which the light strikes the micro-prism 120 surfaces. Accordingly, light that is emitted in a direction that is generally perpendicular to surfaces of luminescent layers 106 and 116 facing X-ray film 110, and/or facing an adjacent reflective layer 104 or 114, may strike surfaces of micro-prisms of reflective layer 104 and/or a reflective layer 114 at angles that are less than the critical angle as measured from the surfaces of the micro-prisms; accordingly, the light may be retroreflected by the micro-prisms generally back toward the emission source of the light in luminescent layer 106 and/or luminescent layer 116 and toward X-ray film 110. As illustrated, for example, in FIGS. 2 and 3, light may be retroreflected by reflective layer 104 in direction D1 toward emulsion layer 108 of X-ray film 110. On the other hand, light that is emitted from luminescent layer 106 and/or luminescent layer 116 in a direction that is not generally perpendicular to surfaces of luminescent layers 106 and 116 facing X-ray film 110, and/or facing an adjacent reflective layer 104 or 114, may strike surfaces of micro-prisms of reflective layer 104 and/or a reflective layer 114 at angles that are greater than the critical angle as measured from the surfaces of the micro-prisms; accordingly, the light may be refracted by and pass through the micro-prisms such that the light is not directed back toward X-ray film 110. Accordingly, light may be more effectively reflected toward X-ray film 110 while reducing the amount of scattered light incident upon X-ray film 110. By using an X-ray film assembly having one or more intensifying screens including a reflective layer with micro-prisms, as described herein, images may be produced on X-ray film 110 using lower amounts of radiation while increasing the sharpness, clarity, and detail of the image produced. As such, patients and medical workers may be exposed to lower amounts of radiation. Additionally, wear and tear on X-ray tubes and other equipment used to produce X-rays may be reduced. In some embodiments, reflective layer 104 and/or reflective layer 114 may comprise a material that is semi-permeable or permeable to light, allowing refracted light to pass through at least a portion of reflective layer 104 and/or reflective layer 114. In additional embodiments, a light-absorbing layer may be disposed on a side of the plurality of micro-prisms of reflective layer 104 and/or reflective layer 114 opposite the respective adjacent luminescent layer 106 or 116. A light-absorbing layer may comprise a low-reflectance material, such as a dark or black material, that absorbs the majority (e.g., greater than 80% or greater than 90%) of incident light. In certain embodiments, at least a portion of reflective layer 104 and/or reflective layer 114 may comprise a light-absorbing material. In additional embodiments, support backing 102 and/or support backing 112 may comprise a light-absorbing material and/or a separate light-absorbing layer may be disposed between reflective layer 104 and/or reflective layer 114 and adjacent support backing 102 or 112. Accordingly, light that is refracted and passes through at least a portion of reflective layer 104 and/or reflective layer 114 may be absorbed so as to prevent scattered light from being reflected back toward X-ray film 110, thereby increasing the image sharpness, detail, and clarity. FIG. 4 illustrates an exemplary X-ray film cassette 130 comprising a first intensifying screen 101 and a second intensifying screen 111 disposed on opposite sides of an X-ray film 110 according to at least one embodiment. As shown in FIG. 4, X-ray film cassette 130 includes a light-proof housing 132 and at least one intensifying screen that is surrounded by housing 132. For example, X-ray film cassette 130 may include a first intensifying screen 101 and a second intensifying screen 111. As shown in FIG. 4, first and second intensifying screens 101 and 111 may be disposed on opposing inner surfaces of housing 132. According to at least one embodiment, X-ray film cassette 130 may include a first housing portion 132A adjacent first intensifying screen 101 and a second housing portion 132B adjacent second intensifying screen 111. X-ray film cassette 130 may be configured to hold an X-ray film 110 between first intensifying screen 101 and a second intensifying screen 111. Further to this end, X-ray film cassette 130 may be opened such that first housing portion 132A and first intensifying screen 101 are separated from second housing portion 132B and second intensifying screen 111, allowing X-ray film 110 to be loaded into and removed from X-ray film cassette 130. The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the exemplary embodiments described herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the instant disclosure. It is desired that the embodiments described herein be considered in all respects illustrative and not restrictive and that reference be made to the appended claims and their equivalents for determining the scope of the instant disclosure. Unless otherwise noted, the terms “a” or “an,” as used in the specification and claims, are to be construed as meaning “at least one of.” In addition, for ease of use, the words “including” and “having,” as used in the specification and claims, are interchangeable with and have the same meaning as the word “comprising.” |
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description | The present application relates to and claims priority to U.S. Provisional Application No. 60/581,185 filed on Jun. 18, 2004, incorporated herein by reference in its entirety. This disclosure generally relates to an apparatus for curing and/or removing porogens from dielectric materials, and in particular, to an apparatus for curing and/or removing porogens from low k dielectric materials with ultraviolet radiation in a controlled environment. As semiconductor and other microelectronic devices progressively decrease in size, the demands placed on device components continue to increase. For example, the prevention of capacitive crosstalk between interconnect lines becomes significantly more important with smaller devices. Capacitive crosstalk is generally a function of both the distance between conductors and the dielectric constant (k) of the material placed in between the conductors. Considerable attention has been focused on electrically isolating the conductors from each other using new insulators having low dielectric constants because although silica (SiO2), which has traditionally been used in such devices because of its relatively low dielectric constant of about 4, met the requirements of earlier (i.e., larger) applications, it will not be adequate for the smaller devices of the future. These low k (i.e., a dielectric constant less than 4) materials are desirable for use, for example, as inter-layer dielectric layers (ILD). To achieve low dielectric constants, one can either use a material that possesses a low dielectric constant, and/or introduce porosity into the material, which effectively lowers the dielectric constant because the dielectric constant of air is nominally 1. Porosity has been introduced in low k materials through a variety of means. In the case of spin on low k dielectrics, a lowering of the k value can be achieved by using high boiling point solvents, by using templates or by porogen based methods that form pores upon subsequent processing to remove a sacrificial material. However, the integration of porous low-k materials in the manufacture of the semiconductor device, in general, has proven difficult. The utilization of UV radiation for the curing of low-k dielectric films has recently been discovered to provide enhanced electrical, mechanical and chemical properties of the resulting dielectric material, as compared to other cure methods. In addition, the UV assisted process is capable to effectively remove porogen material, a sacrificial organic substance that is used to generate porous structures. Test results on different low-k materials have shown that the exposure to different wavelength distributions of UV light combined with the appropriate background chemistry and sufficiently high wafer temperatures results in different modifications of the low-k films. In particular, we have found that some wavelength distributions (A) are very effective for porogen removal and enhanced cross-linking of the low-k matrix, while other wavelength distributions (B) contribute to the cross-linking of the low-k matrix without porogen removal. Therefore a number of different low-k cure flow schemes are possible, which may have benefits for the synthesis and integration of porous low-k dielectrics. No ultraviolet radiation apparatus currently exists that addresses the special problems and concerns associated with curing and/or removing porogens from various dielectric materials. Accordingly, there is a need in the art for an apparatus suitable for processing dielectric materials such as low k materials, oxides, nitrides, premetal dielectrics, barrier layers, and the like for advanced device fabrication. Disclosed herein are apparatuses and processes for treating dielectric materials such as low k dielectrics, premetal dielectrics, and the like for advanced semiconductor devices. In one embodiment, the apparatus comprises a radiation source module comprising a reflector, an ultraviolet radiation source, and a plate transmissive to the wavelengths of about 150 nm to about 300 nm, to define a sealed interior region, wherein the sealed interior region is in fluid communication with a first fluid source; a process chamber module coupled to the radiation source module to define a sealed chamber in operative communication with the ultraviolet radiation source, the process chamber comprising a closable opening adapted to receive a substrate, a support adapted to support the substrate, and a gas inlet in fluid communication with a second fluid source; and a loadlock chamber module in operative communication with the process chamber and a wafer handler; the loadlock chamber comprising an airlock chamber in fluid communication with a third fluid source and a chuck. In another embodiment, an apparatus for processing dielectric materials comprises a radiation source module comprising a reflector, an ultraviolet radiation source adapted to emit broadband radiation, a plate transmissive to the wavelengths of about 150 nm to about 300 nm, to define a sealed interior region, wherein the sealed interior region is in fluid communication with a first fluid source; an optical filter disposed between the radiation source and the substrate; and a process chamber module coupled to the radiation source module to define a sealed chamber in operative communication with the ultraviolet radiation source, the process chamber comprising a closable opening adapted to receive a substrate, a support adapted to support the substrate, and a gas inlet in fluid communication with a second fluid source. A process for treating a dielectric material comprises transferring a substrate from a loadlock chamber into a process chamber, wherein the process chamber is coupled to a radiation source module comprising a reflector, an ultraviolet radiation source, and a plate to define a sealed interior region, wherein the plate is transmissive to wavelengths of about 150 nm to about 300 nm; flowing an inert gas into the process chamber and the sealed interior region; and generating ultraviolet broadband radiation at wavelengths of about 150 nm to about 300 nm and exposing the substrate to the ultraviolet broadband radiation. The above described and other features are exemplified by the following figures and detailed description. As shown in FIG. 1, an apparatus 10 for curing and/or removing porogens from dielectric materials with ultraviolet radiation in a controlled environment generally includes a radiation source module 12, a process chamber module 14 in operative communication with the radiation source module 12, a load lock chamber module 16 proximate to the process chamber module 14 for transferring substrates in and out of the process chamber module 14, and a wafer load station module (not shown) proximate to the load lock chamber module 16 for staging substrates for processing with the apparatus 10. Advantageously, the environment within each module can be controlled and tailored for the particular dielectric material being processed therein. Referring now to FIG. 2, the radiation source module 12 generally comprises a sealed interior region 20 defined by an ultraviolet radiation source 22, a plate 24, and a reflector 26. A portion 27 of the ultraviolet radiation source 22 protrudes from and/or interfaces with the sealed interior region 20 and is substantially transmissive to ultraviolet radiation and substantially opaque to microwaves, thereby acting as a high pass filter. For example, the terminal end 28 of portion 27 protruding from and/or interfacing with the sealed interior region 20 can be formed of an tungsten mesh material with sufficiently small openings to cut-off most microwave radiation while substantially transmitting the ultraviolet radiation. The reflector 26 includes a reflecting layer formed of an aluminum metal, a dichroic material, or a multilayer coating. Optionally, the reflecting layer may further comprise a protective layer of magnesium fluoride, silicon dioxide, aluminum oxide, and combinations comprising at least one of the foregoing materials. Other suitable materials will be apparent to one of ordinary skill in the art in view of this disclosure. It has been discovered that these materials provide greater and more efficient reflectance of ultraviolet radiation having shorter wavelengths, e.g., wavelengths less than 200 nm. The radiation source module 12 further includes a fluid inlet 33 in fluid communication with the sealed interior region 20 and a fluid source 35. The fluid source 35 is configured to purge the atmosphere contained within the sealed interior region 20 during operation. In addition, the fluid source 35 can be used to cool the ultraviolet radiation source, e.g. the electrodeless bulb. Suitable fluids include, but are not intended to be limited to, inert gases for purging ambient air, for example, from the sealed interior region 20. Suitable inert gases include, but are not limited to, nitrogen, argon, helium, combinations comprising at least one of the foregoing gases, and the like. Similarly, the sealed interior region 20 can also be evacuated by means of a vacuum pump, exhaust, or the like (not shown) to allow optimum transmission of UV light. That is, oxygen or other species that absorb ultraviolet radiation at wavelengths less than 200 nm can be removed. As used herein the term, “sealed” as used in reference to the radiation source module (as well as the process chamber) refers to a region within the radiation source module that can be suitably purged during operation. The sealed interior region does not need to be vacuum-sealed and purging can simply provide a positive atmosphere within the interior region (or process chamber). Although in some embodiments, the sealed interior region can be vacuum-sealed depending on the application. The radiation source chamber 12 can also include fluid inlet 34 in fluid communication with a fluid source 36. In this manner, fluid such as water or some other cooling medium can be used to provide cooling to the reflector 26 or like components that may become heated during operation. For example, the reflector 26 may further include a water-cooling jacket wherein the fluid flows therethrough to provide the desired amount of cooling. The fluid selected for cooling can be the same or different from the fluid used for purging the sealed interior region 20. As such, fluid sources 35 or 36 are not intended to be limited to a single fluid and can provide multiple fluids as may be desired for different applications, wherein each fluid can be stored in a pressurized vessel or the like in fluid communication with inlet 33, 34, via a manifold or the like. Purging the sealed interior region 20 of the radiation source module 12 (as well as the process chamber 14) provides numerous advantages during processing of low k dielectric materials, among others. For example, air includes about 21% oxygen, which is known to absorb radiation at wavelengths less than about 200 nm and reacts to form, among other products, ozone. The production of ozone, in turn, exacerbates wavelength attenuation since ozone starts absorbing as high as 250 nm and continues to lower wavelengths. As a result, the process efficiency for ultraviolet curing and/or removal of porogens from the low k material can decrease. Purging the sealed interior region 20 of the radiation source module 12 (and the process chamber 14) or evacuating it prior to exposing a substrate to an ultraviolet radiation pattern reduces wavelength absorption and as a result, increases process efficiency. Other purging fluids can be used to absorb selected wavelengths of the ultraviolet radiation pattern specific to the particular radiation source employed. Suitable absorbing gases include, but are not intended to be limited to, O2, O3, N2O, CO2, H2O and the like. The radiation source module 12 is preferably adapted to emit a broadband radiation pattern having at least one broadband wavelength pattern less than about 400 nm, with about 150 nm to about 300 nm more preferred, and with about 150 nm to about 250 nm even more preferred. The radiation source module 12 as shown illustrates the use of a electrodeless bulb 30, which is coupled to an energy source, e.g., a microwave cavity, to emit the broadband radiation pattern in a manner well known by those skilled in the art to generate the desired broadband ultraviolet radiation pattern. Using a microwave energy source as an example, a magnetron and a waveguide are coupled to the microwave cavity 32 to excite a gas fill within the electrodeless bulb and produce ultraviolet radiation. Different fills can be employed with the microwave electrodeless bulb 28 to provide different radiation patterns. The amount of the fill is such that it can be present at a pressure of at least about 1 atmosphere and preferably 2 to 20 atmospheres at operating temperature when the fill is excited at a relatively high power density. For example, the power density of microwave energy would be at least 50 watts/cc, and preferably greater than 100 watts/cc. The electrodeless bulb 28 can also be made to emit a desired broadband radiation pattern with radiofrequency power. The UV generating electrodeless bulbs with different spectral distributions may be selected depending on the application such as, for example, the use of different microwave electrodeless bulbs, e.g., Type I and Type II microwave electrodeless bulbs available from Axcelis Technologies (Beverly, Mass.). Spectra obtained from the Type I and Type II bulbs and suitable for use in a curing and/or porogen removal process are shown in FIGS. 3 and 4, respectively. Other suitable microwave driven electrodeless bulbs are disclosed in U.S. Pat. No. 5,541,475 to Wood et al., incorporated herein by reference in its entirety. Optionally, in place of the electrodeless bulb, an arc discharge, a dielectric barrier discharge, or an electron impact generator can be used to emit the desired ultraviolet radiation pattern. For example, the dielectric barrier discharge light source generally includes two parallel electrodes with a dielectric-insulating layer disposed on or between one of the electrodes and generally operates at about atmospheric pressures. The substrate to be treated is often used as one of the planar electrodes or typically is placed between two planar electrodes. This dielectric barrier discharge light source is preferably capable of being backfilled with any number of gas mixtures for producing a desired radiation pattern. A computer control can be employed to alter the gas mixture during operation to allow changing of the emitted wavelengths in the radiation pattern. In one embodiment, the substrate is heated from beneath by high intensity lamps while being illuminated from above by the light source. This would provide a programmable substrate temperature. In this embodiment, pins could be employed to support the substrate over a heating window, below which the heating lamps would be located. In this embodiment, one or more of the pins would optionally contain a temperature sensor, e.g., a spring mounted or an embedded thermocouple, to monitor the substrate temperature and feed back this temperature information to a lamp controller to control the temperature, if desired. Alternatively a proximity thermal chuck controls the substrate temperature with an embedded closed loop thermocouple control. The plate 24 within the radiation source module 12 advantageously serves to isolate the ultraviolet radiation source 22 from the underlying process chamber 14 (as previously shown in FIG. 1). Advantageously, the plate 24 eliminates particulate contamination from the substrate to the ultraviolet radiation source 22, isolates the ultraviolet radiation source 22 from the process chamber 14 to permit separate access, and, additionally, permits the use of gases to cool the ultraviolet radiation source 22 and/or microwave cavity, if present. The plate 24 also allows specially chosen process gases to be used in the process chamber 14 without interfering with the operation of the ultraviolet radiation source 22. In one embodiment, the plate 24 is fabricated from a quartz material having an optical transmittance substantially transparent to the desired radiation pattern for curing and/or removing porogens from the low k dielectric material. An example of such a quartz material is commercially available under the trade name Dynasil 1000 from the Dynasil Corporation in West Berlin, N.J. It may be possible to use materials other than quartz, so long as the materials possess the above characteristics. For example, it may be desirable to expose the substrate to ultraviolet radiation having wavelengths below 220 nm specific for porogen removal. The plate 24 is mounted by conventional mounting means in the radiation source module 12, which may optionally include suitable spacers. Furthermore, the plate 24 may be comprised of one or more stackedly arranged plates. In some embodiments, the plate may be coated with an anti-reflectant to minimize back reflections of UV radiation into the radiation source module 12. For example, the plate 24 may be coated with magnesium fluoride or may have deposited thereon silicon, fluorine, and the like. In one embodiment, an optical filter 40, e.g., a screen or the like, is disposed on the plate 24. In the case of a screen, the screen 40 is preferably configured with a plurality of openings, which provide improved uniformity of irradiation to substrate. The openings can vary in size depending on the intensity characteristics of the ultraviolet radiation source so as to promote uniform radiation to an underlying substrate. The screen 40 can be fabricated from a metal and have a mesh form. The screen 40 can include a single zone or multiple zones to provide greater radiation exposure uniformity. FIG. 5 illustrates an exemplary screen 40 having three zones 42, 44, and 46. Zone 42 has a finer mesh pattern than zone 44, which has a finer mesh pattern than zone 46. It has been discovered that without the screen, the centermost portion of the substrate exhibits the greatest intensity of radiation incident to its surface. By changing the aperture density of screen 40 in the manner illustrated, greater radiation uniformity can be obtained. An annular ring 48 retains the mesh screen defined by zones 42, 44, and 46. In another embodiment, the screen 40 is disposed intermediate the process chamber module 14 and the radiation source module 12. In still another embodiment, the screen 40 is embedded within the plate 24. As shown more clearly in FIG. 6, the process chamber 14 generally includes a base unit 52 comprising a bottom wall 54 and sidewalls 56 extending therefrom to form a cavity 58. A chuck assembly 60, e.g., a gravity chuck assembly, or the like, is disposed in the cavity 58. As is generally known to those skilled in the art, the gravity chuck assembly employs gravity as a means for securing the substrate to a support surface such that the substrate is not forced in contact with the support surface by any means other than the weight of the substrate. The chuck may further include a vacuum hold mechanism as may be desired for some applications and chuck assemblies. Coupled to the base unit 52 is structure 62 defined by sidewalls 64 extending therefrom, which is further coupled to the radiation source module 12 to form a sealed chamber 68 in which the substrate can be processed. The process chamber 14 is preferably fabricated from materials inert to the operating environment including, but not limited to, processing gases and reaction byproducts. The sidewalls 64 of the structure 62 include at least one opening 66. Opening 66 is dimensioned for transferring substrates into and out of the process chamber 14 from an adjacent loadlock chamber 16 (also shown in FIG. 1). Other openings (not shown) may also be disposed in the sidewalls 64 for purposes generally known in the art such as, for example, inlet and exhaust/pump manifolds, an optical port for monitoring the process, a mass spectrometer inlet for analyzing gaseous species evolved during processing, e.g., porogens, an oxygen analyzer for monitoring the concentration of oxygen, or the like. For example, an inlet and exhaust manifold may be employed to provide a cross flow of gases proximal to the transmissive plate during purging and/or processing. Still further, the process chamber may include an outlet connected to an exhaust or vacuum pump such that the flow of fluids provides a gas curtain proximal to the transmissive plate so as to minimize deposition of porogen or any outgassed material from the substrate during processing, or to clean a coated plate by using UV activation of a reactive gas within the process chamber 14. In one embodiment, the fluid flow into the process chamber for forming curtain comprises an inlet slot and an opposing outlet slot in proximity to the transmissive plate to effect cross flow of the fluid across the plate, thereby providing the curtain. The process chamber 14 further includes at least one gas inlet 69 in fluid communication with gas a source 71 and the sealed interior region 68. Fluid flow into the sealed chamber 68 can be axial, cross flow, or the like depending on the desired application. For example, the process chamber 14 can be adapted for downstream flow of gases during a purging and/or cleaning process. As such, the purging system, depending on the gases plumbed into the system, can provide preparation of the chamber for an inert condition; and/or chamber cleaning. For example, an in-situ chamber clean function may be desirable since some dielectric materials emit organic volatiles during the curing and/or porogen removal process resulting in deposition of these organic volatiles on the chamber walls and the irradiator plate 24. The in-situ clean function comprises an operating mode at which a substrate-less chamber 14 is purged with oxygen (and/or a reactive gas) and exposed to ultraviolet radiation to generate sufficient amounts of ozone and other excited oxygen species that can react with and remove the organic deposits. For example, periodically cleaning the process chamber includes detecting a change in transmission of the ultraviolet broadband radiation into the process chamber, wherein when the change exceeds a predetermined threshold value, the cleaning process is triggered. Discontinuing the cleaning process occurs when a rate of change of transmission falls below a predetermined rate of change or is at about a 100% transmission for a predefined wavelength band. For purge operations, the purge system is preferably designed for multiple gas options such as He, N2, Ar, and the like as well as absorbing gases as previously described. For some dielectric cure applications, the addition of small amounts of reactive gases may be desirable to enhance the cure results. Thus, the apparatus can be equipped with one or more mass flow controlled gas channels that enable the controlled introduction of reactive gas species, such as O2, CO, CO2, CxHy, CxFy, NxHy and the like, wherein x and y are each independently generally greater than 1 to about 10. The process chamber 14 may further contain an oxygen sensor 67 for detecting the amount of oxygen contained within the chamber. A feedback loop can be provided to prevent operation of the apparatus until the oxygen level is below a predetermined amount. As is known in the art of advanced semiconductor manufacturing, the presence of oxygen can cause unwanted oxidation of the metal interconnects as well as affect treatment of the dielectric materials at high temperatures. As shown in FIG. 7, the chuck assembly 60 generally includes a support 70, an annular isolation ring 72, and a lift pin assembly mechanism 74. The annular isolation ring 72 is sealingly disposed between a lower surface of the support 70 and the base unit 52 of the process chamber 14. The planar surface of the support 70 includes multiple perimeter pins 76, two of which are shown in FIG. 7. In one embodiment, the support 70 is stationary, i.e., non-rotating. In another embodiment, the support 70 is fabricated from aluminum or an aluminum alloy. The lift pin assembly mechanism 74 is disposed below the support 70 and includes an air cylinder or the like for actuating the lift pins 76 through lift pin sleeves 96 (see FIG. 8) during processing. The airlines necessary to operate the lift pin mechanism 74 as well as any other plumbing required for the apparatus 10 are preferably disposed in a selected one of the sidewalls in the base unit 52. In other embodiments, the chuck moves vertically to contact the substrate while supported by the pins. As shown more clearly in FIGS. 8-10, the support 70 includes a planar surface upon which a substrate is placed during processing. Optionally, the support 70 includes gas transfer holes 78 and passages 80 extending therethrough such that a heat transfer gas, e.g., helium or the like, can be passed through the holes 78 and/or passages 80 to increase the heat transfer rate between the substrate and surface of the support 70. The holes 78 and/or passages 80 may also be employed for providing a vacuum to the backside of the substrate 38 for increasing the number of contact points between the bottom surface of the substrate and the surface of the support 70 such as by elastic deformation of the substrate. If a vacuum hold down is utilized, the increased number of contact points between the substrate and the surface of the support 70 resulting from the vacuum increases the rate at which the substrate comes to process temperature. In this case, the holes 78 and/or passages 80 are preferably connected to a vacuum line 82, which, in turn, is connected downstream of a process chamber isolation valve, a flow control valve, or the like (not shown). Advantageously, the decrease in time-to-process temperature reduces the overall process time. Passages 84 (FIG. 9) may also be machined or cast in the support 70 such that a fluid from a cooling system may be circulated to further control the temperature of the substrate. In this manner, the fluid is circulated through cooling conduits 86, which are in fluid communication with passages 84. Resistance heating elements 88 (FIG. 9) may also be cast into the support 70 enabling elevated processing temperatures that may be utilized for increased tool throughput. The support 70 preferably has a shape corresponding to that of substrate and is preferably capable of an operating range of about 200 to about 450° C. In a preferred embodiment, the operating temperature of the support 70 can be varied preferably via a feedback or a closed loop control system using a proportional integral derivative (PID) controller having a heating and cooling capability. The controller would alternately supply a current to heating elements 88 or cooling fluid (air or water) to passages 84 in support 70, as needed. Feedback to the PID controller would be provided by measuring the temperature of substrate during the process using a temperature measuring device such as a spring activated thermocouple 90 mounted within the surface of support 70 as shown in FIG. 10. The thermocouple 90 comprises a spring 92 in operable communication with a contact portion 94 such that the contact portion 94 maintains contact with the backside surface of substrate during support thereof. Alternatively, the temperature of support 70 can be controlled with an open loop process (i.e., without a feedback device) by adjusting the current supplied to heating elements 88 and allowing fluid flow (air or water) through passages 84 cast into support 70 at the appropriate point in the process. Still further, the thermocouple can be embedded within the chuck support to measure the temperature of the substrate Optionally, support 70 includes an irradiance probe 73 for measuring the intensity and spectral characteristics of the ultraviolet radiation. The probe 73 can function in the absence of an overlying substrate to provide a means for characterizing the ultraviolet radiation pattern prior to exposing substrates, which as noted above is dependent on a variety of parameters, e.g., gas fill, bulb cooling, gases within the process chamber, the transmission of the plate, and the like. Advantageously, the above described process chamber 14 provides a substantially sealed environment for processing the substrate. It has been demonstrated that the quality of the cure (and/or porogen removal) and the integrity of the low-k materials depend on a highly inert ambient. The purged sealed structure helps to provide an inert environment having an oxygen concentration of less than 100 parts per million (ppm), and more preferably less than 50 parts per million and even more preferably less than 20 parts per million. A minimum purge gas flow may be used (even in the standby mode) to maintain the process chamber at a substantially oxygen-free gas filling. Turning now to FIG. 11, the loadlock chamber module 16 includes an airlock chamber 102 in operative communication with the processing chamber 14 and a wafer handler (not shown). An opening 104 is disposed in a sidewall of the airlock chamber 102 in operative communication with opening 66 (see FIG. 6) of the process chamber. The airlock chamber 102 includes an additional opening 106 for introducing and removing substrates from the airlock chamber 102. Such a loadlock chamber module 16 can be adjusted to match the operating pressure in the processing chamber 14, thereby allowing transfer of substrates into or out of the process chamber 14 while also allowing the process chamber 14 to maintain a relatively constant pressure, e.g., atmospheric. Moreover, the loadlock chamber 16 includes at least one gas inlet 103 for introducing an inert gas from at least one gas source 105 into the airlock chamber 102. By maintaining an inert atmosphere in the airlock, oxidation of the materials on the substrate, e.g., metal interconnects, low k dielectric, and the like, can be substantially prevented. As the processed substrate is removed from the process chamber, the substrate is generally at an elevated temperature (after having been exposed to ultraviolet radiation in the process chamber typically at an elevated temperature between about 20° to about 450° C., which can exacerbate oxidation of the low k material as well as the metal interconnects in the presence of oxidizing gases, e.g., CO, CO2, O2, ozone, and the like. By maintaining an inert atmosphere until the substrate is sufficiently cooled, minimal oxidation, if any, can occur. Maintaining an inert ambient in the load-lock also helps to minimize the transfer of undesired species into the process chamber. The loadlock chamber module 16 includes at least one robotic arm (not shown) for transferring the substrate to/from the process chamber and to/from the airlock chamber and to/from the wafer handler. The robotic arm can be a single arm whose travel moves a wafer in a substantially linear manner. The airlock chamber preferably includes a chuck for cooling the substrate after processing. In another embodiment, since plasmas can be additionally be used to alter dielectric materials and/or remove porogens, the apparatus 10 may be modified to include one or more plasma reactors in addition to the UV processing chambers disclosed herein above. The plasma chambers can utilize RF or microwave frequencies for excitation of oxidizing, reducing or neutral plasma chemistries. Substrates processed in these chambers could be heated by either a hot chuck or by lamps. In another embodiment, a pre-heating station (not shown) may be added prior to UV exposure, to remove most of the volatiles that outgas from the substrate, before introducing it into the process chamber. During operation, a substrate is loaded from the wafer handler module into the airlock chamber 102 of the loadlock chamber module 16 at atmospheric pressure. The atmosphere is preferably purged with an inert gas to remove oxidizing gases, e.g., air, from the airlock chamber 102. The substrate is then transferred into the process chamber 14, which is preferably purged in a similar manner and may further include absorbing gases, or reactive gases as may be desired for the intended application. The radiation source module 12 is also purged to remove any air from the sealed interior region 20 and may further include absorbing gases, if desired. The substrate is then exposed to a broad ultraviolet radiation pattern emitted from the radiation source 22 at an elevated temperature, if desired. Preferably, the process chamber 14 is configured for automatic substrate handling such that manual handling of the substrate, e.g., wafer, is eliminated. In one embodiment, the process includes purging the interior region 20 of the radiation source module 12, the process chamber 14, and optionally, the loadlock chamber 16 with one or more inert gases to remove the air prior to exposing the substrate 40 to the ultraviolet radiation pattern and/or remove the air prior to transferring the substrate from the process chamber to the loadlock chamber. The substrate temperature may be controlled ranging from about room temperature to about 450° C., optionally by an infrared light source, an optical light source, a hot surface, or the light source itself. The process pressure can be less than, greater than, or equal to atmospheric pressure. In one embodiment, the process pressure is at atmospheric. Typically, the UV cured dielectric material is UV treated for no more than or about 300 seconds and, more particularly, between about 60 and about 180 seconds. Also, UV treating can be performed at a temperature between about room temperature and about 450° C.; at a process pressure that is less than, greater than, or about equal to atmospheric pressure; at a UV power between about 0.1 and about 2,000 mW/cm2; and a UV wavelength spectrum between about 100 and about 400 nm. Moreover, the UV cured dielectric material can be UV treated with a process gas purge, such as N2, Oz, Ar, He, H2, H2O vapor, COz, CxHy, CxFy, CxHzFy, air, and combinations thereof, wherein x is an integer between 1 and 6, y is an integer between 4 and 14, and z is an integer between 1 and 3. Suitable low k dielectric materials that can be processed with the above noted apparatus include, but are not intended to be limited to, commonly used spin-on low k dielectric materials and CVD deposited low k dielectric materials. These low k materials can be organic materials, inorganic materials, or combinations thereof. For example, the dielectric material can be a low k dielectric material, a premetal dielectric material, an oxide, a nitride, an oxynitride, a barrier layer, an etch stop material, a capping layer, a high k material, a shallow trench isolation dielectric material or combinations comprising at least one of the foregoing dielectric materials. More particularly, suitable low k dielectric materials can include hydrogen silsesquioxane (HSQ), alkyl silsesquioxane dielectric materials such as MSQ, carbon doped oxide (CDO) dielectric materials, fluorosilicate glasses, diamond-like carbon, parylene, hydrogenated silicon oxy-carbide (SiCOH) dielectric materials, B-staged polymers such as benzocyclobutene (BCB) dielectric materials, arylcyclobutene-based dielectric materials, polyphenylene-based dielectric materials, polyarylene ethers, polyimides, fluorinated polyimides, porous silicas, silica zeolites, porous derivatives of the above noted dielectric materials, and combinations thereof. The porous derivatives, i.e., mesoporous or nanoporous, can have porogen-generated pores, solvent-formed pores, or molecular engineered pores, which may be interconnected or closed, and which may be distributed, random, or ordered, such as vertically oriented pores. Other suitable dielectrics include, but are not intended to be limited to, silicates, hydrogen silsesquioxanes, organosilsesquioxanes, organosiloxanes, organhydridosiloxanes, silsesquioxane-silicate copolymers, silazane-based materials, polycarbosilanes, and acetoxysilanes. Suitable substrates include, but are not intended to be limited to, silicon, silicon-on-insulator, silicon germanium, silicon dioxide, glass, silicon nitride, ceramics, aluminum, copper, gallium arsenide, plastics, such as polycarbonate, circuit boards, such as FR-4 and polyimide, hybrid circuit substrates, such as aluminum nitride-alumina, and the like. Such substrates may further include thin films deposited thereon, such films including, but not intended to be limited to, metal nitrides, metal carbides, metal silicides, metal oxides, and mixtures thereof. In a multilayer integrated circuit device, an underlying layer of insulated, planarized circuit lines can also function as a substrate. In this example, multiple substrates including the same dielectric material were processed in the Apparatus as described above. FIG. 12 graphically illustrates the effectiveness of the periodic in situ clean function. The in situ clean process included flowing an oxidizing fluid into the process chamber and exposing the oxidizing fluid to the ultraviolet broadband radiation. The irradiance probe measured intensity of the ultraviolet broadband radiation into the process chamber. As a result of outgassing and contaminant deposition onto the transmissive plate during processing of multiple substrates containing the dielectric material, transmission of the ultraviolet broadband radiation decreases as a function of processed substrates. Periodically cleaning the process chamber cleans the plate so as to substantially restore transmission of the ultraviolet broadband radiation. Advantageously, the walls and other surfaces of the process chamber can also be presumed to have been cleaned in addition to the transmissive plate. FIG. 13 graphically illustrates reconditioning of the process chamber after the in situ clean process has been completed. On the left side of the graph, transmittance of the ultraviolet broadband radiation is measured during the in situ clean process described immediately above. After about 5 minutes exposure to the in situ clean process, the plate was substantially cleaned as indicated by the transmittance of the ultraviolet broadband radiation into the process chamber. To remove the oxidizing fluid, the process chamber was the purged with an inert gas. The oxygen probe measured the concentration of oxygen remaining in the process chamber as function of time. While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. |
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claims | 1. A nuclear fuel storage system comprising:a canister comprising a cylindrical shell extending along a vertical centerline;a fuel basket positioned in the canister, the fuel basket formed by a plurality of orthogonally arranged and interlocked slotted plates which collectively define exterior side surfaces of the fuel basket;the fuel basket comprising a plurality of interior cells being defined by the slotted plates, each interior cell configured to hold a fuel assembly comprising spent nuclear fuel;at least some of the slotted plates comprising cantilevered plate extensions, the plate extensions protruding laterally beyond the exterior side surfaces of the fuel basket and defining peripheral gaps between the fuel basket and the canister;wherein the plate extensions are configured to engage the shell of the canister. 2. The system according to claim 1, wherein the lateral plate extensions define vertical edges which terminate proximate to an interior surface of the canister. 3. The system according to claim 2, wherein the vertical edges are linearly straight from top to bottom. 4. The system according to claim 1, further comprising a plurality of vertically elongated reinforcement members inserted in the peripheral gaps formed between the exterior side surfaces of the fuel basket and the shell of the canister, the reinforcement members fixedly coupled to the fuel basket. 5. The system according to claim 4, wherein the reinforcement members are fixedly coupled to the plate extensions at the upper end of the fuel basket, the lower end of the fuel basket, and in between. 6. The system according to claim 5, wherein the reinforcement members have a height which is coextensive with a full height of the fuel basket. 7. The system according to claim 6, wherein the reinforcement members comprise vertically elongated reinforcement plates extending for a full height of the fuel basket. 8. The system according to claim 7, wherein the reinforcement plates being arranged in pairs on the plate extensions of the fuel basket, the plate extensions being sandwiched between the pairs of the reinforcement plates. 9. The system according to claim 8, wherein the pairs of reinforcement plates are bolted to the plate extensions by bolts which pass through the reinforcement plates and plate extensions. 10. The system according to claim 9, wherein each pair of the reinforcement plates is bolted to a respective plate extension proximate to a top end of the fuel basket by a plurality of the bolts and proximate to a bottom end of the fuel basket by a plurality of bolts. 11. The system according to claim 7, wherein the reinforcement plates have a straight strap-like shape. 12. The system according to claim 7, wherein the reinforcement plates have an angled shape. 13. The system according to claim 1, wherein the reinforcement members each further comprise a flow cutout formed in a bottom end of the reinforcement members. 14. The system according to claim 1, wherein the plate extensions of the fuel basket each further comprise a flow cutout formed in a bottom end of the plate extensions. 15. The system according to claim 14, wherein the peripheral gaps form a flow downcomer and the interior cells form a riser which is in fluid communication via the flow cutouts to form a natural convective thermos-siphon flow recirculation circuit. 16. The system according to claim 15, further comprising an inert gas contained in the canister which circulates through the flow recirculation circuit. 17. The system according to claim 7, wherein the reinforcement members further comprise a plurality of vertically elongated tubular shim members positioned in some of the peripheral gaps, the tubular shim members each being fixedly coupled to a respective plate extension of the fuel basket. 18. The system according to claim 17, wherein the tubular shim members are bolted to the respective plate extensions. 19. The system according to claim 18, wherein the tubular shim members are bolted to the plate extensions by bolts which pass through the tubular shim members, plate extensions, and one of the reinforcement plates. 20. The system according to claim 18, wherein the tubular shim members are positioned in the peripheral gaps which do not contain a reinforcement plate. 21. A nuclear fuel storage system comprising:a canister comprising a cylindrical shell extending along a vertical centerline;a fuel basket positioned in the canister, the fuel basket defining a grid array of interior cells each of which is configured to hold a fuel assembly comprising spent nuclear fuel;the fuel basket comprising a plurality cantilevered plate extensions, the plate extensions protruding laterally beyond vertical exterior side surfaces of the fuel basket and defining peripheral gaps between the fuel basket and the canister; anda plurality of vertically elongated reinforcement members positioned in the peripheral gaps, the reinforcement members each being fixedly coupled to the plate extensions. 22. The system according to claim 21, wherein the reinforcement members comprise elongated reinforcement plates of straight or angular configuration extending for a full height of the fuel basket, each reinforcement member being fixedly coupled to a respective plate extension in one of the peripheral gaps. 23. The system according to claim 22, wherein the respective plate extensions are sandwiched between a pair of the reinforcement plates. 24. The system according to claim 22, wherein the reinforcement members further comprise a plurality of vertically elongated tubular shim members positioned in some of the peripheral gaps, the tubular shim members each being fixedly coupled to one side of a respective plate extension opposite to one of the reinforcement plates fixedly coupled to an opposite side of the respective plate extension. |
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claims | 1. A manufacturing method of a radiation detecting element comprising:bonding, by solid state diffusion, a substrate transparent to visible light and a fluorescent screen that emits fluorescence in response to radiation by a dopant added to a material that is the same as a material of the substrate; andthinning the fluorescent screen, whereinthe bonding includes applying pressure to the substrate and the fluorescent screen. 2. The manufacturing method according to claim 1, wherein, the bonding includes applying pressure to the substrate and the fluorescent screen in the bonding directions of the substrate and the fluorescent screen. 3. The manufacturing method according to claim 1, wherein the thinning includes polishing the fluorescent screen. 4. The manufacturing method according to claim 1, wherein the bonding is performed after a bonding surface of the substrate is superposed on a bonding surface of the fluorescent screen. |
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description | The present application is a continuation of U.S. patent application Ser. No. 15/715,631 filed Sep. 26, 2017, which is a divisional of U.S. patent application Ser. No. 14/771,018 filed Aug. 27, 2015, which is a U.S. national stage application under 35 U.S.C. § 371 of International Patent Application No. PCT/US2014/019042 filed Feb. 27, 2014, which claims the benefit of U.S. Provisional Patent Application Ser. No. U.S. 61/770,213 filed Feb. 27, 2013; the entireties of which are all incorporated herein by reference. The present invention relates to nuclear reactor vessels, and more particularly to a nuclear reactor shroud surrounding the fuel core. Many nuclear reactor designs are of circulatory type wherein the water heated in the reactor fuel core region must be separated from the cooler water outside of it. Such a nuclear reactor may be typically equipped with a cylindrical shroud around the fuel core. The shroud serves to separate the internal space in the reactor vessel between an “up-flow” (e.g. riser) region in which primary coolant heated by the core flows inside the shroud and the “downcomer” region in which colder primary coolant returned to the reactor vessel from the Rankine cycle steam generating system flows outside the shroud. It is desirable to minimize heat transfer from the heated hot reactor water inside the riser region of the shroud to the colder downcomer water outside the shroud which is deleterious to the thermodynamic performance of the reactor. The standard practice in shroud design has typically consisted of hermetically enclosing a fibrous or ceramic insulation in a stainless steel (or another corrosion resistant alloy) enclosure. Such a shroud works well until a leak in the enclosure develops, usually caused by the thermal stresses and strains that are inherent to any structure operating under a temperature differential. Concerns regarding failure of the shroud and subsequent dismembering of the insulation have been a source of significant and expensive ameliorative modification efforts in many operating reactors. The present disclosure provides a reactor shroud which minimizes heat transfer between the hot reactor riser water and cold downcomer water in a manner which eliminates drawbacks of the foregoing insulated enclosure designs. In an embodiment of the present invention, the shroud may be comprised of a series of concentric cylindrical shells separated by a small radial clearance. The top and bottom extremities of the shells are each welded to common top and bottom annular plates (“closure plates”) to create an essentially isolated set of narrow & tall annular cavities. Each cavity is connected to its neighbor by one or more small drain holes such that submerging the multi-shell body in water (e.g. demineralized primary coolant in a reactor vessel) would fill all of the internal cavities with water and expel virtually all entrapped air, thereby creating water-filled annular cavities. In one non-limiting embodiment, the thin walled concentric shells may be buttressed against each other with a prescribed gap by small fusion welds made by a suitable process such as spot, plug, or TIG welding. In such a welding process, a small piece of metal (e.g. spacer) equal in thickness to the radial gap or clearance in the cavity serves to enable a fusion nugget to be created between the two shell walls. The number of such nuggets is variable, but preferably is sufficient to prevent flow induced vibration of the shroud weldment during reactor operation. One principal advantage of the multi-shell closed cavity embodiment described herein is that it is entirely made of materials native to the reactor's internal space, namely demineralized water (e.g. primary coolant) disposed within the radial gaps between the concentric shells and metal such as stainless steel. No special insulation material of any kind is used in the reactor shroud (which may degrade and fail over time). Advantageously, the present shroud design provides the desired heat transfer minimization between the hot reactor water inside the riser region of the shroud to the colder downcomer water outside the shroud without insulation, thereby preserving the thermodynamic performance of the reactor. According to one exemplary embodiment, a nuclear reactor vessel includes an elongated cylindrical body defining an internal cavity containing primary coolant water; a nuclear fuel core disposed in the internal cavity; an elongated shroud disposed in the internal cavity, the shroud comprising an inner shell, an outer shell, and a plurality of intermediate shells disposed between the inner and outer shells; and a plurality of annular cavities formed between the inner and outer shells, the annular cavities being filled with the primary coolant water. In one embodiment, the annular cavities are fluidly interconnected by a plurality of drain holes allowing the primary coolant to flow into and fill the cavities from the reactor vessel. According to another embodiment, a shroud segment for a nuclear reactor vessel includes an elongated inner shell; an elongated outer shell; a plurality of elongated intermediate shells disposed between the inner and outer shells; the inner shell, outer shell, and intermediate shells being radially spaced apart forming a plurality of annular cavities for holding water; a top closure plate attached to the top of the shroud segment; and a bottom closure plate attached to the bottom of the shroud segment, wherein the top and bottom closure plates are configured for coupling to adjoining shroud segments to form a stacked array of shroud segments. A method for assembling a shroud for a nuclear reactor vessel is provided. The method includes: providing a first shroud segment and a second shroud segment, each shroud segment including a top closure plate and a bottom closure plate; abutting the top closure plate of the second shroud segment against the bottom closure plate of the first shroud segment; axially aligning a first mounting lug on the first shroud segment with a second mounting lug on the second shroud; and locking the first mounting lug to the second mounting lug to couple the first and second shroud segments together. In one embodiment, the locking step is preceded by pivoting a mounting clamp attached to the first shroud segment from an unlocked open position to a locked closed position. All drawings are schematic and not necessarily to scale. Parts given a reference numerical designation in one figure may be considered to be the same parts where they appear in other figures without a numerical designation for brevity unless specifically labeled with a different part number and described herein. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Referring to FIG. 1, a reactor vessel 20 includes a vertically elongated cylindrical body defining a longitudinal axis LA and having a top 21, closed bottom 22, and a circumferentially extending sidewall 24 extending between the top and bottom. Sidewall 24 defines an internal cavity 25 configured for holding a nuclear fuel core 26. Internal cavity extends axially along the longitudinal axis from the top 21 to the bottom 22 of the reactor vessel 20 in one embodiment. The bottom 22 may be closed by a lower head 23, which may be without limitation dished or hemispherical in configuration. In one embodiment, the internal cavity 25 may be filled with a liquid such as primary coolant which may be demineralized water. The reactor vessel 20 may be made of any suitable metal, including without limitation coated steel or stainless steel for corrosion resistance. Referring to FIGS. 1-3 and 7, a vertically elongated shroud 30 is provided which is disposed in the internal cavity 25 of the reactor vessel 20. Shroud 30 may be cylindrical in shape with a circular annular cross-section; however, other suitable shapes may be used. Shroud 30 is coaxially aligned with the reactor vessel 20 along the longitudinal axis LA. The fuel core 26 may be located inside the shroud 30, and in one non-limiting embodiment nearer to the bottom 22 of the reactor vessel 20. Shroud 30 includes a top 34 and bottom 35 which may be spaced vertically apart from the bottom 22 of reactor vessel 20 to provide a flow passage into the shroud 30 at the bottom of the reactor vessel 20 (see, e.g. directional flow arrows FIGS. 1 and 8). In one embodiment as best shown in FIG. 8, the bottom 35 of the shroud 30 may be spaced apart from bottom 22 of reactor vessel 20 and supported by a plurality of radially oriented and circumferentially spaced apart support plates 42. Support plates 42 are configured to engage the reactor vessel bottom 22 at one extremity and bottom 35 of shroud 30 at another extremity. In one embodiment, support plates 42 may include one or more flow holes 41 to allow primary coolant to flow and circulate through the plates at the bottom of the reactor vessel. In other embodiments, the holes may be omitted. The shroud 30 divides the internal cavity 25 of reactor vessel 20 into an outer annular space which defines a vertical downcomer region 28 (i.e. down-flow region) and an inner space which defines a vertical riser region 27 (up-flow region). Primary coolant flows downwards in reactor vessel 20 through the annular downcomer region 28, reverses direction and enters the bottom 35 of the shroud 30, and flows upwards through riser region 27 through the fuel core 26 where the primary coolant is heated for generating steam in an external steam generator. In one embodiment, the shroud 30 may comprise an elongated outer shell 31, an inner shell 32, and a plurality of intermediate shells 33 disposed between the outer and inner shells. Shells 31-33 are cylindrically shaped in one embodiment. Shells 31-33 are concentrically aligned with respect to each other and spaced radially apart forming an array comprised of a plurality of relatively thin concentric annular cavities 40 between the outer and inner shell 31, 32. In one embodiment, the cavities 40 are fluid-filled with primary coolant, as further described herein. Annular cavities 40 extend longitudinally from the top 34 to bottom 35 of shroud 30. Accordingly, the annular cavities 40 have a length or height substantially coextensive with the length of the shells 31-33. The shells 31-33 may be formed of a suitable corrosion resistant metal, such as coated or stainless steel for example. In one exemplary embodiment, the number of intermediate shells 33 may be at least two to provide at least three annular cavities 40. In non-limiting preferred embodiments, at least six or more intermediate shells 33 (divider shells) may be provided to divide the space between the inner and outer shells 32 and 31 into at least seven annular cavities 40. In one representative embodiment, without limitation, eight intermediate shells 33 are provided to create nine intermediate shells 33. The number of water-filled annular cavities 40 selected correlates to the insulating effect and heat transfer reduction from the inner shell 32 through the shroud to the outer shell 31. The number of intermediate shells 33 will be one less than the number of water-filled annular cavities 40 to be created. In order to provide inter-shell connectivity and maintain the radial gap of annular cavities 40 between intermediate shells 33 and between the innermost and outermost intermediate shells and inner shell 32 and outer shell 31 respectively, spacers 80 may be provided as shown in FIG. 2. Spacers 80 are disposed in annular cavities 40 between the shells 31-33 and have a radial thickness sufficient to provide the desired radial width of each annular cavity. Each annular cavity 40 preferably includes spacers 80 in an exemplary embodiment. To retain the spacers 80 in their desired vertical position, the spacers may be rigidly attached to a shell 31-33 by any suitable means such as fusion welding in an exemplary embodiment. In one embodiment, a spot weld 81 may be used to attach spacer 80 to a shell 31-33 as shown. The spot welds 81 may have any suitable diameter, such as without limitation about 1 inch as a representative example. The number of spot welds 81 (spot nuggets) needed for joining neighboring shells 31-33 together may be estimated by the following empirical formula: Number=(shroud diameter times height (in inches)/100). Preferably, the spot welds 81 and spacers 80 should be spaced as uniformly as possible. In one embodiment, the spacers 80 may be radially staggered such that the spacers between adjacent shells 31-33 do not lie on the same radial axis (see, e.g. FIG. 2 showing a set of spacers aligned radially only in every other annular cavity 40). Other suitable arrangements of spacers 80 may be used. Spacers 80 may have any suitable shape, including circular or polygonal configurations. Preferably, spacers 80 may be formed of metal such as steel or other. Referring to FIGS. 2, 3, and 7, each annular cavity 40 may be connected to its adjoining cavities by one or more small fluid drain holes 90. Drain holes 90 are configured and arranged to hydraulically or fluidly interconnect all of the annular cavities 40. The outer shell 31 includes drain holes 90 which fluidly connect the outermost annular cavity 40 in shroud 30 to the annular downcomer region 28 in reactor vessel 20. This allows the primary coolant water to enter the outermost cavity 40 and then flow inwards successively through the plurality of drains holes in intermediate shells 33 for filling all the annular cavities with the fluid. Submerging the multi-shell shroud 30 body in the water-filled reactor vessel (e.g. demineralized primary coolant) will fill all of the internal annular cavities 40 with water and expel virtually all entrapped air, thereby creating water-filled annular cavities. In one arrangement, the drains holes 90 may be radially staggered as best shown in FIG. 7 so that the holes in one shell 31 or 33 do not radially align with holes in its neighboring shells. This forms a staggered flow path through the shroud 30. The inner shell 32 may not have drain holes 90 and is solid in one embodiment. Preferably, a plurality of drain holes 90 are spaced both circumferentially and longitudinally apart along the entire height or length of the shroud 30 in each shroud segment 30A-C Referring to FIG. 2, the inner and outer shells 32 and 31 may have thicknesses T2 and T1 respectively which are larger than the intermediate shells 33 in one embodiment to stiffen and strengthen the shroud 30. For example, in one representative example without limitation inner and outer shells 32 and 31 may have a plate thickness (T1 and T2) of about ¼ inch and intermediate shells 33 may have a thickness T3 of about ⅛ inch. Each annular cavity 40 has a depth D2 (measured in the radial direction transverse to longitudinal axis LA) which is less than the total depth D1 between the inner and outer shells 32 and 31. In one embodiment, the water-filled annular cavities 40 may have a depth D2 that is less than the thickness T1-T3 of the shells 31-33. In one representative example without limitation, the depth of cavity 40 may be about 3/16 inch. This arrangement provides a plurality of thin water films or chambers comprised of primary coolant sandwiched between the inner and outer shells 32 and 31 in the multi-shell weldment (MSW) shroud wall construction. The thin water films have an insulating effect for shroud 30 which minimizes heat transfer between the hot riser region 27 and colder downcomer region 28 (see FIG. 1). Advantageously, the water films eliminate the need for traditional insulation materials in the shroud which may be wetted or otherwise damaged. In one embodiment, inner shell 32, outer shell 31, and intermediate shells 33 may have vertical heights or lengths which are substantially coextensive. According to one aspect of the invention, the shroud 30 may comprise a plurality of vertically stacked and coupled shroud sections or segments 30A, 30B, and 30C. Referring to FIGS. 1 and 3, each shroud segment 30A-C includes an upper end 48, lower end 49, an annular top closure plate 36 attached to upper end 48, and an annular bottom closure plate 37 attached to lower end 49. The top closure plate 36 and bottom closure plate 37 may be formed of a suitable metal such as steel. Corrosion resistant closure plates 36, 37 formed of coated or stainless steel may be used. Within each shroud segment 30A-C, the annular cavities 40 and shells 31-33 extend longitudinally between the top and bottom closure plates 36 and 37, and may have coextensive lengths or heights. The outer shell 31, inner shell 32, and intermediate shells 33 in each segment 30A-C may be rigidly attached to the top and bottom closure plates, such as via a rigid connection formed by welding for structural strength. In one embodiment, the shells 31-33 may be hermetically seal joined to the top and bottom closure plates such as with full circumferential seal welds. This forms a water-tight joint between the shells 31-33 and the top and bottom closure plates 36 and 37, respectively. Each shroud segment 30A-C is a self-supporting structure which may be transported, raised, and lowered individually for ease of maneuvering and assembly to adjoining segments during fabrication of the shroud 30. To facilitate handling the shroud segments 30A-C individually, the top closure plates 36 may include radially extending lifting lugs 38 which include a rigging hole 39 for attachment of lifting slings or hoists. A suitable number of lifting lugs 38 circumferentially spaced apart at appropriate intervals are provided to properly and safely hoist the shroud segments 30A-C. The weight of each shroud segment 30A-C may be vertically supported by the shroud segment immediately below with the weight being transferred through the top and bottom closure plates 36 and 37, respectively. Accordingly, in some embodiments, the entire weight of the shroud segments 30A-C may be supported by support plates 42 (see, e.g. FIGS. 1 and 8). In one embodiment, adjoining shroud segments 30A-C may be coupled together at joints 43 between segments via a plurality connectors 76 such as of clamps 50. Referring to FIGS. 1 and 3-5, clamps 50 are configured to detachably join and engage the bottom closure plate 37 of one shroud segment (e.g. 30B) to top closure plate 36 of the adjoining lower shroud segment (e.g. 30C). Clamps 50 each include a U-shaped body 51 defining a recess 52 configured to receive a mounting lug 55 formed on bottom closure plate 37 and a mating mounting lug 56 formed on top closure plate 36 as shown. Mounting lugs 55 and 56 are radially extending and circumferentially spaced apart on bottom and top closure plates 37 and 36, respectively. Each mounting lug 55 is arranged in a pair and coaxially aligned along the longitudinal axis LA with a corresponding mounting lug 56. In one embodiment, the mounting lugs 55 and 56 are integrally formed with and a unitary structural part of the bottom and top closure plates 37, 36. Accordingly, the mounting lugs 55, 56 may preferably be formed of metal similarly to bottom and top closure plates 37, 36 for structural strength. In one arrangement, clamps 50 may each be pivotably connected to a mounting lug 55 on the bottom closure plate 37 by a pivot pin 54 which defines a pivot axis. Pivot pins 54 are oriented parallel to longitudinal axis LA so that the clamp 50 may be pivotably swung or moved transversely to the longitudinal axis LA between a closed locked position (see, e.g. FIG. 4) and open unlocked position (see, e.g. FIG. 5). In one embodiment, pivot pin 54 is disposed proximate to one end 58 of the clamp body 51 and the opposing end 57 is open to receive mounting lug 56 of a top closure plate 36 into recess 52. Pivot pin 54 extends axially through the mounting lug 55 and the bottom and top flanges 59, 60 of clamp 50. To secure the clamp 50 in the closed locked position shown in FIG. 4, a locking fastener such as set screw 53 may be provided which is configured and arranged to engage a top surface of mounting flange 55. Set screw 53 may be threadably engaged in threaded bore 61 formed in top flange 60 of clamp 50. The bore 61 extends completely through top flange 60 to allow the bottom end of the set screw shaft to be projected into or withdrawn from clamp recess 51 for engaging or disengaging mounting flange 55. Raising or lowering the set screw 53 alternatingly disengages or engages the set screw with the mounting flange 55. Set screw 53 is preferably withdrawn from A method for assembling shroud 30 comprised of segments 30A-C using clamps 50 will now be described. For brevity, assembly of shroud segment 30B onto segment 30C will be described; however, additional shroud segments may be mounted in a similar manner. Referring to FIG. 3, a pair of shroud segments 30B and 30C are provided each configured as shown. Clamps 50 are in the open unlocked position (see, e.g. FIG. 5). Shroud segment 30B is first axially aligned along longitudinal axis LA with segment 30C. Segment 30B may then be rotated as needed to axially align mounting flanges 55 on bottom closure plate 37 with mounting flanges 56 on top closure plate 36 of segment 30C. Each pair of mounting flanges 55 and 56 may be brought into abutting relationship. In the process, bottom closure plate 37 is brought into abutting contact with top closure plate 36 forming the joint 43 between segments 30B and 30C. Clamp 50 is then pivoted about pivot pin 54. Mounting flanges 55 and 56 are inserted into recess 51 of clamp 50 between flanges 59 and 60 (see, e.g. FIG. 5). The set screw 53 is then tightened to secure the clamp 50 in the closed locked position shown in FIG. 5. It will be appreciated that the order of performing the steps of the fore steps may be varied. In addition, numerous variations of the foregoing assembly process are possible. Referring to FIG. 2, a sealing gasket 44 may be provided in between each pairing of a top closure plate 36 and bottom closure plate 37 to seal the interface at joint 43 therebetween. In one embodiment, the gasket 44 may be metallic formed of steel, aluminum, or another seal material suitable for the environment within a reactor vessel 20. The gasket 44 may be situated in an annular groove 45 formed in the bottom closure plate 37 as shown, or alternatively in the top closure plate 36 (not shown), to seal water seepage at the interface of joint 43 and also provide a certain level of verticality alignment capability during installation and joining of shroud segments 30A-C. In one embodiment, gasket 44 may be circular in transverse cross-section prior to the joint 43 being closed which will compress and deform the gasket. According to another aspect of the invention, a plurality of lateral seismic restraints such as restraint springs 70 may be provided to horizontally support and protect the structural integrity of the shroud 30 inside reactor vessel 20 during a seismic event. In one embodiment as shown in FIGS. 4 and 5, a dual purpose connector 76 (fastener or coupler for joints 43 between shroud segments 30A-C and lateral restraint) may be provided which combine the clamps 50 and seismic springs 70 into a single assembly. Referring to FIGS. 1 and 3-5, seismic springs 70 are disposed between and engage shroud 30 and the interior surface 74 of the reactor vessel 20. A plurality of seismic springs 70 are provided which are circumferentially spaced apart on the outer shell 28 of the shroud 30. In one embodiment, the seismic springs 70 may be spaced apart at equal intervals. Seismic springs 70 are elastically deformable to absorb lateral movement of the shroud 30. In one embodiment, each spring 70 may be in the form of an arcuate leaf spring comprised of a plurality of individual leaves 75 joined together to function as a unit. The leaves 75 may be made of suitable metal such as spring steel having an elastic memory. Other appropriate materials however may be used. The thickness and number of leaves 75 may be varied to adjust the desired spring force K of the spring 70. Seismic springs are arranged with the concave side facing outwards away from shroud 30 and towards reactor vessel 20 when in the fully mounted and active operating position. Opposing ends 72 and 73 of each seismic spring 70 are arranged to engage the interior surface 74 of reactor vessel 20. In one embodiment, seismic springs 70 may be rigidly attached to shroud 30 to provide a stable mounting for proper operation and deflection of the spring to absorb energy during a seismic event. In one possible arrangement, seismic springs 70 may be rigidly attached to clamps 50 via a fastener 71 or another suitable mounting mechanism. Spring 70 may be fastened to clamp 50 at the midpoint between ends 72 and 73 in one embodiment. Accordingly, seismic springs 70 may be pivotably movable with clamps 50 in the manner already described herein. In FIG. 1, for example, the seismic spring 70 and clamp 50 shown between shroud segments 30A and 30B is in the open unlocked position. In this same figure, seismic springs 70 shown between shroud segments 30B and 30C are in the pivoted closed locked position in which the seismic springs 70 are in the active operating position with ends 72 and 73 engaged with the reactor vessel 20. During a seismic event when the shroud 30 may shift laterally/horizontally in one or more directions, the seismic springs 70 will deform and deflect assuming a more flattened configuration until the seismic load is removed, thereby returning the spring elastically to its original more arcuately-shaped configuration shown. In one embodiment, each joint 43 between shroud segments 30A, 30B, and 30C may include seismic springs 70 to horizontal support the shroud 30 intermittently along its entire height. Underlying Operating Principle of the Shroud The multi-shell weldment (MSW) design for shroud 30 described herein is based on the principle in applied heat transfer which holds that an infinitely tall and infinitesimally thin closed end cavity filled with water would approximate the thru-wall thermal resistance equal to that of the metal walls and the water layer conductances. The governing dimensionless quantity that provides the measure of departure from the ideal (conduction only) is Rayleigh number defined as the product of the Prandtl number (Pr) and the Grashof number (Gr). Heat transfer in a differentially heated vertical channel of height H and gap L is characterized by Nusselt number correlation as a function of Rayleigh number as follows:Nu=0.039Ra1/3 Where:Nu is Nusselt Number (=hL/k)h is heat transfer coefficientk is conductivity of waterRa is Rayleigh number (=gβΔTL3ρ2/μ2)*Prg is gravitational accelerationβ is coefficient of thermal expansion of waterΔT is hot-to-cold face temperature differenceρ is density of waterμ is water viscosity As Rayleigh number defined above exhibits an L3 scaling it follows that gap reduction substantially affects Ra number. For example a factor of 2 gap reduction cuts down Ra number by a factor of 8 (almost by an order of magnitude). Thus engineering the shroud with small gaps has the desired effect of minimizing heat transfer. To further restrict heat transfer a multiple array of gaps are engineered in the shroud lateral space to have the effect of resistances in series. An example case is defined and described below to illustrate the concept. A Small Modular Reactor (SMR), such as the SMR-160 available from SMR, LLC of Jupiter, Fla., may have a particularly long shroud (e.g. over 70 feet). In such a case, the principal design concerns are: ease of installation, removal, verticality of the installed structure, mitigation of thermal expansion effects and protection from flow induced vibration of the multi-wall shell. The design features, described below to address the above concerns for such an SMR, can be applied to any shroud design. A. Narrow cavity geometry: The height of each shroud (e.g. shroud segments 30A-C) is approximately three times its nominal diameter. The innermost and outer most shells (e.g. shells 32 and 31) are relatively thick compared to the intermediate (inner) shells (e.g. shells 33). The water cavity is less than 0.1% of the shroud's height. The table below provides representative dimensions for demonstrating the concept: Dimensions of a typical shroud in SMR-160: Inner diameter71⅛inchHeight71ft.(Shroud built in four stacked sections (segments),3 × 20 ft. (lower) and 1 × 11 ft. (top))Number of water annuli (cavities)9Thickness of inner most shell¼inchThickness of outermost shell¼inchThickness of interior shell walls⅛inchThickness of water cavities 3/16inch B. Inter-shell connectivity: The number of spot nuggets (approximately 1 inch diameter) joining neighboring shells should be estimated by the following empirical formula: Number=(shroud diameter times height (in inches)/100). The spot welds should be spaced as uniformly as possible. C. Handling: The top plate 36 of each shroud segment 30A-C is equipped with lift lugs 38 for handling and installation. Typically six lift lug locations, evenly spaced in the circumferential direction, will suffice. D. Stacked construction: The multi-shell weldments (MSW) of shroud segments 30A-C are stacked on top of each other as shown in FIGS. 1 and 2. One or more round metallic gaskets 44 as described above are provided at the interface between the annular top and bottom closure plates 36, 37 of successive stacks of shroud segments 30A-C. The gaskets 44 situated in the annular grooves 45 in the bottom closure plate 37 serve to seal water seepage at the interface of joint 43 and also provide a certain level of verticality alignment capability. E. Thermal expansion: The axial thermal expansion of a tall stack of shroud segments 30A-C will cause severe stresses in adjoining structures such as the return piping that delivers the reactor coolant from the steam generator to the reactor's outer annulus (downcomer). To mitigate the thermal stresses, the upper region of the shroud may be equipped with a multi-ply bellows type expansion joint. F. Seismic restraints: The junctions or joints 43 of the MSW shroud segments 30A-C provide the “hard” locations to join them and to secure them against lateral movement during earthquakes. The dual purpose connector 76 (fastener and lateral restraint) design concept shown in FIGS. 3-5 comprising the clamps 50 and seismic springs 70 as described herein provide the joining and lateral restraint functionality. This dual purpose connector 76 has the following capabilities: (i) The two interfacing closure plates 36 and 37 are prevented from significant rotation or separation from each other during earthquakes. (ii) The connector 76 is amenable to remote installation and removal. (iii) The connector 76 is equipped with the seismic springs 70 (e.g. leaf springs) to enable it to establish a soft contact or a small clearance with the reactor's inside wall under operating condition (hot). A set of three connectors 76, equipment-spaced in the circumferential direction at each closure plate 36, 36 elevation, is deemed to be adequate for the SMR described above. Additional connectors may be employed in other reactor applications at the designer's option. Performance assessment: The efficacy of the MSW design is demonstrated by the case of the SMR-160 described above. Calculations show that the decrease in the hot leg temperature (primary coolant inside shroud 30) using water-filled annular cavities 40 due to heat loss across the shroud is merely 0.355 deg. F. As a point of reference, the idealized temperature loss would be 0.092 deg. F. if the water layers were instead omitted and “solid,” i.e., heat transferred only by conduction through the shroud. It can be seen that the Rayleigh effect, responsible for the movement of water in closed cavities, has been largely suppressed by the MSW design of shroud 30. Extension to vessels and conduits: The concept of establishing a thin water layer inside pipes (hereafter called “water lining”) carrying heated water is proposed to be employed at the various locations in the power plant where minimizing heat loss from the pipe is desired. For example, the lines carrying hot and cooled reactor coolant are water lined to limit heat loss. Water lining is achieved by the following generic construction: (i) An inner thin walled (liner) pipe that is nominally concentric with the main pipe. The liner pipe has a few small holes to make the narrow annulus communicate with the main flow space. (ii) The small gap between the main and liner pipes is held in place by small spacer nuggets attached to the outside surface of the liner pipe. (iii) In piping runs subject to in-service inspection of pressure boundary welds, the liner pipe is discontinued at the location of such welds. The foregoing water lining approach is also proposed to be used to reduce thermal shock to pressure retaining vessel/nozzle junctions (locations of gross structural discontinuity) where large secondary stresses from pressure exist. This is true of penetrations in the reactor vessel, steam generator as well as the superheater. Water lined pressure boundaries will experience significantly reduced fatigue inducing cyclic stresses which will help extend the service life of the owner plant. While the foregoing description and drawings represent exemplary embodiments of the present disclosure, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made within the scope of the present disclosure. One skilled in the art will further appreciate that the embodiments may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the disclosure, which are particularly adapted to specific environments and operative requirements without departing from the principles described herein. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The appended claims should be construed broadly, to include other variants and embodiments of the disclosure, which may be made by those skilled in the art without departing from the scope and range of equivalents. |
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claims | 1. The scanning electron microscope comprising: a stage for mounting an object substrate; an electron gun for emitting electron beam; a converging lens for converging the electron beam emitted from the electron gun; scanning unit for two-dimensionally scanning a surface of the object substrate with the electron beam converged by the converging lens; an objective lens for focusing the electron beam converged by the converging lens in a spot-like shape on the surface of the object substrate; a detector for detecting an intensity of at least one of secondary electron or reflected electron or absorbed electron generated from the object substrate by scanning with the electron beam by the scanning unit and outputting an analog image signal; an A/D conversion unit for sampling the analog image signal detected by and outputted from the detector and converting the analog image signal into a digital image signal; a switching control unit for controlling to switch at least the scanning unit so that a digital image signal having a low magnification based on a wide image taking field of view and a digital image signal having a high magnification based on a narrow image taking field of view are provided to be switched from the A/D conversion unit; and a beam spot diameter control unit for controlling to switch a spot diameter of the electron beam at the surface of the object substrate in accordance with the magnification when the scanning unit is controlled so as to switch by the switching control unit. 2. The scanning electron microscope according to claim 1 , wherein the beam spot diameter control unit controls a spot diameter of the electron beam based on information concerning a surface texture at a portion of the object substrate for taking an image when the detector takes the image with the wide image taking field of view by controlling so as to switch the scanning unit by the switch control unit. claim 1 3. The scanning electron microscope according to claim 1 or 2 : claim 1 2 wherein the beam spot diameter control unit is constituted to control to move the stage in a direction of irradiating with the electron beam. 4. The scanning electron microscope according to claim 1 or 2 : claim 1 2 wherein the beam spot diameter control unit is constituted by controlling the objective lens. 5. The scanning electron microscope according to claim 1 or 2 : claim 1 2 wherein the beam spot diameter control unit is constituted by controlling current of the electron beam emitted from the electron gun. 6. The scanning electron microscope according to claim 1 , further comprising: claim 1 a control unit for controlling to restrain pseudo noise components generated from a portion of the object substrate for taking an image when the detector takes the image with the wide image taking field of view by controlling so as to switch the scanning means by the switching control unit. 7. The scanning electron microscope according to claim 1 , further comprising: claim 1 a signal processing unit for reducing pseudo noise components at high frequencies by carrying out a signal processing in accordance with a surface texture at a portion of the object substrate for an analog image signal outputted from the detector when the detector takes an image with the wide image taking field of view by controlling so as to switch the scanning unit by the switching control unit. 8. The scanning electron microscope according to claim 1 , further comprising: claim 1 a signal processing unit for reducing pseudo noise components at high frequencies by carrying out a signal processing in accordance with a surface texture of a portion of the object substrate for a digital image signal provided by the A/D conversion unit when the detector takes an image with the wide image taking field of view by controlling so as to switch the scanning unit by the switching control unit. 9. The scanning electron microscope according to claim 7 or 8 : claim 7 8 wherein the signal processing unit is constituted to carry out a filtering signal processing. |
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abstract | A device for the adjustment of the anti-scattering grid (G) of a radiological equipment to the different focal lengths that said equipment can provide includes a pair of pressing members (P) mobile in the direction transverse with respect to the plane of the grid (G), which is arranged and restrained between said pressing members (P) and a pair of corresponding underlying contrast members (C), the convex/concave profile of each pair of members (P, C) being obtained as locus of the local deformations, calculated point by point with a suitable spatial resolution, necessary to adjust the orientation of the segments of the grid (G) when going from one reference focal length to a second focal length. |
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claims | 1. A pressure suppression and decontamination apparatus for a reactor container including a dry well space having an upper dry well and a lower dry well, the reactor container housing therein a reactor pressure vessel containing nuclear core fuel, said apparatus comprising:a dry well cooling unit configured to cool a gas in the dry well space and produce a condensate of the gas;a circulation device configured to circulate the gas in the dry well space through said dry well cooling unit;a sprayer head connected to an outlet of a pump, disposed in the upper dry well, and configured to cool the reactor container;a drain pipe extending from said dry well cooling unit to the lower dry well, said drain pipe being configured to discharge the condensate from said dry well cooling unit, the drain pipe being directly connected to a changeover device, the changeover device being directly connected to the cooling unit; anda sprinkling device connected to said drain pipe and configured to sprinkle condensate in the dry well space, the sprinkling device being disposed lower than the dry well cooling unit and connected to receive condensate from the cooling unit via the drain pipe. 2. The pressure suppression and decontamination apparatus according to claim 1, wherein said changeover device connects said sprinkling device with said drain pipe, and wherein said changeover device includes a changeover panel that has a first position that allows the condensate to flow from said dry well cooling unit to an end of said drain pipe in the lower dry well and a second position that allows the condensate to flow from said dry well cooling unit to said sprinkling device. 3. The pressure suppression and decontamination apparatus according to claim 2, wherein said changeover panel is in the second position when said circulation device is in an emergency state. 4. The pressure suppression and decontamination apparatus according to claim 3, wherein said changeover panel is in the second position when a temperature of said changeover device is higher than a melting temperature of an adhesive metal in the changeover device. 5. The pressure suppression and decontamination apparatus according to claim 3, wherein said changeover panel is configured to move between the first position and the second position by mechanical means. 6. The pressure suppression and decontamination apparatus according to claim 1, wherein said sprinkling device is provided with a plurality of sprinkling holes at an end thereof. 7. The pressure suppression and decontamination apparatus according to claim 1, wherein said sprinkling device is provided with a collision plate, against which a flow of the condensate collides. 8. The pressure suppression and decontamination apparatus according to claim 1, wherein said sprinkling device is provided with a sprinkling blade configured to scatter a flow of the condensate. 9. The pressure suppression and decontamination apparatus according to claim 1, further comprising:a rotating mechanism configured to rotate through with a flow of the condensate flowing through said sprinkling device;a shut-off plate provided at an opening of a casing of said dry well cooling unit and an exhaust fan provided adjacent to said shut-off plate; anda connecting shaft connecting said rotating mechanism and said exhaust fan. 10. The pressure suppression and decontamination apparatus according to claim 9, wherein said shut-off plate is configured to be in a closed position during operation of said circulation device and configured to be in an open position during stoppage of said circulation device. 11. The pressure suppression and decontamination apparatus according to claim 1, wherein said sprinkling device is provided in the bottom dry well. 12. The pressure suppression and decontamination apparatus according to claim 1, wherein said sprinkling device is provided in the upper dry well. 13. A pressure suppression and decontamination apparatus for a reactor container including a dry well space having an upper dry well and a lower dry well, the reactor container housing therein a reactor pressure vessel containing nuclear core fuel, said apparatus comprising:means for cooling a gas in the dry well space to produce a condensate of the gas;a sprayer head connected to an outlet of a pump, disposed in the upper dry well, and configured to cool the reactor container;a drain pipe extending from said means for cooling to the lower dry well, said drain pipe being configured to discharge the condensate from said means for cooling, the drain pipe being directly connected to a changeover device, the changeover device being directly connected to the means for cooling; andmeans for sprinkling the condensate in the dry well space, said means for sprinkling being connected to said changeover device, the means for sprinkling being disposed lower than the means for cooling and connected to receive condensate from the means for cooling via the changeover device. 14. The pressure suppression and decontamination apparatus according to claim 13, wherein the changeover device fluidly connects said means for cooling to either an end of said drain pipe in the lower dry well or said means for sprinkling. 15. The pressure suppression and decontamination apparatus according to claim 1, wherein the sprayer head is connected to the pump via a residual heat removing line connected to the outlet of the pump and extending upward from the pump toward the sprayer head. |
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description | The present invention relates to chemical optimisation of a molten salt fuel for a fission reactor. Nuclear fission reactors using fissile fuels in the form of molten halide salts have many advantages over solid fuelled reactors but generally suffer from problems due to continuous changes in the chemical composition of the molten fuel salt during operation as fission products accumulate and a net release of halogen from the actinide tri or tetrahalide fuel occurs. Most designs of molten salt reactors incorporate a continuous chemical treatment process in the fuel circulation to manage this problem, however doing so involves adding complex chemical engineering systems into a highly radioactive environment. A much simpler design of molten salt reactor was described in GB 2508537 in which the fuel salt was held in static tubes in which convection or other mixing processes allowed heat to pass from the fuel salt to the tube wall at a sufficient rate for the reactor to have a practical energy production. Such static fuel tubes do not permit continuous active adjustment of the chemistry of the fuel salt. In GB 2508537 it was suggested that inclusion of metals such as niobium, titanium or nickel in the fuel salt or on the fuel tube would be useful in scavenging excess halogen released during fission but no specific suggestions were made for controlling deleterious effects of fission products. According to an aspect of the present invention, there is provided use in a nuclear fission reactor of a sacrificial metal in a molten salt fuel containing actinide halides in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. According to a further aspect of the present invention, there is provided a method of maintaining oxidation state of a molten salt containing actinide halides. The method comprises contacting the molten salt continuously with a sacrificial metal, the sacrificial metal being selected in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. According to a further aspect of the present invention, there is provided a fuel tube for use in a nuclear fission reactor. The fuel tube is configured to contain a molten salt comprising actinide halides. The fuel tube comprises a sacrificial metal such that in use the sacrificial metal is in contact with the molten salt, or with liquid condensed from vapour evolved from the molten salt. The sacrificial metal is selected in order to maintain a predefined ratio of actinide trihalide to actinide tetrahalide without reducing actinide trihalide to actinide metal. According to a further aspect of the present invention, there is provided a method of managing gas production in a fission reactor comprising fuel tubes containing a molten salt fissile fuel. The method comprises contacting the molten salt fissile fuel with a sacrificial metal. The sacrificial metal is selected in order to control a level of volatile iodine compounds released from the molten salt. The method further comprises permitting gasses produced during fission of the molten salt fissile fuel to pass out from the fuel tubes into a coolant surrounding the fuel tube or into a gas space in contact with the coolant. Further aspects are set out in claim 2 et seq. A systematic analysis of the effects of incorporating sacrificial metals into the fuel salt or fuel tube has been carried out resulting in the identification of particularly effective metals for this purpose. Three factors dictate the suitability of any particular sacrificial metal. These are maintaining a low redox state and hence low metal corrosive power and low concentration of actinide tetrahalides as indicated by a high ratio of trivalent to tetravalent actinides in the molten salt while not reducing actinide (usually uranium) halides to the metal form at temperatures approaching the boiling point of the salt mixture chemically binding potentially volatile fission products in the molten salt and preventing their entering the gaseous phase above the salt. Particularly important is to minimise volatile iodine compounds especially TeI2. Converting reactive tellurium to stable tellurides to prevent tellurium induced embrittlement of metals, especially nickel alloys, in contact with the molten salt Thermodynamic calculations of these three factors have been carried out using a software program HSC Chemistry 7. The results are shown in Table 1. The parameters of the thermodynamic calculation were as follows. The sacrificial metal was provided as a separate pure metallic phase in excess over other reactants. Salt composition in moles:NaCl428UCl3225UCl410Cd0.38I0.84In0.04Sb0.14Se0.24Te1.47 This represents a typical fuel salt towards the end of its useful life in a fast spectrum nuclear reactor. The group 1 and 2 metals, lanthanides, noble metals and noble gasses have been excluded as they were shown to have no effect on the chemistry involved. Gas composition was determined at 600° C. and reduction of uranium to the metal at 1500° C. Examination of table 1 indicates that zirconium, titanium, niobium, vanadium, zinc, chromium, silver and manganese are suitable as sacrificial metals to control redox state without producing uranium metal in situations where control of volatile species is not important. Where, in addition, control of dangerous volatile species such as iodine is important then only zirconium, titanium, vanadium, chromium and silver are useful. These same metals with the exception of vanadium are also effective in controlling tellurium levels. Silver as a sacrificial metal appears to have unique properties. Despite its high Pauling electronegativity, it is very effective at reducing UCl4 concentrations, reducing volatile iodine species and scavenging tellurium. The high affinity for iodine is a known property of silver but the efficacy in reducing UCl4 to UCl3 is unexpected. Combinations of multiple sacrificial metals produce still more favourable results where particular sacrificial metals are more effective against the three factors set out above. While data has been presented for chloride salts, the same principles and useful sacrificial metals can be applied to fluoride salt systems. While passive control of molten salt chemistry with sacrificial metals is of general value for molten salt reactors, it is particularly important for reactors such as that described in GB 2508537 where access to the molten salt for active management of the chemistry, for example by adding small amounts of reactive metals, is challenging. In such a reactor it is useful for the sacrificial metal to be applied to the vessel containing the molten fuel salt both above and below the level of the salt. This prevents occlusion of the sacrificial metal by deposited noble metal fission product. It can also be advantageous, particularly where the sacrificial metal has a significant neutron absorption, for the sacrificial metal not to be located near the centre of the reactor core so that any neutron absorption is minimised. The sacrificial metal can be provided in a variety of ways. FIGS. 1a to 1e show examples of fuel tubes incorporating sacrificial metal. FIG. 1a shows a fuel tube 101a containing molten salt 103a and an internal coating 102a of the sacrificial metal applied to the inner wall of the fuel tube. The sacrificial metal can be applied to the inner wall of the fuel tube by a variety of methods including, but not restricted to, electroplating, plasma spraying, dipping into molten metal, brazing, welding, chemical vapour deposition, sputtering, vacuum deposition, conversion coating, spraying, physical coating and spin coating. Alternatively, as shown in FIG. 1b, the internal coating 105b may be applied to only part of the fuel tube 101b, provided that part is in contact with the fuel salt 103b. FIG. 1c shows a further embodiment, in which a metal insert 104c made from or coated with the sacrificial metal is placed within the molten salt 103c inside the fuel tube 101c. This insert may be shaped so as to aid the convective mixing of the fuel salt, e.g. spiral shaped. FIG. 1d shows a yet further embodiment, where the sacrificial metal is provided as particles 107d suspended in the molten salt 103d within the fuel tube 101d, or as coatings on such particles. FIG. 1e shows an embodiment where the sacrificial metal is provided as particles 106e which are allowed to sink in the fuel salt 103e to the bottom of the fuel tube 101e. Use of a sacrificial metal such as titanium, vanadium, chromium or silver reduces the vapour pressure of many radioactive species produced by the fuel salt to very low levels. This makes possible much simpler methods to manage the gasses released from the fuel which, with suitable sacrificial metals present, are predominantly the noble gasses, xenon and krypton, cadmium and zirconium halides although the concentration of the latter is substantially reduced if zirconium is used as the sacrificial metal. Accumulation of these gasses in fuel elements is a major limitation in the longevity of such fuel elements as if the gas is permitted to accumulate it generates high pressures which can rupture the cladding of the fuel elements. It is known that, particularly in sodium cooled fast reactors, fission gasses can be allowed to vent from the fuel elements into the sodium coolant. This practice was used in the early days of development of such reactors but was abandoned because of the presence of highly radioactive, relatively long half life, cesium in the vented gas. The cesium contaminated the sodium coolant and made disposal of the sodium extremely challenging as well as creating a major hazard in the event of a sodium fire. The practice was therefore discontinued. Similar venting procedures have never been suggested for reactors other than sodium cooled reactors. Molten salt reactors are unique in not accumulating cesium in the form of the volatile metal, which is released as a gas from metallic nuclear fuel elements and accumulated in partially leaking high pressure gas microbubbles in ceramic nuclear fuel elements. In molten salt reactors the cesium forms non-volatile cesium halide which has negligible vapour pressure at the temperatures involved. It is therefore possible to vent fission gas from molten salt reactors into the coolant without causing serious levels of contamination. This is particularly relevant for the molten salt reactor design described in GB 2508537 where the alternative is a relatively complex pipework arrangement to collect the gasses. The gasses released in this way still contain appreciable quantities of radioactive iodine but of short half life. The radioactive iodine will contaminate the coolant but will decay to harmless levels in a relatively short time period. However, inclusion of a sacrificial metal such as magnesium, zirconium, scandium, titanium, manganese, aluminium, vanadium, chromium and/or silver reduces the amount of volatile iodine to a lower level. There is thus a major advantage to combining the use of sacrificial metals as described above with a gas venting system for the fuel tubes. Suitable gas venting systems are described in the literature (ORNL-NSIC-37, Fission Product release and transport in liquid metal fast breeder reactors) and include “diving bell” apparatus, narrow or capillary tubing and gas permeable sinters located above level of the fuel salt. The gas can be vented into the gas space above the coolant salt or directly into the coolant salt where it will bubble to the surface. FIG. 2a to c shows examples of three methods to allow fission gas emission from fuel tubes. The method shown in 2a uses closure of the upper opening of the fuel tube 203a with a sintered metal plug 201a where the sinter pore size is adjusted to allow gasses to pass but not to allow liquids, either the fuel salt 202a or the coolant outside the fuel tube to pass. FIG. 2b shows a fuel tube 203b containing fuel salt 202b where the fuel tube is capped by a diving bell assembly 205b. The diving bell assembly 205b allows gas to pass from the fuel tube 203b to the coolant 207b via vents 206b in the wall of the fuel tube, but coolant 207b sucked into the diving bell assembly 205b cannot mix with the fuel salt 202b. FIG. 2c shows a fuel tube 203c vented directly to the gas space above the coolant 207c via a narrow tube or capillary tube 208c. |
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description | Preferred embodiments of an EUV photon generating source are described below. The system generally includes a preionizer for generating a pinch plasma symmetrically defined around a central axis, a power supply circuit connected to electrodes for creating an azimuthal magnetic field for rapidly collapsing the plasma to the central axis to produce an EUV beam output along the central axis. In a first embodiment, the system preferably further includes an ionizing unit preferably of corona type generating UV light for ionizing dust particles that tend to travel along with the beam. An electrostatic particle filter is provided for collecting the charged dust particles resulting in a cleaner beam path having many advantages. In a second embodiment, the system preferably further includes one or more, and preferably a set of, baffles for diffusing the effect of acoustic waves emanating from the pinch region such as the flow of gases and contaminant particulates traveling with the acoustic waves, as well as to prevent reflections back into the pinch region. In a third embodiment, the system preferably further includes a clipping aperture spaced a proximate distance from the pinch region to match the divergence of the beam and reduce the influence of reflections and acoustic waves along the beam path away from the pinch region beyond the aperture location. The aperture comprises a thermally stable material with relatively high thermal conductivity and relatively low coefficient of thermal expansion, and is positioned to maintain that thermal stability. The aperture preferably comprises Al2O3. In a fourth embodiment, the system generates a low energy prepulse which is applied to the electrodes just before the main electrical pulse. The prepulse creates more homogeneous conditions in the already preionized plasma preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse. In a fifth embodiment, the system includes a reflecting surface opposite a beam output side of the central axis for reflecting radiation in a direction of the beam output side and preferably configured for focusing or collimating the beam. The reflecting surface is preferably of EUV multilayer type. The reflecting surface may be flat or hyperbolically-shaped or otherwise curved to focus the reflected radiation. Referring now to FIG. 1, an EUV generating source is schematically illustrated in cross section in accord with a preferred embodiment. Many preferred components of the EUV source are described at U.S. Pat. No. 5,504,795 which is hereby incorporated by reference. The EUV source includes a pinch chamber 10 having a pinch region 12 defining a central axis 14 at the end of which is an EUV photon transmitting window 18. A dielectric liner 24 surrounds the pinch region 12. A gas supply inlet 20 and an outlet 22 controllably supply active and diluent gases to the pinch region 12. The outlet 22 is connected to a vacuum pump 23. Other gas supply systems are possible such as may be borrowed and/or modified from excimer laser technology (see U.S. Pat. Nos. 4,977,573 and 6,212,214, and U.S. patent applications Ser. Nos. 09/447,882 (now issued U.S. Pat. No. 6,490,307), Ser. No. 09/734,459 (now issued U.S. Pat. No. 6,389,052), Ser. No. 09/780,120 (abandoned) and Ser. No. 09/453,670 (now issued U.S. Pat. No. 6,466,599), which are each assigned to the same assignee as the present application, and U.S. Pat. Nos. 5,978,406 and 5,377,215, all of which are hereby incorporated by reference). The gas may be circulated and electrostatic and or cryogenic purification filters may be inserted into the gas loop (see U.S. Pat. Nos. 4,534,034, 5,136,605 and 5,430,752, which are hereby incorporated by reference). A heat exchanger may also be provided in the gas loop (see the ""670 application, mentioned above, and U.S. Pat. No. 5,763,930, which is hereby incorporated by reference). The gas mixture includes an x-ray emitting gas such as xenon, krypton, argon, neon, oxygen or lithium. The gas mixture also preferably includes a low atomic number diluent gas such as helium, hydrogen, deuterium, and possibly nitrogen. Preferably xenon and helium are used. A preionization electrode 26 is connected to a preionization unit 27 for preionizing the gas in the pinch region 12. Many preionization unit types are possible such as e-beam, conical pinch discharge and RF preionization (see the ""795 patent and C. Stallings, et al., Imploding Argon Plasma Experiments, Appl. Phys. Lett. 35 (7), Oct. 1, 1979, which is hereby incorporated by reference). Some known laser preionization systems may be modified to provide preionization for the EUV source, as well (see U.S. Pat. Nos. 5,247,535, 5,347,532 and U.S. patent applications Ser. Nos. 09/247,887 (issued U.S. Pat. No. 6,650,679), Ser. No. 09/692,265 ([pending]) and Ser. No. 09/532,276 (issued U.S. Pat. No. 6,456,643), which are assigned to the same assignee as the present application and are hereby incorporated by reference). The preionization unit 27 and electrode 26 preionizes the pinch plasma in a symmetrical shell around the central axis 14, as shown, prior to the application of the main pulse to the main electrodes 30 and 32. The preferred main electrodes 30, 32 are as shown in FIG. 1. The anode 30 and the cathode 32 are shown located at opposite ends of the pinch region 12. Many other anode-cathode configurations are possible (see U.S. Pat. Nos. 3,961,197, 5,763,930, 4,504,964 and 4,635,282, which are hereby incorporated by reference). A power supply circuit 36 including a voltage source 37, a switch 38 and capacitor 39 connected to electrodes 30, 32 generates electrical pulses that produce high electric fields in the pinch region which in turn create azimuthal magnetic fields causing the preionized plasma to rapidly collapse to the central axis 14 to produce an EUV beam output along the central axis 14. Many power supply circuits are possible (see U.S. Pat. No. 5,142,166 which is hereby incorporated by reference). The anode 30 and cathode 32 are separated by an insulator 40. A prepulse is preferably generated in accord with a preferred embodiment. The prepulse occurs just prior to the main pulse and after the plasma is substantially preionized by the preionization unit 27 and electrode 26. The prepulse is a relatively low energy discharge provided by the main electrodes 30, 32. The prepulse creates more homogeneous conditions in the already preionized plasma preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse. A prepulse circuit is described at Giordano et al., referred to and incorporated by reference, below, and may be modified to suit the EUV source of the preferred embodiment. In summary with respect to the first through fifth embodiments, an EUV photon source, e.g., a Z-pinch, HCT-pinch, capillary discharge, plasma focus, and/or laser produced plasma device, may include one or more advantageous features according to preferred embodiments herein. The EUV source may include a preionizer and multiple electrodes for generating a plasma symmetrically defined around a central axis, a power supply circuit connected to electrodes for generally creating an azimuthal magnetic field or an electric filed and/or discharge for energizing a plasma formed around the central axis which emits EUV radiation, to produce an EUV beam output. Among the advantageous features according to preferred embodiments are an ionizing unit preferably of corona type generating UV light ionizes contaminant particulates along the beam path and an electrostatic particle filter collects the charged particulates. Also, one or more, and preferably a set of, baffles may be used to diffuse the effect of acoustic waves emanating from the pinch region such as the flow of gases and contaminant particulates traveling with the acoustic waves, and to prevent reflections back into the plasma region. A clipping aperture may also be included formed of a thermally stable material such as a ceramic such as sapphire or alumina and spaced a proximate distance from the pinch region to match the divergence of the beam and reduce the influence of reflections of particulates and acoustic waves along the beam path. A low energy prepulse may also be applied to the electrodes just before the main electrical pulse creating more homogeneous conditions in the preionized plasma shell preventing electrode burnout at hotspots from arcing due to the high voltage, fast rise time of the main pulse. Many other configurations of the above (and below) elements of the preferred embodiments are possible. For this reason, in addition to that which is described and/or incorporated by reference above and below herein, the following are hereby incorporated by reference: Weinberg et al., A Small Scale Z-Pinch Device as an Intense Soft X-ray Source, Nuclear Instruments and Methods in Physics Research A242 (1986) 535-538; Hartmann, et al., Homogeneous Cylindrical Plasma Source for Short-Wavelength laser, Appl. Phys. Lett. 58 (23), 10 Jun. 1991; Shiloh et al., Z Pinch of a Gas Jet, Phys. Rev. Lett. 40 (8), 20 Feb. 1978; Edita Tejnil, et al., Options for at-wavelength inspection of patterned extreme ultraviolet lithography masks, SPIE Vol. 3873, Part of the 19th Annual Symposium on Photomask Technology (September 1993) Choi et al., Temporal Development of Hard and Soft X-ray Emission from a Gas-Puff Z Pinch, 2162 Rev. Sci. Instrum. 57 (8) August 1986; McGeoch, Appl. Optics, see above; Pearlman, et al., X-ray Lithography Using a Pulsed Plasma Source, 1190 J. Vac. Sci. Technol. 19 (4) November/December 1981; Matthews et al., Plasma Sources for X-ray Lithography, 136 SPIE Vol. 333 Submicron Lithography (1982); Mather, Formation of a High Density Deuterium Plasma Focus, Physics of Fluids, 8 (3) February 1965; Giordano et al. Magnetic Pulse Compressor for Prepulse Discharge in Spiker Sustainer Technique for XeCl Lasers, Rev. Sci. Instrum. 65 (8), August 1994; Bailey et al., Evaluation of the Gas Puff Z Pinch as an X-ray Lithography and Microscopy Source, Appl. Phys. Lett. 40(1), (Jan. 1, 1982); U.S. Pat. Nos. 3,150,483, 3,232,046, 3,279,176, 3,969,628, 4,143,275, 4,203,393, 4,364,342, 4,369,758, 4,507,588, 4,536,884, 4,538,291, 4,561,406, 4,618,971, 4,633,492, 4,752,946, 4,774,914, 4,837,794, 5,023,897, 5,175,755, 5,241,244, 5,442,910, 5,499,282, 5,502,356, 5,577,092, 5,637,962; as well as any additional sources referred to elsewhere herein. In addition to the above references and those cited elsewhere in the present application, the following are hereby incorporated by reference into this Detailed Description of the Preferred Embodiments, as disclosing alternative embodiments of elements or features of the preferred embodiments not otherwise set forth in detail above or below herein. A single one or a combination of two or more of these references may be consulted to obtain a variation of the preferred embodiments within the scope of the present invention: U.S. Pat. Nos. 3,961,197, 4,229,708, 4,264,375, 4,267,525, 4,336,506, 4,369,514, 4,388,720, 4,395,770, 4,494,043, 4,498,182, 4,504,964, 4,592,056, 4,635,282, 4,860,328, 4,872,189, 5,117,432, 5,177,774, 5,243,638, 5,327,475, 5,377,215, 5,499,282, 5,504,795, 5,736,930, 5,963,616, 6,031,241, 6,064,072, 6,084,198, and 6,172,324; U.S. patent applications Ser. Nos. 60/312,277 and 09/693,490 (issued U.S. Pat. No. 6,414,438), which are assigned to the same assignee as the present application; Gas Plasmas Yield X Rays for Lithography, Electronics, 40, (Jan. 27, 1982); Robert G. Jahn, Physics of Electric Propulsion, 257-325, McGraw-Hill (1968); C. Stallings, et al., Imploding Argon Plasma Experiments, Appl. Phys. Lett. 35(7), 524-526 (Oct. 1, 1979); W. T. Silfvast, et al., Laser Plasma Source Characterization for SXPL, OSA Proceedings on Soft X-Ray Projection Lithography, 1993, Vol. 18 (1993), Andrew M. Hawryluk and Richard H. Stulen, eds.; H. Mahr et al., use of Metastable Ions for a Soft X-Ray Laser, Optics Communications, Vol. 10, No. 3 (March 1974); Emission Spectra of core Excited Even-Parity 2P States of neutral Lithium, Phys. Rev. Lett., Vol. 44, No. 17 (28 Apr. 1980); S. A. Mani et al., Lithium-Ion Soft X-Ray Laser, J. Appl. Phys., Vol. 47, No. 7 (July 1976); W. Hartmann et al., Homogeneous Cylindrical Plasma Source for Short-Wavelength Laser, Appl. Phys. Lett., 58(23) (10 Jun. 1991); Yutaka Nagata, et al., Soft X-Ray Amplification o the Lyman-xcex1 Transition by Optical-Field-Induced Ionization, Phys. Rev. Lett., Vol. 71, No. 23 (6 Dec. 1993); James J. Rocca, et al., Study of the Soft X-Ray Emission From Carbon Ions in a Capillary Discharge, IEEE J. Quantum Electronics, Vol. 29, No. 1 (January 1993); Marlo C. Marconi, et al., Time-Resolved Extreme Ultraviolet Emission from a Highly Ionized Lithium Capillary Discharge. Appl. Phys. Lett., 54(22), (29 May 1989); and W. T. Silfvast, et al., Simple Metal-Vapor Recombination Lasers Using Segmented Plasma Excitation, Appl. Phys. Lett. 36(8), (15 Apr. 1980). Referring again to FIG. 1, between the pinch region 12 and the EUV transmitting window 18 are several advantageous features in accord with preferred embodiments. A clipping aperture 300 is spaced a proximate distance from the pinch region 12. The clipping aperture 300 may be formed as shown or may be offset at an angle such as is described at U.S. Pat. No. 5,161,238, which is assigned to the same assignee as the present application and is hereby incorporated by reference. That is, the aperture 300 may include walls that reflect clipped-out portions of the beam away from the beam path. Further measures may be taken to prevent the clipped-out portions from reflecting from other surfaces after being reflected away by the aperture 300 to disturb the beam, such as by providing a beam dump (not shown). The clipping aperture 300 comprises a material exhibiting a high thermal stability. That is, the clipping aperture preferably has a high thermal conductivity and a low coefficient of thermal expansion. The clipping aperture preferably comprises a ceramic material such as Al2O3, sapphire or alumina. The clipping aperture is positioned close to the pinch region, but not too close to the pinch region 12 that thermal effects degrade its performance. The clipping aperture 300 blocks acoustic waves and particulates traveling with the acoustic waves from following the beam on the remainder of its journey through the pinch chamber 10. The aperture 300 is further preferably configured to reflect and/or absorb the acoustic waves so that they do not reflect back into the pinch region 12. The size of the clipping aperture 300 is selected to match the divergence of the beam. The aperture 300 may also be water, oil or fan cooled, or otherwise thermally controlled as may be understood by those skilled in the art. A set of baffles 400 is preferably provided after the clipping aperture. The baffles 400 may be configured similar to those described at U.S. Pat. No. 5,027,366, which is hereby incorporated by reference, or otherwise as understood by those skilled in the art. The baffles 400 serve to diffuse the effect of acoustic waves emanating from the pinch region such as the flow of gases and contaminant particulates traveling with the acoustic waves, as well as to prevent reflections back into the pinch region. The baffles 400 preferably absorb such disturbances. An ionizing unit 500 is shown located after the baffles 400. The ionizing unit 500 may be located before the baffles 400 or between two sets of baffles 400. The ionizing unit preferably emits UV radiation. As such, the ionizing unit 500 is preferably corona type, such as corona wires or electrodes. Some corona designs are described at U.S. Pat. Nos. 4,718,072, 5,337,330 and 5,719,896, and U.S. patent applications Ser. Nos. 09/247,887 (issued U.S. Pat. No. 6,650,679), and Ser. No. 09/692,265, each application being assigned to the same assignee as the present application, and all of these parents and patent applications are hereby incorporated by reference. The UV light from the ionizer unit 500 ionizes dust particles that tend to travel along with the beam. An electrostatic particle filter 600a, 600b is provided for collecting the charged dust particles resulting in a cleaner beam path. Fewer of these contaminants are deposited on the window 18 and elsewhere in the chamber 14. Also, the ionizer, precipitator arrangement reduces reflections from the particulates by the EUV beam, as well as other disturbances to the beam. In accordance with preferred embodiments, the EUV source schematically illustrated at FIG. 1 and described above exhibits output emission characteristics advantageously suitable for industrial applications, and particularly having output emission characteristics more suitable for photolithographic, mask writing and mask and wafer inspection applications. The clipping aperture 300 and/or set of baffles 400 reduce the influence of acoustic waves emanating from the pinch region 12. The clipping aperture 300 also matches and/or defines the divergence of the beam. The prepulse generated prior to the main pulse serves to homogenize the plasma shell to reduce the probability that arcing will degrade the pinch symmetry and the resulting EUV beam and that hotspots due to the arcing will deteriorate the electrodes 30, 32. The ionizer 500 and precipitator 600a, 600b serve to remove particulates from the beam path preventing adverse effects on the beam and components such as the beam exit window 18 of the chamber 10 where the particulates may become otherwise deposited. FIGS. 2-5 schematically illustrate EUV generating sources corresponding to four general techniques, i.e., Z-pinch, HCT-pinch (hollow cathode triggered pinch), capillary discharge (CD) and plasma focus or dense plasma focus. Although not specifically illustrated, other EUV sources may be used with features of the preferred embodiments such as laser produced plasma (LPP) sources. One or more features of the preferred embodiments described above and below herein may be advantageously included with any of these general techniques for generating EUV radiation. The systems specifically shown at each of FIGS. 2-5 include a reflecting surface opposite a beam output side of the central axis for reflecting the beam toward the output side of the central axis, and preferably also substantially focusing or collimating the beam. The reflecting surface is preferably of EUV multilayer type, and the reflecting surface may be flat, or preferably may be hyperbolically-shaped or otherwise curved to either focus or collimate the reflected radiation. Any of the embodiments shown at FIGS. 2-5 may further or alternatively include any of the features described above with reference to FIG. 1 including the aperture 300, the baffles 400, the ionizer 500 and/or the precipitator 600a, 600b. Moreover, an advantageous EUV generating source in accordance with a preferred embodiment may include one of more features of the embodiment described above with reference to FIG. 1 in combination with the reflecting surface schematically shown at FIGS. 2-5. Also, any of the embodiments of FIGS. 2-5 may be combined with one or more features of the embodiment of FIG. 1 either with or without also including the reflecting surface, although EUV sources including any of the advantageous reflecting surfaces of FIGS. 2-5 are preferred. FIG. 2 schematically illustrates an EUV generating source, and particularly a Z-pinch device, including a reflecting surface opposite a beam output side of the central axis according to a sixth embodiment. The EUV source schematically shown at FIG. 2 includes an anode 702 and a cathode 704 electrically separated by an insulator 706. The exemplary and illustrative Z-pinch device shown at FIG. 2 also includes a clipping aperture 708 for matching and/or defining a divergence for the EUV beam. The clipping aperture 708 may include one or more features of the aperture 300 of FIG. 1. Although not shown at FIG. 2, the Z-pinch device may also include any of baffles 400, ionizer 500 and precipitator 600a, 600b described with reference to the system shown at FIG. 1, e.g., after the clipping aperture 708, 300 along the EUV beam path. The EUV source of FIG. 2 further includes an EUV mirror 710 or EUV reflecting surface 710. In operation, the Z-pinch EUV source of FIG. 2 rapidly generates a dense plasma 712, e.g., when several kilovolts and several kiloAmps are applied to the electrodes 702, 704. EUV radiation 714 emanates from the dense plasma 712 particularly in each of the two opposing, axial directions (i.e., to the left and to the right in FIG. 2). On the output side of the plasma 712 (i.e., the right in FIG. 2) is an opening defined in the anode 702 for allowing the radiation emanating from the plasma 712 and propagating to the right in FIG. 2 to escape the Z-pinch chamber. The clipping aperture 714 is preferably configured in size, and perhaps shape, in one- and preferably two-dimensions, to match a preferred dimension, profile and/or divergence of the EUV beam. The EUV mirror 710 reflects the radiation 716 emanating from the plasma 712 and initially propagating away from the output side of the Z-pinch chamber. The EUV radiation 716 is redirected to propagate toward the output side of the chamber so that the radiation 716 may be applied to an industrial application along with the original EUV radiation 714. The mirror 710 may be flat, elliptical, concave spherical, cylindrical, aspherical, conical or otherwise curved to focus the beam if desired, while the mirror 710 is preferably hyperbolic when an advantageously collimated beam is desired, as illustrated at FIG. 2. Details of this preferred mirror 710 is described in more detail below following general descriptions of the embodiments of FIGS. 3-5. FIG. 3 schematically illustrates an EUV generating source, and particularly a hollow cathode triggered (HCT) pinch device, including a reflecting surface opposite a beam output side of the central axis according to a seventh embodiment. The exemplary and illustrative HCT-pinch EUV source schematically shown at FIG. 3 includes an anode 722 and a hollow cathode 724 electrically separated by an insulator 726. Although not shown at FIG. 3, the HCT-pinch device may also include any of clipping aperture 300, baffles 400, ionizer 500 and precipitator 600a, 600b described with reference to FIG. 1. The EUV source of FIG. 3 further includes an EUV mirror 730 or EUV reflecting surface 730. In operation, the HCT-pinch EUV source of FIG. 3 rapidly generates a dense plasma 732, when a potential difference is applied to the electrodes 722, 724. EUV radiation 714 emanates from the dense plasma 732 particularly in each of the two opposing, axial directions (i.e., to the top and to the bottom of the page in FIG. 3). On the output side of the plasma 732 (i.e., at the top of the device of FIG. 2) is an opening for allowing the EUV radiation 734 emanating from the plasma 732 and propagating upward in FIG. 3 to escape the HCT-pinch device. The EUV mirror 730 reflects the radiation emanating from the plasma 732 and initially propagating away from the output side of the HCT-pinch device. This additional radiation 736 is redirected by the mirror 730 to propagate toward the output side of the chamber. This additional EUV radiation 736 may be applied to an industrial application along with the original EUV radiation 734. As with the mirror 710 of the Z-pinch embodiment of FIG. 2, the mirror 730 may be flat, elliptical, concave spherical, cylindrical, aspherical, conical or otherwise curved to focus the beam if desired, while the mirror 730 is preferably hyperbolic when an advantageously collimated beam is desired. FIG. 4 schematically illustrates an EUV generating source, and particularly a capillary discharge (CD) device, including a reflecting surface opposite a beam output side of the central axis according to a eighth embodiment. The exemplary and illustrative capillary discharge EUV source schematically shown at FIG. 4 includes an anode 742 and a cathode 744 electrically separated by an insulator 746 including a capillary 747 within which a plasma 752 is created. The capillary discharge device shown at FIG. 4 also includes a clipping aperture 748 for matching and/or defining a divergence for the EUV beam. The clipping aperture 748 may include one or more features of the aperture 300 of FIG. 1 and/or the aperture 708 of FIG. 2. The gases used to form the plasma 752 of the device of FIG. 4, as well as for the devices of FIGS. 1 and 3-5, or another device in accordance with a preferred embodiment, may be supplied through gas supply 758, as shown, or otherwise as understood by those skilled in the art. Although not shown at FIG. 4, the Z-pinch device may also include any of baffles 400, ionizer 500 and precipitator 600a, 600b described with reference to the system shown at FIG. 1, e.g., after the clipping aperture 752, 708, 300 along the EUV beam path. The EUV source of FIG. 4 further includes an EUV mirror 750 or EUV reflecting surface 750. In operation, the capillary discharge EUV source of FIG. 4 rapidly generates a dense plasma 752 within the capillary 747, when a potential difference is applied to the electrodes 742, 744. EUV radiation 754 emanates from the dense plasma 752 particularly in each of the two opposing, axial directions (i.e., to the left and to the right in FIG. 4). On the output side of the plasma 752 (i.e., to the right of the device of FIG. 4) is an opening for allowing the EUV radiation 754 emanating from the plasma 752 and propagating to the right in FIG. 4 to escape the capillary discharge device. The EUV mirror 750 reflects the radiation 756 emanating from the plasma 752 within the capillary 747 and initially propagating away from the output side of the capillary discharge device. This additional radiation 756 is redirected by the mirror 750 back through the capillary 747 to propagate toward the output side of the chamber. This additional EUV radiation 756 may be applied to an industrial application along with the original EUV radiation 754. As with the mirror 710 of the Z-pinch embodiment of FIG. 2 and the mirror 730 of the HCT-pinch device of FIG. 3, the mirror 750 may be flat, elliptical, concave spherical, cylindrical, aspherical, conical or otherwise curved to focus the beam if desired, while the mirror 750 is preferably hyperbolic when an advantageously collimated beam is desired. FIG. 5 schematically illustrates an EUV generating source, and particularly a plasma focus source, including a reflecting surface opposite a beam output side of the central axis according to a ninth embodiment. The exemplary and illustrative plasma focus EUV source schematically shown at FIG. 5 includes an inner electrode 762 and an outer electrode 764 electrically separated by an insulator 766. Although not shown, the plasma focus device of FIG. 5 may also include a clipping aperture for matching and/or defining a divergence for the EUV beam, similar to the aperture 300, 708 or 748 of FIG. 1, 2 or 4 described above. Although also not shown at FIG. 5, the plasma focus device may also include any of baffles 400, ionizer 500 and precipitator 600a, 600b, described with reference to the system shown at FIG. 1, along the EUV beam path to the right in FIG. 5. The EUV source of FIG. 5 further includes an EUV mirror 770 or EUV reflecting surface 770. In operation, the capillary discharge EUV source of FIG. 5 rapidly generates a dense plasma 772 when a potential difference is applied to the electrodes 762, 764. EUV radiation 774 emanates from the dense plasma 772 particularly in each of the two opposing, axial directions (i.e., to the left and to the right in FIG. 5). On the output side of the plasma 772 (i.e., to the right of the device of FIG. 5) is an opening for allowing the EUV radiation 774 emanating from the plasma 772 and propagating to the right in FIG. 5 to escape the plasma focus device. The EUV mirror 770 reflects the radiation 776 emanating from the plasma 772 and initially propagating away from the output side of the plasma focus device. This additional radiation 776 is redirected by the mirror 770 to propagate toward the output side of the chamber. This additional EUV radiation 776 may be applied to an industrial application along with the original EUV radiation 774. As with the mirror 710 of the Z-pinch embodiment of FIG. 2 and the mirror 730 of the HCT-pinch device of FIG. 3 and the mirror 750 of the capillary discharge device of FIG. 4, the mirror 770 may be flat, elliptical, concave spherical, cylindrical, aspherical, conical or otherwise curved to focus the beam if desired, while the mirror 770 is preferably hyperbolic when an advantageously collimated beam is desired. As briefly described above and as illustrated at each of FIGS. 2-5, an EUV reflective multi-layer mirror is preferably used with any of the preferred embodiments including the exemplary device illustrated at FIG. 1. The EUV multi-layer mirror increases the usable angle in gas discharge based photon sources such as Z-pinch, HCT-pinch, capillary discharge and plasma focus, as well as for laser produced plasma (LPP) sources. The EUV mirror can be flat or of curved shape with collimating and/or imaging properties. The output power of the EUV generating source is advantageously increased by using the preferred EUV mirror, while substantially all other parameters of the system may be left unaltered. In order to raise the output power of a gas discharge-based EUV photon source, the electrical power would typically be increased. Under the same discharge conditions, this can lead to higher power in the electrode system correlated with higher temperatures. A device according to the preferred embodiment including the advantageous mirror has increased output power (compared with a same system except without the mirror), while substantially all other parameters of the system may be left unaltered. Gas discharge based photon sources generate a hot, dense plasma, which emits radiation into a solid angle of 4xcfx80 steradians (sr). Absent the advantageous mirror 710, 730, 750, 770 (hereinafter only xe2x80x9c710xe2x80x9d will be referenced, although what follows is intended to describe any of the mirrors 710, 730, 750, 770) of the preferred embodiments, radiation emitted in any direction other than that which includes the open solid angle of the electrode system and/or that is further defined by an aperture 300, 708, 748 (hereinafter only xe2x80x9c300xe2x80x9d will be referenced, although what follows is intended to describe any of the apertures 300, 708, 748), and the distance of the opening or the aperture 300 to the plasma, would be absorbed within the source and would not be included in the output radiation beam. The preferred mirror 710 reflects some of this radiation and guides it through the accessible opening and/or aperture 300. The mirror 710 is configured to reflect EUV radiation around 11 nm to 15 nm, such as 13.4 nm or 11.5 nm, and is therefore preferably an EUV multilayer mirror, e.g., including layers and/or bilayers of molybdenum (Mo)-, silicon (Si)- and/or beryllium (Be)-containing species, or other layers as understood by those skilled in the art for providing substantial reflection of the EUV radiation, and preferably particularly adapted to the wavelength of the radiation and the angle of incidence. This angle can vary laterally on the surface of the mirror and thus gradient multilayers are preferred. In each of the above-described EUV sources, the plasma is typically formed into the shape of a small column (e.g., 0.5 mm to 3.0 mm wide). The optical thickness along the central axis for the emitted radiation is high. The reflected radiation does not pass through the plasma itself, because the plasma is opaque to the EUV radiation. The shape of the preferred mirror 710 is therefore preferably adapted so that a substantial amount of the reflected radiation gets passed the plasma and continues within the acceptance angle of the system that is defined by the opening and/or aperture 300. The preferred mirror 710 is also adapted to the emission characteristics of the source, which as mentioned, can tend to be weighted along the central axis in each direction. The imaging, focusing and/or collimating properties of the preferred mirror 710 are such that a large proportion of the reflected radiation is both guided around the plasma column and through the opening and/or aperture 300 of the EUV system. Among many choices of contour, a flat mirror 710 will improve the output power of the source only slightly, but may be useful in conjunction with another mirror on one or more sides of the plasma column and/or when the plasma is significantly blocking the beam path to the opening and/or aperture 300, with the advantage of ease of manufacture. An elliptical or spherical mirror with adapted focal length may be used to focus the radiation in front of or just passed the output opening and/or aperture 300, and can be advantageous for application processing proximate to the EUV source and/or using additional imaging or beam shaping optics, e.g., a reflective imaging system for photolithographic reduction. A hyperbolically-shaped mirror may be used to generate almost parallel radiation or a collimated beam, such as when it is desired that the beam travel a significant distance prior to being re-directed or shaped with additional EUV optics or for direct application to a workpiece, or when a performance of an imaging system can be enhanced by using collimated input radiation and/or when collimated radiation produces the highest beam transport efficiency (note that the beam path may be preferably enclosed and the atmosphere prepared to be free of contaminants and/or photoabsorbing species of the EUV radiation, e.g., by evacuation and/or purging with inert gas; see U.S. Pat. Nos. 6,327,290, 6,219,368, 6,345,065, 6,219,368, 5,559,584, 5,221,823, 5,763,855, 5,811,753 and 4,616,908, and U.S. patent applications Ser. No. 09/598,552 (issued U.S. Pat. No. 6,442,182), Ser. No. 09/712,877 (issued U.S. Pat. No. 6,529,533), 09/727,600 (issued U.S. Pat. No. 6,495,795) and Ser. No. 09/131,580 (issued U.S. Pat. No. 6,399,916), which applications are assigned to the same assignee as the present application, and all of these patents and patent applications are hereby incorporated by reference). One can generally use this degree of freedom of changing the mirror shape, contour, degree of curvature, etc., to adapt the emission properties of the EUV source to the optical system of the application. Estimates of the improvement of the output powers of the EUV sources, described above with reference to FIGS. 2-5, due to the presence of the mirror 710, 730, 750, 770 can be deduced by considering the geometries of the electrode systems (see Table A below). The solid angles of the emitted radiation depend on the electrode geometries. I0 is the intensity emitted isotropically by the plasma into a solid angle of 4xcfx80 sr. The output is calculated out of these two values. The estimated mirror acceptance angle is the upper value, limited by the electrode systems. The reflectivity of the mirrors is set to 70%, close to the best current demonstrated values for normal incidence radiation. The increase of output power is calculated by multiplication of the solid angles of the mirrors 710, 730,750, 770 and their reflectivity. The xe2x80x9cimprovementxe2x80x9d value is the quotient of the increase of output and the initial output of each source. As shown in Table A, the highest increase of the output power due to the presence of mirrors 710, 730 is expected for the Z-pinch and HCT-pinch geometries, and is 230% and 70%, respectively. The usable angles of capillary discharges and plasma focus devices initially are very high such that the expected improvement due to the presence of the mirrors 750, 770 is smaller in relation to the output power. However, the collimating or focusing property of the mirrors 750, 770 can yield greater improvement in the quality of the output beam for the capillary discharge and plasma focus systems than appears from these calculations (and the same may be true for the Z-pinch and HCT-pinch devices). The preferred mirrors 710, 730, 750, 770 become treated by heat and ion bombardment from the plasma. These can tend to shorten the lifetimes of the mirrors 710, 730, 750, 770. Therefore, special heat resistant kinds of multilayer systems are preferred for use with the EUV sources described herein. In particular, preferred mirrors 710, 730, 750, 770 may be formed from combinations of Mo2Cxe2x80x94Si or Moxe2x80x94Sixe2x80x94Mo2C, or other such structures that may be understood and/or later achieved by those skilled in the art as being particularly heat and/or other damage resistant and having a long lifetime, while still providing substantial reflectivity (e.g., 50% or more, and preferably 70% or more). Those skilled in the art will appreciate that the just-disclosed preferred embodiments are subject to numerous adaptations and modifications without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope and spirit of the invention, the invention may be practiced other than as specifically described above. The invention is therefore not limited by any of the description of the preferred embodiments, and is instead defined by the language of the appended claims, and structural and functional equivalents thereof. In addition, in the method claims that follow, the steps have been ordered in selected typographical sequences. However, the sequences have been selected and so ordered for typographical convenience and are not intended to imply any particular order for performing the steps, except for those claims wherein a particular ordering of steps is expressly set forth or understood by one of ordinary skill in the art as being necessary. |
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abstract | The present disclosure relates to a method and to an irradiation system for irradiating a moving target volume with an ion beam, in particular for tumor therapy, wherein ion radiography measurements of the target volume are performed and the irradiation for deposition purposes and for radiography purposes is performed with the same ion beam but consecutively in time by alternating the energy of the ion beam between a higher radiography energy and a lower deposition energy using, for example, a passive energy modulator proximal with respect to the patient. |
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056334230 | claims | 1. A process for decontamination of radioactive liquid effluents, comprising the steps of placing a consumable anode and a cathode in the liquid effluent in a reactor, bringing the pH of the effluent to a value equal to or above 1, and establishing a direct current between the electrodes while maintaining the potential of the anode at a value equal to or above 2 V/NHE until the consumed electricity quantity is equal to or above 8 coulombs/milliliter, wherein said consumable anode is constituted by a metal alloy comprising between 20 and 70 wt. % iron, between 20 and 40 wt. % cobalt and between 5 and 30 wt. % aluminum, the total sum of the weight percentages of these three elements being equal to or below 100. 2. A process according to claim 1, wherein the step of establishing a direct current between the electrodes includes maintaining the potential of the anode at substantially 5.0 V/NHE. 3. A process according to claim 1 or 2, including the further steps of extracting the sludge formed in the reactor, reinjecting into said reactor a part of the extracted sludge, and separating the remaining part of the extracted sludge by solid/liquid separation. 4. A process according to claim 1 or 2, wherein said consumable anode also comprises less than 20 wt. % nickel. 5. A process according to claim 1 or 2, wherein consumable anode also comprises less than 10 wt. % titanium. 6. A process according to claim 1 or 2, wherein said consumable anode also comprises less than 5 wt. % copper. 7. A process according to claim 1 or 2, wherein said consumable anode also comprises less than 5 wt. % niobium. 8. A process for decontamination of radioactive liquid effluents, containing antimony, or ruthenium, or strontium, or cesium or actinides, comprising the steps of placing a consumable anode and a cathode in the liquid effluent in a reactor, bringing the pH of the effluent to a value equal to or above 1, and establishing a direct current between the electrodes while maintaining the potential of the anode at a value equal to or above 2 V/NHE, wherein said consumable anode is constituted by a metal alloy comprising between 20 and 70 wt. % iron, between 20 and 40 wt. % cobalt and between 5 and 30 wt. % aluminum, the total sum of the weight percentages of these three elements being equal to or below 100. 9. A process according to claim 8, wherein the step of establishing a direct current between the electrodes includes maintaining the potential of the anode at substantially 5.0 V/NHE. 10. A process according to claim 8 or 9, wherein the step of establishing a direct current between the electrodes includes maintaining the current until the consumed electricity quantity is equal to or above 8 coulombs/milliliter. 11. A process according to claim 8 or 9, including the further steps of extracting the sludge formed in the reactor, reinjecting into said reactor a part of the extracted sludge, and separating the remaining part of the extracted sludge by solid/liquid separation. 12. A process according to claim 8 or 9, wherein said consumable anode also comprises less than 20 wt. % nickel. 13. A process according to claim 8 or 9, wherein consumable anode also comprises less than 10 wt. % titanium. 14. A process according to claim 8 or 9, wherein said consumable anode also comprises less than 5 wt. % copper. 15. A process according to claim 8 or 9, wherein said consumable anode also comprises less than 5 wt. % niobium. |
055301746 | summary | BACKGROUND OF THE INVENTION The present invention relates to a method of vitrifying a high-level radioactive liquid waste generated in the step of reprocessing spent nuclear fuels. More particularly, the present invention is concerned with a vitrification method by which a vitrified waste having a high waste content can be obtained. A high-level radioactive liquid waste (hereinafter referred to simply as "high-level liquid waste",) is generated in the step of separating U and Pu by reprocessing spent nuclear fuels generated in nuclear power stations. This high-level liquid waste contains various components such as fission products contained in spent nuclear fuels in the form of a solution in nitric acid or a precipitate in a nitric acid medium without being dissolved. Further, the high-level liquid waste contains Na added as a reagent in the reprocessing step and also Fe, Cr and Ni which are corrosion products. Such a high-level liquid waste is mixed with a raw glass material consisting mainly of SiO.sub.2 and B.sub.2 O.sub.3 in a glass melting furnace at high temperatures and melt-solidified into a vitrified waste. In this process, the nitrate component in the high-level liquid waste is removed in the form of steam and NO.sub.x while the fission products are homogeneously mixed with the raw glass material and vitrified. The resultant vitrified waste is stored for cooling for 30 to 50 years and thereafter disposed of in a stratum more than hundreds of meters deep underground. Table 1 gives some examples of the chemical compositions of raw glass materials conventionally employed in the vitrification of a high-level liquid waste by Power Reactor and Nuclear Fuel Development Corporation (Doryokuro Kakunenryo Kaihatsu Jigyodan) who is the assignee of the present invention. TABLE 1 ______________________________________ Examples of chemical compositions of conventional raw glass materials [unit: wt. %] Designation of raw glass material compsn. component PF500 PF606 PF798 ______________________________________ SiO.sub.2 61.83 68.52 62.30 B.sub.2 O.sub.3 20.18 19.60 19.00 Al.sub.2 O.sub.3 5.04 3.50 6.70 CaO 2.88 1.39 4.00 ZnO 2.88 1.39 4.00 Li.sub.2 O 4.32 2.80 4.00 miscellaneous 2.88 2.79 0.00 component ratio B.sub.2 O.sub.3 /SiO.sub.2 0.33 0.29 0.31 ZnO/Li.sub.2 O 0.67 0.50 1 Al.sub.2 O.sub.3 /Li.sub.2 O 1.17 1.25 1.68 ______________________________________ In the conventional vitrification, the waste such as fission products and the raw glass material are mixed generally in proportions of about 25% (on the basis of oxide weight, the same shall apply hereinafter) of the waste and about 75% of the raw glass material. That is, the raw glass material is contained in the vitrified waste in an amount about thrice greater than that of the waste components such as fission products to be primarily vitrified. This is because, when the waste content is increased while lowering the proportion of the raw glass material, the phenomenon called phase separation occurs such that a water-soluble separated phase composed mainly of Mo which is known as "yellow phase", is separated in the vitrified waste, thereby gravely deteriorating the nuclide confinement performance of the vitrified waste. Further, the fission products contained in the waste generate heat in accordance with their decay, so that an increase in the waste content of the vitrified waste raises the temperature of the central part of the vitrified waste to thereby change the properties of the vitrified waste. This is also the reason for the incapability of increasing the waste content of the vitrified waste. For highly reducing the volume of the vitrified waste, it is desired to develop a method of vitrifying a high-level liquid waste in which, even if the waste content of the vitrified waste is increased over the conventional level of about 25%, the same leaching rate as that of the conventional vitrified waste is ensured without suffering from the yellow phase separation. |
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description | The present application is a U.S. national stage application under 35 U.S.C. §371 of PCT Application No. PCT/US2013/036592, filed on Apr. 15, 2013, which claims the benefit of U.S. Provisional Patent Application No. 61/624,066 filed Apr. 13, 2012, the entireties of which are incorporated herein by reference. The present invention relates container systems for holding radioactive waste, and more particularly to a waste canister that eliminates the need for a thick top lid on such containers. The thick top lid is one of the most expensive components of a radioactive waste canister. Such canisters may be used to store and transport non-fuel radioactive waste from nuclear generation plants such as activated reactor internals, control components, sundry non-fissile materials, and waste from operations such as resins, and in some applications vitrified nuclear waste fuel (“glass logs”) encased in an outer metal cylinder. On existing canisters, the thick top lid is needed to shield personnel from radiation who are working on the lid (e.g. welding, bolting, fluid operations, etc.). The lid must also be thicker because the lid further performs the main canister lifting connection, and therefore must have the thickness needed for structural reasons to support the weight of the entire canister when hoisted via a crane or similar equipment used to move the canister. For these reasons, the thick top lid of a waste canister adds considerably to the overall weight and expense of the canister. An improved radioactive waste canister is desired. The present invention provides an improved radioactive waste canister system that overcomes the deficiencies of existing thick canister top lids. An embodiment of a canister system according to the present disclosure uses a thinner top-closure main confinement lid and a supplemental shielded lifting lid that combines the shielding and lifting functions into one component. In one embodiment, the confinement lid is detachably mounted to the underside of the lifting lid to form a two-part lid assembly. The confinement lid just performs the function of containment for radionuclides rather than also having a structural lifting role, thereby allowing the main closure confinement lid to be thinner in construction. The confinement lid is intended to remain in place on the canister after being loaded with radioactive waste and closed. The lifting lid is intended for temporary use for operator shielding during closure of the canister with confinement lid and for lifting. Advantageously, the two-pan lid system disclosed herein reduces the overall cost and weight of the final closed canister. The canisters described herein are configured and dimensioned to be portable and transported by equipment suited for such applications, as opposed to permanently located spent nuclear fuel containment facilities. In one embodiment, canister lifting may be performed by a set of lifting bolts. The lifting bolts extend through the shielded lifting lid and main confinement lid into threaded lifting blocks that are attached to the canister body such as by welding. In use, the two-part lid system is typically used for temporary radioactive waste material storage and transport of the waste canister to a more remote location. Thereafter, the lifting lid is then removed remotely and an overpack lid is installed over the confinement lid to provide the necessary shielding of the canister for longer-term storage. Accordingly, the shielded lifting lid may advantageously be reused and can therefore be thicker than a traditional canister top lid as it is not dedicated for use with a single waste canister. Furthermore, the lifting lid may also be larger in diameter to cover the annulus space inside the top of the waste canister. According to one embodiment of the present invention, a radioactive waste container system includes a canister having an interior chamber for holding radioactive waste and an open top, and a lid assembly comprising a confinement lid and a shielded lifting lid. The confinement lid is detachably mounted to the lifting lid. The confinement lid is configured for mounting on the canister and has a first thickness. The lifting lid includes a lifting attachment and has a second thickness. The confinement lid is independently mountable on canister from the lifting lid. According to another embodiment of the present invention, a radioactive waste container system includes a canister having an interior chamber for holding radioactive waste and an open top, and a lid assembly comprising a lower confinement lid and an upper shielded lifting lid; the confinement lid being detachably bolted to the lifting lid. The lifting lid includes a plurality of first bolt holes having a first diameter and a plurality of second bolt holes having a second diameter, the first diameter being larger than the second diameter. The confinement lid includes a plurality of third bolt holes having a third diameter, wherein each of the third bolt holes is concentrically aligned with one of the first or second bolt holes of the lifting lid. A plurality of first mounting bolts is inserted through the first bolt holes and threadably attaches the confinement lid to the canister without engaging the lifting lid. An exemplary method for storing radioactive waste using a container system is provided. The method includes the steps of: detachably mounting a confinement lid to a shielded lifting lid, the confinement lid and shielded lifting lid collectively forming a lid assembly; placing a canister having an interior chamber for holding radioactive waste into an outer protective overpack; lifting the lid assembly using the lifting lid; placing the lid assembly on an open top of the canister; attaching the confinement lid to the canister using a first set of mounting bolts without threadably engaging the lifting lid with the bolts; detaching the lifting lid from the confinement lid; and removing the lifting lid from the canister. All drawings are schematic and not necessarily to scale. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”. “above,” “below.” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally.” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. The present invention provides a separate, reusable shielded lifting lid for waste canister lid bolting and lifting. Accordingly, the lifting lid is bolted and not welded to the canister. The canister loading is dry in an overpack such as a metal cylindrical jacket holding the radioactive waste inside. Canisters typically have thick (e.g. 10 inch) steel lids on each canister to protect the operator from radiation during canister closure operations. The thick lids are heavy and expensive, and further not reusable as they remain attached to the canister for longer-term storage. Advantageously, the present invention allows use of a significantly thinner main closure confinement lid (e.g. about 3 to 5-inch thick in exemplary embodiments) for radionuclides containment. After radioactive waste contents are placed in the canister, the confinement lid is installed and held in place by gravity alone in some embodiments. The confinement lid thickness, however, has generally poor radiation shielding value. Accordingly, the confinement lid is installed using a thicker and reusable shielded lifting lid which serves as an upper over-lid to the lower confinement lid. The two-pan lid system combination of the confinement lid and shielded lifting lid provide the thickness required to shield the operator from the radioactive canister contents during the canister closure bolting operations. In use, the shielded lifting lid in one exemplary and non-limiting embodiment has holes that match the bolt spacing to allow the operator to install the confinement lid bolts in a radiation shielded environment. After the lifting lid bolts are installed, the operator hooks up the lifting rigging to the shielded lifting lid and moves away from the canister to a more distal and remote location. The shielded lifting lid may then be removed from the top of the canister, preferably with the confinement lid remaining in place, and a heavy overpack lid is installed for longer term storage and radiation shielding. Using this method, the waste canister and overpack advantageously are shorter, lighter, better shielded, and less expensive to fabricate. FIGS. 1 and 2 depict a radioactive canister system according to the present disclosure including a waste canister 100 having a generally cylindrical body defining an interior chamber 101 and comprised of a top 102, bottom 104, and cylindrical sidewall 106 extending therebetween. Top 102 is open for insertion of radioactive waste and bottom 104 is preferably closed in one embodiment. A main closure confinement lid 200 is shown attached to top 102 of canister 100 by a plurality of fasteners such as mounting bolts 154 which may be circumferentially spaced apart around the top of the canister, as further described herein. In one embodiment, canister 100 may be a non-fuel radioactive waste canister (NWC). Referring to FIG. 2, canister 100 has an interior configured to store the size and shape of radioactive waste to be deposited in the canister. In one embodiment, the canister may include a basket insert 120 configured for holding a plurality of metal waste cylinders 121 (see, e.g. FIG. 6) each containing radioactive waste materials. Basket insert 120 includes a pair of vertically spaced apart top and bottom plates 122, 124 which are connected via a plurality of tie rods 126. Top plate 122 and bottom plate 124 include a plurality of horizontally spaced apart circular openings 123 each having a diameter which is configured and dimensioned to receive waste cylinders 121 therethrough, as shown in FIG. 6. Referring to FIGS. 2 and 3, the top portion of tie rods 126 may be threaded for attachment to top plate 122 by a threaded nut 125. Top plate 122 may be spaced by a vertical distance below the top 102 of canister 100. Bottom plate 124 may be elevated by a vertical distance above the bottom 104 of canister 100 by a plurality of vertical tubular sleeves 128 having a bottom end resting on bottom 104 of the canister 100 and a top end attached to bottom plate 124 as better shown in FIG. 4. In one embodiment, sleeves have an inside diameter sized to receive the bottom end portion of tie rods 126 which are slidably received in the sleeves. This provides for vertical adjustment in the height of the basket insert 120 to accommodate the height of waste cylinders 121 to be stored inside canister 100. Bottom plate 124 remains fixed and stationary in position. The top plate 122 with attached tie rods 126, however, is movable upwards and downwards with respect to the canister and bottom plate 124 to reach a desired position depending on the height of waste cylinders 121. In some embodiments, the top plate 122 may be thereafter be fixed in the desired position after vertical adjustments are made by securing the top plate to the interior of the canister sidewall 106 such as by welding or other suitable means. Accordingly, adjustable basket insert 120 may accommodate a variety of waste cylinder heights. Basket insert 120 (i.e. top plate, bottom plate, tie rods, etc.) may be made of any suitable material, including without limitation a corrosion resistant metal such as stainless steel in one embodiment. FIG. 5 shows canister 100 loaded into an outer overpack 130 for transport and storage of radioactive waste. The overpack provides protection during transport and storage of the waste by encapsulating the waste canister in an outer protective jacket. Overpack 130 has an open top 132, and is configured and dimensioned to completely receive canister 100 through the top 102. Overpack 130 has an open interior defining an interior surface 133 and an exterior surface 135 (see also FIG. 9). Overpack 130 is generally cylindrical in shape further including a cylindrical sidewall 134 and flat closed bottom 136 (see FIG. 15) configured for resting on a flat surface such as concrete slab. Preferably, in one embodiment, overpack 130 has a greater height than canister 100 so that the canister is recessed below the open top 132 of the overpack when fully inserted therein. Overpack 130 may be made of any suitable material or combination of materials (see, e.g. FIG. 9) which may include neutron absorbing materials such as without limitation concrete, lead, or boron. An example of a suitable overpack for use with canister 100 may be a HI-SAFE™ transport overpack as used in vertical non-fuel waste storage systems available from Holtec International of Marlton, N.J. The sidewalls 134 forming the spaced apart cylindrical walls that define an annular space between the inner and outer surfaces 133 and 135 respectively may be formed of a corrosion resistant metal also selected for strength to protect the inner canister 100, such as stainless steel as one non-limiting example. The neutron absorbing material may be disposed between the inner and outer surfaces 133 and 135. In some embodiments, overpack 130 may also include Metamic® for radiation shielding which is a discontinuously reinforced aluminum/boron carbide metal matrix composite material also available from Holtec International. Referring to FIGS. 2-3 and 5, the top of the canister 100 may include a peripheral contamination boundary seal which cooperates with the confinement lid 200 to prevent leakage of radiation from the canister, particularly at the lid bolting locations. In particular, the boundary seal shields the mounting blocks 150 to prevent radiation streaming. In one embodiment, the boundary seal may be configured as an annular shielding flange 140 that extends circumferentially around the upper peripheral edge of the top 102 of the canister. Confinement lid 200 rests on the shielding flange when bolted to the canister 100. Shielding flange 140 may be horizontally flat and extend inwards in a direction perpendicular to and from sidewall 106 towards the vertical axial centerline CL of the canister 100. In one embodiment, shielding flange 140 is attached to the uppermost top edge of the sidewall 106 as shown. Shielding flange 140 may have an at least partially scalloped configuration in top plan view in some embodiments as shown to accommodate insertion of waste cylinders 121 into the canister. According, the scallops 142 if provided are preferably concentrically aligned with the circular openings 123 in basket insert 120 in top plan view. This minimizes the required diameter of the canister 100 for holding the waste cylinders 121. In other possible embodiments, however, shielding flange 140 may have an uninterrupted shape forming a continuous ring in top plan view. At the lid bolting locations, shielding flange 140 is configured to cover a with a plurality of mounting blocks 150 which are circumferentially spaced around the interior of canister 100 disposed adjacent to sidewall 106 to provide a radiation-shielded bolting system for attaching confinement lid 200 and shielded lifting lid 300 to the canister. Shielding flange 140 may be formed of any suitable material including metals which are corrosion resistant such as stainless steel. With continuing reference to FIGS. 2-3 and 5, mounting blocks 150 may have a generally arcuate and curved shape in top plan view which complements the inside radius of curvature of the sidewall 106 to which mounting blocks 150 may be attached. Mounting blocks 150 may be rigidly/fixedly attached to the canister sidewall 106 by a suitably strong mechanical connection capable of supporting at least the entire dead weight of canister 100 and basket insert 120 for lifting and loading the canister into overpack 130. Accordingly, in one preferred embodiment, mounting blocks 150 are welded to at least sidewall 106 of the canister body for strength. In some embodiments, the mounting blocks 150 may be abutted against but are not fixedly connected to the underside of radiation shielding flange 140 so that lifting loads are not transferred to the flange directly but rather bypass the flange to the mounting blocks 150 via the bolting provided. Any suitable number of mounting blocks 150 may be provided; the number and circumferential spacing being dependent on the magnitude of the structural load imparted to the blocks dependent on whether the canister 100 will be lifted in an empty condition or in a fully loaded condition with filled waste cylinders 121 positioned in the canister. It is well within the ambit of those skilled in the art to determine an appropriate number and circumferential spacing of the mounting blocks 150. In one embodiment, the mounting blocks 150 are each configured for both lifting canister 100 and attaching both the lower confinement lid 200 and upper lifting lid 300. As best shown in FIGS. 3 and 9, mounting blocks 150 each include a plurality of threaded mounting sockets 152 for forming a threaded connection with complementary threaded mounting bolts 154 and 156 used for attaching confinement lid 200 and shielded lifting lid 300 respectively to the canister 100. In one non-limiting example, three threaded mounting sockets 152 may be provided in each mounting block. However, other suitable numbers of mounting sockets may be used. In certain embodiments, the mounting sockets 152 extend only partially into the mounting blocks 150 as shown. Radiation shielding flange 140 includes mating holes 144 which are each concentrically aligned with the threaded mounting sockets 152 of the mounting block to provide access for mounting bolts 154, 156 to the mounting sockets in the block. Because shielding flange 140 in some embodiments in not intended to be a load-bearing member relied upon for lifting the canister, holes 144 may not be threaded so that the weight of the canister is transferred through the flange via the mounting bolts 156 to the shielded lifting lid 300. In one embodiment, mounting bolts 154 and/or 156 may be threaded bolts having an integral or separate washer disposed adjacent to the head, as best shown in FIG. 11. Mounting bolts 154 are used for attaching the lower confinement lid 200 to canister 100 via mounting blocks 150. In one embodiment, mounting bolts 154 are not used for lifting the canister 100 but rather for lid securement. By contrast, mounting bolts 156 serve a dual purpose and may be used for both attaching the lower shielded lifting lid 300 to canister 100 and supporting the weight of the canister during lifting operations via mounting blocks 150 engaged by bolts 156. In one preferred embodiment, mounting bolts 156 may have a longer shank than mounting bolts 154 as shown. This arrangement ensures that the depth of threaded engagement between the threaded mounting sockets 152 of the mounting blocks 150 and mounting bolt 156 is sufficient for lifting the canister 100, as further explained herein. The confinement lid 200 is generally circular in shape (top plan view) and shown in FIGS. 1, 9, and 11. Confinement lid 200 includes a plurality of bolt holes 202 spaced circumferentially around the peripheral side 204 of the lid as best shown in FIG. 1 (including at locations where mounting bolts 154 are shown installed). Bolt holes 202 penetrate top surface 206 of the confinement lid, and in one embodiment are not threaded. The bolt holes 202 may be arranged in groups corresponding to the location and arrangement of the mounting blocks 150 inside the canister 100. The bolt holes 202 have a diameter sized to at least pass the shank of mounting bolts 154 and 156 through the holes to threadably engage the mounting blocks 150. Accordingly, some of the bolt holes 202 are configured to receive the shanks of the confinement lid mounting bolts 154 and others are configured to receive the shank of shielded lifting lid mounting bolts 156. In cases where the mounting bolts 154 and 156 have shanks of the same diameter, the bolt holes 202 may all have the same diameter. Where the shanks of bolts 154 and 156 are different in diameter, the holes 202 may have correspondingly different diameters for each bolt. The confinement lid 200 may have a uniform thickness from peripheral side 204 to peripheral side 204 as best shown in FIG. 9 in one embodiment. In other embodiments, the thickness may vary at different locations on the lid 200. Confinement lid 200 may be made of any suitable material, preferably an appropriate metal for the application. In an exemplary embodiment, without limitation, the confinement lid 200 for example may be made of stainless steel for corrosion resistance. The upper shielded lifting lid 300 is not intended to remain on canister 100 for longer term waste storage. Instead, in some embodiments, the lifting lid 300 is configured and structured for transporting and initially lifting the canister 100 into position in the cylindrical overpack 130 prior to loading the waste cylinders 121 after which the lifting lid is removed, and then after the waste cylinders are loaded in the canister, the lifting lid is replaced on the canister to shield the operator for bolting the lower confinement lid 200 in place after which the lifting lid is removed again. It will be appreciated that this scenario for using the shielded lifting lid 300 may be varied in other embodiments. Referring to FIGS. 7-12, shielded lifting lid 300 is generally circular in shape (top plan view) and includes a plurality of bolt holes 302 spaced circumferentially around the peripheral side 304 of the lid as best shown in FIG. 1. In one embodiment, holes 302 are not threaded. The bolt holes 302 may be arranged in clustered groups or sets corresponding to the location and arrangement of the mounting blocks 150 inside the canister 100. The bolt holes 302 have a diameter sized to at least pass the shank of mounting bolts 154 and 156 through the holes to threadably engage the mounting blocks 150. Accordingly, some of the bolt holes 302 are configured to receive the shanks of the confinement lid mounting bolts 154 and others are configured to receive the shank of shielded lifting lid mounting bolts 156. In cases where the mounting bolts 154 and 156 have shanks of the same diameter, the bolt holes 302 may all have the same diameter. Where the shanks of bolts 154 and 156 are different in diameter, the holes 302 may have correspondingly different diameters for each bolt. According to another aspect of the invention, bolt holes 302 have different diameters in one embodiment even if the mounting bolts 154, 156 are used have the same shank diameter. The confinement lid mounting bolts 154 need not engage the upper shielded lifting lid because bolts 154 are only required to secure the lower confinement lid to canister 100. Accordingly, in the embodiment shown in FIG. 11, the bolt holes 302 for the confinement lid mounting bolts 154 may have a larger diameter than the bolt holes 302 for the lifting lid mounting bolts 156. In this arrangement, the bolt holes 302 for the confinement lid mounting bolts 154 are sized with a diameter large enough to allow the shank and entire head of bolts 154 to pass through the bolt holes so that the head and integral washer directly engage the top surface 206 of the confinement lid 200 (see, e.g. FIG. 1). When completely installed, the heads of the mounting bolts 154 are recessed below the top surface of the lifting lid 300 as shown. By contrast, since the mounting bolts 156 for the lifting lid 300 also serve a lifting function for the canister 100, the bolt holes 302 have a diameter sized so that the heads of bolts 156 do not pass through the bolt holes and instead engage the top surface 306 of the lifting lid (thereby projecting above the top surface and remaining exposed as shown in FIG. 11). In this manner, the bolts 156 transfer the dead load and weight of the canister 100 from the mounting blocks 150 directly to the shielded lifting lid 300 without involvement of the confinement lid 200. Accordingly, to accommodate the foregoing arrangement, the lifting lid mounting bolts 156 preferably have a longer shank than the confinement lid mounting bolts 154 in this embodiment. As shown in FIGS. 9 and 10, several spaced apart clusters comprised of three bolt holes 302 may be provided in the non-limiting embodiment shown which are spaced circumferentially around and proximate to the peripheral side 304 of the shielded lifting lid 300. Each cluster of bolt holes 302 is spaced apart by an arcuate distance from adjacent clusters of holes 302. The clusters of bolts holes 302 are each vertically aligned with a corresponding mounting block 150 (see also FIG. 3). In this embodiment, the center hole 302 has a smaller diameter for the lifting lid mounting bolt 156 than the two adjacent outer holes 302 have larger diameters for the confinement lid mounting bolts 154. Other suitable arrangements of holes 302 may be provided. The bolt holes 202 in the confinement lid 200 may also arranged in clusters of three to mate with the bolt holes 302 of the lifting lid 300. All three of the bolt holes 202 in each cluster in the confinement lid, however, may have the same diameter. Advantageously, having two different size bolt holes 302 for the confinement lid mounting bolts 154 and the lifting lid mounting bolts 156 reduces possible installation error and ensures that the operator will not confuse which holes are intended for each. This plays a role in deploying the two-part lid system when the confinement lid 200 and its respective bolts 154 are eventually left in place after bolting the confinement lid to the canister 100 and the lifting lid mounting bolts 156 are removed by the operator, as further described herein. The shielded lifting lid 300 may have a non-uniform thickness from peripheral side 304 to peripheral side 304 as best shown in FIG. 9. Accordingly, in one possible embodiment as shown, the peripheral portion of lifting lid 300 may include an outer annular step or shoulder 308 having a smaller thickness than the inner central portion 314 of the lid. The shoulder 308 is configured to complement and abuttingly engage a corresponding top annular rim 138 of the overpack 130 such that portions of the lifting lid 300 adjacent to peripheral side 304 overlap the top of the rim to prevent radiation streaming as shown. Rim 138 therefore defines an annulus for receiving shoulder 308. Accordingly, as shown in FIG. 9, shielded lifting lid 300 has a larger diameter than confinement lid 200 to account for the overlap with the annular rim 138 of the overpack 130. The central portion 314 of the lifting lid 300 preferably has a thickness and a diameter sized to allow at least partial insertion of the central portion into the overpack 130 such that the outwards facing annular sides of the central portion abuts the interior surface 133 of the overpack as shown. This arrangement further prevents radiation streaming from the canister 100 when the lifting lid 300 is in place on the canister. Because shielded lifting lid 300 serves a structural purpose for lifting the canister 100, the lifting lid preferably has a thickness which is greater than the confinement lid 200. In one embodiment, the lifting lid has a thickness which is at least twice the thickness of the confinement lid. Shielded lifting lid 300 may be made of any suitable material, preferably an appropriate metal for the application. In exemplary embodiments, without limitation, the lifting lid 300 for example may be made of carbon steel or stainless steel. Referring to FIGS. 7 and 8, the lower confinement lid 200 is detachably mounted to upper shielded lifting lid 300 so that the lid assembly 200/300 may be lifted and moved as a single unit as shown with the lifting lid supporting the confinement lid when not attached to the canister 100. When needed during the canister closure operations, the lifting lid 300 may be uncoupled from the confinement lid 200. In one embodiment, a plurality of circumferentially spaced fasteners such as threaded assembly bolts 131 may be provided to attach lifting lid 300 to confinement lid 200. Assembly bolts 131 which are inserted through the lifting lid 300 and engage complementary threaded sockets 208 (shown in FIG. 1) formed in the confinement lid (such arrangement and operation being apparent to those skilled in the art without further elaboration). A suitable number of assembly bolts 131 are provided to support the lower confinement lid 200 from the upper shielded lifting lid 300 during hoisting. Accordingly, confinement lid 200 may be considered to be fully supported by the lifting lid 300 during lifting of the lid assembly 200/300. As shown in FIGS. 7 and 8, shielded lifting lid 300 includes a lifting attachment such as lifting lugs 402 and pin 404 for grappling and hoisting the lid. Other suitable lifting attachments configured for grappling such as for example lifting bails may be used. An exemplary method for storing radioactive waste using the present container system with two-part lid assembly 200/300 (confinement lid 200, lifting lid 300) according to the present disclosure will now be described. As a preliminary step, the lower confinement lid 200 is detachably mounted to the upper shielded lifting lid 300 using assembly bolts 131 to collectively form the lid assembly 200/300, shown in FIG. 7. Referring to FIGS. 1 and 2, the method begins with a canister 100 first being provided with an empty basket insert 120 disposed inside the canister as shown. Next, the empty canister 100 is lifted and placed into the overpack 130 as shown in FIG. 5. In one embodiment, this step may be performed by bolting the lid assembly 200/300 to canister 100 using the mounting bolts 156 to threadably engage the mounting blocks 150, and grappling and attaching a hoist 400 to the upper lifting lid 300 using lifting lugs 402 and pin 404 as shown in FIG. 7. The hoist 400 may be part of the lifting equipment such as a crane or other suitable equipment operable to raise and lower the canister. After positioning the basket insert 120 into the canister 100, the mounting bolts 156 may be removed to disconnect the canister from the lid assembly. The lid assembly 200/300 may then be lifted by the hoist and removed (see FIG. 5). Next, one or preferably more lid alignment pins 406 may be threaded into some of the threaded sockets 152 of the mounting block to eventually help properly align the lid assembly 200/300 with the canister (see FIG. 5). In one non-limiting example, three alignment pins 406 are used spaced apart on the canister. The alignment pins 406 are preferably installed locally by an operator prior to loading the radioactively “hot” waste cylinders 121 into the canister. Following installation of the alignment pins 406, the waste cylinders 121 are loaded into the canister 100, and more specifically positioned in their respective locations provided in basket insert 120 as shown in FIG. 6. Loading of the waste cylinders is performed remotely (i.e. at a distance) by an operator using suitable equipment to protect the operator from radiation. After loading the waste cylinders 121, the lid assembly 200/300 is remotely hoisted by the operator over and vertically positioned above the top 102 of the canister 100, as shown in FIG. 7. Using the lid alignment pins 406, the operator vertically aligns holes 302 in shielded lifting lid (with holes 202 in confinement lid being concentrically aligned with holes 302) with corresponding pins 406 to properly orient the lid rotationally with respect to the canister. When the pins 406 and their corresponding holes have been axially aligned, the operator lowers lid assembly 200/300 onto the canister 100 as shown in FIG. 8 (see pins 406 extending through holes 302). The operator will now be shielded from radiation emitted from the canister so that the confinement lid 200 may be bolted in place locally. Next, the lid alignment pins 406 and assembly bolts 131 which hold the lower confinement lid 200 to upper shielded lifting lid 300 may be removed (see, e.g. FIG. 10). All of the confinement lid mounting bolts 154 may then be installed to mount the confinement lid 200 to the canister 100 using the mounting blocks 150. The mounting bolts 154 are threaded through bolt holes 302 until the heads of the bolts engage the top surface 206 of the confinement lid 200 and the bolts are tightened to the required torque (see FIGS. 11 and 12). Prior to removing the shielded lifting lid 300, a set of overpack lid alignment pins 408 may next be installed in threaded sockets 510 of the overpack 130. With the confinement lid 200 now fully fastened to canister 100, the shielded lifting lid 300 may next be removed via the hoist remotely by an operator as shown in FIG. 15. In the following steps, the overpack lid 500 is installed on overpack 130 following closure of canister 100 described above. FIG. 15 shows the shielded lifting lid 300 being removed and the overpack lid 500 staged for installation. FIG. 13 shows overpack lid 500 in greater detail. Overpack lid 500 is circular in shape (top plan view) and includes a plurality of mounting holes 502, top surface 504, peripheral sides 506, and a lifting bail 508 attached towards the center of the lid for engagement by a hoist. Overpack lid 500 serves a structural role of protecting the canister 100 disposed inside the overpack 130, and in some embodiments supporting the weight of the overpack when mounted thereto for transport and lifting. Accordingly, overpack lid 500 may have a thickness greater than the thickness of the confinement lid 200. Referring now to FIGS. 15 and 16, the overpack lid 500 is grappled and lifted via the attached hoist 400 by crane or other equipment, vertically aligned with overpack 130 using the alignment pins 408 in a manner similar to alignment pins 406, and lowered onto the overpack. Alignment pins 408 are then removed and mounting bolts 512 are then installed in the threaded sockets 510 of the overpack 130 to complete installation and securement of the overpack lid 500, as shown in FIG. 17. Optionally, the lifting bail 508 may be removed. FIG. 18 shows the overpack 130 with overpack lid 500 fully installed and canister 100 disposed inside loaded with waste cylinders 121. Protective caps 514 may be installed over mounting bolts 512. An operator is shown in FIG. 18 to provide perspective on the size of overpack 130 in one non-limiting embodiment, which may be about 6 or more feet in diameter and about 6 or more feet in height. Any suitable size overpack may be used. As noted herein, the shielded lifting lid 300 is reusable. Accordingly, in some embodiments, the exemplary method described above may further comprise a step of detachably mounting a second different confinement lid 200 to the shielded lifting lid 300; the second confinement lid and shielded lifting lid collectively forming a second lid assembly. It will be appreciated that the two-part lid assembly 200/300 may also be used in applications where the confinement lid 200 is intended to be welded to the canister 100 for closure rather than by bolting. While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention. |
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052788792 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, there is shown a PWR-type fuel rod assembly 11, which comprises a plurality of fuel rods 12 mounted in a holder or skeleton 13 which comprises a top end member 14, a plurality of spacer grids 16, and a plurality of guide tubes 17 which extend along the approximately fourteen foot length of the fuel rod assembly 11. A BWR-type fuel rod assembly is similar to the PWR type, except that the BWR-type has water tubes and a spacer grid support tube in place of the guide tubes 17. The present invention is applicable to both the PWR-type and BWR-type fuel rod assemblies as well as any other fuel rod assembly having spacer grids 16. In essence, the present invention is directed to a novel apparatus and method for disposing of the spacer grids 16. As further illustrated in FIG. 1, the fuel rod assembly 11 is mounted in a rod assembly or cell holder 49 of generally rectangular cross-section. Member 14 is removed by cutting through the guide tubes 17. This permits removal of the rods from the fuel rod assembly 11. After the fuel rods from two or more fuel assemblies 11 are removed and packed in a fuel rod canister (not shown), various parts of the now empty skeleton, including the spacer grids, must be disposed of by chopping them up, compressing them, and depositing them in scrap canisters. FIG. 2 depicts the various elements of a rod consolidation system 20, a majority of the components of which remain below the water line 21 of the storage pool 22. At the top of the pool is a deck 23 adjacent thereto which has thereon the major control components of the rod consolidation system 20. These components can comprise a computer control cabinet 24 which controls a five or six axes commercially available robot 26 which, in turn, handles the long reach tools 42, 43 for the rod consolidation system 20 and the methods of rod consolidation. Many of the functions of the rod consolidation system 20 are performed by the robot 26 and its associated long reach tools under the control of the computer control cabinet 24. Adjacent to the computer control cabinet 24 is a monitoring station 27 which includes a closed circuit television monitor 28 for monitoring operations by means of a plurality of underwater television cameras 29. A protective wire cage 32 situated on the deck 23 protects both the operator and the equipment from any accidental contact with the robot 26. Attached to the free or distal end 33 of the arm of robot 26 is a shaft 34 having, at its lower or distal end 36 a quick change coupler 37. Quick change couplers are commercially available items, and any of a number of types of such couplers may be used. A bracket 38 mounted on a curb at the top of the pool 22 has mounted thereto first and second tool racks 39, 41 for holding a plurality of long reach tools 42, 43, each having at its top end, a quick change coupler 44, 46, respectively, which matches quick change coupler 37. Each of the tools 42, 43 is designed to perform a specific task, and when that task is to be performed, the robot 26 removes that tool 42, 43 from the rack 39, 41 by means of the coupling, causes the tool 42, 43 to perform the task, and returns the tool 42, 43 to the corresponding rack 41. This arrangement has the important advantage of enabling almost all of the steps of the consolidation process to be performed within the pool, without the necessity of active human intervention. Also mounted to the bracket 38 is a depending frame member 47 to which is mounted a work table 48, shown exploded in FIG. 2. Alternatively, the work table 48 can be supported by a header 54 and joined thereto by an appropriate connecting structure. Work table 48 has mounted in apertures therein four fuel rod assembly holders 49, two scrap canister holders 51, and two fuel rod canister holders 52, 53. Holders 49, 52, and 53 rest in apertures in a support base 54, which also functions as a manifold for a pair of vacuum filter assemblies 56, 57, each comprising a respective pump 58, 59 and a respective filtering element 61, 62. Alternatively, the system can be configured to comprise a pair of filter assemblies 56, 57 with only one pump 58. Also mounted on work table 48 is a guide tube chopper and compactor 64, adjacent a scrap canister holders 51. The compactor 64 has a foldable chute 64 for emptying the compacted trash into its adjacent scrap canister. Television cameras 29 are mounted to the depending frame member 47 above the table 48. These television cameras are commercially available items having zoom lenses and integral lighting contained in conventional waterproof housings. The television cameras monitor the operation of the system 20, and more particularly, the location of the long reach tools 42, 43 during operation. It is possible, using an appropriate tool calibrator fitted with proximity switches and located at the work table elevation in conjunction with the computer control cabinet 24 and the robot 26, to position the distal or operative end of each tool 42, 43 to within twenty one-thousandths (0.020) of an inch, thereby exceeding any accuracy obtainable when the tools 42, 43 are manipulated by any other means. Mounted on the table 48 at the corners thereof are locator pins 73. Any of the long reach tools can connect to an electromagnetic locator member. Before operations are begun with a given reach tool, this locator is placed over each of the locator pins 73 in turn and it generates an electrical signal which is transmitted to the computer. The combined inputs of the locating pins 73 enables the computer to determine the precise location of all of the various elements on the work table. Alternatively, the electrical signals may be generated from two fixed locations when any of the distal ends of the reach tools is positioned within the fixed electrical signal devices. Copending patent application Ser. No. 07/570,812, entitled "Method And Apparatus For Consolidation Of Spent Nuclear Fuel Rods," which is incorporated herein by reference, describes an apparatus and method for removing fuel rods from the four fuel rod assembly holders 49 and placing the fuel rods into the two fuel rod canister holders 52, 53. Furthermore, co-pending patent application Ser. No. 07/831,404, entitled "Guide Plate For Locating Rods In An Array," which is incorporated herein by reference, describes an apparatus and method for precisely locating a rod pulling pole over the fuel rods in the fuel rod assembly 11 and for precisely packing the fuel rods in a fuel rod canister within a fuel rod canister holder 52, 53. After all the fuel rods have been removed from the fuel rod assemblies 11 within holders 49, a rod assembly skeleton remains in each of the holders 49. The rod assembly skeleton comprises guide tubes 17, spacer grids 16, and lower end fitting 9. The rod assembly skeletons are elevated enough to enable cutters located on the work table to cut the guide tube 17, to cut the spacer grids 16 from the guide tubes 17, and to continue doing so until the rod assembly skeletons are all disassembled. The pieces of the guide tubes 17 are deposited in the compactor 64, where they are repeatedly cut and compacted and then dropped into the adjacent scrap canister 51. In accordance with the present invention, the spacer grids 16 after being cut from the fuel assembly skeleton are deposited into a novel compactor, or grid crusher apparatus 70, shown in FIGS. 2-8. Preferably, the crusher apparatus 70 is positioned anywhere on the work table 48. While in the grid crusher apparatus 70, the spacer grids 16 are crushed within a rectangular basket and then the basket is placed in a storage canister situated, for example, in canister holder 51. The novel grid crusher apparatus 70 and associated methodology is described in further detail hereafter. The grid crusher apparatus 70 is supported at its base 72, as shown in FIG. 3. The base 72 is supported vertically by the support base 54 of FIG. 2 and laterally by the work table 48 of FIG. 3. The grid crusher apparatus 70 has a ram assembly 74 which is positioned over a basket 76 by a cylinder 86. A spacer grid 16 (FIG. 4A-4C) is placed in the basket 76. The basket 76 containing the spacer grid 16 is then raised toward the ram assembly 74 so that the spacer grid is crushed within the basket 76. The foregoing process is repeated for each new spacer grid placed within the basket 76. Essentially, the spacer grids 16 are smashed one on top of another within the basket 76. In the preferred embodiment, the spacer grids 16 contained within two entire nuclear fuel rod assemblies, or a total of about 14 to 18 spacer grids depending on the fuel assembly type, are crushed within each basket 76. The ram assembly 74 has a pivotal yoke 78 adapted to move a ram contact end 82 in line with the upward movement of the basket 76. The pivotal yoke 78 pivots about an axis 84 and is forced to move via a cylinder 86, which is a hydraulic cylinder in the preferred embodiment. The cylinder 86 is connected to the yoke 78 at a pivotal joint 88 and is connected to the grid crusher apparatus 70 via a pivotal joint 92 and a transverse support member 94. It should be noted that the yoke 78 could be moved via many conventional means, such as a motor driven apparatus or a hydraulic cylinder in other configurations. In accordance with a significant feature of the present invention, the ram assembly 74 has an outer substantially rectangular sleeve ram 96 with a sleeve ram contact end 98 and a central ram 102 longitudinally movable within the sleeve ram 96. The operation of the outer substantially rectangular sleeve ram 96 and central ram 102 is described hereafter relative to FIGS. 4A through 4C. At the initial stages of the crushing action, the central ram 102 fully protrudes from the sleeve ram 102, as shown in FIG. 4A. However, as a crushing action commences and the inner walls or straps 16b of the spacer grid 16 are contacted by the central ram 102, the central ram 102 retracts into the sleeve ram 96 via application of a preselected force to the central ram 102 at the ram contact end 82, as illustrated in FIG. 4B. The central ram 102 moves until the central ram 102 is flush with the contacting end 98 of the sleeve ram 96, as shown in FIG. 4C. At this point, both the sleeve ram 96 and the central ram 102 contact and concurrently crush the spacer grid 16 so as to complete the crushing action. Reference numerals 16'", 16", 16' represent those spacer grids which have been previously crushed, in succession respectively, in the base of the basket 76. The foregoing operation of the ram assembly 74 causes the outer walls or straps 16a of the spacer grid to fold, or angle, inwardly, as shown in FIG. 4B, during the crushing action to prevent the outer straps 16a from becoming wedged between the basket 76 and sleeve ram 96 of FIG. 3. An important feature of the present invention is that the basket 76 provides an adequate container for the grids 16 whether the grids 16 collapse in a ductile manner or shatter due to the effect of radiation hardening. This is important because shattering can discharge debris which can cause jamming of equipment, undesirably disperse debris, or generate other undesirable consequences. Another significant feature of the present invention is the minimization of ram crushing surfaces. Experience has shown that when high intensity forces are used to crush metal items, portions of the metal items are "smeared" into the crushing surfaces, resulting in a metal build-up. In the present invention, there is only one ram end which contacts the spacer grids 16. Only the basket 76 contacts the sides and bottom of the spacer grids during crushing action. Hence, the only build-up of metal occurs at the ram contact end 82 of the sleeve ram and central ram. It should be noted that the foregoing ram contact end surfaces may be provided with a removable face plate which can be readily dropped or otherwise disposed of while the grid crusher apparatus is still under water, i.e., before removing the grid crusher apparatus 70 from the pool. In the preferred embodiment, a hydraulic means 104 impedes the movement of the central ram 102, and thus, defines the preselected force necessary to move the central ram 102 flush with the contacting end 98 of the sleeve ram 96. A ram assembly hydraulic line 106 is disposed, as shown in FIG. 5, to provide hydraulic fluid to a hydraulic cylinder (not shown) located within the confines of the inner ram chamber 108 defined by the inner walls of the sleeve ram 96 and central ram 102. In the alternative, as indicated in FIG. 5 by phantom lines, a spring 112 may be situated in the chamber 108 so as to exert force against the central ram 102 and impede movement of the central ram 102 inwardly. For moving the basket 76 in an upward manner towards the ram assembly 74, the grid crusher apparatus 70 can be provided with any conventional basket driving means. In the preferred embodiment, a movable box-like compartment for holding and moving the basket 76 upwardly is defined by lateral walls 111 and a basket base plate 132. The wall 111 are strong enough to support and maintain the thin walls of the basket 76 as spacer grids 16 are crushed therein. The compartment is movable within a housing defined by walls 113, which remains fixed relative to the yoke 78. Preferably, the basket driving means has a hydraulic cylinder 114 disposed beneath the basket 76. In the preferred embodiment, the basket driving means provides about 60 to 80 tons of force for spacer grids 16 from a BWR-type fuel rod assembly and about 250 to 300 tons of force for spacer grids from a PWR-type fuel rod assembly. The hydraulic cylinder 114 comprises a ram chamber 116, which is fed hydraulic fluid by a ram hydraulic line 118 so as to effectuate movement of the basket 76 upwardly towards the ram assembly 74. The hydraulic cylinder 114 further comprises a return chamber 122 adapted to receive hydraulic fluid from a return hydraulic line 124 so as to effectuate movement of the basket 76 downwardly away from the ram assembly 74. The ram chamber 116 and the return chamber 122 are defined and divided by an inner piston 126. It should be noted that the basket driving means could take the form of a pneumatic structure, ball/roller screw-driven apparatus, or other conventional configuration having similar functionality. The grid crusher apparatus 70 further includes an ejection cylinder 128, which also serves as the piston rod for crushing grids. The ejection cylinder 128 contains a piston rod 134 which is configured to eject the basket 76 from the grid crusher apparatus via upward movement of a basket ejection plate 132. As indicated in FIG. 5, the basket ejection cylinder 128 is disposed to move longitudinally within the ram cylinder 114. The basket ejection cylinder 128 preferably comprises a hydraulic driving means for driving a piston rod 134 connected to the basket ejection plate 132. Hydraulic fluid is fed to an ejection chamber 136 via an ejection hydraulic line 138. Moreover, the basket ejection plate 132 is returned by mechanical spring force applied via a spring 142, the cross section of which is illustrated in FIG. 5. Obviously, the spring 142 and/or the hydraulic means associated with the basket ejection cylinder 128 could be replaced by comparable conventional means, including pneumatic, hydraulic, or ball/roller screw-driven apparatuses. During a crushing action when the basket 76 moves upwardly towards the ram assembly 74, water is suctioned from the interior of the basket 76 in order to prevent contamination of the pool by crud or debris generated by the crushing action. For the foregoing purpose, the basket 76 is provided with apertures 76a-76d at its corners, through which debris is suctioned. Apertures 76a-76d are aligned with corner notches in basket ejection plate 132. In addition, the basket support assembly 144 also contains apertures 144a-144d. The apertures 144a-144d are best illustrated in FIG. 6. As further shown in FIG. 6, the flow through the apertures 144a-144d empties into the chamber below apertures 144a-144d and surrounded by the housing walls 113. This chamber is connected to respective outer pipes 146a-146d. The pipes 146a-146d run longitudinally down the periphery of the grid crusher apparatus 70 to the hollow base 72 which is connected to the support header 54. Reduced pressure is maintained in the pipes 146a-146d so as to pull debris from the interior of the basket 76. To facilitate crushing action within the basket 76, the grid crusher apparatus 70 is provided with a basket gripper mechanism 152 disposed to grip the top edges of the basket 76. The assembly of the basket gripper mechanism 152 is shown in FIG. 7, and its operation is illustrated in FIGS. 8A and 8B. As shown in FIG. 7, the gripper mechanism 152 comprises a plurality of grippers 154 disposed around the upper periphery of the movable box-like compartment defined by walls 111 and a periphery ring 158. There are preferably two grippers 154 per each wall 111 and consequently a total of eight grippers 154. Each gripper 154 has a gripping end 154a for engaging the basket 76 and a lever end 154b, and each gripper 154 pivots about a respective axis rivet 156. Moreover, the gripping ends 154a of each gripper 154 are normally forced outwardly by spring plungers 157, or other comparable means, situated to impose an inward force on the respective lever ends 154b. In operation, when the basket 76 is positioned away from the ram assembly 74 in its start position, as illustrated in FIG. 8A, the gripping ends 154a of the plurality of grippers 154 are forced outwardly by the spring plungers 157. This permits obstruction-free ingress and egress of the basket 76 into and out of the movable box-like compartment defined by walls 111 of the grid crusher apparatus 70. When the grid crusher apparatus 70 moves the basket 76 upwardly towards the ram assembly 74, as illustrated in FIG. 8B, the periphery ring 158 is carried upwardly along with the basket 76. The periphery ring 158 is forced downwardly about and guided by pins 162 via force from respective springs 164. As a consequence, the periphery ring 158 forces the gripping ends 154a of grippers 154 inwardly so that the gripping ends 154a engage the top of the basket 76, notwithstanding the spring force from spring plungers 157 attempting to force the gripping ends 154a outwardly. In this manner, the basket 76 is gripped by the gripping mechanism 152. Because of the gripping action exercised by the gripping mechanism 152, the basket 76 can be easily pulled down from the ram assembly 74 after a crushing action without adverse disengagement of the basket 76 from the grid crusher apparatus 70. It will be apparent to those skilled in the art that numerous modifications may be made to the preferred embodiment without departing from the principles of the present invention. All such modifications are intended to be incorporated within the scope of the present invention. |
summary | ||
041892542 | claims | 1. a system for the storage of radioactive material in rock comprising a substantially spherical cavity excavated in the rock, said cavity being surrounded by a shell of rock and said shell being surrounded by a shell of clay, characterized in that within the cavity is arranged a vertically standing tubeshaped member of a heat resistant and mechanically strong material which divides the cavity into an outer space and an inner space and is provided at its lower and upper ends with openings connecting the outer space with the inner space, that both the inner space and the outer space are filled with substantially spherical bodies of a heat resistant and mechanically strong material which bodies are provided with through openings and arranged so that these openings extend at an angle to the horizontal plane, and that the radioactive material to be stored is formed into rods which are placed within said openings in part of said spherical bodies in such manner that the rods of radioactive material are at a certain distance from the insides of the openings, and that those spherical bodies which contain radioactive material are situated in the lower part of the interior of the tubeshaped member. 2. A system as claimed in claim 1, in which said tubeshaped member consists of a cylindrical tube of concrete which is open at both ends and also provided with apertures around its periphery adjacent to both ends. 3. A system as claimed in claim 1, in which said spherical bodies are made of concrete. 4. A system as claimed in claim 1, in which said spherical bodies are provided with hooks or straps for lifting and transport of the bodies. 5. A system as claimed in claim 1, in which the inside of the cavity is lined with a layer of reinforced concrete. |
claims | 1. A system for curing a workpiece, comprising:a chamber housing;a substrate support in the chamber housing for supporting a workpiece;a radiation source operable to direct radiation onto a workpiece supported on the substrate support in order to cure the workpiece; anda pump liner including a ring-shaped element having a central opening shaped to fit around a periphery of the workpiece, the ring-shaped element having a gas inlet plenum and a gas outlet plenum for receiving a flow of purge gas into a first channel in the ring-shaped element and exhausting the flow of purge gas from a second channel in the ring-shaped element, the pump liner having a plurality of injection slits positioned near the central opening and operable to direct a substantially laminar flow of purge gas across a surface of the workpiece being cured by the radiation, the pump liner further having a plurality of receiving slits positioned near the central opening and opposite the plurality of injection slits operable to receive the flow of gas directed across the wafer, the receiving slits being further operable to receive any species outgassed from the workpiece during the curing process. 2. A system according to claim 1, further comprising:a source of purge gas operable to direct the flow of purge gas to the pump liner. 3. A system according to claim 1, wherein:the flow of purge gas has a mass and momentum sufficient to carry away a species outgassed from the workpiece during curing. 4. A system for curing a workpiece, comprising:a chamber housing;a substrate support in the chamber housing for supporting a workpiece;a radiation source operable to direct radiation onto a workpiece supported on the substrate support in order to cure the workpiece; anda pump liner having a gas inlet plenum and a gas outlet plenum for receiving and exhausting a flow of purge gas, the pump liner having a plurality of injection slits operable to direct a substantially laminar flow of purge gas across a surface of the workpiece being cured by the radiation, the pump liner further having a plurality of receiving slits opposite the plurality of injection slits operable to receive the flow of gas directed across the wafer, the receiving slits being further operable to receive any species outgassed from the workpiece during the curing process, the pump liner having a plurality of contact members for contacting the chamber housing, the contact members minimizing a contact area between the pump liner and the chamber housing in order to reduce the ability for heat flow from the pump liner to the chamber housing. 5. A system according to claim 1, wherein the pump liner is an aluminum pump liner. 6. A system according to claim 1, wherein at least a portion of an exposed surface of the pump liner is anodized. 7. A system according to claim 1, wherein:the radiation source is further operable to direct radiation to at least a portion of the pump liner, whereby a temperature of the pump liner is increased. 8. A system according to claim 1, further comprising:a window positioned between the radiation source and the workpiece support, the window having a diameter sufficient such that the radiation source can direct radiation to an entire workpiece surface to be cured and at least a portion of the pump liner,wherein the flow of purge gas substantially minimizes the collection of outgassed species on the window. 9. A system according to claim 1, further comprising:a heating element in thermal contact with the pump liner, the heating element operable to bring the pump liner to a pre-determined temperature before the flow of purge gas is directed across the surface of the workpiece. 10. A system according to claim 1, wherein:the radiation source includes at least one ultraviolet (UV) lamp. 11. A pump liner for directing a flow of purge gas across a workpiece in a processing chamber, comprising:a ring-shaped element having a central opening adapted to fit around a periphery of a workpiece, the ring-shaped element having an inlet plenum operable to receive a flow of purge gas into a first channel in the ring-shaped element and an exhaust plenum operable to direct the flow of purge gas out of a second channel in the ring-shaped element;a plurality of injection ports positioned near the central opening of the ring-shaped element and operable to direct the flow of purge gas, received by the inlet plenum, from the first channel and across a surface of the workpiece, the injection ports operable to direct a substantially laminar flow of the purge gas across the surface; anda plurality of receiving ports positioned near the central opening of the ring-shaped element, the receiving ports being substantially opposite the plurality of injection ports, and operable to receive the flow of purge gas directed across the surface of the workpiece, as well as any species outgassed by the workpiece carried by the flow, and direct the flow and outgassed species through the second channel and out of the ring-shaped element through the exhaust plenum. 12. A pump liner according to claim 11, wherein:the pump liner is formed of aluminum. 13. A pump liner according to claim 11, wherein:at least a portion of an exposed surface of the pump liner is anodized. 14. A pump liner according to claim 11, wherein:each of the plurality of injection ports and plurality of receiving ports includes a plurality of slits in the ring-shaped element. 15. A pump liner according to claim 11, wherein:the ring-shaped element further has a plurality of contact members for contacting a chamber housing, the contact members minimizing a contact area between the ring-shaped element and the chamber housing in order to reduce the ability for heat flow from the ring-shaped element to the chamber housing. 16. A pump liner according to claim 11, wherein:the ring-shaped element includes first and second mating portions. 17. A pump liner according to claim 11, wherein:each of the plurality of injection ports and plurality of receiving ports is at least one of shaped, sized, and positioned to provide for the substantially laminar flow. 18. A pump liner according to claim 11, wherein:the plurality of injection ports includes a plurality of injection ports of at least one of different shapes and different sizes. 19. A method for curing a workpiece, comprising:positioning a workpiece to be cured on a workpiece support in a processing chamber;directing radiation toward a surface of the workpiece on the workpiece support, the radiation selected to cure at least a layer of material on the surface;providing a flow of purge gas across the irradiated surface of the workpiece, the flow of purge gas emanating from a pump liner including a ring-shaped element having a central opening shaped to fit around a periphery of the workpiece and having a plurality of injection slits and a plurality of receiving slits positioned near the central opening of the ring-shaped element for directing a substantially laminar flow of purge gas across the irradiated surface of the workpiece, the ring-shaped element having an inlet plenum for receiving the flow of purge gas into a first channel in the ring-shaped element, the flow of purge gas sufficient to transport any species outgassed from the irradiated surface of the workpiece; andexhausting the flow of purge gas and the outgassed species after the flow passes across the irradiated surface and is received by the receiving slits of the pump liner, the ring-shaped element of the pump liner having an exhaust plenum operable to direct the flow of purge gas out of a second channel in the ring-shaped element. 20. A method according to claim 19, further comprising:selecting at least one of a shape, size, position, and number of at least one of the plurality of injection slits and a plurality of receiving slits in order to provide for the substantially laminar flow. 21. A method according to claim 19, further comprising:directing a portion of the radiation toward a portion of the pump liner in order to increase an operating temperature of the pump liner. 22. A method for curing a workpiece, comprising:positioning a workpiece to be cured on a workpiece support in a processing chamber;directing radiation toward a surface of the workpiece on the workpiece support, the radiation selected to cure at least a layer of material on the surface;providing a flow of purge gas across the irradiated surface of the workpiece, the flow of purge gas emanating from a pump liner having a plurality of injection slits and a plurality of receiving slits for directing a substantially laminar flow of purge gas across the irradiated surface of the workpiece, the flow of purge gas sufficient to transport any species outgassed from the irradiated surface of the workpiece;exhausting the flow of purge gas and the outgassed species after the flow passes across the irradiated surface and is received by the receiving slits of the pump liner; andminimizing a contact area between the pump liner and a body of the processing chamber in order to minimize an amount of heat flow from the pump liner to the body. 23. A method according to claim 19, further comprising:anodizing the pump liner in order to increase an emissivity of the pump liner. 24. A method according to claim 19, wherein:providing a flow of purge gas includes providing a flow of argon gas. 25. A method according to claim 19, wherein:providing a flow of purge gas includes providing a flow of purge gas at a distance of less than 0.150″ above the irradiated surface. |
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claims | 1. A core of a light water reactor having a plurality of fuel assemblies, which are loaded in said core, having nuclear fuel material containing a plurality of isotopes of transuranium nuclides, an upper blanket zone, a lower blanket zone, and a fissile zone, in which said transuranium nuclides are contained, disposed between said upper blanket zone and said lower blanket zone;wherein a ratio of Pu-239 in all said transuranium nuclides contained in said loaded fuel assembly is in a range of 40 to 60% when burnup of said fuel assembly is 0;a sum of an axial length of said lower blanket zone and an axial length of said upper blanket zone is in a range of 250 to 600 mm; andthe axial length of said lower blanket zone is in a range of 1.6 to 12 times the axial length of said upper blanket zone. 2. The core of the light water reactor according to claim 1, wherein the axial length of said upper blanket zone is in a range of 30 to 105 mm. 3. The core of the light water reactor according to claim 1,wherein said core has an inner blanket zone between said upper blanket zone and said lower blanket zone;said fissile zone includes a upper fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said inner blanket zone, and a lower fissile zone containing said transuranium nuclides and disposed between said inner blanket zone and said lower blanket zone; andan axial length of said upper fissile zone is larger than an axial length of said lower fissile zone within a range of 10 to 25 mm. 4. The reactor core of the light water reactor according to claim 1,wherein an upper end of a neutron absorber zone of a safety rod provided in said light water reactor is positioned in a region between a lower end of said core and 5 mm below said lower end of said core. 5. A fuel assembly having nuclear fuel material containing a plurality of isotopes of transuranium nuclides, an upper blanket zone, a lower blanket zone, and a fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said lower blanket zone;wherein a ratio of Pu-239 in all said transuranium nuclides contained in said nuclear fuel material is in a range of 40 to 60% when burnup of said fuel assembly is 0;a sum of an axial length of said lower blanket zone and an axial length of said upper blanket zone is in a range of 250 to 600 mm, andthe axial length of said lower blanket zone is in a range of 1.6 to 12 times the axial length of said upper blanket zone. 6. The fuel assembly according to claim 5,wherein the axial length of said upper blanket zone is in a range of 30 to 105 mm. 7. The fuel assembly according to claim 5,wherein said fuel assembly has an inner blanket zone between said lower blanket zone and said upper blanket zone;said fissile zone includes an upper fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said inner blanket zone, and a lower fissile zone containing said transuranium nuclides and disposed between said inner blanket zone and said lower blanket zone; andan axial length of said upper fissile zone is larger than an axial length of said lower fissile zone within a range of 10 to 25 mm. 8. The fuel assembly according to claim 5,wherein nuclear fuel material containing a neutron absorber is disposed below said lower blanket zone. |
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053848136 | abstract | A storage rack for storing nuclear fuel rod assemblies is provided with an array of cell housings having damping elements which are preloaded against the outer walls of the individual cells. The damping elements are slabs which when preloaded against the cell walls provide a coulomb damping function which is highly effective in absorbing vibration from rough handling or seismic events. The cell housings may be located in alternating positions in the array and cells may be formed from the outer walls of the surrounding cell housings. The cell housings are held together in the array by support bars which are affixed to the top and bottom ends of the cell housings. The support bars may include recesses to align the cell housings. |
055047882 | summary | FIELD OF THE INVENTION The present invention is directed to the field of nuclear power plant inspection devices. In particular, the present invention is directed to the field of nuclear power plant steam generator inspection. BACKGROUND OF THE INVENTION Nuclear power plants typically contain three major components as shown in FIG. 1: a reactor which produces superheated water which is transported to one or more steam generators; and a power turbine, driven by the steam, which generates electrical power. The superheated water is transported to the steam generator by a tube sheet. The tube sheet in a nuclear steam generator typically forms a pair of tube members or tube rows separated by a lane, and held together by a plurality of support plates, separated at periodic intervals. The height of each tube row may exceed thirty-two feet, and include six to eight or more support plates, each separated horizontally at three to six foot intervals. In the steam generator, the tube sheets carrying the superheated water are quenched with cool water, which generates the steam which drives the turbine. The water exits through a plurality of access ports situated at the bottom of each lane. This procedure for generating steam presents several problems. First, the water used to quench the tube sheet is supplied directly from adjacent rivers or reservoirs. Such water often has impurities or chemicals which may pierce or corrode both the steam generator tubes and the support plates. Periodic inspections of nuclear steam generators are required for obvious safety reasons connected to their operation, and steam generator cleanliness has been a problem due to such pipe corrosion and damage. The highly corrosive environment of the steam generator is particularly problematic for many of the older nuclear reactors in service throughout the world. Heretofore, the tubes and support plates of these steam generators were inaccessible from visual inspection. Information was gathered by complicated systems which could not adequately inspect all sections of the tubes and support plates. Because of the highly radioactive environment and the heat of the pipes, direct human inspection has typically been restricted to between three and five minutes per man per six month period. This time period does not provide an ample opportunity for the careful inspection for corrosion, holes and leaks. It is particularly difficult to inspect within the narrow lanes and the tubes at the support plates, because of the heat, radioactivity and narrowness of the lanes separating the tube sheet members and the small access ports. There are a number of issued patents directed to mechanical steam generator inspection and repair devices. U.S. Pat. No. 4,673,027 for example, discloses a device for inspecting and repairing the tubes of a nuclear reactor steam generator. The device includes a manipulator which is insertible in the chamber and which may be locked onto the tube sheet for supporting remotely controlled and monitored inspection instruments in tools. The manipulator includes a support leg which is adjustable in length in an axial direction, a main arm connected to and movable relative to the support leg and an equipment carrier which is connected to the main arm. U.S. Pat. No. 4,653,971 discloses a device for selectively positioning a tool carried by a vehicle which moves on a perforated plate, while the device utilizes an elbow which swings a telescoping arm in the position. Similarly, U.S. Pat. No. 4,945,979 discloses an improved robotic arm for effecting a tube plugging operation. The system also includes an elbow control mechanism. U.S. Pat. No. 4,205,939 discloses an apparatus for remotely repairing the tubes in a steam generator. The device includes a boom pivotally mounted on a column and a system for rotating the column and the boom therewith. The disclosed device further includes a tool which is operable on the tubes. U.S. Pat. No. 4,231,419 discloses a manipulator for inspecting and repairing the tubes of heat exchangers. An inspection arm is inserted and removed through a lead-in nozzle and a swivel arm carries an extendable and retractable mouthpiece carrier with a mouthpiece which can be aligned into the tube openings. Finally, U.S. Pat. No. 4,919,194 discloses a method of positioning a robot for inspecting and maintaining operations within a nuclear plant. While each of the above mechanism has been utilized to inspect and/or repair nuclear power steam generators and include the use of robotic manipulators or arms, none have been successfully utilized to inspect the outer diameter of the steam tube bundle or the support plates None of the above devices can enter the 1", 2", 4", or 6" diameter apertures situated proximate to the tubes The device disclosed in U.S. Pat. No. 4,673,027, for example, is described as entering the steam generator through a manhole, typically called the primary channel head. There has been a long felt need for a steam generator tube sheet and support plate inspection system which can be inserted through the access ports of the steam generator, and which can be used to thoroughly inspect the tubes and support plates situated within the lanes between the tube rows. There further has been a long felt need for a support plate inspection and cleaning device which facilitates the inspection and cleaning of the rear of a steam generator and which may be insertable through the smallest access ports in the steam generator. SUMMARY OF THE INVENTION In view of this long felt need and in accordance with the present invention, a support plate inspection device and method for inspecting within the lanes separating the tube sheets of a nuclear steam generator are disclosed. The device of the present invention facilitates the inspection of the tube sheet and support plates of a nuclear steam generator and particularly inspection within the lanes situated between the tubes. In a preferred embodiment, the device comprises a boom means for extending into an access port of a steam generator and into a lane separating two rows of tube members, said boom means being uprightable within said lane; and video camera means attached to said boom means for inspecting the tubes and support plates within said lane. In a more preferred embodiment, the present invention is directed to a support plate inspection device comprising first boom coupled by a rotatable connector to a second boom, said first and second booms being insertable through the access port of a steam generator and into a lane between two rows of tubes, said rotatable connector facilitating the rotational movement of said second boom such that said second boom can be held upright through said tube lane and adjacent to the tubes and support plates of a steam generator, the second boom having a charge coupled device (CCD) video camera attached thereto such that said second boom and CCD video camera can be uprighted and positioned adjacent to the support plates in a steam generator such that the tubes and support plates can be examined by said CCD video camera. In more preferred embodiments, the second boom comprises a plurality of telescoping members which can extend a length of up to approximately 32 feet, the height of a standard steam generator tube. The CCD video camera is preferably mounted to a pan and tilt means which is under the control of a remote joy stick. The CCD video camera also preferably includes an auto-focus mechanism. In yet more preferred embodiments, the present invention includes means for cleaning the tubes and support plates. The present invention is also directed to a method for inspecting the support plates and tube sheet of a nuclear steam generator. The method comprises the following steps: inserting boom means through an access port of said generator and within a lane separating two tube sheets, said boom means having a CCD video camera attached thereto; and uprighting said boom means within said lane such that said CCD video camera may be held adjacent to said tube sheet and support plates such that said tube sheet and support plates can be inspected by said CCD video camera. These and other advantages and features of the present invention will become apparent from the detailed description which follows. |
abstract | A methodology is disclosed for compaction of a ceramic matrix of certain nuclear fuels incorporating neutron poisons, whereby those poisons aid in reactor control while aiding in fuel fabrication. Neutronic poisons are rare-earth oxides that readily form eutectics suppressing fuel fabrication temperature, of particular importance to the fully ceramic microencapsulated fuel form and fuel forms with volatile species. |
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claims | 1. Multiple beam lithography system comprising:a beam source for providing a multitude of beams,a blanker array comprising a blanker for each beam out of the multitude of beams, said array adapted for substantially allowing a plurality of beams to pass through,a control device for providing the blanker array with a temporal blanking pattern indicating for each beam when it should be blanked and when not, thereby modulating each beam with an unique temporal blanking pattern, anda measuring device arranged downstream of the blanker array, comprising a sensor having a sensor area arranged for directly and simultaneously sensing the plurality of individually modulated beams for providing an aggregated signal of the plurality of beams as a function of time. 2. Multiple beam lithography system according to claim 1, further comprising a demodulator adapted for demodulating said aggregated signal into an intensity value for each individual beam. 3. Multiple beam lithography system according to claim 2, wherein the demodulator comprises an electronic data processor adapted providing the control device with said temporal blanking patterns and for calculating a measure of the intensity of individual beams based on their corresponding temporal blanking patterns and the aggregated signal of the plurality of beams as a function of time. 4. System according claim 1, wherein the sensor area is arranged for simultaneously sensing all beams of the multitude of beams of the system. 5. System according to claim 1 or 4, in which the sensor area is a contiguous area. 6. System according to claim 1, wherein the multitude of beams comprises a multitude of charged particle beams, and the measuring device comprises a current measuring sensor arranged for measuring an aggregated current generated by the plurality of beams. 7. System according to claim 6, wherein the current measuring sensor comprises one or more than one Faraday cup, current clamp and/or scintillating material and photon counter. 8. System according to claim 1, further comprising a target positioning system comprising a stage for carrying and moving a target to be exposed to the beams, wherein the measuring device is mounted on the stage. 9. System according to claim 1, further comprising a converging element for directing the plurality of beams onto the sensor area. 10. System according to claim 1, in which the measuring device further comprises a knife edge or knife edge array placed in front of the sensor area. 11. System according to claim 10, in which the knife edge or knife edge array is placed substantially in an image plane of the system. 12. Method for simultaneous measurement of a multitude of beams in a system according to claim 1,said method comprising the steps of:i) providing a multitude of temporal blanking patterns comprising a temporal blanking pattern for each blanker, each temporal blanking pattern representing a modulation of an associated beam over a time interval,ii) modulating the multitude of beams during the time interval by streaming to each blanker associated with a beam an associated temporal blanking pattern, sensing an aggregated beam intensity signal of all unblanked beams, and measuring said signal during the streaming of the temporal patterns as a function of time,iii) calculating a measure of the intensity of individual beams based on their associated temporal blanking patterns and the signal as a function of time. 13. Method according to claim 12, wherein step iii) comprises demodulating said signal by calculating a measure of the intensity of individual beams based on their associated temporal blanking patterns and the signal as a function of time. 14. Method according to claim 12, wherein the temporal blanking patterns of said multitude of beams are substantially orthogonal with respect to each other. 15. Method according to claim 12, wherein during steps i) and ii) substantially only half of the multitude of beams is switched on. 16. Method according to claim 14, wherein the multitude of temporal blanking patterns is generated using pseudo random numbers. 17. Method according to claim 12, wherein the temporal blanking patterns are chosen such that each temporal blanking pattern contains a large number of on-off transitions. 18. Method according to claim 12, wherein the temporal blanking patterns are arranged such that at substantially any time the total amount of unblanked beams is substantially constant. 19. Method according to claim 12, wherein the measuring device comprises a current measuring sensor arranged for measuring an aggregated current generated by the plurality of beams as a function of time, in which the measuring device further comprises a variable gain amplifier which can be switched betweena first setting comprising a high gain and low noise setting, anda second setting comprising a low gain and high noise setting,wherein said method comprises the step of setting the variable gain amplifier to the first setting when the aggregate current is expected to be small, or setting the variable gain amplifier to the second setting when the aggregate current is expected to be large. 20. Measuring device suitable for use in a system according to claim 1, said device comprising a sensor having a sensor area arranged for simultaneously sensing a plurality of beams for providing an aggregated signal of the plurality of beams, further comprising a knife edge or knife edge array placed in front of the sensor area. 21. Multiple beam lithography system comprising a multiple beam column for projecting multiple beams onto a target, wherein the column comprises:a beam source for providing a multitude of beams,a blanker array arranged between the beam source and the target, comprising a blanker for each beam out of the multitude of beams, wherein said array is adapted for substantially allowing a plurality of beams to pass through,a control device for providing the blanker array with a blanking pattern indicating for each beam when it should be blanked and when not,projection means for projecting the plurality of beams onto the target,a sensor arranged downstream of the multiple beam column for examining the throughput of the multiple beam column, wherein the sensor comprises a sensor area which is adapted for sensing all beams of the multitude of beams simultaneously, and wherein the sensor is arranged for providing an aggregated signal of the plurality of beams as a function of time, anda demodulator adapted for demodulating said aggregated signal by calculating a measure of the intensity of individual beams based on their corresponding temporal blanking patterns and the aggregated signal of the plurality of beams as a function of time. 22. Method according to claim 12, wherein several beams are left unblanked at any time. |
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description | The present invention relates to liners for analyzer magnet chambers and in particular to liners for Kestrel Analyzer Magnet Chambers. Referring to FIG. 6 the present liners for Kestrel Analyzer Magnet Chambers are constructed of many pieces 601 and are held in place within the chamber by wires. The wires are threaded through holes 602 in the liner pieces 601. When the liners need replaced the present construction of the liners 601 lead to a long down time. Referring to FIG. 1 a plan view of the chamber of a Kestrel Analyzer Magnet Chamber 1 is shown. Liners line the sides of the chamber to prevent wear caused by the beam 8. Liners exist on all sides; a curved liner 7 lines the curved side and straight liners 4 and 2 line the two straight sides. Access to replace the liners is by removing the neutral beam dump 6. The current liners are made up of multiple pieces 601 held together by wires 21 through holes 602 in the pieces. As can be seen in FIG. 2, to remove the liners it is necessary to remove the wires 21 attached to the side of the chamber 1. This presents a problem as kinks along the wires impede the removal of the liner pieces 601. The wires have to be removed at both ends if they are damaged or should the liners be stuck. While the wires at the neutral beam dump end are easily removed, removing the wires at the other end requires dismantling the chamber 1. It would be desirable to have liners that could be replaced easily and without the need to dismantle the entire chamber. An object of at least one embodiment of the invention is to provide a liner that overcomes the above disadvantages or at least provides the public or industry with a useful choice. Accordingly in a first embodiment the present invention consists in a waveguide liner for an analyzer magnet chamber having three interlocking pieces of graphite, said liners having sufficient size to allow them to stand freely without being secured. Preferably said three pieces are of uniform construction enabling said pieces to be interchanged. Preferably wherein each said piece includes a hole, said hole facilitating ease of installation and removal. Preferably each said piece includes a pair of substantially parallel longitudinal groves at the rear of said liner, said gloves spaced and sized to accommodate retaining cables of a Kestrel analyzer magnet chamber. Preferably each said piece at each end includes an overlapping portion. Preferably at a first end said overlapping portion is a cut out at the front, and at said second end said overlapping portion is a cut out at the rear, said cut outs of said adjacent pieces being arranged to overlap. The invention may further be said to consist in any alternative combination of parts or features mentioned herein or shown in the accompanying drawings. Known equivalents of these parts or features which are not expressly set out are nevertheless deemed to be included. Referring to the figures it will be appreciated that the invention may be implemented in various forms and modes. The following description of the disclosed embodiment of the invention is given by way of example only. Referring to FIGS. 3 and 4 the replacement liner of the present invention is illustrated. The liner 10 has a serrated front 12, as in used in the existing 21 piece liners. Each liner piece has at each end cut outs 11 and 13 to allow multiple liners to interconnect. While the illustrated liner pieces have over lapping parts at each end other interconnection means such as tongue and grove joints could also be used. At the rear of the liner pieces groves 15 are included to accommodate the wires 21 of the existing liners. A hole 9 allows for the liners to be hooked for insertion and removal for example with a piece of wire. The liner pieces are designed so that they have sufficient mass to stand against the wall of the chamber without needing to be restrained by a wire. The existing pieces 601 are not of sufficient mass to stand without being restrained. Not being restrained by a wire means that replacement of the liner parts without having to dismantle the chamber is possible. This advantage reduces significantly the down time caused when the parts wear out. In the present invention as seen in FIG. 5 multiple liner pieces 10a, 10b and 10c are interconnected and used together. The use of three pieces has been specifically chosen. Most of the wear caused by the beam 8, occurs in the middle 20 of the liner and by having three equal pieces, it is easy to replace the worn piece or to interchange the pieces to ensure even wear. Multiple pieces have been chosen rather than a single piece to increase the overall life of the liners because the pieces can be interchanged. While the existing 21 piece liner allows for the pieces 601 to be interchanged, because the pieces 601 are held together by wire removal and dismantling causes significant down time, and in a manufacturing environment the down time causes significant loses. The foregoing describes the invention with reference to the disclosed embodiment. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope of the invention as defined in the accompanying claims. |
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abstract | A radiation-attenuation garment system having a plurality of radiation-attenuating material panels adapted to conform to the contours of a body. The radiation-attenuation garment system includes a shirt and underwear shorts formed by compression material. A plurality of radiation-attenuating material panels are removably disposed within the shirt and underwear shorts to protect the wearer from radiation exposure in the areas having the radiation attenuation panels. |
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claims | 1. A system for creating an image of an object that contains a contrast agent including a chemical element having a K EDGE, CONTRAST AGENT , said system comprising: an X-ray source configured to emit an X-ray beam having a spectrum of X-ray radiation, said X-ray source configured to emit said beam along a fixed direction relative to said X-ray source; means for moving said X-ray source to cause said beam to move; a detector positioned to interpose said object between said detector and said X-ray source, said detector for receiving radiation and producing electrical current that is proportional to the intensity of the radiation received; a first filter having a chemical element with a K EDGE greater than K EDGE, CONTRAST AGENT and a second filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value less than K EDGE, CONTRAST AGENT , said first and second filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be processed to simulate quasi-monochromatic radiation having an average energy greater than K EDGE, CONTRAST AGENT ; a third filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value greater than K EDGE, CONTRAST AGENT and a fourth filter having a chemical element with a K EDGE less than K EDGE, CONTRAST AGENT , said third and fourth filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be processed to simulate guasi-monochromatic radiation having an average energy less than K EDGE, CONTRAST AGENT ; a means for mounting said first, second, third and fourth filters on said X-ray source and for successively positioning each said filter into contact with said beam to filter said beam, said mounting means to cause said filters to move with said X-ray source; and a processor connected to said detector for producing an image of said object from said electrical current. 2. A system as recited in claim 1 further comprising a means for moving said detector to allow said detector to maintain a continuous angular orientation with respect to said X-ray source as said X-ray source moves. claim 1 3. A system as recited in claim 1 wherein said processor is configured to subtract said electrical current produced by said detector while said second filter is in contact with said beam from said electrical current produced by said detector while said first filter is in contact with said beam to produce a first intermediary: difference signal said processor being further configured to subtract said electrical current produced by said detector while said fourth filter is in contact with said beam from said electrical current produced by said detector while said third filter is in contact with said beam to produce a second intermediary difference signal; and wherein said processor is configured to subtract said second intermediary difference signal from said first intermediary difference signal to produce an image signal. claim 1 4. A system for creating an image of an object that contains a contrast agent including a chemical element having a K EDGE, CONTRAST AGENT , said system comprising: a means for directing a spectrum of electromagnetic radiation onto a plurality of paths, each said path extending through said object; a first filter having a chemical element with a K EDGE greater than K EDGE, CONTRAST AGENT and a second filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value less than K EDGE, CONTRAST AGENT , said first and second filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be processed to simulate quasi-monochromatic radiation having an average energy greater than K EDGE, CONTRAST AGENT ; a third filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value greater than K EDGE, CONTRAST AGENT and a fourth filter having a chemical element with a K EDGE less than K EDGE, CONTRAST AGENT , said third and fourth filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be processed to simulate quasi-monochromatic radiation having an average energy less than K EDGE, CONTRAST AGENT ; a means for successively interposing each said filter on each said path to create a plurality of filtered radiation signals for each said path; a means for receiving said filtered radiation signals for each said path, and producing an electrical signal for each said filtered radiation signal received, each said electrical signal being proportional to the intensity of radiation received; and a processor for operation on said electrical signals to produce an image of said object. 5. A system as recited in claim 4 wherein said means for directing a spectrum of electromagnetic radiation onto a plurality of paths comprises: claim 4 a radiation source configured to emit radiation in at least one direction; and a means for moving said radiation source to cause said source to successively emit said radiation in a plurality of directions. 6. A systems recited in claim 5 wherein said means for receiving said filtered radiation signals for each said path comprises: claim 5 at least one radiation detector, each said radiation detector oriented to detect radiation, in at least one direction; and a means for moving each said radiation detector to cause each said radiation detector to successively detect radiation in a plurality of directions. 7. A system as recited in claim 4 wherein said interposing means is positioned to successively interpose each said filter on each said path before said radiation passes through said object. claim 4 8. A system as recited in claim 4 wherein said means for successively interposing each said filter on each said path comprises: claim 4 a wheel defining an axis and formed with a plurality of holes, each said hole for accommodating a said filter; and means for selectively rotating said wheel about said axis. 9. A system as recited in claim 5 wherein said means for successively interposing each said filter of a said filter set on each said path comprises: claim 5 a wheel defining an axis and formed with a plurality of holes, each said hole for accommodating a said filter; and means for selectively rotating said wheel about said axis, said means mounted on said radiation source to cause said rotating means and said wheel to move with said radiation source. 10. A system as recited in claim 4 wherein said processor is configured to subtract said electrical signal produced with said second,filter interposed along a first path from said electrical signal produced with said first filter interposed along a said first path to produce a first intermediary difference signal; said processor being further configured to subtract said electrical signal produced with said fourth filter interposed along said first path from said electrical signal produced with said third filter interposed along first path to produce a second intermediary difference signal; and said processor is configured to subtract said second intermediary difference signal from said first intermediary difference signal to produce an image signal for said first path. claim 4 11. A system as recited in claim 4 wherein said contrast agent comprises the chemical element iodine, said first filter comprises the chemical element Cs at a thickness of about 290.0 xcexcm and said second filter comprises chemical element I at a thickness of about 120.0 xcexcm, said third filter comprises the chemical element I at a thickness of about 450.0 xcexcm and said fourth filter comprises the chemical element Te at a thickness of about 385.0 xcexcm. claim 4 12. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Xe, said first filter comprises the chemical element Ba at a thickness of about 180.0 xcexcm and said second filter comprises the chemical element Cs at a thickness of about 350.0 xcexcm, said third filter comprises the chemical element I at a thickness of about 450.0 xcexcm and said fourth filter comprises the chemical element Te at a thickness of about 385.0 xcexcm. claim 4 13. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Cs, said first filter comprises the chemical element Ba at a thickness of about 180.0 xcexcm and said second filter comprises the chemical element Cs at a thickness of about 350.0 xcexcm, said third filter comprises the chemical element Cs at a thickness of about 1340.0 xcexcm and said fourth filter comprises the chemical element I at a thickness of about 550.0 xcexcm. claim 4 14. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Ba, said first filter comprises the chemical element La at a thickness of about 105.0 xcexcm and said second filter comprises the chemical element Ba at a thickness of about 200.0 xcexcm, said third filter comprises the chemical element Ba at a thickness of about 805.0 xcexcm and said fourth filter comprises the chemical element Cs at a thickness of about 1575.0 xcexcm. claim 4 15. A system as recited in claim 4 wherein said contrast agent; comprises the chemical element Sm, said first filter comprises the chemical element Eu at a thickness of about 136.0 xcexcm and said second filter comprises the chemical element Sm at a thickness of about 100.0 xcexcm, said third filter comprises the chemical element Sm at a thickness of about 465.0 xcexcm and said fourth filter comprises the chemical element Nd at a thickness of about 545.0 xcexcm. claim 4 16. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Eu, said first filter comprises the chemical element Gd at a thickness of about 120.0 xcexcm and said second filter comprises the chemical element Eu at a thickness of about 185.0 xcexcm, said third filter comprises the chemical element Eu at a thickness of about 690.0 xcexcm, and said fourth filter comprises the chemical element Sm at a thickness of about 500.0 xcexcm. claim 4 17. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Gd, said first filter comprises the chemical element Tb at a thickness of about 140.0 xcexcn and said second filter comprises the chemical element Gd at a thickness of about 152.0 xcexcm, said third filter comprises the chemical element Gd at a thickness of about 500.0 xcexcm and said fourth, filter comprises the chemical element Eu at a thickness of about 770.0 xcexcm. claim 4 18. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Tb, said first filter comprises the chemical element Dy at a thickness of about 130.0 xcexcm and said second filter comprises the chemical element Tb at a thickness of about 140.0 xcexcm, said third filter comprises the chemical element Tb at a thickness of about 515.0 xcexcm and said fourth filter comprises the chemical element Gd at a thickness of about 565.0 xcexcm. claim 4 19. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Dy, said first filter comprises the chemical element Ho at a thickness of about 130.0 xcexcm and said second filter comprises the chemical element Dy at a thickness of about 140.0 xcexcm, said third filter comprises the chemical element Dy at a thickness of about 540.0 xcexcm and said fourth filter comprises the chemical element Tb at a thickness of about 582.0 xcexcm. claim 4 20. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Ho, said first filter comprises the chemical element Er at a thickness of about 130.0 xcexcm and said second filter comprises the chemical element Ho at a thickness of about 140.0 xcexcm, said third filter comprises the chemical element Ho at a thickness of about 550.0 xcexcm and said fourth filter comprises the chemical element Dy at a thickness of about 585.0 xcexcm. claim 4 21. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Er, said first filter comprises the chemical element Tm at a thickness of about 135.0 xcexcm and said second filter comprises the chemical element Er at a thickness of about 145.0 xcexcm, said third filter comprises the chemical element Er at a thickness of about 550.0 xcexcm and said fourth filter comprises the chemical element Ho at a thickness of about 600.0 xcexcm. claim 4 22. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Lu, said first filter comprises the chemical element Hf at a thickness of about 110.0 xcexcm and said second filter comprises the chemical element Lu at a thickness of about 155.0 xcexcm, said third filter comprises the chemical element Lu at a thickness of about 595.0 xcexcm and said fourth filter comprises the chemical element Yb at a thickness of about 900.0 xcexcm. claim 4 23. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Hf, said first filter comprises the chemical element Ta at a thickness of about 97.0 xcexcm and said second filter comprises the chemical element Hf at a thickness of about 127.0 xcexcm, said third filter comprises the chemical element Hf at a thickness of about 440.0 xcexcm and said fourth filter comprises the chemical element Lu at a thickness of about 610.0 xcexcm. claim 4 24. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Ta, said first filter comprises the chemical element W at a thickness of about 84.0 xcexcm and said second filter comprises the chemical element Ta at a thickness of about 100.0 xcexcm, said third filter comprises the chemical element Ta at a thickness of about 330.0 xcexcm and said fourth filter comprises the chemical element Hf at a thickness of about 425.0 xcexcm. claim 4 25. A system as recited in claim 4 wherein said contrast agent comprises the chemical element W, said first filter comprises the chemical element Re at a thickness of about 80.0 xcexcm and said second filter comprises the chemical element W at a thickness of about 90.0 xcexcm, said third filter comprises the chemical element W at a thickness of about 330.0 xcexcm and said fourth filter comprises the chemical element Ta at a thickness bf about 396.0 xcexcm. claim 4 26. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Re, said first filter comprises the chemical element Os at a thickness of about 80.0 xcexcm and said second filter comprises the chemical element Re at a thickness of about 88.0 xcexcm, said third filter comprises the chemical element Re at a thickness of about 320.0 xcexcm and said fourth filter comprises the chemical element W at a thickness of about 357.0 xcexcm. claim 4 27. A system as recited in claim 4 5 wherein said contrast agent comprises the chemical element Os, said first filter comprises the chemical element Ir at a thickness of about 80.0 xcexcm and said second filter comprises the chemical element Os at a thickness of about 83.0 xcexcm, said third filter comprises the chemical element Os at a thickness of about 315.0 xcexcm and said fourth filter comprises the chemical element Re at a thickness of about 346.0 xcexcm. claim 4 28. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Ir, said first filter comprises the chemical element Pt at a thickness of about 90.0 xcexcm and said second filter comprises the chemical element Ir at a thickness of about 90.0 xcexcm, said third filter comprises the chemical element Ir at a thickness of about 330.0 xcexcm and said fourth filter comprises the chemical element Os at a thickness of about 340.0 xcexcm. claim 4 29. A system as recited in claim 4 wherein said contrast agent comprises the chemical element Bi, said first filter comprises the chemical element Th at a thickness of about 170.0 xcexcm and said second filter comprises the chemical element Bi at a thickness of about 250.0 xcexcm, said third filter comprises the chemical element Bi at a thickness of about 972.0 xcexcm and said fourth filter comprises the chemical element Pb at a thickness of about 870.0 xcexcm. claim 4 30. A method for creating an image comprising the steps of: providing an object that contains a contrast agent having a chemical element with K EDGE, CONTRAST AGENT ; directing a spectrum of electromagnetic radiation onto a plurality of paths, each said path extending through said object; providing a first filter having a chemical element with a K EDGE greater than K EDGE, CONTRAST AGENT ; providing a second filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value less ta K EDGE, CONTRAST AGENT , said first and second filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be processed to simulate guasi-monochromatic radiation having an average energy greater than K EDGE, CONTRAST AGENT ; providing a third filter having a chemical element with a K EDGE in an inclusive range between K EDGE CONTRAST AGENT and a value greater than K EDGE, CONTRAST AGENT ; providing a fourth filter having a chemical element with a K EDGE less than K EDGE, CONTRAST AGENT , said third and fourth filter chemical elements having respective thicknesses for producing respective filtered radiation signals that can be Processed to simulate quasi-monochromatic radiation having an average energy less than K EDGE, CONTRAST AGENT ; successively interposing each said filter of one:said filter set on each said path to create a plurality of filtered radiation signals for each said path; receiving said filtered radiation signals for each said path and producing an electrical signal for each said filtered radiation signal received, each said electrical signal being proportional to the intensity of radiation received; and processing said electrical signals to produce an image of said object. 31. A method as recited in claim 30 further comprising the step of administering a said contrast agent into said object. claim 30 32. A method as recited in claim 30 wherein said object is a human body. claim 30 |
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045377413 | abstract | An enlarged funnel is releasably mounted at the open end of a length of cladding by an encircling length of shrink tubing which securely engages outer surfaces of both the funnel and cladding. The shrink tubing overlaps an annular shoulder against which pulling force can be exerted to remove the tubing from the cladding. The shoulder can be provided on a separate collar or ring, or on the funnel itself. |
claims | 1. A method of operating an ion implantation system comprising:generating an ion beam of a primary charge state;projecting the ion beam onto a target substrate;detecting off angle ions on trajectories off the target substrate, wherein a concentration of the off angle ions indicates an amount of charge contamination within the ion beam; andinterlocking ion implantation when the amount of charge contamination exceeds or equals a predetermined threshold. 2. The method according to claim 1, wherein detecting off angle ions comprises locating at least one ion detector at a trajectory off of the target substrate. 3. The method according to claim 2, wherein locating at least one ion detector at a trajectory off of the target substrate comprises locating at least one ion detector on an outside trajectory of a corrector magnet. 4. The method according to claim 2, wherein locating at least one ion detector at a trajectory off of the target substrate comprises locating at least one ion detector on an inside trajectory of a corrector magnet. 5. The method according to claim 2, wherein locating at least one ion detector at a trajectory off of the target substrate comprises locating at least one ion detector at a trajectory based at least in part on the primary charge state of the ion beam. 6. The method according to claim 2, wherein locating at least one ion detector at a trajectory off of the target substrate comprises rotating at least one ion detector through a range of trajectories and determining a location of contamination based on a trajectory having the highest detected beam current. 7. The method according to claim 1, wherein interlocking ion implantation comprises pausing implantation with the ion beam off of the target substrate until a condition contributing to the off angle ions is mitigated. 8. The method according to claim 1, wherein interlocking ion implantation comprises generating an alert on a user interface integral to the ion implantation system. 9. The method according to claim 8, wherein generating an alert comprises determining, based on a pattern of the detected off angle ions, a contamination location and outputting the location via the interface. 10. A method of detecting ion beam contamination in an ion implantation system comprising:detecting ions on trajectories off of a target substrate with at least one ion detector;determining a level of ion beam charge contamination based on a concentration of the detected ions; andinterlocking ion implantation when the level of ion beam charge contamination exceeds a predetermined threshold. 11. The method according to claim 10, wherein interlocking ion implantation comprises pausing ion implantation by scanning the ion beam off of the target substrate until a condition causing the ion beam charge contamination has been mitigated. 12. The method according to claim 10, wherein interlocking ion implantation comprises generating an alert on an interface integral to the ion implantation system. 13. The method according to claim 12, wherein interlocking ion implantation comprises determining, based in part on the detected ions, a location of the ion beam charge contamination, and outputting the location via the interface. 14. The method according to claim 10, wherein determining a level of ion beam charge contamination based on a concentration of the detected ions comprises locating at least one ion detector at a trajectory off of the target substrate and measuring a ratio of off-target ion beam current to primary beam current. 15. The method according to claim 14, wherein locating at least one ion detector at a trajectory off of the target substrate comprises locating at least one ion detector on an outside trajectory of a corrector magnet of the ion implantation system. 16. The method according to claim 14, wherein locating at least one ion detector at a trajectory off of the target substrate comprises locating at least one ion detector on an inside trajectory of a corrector magnet of the ion implantation system. 17. The method according to claim 14, wherein locating at least one ion detector at a trajectory off of the target substrate comprises rotating at least one ion detector through a range of trajectories and determining a location of ion beam charge contamination based on a trajectory having a highest ion beam current. 18. An ion implantation interlock system comprising:an ion beam scanner for scanning an ion beam across a target substrate;at least one ion detector located at an end station and positioned along an ion trajectory off of a trajectory of the ion beam; anda control program stored in a computer readable storage device in electrical communication with the at least one ion detector that, based on out-trajectory ions detected by the at least one ion detector, determines a level of ion beam contamination, and interlocks ion implantation when the level of ion beam contamination exceeds a predetermined threshold. 19. The system according to claim 18, wherein interlocking ion implantation comprises pausing ion implantation with the ion beam off of the target substrate until a condition causing the ion beam contamination has been mitigated. 20. The system according to claim 18, wherein interlocking ion implantation comprises generating an alert on an interface in electrical communication with the control program. 21. The system according to claim 20, wherein interlocking ion implantation comprises determining, based at least in part on a pattern of the off trajectory ions and a charge state of the ion beam, a source of the ion beam contamination and providing information identifying the source via the interface. |
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053234316 | claims | 1. A device for removably securing a reactor vessel washer to a reactor vessel stud and operable for use with a reactor vessel including a dome having a first flange positioned abutting a second flange of a reactor body, a plurality of reactor studs disposed in both the first and second flanges; and a nut and washer, both having an inner peripheral surface, sued for tightening the studs and for attaching the dome to the body, the device comprising a retainer including a first wedge having a tapered body which wraps circumferentially and partially around a shaft of the stud, and at least a portion of the tapered body is disposed between the washer inner peripheral surface and the stud for maintaining the positional relationship between the washer and the stud. 2. The device as in claim 1 wherein said retainer includes: a generally U shaped strap having a pair of end portions and arranged to extend circumferentially around a portion of the stud; said first wedge having a tapered body and a portion of the wedge body disposed at least partially between the washer and stud for maintaining the positional relationship of the washer and the stud; a second wedge having a tapered body and a portion of the wedge body disposed at least partially between the washer and stud for maintaining the positional relationship of the washer and the stud. a first clamp having a generally semi-circular shape and disposed on the stud and abutting a first surface of the washer; and a second clamp having a generally semi-circular shape and disposed on the stud and abutting a second surface of the washer. (a) a generally U shaped strap having first and second ends and disposed circumferentially around a portion of the stud; and (b) first and second wedges each having a tapered body and secured to said first and second ends, at least a portion of each of said first and second wedges disposed at least partially between the washer and stud for maintaining the positional relationship of the stud and washer. 3. The device as in claim 2 wherein said wedge is nylon. 4. A device for removably securing a reactor vessel washer to a reactor vessel stud and operable for use with a reactor vessel including a dome having a first flange positioned abutting a second flange of a reactor body, a plurality of reactor studs disposed in both the first and second flanges, and a nut and washer, both having an inner peripheral surface, used for tightening the studs and for attaching the dome to the body, the device comprising: 5. A device for removably securing a reactor vessel washer to a reactor vessel stud; the reactor vessel includes a dome having a first flange positioned abutting a second flange of a reactor body, a plurality of reactor studs are disposed in both the first and second flanges for attaching the dome to the body, and a nut and washer are used for tightening the studs, the device comprises: 6. The device as in claim 5 wherein said washer has an inner peripheral surface and at least a portion of the tapered body of each of said wedges is adapted to urge between the inner peripheral surface and the stud. 7. The device as in claim 6 wherein said wedges are nylon. |
description | This application is a divisional of U.S. application Ser. No. 12/542,926, filed Aug. 18, 2009, which claims priority under 35 U.S.C. §119 to German Patent Application DE 10 2008 045 336.6, filed Sep. 1, 2008, which is hereby incorporated by reference in its entirety. The disclosure relates to a processing system that can provide multiple energy beams for modifying and/or inspecting an object. The multiple energy beams may include a laser beam and a particle beam, such as an electron beam or an ion beam. In the manufacture of miniaturized devices there exists a desire to modify an object by removing material from the object or by depositing material on the object. Conventional systems used for modifying the object include a microscope for inspecting the object to monitor a process of the modification. An example of such conventional system is an electron microscope, in which an electron beam generated by the electron microscope is used for inspecting the object and also for activating a processing gas modifying the object. Another example of a conventional processing system includes an electron microscope to generate an electron beam and an ion beam column to generate an ion beam, where the electron beam and the ion beam can be directed to a same location of an object to be modified. Here, the ion beam can be used to modify the object, and the electron beam can be used to monitor the progress of such sample modification. A process gas can be supplied to the object to modify the object by an interaction with the process gas which is activated by the electron beam and/or the ion beam. The conventional system using a particle beam, such as an electron beam or an ion beam, for modification of the object has an advantage in that the processing of the object can be performed with a relatively high accuracy. A disadvantage of such system is that the modification of the object can be slow and that a high processing time can be involved if a larger amounts of materials are to be removed from or deposited on the object. Other known processing systems use a laser beam to remove material from an object. The removal rate, i.e. an amount of material removed per unit time, of the laser system is typically greater than that of a charged particle beam system. However, the accuracy of the modification of the object employing the laser system is typically much lower than the accuracy achievable with a particle beam system. In some embodiments, the disclosure provides a processing system that directs multiple energy beams toward an object to perform process the object (e.g., modify of the object, inspect the object). In some embodiments, a processing system includes a particle beam column to generate a particle beam directed to a first processing location, and a laser system to generate a laser beam directed to a second processing location. In certain embodiments, the particle beam column may include an electron beam column or an ion beam column, where the particle beam column can also be configured to operate as a particle beam microscope by including a secondary particle detector. The secondary particle detector may include an electron detector or an ion detector. In some embodiments, the first processing location substantially coincides with the second processing location such that the object can be moved to the a location and can be processed at that location by both the laser beam and the particle beam without having to move the object for subsequent laser beam and particle beam processing. In certain embodiments, the first processing location onto which the particle beam is directed is spaced apart from the second processing location onto which the laser beam is directed. The spaced apart processing locations can have an advantage if particles or other contaminations are generated by the laser beam, because the spacing can considerably reduce the deposition of such particles or other contaminants on components of the particle beam column as compared to situations where the first and second processing locations coincide. In certain embodiments, the processing system includes a protector for protecting components of the particle beam column from particles or other contaminations produced during a processing with the laser beam. It is possible that a considerable amount of particles and other contaminations is released from the object during a laser processing and that such particles and contaminations can deposit on sensitive components of the particle beam system. Exemplary sensitive components of the particle beam system include electrodes and apertures of the particle beam column. Deposition on such components of the particle beam column may result in a deterioration of a performance of the particle beam column. For example, focussing of the particle beam may be deteriorated or imaging quality of the particle beam column may be deteriorated. In some embodiments, the protector includes a plate and an actuator configured to move the plate back and forth between a first position in which the components of the particle beam system are protected from particles and contaminations released during the laser processing, and a second position particle in which the components of the particle beam system are not protected from the particles and contaminations released during the laser processing. In certain embodiments, the protector is configured such that, in its first position, particles and other contaminations generated by the laser beam are prevented from hitting sensitive components of the particle beam column, while processing of the object using the particle beam is prevented by the plate. In the second position, the plate is in a retracted position in which processing or inspection of the object using the particle beam column is possible. In some embodiments, the protector includes a door separating a first vacuum space in which the first processing location is located from second vacuum space in which the second processing location is located. The door may provide a shutter which closes an opening between the two vacuum spaces, where the shutter may allow, in its closed position, to maintain a pressure difference between the first and second vacuum spaces. For this purpose, each of the first and second vacuum spaces may include separate vacuum ports connection to vacuum pumps. In embodiments where the first processing location is spaced apart from the second processing location, in general, the object has to be moved between the two processing locations to allow processing by both the laser beam and particle beam. In some embodiments, the object is mounted on an object mount of a stage, where the stage includes at least one actuator to displace the object mount relative to the base. It is then possible to position the stage relative to the particle beam column and control the at least one actuator such that plural different locations of the object are located at the first processing location of the particle beam, without moving the base of the stage relative to the particle beam column. The base of the stage can be maintained at a fixed position on a suitable support, for example. In certain embodiments, the processing system includes a transport device configured to move the stage back and forth between first and second predetermined positions. If the stage is positioned in the first position, the object mounted on the stage is located close to the first processing location to be processed by the particle beam, and if the stage is positioned in its second position, the object mounted on the stage is positioned close to the second processing location to be processed by the laser beam. In such configuration, the object can be moved back and forth between the first and second processing locations without removing the object from the object mount of the stage. According to exemplary embodiments, the transport device includes an actuator performing a translation of the stage from the first position to the second position. The transport device may include a carrier, such as a rail, to support the stage during translation between the first and second positions. In some embodiments, in which the first and second processing locations are spaced apart from each other, the transport device includes a gripper configured to grip the object for movement between a first stage and a second stage, where the first stage mounts the object for processing by the particle beam, and the second stage is configured to mount the object for processing by the laser beam. In some embodiments, the transport device for moving the object between the first and second processing locations includes an actuator for performing the movement. The actuator can include a rod traversing a wall of the vacuum vessel, where a sealing between the vacuum vessel and the rod is arranged such that a distance between the sealing and the first processing location is greater than a distance between the sealing and the second processing location. In the exemplary embodiments described below, components that are alike in function and structure are generally designated by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the description of other embodiments and the summary may be referred to. FIG. 1 is a schematic front view of a portion of a processing system 1 and illustrates a functionality of an object mount 3 which can be used in some embodiments of the processing system to mount an object 5 in front of a particle beam column 7. The particle beam column 7 is, in the illustrated example, an electron beam column for generating an electron beam 11 directed towards a processing location 9. The object mount 3 is configured to hold the object 5 such that a surface thereof is located at the processing location 9 and such that the object can be displaced in a x-direction, in a y-direction, a z-direction and such that the object can be tilted about an axis 13 oriented parallel to the y-direction, where the axis 13 is located close to the processing location 9 or intersects the processing location 9. The object 5 is mounted on and fixed to an object mount 15 of a stage 17. The object 5 can be abutted against an end stop on the object mount 15, and can be adhered to the object mount or fixed to the object mount 15 by a clamp and/or another suitable mechanism. The stage 17 includes a base 19 and an intermediate component 21 which can be displaced by an actuator 18, such as a motor, in the y-direction as indicated by an arrow 23. The object mount can be displaced relative to the intermediate component 21 in the x-direction by operating a further actuator 20 as this is schematically indicated by an arrow 25 in FIG. 2. The base 19 rests on a bracket 27 which is articulated to a base 29 of the object mount 3 such that the base 19 can be pivoted about the axis 13. The option of pivoting the object 5 about the axis 13 is indicated by an arrow 24 in FIG. 2. The stage 17 may further include an additional intermediate component mounted between the intermediate component 21 and the base 15 to displace the object 5 relative to the base 29 in the z-direction, such that the object mounted on the object mount can be displaced relative to the base of the object mount in three independent directions. FIG. 4 is a schematic illustration of the processing system 1, in which the base 29 illustrated with reference to FIG. 1 above is not shown in FIG. 4. The processing system 1 includes two particle beam columns which include the electron beam column 7 for generating the electron beam 11 directed to the processing location 9, and an ion beam column 41 for generating an ion beam 43 which is also directed to the processing location 9. The electron beam column 7 includes an electron source 45 having a cathode 47, an electrode system 49, a condenser lens system 51 for generating the beam 11. The electron beam 11 traverses a secondary electron detector 53 and an objective lens 54 for focussing the electron beam 11 at the processing location 9. Beam deflectors 55 are provided for varying the position onto which the electron beam 11 is incident on the object 5. The deflectors 55 can be used to scan the electron beam 11 across a surface of the object 5. Secondary electrons generated during such scanning can be detected with the detector 53 to generate an electron microscopic image of the object 5 in the scanned region at the processing location 9. Additional secondary particle detectors, such as an electron detector 57 or an ion detector can be located adjacent to the electron beam column 7 close to the processing location 9 and within a vacuum chamber 59 to also detect secondary particles. The ion beam column 41 includes an ion source 61 and electrodes 63 for shaping and accelerating an ion beam 43. Beam deflectors 65 and focussing coils or focussing electrodes 67 are provided to focus the ion beam 43 at the processing location 9 and to scan the ion beam 43 across a region of be object 5. A gas supply system 69 includes a reservoir 71 for a processing gas which can be selectively supplied via a conduit 73 ending close to the processing location 9 by operating a valve 75. The processing gas can be activated by the ion beam or the electron beam to selectively remove material from the object 5 or to selectively deposit material on the object 5. Such processing can be monitored using the electron microscope 7. A removal of material from the object 5 can be also achieved by directing the ion beam onto the object without supplying of a processing gas. The vacuum chamber 59 is defined by a vacuum vessel 79 which can be evacuated by a vacuum pump connected to the vessel at a pumping port 81 and which can be vented via a venting port 83. The electron beam column includes a vacuum vessel 84 having a small aperture traversed by the electron beam 11 and separating upper and lower vacuum spaces wherein the electron source is located in the upper vacuum space which is separately pumped via a pumping port 85, such that the electron source 45 can be permanently maintained under high vacuum conditions even when the processing gas is supplied to the processing location 9. Background information about systems using plural particle beams for processing of an object can be obtained, for example, from US 2005/0184251 A1, U.S. Pat. No. 6,855,938 and U.S. patent application Ser. No. 12/448,229, wherein the full disclosure of these documents is incorporated by reference herein. The processing system 1 further includes a laser system 91 which is configured to direct a laser beam 93 to a second processing location 95. For this purpose, the laser system 91 includes a laser 97 and collimation optics 99 to shape the laser beam 93. The laser beam is directed via one or more mirrors 101 or via a light guide to a location close to the vacuum chamber 97 where it is incident on a mirror 103 which directs the beam towards the second processing location 95 and which is pivotable as indicated by arrow 105 such that the beam 93 can be scanned across a object disposed at the processing location 95. The laser beam 93 enters the vacuum space 109 by traversing a window 107. The vacuum space 109 is also defined by the vacuum chamber 79 and can be separated from the vacuum space 59 by closing a door 111. The door 111 includes a shutter plate 113 which is indicated in FIG. 4 by continuous lines in an open position and in broken lines when it is positioned in a closing position. An actuating rod of the door is used to displace the shutter plate 113 from its open position to its closed position. The door 111 can be adapted such that it is, in its closed position, vacuum tight by providing a suitable sealing 112 between the shutter plate 113 and the vacuum vessel 97. It is then possible to maintain different vacuum pressures in the vacuum spaces 59 and 109 if the door is in its closed position. The vacuum space 109 can be separately evacuated via a vacuum port 115 and vented via a venting port 116. The object 5 can be moved back and forth between the processing location 9 and the processing location 95 by operating the transport system 121. The transport system 121 includes a rod 123 traversing a vacuum seal 125 to extend into the vacuum space 109. The vacuum seal 125 is located at a distance from the processing location 95 which is smaller than a distance between the vacuum seal 125 and the processing location 9. A connector 127 is provided at an end of the rod 123 wherein the connector 127 is configured to be mechanically connected to the base 19 of the stage 17. The connector can be further configured to provide an electrical connection to the stage to control the actuators of the stage in order to displace the object 5 relative to the base of the stage in the at least two or three independent directions. Electrical signals for controlling the actuators con me supplied via wires 126 extending from a controller 128 located outside of the vacuum vessel 79 through an interior of the rod 123 to the connector 127. Sensors, such as one ore more position sensors, can be provided on the stage 17 to measure a current position of the object mount 15 relative to the base 19 of the stage, such that the controller 128 can perform the control of the actuators based on the signals provided by the sensors supplied to the controller via the connector 127 and wires 126 extending through the rod 123. In the situation shown in FIG. 4, the stage 17 is located such that the object 5 is located at the processing location 9 such that it can be inspected or modified by the electron beam 11 or the ion beam 43. The stage 17 is shown in broken lines in FIG. 4 in a position such that the object 5 is located at the processing location 95 for processing by the laser beam 93. The transport system 21 can move the stage 17, together with the object 5 mounted thereon, back and forth between these two positions. For this purpose, the transport system 121 includes a rail or supporting bar 131 to support the stage 17 against gravity during its transport movement between the processing locations. When the stage is positioned at the processing location 9, the stage is carried by the bracket 27 of the object mount 3 as illustrated above. As shown in FIG. 4, a space 133 is provided between the support bar 131 to allow tilting of the bracket 27 about axis 13 without interference with the support bar 131 after the bar 123 is released from the connector 127 and sufficiently retracted. It is however possible to pull the base 19 of the stage 17 across the distance 133 onto the supporting bar 131. The supporting bar 131 further includes a further space 135 which is traversed by the shutter plate 113 when the door 111 is in its closed position. The door 111 can be closed when the transport system 123 has pulled the stage 17 to the position at the processing location 95, or if the stage is pushed to the position at the processing location 9 and the rod 123 is released from the connector 127 and completely drawn back into the vacuum space 109. The object 5 is processed with the laser beam 93 at the processing location 95, wherein particles or contaminations evaporating from or released from the object will deteriorate the vacuum conditions in vacuum space 109. It is possible to close the door 11 to separate the vacuum space 59 from the vacuum space 109 to prevent a deterioration of the vacuum in the vacuum space 59. It is in particular possible to prevent contamination of the vacuum space 59 and contamination of components of the particle beam columns 7 and 41. Processing of the object 5 with the laser beam 93 is monitored using an end point detector 141 which may include, for example, a light source 143 for generating a measuring light beam 144 and a light detector 45. The measuring light beam 144 is directed towards the processing location 95 and enters the vacuum space 109 by traversing the window 146. The light detector 145 receives emerging light 147 originating from processing location 95 through a window 148. The light received by the detector 145 can be analysed to determine a processing condition of the object 5, and the processing of the object 5 by the laser beam 93 can be terminated based on such determination. After the processing by the laser beam 43 is terminated, the door 111 is opened and the transport system 121 moves the object 5 together with the stage to the processing location 9. A further processing of the object 5 can be performed at the processing location 9 by operating the ion beam 43 or electron beam 11, and the object 5 can also be imaged by the electron microscope 7. A positioning of the stage 17 on the bracket 27 can be performed with a high accuracy. For example, an end stop 22 can be used to precisely position the stage on the bracket 27 wherein the transport system 121 abuts the base of the stage 17 against the end stop 22 before releasing the connector 127. It is also possible to precisely position the stage on the bracket 17 by using micro switches or proximity sensors and by operating the transport system 121 until such sensors provide a desired measuring signal. FIG. 3 shows an exemplary embodiment in which an optical distance measuring system 151 is used for positioning a stage 17a relative to a support 27a. The optical distance measuring system 151 emits a light beam 152 reflected from a mirror 153 mounted on a base 19a of the stage 17a. The light reflected from the mirror is analysed for determining a distance between the base 19a and the measuring system 151. The transport system 121 is operated until the measured distance equals a desired distance to a sufficient accuracy. FIG. 5 shows a further embodiment of a processing system 1b which has a configuration similar to the configuration of the processing system illustrated with reference to FIG. 4 above. The processing system 1b differs from the processing system illustrated above in that a transport system 121 for displacing an object 5b back and forth between a processing location 9b for processing by particle beams 11b and 43b, and a processing location 95b for processing by a laser beam 93b. The processing system includes a rod 123b and a gripper 127b attached to an end of the rod 123b for gripping the object 5b. The object is moved between the processing locations 9b and 95b without moving a stage 17b. The stage 17b remains at its position relative to the processing location 9b and is used to correctly position and orient the object 5b relative to the particle beams 11b and 43b. A separate stage 18b is provided at the processing location 95b. The gripper 127b can place the object 5b on the stage 18b. The stage 18b may have a configuration which is less complicated than a configuration of the stage 17b. For example, it might be unnecessary to tilt the object about an axis or it may be unnecessary to move the object in three independent directions since the laser beam 93b can be scanned by a pivotable mirror 103b across a region of the object 5b which is larger than a region across the electron beam 11b or the ion beam 43b can be scanned. It may be also unnecessary to provide positional movements in a z-direction, since the collimating optic 99b can be moved in z-direction for changing the focus of the laser beam in z-direction. FIG. 6 is a schematic illustration of a further embodiment of a processing system 1c having a configuration similar to a configuration of the processing systems illustrated with reference to FIGS. 4 and 5 above. The processing system 1c differs from the processing systems illustrated above in that a processing location 9c for processing an object 5c using a particle beam substantially coincides with a processing location 95c for processing the object 5c using a laser beam 93c. The processing locations 9c and 95c are located in a common vacuum space 59c. The processing system 1c does not include a transport system for moving the object between different processing locations. However, the processing system 1c includes a protection system 161 including a cup-shaped protector 163 partially enclosing components of a particle beam column 7c when the protection system is in a protecting position as shown in FIG. 6. The protection system 161 further includes a cup-shaped protector 165 partially enclosing components of an ion beam column 41c when the protection system is in the protection position. The protectors 163 and 165 protect components of the electron beam column 7c and the ion beam column 41c during processing of the object 5c with the laser beam 93c. After termination of the processing by the laser beam 93c, the protectors 163 and 165 which are mounted on a rod 167 can be retracted into a retracted position in which they do not interfere with a processing of the object 5c with the electron beam 11c or the ion beam 43c. The rod 167 may traverse a vacuum vessel 79b defining the vacuum space 59b by traversing a suitable sealing 169. The rod 167 can be operated by an actuator, such as a motor, or by hand, for displacing the protectors 163, 165 between the protecting position and the retracted position. Protectors and those illustrated above can also be used to protect particle detectors disposed in the vacuum space 59b close to the object 5b while performing the processing with the laser beam. In the embodiments illustrated above, an electron beam column and an ion beam column are provided. It is, however, also possible to provide only one particle beam column, such as the electron beam column or the ion beam column, wherein the single particle beam column is integrated in a processing system together with a laser system for processing the object. In the embodiments illustrated with reference to FIGS. 4 and 5 above, the processing location for processing using at least one particle beam is located at a relatively large distance from a processing location for processing by a laser beam. Moreover, a door is provided for separating the corresponding vacuum spaces from each other. It is, however, also possible to merely provide a protector between the processing location for laser processing and the processing position for particle beam processing, wherein the protector intercepts particles released during the laser beam processing. The protector can be formed as a plate which is attached to a rod or other suitable tool for displacing the protector. In some of these embodiments it may be unnecessary to provide the protector with a function of a vacuum tight shutter such that the two processing locations can be located in a same vacuum space. However, it is also possible to separate the corresponding vacuum spaces by a vacuum lock including more than one shutter such that the object is placed in a space between two closed shutters when it is transferred from one processing position to the other. The above illustrated embodiments, the laser processing system generates a laser beam which traverses a window in a vacuum vessel to enter the vacuum space, wherein a raster device, such as a pivotable mirror (103) is located outside of the vacuum space. It is, however, also possible to direct the laser beam into the interior of the vacuum space by another mechanism, such as a light guide, and it is also possible to have the collimation optics located within the vacuum space. In the above illustrated embodiments, an end point detector for determining a termination of the laser processing includes a light source for generating a measuring beam and a detector. According to other embodiments, it is possible to determinate the processing by the laser beam based on other principles. For example, light generated by the processing laser beam and reflected from the object can be detected to monitor the laser processing. It is further possible to detect a light generated by a laser induced plasma generated during the operation of the processing laser. It is further possible to provide a plasma source for generating a plasma close to the process object, wherein material removed from the object experiences charge carrier recombinations which generate characteristic light which is indicated of the type of material currently processed. A determination for terminating the laser processing can be based on detection of such characteristic light. |
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description | The present invention relates generally to ion implantation, and particularly to systems and methods for identifying beam energy. Ion implantation is a physical process, as opposed to diffusion, which is a chemical process that is employed in semiconductor apparatus fabrication to selectively implant dopant into a semiconductor workpiece and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and the semiconductor material. For ion implantation, dopant atoms/molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a workpiece or wafer. The dopant ions physically bombard the workpiece, enter the surface and typically come to rest below the workpiece surface in the crystalline lattice structure thereof. In RF based accelerators, ions are repeatedly accelerated through multiple RF voltage driven acceleration gaps. Due to the time varying nature of RF acceleration fields and the multiple numbers of acceleration gaps (usually greater than 20) there are a large number of parameters which influence the final beam energy. Although it may not be technically impossible, “set and forget” techniques can not be used in setting up the final beam energy and fine adjustments have to be performed on the parameters to maximize beam transmission through a filter with known passband. An energy filter is used not only as a simple filter to reject unwanted portions of the energy spectrum, but also and more importantly as an energy standard to which all the acceleration parameters are tuned. In this sense, the energy filter plays the ultimate role in determining the final beam energy. However, quite often the design of the energy filter has to be compromised, mostly because of space restrictions or some other imposed conditions limiting proper functioning and as a result, precision in the final beam energy is uncertain. There have been several attempts to develop an independent measurement system of beam energy, but no particular method has been incorporated into production machines. Accordingly, suitable systems or methods for identifying beam energy are desired, that accurately measures the final beam energy. The following presents a simplified summary of the invention in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention according to one or more embodiments creates a beam energy identification system utilizing a beam scanner which scans an accelerated ion beam at a frequency to create a wide uniform ion beam in one direction for uniform ion implantation on a workpiece, or a semiconductor wafer. One embodiment of this invention comprises two narrow Faraday cups placed at a distance downstream of scanner and a difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two narrow Faraday cups is used to calculate the energy of ion beam. According to yet another aspect of the invention, two narrow Faraday cups are placed downstream of a scanner after going through a beam parallelizing lens (e.g., an electromagnetic lens, called an angle corrector magnet) to parallelize the fanning-out beam exiting the scanner. Again, a measured difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two Faraday cups is used to calculate the energy of the ion beam. To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. It will be appreciated by those skilled in the art that the invention is not limited to the exemplary implementations and aspects illustrated and described hereinafter. For the sake of providing a clear description of the invention, the systems and the methods will be described in connection with scanned pencil ion beam implantation. However, it is to be expressly understood that these descriptions are not intended to be self-limiting in any manner Referring now to the figures, in accordance with one exemplary aspect of the present invention, FIG. 1 illustrates a typical hybrid parallel scan single wafer ion implantation system 100. The implantation system 100 is also a type referred to as a post acceleration implanter, since a main accelerator 113 is placed after a mass analyzer 104 and before an energy filter 130. Most ion implanters of this type have the energy filter 130 after the accelerator 113 to remove unwanted energy spectrum in the output of accelerator 113. The filtered ion beam goes through a beam scanner 119 and then through an angle corrector lens 120 to convert the fanned-out beam 111 into a parallel shifted ion beam 115. A workpiece and/or substrate 134 is moved orthogonal (shown as moving in and out of the paper) to the ion beam 115 in the hybrid scan scheme to irradiate the entire surface of the workpiece 134 uniformly. As stated above, various aspects of the present invention may be implemented in association with any type of ion implantation system, including, but not limited to the exemplary system 100 of FIG. 1. The exemplary hybrid parallel scan single wafer ion implantation system 100 comprises a source chamber assembly 112 which includes an ion source 102 and an extraction electrode assembly 121 to extract and accelerate ions to an intermediate energy. A mass analyzer 104 removes unwanted ion mass species; the accelerator assembly 113 accelerates the ions to a final energy. The beam scanner 119 scans a pencil beam exiting from the accelerator assembly 113 back and forth at a fast frequency into the angle corrector lens 120 to convert the fanning out scanned beam 111 from the beam scanner 119 to the parallel shifted beam 115 and the workpiece 134 which is housed in a process chamber. The accelerator assembly 113, for example, can be RF linear particle accelerator (LINAC) in which ions are accelerated repeatedly by an RF field, or a DC accelerator, for example, a tandem electrostatic accelerator, which accelerates ions with a stationary DC high voltage. The beam scanner 119, either electrostatically or electromagnetically scans the ion beam 110 left to right into the angle corrector lens 120, which converts the fanning-out beam 111 into the parallel shifted ion beam 115. The angle corrector lens 120 is most likely to be an electromagnetic magnet as shown, but there is also an electrostatic version, for example. The final parallel shifted ion beam 115 out of the angle corrector lens 120 is directed onto the workpiece 134. FIG. 2 illustrates a beam energy identification system 200 utilized in an exemplary hybrid parallel scan single wafer ion implantation system 100 (e.g., FIG. 1), wherein a stationary pencil ion beam 202 is scanned with an electrostatic beam scanner 204 in one axis, the fast scan axis (usually greater than 100 Hz), a fanned out beam 211 can be converted to a parallel shifted beam 215 by an angle corrector lens 220, typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece 234 is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system 100 the electrostatic beam scanner 204 is most often positioned after the ion beam 202 acquires full acceleration energy. The beam scanner 204 can be either electrostatic or electromagnetic, but for simplicity of discussion, it is assumed that the scanner 204 is an electrostatic scanner. For an electromagnetic scanner, the mathematical relationship is slightly more complex than for the electrostatic scanner 204 and it requires knowing the mass of the ions. For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam 202 by the electrostatic scanner 204 is a linear function of scan voltage (for an electrostatic scanner) and the inverse of beam energy. The calculation for a deflection angle (Δθ1S) is shown below as Equation 1. In this embodiment of the present invention the angle corrector magnet 220 is deactivated which allows the deflected beam 211, deflected by the scanner to pass through the angle corrector magnet 220 without deflection.Δθ1S=(K1S)(ΔV1S)/(E/q) (electrostatic equation) (Eq. 1) wherein: Δθ1S is a change of deflection angle K1S is a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner voltage (V1S) ΔV1S is the change in electrostatic scanner voltage E is the beam energy q is the charge value of the ions Rearranging the terms described above can be done to determine the beam energy (E), shown below as Equation 2:E=(Δθ1S)(q)/((K1S)(ΔV1S)) (electrostatic equation) (Eq. 2) Now referring to an electromagnetic scanner 215 (as opposed to an electrostatic scanner 204) the change of beam deflection angle (Δθ1M) is shown below as Equation 3. In this embodiment of the present invention the angle corrector magnet 220 is deactivated which allows the scanner deflected beam 211 to pass through the angle corrector magnet 220 without deflection.Δθ1M=(K1M)(q)(ΔB1M)/(sqrt(Em)) (electromag. eq.) (Eq. 3) wherein: Δθ1M is the change of beam deflection angle; K1M is constant (of the 1st order) throughout the ranges of the beam energy (E) and a magnetic field in the electromagnetic scanner; ΔB1M is the change in the electromagnetic scanner magnetic field; E is the beam energy; q is the charge value of the ions; and m is the mass of ions. Rearranging terms to determine the beam energy (E) is shown below as Equation 4:E=(K1MΔB1Mq Δθ1M)2/m (electromag. eq.) (Eq. 4) Yet another embodiment of the present invention is an ion beam energy identification system 300; depicted in FIG. 3 that can also be used in a hybrid scan single wafer ion implantation system 100. In this kind of system a beam scanner is most often situated after the ion beam 302 acquires full acceleration energy. The primary angle of deflection of the ion beam 202 by the scanner 204 is a linear function shown as Equation 5 that adds an additional correction factor f1M. The system 300 can be utilized in an exemplary hybrid parallel scan single wafer ion implantation system 100 (e.g., FIG. 1), wherein a stationary pencil ion beam 302 is scanned (usually at a frequency greater than 100 Hz) with an electrostatic beam scanner 304 in one axis. In the fast scan axis, a fanned out beam 311 is converted to a parallel shifted beam 315 by activating an angle corrector lens 320, typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece 334 is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system the beam scanner 304 is most often positioned after the ion beam 302 acquires full acceleration energy. The beam scanner 304 can be either electrostatic or electromagnetic, but for simplicity of discussion, it is first assumed that the scanner 304 is an electrostatic scanner. For an electromagnetic scanner as discussed supra, the mathematical relationship is slightly more complex than for an electrostatic scanner and it requires knowing the mass of the ions. For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam 302 by the electrostatic scanner 304 is a linear function of scan voltage (for an electrostatic scanner) and the inverse of the ion beam energy. The calculation for the shift of beam position (Δθ2S) is shown below as Equation 5. In this embodiment of the present invention the angle corrector magnet 220 is activated which allows the fanned out beam 211 to be converted into a parallel ion beam 315 as illustrated in FIG. 3.Δθ2S=(f2S)(k2S)(ΔV2S)/(E/q) (Eq. 5) wherein: Δθ2S is the shift of beam position; f2S is a correction factor to account for effect of corrector magnet; K2S is approximately constant throughout ranges of the beam energy and electrostatic scanner voltage; ΔV2S the change in electrostatic scanner voltage; E the beam energy; and q is the charge value of the ions. Rearranging terms:E=(Δθ2S)(q)/((f2S)(k2S)(ΔV2S)) (Eq. 6) Now referring to another embodiment of the present invention is an electromagnetic scanner 315 (as opposed to the electrostatic scanner 204) the shift of beam position (Δθ2M) is shown below as Equation 7. In this embodiment of the present invention the angle corrector magnet 320 is activated which allows the deflected beam by the scanner 311 to pass through the angle corrector magnet 320 and to be deflected into a parallel ion beam 315.Δθ2M=(f2M)(k2M)q(ΔB2M)/sqrt(Em) (Eq. 7) wherein: Δθ2M is the shift of beam position; f2M is a correction factor to account for effect of corrector magnet; K2M is approximately constant throughout ranges of the beam energy and electromagnetic scanner current; ΔB2M the change in magnetic field in the electromagnetic scanner; E the beam energy; m is the mass of ions; and q is the charge value of the ions. Rearranging terms:E=(qK2Mf2MΔB2MΔθ2M)2/m (Eq. 8) FIG. 4 illustrates an exemplary method of beam energy identification 400 that will be described in detail with respect to FIG. 2. Although the methodology 400 is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. The method 400 begins at 404 with generating an ion beam 202 and scanning the ion beam 202 in a fast scan axis with an ion beam scanner 204 (e.g., FIG. 2), for example. The ion beam 202 (FIG. 2) is extracted at 404 and scanned at a frequency of greater than 100 Hz. The ion beam 202 in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner 204 can be an electrostatic ion beam scanner 215 (FIG. 2) or an electromagnetic ion beam scanner 217. Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a deflected ion beam 211 (FIG. 2) and thus ascertain the ion beam energy associated therewith. At 406 a first Faraday cup 216 is located to capture a first deflected ion beam peak 211a and a second Faraday cup 218 is located to capture a second deflected ion beam peak 211b. It is determined at 408 if the scanner is an electrostatic scanner 215 or an electromagnetic scanner 217. If the scanner is the electrostatic scanner 215 the voltage is varied to obtain peak of a first deflected ion beam 211a (FIG. 2) in the first Faraday cup 216 (FIG. 2) and a second deflected ion beam peak 211b (FIG. 2) in the second Faraday cup 218 (FIG. 2). An angle corrector magnet 220 (FIG. 2) is deactivated so that the deflected ion beam 211 by the scanner travels to the Faraday cups 216 and 218 un-deflected. The beam energy (E) is calculated at 414 (FIG. 4) utilizing the change in voltage. Referring to the equation derived previously as Eq. 2.E=(Δθ1S)(q)/((K1S)(ΔV1S)) (electrostatic equation) (Eq. 2) wherein: Δθ1S is an shift of beam angle; K1S is a constant (of the 1st order) throughout the ranges of beam energy (E1S) and scanner voltage (V1S); ΔV1S is the change in electrostatic scanner voltage; E is the beam energy; and q is the charge value of the ions. If it is determined at 408 that the scanner is the electromagnetic scanner 217 the current is varied to obtain the peak of a first deflected ion beam peak 211a (FIG. 2) in the first Faraday cup 216 (FIG. 2) and a second deflected ion beam peak 211b (FIG. 2) in the second Faraday cup 218 (FIG. 2). The angle corrector magnet 220 (FIG. 2) is deactivated so that the deflected ion beam 211 by the scanner travels to the cups 216 and 218 un-deflected. The beam energy (E) is calculated utilizing the change in magnetic field in the scanner at 414. Referring to the equation derived previously as Eq. 4.E=(K1MΔB1Mq Δθ1M)2/m (Eq. 4) wherein: Δθ1M is shift of beam angle; K1M is a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner current; ΔB1M is the change in the magnetic field in electromagnetic scanner; E is the beam energy m is the mass of ions; and q is the charge value of the ions. FIG. 5 illustrates yet another exemplary method for beam energy identification 500 that will be described in detail with respect to FIG. 3. Although the methodology 500 is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. The method 500 begins at 504 with generating an ion beam 302 and scanning the ion beam 302 in a fast scan axis with an ion beam scanner 304 (e.g., FIG. 3), for example. The ion beam 302 (FIG. 3) is extracted at 504 and scanned at a frequency of greater than 100 Hz. The ion beam 302 in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner 304 can be an electrostatic ion beam scanner 315 (FIG. 3) or an electromagnetic ion beam scanner 317. Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a parallel ion beamlets created from the parallel ion beam 315 (FIG. 3) and thus ascertain the ion beam energy associated therewith. At 506 a first faraday cup 322 is located to capture a first parallel ion beam peak 315a and a second faraday cup 324 is located to capture a second parallel ion beam peak 315b. It is determined at 508 if the scanner 304 is an electrostatic scanner 313 or an electromagnetic scanner 317. If the scanner 304 is an electrostatic scanner 313 the voltage is varied to obtain a first parallel ion beam peak 315a (FIG. 3) in the first Faraday cup 322 (FIG. 3) and a second parallel ion beam peak 315b (FIG. 3) in the second Faraday cup 324 (FIG. 3). An angle corrector magnet 320 (FIG. 3) is activated so that the parallel ion beam 315 travels to the cups 322 and 324. The ion beam energy (E) is calculated at 514 (FIG. 5) utilizing the change in scanner voltage. Referring to the equation derived previously as Eq. 6.E=(Δθ2S)(q)/((f2S)(k2S)(ΔV2S)) (electrostatic equation) (Eq. 6) wherein: Δθ2S is the second electrostatic shift of beam position; f2S is a correction factor to account for effect of corrector magnet; K2S is approximately constant throughout ranges of the second electrostatic beam energy 2 and electrostatic scanner voltage; ΔV2S the second change in electrostatic scanner voltage; E the beam energy; and q is the charge value of the ions. Wherein, the method 500 ends if the scanner was the electrostatic scanner 313. If it is determined at 508 that the scanner 304 (FIG. 3) is an electromagnetic scanner 317 the current is varied to obtain a parallel ion beam peak 315a (FIG. 3) in the first Faraday cup 322 (FIG. 3) and a second parallel ion beam peak 315b (FIG. 3) in the second Faraday cup 324 (FIG. 3). The angle corrector magnet 320 (FIG. 3) is activated so that the parallel ion beam 315 travels to the cups 322 and 324. The beam energy (E) is calculated utilizing the change in current at 514. Referring to the equation derived previously as Eq. 8.E=(K2MΔB2Mq Δθ2M)2/m (electromagnetic equation) (Eq. 8) wherein: Δθ2M is the shift of beam position; K2M is a constant (of the 1st order) throughout the ranges of a beam energy (E) and scanner current; ΔB2M is the change in a magnetic field of the electromagnetic scanner; E is a beam energy; and q is a charge value of the ions. Wherein, the method 500 ends if the scanner is an electromagnetic scanner 317. Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, apparatus, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” |
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059109718 | abstract | The current invention involves a means for the production and extraction of the isotope molybdenum-99 for medical purposes in a waste free, simple, and economical process. Mo-99 is generated in the uranyl sulphate nuclear fuel of a homogeneous solution nuclear reactor and extracted from the fuel by a solid polymer sorbent with a greater than 90% purity. The sorbent is composed of a composite ether of a maleic anhydride copolymer and .alpha.-benzoin-oxime. |
claims | 1. A beam control assembly to shape a ribbon beam of ions for ion implantation, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, the beam control assembly comprising:a first bar;a first coil disposed on the first bar, wherein the first coil is the only coil disposed on the first bar, wherein the first coil includes windings of electrical wire, and wherein the first coil is configured to move along the first bar to be located at different positions in the first dimension on the first bar;a second bar disposed opposite the first bar with a gap defined between the first bar and second bar, wherein the ribbon beam travels between the gap;a second coil disposed on the second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, and wherein the second coil is configured to move along the second bar to be located at different positions in the first dimension on the second bar;a first electrical power supply connected to the first coil without being electrically connected to any other coil; anda second electrical power supply connected to the second coil without being electrically connected to any other coil. 2. The beam control assembly of claim 1, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first bar is located at a first position in the second dimension and extends into the first dimension, wherein the second bar is located at the first position in the second dimension and extends into the first dimension. 3. The beam control assembly of claim 1, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first bar is located at a first position in the second dimension and extends into the first dimension, wherein the second bar is located at a second position in the second dimension and extends into the first dimension, and wherein the first and second positions are different. 4. The beam control assembly of claim 1, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first coil is fixed to a first position in the first dimension on the first bar, and wherein the second coil is fixed to the first position in the first dimension on the second bar. 5. The beam control assembly of claim 1, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first coil is fixed to a first position in the first dimension on the first bar, and wherein the second coil is fixed to a second position in the first dimension on the second bar, and wherein the first and second positions are different. 6. The beam control assembly of claim 1, further comprising:a third bar adjacent to the first bar;a third coil disposed on the third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire;a fourth bar adjacent to the second bar;a fourth coil disposed on the fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire;a third electrical power supply connected to the third coil without being electrically connected to any other coil; anda fourth electrical power supply connected to the fourth coil without being electrically connected to any other coil. 7. The beam control assembly of claim 6, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the third bar is located at a third position in the second dimension and extends into the first dimension, wherein the fourth bar is located at the third position in the second dimension and extends into the first dimension. 8. The beam control assembly of claim 6, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the third bar is located at a third position in the second dimension and extends into the first dimension, wherein the fourth bar is located at a fourth position in the second dimension and extends into the first dimension, and wherein the third and fourth positions are different. 9. The beam control assembly of claim 6, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the third coil is configured to move along the third bar to be located at different positions in the first dimension on the third bar, and wherein the fourth coil is configured to move along the fourth bar to be located at different positions in the first dimension on the fourth bar. 10. The beam control assembly of claim 6, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the third coil is fixed to a third position in the first dimension on the third bar, and wherein the fourth coil is fixed to the third position in the first dimension on the fourth bar. 11. The beam control assembly of claim 6, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the third coil is fixed to a third position in the first dimension on the third bar, and wherein the fourth coil is fixed to a fourth position in the first dimension on the fourth bar, and wherein the third and fourth positions are different. 12. The beam control assembly of claim 6, wherein the first, second, third, and fourth bars extend in the first dimension across the entire beam width. 13. The beam control assembly of claim 12, wherein the first, second, third and fourth bars extend from one side of the beam control assembly. 14. The beam control assembly of claim 6, wherein the first, second, third, and fourth bars extend in the first dimension across a portion of the beam width. 15. The beam control assembly of claim 14, wherein the first and second bars extend from one side of the beam control assembly, and wherein the third and fourth bars extend from an opposite side of the beam control assembly as the first and second bars. 16. The beam control assembly of claim 6, wherein a portion of the ribbon beam adjacent to the first coil overlaps with a portion of the ribbon beam adjacent to the third coil. 17. An ion implanter to implant ions using a ribbon beam of ions, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, comprising:an ion source;an accelerator configured to accelerate the ion disposed adjacent to the ion source;a beam control assembly disposed adjacent to the accelerator, the beam control assembly comprising:a first bar;a first coil disposed on the first bar, wherein the first coil is the only coil disposed on the first bar, wherein the first coil includes windings of electrical wire, and wherein the first coil is configured to move along the first bar to be located at different positions in the first dimension on the first bar;a second bar disposed opposite the first bar with a gap defined between the first bar and second bar, wherein the ribbon beam travels between the gap;a second coil disposed on the second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, and wherein the second coil is configured to move along the second bar to be located at different positions in the first dimension on the second bar;a first electrical power supply connected to the first coil without being electrically connected to any other coil; anda second electrical power supply connected to the second coil without being electrically connected to any other coil; anda target area disposed adjacent to the beam control assembly, the target area configured to position a work piece. 18. The ion implanter of claim 17, wherein the beam control assembly further comprises:a third bar adjacent to the first bar;a third coil disposed on the third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire;a fourth bar adjacent to the second bar;a fourth coil disposed on the fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire;a third electrical power supply connected to the third coil without being electrically connected to any other coil; anda fourth electrical power supply connected to the fourth coil without being electrically connected to any other coil. 19. A method of controlling a ribbon beam of ions, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, the method comprising:applying an electrical charge to a first coil using a first electrical power supply, wherein the first electrical power supply is connected to the first coil without being electrically connected to any other coil, wherein the first coil is disposed on a first bar, wherein the first coil is the only coil disposed on the first bar, and wherein the first coil includes windings of electrical wire; andapplying an electrical charge to a second coil using a second electrical power supply, wherein the second electrical power supply is connected to the second coil without being electrically connected to another other coil, wherein the second coil is disposed on a second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, wherein the second bar is disposed opposite the first bar with a gap defined between the first bar and second bar, and wherein the ribbon beam travels between the gap;moving the first coil along the first bar to be located at a different position in the first dimension on the first bar; andmoving the second coil along the second bar to be located at a different position in the first dimension on the second bar. |
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claims | 1. A movable device for submersibly cleaning surfaces placed in liquid in a nuclear power plant or repository for spent nuclear fuel, the movable device comprising:a pump comprising an outlet passage configured to connect with a flexible conduit;a nozzle connected to said pump and arranged to face surfaces to be cleaned, the pump creating a suction pressure at the nozzle;a first cleaning mechanism and a second cleaning mechanism, each cleaning mechanism configured to remove debris on the surfaces to be cleaned; andan adjustable flotation means configured to adjust a flotation capability of the movable device depending on a type of cleaning application;wherein the suction from the nozzle will steady the movable device on a horizontal surface, when the device is used on a horizontal surface, and such that the suction action draws the movable device against a vertical surface to be cleaned, when the movable device is used on a vertical surface;said nozzle being arranged to collect debris and dirt removed by the first and second cleaning mechanisms;wherein each of said first and second cleaning mechanisms comprise cleaning members positioned outside of the nozzle and capable of directing the removed debris towards the nozzle; andwherein:the first cleaning mechanism is arranged on a first end of the movable device, the first cleaning mechanism has a first elongated rotatable hollow shaft, the first elongated rotatable hollow shaft comprising:a first fixture and a second fixture rotatably journalled to the first elongated rotatable hollow shaft,a first set of rotatable cleaning members arranged on the first elongated rotatable hollow shaft and positioned around the first fixture and the second fixture;a first drive shaft of a first electric motor attached to a first drive cog wheel positioned on at least one of the first fixture and the second fixture such that the first electric motor rotates the first elongated rotatable hollow shaft;the second cleaning mechanism is arranged on an opposing second end of the movable device, the second cleaning mechanism has a second elongated rotatable hollow shaft, the second elongated rotatable hollow shaft comprising:a third fixture and a fourth fixture rotatably journalled to the second elongated rotatable hollow shaft,a second set of rotatable cleaning members arranged on the second elongated rotatable hollow shaft and positioned around the third fixture and the fourth fixture;a second drive shaft of a second electric motor attached to a second drive cog wheel positioned on at least one of the third fixture and the fourth fixture such that the second electric motor rotates the second elongated rotatable hollow shaft;further wherein the first and second sets of cleaning members facilitate collection of the debris and dirt from two directions. 2. The movable device according to claim 1, wherein said flotation means comprises exchangeable flotation bodies having different flotation capabilities. 3. The movable device according to claim 1, wherein said flotation means comprises a fillable volume capable of containing different volumes of flotation gas. 4. The movable device according to claim 1, wherein the first set and second set of cleaning members are in contact with the surface to be cleaned. 5. The movable device according to claim 1, wherein the first set of cleaning members comprise at least one of brushes, sponges and rakes; and the second set of cleaning members comprise at least one of brushes, sponges and rakes. 6. The movable device according to claim 1, further comprising a remote control system for controlling the driving of the movable device. 7. The movable device according to claim 1, further comprising a positioning system capable of tracking and storing an actual position of the movable device during the cleaning operation. 8. A method of using a movable device for submersibly cleaning surfaces placed in liquid in a nuclear power plant or repository for spent nuclear fuel, the movable device comprising:a pump comprising an outlet passage configured to connect with a flexible conduit;a nozzle connected to said pump and arranged to face surfaces to be cleaned, the pump creating a suction pressure at the nozzle;a first cleaning mechanism and a second cleaning mechanism, each cleaning mechanism configured to remove debris on surfaces to be cleaned;an adjustable flotation means configured to adjust a flotation capability of the movable device depending on a type of cleaning application;wherein the suction from the nozzle will steady the device on a horizontal surface, when the movable device is used on a horizontal surface, and such that the suction action draws the device against a vertical surface to be cleaned, when the movable device is used on a vertical surface;said nozzle being arranged to collect debris and dirt removed by the first and second cleaning mechanisms;wherein each of said first and second cleaning mechanisms comprise cleaning members positioned outside of the nozzle and capable of directing the removed debris towards the nozzle; andwherein:the first cleaning mechanism is arranged on a first end of the movable device, the first cleaning mechanism has a first elongated rotatable hollow shaft, the first elongated rotatable hollow shaft comprising:a first fixture and a second fixture rotatably journalled to the first elongated rotatable hollow shaft,a first set of rotatable cleaning members arranged on the first elongated rotatable hollow shaft and positioned around the first fixture and the second fixture;a first drive shaft of a first electric motor attached to a first drive cog wheel positioned on at least one of the first fixture and the second fixture such that the first electric motor rotates the first elongated rotatable hollow shaft; andthe second cleaning mechanism is arranged on an opposing second end of the movable device, the second cleaning mechanism has a second elongated rotatable hollow shaft, the second elongated rotatable hollow shaft comprising:a third fixture and a fourth fixture rotatably journalled to the second elongated rotatable hollow shaft,a second set of rotatable cleaning members arranged on the second elongated rotatable hollow shaft and positioned around the third fixture and the fourth fixture;a second drive shaft of a second electric motor attached to a second drive cog wheel positioned on at least one of the third fixture and the fourth fixture such that the second electric motor rotates the second elongated rotatable hollow shaft,each of the first set and second set of cleaning members facilitate collection of the debris and particles from two directions,wherein said method of using the movable device comprises using the movable device such that debris removed by the cleaning members is directed, by the cleaning members, from two opposite sides of the movable device towards the nozzle, and wherein said method of using the movable device comprises using the movable device both for cleaning a horizontal surface and for cleaning a vertical surface and to adjust the flotation means such that the flotation capability is altered depending on whether the horizontal or the vertical surface is cleaned. |
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summary | ||
claims | 1. A method for assessing chemical reactor tubes, comprising the steps of:inserting a hollow tube body into a reactor tube; andactivating a “start” innut which communicates with a central processor, causing the central processor to begin an automated process which includes the steps of said central processor communicating with an electronic sensor to determine whether the hollow tube body is fully inserted into the reactor tube, and, then, upon determining that the hollow tube body is fully inserted into the reactor tube, said central processor automatically communicating with a first valve, causing the first valve to open and inflate a seal which seals between said hollow tube body and said reactor tube; said method also including injecting a controlled gas flow through said hollow tube body into said reactor tube; and measuring the pressure in said hollow tube body. 2. A method for assessing chemical reactor tubes as recited in claim 1, wherein activating said “start” input further causes the measurement of the oressure in said hollow tube body to be automatically electronically recorded along with an identifier of the chemical reactor tube in which said hollow tube body is inserted when the pressure measurement is taken. 3. A method for assessing chemical reactor tubes as recited in claim 1, wherein said hollow tube body is mounted on a hand-held wand, and further including a plurality of said hollow tube bodies mounted on said hand-held wand in an arrangement in which the hollow tube bodies are spaced apart from each other the same distance that the reactor tubes are spaced apart from each other, and said method further includes the step of inserting said plurality of hollow tube bodies into a respective plurality of chemical reactor tubes by manually moving said hand-held wand. 4. A method for assessing chemical reactor tubes as recited in claim 3, and further comprising the step of measuring the distance from a first point fixed relative to said hollow tube bodies to a second point fixed relative to the chemical reactor tubes; using that distance measurement to automatically determine which chemical reactor tubes are being measured; and automatically associating the pressure measurements with the chemical reactor tubes being measured. 5. A method for assessing chemical reactor tubes as recited in claim 4, and further comprising the step of electronically recording the pressure measurements for the plurality of chemical reactor tubes along with identifiers for the respective chemical reactor tubes being measured. 6. A method for assessing chemical reactor tubes as recited in claim 5, wherein said step of measuring the pressure includes using a pressure sensor mounted on said hand-held wand. 7. A method for assessing chemical reactor tubes, comprising the steps of:inserting a hollow tube body into a reactor tube; andinitiating an automated seauence of events, including the steps of ensuring that a seal is fully inserted into the chemical reactor tube; then inflating the seal which seals between said hollow tube body and said reactor tube;injecting a controlled gas flow through said hollow tube body into said reactor tube; andmeasuring the pressure in said hollow tube body;wherein there is a plurality of said hollow tube bodies, each being inserted into its respective reactor tube, and wherein said automated sequence of events further includes the steps of simultaneously injecting a controlled gas flow through each of said hollow tube bodies and then cycling a multiplex valve to sequentially put each of the hollow tube bodies in fluid communication with a single pressure sensor. 8. A method for assessing chemical reactor tubes, comprising the steps of:inserting a hollow tube body into a reactor tube; andinitiating an automated seguence of events, including the steps of ensuring that a seal is fully inserted into the chemical reactor tube; then inflating the seal which seals between said hollow tube body and said reactor tube;injecting a controlled gas flow through said hollow tube body into said reactor tube;measuring the pressure in said hollow tube body;measuring the distance from a first point fixed relative to said hollow tube body to a second point fixed relative to the chemical reactor tube;using that distance measurement to automatically determine which reactor tube is being measured; andautomatically associating the measurement with the chemical reactor tube being measured. |
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claims | 1. A scanning ring field lithography apparatus for patterning images on a substrate, comprising: a radiation source emitting extreme ultraviolet radiation having a wavelength ranging from approximately 4 to 30 nanometers; a condenser; a mask for generating patterned images; and reflective focusing optics positioned between the mask and the substrate, comprising four optical elements providing five reflective surfaces, the reflective focusing optics configured for projecting a reduced focused image on the substrate in the shape of an arcuate slit. 2. The apparatus of claim 1 , wherein the five reflective surfaces are characterized as concave, convex, concave, convex and concave, when viewed in order from object to image. claim 1 3. The apparatus of claim 1 , wherein the second reflective surface and the fourth reflective surface are part of a common optical element. claim 1 4. The apparatus of claim 1 , wherein at least three of the five reflective surfaces of the reflective focusing optics are aspheric surfaces. claim 1 5. The apparatus of claim 1 , wherein the reflective surfaces are coaxial with respect to each other. claim 1 6. The apparatus of claim 1 , wherein the first reflective surface deviates from a best fitting spherical surface by less than approximately 6.50 xcexcm, the second reflective surface deviates from a best fitting spherical surface by less than approximately 12.60 xcexcm, the third reflective surface deviates from a best fitting spherical surface by less than approximately 1.50 xcexcm, the fourth reflective element deviates from a best fitting spherical surface by less than approximately 0.50 xcexcm, and the fifth reflective element deviates from a best fitting spherical surface by less than 7.80 xcexcm. claim 1 7. The apparatus of claim 1 , wherein the extreme ultraviolet radiation passes through the reflective focusing optics and is telecentric at the substrate. claim 1 8. The apparatus of claim 1 , wherein an aperture stop is accessibly located proximate to the fourth reflective surface. claim 1 9. The apparatus of claim 1 , wherein the numerical aperture of the reflective focusing optics is between approximately 0.10 and 0.15. claim 1 10. The apparatus of claim 1 , wherein the mask is reflective and is positioned on the same side of the reflective focusing optics as the substrate. claim 1 11. The apparatus of claim 1 , wherein the chief ray angle of radiation at the mask is less than approximately 7.5 degrees. claim 1 12. The apparatus of claim 1 , wherein the reflective focusing optics are characterized by a balanced static centroid distortion curve across the width of the arcuate slit. claim 1 13. A method of projecting a mask image onto a substrate using a scanning ring field lithography apparatus, comprising: producing extreme ultraviolet radiation having a wavelength ranging from approximately 4 to 30 nanometers; condensing the radiation and directing it to a mask; patterning the condensed radiation with the mask; reducing the patterned radiation with reflective focusing optics comprising four optical elements and five reflective surfaces; and projecting a focused image on the substrate in the shape of an arcuate slit. 14. The method of claim 13 , further comprising exposing a photoresist layer coated on the substrate with the reduced patterned radiation. claim 13 15. The method of claim 13 , wherein reducing the patterned radiation is carried out by the five reflective surfaces characterized as concave, convex, concave, convex and concave when viewed from object to image. claim 13 16. The method of claim 13 , wherein reducing the patterned radiation is carried out using a common optical element as the second reflective surface and the fourth reflective surface. claim 13 17. The method of claim 13 , wherein the extreme ultraviolet radiation passes through the reflective focusing optics and is telecentric at the substrate. claim 13 18. The method of claim 13 , further comprising positioning the mask on the same side of the reflective focusing optics as the substrate. claim 13 19. The method of claim 13 , further comprising directing the radiation at the mask having a chief ray angle less than approximately 7.5 degrees. claim 13 20. The method of claim 13 , further comprising producing extreme ultraviolet radiation from a source selected from the group consisting of pulsed sources and continuous sources. claim 13 |
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claims | 1. An assembly for a fixed-energy cyclotron, wherein the cyclotron is configured to produce a particle beam, the assembly comprising:a target holder assembly comprising a target body that includes:a first region configured to hold a target material;a second region with a receiving slot; anda third region including a receiving section for receiving the particle beam from the cyclotron; anda removable degrader comprising an attenuation disc;wherein:the receiving slot is configured to receive the removable degrader;the removable degrader is configured for removable insertion into the receiving slot such that, when (a) the removable degrader is in the receiving slot, (b) the target material is held in the first region of the target body, and (c) the particle beam travels into the receiving section, the attenuation disc is positioned in a path of the particle beam that extends from the receiving section to the target material; andthe attenuation disc is configured to reduce an energy level of the particle beam prior to the particle beam reaching the target material. 2. The assembly of claim 1, wherein the target holder assembly and the removable degrader are configured to allow for removal of the removable degrader without removal of the target holder assembly from the cyclotron. 3. The assembly of claim 1, wherein:the target body includes a first target body in which the first region is located, a second target body in which the second region is located, and a third target body in which the third region is located; andthe second target body and the third target body are configured to attach to the cyclotron independently from the first target body, to allow a pressure between the first target body and the second target body to be adjusted independently from a pressure between the second target body and the third target body, and from a pressure between the third target body and the cyclotron. 4. The assembly of claim 3, wherein the first target body is configured to shift towards the second target body when the removable degrader is inserted into the receiving slot to form an air tight seal around the attenuation disc. 5. The assembly of claim 3, wherein the target holder assembly further comprises a vacuum foil between the second target body and the third target body, and wherein the attenuation disc is positioned between the vacuum foil and the target material when the removable degrader is inserted into the receiving slot. 6. The assembly of claim 1, wherein:the removable degrader further comprises:a frame;an inner ring;a first circular channel formed by the inner ring and the frame at a first side of the attenuation disc;a second circular channel formed by the inner ring and the frame at a second side of the attenuation disc;a first O-ring within the first circular channel; anda second O-ring within the second circular channel; andthe first and second circular channels circumscribe the attenuation disc. 7. The assembly of claim 1, wherein the removable degrader is made from a single piece of aluminum. 8. The assembly of claim 1, wherein a thickness of the attenuation disc is about 0.6 to 0.9 mm. 9. The assembly of claim 8, wherein the thickness of the attenuation disc is uniform. 10. A method of adjusting an energy level of a particle beam of a fixed-energy cyclotron prior to the particle beam reaching a target material, the method comprising:inserting a removable degrader with an attenuation disc into a receiving slot of a target holder assembly, wherein:the removable degrader is configured for removable insertion into the receiving slot such that, when inserted, the attenuation disc is positioned in a path of the particle beam that extends from the cyclotron to the target material, andthe attenuation disc is configured to adjust the energy level of the particle beam prior to the particle beam reaching the target material. 11. The method of claim 10, wherein the target holder assembly and the removable degrader are configured to allow for removal of the removable degrader without removal of the target holder assembly from the cyclotron. 12. The method of claim 11, wherein the attenuation disc is configured to reduce the energy level of the particle beam. 13. The method of claim 12, further comprising:removing the removable degrader from the receiving slot without removing the target holder assembly from the cyclotron; andinserting a second removable degrader with a second attenuation disc into the receiving slot;wherein:the second removable degrader is configured for removable insertion into the receiving slot such that, when inserted, the second attenuation disc is positioned in the path of the particle beam, andthe second attenuation disc has a thickness that is different than a thickness of the attenuation disc. 14. A method of independently adjusting energy levels of first and second particle beams of a cyclotron prior to the particle beams reaching their respective first and second target materials, the method comprising:(a) inserting a first removable degrader with a first attenuation disc into a first receiving slot of a first target holder assembly; and(b) inserting a second removable degrader with a second attenuation disc into a second receiving slot of a second target holder assembly;wherein the first and second removable degraders are configured for removable insertion into the respective first and second receiving slots such that, when inserted, the respective first and second attenuation discs are positioned in respective paths of the first and second particle beams that extend from the cyclotron to the respective first and second target materials. 15. The method of claim 14, wherein the first attenuation disc has a first thickness and the second attenuation disc has a second thickness, and wherein the first thickness and second thickness are different. 16. The method of claim 14, wherein the first and second target holder assemblies and the first and second removable degraders are configured to allow for removal of the first and second removable degraders without removal of the first and second target holder assemblies from the cyclotron. |
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claims | 1. A multilayer mirror comprising:a substrate;a multilayer coating on the substrate; anda capping layer on the multilayer coating, the capping layer comprisingan outermost layer comprising Nb2O5 or TiO2, anda multilayer structure positioned between the outermost layer and the multilayer coating, the multilayer structure comprising a plurality of bilayers, each of the bilayers comprising a spacer layer comprising a first material and an absorber layer comprising a second material different from the first material, one of the first material and the second material comprising ZrN. 2. The multilayer mirror as claimed in claim 1 wherein the other of the first material and the second material comprises B4C. 3. A multilayer mirror comprising:a substrate;a multilayer coating on the substrate; anda capping layer on the multilayer coating, the capping layer comprising:an outermost layer comprising Ta2O5 anda multilayer structure positioned between the outermost layer and the multilayer coating, the multilayer structure comprising a plurality of bilayers, each of said bilayers comprising a spacer layer comprising a spacer layer nitride material resistant to hydrogen diffusion and blistering and an absorber layer comprising an oxide material resistant to ion penetration. 4. A multilayer mirror comprising:a substrate;a multilayer coating on the substrate; anda capping layer on the multilayer coating, the capping layer comprisingan outermost layer comprising ZrN, anda multilayer structure positioned between the outermost layer and the multilayer coating, the multilayer structure comprising a plurality of bilayers, each of the bilayers comprising a spacer layer comprising a first material and an absorber layer comprising a second material different from the first material, at least one of the bilayers comprising ZrN. 5. A multilayer mirror comprising:a substrate;a multilayer coating on the substrate; anda capping layer on the multilayer coating, the capping layer comprisingan outermost layer comprising Nb2O5 or TiO2, anda multilayer structure positioned between the outermost layer and the multilayer coating, the multilayer structure comprising a plurality of bilayers, each of the bilayers comprising a spacer layer comprising a first material and an absorber layer comprising a second material different from the first material, one of the first material and the second material comprising ZrO2 and the other of the first material and the second material comprising ZrN. |
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043449140 | description | DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Referring initially to FIG. 1, the core region 11 of a nuclear reactor 12 includes a plurality of fuel pins 13 of rod-like configuration which contain the fissionable material. Fuel pins 13 extend vertically in parallel side by side relationship with each other within a housing or wrapper 14 which is typically of hexagonal cross section. A flow 16 of fluid such as liquid sodium for example is directed upwardly through the bundle of fuel pins 13 to extract the thermal energy generated by the fission reaction. Fuel pins 13 are supported at the bottom ends through fuel pin end members 17 which engage on parallel attachment rails 18 that extend transversely within housing 14 below the fuel pin assembly 23, a row of the fuel pins being supported on each individual rail. Rails 18, in this example, are of circular cross section and are formed along the upper edges of a series of spaced apart, parallel, upstanding support plates 19 which are secured to housing 14, the plates having a thickness smaller than the diameter of the rounded surfaces 21 of the rails. To maintain a small spacing between adjacent fuel pins 13 and between the outermost pins and the wall of housing 14, a wire 22 is wrapped spirally around each pin with the exception of one or more specialized fuel pins to be hereinafter described. Aside from certain of the fuel pin end members 17, the reactor 12 may otherwise be of known construction and thus need not be further described. The fuel pin end members 17a and 17b in this example are of two different types. End members 17a of the first type are conventional and do not enable disengagement of the associated fuel pins 13a from rails 18 except by the cumbersome process of removing the entire fuel pin assembly 23 from housing 14 to enable sidward sliding of the fuel pin 13a off the end of the rail 18. The fuel pins 13a cannot be withdrawn from the fuel pin assembly 23 by a direct upward force as the rails 18 cannot pass through the relatively narrow slots at the lower portions of the end members 17a. Predetermined ones 13b of the fuel pins 13 have lower end members 17b embodying the present invention and constitute what is herein termed a retrievable fuel pin. The retrievable fuel pins 13b may be withdrawn directly upwardly from the associated rail 18 by an axially directed force of predetermined magnitude and the same pin or a replacement may be installed by being pushed axially downward into the assembly 23 with a sufficient force. The end member 17b construction which provides for a retrievable fuel pin 13b may be understood by reference to FIGS. 2, 3 and 4 in conjunction. The end member 17b in a preferred embodiment is constructed as a single integral element which, in addition to fastening the fuel pin 13b to an attachment rail 18, also functions as a bottom end closure of the fuel pin. End member 17b is formed of a resilient material, for reasons to be hereinafter discussed, that is nonreactive with the fluid of flow 16 and which is stable in the high temperature environment of the core region 11. In most instances spring steel is a suitable material for the end member 17b. End member 17b has an end plug portion 27 of circular cross section which fits into the lower end of the cylindrical cladding 28 in coaxial relationship therewith and which is weld sealed to the cladding. A circular flange 29 at the lower end of the plug portion facilitates such securing of the end member 17b to the other components of the fuel pin 13b. The lower portion of the end member 17b is divided into a pair of spaced apart blades 31 by a slot 32 which extends upward from the lower end of the end member to a point slightly below flange 29. At an intermediate position along slot 32, the facing surfaces 33 of the blades 31 which define the slot 32 have a circular profile conforming with the rounded surface 21 of rail 18 and which is of similar diameter to define a rail seat region 34 of the slot. Immediately below the seat region 34, the facing surfaces 33 are closer together to define lands 36 spaced apart a distance similar to the thickness of the support plate 19 of the rail 18 to define a land region 37 of the slot. Below the land region 37, the slot 32 has a slightly greater width. At the lowermost or outer region 38 of the slot 32, the facing blade surfaces 33a and 33b are divergent causing the outer end region of the slot to be of progressively greater width towards the lower ends 39 of the blades 31. The lower ends or tips 39 of the blades 31 also have convergent side surfaces 41 causing the tips of the blades to be pointed. To impart sufficient elasticity to the blades 31 a relatively narrower inner portion 42 of slot 32 extends upwardly from seat region 34 and terminates at a bore 43 located below flange 29. The foregoing description of the widths of various regions of the slot 24 in relation to the diameter of rail 18 and the thickness of rail support plate 19 should be understood to refer to conditions when the end member 17b is not stressed or under spring tension. As will be described in connection with operation of the invention, the blades 31 are temporarily forced apart and temporarily enlarge the various regions of the slot as the end member 17b is in the process of being engaged on rail 18 or is being disengaged therefrom. In operation, with reference to all figures in conjunction, the retrievable fuel pin 13b may be initially installed in the fuel pin assembly 23 in either of two ways. As the nonretrievable fuel pins 13a must be fitted onto the ends of the rails 18 and then be slid sidewardly into position before the assembly 23 as a whole is installed in housing 14, it may be convenient to install the retrievable fuel pins 13b initially in the same manner. Alternately and unlike the nonretrievable fuel pins 13a, the retrievable pins 13b may be engaged on rails 18 by a strictly downward axial movement. Provided that sufficient force is exerted, the rail 18 wedges lands 36 apart and is then received in the conforming seat region 34 of slot 32 at which point the resiliency of the material of the end member 17b snaps the blades 31 back towards each other. The retrievable fuel pin 13b is thus clamped to rail 18 by a spring clip action since withdrawal of the end member 17b requires a sizable upward force sufficient to again wedge the lands 36 apart against the resistance created by the resiliency of the end member material. To assure that the fuel pin 13b remains fastened to rail 18 during reactor operation, the blades 31 are proportioned in relation to the spring constant of the end member material and to the thickness of lands 36 to prevent upward motion of the fuel pin 13b until the upward force on the fuel pin exceeds a predetermined magnitude which is greater than the combined upward forces which the fuel pin may experience in the course of reactor operation. Such upward forces which may be experienced during reactor operation may arise from several causes including the hydraulic pressure differential between the upper and lower ends of the fuel pin 13b that results from the upward flow 16 of fluid, floatation force on the fuel pin from the fluid environment, and possible momentum forces arising from vibration or motion of the reactor as a whole. It is preferable that a sizable safety margin be provided for in fixing the pull free force required to detach the end member 17b from the rail 18. In one specific embodiment of the invention in which the maximum lifting forces that may be experienced by the pin 13b during operation of the reactor, from the causes described above, is about 1.1 lb (0.15 N), the blades 31 are proportioned to require an upward force of 10 lbs (1.4 N) before the end member 17b disengages from rail 18, this particular value being given for purposes of example only as other pull free forces may be appropriate in other embodiments of the invention. The fuel pin 13b may be retrieved, after a period of reactor operation, by gripping the upper end with grappling mechanism of known construction and pulling directly upward with sufficient force to spread the blades 31 sufficiently to allow rail 18 to pass between lands 36. The same pin 13b may be reinstalled or a replacement pin may be substituted by a downward axial movement of sufficient force. The divergent configuration of the lower end of slot 32 together with the pointed configuration of the tips 39 of blades 31 automatically corrects for angular misorientation and/or for misalignment between end member 17b and rail 18 during the process of installation of guiding the end member into the correct position, relative to the rail, for engagement. A rare exception occurs if the pointed tips 39 contact the rail 18 while in exact alignment with the rail centerline in which case the fuel pin may be backed off and turned slightly after which the installation process may proceed. It has been pointed out that the nonretrievable fuel pins 13a have a spiral wire 22 winding to assure the desired fuel pin spacing is maintained. If such a wire is present on the retrievable fuel pin 13b, it must be turned in the manner of a screw while being withdrawn and must be turned in an opposite direction while being installed to avoid interference with the wires 22 of adjacent fuel pins. To avoid this complication in instances where the retrievable fuel pin 13b is surrounded by nonretrievable fuel pins 13a, the wire 22 may simply be omitted from the retrievable fuel pin. The wires 22 of the surrounding fuel pins 13a establish the desired spacing by contact with the sides of the retrievable pin 13b. Only a small number of the fuel pins 13b are of the retrievable form in this particular reactor 12 since the purpose of the retrievability in this example is to facilitate analysis of the physical and chemical changes that occur in fuel pins over a period of time. Analysis of only a representative sample of the fuel pins is necessary for this purpose. As is apparent, any or all of the other fuel pins may be of the retrievable form in instances where that is advantageous. For example in reactor systems in which it is possible to identify a malfunctioning fuel rod from among the others without removing the entire assembly 23, the capability of removing and replacing any of the fuel pins will simplify maintenance procedures. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously modifications and variations are possible in light of the above teaching. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modification as are suited to the particular use contemplated. It is intended that the scope of the invention is defined by the claims appended hereto. |
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description | This invention relates to systems and methods for inspecting and testing semiconductors wafers during circuit fabrication and, in particular, for testing wafers in a voltage-contrast mode. Integrated circuits are very complex devices that include multiple layers. Each layer may include conductive material, isolating material and/or semi-conductive materials. These various materials are arranged in patterns, usually in accordance with the expected functionality of the integrated circuit. The patterns also reflect the manufacturing process of the integrated circuits. Conductive layers usually include conductors made of conductive materials, whereas the conductors are separated by isolating materials such as various oxides. The dielectric layers are located between the conductive layers in an interlaced manner. Conductors of distinct conductive layers may be connected to each other and/or to the substrate by conductive materials (termed interconnects or vias) located within the dielectric layers. The substrate may include semi-conducting materials and at least a portion of the substrate is connected to a virtual ground. Various inspection and failure analysis techniques evolved for inspecting integrated circuits both during the fabrication stages, between consecutive manufacturing stages, either in combination with the manufacturing process (also termed “in line” inspection techniques) or not (also termed “off line” inspection techniques). Various optical as well as charged particle beam inspection tools and review tools are known in the art, such as the Compluss™ and SEMVision™ of Applied Materials Inc. of Santa Clara, Calif. Manufacturing failures may affect the electrical characteristics of the integrated circuits. Some of these failures result from unwanted disconnections between various elements of the integrated circuits. An under-etched via or conductor can be floating instead of being connected to a conducting sub-surface structure. Such a failure can be detected due to charging differences between said defective structure and non-defective structures. In order to facilitate voltage contrast analysis there must be a charging difference between the defective structure and its surroundings. Typically the sub-surface structure is electrically connected to the substrate of the wafer or is otherwise connected to an external voltage source or to the ground. Thus, the charging of the structure surrounding can be relatively easily controlled. The charging of the wafer is usually controlled with an electrode (also known as charge control plate or CCP) positioned above the wafer and held at either a positive or negative voltage as shown in FIG. 1. In order to assure proper charging control the inspected structures (or at least the non-defective structures) are connected to the ground or to some reference voltage source. U.S. Pat. No. 6,627,884 of McCord, et al. titled “Simultaneous flooding and inspection for charge control in an electron beam inspection machine”, and U.S. Pat. No. 6,586,736 of McCord titled “Scanning electron beam microscope having an electrode for controlling charge build up during scanning of a sample”, which are incorporated herein by reference describe systems that include a charge control plate. Various wafers such as silicon over insulator (SOI) wafers and short loop wafers have sub surface structures that are intentionally floating. Thus, scanning the wafers with a charged particle causes charging effects that are hard to manage. FIG. 1 illustrates a cross section of a typical prior art SOI wafer. The lowest layer is a substrate 210. The substrate is usually made of silicon. An oxide layer (also referred to as BOX) 220 is manufactured above the substrate 210. The upper layer of the SOI wafer includes an inter-dielectric layer 240 through which contact holes were fabricated and then filled with conductive structures (also termed conductors) 250 such as vias, metal lines and the like. Trench insulators, such as oxide-made trench insulators 260 as well as silicon epilayer islands 230, 232 and 234, that are insulated from each other by trench isolators 260 are formed between the inter-dielectric layer 240 and the oxide layer 220. Non-defective conductors are connected to the silicon epilayer islands while defective conductors are isolated from said islands. During electron beam inspection of the SOI wafer each of the epilayer islands 230, 232 and 234 acts like a capacitor and is charged to a certain voltage level. This charge does not discharge through the substrate 210 because each island is isolated, by the oxide layer 220 and trench insulators 260. Many conductors 250 are connected to each silicon epilayer island. Thus, a charge that is built as a result of scanning some conductors affects the charge of conductors that were not yet scanned. Once the SEM 10 scans the latter conductors the contrast between them and their vicinity can be dramatically reduced and even eliminated. There is a need to provide a system and method for an effective voltage contrast analysis, especially in the presence of severe charging effects. A system for electrically testing a semiconductor wafer, the system includes: (a) a charged particle beam source; (b) an electrode located at a vicinity of the wafer; (c) at least one detector, connected to the electrode, adapted to collect charged particles scattered from the wafer; and (d) a controller adapted to: (i) control the charged particle beam such that the charged particle beam scans along at least one scan line while maintaining the electrode at a first voltage that differs from a voltage level of a first scanned portion of the wafer, and to allow the detector to collect charged particles scattered from the first scanned portion; (ii) control the charged particle beam such that the charged particle beam scans along at least one other scan line while maintaining the electrode at a second voltage that differs from a voltage of a second scanned portion such as to control a discharging state of at least an area that includes the first and second scanned portions; and (iii), repeat (i) and (ii) until a predefined section of the wafer is scanned. A method for electrically testing a semiconductor wafer, the method includes: (a) scanning a charged particle beam along at least one scan line while maintaining an electrode located at a vicinity of the wafer at a first voltage that differs from a voltage level of a first scanned portion of the wafer, and collecting charged particles scattered from the first scanned portion; (b) scanning a charged particle beam along at least one other scan line or the same scan line while maintaining the electrode at a second voltage that differs from a voltage level of a second scanned portion such as to control a charging state of at least an area that comprises the first and second scanned portions; and (c) repeating the scanning stages until a predefined section of the wafer is scanned. According to an embodiment of the invention stage (b) scans wafer portions that were previously scanned during stage (a), conveniently for discharging at least an area that includes the first and second scanned portions. Conveniently, the electrode is maintained at a higher voltage than a first scanned portion of the wafer. Conveniently, the electrode is maintained at a lower voltage than a second scanned portion. According to an embodiment of the invention stage (b) scans wafer portions before they are scanned during stage (a), conveniently for charging at least an area that includes the first and second scanned portions. Conveniently, the electrode is maintained a vicinity of the wafer at a lower voltage than a first scanned portion of the wafer. Conveniently, the electrode is maintained at a higher voltage than a second scanned portion. The following description relates to charged particle microscopes, such as Scanning Electron Microscopes (SEMs), such as step and repeat type SEMs, in which a wafer is scanned by repetitive steps of scanning an area of the wafer (said area defined by the field of view of the SEM) and mechanically introducing a movement between the wafer and SEM to facilitate the scanning of another area. Said movement may also be implemented by electrostatic and/or magnetic fields introduced by various electrostatic and/or magnetic elements such as lens, deflectors and the like. It is noted that other charged particles and even photons may be utilized for detecting voltage contrast. It is further noted that this invention may also be implemented by introducing a substantially constant movement between the SEM and the wafer. The movement may be linear or even rotational, and/or any combination of both movements. The following examples relate to positive charging and to discharging of wafer portions. It is noted that this is not necessarily so and that this method and system can be applied for negative charging. Furthermore, the invention can be applied to pre-charging as well as discharging. The term “charging state” relates to the distribution of charge at certain areas or portions of a wafer. It may reflect the total charge, charge density or any other statistics reflecting said charge distribution. FIG. 2 illustrates scanning electron microscope (SEM) 10 that is capable of voltage contrast analysis, according to an embodiment of the invention. SEM 10 includes an electron gun 22, an anode 24 and a high voltage power supply 26 that are operable to generate a primary electron beam 40. SEM 10 further includes a detector 14 that has an aperture 13 through which the primary electron beam 40 can pass, an objective lens 12 capable of focusing the primary electron beam onto the wafer 100, an electrode 30 positioned at the vicinity of the wafer 100, an electrode power supply 32, a controller 60 and a stage 50. Objective lens 12 usually includes an electrostatic lens and a magnetic lens that introduce an electrostatic field and a magnetic field that leak from the objective lens. SEM 10 includes additional components such as deflecting units that deflect the primary electron beam such as to scan the wafer, and also includes additional control and voltage supply units that were omitted from FIG. 2 for simplicity of explanation. In SEM 10 the primary electron beam 40 is directed through aperture 13 within the detector 14 to be focused by the objective lens 12 onto an inspected wafer 100. The primary electron beam interacts with wafer 100 and as a result various types of electrons, such as secondary electrons, back-scattered electrons, Auger electrons and X-ray quanta are reflected or scattered. Secondary electrons can be collected easily and most SEMs mainly detect these secondary electrons. SEM 10 detects secondary electrons by detector 14. The detector 14 is connected to controller 60 that is capable of generating an image of the scanned wafer in response to the amplitude of collected secondary electrons and the location of the primary electron beam 40 in relation to the wafer. Controller 60 is also connected to the stage 50 for controlling a mechanical movement introduced between wafer 100 and other parts of the SEM 10, such as the electrode. Controller 60 controls the various components of the SEM 10, including the electrode voltage supply unit 32, the deflecting units (not shown) and the like. Typically the deflection units are controlled by a X-scan signal and a Y-scan signal. It is noted that the controller can include multiple software and hardware components, can be a single device or multiple devices. Conveniently, the stage 50 moves the wafer along a Y-axis while the electrical beam is deflected along an X-axis. This is not necessarily so and other combinations can be applied, including introducing mechanical movement along a first axis and deflecting the electron beam along a second axis that is not normal to the first axis. Furthermore, the direction of successive scans can be the same or opposite of each other. Although FIG. 2 illustrates a single electrode, this is not necessary and multiple electrodes, as well as an electrode that is segmented to multiple portions, can be applied to control the charging of the wafer 100. FIG. 3 illustrates a beam deflection pattern 300, according to an embodiment of the invention. The beam scan pattern 330 (illustrated in FIG. 4) differs from the beam deflection pattern 300 due to the mechanical movement of the wafer 100 along the Y-axis. Multiple scan lines that are formed due to the deflection pattern and the mechanical movement are further illustrated at FIG. 4. The beam deflection pattern 300 is rectangular and includes a horizontal scan and image portion 302, vertical blanking portions 304 and 308 and a horizontal discharge portion 306. During the scan and image portion the primary electron beam 40 is focused onto the wafer to provide a spot that is deflected, from left to right. When the primary electron beam 40 is deflected from left to right electrode 30 is held at a first voltage that is more positive than the voltage of the first scanned portion of the wafer. During this scan and image portion 302 SEM 10 collects scattered secondary electrons from the wafer 100 by detector 14 that sends detection signals to controller 60 that in turn is capable of generating an image of the first portion. The scan and image portion is followed by a blanking portion 304 that includes blanking the primary electron beam 40 and configuring beam deflector to direct the primary electron beam 40 to a point that was previously scanned. Schematically, this blanking portion 304 is illustrated as a vertical line. The blanking portion 304 is followed by a discharge portion 306 during which the primary electron beam 40 is deflected from right to left while the electrode 30 is maintained at a second voltage that is lower than the voltage of the second portion such as to control a discharging of an area that includes the first and second portions. The discharge portion 306 is followed by a blanking period 308 that includes blanking the primary beam 40 and configuring beam deflector to direct the primary electron beam 40 to the starting point of the scan and image portion 302. Schematically, this blanking portion 308 is illustrated as a vertical line. The scanning pattern includes many repetitions of portions 302–308, whereas the mechanical movement of the wafer 100 causes the deflected primary electron beam to scan different portions of the wafer 100. FIG. 4 illustrates a beam scanning pattern 330 resulting from multiple iterations of the beam deflection pattern 300 and the movement of the wafer 100, according to an embodiment of the invention. As the wafer 100 is translated along a Y-axis, the horizontal deflection portion amount in scan lines that are slightly oriented in relation to the horizon. A first iteration of beam deflection pattern 300 results in first scan line 332 (Corresponding to the scan and image portion 302 of beam deflection pattern 300), and a second scan line 334 (corresponding to the discharge portion 306). It is noted that each of said periods is followed by a blanking period during which the primary electron beam does not scan the wafer 100. A second iteration of the beam deflection pattern 300 results in first scan line (Corresponding to the scan and image portion 302 of beam deflection pattern 300), and a second scan line (corresponding to the discharge portion 306). It is noted that each of said periods is followed by a blanking period during which the primary electron beam does not scan the wafer 100. It is noted that the scan and image portion of the scanning pattern can include multiple consecutive scan lines so that the primary electron beam 40 can scan along multiple scan lines before the electrode 30 is maintained at the second voltage. During the discharge portion electrons are forced back to the wafer 100 by the negative biased electrode 30 and the positive charge generated in the epi-island is passivated. The backwards deflection in Y is utilized to prevent negative charging of the surface oxide from affecting the next line. Once the retrace (second scan line) is complete, the electrode 30 is switched back to the positive voltage, the Y-deflection is reset and the next line is acquired. The first and second voltages applied to the electrode 30 depend on various parameters, such as the yield of the inter-dielectric layer 240. The yield reflects the ratio between the amount of electrons that hit the inter-dielectric layer 240 and the amount of electrons that are emitted from that layer. For example, a yield that is greater than one means that more electrons exit the layer than hit the layer, thus the layer is positively charged. A yield that is smaller than one means the fewer electrons leave the layer and that the layer is negatively charged. The inventor found that inter-dielectric layers 240 having yield of about 1.1 to 1.3 can be effectively discharged by applying a second voltage (negative voltage) that is relatively small. The inventor used a negative voltage of 30 v although other voltages can be applied. When scanning the wafer with a pixel rate of about 160 Mega pixels per second, and with scan lines of about 5000 pixels a scan and image period of about 34 micro-seconds was achieved while a discharge period of 7 microseconds was sufficient to discharge the wafer. According to another embodiment of the invention the current of the primary electron beam can be altered so that during a scan and image a primary electron beam characterized by a first current is used to scan the wafer while the discharge portion includes scanning the wafer with a primary electron beam characterized by another current. Higher discharge currents can reduce the length of the discharge period. FIG. 5 illustrates an electrode power supply, according to an embodiment of the invention. The electrode power supply 32 includes two power MOSFET transistors 402 and 404 that are serially connected to each other. The MOSFET transistors are connected to each other in series and form an output node of the electrode power supply 32 that is connected to the electrode 30. A first MOSFET transistor 402 is controlled by first driver 412 and is selectively connected to a first voltage supply 422 that provides positive voltage. The first driver 412 is controlled by a control unit 444 that provides control signals via a first optocoupler 432. The control unit 444 allows the positive voltage of the first power supply 422 to be provided to the electrode 30 during discharge portions of the scanning pattern. A second MOSFET transistor 404 is controlled by second 414 and is selectively connected to a second voltage supply 424 that provides negative voltage. The second driver 414 is controlled by a control unit 444 that provides control signals via a second optocoupler 434. The control unit 444 allows the negative voltage of the second power supply 424 to be provided to the electrode 30 during scan and image portions of the scanning pattern. Conveniently, only up to one MOSFET transistor is active at any given moment. In order to prevent currents between the MOSFET transistors the control unit 444 causes both MOSFET transistors 402 and 404 to be deactivated before one of them is activated. In other words, the control unit 44, by timing the control signals to the optocouplers 432 and 432 assures that each MOSFET transistor is completely turned OFF before the other MOSFET transistor is turned ON. The period during which both MOSFET transistors are turned off is also referred to as a blanking period. The inventor used positive supply voltages during the scan and image periods in the range of about 0–1000 volts and a negative voltage, during the discharge period, of about 20 V, although positive voltages of few volts to a few tens of volts can also be applied. The inventor practiced the method on SOI wafers that include isolated epilayer islands but it can be applied to other wafers, including bulk wafers or other wafers that suffer from charging problems. FIGS. 6a–6d are timing diagrams of various signals, according to an embodiment of the invention. The timing diagrams illustrate an idle period 510 (from T0 to T1) that is followed by a scan and image period 520 (from T1 to T3), by a discharge period 530 (from T3 to T6) and finally another idle period 540 (from T6 to T7). The scan and image period 520 corresponds to the scan and image portion of the scanning pattern while the discharge period 530 is associated with the discharge portion of the scan pattern. The transition from the scan and image period 520 to the discharge period 530 is associated with a first blanking period 550 (from T2 to T4), while the transition from the discharge period 530 to the second idle period 540 is associated with a second blanking period 560 (from T5 to T7). Both blanking periods were discussed previously in relation to the MOSFET transistors 402 and 404. During these blanking periods the charged electron beam can be blanked and is translated along the Y axis, but this is not necessarily so. The idle periods 510 and 540 are optional. During the idle period the primary electron beam is not scanned. The idle periods are usually required for re-setting the control circuits after the discharging periods. It is assumed that the scanning pattern of FIG. 3 is implemented. During the scan and image period the primary electron beam is scanned from left to right, as illustrated by the ramp of the X-ramp deflection signal. During the discharge period 530 the primary electron beam is deflected from right to left (as illustrated by the slope in FIG. 6a). The first fast vertical translation of the primary electron beam (corresponding to the first blanking period 304) is illustrated by a vertical line that occurs at T3, as illustrated in FIG. 6b. The second fast vertical translation of the primary electron beam (corresponding to the second blanking period 308) is illustrated by a vertical line that occurs at T6, as illustrated in FIG. 6b. During the discharge period 530, and especially between the blanking periods the voltage supplied to the electrode 30 changes from a first voltage level to another voltage level, for example from positive to negative, as illustrated by FIG. 6d titled “CCP TTL”. According to an embodiment of the invention the first and second voltage are substantially the same, conveniently during a pre-charging mode. Conveniently, the primary electron beam 40 is blanked during idle periods 510 and 540 and during blanking periods 550 and 560, as illustrated by FIG. 6c that illustrates a blanking signal “blanked”. The blanking of the primary electron beam 40 allows to avoid charging the wafer in a non-linear way in the proximity of the next line to be acquired. Such non-linear charging can create contrast artifacts in the image causing the image processing to report false defects. The inventors used an idle periods of about 6 microseconds, while the blanking periods are of about 1 microseconds. The charged particle beam deflection can be implemented by various prior art methods. The inventors stored the scanning pattern in a FIFO structure. Altering the scan patterns as well as timings requires only inputting new data to the FIFO. FIG. 7 is a flow chart of a method 600 for electrically testing a semiconductor wafer, according to an embodiment of the invention. Method 600 starts by stage 610 of scanning a charged particle beam along at least one scan line while maintaining an electrode located at a vicinity of the wafer at a first voltage that differs that a voltage level of a first scanned portion of the wafer, and collecting charged particles scattered from the first scanned portion. The first scanned portion is defined by the at least one scan line. According to an aspect of the invention the method operates at a positive charging mode of operation and the first voltage is more negative than the voltage of the first scanned portion of the wafer. According to another embodiment of the invention the method operates at a negative charging mode of operation and the first voltage is more positive than the first scanned portion of the wafer. Stage 610 is followed by stage 620 of scanning a charged particle beam along at least one other scan line while maintaining the electrode at a second voltage that differs from a voltage level of the second scanned portion such as to control a discharge state of at least an area that conveniently includes the first and second scanned portions. The second scanned portion is defined by the at least one scan line. According to an aspect of the invention the method operates at a positive charging mode of operation and the second voltage is more positive than the voltage of the second scanned portion of the wafer. According to another embodiment of the invention the method operates at a negative charging mode of operation and the second voltage is more negative than the second scanned portion of the wafer. Stage 620 is followed by stage 630 of determining if a predefined section of the wafer was scanned during at least stage 610. If the answer is positive stage 630 is followed by stage 640 of generating an image of the predefined section of the wafer in response to electrons collected during stage 610. Stage 630 is followed by stage 610 if the predefined section was not completely scanned. It is noted that during each iteration of stages 610 and 620 a different portion of the wafer is scanned. Conveniently, stages 610 and 620 include introducing a mechanical movement between the wafer and the electrode. Conveniently, stage 610 includes scanning the first scanned portion with a charged particle beam of a first current and stage 620 includes scanning the second scanned portion with a charged particle of a second current that differs from the first current. Preferably, the second current exceeds the first current. According to an embodiment of the invention the charged particle beam of stage 610 differs from the charged particle beam of stage 620 by its landing energy. Conveniently, the transition from stage 610 to stage 620 involves a deflection of the beam, or at least setting the deflection circuits of the SEM such as to direct a beam to a certain point that is vertically displaced from an ending point of stage 610. Said transition also includes a fast alteration of the voltage supplied to the electrode. Typically, this alteration includes connecting the electrode to a first voltage supply, blanking the first voltage supply and then connecting the electrode to a second voltage supply. Conveniently, method 600 includes a preliminary stage 605 of determining at least one characteristic of stage 610 and stage 620 in response to estimated charging characteristics of the first and second portions of the wafer. It is further noted that the estimation can be altered during the repetitions of stages 610 and 620. Typically the characteristic is the duration of each stage, the current of the charged particle beam, and/or the size of each portion. While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. Rather, it is intended to cover various modifications within the spirit and scope of the appended claims. |
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description | This application claims the priority of European Application No. 09150337.5, filed on Jan. 9, 2009, the disclosure of which is incorporated herein by reference. The invention relates to a storage rack arrangement for the storage of nuclear fuel elements. Nuclear fuel elements and in particular spent nuclear fuel elements are stored in storage pools which are filled with a coolant such as water which simultaneously serves as a shield against the radiation of the fuel elements. The spent nuclear fuel elements remain in the storage pool for so long until they are supplied for reprocessing or, on a case by case basis, final disposal. Storage racks have been developed for the safe storage of nuclear fuel elements, wherein a storage pool can accept a plurality of storage racks which can be arranged side by side and, on a case by case basis, also above one another. A storage rack is known from document DE 29 30 237 A1 for the storage of nuclear fuel elements which contains a plurality of vertical shafts or channels for the reception of the fuel elements, with the walls of the chancels being formed from sheet metal strips arranged above one another. The sheet metal strips are provided with incisions at their lower and upper margins by means of which the sheet metal strips pushed into one another cross-wise are mutually held. The sheet metal strips are arranged between an upper grid plate and a lower grid plate which are connected by braces. The channels and the fuel elements are supported on the lower grid plate in the described storage rack. A further storage rack for the storage of nuclear fuel elements in a storage pool is described in the document U.S. Pat. No. 4,042,828. The storage rack contains a plurality of upright enclosures arranged in rows and forming channels for the reception of the fuel elements. The enclosures which have a square cross-section are arranged in an open rack frame and are open at the lower and upper ends so that the water contained in the storage pool can circulate in the enclosures to cool the fuel elements. The fuel elements placed into the enclosures are supported individually on the floor of the storage pool via supports. It has been found that the above-described storage racks from the prior art only satisfy the demands of a safe storage of the fuel elements with reservations in that noticeable displacements of the storage racks in the storage pools are in particular determined during earthquakes. A storage rack fully loaded with fuel elements typically has a weight between 30 tons and 60 tons so that the forces which occur during an earthquake between adjacent storage racks and between the storage racks and the walls of the storage pool are substantial and there is the risk that the storage racks and the fuel elements stored therein and/or the lining of the storage pool may be damaged during an earthquake and that radionuclides may be released in this process. FIGS. 9, 13 and 14 from the aforesaid document U.S. Pat. No. 4,042,828 show holding clamps by means of which storage racks disposed next to one another can be connected. A displacement between the storage racks during an earthquake can be avoided at least in principle by a connection of the storage racks. The manner of construction of the storage racks described in the named document, however, appears unsuitable to take up larger horizontal forces so that the security against earthquakes can only be increased with limitations by means of the holding clamps. To get to grips with the problem of the earthquake-induced storage rack displacements and the risk associated therewith of the collision with the walls of the storage pool or other apparatus installed in the storage pool, attempts have been made to support the storage racks at the walls of the storage pool and/or to anchor them or screw them tight to the floor of the storage pool. In the past, a plurality of storage pools have been built which are based on this fixed storage rack principle. It was, however, quickly found that this fixed storage rack principle is subject to limitations. At higher earthquake loads and at a higher storage density or at higher masses of the storage racks, locally extremely high peak loads arise at the anchorage points or support points which would necessarily result in damage to these structures, in particular also in leaks in the liner of the storage pool. For this reason, a solution was sought which is suitable for higher earthquake loads and higher storage densities. A substantial improvement for this problem is provided by the so-called “free-sliding” principle which has established itself in newly built fuel element stores in the past few years. In this principle, the storage racks are installed freely in the storage pool and can move in a free-sliding manner in an earthquake. A large portion of the seismic energy is destroyed by the friction occurring on the movement. This principle allows the elimination of the locally extremely high peak loads at the anchorage points or support points of the storage racks, but also has specific disadvantages. One disadvantage is that the earthquake-induced storage rack displacements require a certain free zone all around the storage racks. This is equal to a loss of storage area, which is very expensive. A further disadvantage is that these displacements result in the formation of irregular spacings of different magnitudes between the support racks and that an irregular arrangement of the storage racks can thereby arise after an earthquake which can result in problems with the later handling of the stored fuel elements. A further disadvantage results from the fact that storage racks which are loaded partly and in particular unilaterally are excited to sway at high horizontal earthquake accelerations, with the feet of the storage racks, for example, being able to lift 10 to 20 mm from the floor of the storage pool. Such a sway of the storage racks generates very high impact forces on the floor of the storage pool, whereby the risk of a leak of the storage pool is substantially increased. In addition, an increased tendency to storage rack displacement in the direction of the unloaded site is observed which additionally degrades the stability 20 of the storage racks. It is the object of the invention to provide a storage rack arrangement for the storage of nuclear fuel elements in a storage pool which is built up according to the “free-sliding” principle, but which avoids or greatly reduces the above-described disadvantages of this principle. This object is satisfied in accordance with the invention by the storage rack arrangement described herein. The storage rack arrangement in accordance with the invention for the storage of nuclear fuel elements in a storage pool includes at least two storage racks which each contain a plurality of vertical channels arranged next to one another for the reception of the fuel elements, with positioning elements being provided at the storage racks at the bottom. In addition, storage racks arranged next to one another are connected to one another at the top and the storage rack arrangement additionally includes one or more base plates which are provided with positioning members which fit with the positioning elements of the storage racks and which, together with the positioning elements, position the storage racks with respect to the base plate or base plates, in particular position them in the horizontal direction, to prevent a displacement of the storage racks on the base plate or plates. In an advantageous embodiment variant, the positioning elements are made as support elements on which the storage racks are supported and the positioning members are made as seats in the base plate or plates to receive the positioning elements of the support racks and/or are made as projecting parts on the base plate or plates, with the projecting parts and the positioning elements of the storage racks engaging into one another to prevent a displacement of the storage racks with respect to the base plate or base plates. In a further advantageous embodiment variant, the support elements are each provided with support members, for example with vertically adjustable support members, to support the storage racks on the base plate or plates and/or on the floor of the storage pool. Advantageously, no fixed connection is provided between the storage racks and the base plate or plates, but rather only plug connections or holders are provided so that the storage racks can be positioned simply and can be removed if necessary. For example, in that the positioning elements of the storage racks form plug connections or holders with a respective held part in each case together with the positioning members of the base plate or base plates which can, for example, be joined together by lowering the storage racks to secure the storage racks against horizontal displacement with respect to the base plate or base plates. The base plate or base plates are advantageously displaceable on the floor of the storage pool so that a fuel element store in accordance with the “free-sliding” principle can be built up with the storage rack arrangement. In an advantageous embodiment, storage racks arranged next to one another are each positioned with and/or connected to at least one common base plate. If a plurality of base plates are used, they can be arranged at the periphery of the storage racks, for example substantially at the total periphery of the storage racks. The base plate or base plates can also extend over at least 80% of the base area of the storage rack arrangement or substantially over the total base surface of the storage rack arrangement. Furthermore, the base plate or base plates can be larger than the base area of a storage rack and/or the base plate or base plates can project with respect to the storage racks. In an advantageous embodiment variant, the base plates are connected to one another independently of the connection of the storage racks. In a further advantageous embodiment, the storage racks are each provided with lateral braces. On a case by case basis, the storage racks can be provided on each side with at least three substantially vertically extending braces. Advantageously, the braces of adjacent storage racks are connected to one another in an upper section and/or at the upper end, for example by means of a screw connection. The storage rack arrangement in accordance with the invention has the advantage that the storage racks are connected to one another at the top in a stable fashion, whereas they are secured at the bottom against displacement on the base plate or plates thanks to the positioning members. If a fixed connection between the storage racks and the base plate or plates is omitted, individual storage racks can be replaced simply, if necessary, or the store can be expanded if there is room in the storage pool. A further advantage is that the base plates are displaceable as required on the floor of the storage pool so that the base plates can be displaced freely together with the storage racks as a block or as a storage rack arrangement under seismic accelerations. It is advantageous in this respect that the horizontal component of shocks is not completely transferred from the storage pool floor to the storage rack arrangement. This applies in particular to the transmission of the higher frequency portions of the horizontal component which is greatly damped by the high mass of the storage rack arrangement and the displaceable arrangement thereof. Furthermore, strains in the storage rack arrangement which can arise due to thermally induced length changes can be limited to a non-harmful amount thanks to the displaceable arrangement of the storage racks. It is moreover advantageous that the base plates act as hydraulic damping elements with respect to the vertical component of shocks. In addition, the sway and tilting movements of the individual storage racks are effectively damped by the connection in the upper part of the storage racks in that the connection limits the oscillation amplitudes of the individual storage racks. The seismic analyses show that the base plates on which the storage racks are supported have a large damping effect on the vertical movements and above all on the horizontal movements. Furthermore, the displacements of the storage rack arrangement are also greatly reduced by the connection of adjacent storage racks since those storage racks which are loaded partly and in particular unilaterally are coupled to the comparatively large mass of the other storage racks, which decisively brakes the movement process. The above description of embodiments and embodiment variants only serves as an example. Further advantageous embodiments can be seen from the dependent claims and from the drawing. Furthermore, individual features from the embodiments and embodiment variants described or shown can also be combined with one another within the framework of the present invention to form new embodiments. The embodiment of a storage rack arrangement 10 shown in FIG. 1 for the storage of nuclear fuel elements in a storage pool includes at least two storage racks 1.1-1.3 which each contain a plurality of vertical channels arranged next to one another for the reception of the fuel elements, with positioning elements 6 being provided at the storage racks at the bottom. In addition, storage racks 1.1-1.3 arranged next to one another are connected to one another at the top and the storage rack arrangement 10 additionally includes one or more base plates 2.1-2.3 which are provided with positioning members 8 which fit with the positioning elements 6 of the storage racks and which, together with the positioning elements, position the storage racks with respect to the base plate or base plates and in particular fix the horizontal position of the storage racks with respect to the base plate or base plates to prevent a displacement of the storage racks on the base plate or plates. Advantageously, no fixed connections are provided between the storage racks 1.1-1.3 and the base plate or plates 21.-2.3, but rather plug connections or holders, for example in that the positioning elements 6 are each formed together with the associated positioning member 8 as a plug connection or as a holder with a part to be held. The plug connections or holders with the respective parts to be held can be joined together on the installation of the storage rack arrangement, e.g. by lowering the storage racks onto the base plate or base plates, so that the storage racks are secured against horizontal displacement with respect to the base plate or base plates. In an advantageous embodiment variant, the positioning elements 6 are, as shown in FIG. 1, made as support elements on which the storage racks 1.1-1.3 are supported and the positioning members 8 are made as seats 1.2 in the base plate or plates 2.1-2.3 and/or as projecting parts on the base plate or plates. In a further advantageous embodiment variant, the support elements 6 are each provided with support members 6a, for example with vertically adjustable support members, to support the storage racks 1.1-1.3 on the base plate or plates 2.1-2.3 and/or on the floor 12 of the storage pool. Irregularities of the storage pool floor can be compensated by means of the vertically adjustable support members which can, for example, contain a thread. The base plate or base plates 2.1-2.3 are advantageously displaceable on the floor 12 of the storage pool so that a fuel element store in accordance with the “free-sliding” principle can be built up with the storage rack arrangement 10. On a case by case basis, a liner 11 on which the base plate or base plates are displaceable can be provided on the floor 12 of the storage pool. The liner 11 serves for the sealing of the storage pool and can, for example, be manufactured of steel. In the embodiment shown in FIG. 1, the storage rack arrangement 10 contains three storage racks 1.1-1.3 arranged in a row next to one another in one direction. It is, however, also possible to arrange two storage racks or more than three storage racks in a row next to one another and/or to add one or more further rows in a direction perpendicular thereto to form a storage rack arrangement of the desired size. In an advantageous embodiment, storage racks 1.1-1.3 arranged next to one another are each positioned with and/or connected to at least one common base plate 2.1-2.3. The dimensions of the base plate or base plates can be selected largely freely as long as the positioning storage rack is designed in a manner extending across storage racks. It can be advantageous in practice to select the base plate or base plates to be so large that at least two positioning elements of the same storage rack disposed next to one another as well as two positioning elements of an adjacent storage rack can be positioned by means of a base plate. If a plurality of base plates 2.1-2.3 are used, they can be arranged at the periphery of the storage racks 1.1-1.3, for example substantially at the total periphery of the storage racks. The base plate or base plates can also extend over at least 80% of the base area of the storage rack arrangement or substantially over the total base surface of the storage rack arrangement. Furthermore, the base plate or base plates can be larger than the base area of a storage rack and/or the base plate or base plates can project with respect to the storage racks. In an advantageous embodiment variant, the base plates 2.1-2.3 are connected to one another independently of the connection of the storage racks 1.1-1.3. In a further advantageous embodiment, the storage racks 1.1-1.3 are each provided with lateral braces 4.1-4.4. On a case by case basis, the storage racks can be provided on each side with at least three substantially vertically extending braces. The braces of adjacent storage racks are advantageously each connected to one another at the top, for example at the upper end and/or in an upper section, in particular at a section at the upper end, for example, as shown in FIG. 3, by means of bolts or screw connections 5, 5.1, 5.2. Two respective adjacent storage racks can also be connected to one another at the top in a different manner. For example, if the storage racks each contain an upper grating, for example in the form of a grid plate or terminal plate, or an upper frame, the upper grating or frame of the one storage rack can be connected to the upper grating or frame of the other storage rack. Independently of the embodiment and embodiment variant of the storage racks 1.1-1.3, the base plate or base plates 2.1-2.3 or the support elements 6 or the support members 6a can be provided on the lower side with an additional sliding layer, for example a chromium layer. FIGS. 2A and 2B show an embodiment of a storage rack for a storage rack arrangement in accordance with the present invention; once viewed obliquely from above and once viewed obliquely from below. The storage rack 1 in the embodiment shown includes a channel structure which contains a plurality of channels 9 arranged next to one another with walls 3.1′, 3.1″, 3.2′, 3.2″ for the reception of the fuel elements and a support plate 7 which is connected to the channel structure. Furthermore, the storage rack 1 can, for example, include braces 4.1′, 4.1″, 4.2′, 4.2″ which can be connected to the support plate 7 and to the upper part of the channel structure. On a case by case basis, a grating and/or a terminal plate is/are provided in the upper part of the channel structure and the braces 4.1′, 4.1″, 4.2′, 4.2″ can be connected to them. In an advantageous embodiment, the braces 4.1′, 4.1″, 4.2′, 4.2″ are connected over the total height of the storage rack to the channel structure and/or to the walls 3.1′, 3.1″, 3.2′, 3.2″ of the channels, for example in a throughgoing, point-wise manner or at regular intervals. The channel structure is thereby stabilized with respect to the effect of vertical forces and the braces are secured against buckling. In a further advantageous embodiment, the fuel elements are supported on the support plate 7 during storage. For this purpose, the support plate 7 can be provided with openings and/or slits and respective projecting cams 3.2a″ can be formed at the channel structure and/or at the walls 3.1′, 3.1″, 3.2′, 3.2″ of the channels 9, said cams being pushed into or through the openings or slits of the support plate and being anchored and/or secured against being pulled out on the side of the support plate disposed opposite the channel structure. This embodiment has the advantage that the support plate can have a comparatively small material thickness since the support plate is stiffened sufficiently by the connection to the channel structure to take up the weight of the fuel elements. The cams can, for example, as shown in FIG. 2B, project on the side of the support plate 7 disposed opposite the channel structure and can be anchored by means of latch elements, for example by means of wedges and/or straight or conical bolts and/or splints. Circulation openings 9a are advantageously provided in the support plate 7 so that the water contained in the storage pool can flow through the channels 9 on the storage of the fuel element to cool the fuel elements. The channel structure and/or the walls 3.1′, 3.1″, 3.2′, 3.2″ of the channels 9 are advantageously made up of material absorbing neutrons such as a boron alloy or steel doped with boron or contain material absorbing neutrons. The channel structure can be made with double walls as required. In a further advantageous embodiment, the storage rack 1 additionally includes one or more support elements 6 for the support of the storage rack and/or of the support plate 7. The support elements can, for example, be aligned or centered at the cams of the channel structure. The support elements 6 are on a case by case basis shaped from sheet metal or sheet metal parts, with the lateral metal sheets or metal sheet parts of the support elements advantageously being arranged on the side of the support plate disposed opposite the channel structure directly beneath the walls 3.1′, 3.1″, 3.2′, 3.2″ of the channels 9. The support elements 6 are advantageously fixable to selectable positions of the support plate, for example by means of bolts and/or screws. In an advantageous embodiment variant, the support elements 6 are each provided with support members 6a, for example with vertically adjustable support members, to support the storage rack 1 on the base plate or plates and/or on the floor of the storage pool. The support elements 6 or the support members 6a are advantageously used as positioning elements to position the storage rack 1 with respect to a base plate arranged beneath the storage rack. The storage rack arrangement in accordance with the invention has the advantage that the storage racks cannot be individually displaced toward one another thanks to the positioning members on the base plate or base plates. Furthermore, thanks to the connection of the storage racks in the upper part and to the positioning members on the base plate or base plates, the security against earthquakes of the storage rack arrangement can be increased with respect to the initially described prior art in that both the horizontal component and the vertical component of shocks are effectively damped. |
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046860797 | abstract | A fuel assembly has a fuel spacer consisting of a water rod having an outer diameter greater than that of fuel rods and a large number of circular sleeves into which the fuel rods are inserted. The fuel spacer has four bridge members. Both ends of these bridge members are fitted to two of eight circular sleeves which are adjacent one another in the diagonal direction of the fuel spacer. Both ends of each bridge member are bent so that its center projects outwardly away from the water rod. |
abstract | An electron microscope is offered which can analyze the three-dimensional structure of a specimen without sectioning it by making use of computerized tomography. The microscope has solved the problems intrinsic to the microscope and permits application of computerized tomography to general cases. A series of transmission images is obtained by tilting the specimen by plural angles. Two-dimensional correlation processing is performed between each of the series of images and a reference image. The same field of view is selected and extracted. Thus, positional deviation of the specimen is corrected. |
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abstract | In order to provide an electron microscope which enables the operator to position the field-of-view easily and accurately on a target fault, the electron microscope for observing a surface or inside of a semiconductor wafer or a mask for exposing a semiconductor pattern for faults and/or foreign objects, is provided comprising a function of loading measurement data of coordinates or sizes of faults or objects which were observed by another wafer or mask inspecting apparatus, moving the field of view of the electron microscope to the area where said fault or object exists, and displaying the coordinates of faults or objects which were obtained by another wafer or mask inspecting apparatus, the field-of-view of the electron microscope and its vicinity, a function of a pointing device switch which moves the field-of-view of the electron microscope to a position which is pointed to by a pointer on said display, and a function of changing the display as said field-of-view moves. |
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050874110 | abstract | The device comprises a pipe for aspiration and delivery of water from a well, a column suspended from a traveling crane located above the well and an aspiration head fixed at the end of the column opposite to the crane. The aspiration head is composed of two hollow walls assembled to one another, between which there is a filtration wall separating the internal volume of the head into a first part having an aspiration opening and a second part connected via a conduit to the aspiration pipe. |
abstract | A plurality of slots, which incline in directions that focus toward a source of radiation, are formed in plates constructed of a radiation-absorbing substance. Similarly, a plurality of slots, which incline in directions that focus toward the radiation source, are formed in support members constructed of a radiation-absorbing substance. If the support members and the plates are combined by the engagement between the slots, a scatter-ray removing grid in the form of a lattice is constructed such that each support member and each plate incline toward the radiation source. |
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045129215 | claims | 1. A method of removing corrosion products from the coolant system of a water-cooled nuclear reactor comprising the steps of: (a) adding at least one soluble weak-acid organic complexing agent selected from the group consisting of oxalic acid, citric acid, nitrilotriacetic acid and hydroxyethylethylenediaminetriacetic acid to the coolant to form a decontamination solution; (b) adjusting the pH of the decontamination solution to from 2.5 to 4.0; (c) circulating and decontamination solution at a temperature of from 60.degree. to 100.degree. C. throughout the coolant system to dissolve the corrosion products to form a complexed ion solution of Fe.sup.+2, Fe.sup.+3, .sup.60 Co.sup.+2, and other metal ion complexes; and (d) removing the Fe.sup.+2, Fe.sup.+3 and .sup.60 Co.sup.+2 complexes from the complexed ion solution and regenerating the decontamination solution by passing the complexed ion solution through an anion exchange resin, said anion exchange resin having been presaturated with the anions of the weak-acid organic complexing agent of the decontamination solution such that the concentration of the agents on the resin is substantially the same concentration of the agents in the decontamination solution and having the same pH of the decontamination solution. (a) adding at least one soluble weak-acid organic complexing agent selected from the group consisting of oxalic acid, citric acid, nitrilotriacetic acid and hydroxyethylethylenediaminetriacetic acid to the coolant to form a decontamination solution; (b) adjusting the pH of the decontamination solution to from 2.5 to 4.0; (c) circulating the decontamination solution at a temperature of from 60.degree. to 100.degree. C. throughout the coolant system to dissolve the corrosion products to form a complexed ion solution of Fe.sup.+2, Fe.sup.+3, .sup.60 Co.sup.+2, and other metal ion complexes; and (d) passing the complexed ion solution through a cation exchange resin; 2. The method of claim 1 wherein the decontamination solution contains from 0.2 to 4.0 ppm dissolved oxygen. 3. The method of claim 2 wherein the weak-acid organic complexing agents comprise from 0.005 to 0.02M in oxalic acid and from 0.002 to 0.01M in citric acid. 4. The method of claim 1 wherein the nuclear reactor is a boiling water reactor. 5. The method of claim 1 further comprising the step of recirculating the regenerated decontamination solution through the coolant system. 6. In the method of removing corrosion products from the coolant system of a water-cooled nuclear reactor by: 7. The method of claim 6 further comprising the step of recirculating the regenerated decontamination solution through the coolant system. 8. The method of claim 5 or 7 further comprising the step of purifying the coolant system to remove the organic complexing agents and any metal ion complexes remaining in the system by passing the regenerated decontamination solution through a mixed-bed of anion and cation exchange resins. |
055454275 | claims | 1. A method of covering controlled thermonuclear fusion reactors comprising the steps of preparing a lithium aluminosilicate of the formula Li.sub.4+x Al.sub.4-3x Si.sub.2x O.sub.8 with 0<x<0.28 and depositing said lithium aluminosilicate as a covering material on said reactor. 2. The method of claim 1, wherein the step of preparing the lithium aluminosilicate comprises: a) mixing a short chain anhydrous alcohol including a first alkyl group, a liquid, unpolymerized aluminum alkoxide including a second alkyl group, and, a silicon alkoxide, with a hydrated or unhydrated lithium hydroxide, and exchanging said first and second alkyl groups, b) adding water to the mixture obtained in stage a) in order to hydrolyze it, c) drying at a temperature below 300.degree. C. the hydrolyzed product obtained in stage b) in order to evaporate the alcohols and water and obtain a crystalline powder, d) shaping the powder obtained in stage c) by isostatic or non-isostatic cold pressing, by pouring a slop, by spinning or by extruding and 24 e) subjecting the shaped powder to a thermal sintering treatment at a temperature of 800.degree. to 1200.degree. C. in order to obtain a sintered lithium aluminosilicate or gamma lithium aluminate ceramic. 3. Method according to claim 2, wherein step (a) is performed in a solution of aluminium alkoxide and optionally silicon alkoxide in the short chain anhydrous alcohol, to this solution is rapidly added hydrated or unhydrated lithium hydroxide and mixing takes place accompanied by stirring. 4. Method according to any one of the claims 2 or 3, wherein step (a) further includes the addition of at least one doping agent selected from the group consisting of Na, K and Zn as well as a transition element for the formation of the lithium aluminate or aluminosilicate doped by said agent. 5. Method according to claim 2, wherein the hydrated or unhydrated lithium hydroxide is added to the solution in the form of a powder, solution or suspension of lithium hydroxide in the same short chain anhydrous alcohol as that of the solution. 6. Method according to any one of the claims 3 and 5, wherein the aluminium alkoxide is secondary aluminium butoxide. 7. Method according to either of the claims 2 and 3, wherein the silicon alkoxide is tetraethoxysilane. 8. Method according to any one of the claims 2 or 3, wherein monohydrated lithium hydroxide is used in step a). 9. Method according to any one of the claims 2 or 3, wherein the short chain alcohol is ethanol. 10. Method according to claim 3, wherein the aluminium alkoxide and alcohol quantities of the solution are such that the alcohol:aluminium alkoxide molar ratio is 8 to 30. 11. Method according to claim 2, wherein the water quantity added in step b) is such that the water:aluminium alkoxide molar ratio is 5 to 20. 12. Method according to any one of the claims 2 or 3, wherein step (a) is performed under a nitrogen atmosphere. 13. Method according to claim 2, wherein the sintering heat treatment is carried out in an oxygen atmosphere. 14. A tritium-producing covering material for controlled thermonuclear fusion reactors comprising a lithium aluminosilicate of the formula: EQU Li.sub.4+x Al.sub.4-3x Si.sub.2x O.sub.8 with 0<x<0.28. 15. The tritium producing covering material of claim 14, wherein said lithium aluminosilicate has a grain size of 0.1 to 10 micro meters. 16. The tritium producing covering material of claim 14, wherein said lithium aluminosilicate has a grain size of 0.3 micro meters. 17. The tritium producing covering material of claim 14, wherein said lithium aluminosilicate is further comprised of at least one doping agent selected from the group consisting of Na, K and Zn as well as a transition element. 18. The tritium producing covering material of claim 14, wherein said lithium aluminosilicate has a relative density of about 95%. |
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description | This application claims the benefit of U.S. Provisional Application Ser. No. 60/667,320, filed Apr. 1, 2005 entitled “Over Temperature and Over Power Delta-T Operating Margin.” 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, to an Over Temperature Delta Temperature and Over Power Delta Temperature operating margin recovery method for increasing the Over Temperature Delta Temperature and Over Power Delta Temperature setpoints of a nuclear Reactor Trip System thereby increasing the safe operating margin of the reactor. The invention further relates to a reactor system, such as the Reactor Trip System, employing an Over Temperature Delta Temperature, Over Power Delta Temperature recovery method. 2. Background Information To ensure that the specified acceptable fuel design limits of a nuclear reactor, such as a pressurized water reactor (PWR), are not exceeded, a Reactor Trip System (RTS) is typically employed. The RTS is designed to automatically initiate the rapid insertion of the control rods, commonly referred to as the reactor scram function, of the reactivity control system by interrupting electrical power to the rod control system and allowing the control rods to fall by gravity into the reactor core. Generally, the RTS includes a variety of different devices (e.g., without limitation, power sources, sensors, communication links, software/firmware, initiation circuits, logic matrices, bypasses, interlocks, switchgear, actuation logic, and actuated devices) which are required to initiate a reactor trip. Using such devices, the RTS initiates a trip and shuts down the reactor when established setpoints are surpassed. Among the reactor trip functions the RTS provides are, for example, core heat removal trips including, without limitation, an Over Power Delta Temperature (OPDT) trip, which is designed to effectuate a reactor trip in order to protect against excessive power (i.e., fuel rod rating protection), and an Over Temperature Delta Temperature (OTDT) trip. Conventionally, the OTDT and OPDT setpoints for such trips are calculated based upon dynamic compensations of measured temperature differences in both the hot leg and cold leg of the Reactor Coolant System (RCS), the average of hot leg and cold leg temperature, and the core power distribution in the core of the reactor. However, due to the method of measuring temperature in the hot leg and due to the temperature streaming in the hot leg, steady state temperature fluctuations exist which adversely challenge the OPDT and OTDT trip setpoints. More specifically, several nuclear power plants have been known to experience aperiodic hot leg temperature (Thot) fluctuations that originate, for example, in the reactor vessel upper plenum and wherein the temperature in the hot leg rapidly increases by about 1° F. to about 3° F. in a fast ramp up, remains at an elevated temperature for several seconds, and finally returns to the original temperature. Among other disadvantages, such temperature oscillations undesirably lead to a reduction in the OPDT or OTDT safe operating margin. In turn, this could result, for example, in a partial turbine runback, an actual turbine runback (i.e., when more than one channel is affected) or, in the extreme case, a reactor trip. Such hot leg temperature fluctuations are attributed to the aforementioned hot leg flow streaming phenomenon of the Reactor Coolant System (RCS). Such flow streaming adversely impacts the measured RCS average temperature, which is often used as an input to the Rod Control System and, therefore, can cause spurious control rod stepping when the Rod Control System is in automatic mode. In order to avoid such rod stepping, several power plants have been forced to operate in manual rod control mode. Additionally, in an attempt to accommodate the aforementioned fluctuations, a plurality of filters have been required to be employed in the RTS in order to provide filtering functions in both the cold and hot legs, and after the average temperature has been obtained for both legs. There is a need, therefore, for a modification of protection functions of the RTS and, in particular, of the Over Power Delta Temperature (OPDT) and Over Temperature Delta Temperature (OTDT) trip functions. There is, therefore, room for improvement in OPDT and OTDT operating margin recovery methods and in reactor systems employing the same. These needs and others are met by the present invention, which is directed to an Over Pressure Delta Temperature (OPDT), Over Temperature Delta Temperature (OTDT) operating margin recovery method. As one aspect of the invention, a method is provided for recovering operating margin in a nuclear reactor. The nuclear reactor has a core temperature and a core power distribution and includes a steam generator, a Reactor Coolant System (RCS) having a hot leg with a temperature, Thot, and a cold leg with a temperature, Tcold, a Reactor Trip System (RTS) having an Over Temperature Delta Temperature (OTDT) trip function and an Over Power Delta Temperature (OPDT) trip function, and a control system. The method comprises: measuring a temperature in the hot leg of the RCS and providing hot leg temperature signal representative thereof; filtering the hot leg temperature signal to smooth signal perturbations resulting from temperature fluctuations; measuring a temperature in the cold leg of the RCS and providing an unfiltered cold leg temperature signal representative thereof; establishing an OTDT setpoint for the RTS from the filtered hot leg temperature signal and the unfiltered cold leg temperature signal; establishing an OPDT setpoint for the RTS from the filtered hot leg temperature signal and the unfiltered cold leg temperature signal; measuring at least one of the core temperature and power distribution of the nuclear reactor; comparing the measured core temperature to the OTDT setpoint; comparing the measured core power distribution to the OPDT setpoint; and tripping the nuclear reactor when either the measured core temperature or the core power distribution of the reactor respectively exceeds the OTDT or OPDT setpoint. The method may further comprise sending a trip signal to the reactor control system in order to initiate a reactor trip when the measured core temperature exceeds the OTDT setpoint, and/or sending a trip signal to the reactor control system in order to initiate a reactor trip when the measured core power distribution exceeds the OPDT setpoint. The method may also comprise providing a single filter in the hot leg of the RCS, and employing the single filter to perform the step of smoothing signal perturbations resulting from temperature fluctuations only in the hot leg of the RCS. Accordingly, the previously known requirements of providing separate Tavg and Delta-T filters and of filtering in both the hot leg and the cold leg may be eliminated. The method may include the steps of isolating the hot leg and cold leg temperatures, Thot, Tcold, for use in the OTDT and OPDT functions, and providing separate dynamic compensations for the OTDT and OPDT functions based upon the values of the isolated Thot and Tcold. As another aspect of the invention, a reactor system is provided for a nuclear reactor having a core temperature and a power distribution. The reactor system comprises: a steam generator; a RCS including a hot leg with a temperature, Thot, and a cold leg with a temperature, Tcold, at least the hot leg being in fluid communication with the steam generator; and a filter. The reactor system is adapted to measure a temperature in the hot leg of the RCS and provide a hot leg temperature signal representative thereof, filter the hot leg temperature to smooth temperature perturbations resulting from temperature fluctuations, measure a temperature in the cold leg of the RCS and provide an unfiltered temperature signal representative thereof, establish a first trip setpoint for the nuclear reactor from the filtered hot leg temperature signal and the unfiltered cold leg temperature signal, establish a second trip setpoint for the nuclear reactor from the filtered hot leg temperature signal and the unfiltered cold leg temperature signal, measure the core temperature and the power distribution of the nuclear reactor, compare the measured core temperature to the first trip setpoint, compare the measured core power distribution to the second trip setpoint, and trip the nuclear reactor when either the measured core temperature or the core power distribution respectively exceeds the first trip setpoint or the second trip setpoint. The filter may comprise a single filter disposed in the hot leg of the RCS and being structured to provide the filtering to smooth signal perturbations due to temperature fluctuations in only the hot leg of the RCS. Use of the single filter disposed in the hot leg only may eliminate the requirement of providing separate Tavg and Delta-T filters in the RCS and the requirement of filtering in both the hot leg and the cold leg. The reactor system may be a RTS including an OTDT trip function and an OPDT trip function. The first trip setpoint may be an OTDT setpoint for the RTS and the second trip setpoint may be an OPDT setpoint for the RTS. The RTS may include a first comparator for comparing the measured core temperature to the OTDT setpoint, and a second comparator for comparing the measured core power distribution to the OPDT setpoint. The nuclear reactor may include a reactor control system and the RTS may be adapted to send a trip signal to the reactor control system in order to initiate a reactor trip when the measured core temperature exceeds the OTDT setpoint, and/or to send a trip signal to the reactor control system in order to initiate a reactor trip when the measured power distribution exceeds the OPDT setpoint. The RTS may also be structured to isolate the temperatures, Thot, Tcold, of the hot leg and cold leg for use in the OTDT and OPDT functions and, based upon the values of the isolated Thot and Tcold, to provide separate dynamic compensations for the OTDT and OPDT functions. The nuclear reactor may be a pressurized water reactor and the reactor system may be a Reactor Trip System structured to trip the pressurized water reactor when one of the first trip setpoint and the second trip setpoint is exceeded. FIG. 1 shows, in simplified form, a pressurized water nuclear reactor (PWR) 2 and a hot leg fluid temperature measurement assembly 4 for the steam generator 6 thereof. Generally, the reactor 2 receives water over line 8 and heats the water, which exits the reactor 2 on another line 10, known as the hot leg. The hot leg 10 is shown in FIG. 1 in enlarged simplified, cross-sectional form to illustrate three sensors A, B, C which are disposed on a circular plane normal to the direction of fluid flow in the line. The sensors A, B, C, which comprise, for example, thermocouples or any other known or suitable thermally responsive resistance devices, are coupled to a processor 12 by leads A1, B1, C1. In the example of FIG. 1, the processor 12 includes a memory unit 14 and a display 16 for indicating temperatures TA, TB, TC (not expressly shown) which are provided by sensors A, B, C, respectively. In an attempt to reduce the bias or offset error in the aggregate measured temperature in the hot leg 10 to a repeatable value, it is known to assign different weighing factors to TA, TB, TC based upon their relative magnitudes. For instance, assuming TA produces the lowest measured temperature, it receives a smaller weighting value such that if the weighting factor for TA is 20 percent, the weighting factors for TB and TC are each 40 percent. In this manner, a 20 percent factor is assigned to the noisiest sensor (i.e., TA), and the error is 20 percent of the sum of the offsets of the other two sensors, TB and TC. This error can be accounted for in the analysis or in scaling. Thus, by assigning only 20 percent weighted value to the noisiest sensor, the impact of the temperature fluctuation can be reduced and operating margins can be increased. The foregoing method and system are generally well known and are described in further detail in U.S. Pat. No. 5,253,190. While the foregoing marks an advancement in the art with respect to measurement of the temperature of fluid in the hot leg 10 of the steam generation system 6, there remains a real and recognizable need for further improvement in the establishment of setpoints for the Reactor Trip System (RTS) and, in particular, in the recovery of reactor operating margin by improving the system and method for establishing the Over-Temperature Delta Temperature (OTDT) and Over-Power Delta Temperature (OPDT) trip setpoints. In FIG. 2, a known method or control scheme 18 and a portion of the RTS 20 is shown in simplified form. As previously discussed, OTDT and OPDT setpoints 22, 24 are currently calculated based upon dynamic compensations of the average of the hot leg and cold leg temperature, Tavg, and the core power distribution (not shown) in the core of the reactor 2 (FIG. 1). In operation, the OTDT setpoint 22 is generated by the setpoint circuit generally illustrated by reference character 30 in FIG. 2. The OTDT setpoint 22 is also impact by the pressue and F-Delta-T signals. Comparator 32 then compares the reactor core temperature (i.e., the cold and hot leg temperature difference) or Delta-T in the temperature output signal 13 of hot leg 10 and the temperature output signal 15 of cold leg 11 of the RCS 21 to the OTDT setpoint 22 that was generated by circuit 30. If the Delta-T is exceeded, a trip signal 34 is issued to the reactor control system (indicated generally in FIG. 2 by reference character 42) to inhibit movement (i.e., withdrawal) of the control rods (not shown) and/or to initiate a reactor trip. Similarly, the OPDT setpoint 24 is implemented by the setpoint circuitry generally illustrated by reference character 36 in FIG. 2. In this circuit 36, the core power distribution is measured by Delta-T and any peaks in power are noted and compared to OPDT setpoint 24 by comparator 38. If the Delta-T exceeds the OPDT setpoint, trip signal 40 is generated to stop further control rod movement and/or to initiate a reactor trip depending on the severity with which the setpoint 24 was surpassed. Due to the aforementioned method of measuring temperature in the hot leg 10, discussed previously in connection with FIG. 1, and to temperature streaming (i.e., temperature signal perturbations due to such things as, for example, stratification, and mixing, which can result in differences and fluctuations in temperature readings at different radial locations in the same longitudinal location of the fluid line) and other fluid flow phenomenon in the hot leg 10 associated therewith, steady state temperature fluctuations occur which adversely affect (i.e., reduce) the OTDT and OPDT setpoints 22, 24. Furthermore, filters 26, 28 are required to filter and smooth out signal perturbations resulting from these temperature fluctuations and thereby resist the decrease of setpoints 22, 24. As shown in FIG. 2, the existing RCS 20 requires at least two separate filters 26, 28. Specifically, filter 26 is required to perform Tavg signal filtering and a second filter 28 is required to perform Delta-T signal filtering, in order to accommodate the aforementioned adverse temperature fluctuations. Such known dual filtering is performed in both the hot and cold legs 10, 11 of the RCS 21 and results in the OTDT and OPDT trip margin recovery. However, this dual filtering will take place even if there is a change in the cold leg 11, thus disadvantageously impacting (i.e., reducing) the reactor safety margin in accordance with the RTS 20. The present invention provides a method 118 and Reactor Trip System (RTS) 120 which overcomes these disadvantages and thereby serves to improve (i.e., increase) the OTDT and OPDT trip function setpoints 122, 124 and regain valuable operating margin while not impacting the safety margin. Hot Leg Only Filtering and OTDT, OPDT Operating Margin Recovery As shown in FIG. 3, the present invention provides an OTDT and OPDT operating margin recovery method 118 and RTS 120 wherein filtering to accommodate undesirable temperature fluctuations is performed in only the hot leg 10, through use of a single filter 126. Specifically, a low-pass filter having a variable time constant of, for example and without limitation, from about one to about four seconds is introduced on the hot leg 10. Additionally, it is an object of the invention to isolate the hot and cold leg temperatures, Thot and Tcold, and temperature signals 13, 15 associated respectively therewith, to be used in the OTDT and OPDT channels or circuits 130, 136 separately. Specifically, in accordance with the existing filtering scheme of FIG. 2 the cold leg 11 temperature changes due, for example, to an event such as, for example and without limitation, a steambreak, the magnitude of Delta-T is filtered and reduced (see, for example, the Delta-T plot and, in particular, the first spike, shown in solid line drawing in FIG. 4). Conversely, in accordance with the proposed filtering scheme of FIG. 3, the change in cold leg 11 temperature will impact the Delta-T (see, for example, the Delta-T plot shown in solid line drawing in FIG. 5) and the Thot filter will not change the Delta-T signal or the OPDT (see, for example, the margin plot shown in solid line drawing in FIG. 7) and thus, a reactor trip will occur as required, thereby protecting the reactor core as intended. Accordingly, the proposed filtering scheme and method of the invention, shown in FIG. 3, advantageously enables separate dynamic compensations for the hot leg temperature fluctuations that will not impact the OPDT trip functions. Filtering only Thot temperature signal 13 is also beneficial, for example, during the load rejection transients without impacting the Departure from Nucleate Boiling Ratio (DNBR) margin. Specifically, during load rejections, the temperature in the cold leg 11 increases first, and the core Delta-T decreases. When a filter in accordance with the invention is present in the hot leg 10, the decrease in Delta-T is more pronounced. Hence, a gain or recovery of operating margin is achieved. It has been noted that these load rejections may be between about 10% to about 50%, and are generally bounded by the loss of load transient in the safety analysis. If the proposed modification in accordance with the invention is employed, then for plants where the load rejection is less than about 50%, it is anticipated that the plant will be able to ride through the transient with out challenging any safety systems. Moreover, hot leg only filtering in accordance with the invention has minimal impact on the safety criteria and the Final Safety Analysis Report (FSAR) analysis. Implementing filtering in only the hot leg 10 of the RCS 120 arrests (i.e., minimizes) the decrease of the OTDT and OPDT setpoints 122, 124 during steady state hot leg 10 temperature fluctuations, and thus optimizes reactor operating margin. Specifically, the T-avg increases slowly when the T-Hot filter 126 is employed, which in turn results in the setpoint decreasing slowly. Accordingly, known adverse challenges to OTDT/OPDT trip functions, such as temperature streaming and signal and temperature fluctuations are minimized by T-hot filtering only, in accordance with the invention. More specifically, comparing FIG. 3 to FIG. 2, it will be appreciated that a single filter 126 is implemented only in hot leg 10, replacing the previously required separate filters 26, 28 needed for Tavg and Delta-T filtering in both the hot and cold legs 10, 11 and thereby greatly simplifying the control scheme or operating margin recovery method 118. By eliminating the requirement for separate Tavg and Delta-T filtering in the setpoint circuits 130, 136 of the RCS 120, there is significantly less erosion of the available reactor operating margin. This is, in part, because every time additional filtering is undertaken, the setpoints 122, 124 are necessarily lowered and the operating margin decreased. In other words, by eliminating the Tavg and Delta-T filters 26, 28 (FIG. 2), the OTDT and OPDT setpoints 122, 124 are set at a higher value and, therefore, the reactor operating margin is greater. Accordingly, the invention minimizes the occurrence of highly undesirable interruptions in reactor operations resulting, for example, from marginal over temperature or over power transients, which never jeopardized the safe operation of the reactor, but which nonetheless previously triggered the RTS 20 (FIG. 2) because established OTDT and OPDT setpoints 22, 24 were low, and were easily exceeded. The higher OTDT and OPDT setpoints 122, 124 provided by the method and system of the invention result in the recovery of substantial reactor operating margin. Specifically, trip signals 134, 140 are prompted to trigger reactor control system 142 to initiate a reactor trip less frequently. In summary, as shown in FIGS. 4, 5, 6 and 7, the T-hot filtering scheme of the invention (1) does not undesirably filter or alter (i.e., reduce) the Delta-T fluctuation magnitude and, therefore, does not require a change in the plant safety analysis; and (2) reduces (i.e., minimizes) the amount of decrease in the OTDT/OPDT setpoints 122, 124, thus increasing the operating margin in comparison to the prior proposal (FIG. 2). The benefits and advantages of the method and system of the invention can be more fully understood with reference to the following EXAMPLE. The EXAMPLE is provided to illustrate but one example of the reactor operating margin recovery afforded by the invention, and is not limiting upon the scope of the invention in any way. For the EXAMPLE, hot leg only filtering, in accordance with the invention, was performed on a representative nuclear reactor plant model and compared to the known dual, Tavg and Delta-T filtering method, previously discussed. For the EXAMPLE, the filter variable time constant value was about four seconds for the hot leg only filter 126 (FIG. 3), and about four seconds on both the Tavg and Delta-T filters 26, 28 (FIG. 2). It will be appreciated, however, that the exemplary four second time constant represents but one possible example, offered solely for purposes of illustration, and that any suitable alternative filter time constant ranging, for example and without limitation, from about one second to about 10 seconds, could alternatively be employed. A number of parameters were then compared and the following results were realized: 1. Load Rejection Analysis: the Thot only filter 126 of the invention provided about 2-3 percent more load rejection capability than the existing Tavg, Delta-T filters 26, 28 of the known RTS 20 (FIG. 2). For example, with the existing filtering scheme, if the plant can ride through a 36% to 37% load rejection form 100% with the proposed T-hot only filtering, then in accordance with the invention, the plant would be able ride through a 39% to 40% load rejection without a reactor trip. 2. Steam Line Break (SLB) at 100% Power Analysis: Thot only filtering in accordance with the invention provided about 4-5 percent more power peak than the existing system 20 (FIG. 2) and hence, providing the safety margin. 3. Steady State Fluctuations: the exemplary operating margin recovery method 118 provided substantially the same operating margin gain as if Tavg and Delta-T filtering were provided, thereby illustrating the efficiency of the individual Thot filter 126 and method 118 of the invention. 4. Rod Withdrawal at Power (RWAP) Transients: the results for the RWAP transient analysis, may become more limiting with respect to the minimum DNBR with T-hot only filtering. However, by optimizing the time constant of the filter 126 in hot leg 10, the safety margin can be maintained. Moreover, any difference is far outweighed by the advantages of the exemplary single filter system 120 and method 118 of the invention, as described hereinabove. 5. Rod Control System Impact: Thot only filtering, in accordance with the invention provided better rod control because the Tavg is used for the control system. Using the filters in the hot leg 10 in accordance with the invention reduces the Tavg fluctuations and thus reduces the rod movements. Accordingly, the foregoing EXAMPLE, clearly demonstrates that the invention provides an improved OTDT/OPDT operating margin recovery method 118 and reactor system 120, which among other advantages, eliminate the requirement of having two separate Tavg and Delta-T filtering processes by utilizing Thot filtering only. Additionally, the invention improves the OTDT and OPDT trip functions and, in particular, increases the OTDT and OPDT trip setpoints 122, 124 resulting in the recovery of valuable reactor operating margin (e.g., up to about three percent or more). The foregoing advantages offered by the invention, and in accordance with the aforementioned EXAMPLE, will be still further understood and appreciated with reference to FIGS. 4-7 which provide graphical comparisons of the Delta-T and Margin to OPDT, respectively, of the existing Tavg and Delta-T filtering scheme previously shown and described with respect to FIG. 2, compared to the improved T-hot filtering system and method of the invention, shown in FIG. 3. It will be appreciated that the graphs are provided solely for simplicity of illustration and are not meant to be limiting upon the scope of the invention. FIG. 4 shows a plot comparing the Delta-T fluctuations experienced by the known method and filtering system shown in FIG. 2 in response to a steamline break condition, with the solid line representing the Delta-T in accordance with existing filtering system, and the dashed line representing the measured Delta-T for the same event. The first Delta-T increase (i.e., spike or peak) is due to T-Cold fluctuation. The second peak is due to T-hot fluctuation. The method of FIG. 2 filters both, as shown. However, as shown in FIG. 5, in accordance with the improved filtering system and method of the invention, the first spike will not be filtered (see, for example, the solid line drawing of FIG. 5), and the second spike will be attenuated. The comparison was conducted for a duration of 300 seconds, with the filters in both systems having the same time constant of about four seconds, and the lead/lag values being set at 3/3. As shown, the traditional filtering scheme (FIG. 2) results in the Delta-T fluctuation magnitude being filtered and reduced significantly for both spikes, whereas filtering only in the hot leg in accordance with the invention (FIG. 3) generally did not result in a change of the Delta-T fluctuation magnitude for the first spike. This confirms the fact that the invention provides a system and method which accurately reflects the full spectrum of the affect of a transient condition, such as the steamline break, shown, such that the reactor will trip, as intended. Conversely, the Delta-T fluctuation magnitude in accordance with the existing method, for the first spike shown in solid line drawing in FIG. 4, is substantially reduced, thereby requiring a change to be made in the plant safety analysis in order ensure that the reactor trips, as intended. FIGS. 6 and 7 illustrate an example of the aforementioned improvement in the RTS setpoints offered by the present invention. The system parameters for the plot of FIGS. 6 and 7 were substantially similar to those discussed in connection with FIGS. 4 and 5. Specifically, FIG. 6 compares the margins to OPDT trip for the existing filtering scheme of FIG. 2. As shown with reference to the dashed line drawing, the measured margin is increased for both spikes, shown in solid line drawing. However, as shown in FIG. 7 in solid line drawing, in accordance with the method of the invention (FIG. 3), there was no increase in the margin for the first spike, compared to the measured margin to OPDT trip. Thus, the same safety margin is maintained. Accordingly, the invention provides a number of benefits including, without limitation, the recovery of up to about three percent OPDT and OTDT operating margin when the fluctuations are due to Thot fluctuation, no margin recovery for the OPDT when the fluctuations are due to T-cold fluctuation, the accommodation of temperature fluctuations without turbine runbacks, reduced challenges to reactor safety systems, minimized rod stepping (when operating in automatic rod control), and the ability to support more aggressive fuel management due to the additional operating margin. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof. |
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054065984 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the apparatus for monitoring power of a nuclear reactor according to the present invention will now be described hereunder with reference to the accompanying drawings. FIG. 1 is a schematic view which illustrates the overall structure of the apparatus for monitoring power of a nuclear reactor according to a first embodiment of the present invention. Reference numeral 1 in FIG. 1 represents a nuclear reactor, such as a boiling type nuclear reactor (BWR), in which a core 2 is accommodated and the core 2 is provided with a plurality of neutron flux detecting or measuring devices 3. Each of the neutron flux detection devices 3 is, as a nuclear reactor instrumental system, disposed in the core 2 per about four fuel assemblies 4 as shown in FIG. 2 to monitor and make instrument of the power of the nuclear reactor, the axial and radial distributions of the power from the reactor core 2 in an output power operational state of the nuclear reactor. For example, a 1100 MWe class BWR has the core 2 in which 48 neutron flux detection devices 3 are disposed, each neutron flux detection device 3, as shown in FIG. 3, having four neutron flux detectors 5 disposed vertically to serve as local power range monitors (LPRM). The four neutron flux detectors are generally called A, B, C and D when viewed from a lower portion. The core 2 of the nuclear reactor 1 usually has 100 or more neutron flux detectors 5. For example, a 1100 MWe class BWR has the core in which 43.times.4=172 (channels) neutron flux detectors are present. A power signal in the form of an analog signal is, as an LPRM signal, taken out from each neutron flux detector 5. The LPRM signals from the neutron flux detectors 5 are averaged into groups each consisting of about 20 signals by an average power range monitor (APRM), and equally averaged to be formed into APRM signals. Further, the nuclear reactor 1 includes a core present state, data measuring device 7 as shown in FIG. 1, the core present state data measuring device 7 being used to measure the quantity of state, such as the quantity of flow of a coolant, the temperature of the coolant and the pressure of the same or a core operational state signal (a signal denoting the measured quantity of state of the plant), which is present data (process data) of the core, such as the quantity of the insertions of the control rod. The core operational state signal is also an analog signal. Power data signals transmitted from each neutron flux detector 5 of the neutron flux detection or measuring device 3 and the core present state data measuring device 7 are supplied to a data sampler 8. The data sampler 8 samples and digitizes data denoted by the analog power data signals (each LPRM signal and the core operational state signal). Each LPRM signal and the core operational state signal digitized by the data sampler 8 are, as data about the neutron flux and that about the reactor core, transmitted to a process control computer (a process computer) 9 serving as neutron flux distribution calculating means and to a filter calculating device 10. The process control computer 9 is started periodically or at timing in accordance with a requirement made by an operator to calculate the neutron flux distribution in the fundamental mode in the core 2 at the moment of starting. The process control computer 9 calculates the neutron flux distribution in the fundamental mode of the core 2 in the present state, the foregoing function corresponding to a monitoring function of the process control computer 9. The process control computer 9 has a prediction function in addition to the monitoring function, the prediction function being so arranged that the state of the reactor core instructed by the operator is calculated and predicted in accordance with the result of the latest monitoring function to calculate the neutron flux distribution in the fundamental mode in the predicted state of the core. The neutron flux distribution of the reactor core in the present state calculated by the process control computer 9 and the results of calculations of the neutron flux distribution of the core 2 in the predicted state are, via an input/output device 11, which is input/output means, transmitted to be notified to the operator and supplied to power distribution monitoring device 12 so that the state or the core is displayed by a display device 13. The results of the calculations performed by the process control computer 9 are supplied to a higher mode calculating device 14. The higher mode calculating device 14 is started in synchronization with the process control computer 9 to solve Equation (2) as to calculate the higher mode of the neutron flux calculated by the process control computer 9, the results of calculations being supplied to the filter calculating device 10. The higher mode calculating device 14 may be included in the process control computer 9 in place of the individual disposition as to be integrally included. Specifically, the method of calculating the higher mode has been disclosed in, for example, document "DETAILED NUMERICAL CALCULATIONS AND EXERCISE" written by Hayato Togawa, published by KYORITSU SHUPAN. The filter calculating device 10 receives each LPRM signal sampled and digitized by the data sampler 8. In accordance with a digital signal of the supplied measurement signal, the optimum filter is obtained in accordance with the phase difference and the amplitude difference between the signals. On the other hand, the filter calculating device 10 obtains a filter corresponding to a higher mode calculated and extracted by the higher mode calculating device 14. That is, the filter calculating device 10 obtains filters corresponding to the state of the reactor core or the changing characteristics of the respective LPRM signals measured directly. In the filter calculating device 10, each LPRM signal which has been measured directly and supplied to the filter calculating device 10 is filter-processed (average-operated) by the filter corresponding to the phase difference and the amplitude difference and the filter corresponding to the extracted higher mode. The processed filter signal is supplied to a stability monitoring device 15 serving as stability monitoring means which is connected in an on-line manner and to an input/output device 11. The input/output device 11 transmits a filtered LPRM signal to be notified to the operator. The stability monitoring device 15 receives the filtered LPRM signal to monitor the decay ratio, the resonant frequency (the period of the oscillations) and the amplitude and the like showing the stability as to detect an oscillation phenomenon and discriminate/evaluate an oscillation mode so that the stability of the state of the reactor core is estimated. The process of calculations for obtaining desired filters to be performed in the filter computing device 10 will now be described. The obtained filters are categorized into two types consisting of a filter of a type obtainable by calculating each LPRM signal always supplied from the data sampler 8 and a filter of a type obtainable by extracting the higher mode distribution calculated by the higher mode calculating device 14. The former filter is a filter calculated in accordance with the respective LPRM signals, which are actual measurement signals detected sequentially or continuously, while the latter filter is a filter calculated in accordance with information supplied from the process control computer 9 and reflecting the power distribution in the core 2 corresponding to the change of the operational state, for example, the change of the operational state taken place due to the operation of the control rods or the change of the operational point realized by controlling the re-circulation flow. The latter filter can be obtained by way of the process control computer 9 at the time of the intentional change of the state of the reactor core of the nuclear reactor. The former filter obtainable by the filter calculating device 10 is obtained by sequentially or at short time intervals (several tens seconds) (or continuously) obtaining the statistic quantity of the respective LPRM signals, which are the actual measurement signals, that is, the cross correlation function and variance of the respective LPRM signals. The dispersed values reflect the degree of the changes of the respective LPRM signals (the amplitude difference), and therefore, the variance show the importance (weight) of the LPRM signal. The cross correlation function shows the degree of the correlated relationship among the respective LPRM signals by expressing the phase difference of the oscillations of the respective signals. That is, the former filter can be obtained in accordance with the amplitude difference and the phase difference among the respective LPRM signals. The variance and the cross correlation function are defined by a general manner. The variance and the cross correlation functions respectively are defined by an unbiased estimator as follows: [Numerical Formula 8] ##EQU3## [Numerical Formula 9] ##EQU4## The former filter, which is the first filter, is calculated in such a manner that, for example, the variance value of LPRM signal k (where k is a suffix) is used to obtain standard deviation .delta.k which is the square root of the variance, mean standard deviation value .delta. of all LPRM signals is obtained, the ratio of the standard deviation .delta.k and the mean standard deviation value .delta. is obtained, and the ratio .delta.k/.delta. is made to be a first filter attribute W1 (k). The filter attribute W1 (k) is used to weight the signal. The importance of the LPRM signal corresponding to the degree of the first filter attribute W1 (k) is use to select a LPRM signal having the largest amplitude as a standard signal. Then, the cross correlation function between the standard signal and the residual LPRM signals is calculated. The delay time, at which the cross correlation function is the largest, corresponds to the phase difference from the standard signal. If the delay time is zero, no phase difference presents between the two signals. If the delay time is the half of the amplitude period, the phase difference is 180.degree. C., that is, the two signals are in opposite phases. Assuming that the delay time for the LPRM signal k from the standard signal is tk and the filter attribute at time t is W2 (k, t), the filter attribute W2 (k, t) is given by W2 (k, t)=Wk (t-tk) when the LPRM signal k is expresses by Xk (t). That is, the former filter has two filter attributes W1 (t) and W2 (k, t) which are respectively expressed by [Numerical Formula 10] EQU W1(t)=.sigma.k/.sigma. (10) [Numerical Formula 11] EQU W2(k,t)=Xk(t-tk) (11) The first and second filter attributes W1 (t) and W2 (k, t) are automatically estimated in a relatively short time of several tens of seconds in accordance with the change of the LPRM signal. The first filter attribute W1 (k) of the former filter is a weighting coefficient for weighting a portion, in which the LPRM signal is considerably changed and which is therefore assumed to be the oscillation source to use the portion in an emphasized manner. The second filter W2 (k, t) is a phase correction coefficient which eliminates cancelling between the LPRM signals occurring due to the detected phase difference among LPRM signals and which eliminates (synchronizes) the phase difference between the signals to improve the signal sensitivity. A method of obtaining filter coefficient W3 (k, m) of the latter filter will now be described. The foregoing filter coefficient is a third filter coefficient corresponding to the change of the power distribution occurring due to the change of the operational region or the like. The process control computer 9 is started at timing at which data about the reactor core of data about the neutron flux is supplied upon the request from the operator, the process control computer 9 being arranged to calculate the neutron flux distribution (the fundamental mode) in the state of the core at the start time. The central flux distribution in the fundamental mode is a mode which is present most stably in the core 2. In particular, the power distribution in the core 2 is changed while preventing a considerable deviation of the fundamental mode even if a local disturbance or a feedback is effected in the core 2. If the reactor power is changed in accordance with the fundamental mode, the reactor power can be detected in the conventional manner in which the APRM signal which is obtained by simple averaging and which is supplied from the average power range monitor (APRM) is used. If a local feedback effect or the like is applied to the reactor core 2, there is a possibility a higher mode except the fundamental mode is excited. A typical higher mode is an oscillation event called "regional oscillations". The foregoing oscillation event excites a spatial higher mode. By using the spatial higher mode distribution as the third filter coefficient W3 (k, m), the latter filter is made to be a filter that selectively emphasizes the change of the excited spatial higher mode. The reason why the latter filter employs the spatial higher mode distribution as the third filter coefficient W3 (k, m) is as follows. An assumption is made that the neutron flux distribution in the core in the fundamental mode is .PHI.0 and the neutron flux distribution in an m-th harmonics is .PHI.m. Since the transient neutron flux distribution f (t) at the time of the oscillation, such as the regional oscillations, can be assumed to be a superposing distribution of the neutron flux distributions .PHI.0 and .PHI.m of the fundamental mode and the higher mode, the following equation is held. [Numerical Formula 12] ##EQU5## If the neutron flux distribution in the core 2 is uniformly changed in the overall reactor core, magnitude function A0 (t) of the fundamental mode controls and the magnitude function Am (t) of the higher mode is a value substantially approximating zero. In an oscillation effect, such as the regional oscillations, in which the spatial higher mode is excited, the magnitude function A0 (t) of the fundamental mode is substantially constant but a certain component in A0 (t) is changed mainly. The neutron flux distributions .PHI.0 and .PHI.m of the fundamental mode and the higher mode hold an orthogonal relationship with each other. Therefore, integrating the neutron flux distribution for the overall reactor core (the capacity of the reactor core): [Numerical Formula 13] ##EQU6## where wmn is called a Krnecker's delta. Equation (13) can be expressed by the following formula: [Numerical Formula 14] ##EQU7## Therefore, by using an n-th harmonics .PHI.n as the latter filter, an average signal is expressed as follows: [Numerical Formula 15] ##EQU8## Therefore, only the change of higher mode components for use in the filter can selectively be extracted. As a result, by adding a higher mode distribution calculating function to the process control computer 9 or by independently providing a higher mode distribution calculating device 14, the higher mode of the neutron flux distribution in the core 2 at the time of the start of the process control computer 9 and by using the neutron flux distribution .PHI.n in the higher mode as the filter, the change of the mode of the ruling neutron flux distribution in the regional oscillations can be emphasized and extracted. Since the neutron flux distribution in the higher mode cannot be easily excited in proportion to the increase in the order, the higher mode, to which attention is paid actually, is limited to about first to third harmonics. In order to take a countermeasure against a pump trip or the like occurring at the transient operation of the nuclear reactor, the state of the core after the transient effect has been settled is estimated by the process control computer 9 or the higher mode calculating device 14 simultaneously with the transient effect. Further, the higher mode distribution in the estimated state is obtained to be stored as the third filter coefficient W3 (k, m). By performing switching to the filter corresponding to the transient event at the time of the occurrence of the transient event, adaptation to the state of the reactor core at the time of the transient event can be performed. The operation of the apparatus for monitoring the power of the nuclear reactor will now be described. The reactor power distribution in the core 2 of the nuclear reactor 1 is detected by each neutron flux detector 5 of the neutron flux detection or measuring device 3 in such a manner that the axial and radial neutron flux distributions in the core 2 are measured. The analog LPRM signals transmitted from the respective neutron flux detector 5 and the core operational state signal transmitted from the core present state data measuring device 7 are supplied to the data sampler 8 to be digitized. The LPRM signal and the core operational state signal sampled and digitized by the data sampler 8 are supplied to the process control computer 9. In the process control computer 9, the signals are calculated periodically or at a request made by the operator. The result of the process is notified to the operator by way of the input/output device 11 and also supplied to the power distribution monitoring device 12 so that the reactor power distribution is monitored, the state of the reactor core being displayed by the display device 13. The process control computer 9 is, as shown in FIGS. 4 and 5, supplied with the LPRM signal in the core 2 detected by each neutron flux detector 5 and the plant state quantity measurement signal, which is the reactor core operational state signal supplied from the core present data measuring device 7 to calculate and estimate the state in the core 2 periodically or at the requirement made by the operator. The process control computer 9 calculates (monitoring function) the neutron flux distribution of the fundamental mode in the core 2 and calculates (prediction function) the neutron flux distribution .PHI.0 in the fundamental mode in the core state instructed by the operator in accordance with the results of the calculations. The core state signal (a process signal) calculated by the process control computer 9 is supplied to the higher mode calculating device 14 in which the higher mode of the neutron flux distribution in the core 2 is estimated. That is, the neutron flux distribution (the power distribution) .PHI.n in the spatial higher mode is calculated. The spatial higher mode power distribution signal thus calculated is supplied to the filter calculating device 10, which is used to obtain the filter reflecting the power distribution in the core 2 realized due to the change of the operational state. The filter has the third filter W3 (k, m) to selectively emphasize the change of the spatial higher mode, the filter serving as a filter for extracting the higher mode. The filter calculating device 10 is sequentially or continuously supplied with each LPRM signal, which is the actual measurement signal, from the data sampler 8, the filter calculating device 10 being able to obtain a filter corresponding to the amplitude difference and the phase difference among the LPRM signals. The filter has the first and second filter coefficients W1 (t) and W2 (k, t). The respective LPRM signals are caused to pass through the high mode extraction filter and the filter corresponding to the amplitude difference and the phase difference of the respective LPRM signals obtained by the filter calculating device 10 to be filtered so that extraction of the spatial higher mode, weighting the signals and an averaging operation for correcting the phase difference are performed. The LPRM signals (the filter signals) subjected to the averaging process by using the respective filters obtained by the filter calculating device 10 are then received by the stability monitoring device 15 so that the decay ratio, the resonant frequency and the amplitude, which are the stability indexes, are monitored. In accordance with the result of the monitoring, the oscillation phenomenon is detected to discriminate and evaluate the oscillation mode. The apparatus for monitoring the power of the nuclear reactor is so arranged that the LPRM signals, which are the actual measurement signals, are allowed to pass through the respective filters obtained by the filter calculating device 10. As a result, power responses having large amplitudes as shown in FIGS. 7A and B can be obtained. Since the conventional apparatus for monitoring power of a nuclear reactor is so simply arranged that the respective LPRM signals, which are the actual measurement signals, are equally averaged to obtain the APRM signal, the respective APRM signals are equally averaged, and therefore, cancelling takes place among the APRM signals. FIG. 6, FIGS. 7A and B show schematic examples in which filtering is performed by using the higher mode extraction filter, the weighting filter and the phase correction filter in contrast with the conventional example in which the APRM signal is obtained by the equal averaging method. An example of response of the decay ratio obtained from the response after the process performed by making use of the higher mode extraction filter shown in FIG. 6 is shown in FIG. 8. FIG. 8 shows an example of the response realized by monitoring by making use of the stability monitoring device 15, this example using plant data in which regional oscillations have been observed. In this response example, time series data of the regional oscillations is used, and power signals are monitored by the stability monitoring device 15, the power signals being signals obtained by averaging all LPRM signals by applying the filter (its filter coefficient is W3 (k, m)) reflecting the spatial higher mode distribution to all LPRM signals. The oscillation state of the regional oscillations is an example in which a first mode is excited as the higher mode. The fundamental mode shown in FIG. 8 corresponding to a conventional case where the state of the reactor core is monitored by using the APRM signal. Defining the unstable region in the operation of the nuclear reactor to be a state in which the decay ratio is 0.8 or more, the result of the monitoring performed in accordance with the response of the neutron flux distribution of the fundamental mode component of the neutron flux distribution shows that the decay ratio is 0.8 or less and a discrimination is made that the reactor core state is stable. However, it can be understood from the response of the neutron flux distribution of the higher mode component that the decay ratio exceeds 0.8 and rapidly makes unstable the oscillations. The unstability of the core state coincides with the observed data about the actual regional oscillations. Therefore, it can be understood that the stability of the core state can accurately be discriminated from the response of the decay ratio obtained from the first mode component of the higher mode. That is, FIG. 9 shows the magnitudes of the oscillations of the fundamental mode and the first mode components of the neutron flux distribution, that is, the amplitudes of parameters corresponding to A0 (t) and A1 (t) of Equation (12). As can be understood from the response examples of the fundamental mode component and the first mode component of the neutron flux distribution shown in FIG. 9, the amplitude of the primary mode component is small in the vicinity of 500 seconds which has been discriminated to be unstable in terms of the decay ratio shown in FIG. 8, and the amplitude rapidly grows and oscillations are generated. By computing both of the decay ratios and the magnitudes of the oscillations to comparisons, the oscillation state can be monitored more finely. Therefore, the power oscillation phenomenon of the reactor core and the oscillation mode can be monitored more accurately. Although the response examples shown in FIGS. 8 and 9, the higher mode extraction filter is used to discriminate and evaluate the stability of the state of the reactor core, the discrimination and the evaluation of the stability of the state of the reactor core can be performed similarly by using the weighting filter W1 (k) or the phase correction filter W2 (k, t) obtainable by the filter computing device. The system for monitoring the power of a nuclear reactor of this embodiment is a stability monitoring apparatus that obtains the filters for specifically extracting the oscillation modes in accordance with the spatial higher mode power distribution to discriminate the stability of the core in response to the LPRM signal processed by the filters. The system for monitoring the power of a nuclear reactor uses the two types of filters calculated by the filter calculating device 10, the two types of the filters being the filter that corresponds to the change of the power distribution taken place due to the change of the operational state and adapted to the change of the power distribution at the transient state and the filter corresponding to the sequential change of the power signals, which are the actual measurement signals. Therefore, the monitoring of the stability of the core can be performed further accurately. The system for monitoring the power of a nuclear reactor is able to accurately detect and discriminate the stability of the state of the core including the power change, which has been difficult to be detected by the conventional APRM signal as compared with the conventional APRM signal obtained by simply averaging the analog signals. Therefore, the safety can be improved and the availability can be improved. A second embodiment of the system for monitoring the power of a nuclear reactor will now be described. The system for monitoring the power of a nuclear reactor according to this embodiment is basically different from the system for monitoring the power of a nuclear reactor shown in FIG. 1 in that a subcriticality evaluation device 17 serving as subcriticality evaluation means as shown in FIG. 10. The same structures as those of the apparatus for monitoring the power of a nuclear reactor shown in FIG. 1 are given by the same reference numerals and their descriptions are omitted here. The subcriticality evaluation device 17 is connected to the process control computer 9, the results of calculations performed by the process computer 9 being supplied to the subcriticality evaluation device 17 as shown in FIG. 10. The subcriticality evaluation device 17 estimates the subcriticality in the operational state in accordance with the results of the calculations performed by the process control computer 9. The subcriticality of a nuclear reactor is affected by a temporary state of the reactor core as described above because it depends upon the power distribution, that is, the distribution form of the fundamental mode. FIGS. 11A and 11B show, together with the subcriticality, the neutron flux distribution in the fundamental mode in a certain state of the reactor core of a 1,100,000 KWe class boiling water nuclear reactor similarly to FIGS. 17A and 17B and FIGS. 18A and 18B. In FIG. 11A, a relatively flat neutron flux distribution is realized, and therefore, the subcriticality exceeds 1. In FIG. 11B, the control rods are inserted into the central portion of the reactor core, and therefore, a neutron flux distribution, the periphery of the reactor core is raised, is realized and the subcriticality is 1 or less. As can be understood from FIGS. 11A and 11B, the subcriticality depends upon the distribution form of the fundamental mode of the neutron flux and is further reduced in a state of the reactor core further approximating the first mode distribution form, that is, the fundamental mode is high in the periphery of the reactor core. As an index for evaluating the difference in the distribution form of the neutron flux, RL value obtainable by the following Equation (16) can be employed. [Numerical Formula 16] EQU RL=Sum.phi..sub.1.sup.2 L1/SumL1 (16) where .phi.1: fundamental mode averaged in the axial direction of fuel bundle 1 L1: distance of fuel bundle 1 from the center of reactor core PA0 SnC: LPRM data calculated from the neutron flux of n-th mode. The sum of Equation (16) is obtained from all fuel bundles (the fuel assemblies) in the reactor core. The RL value takes small value with a flat power distribution (the neutron flux distribution) as shown in FIG. 11A, while it takes large values with a periphery high power distribution as shown in FIG. 11B. It can be understood that the RL value holds a controversial relationship with the subcriticality. FIG. 12 shows the relationship between the subcriticality and the RL value at the oscillation commencement point in an oscillation case of the reactor power which has taken place in an overseas plant recently. The oscillation case shown in FIG. 12 includes core-wide and regional oscillations. In FIG. 12, the white circles indicate the core-wide oscillation and the black circles indicate the regional oscillations. As can be understood from FIG. 12, the regional oscillations are observed in a state where the subcriticality is small, and FIG. 12 confirms the relationship between the subcriticality and the RL value. Therefore, by previously obtaining the relationship between the subcriticality and the RL value for a specific operation cycle for the nuclear reactor, the subcriticality in the state of the reactor core can instantaneously be estimated from the relationships expressed by Equation (16) and FIG. 12 by only obtaining the fundamental mode of the neutron flux distribution in an arbitrary state of the reactor core. Further, if the subcriticality estimated by the foregoing method meets the following condition, the subcriticality evaluation device 17 discriminates that the regional oscillations can be excited and notifies this to the operator by way of the input/output device 11. [Numerical Formula 17] EQU .DELTA..lambda.<EPS (17) where EPS is a predetermined value. The input/output device 11 has the following functions: a. To display the result of the monitoring function of the process control computer 9; PA1 b. To be used to estimate the state of the reactor core when the process control computer 9 is caused to execute its prediction function; PA1 c. To display the result of the monitoring of the power control device. FIG. 13 illustrates a flow of the process to be performed in the system for monitoring the power of a nuclear reactor according to this embodiment. Referring to FIG. 13, the operation of this embodiment will now be described. When the system for monitoring the power of a nuclear reactor is started in step S1, the process control computer 9 is started periodically in step S2 or at the time of a requirement in step S3 made by the operator. When the periodical starting is performed, the process control computer 9, in step S4, reads the LPRM signals from the respective neutron detectors 5 through the data sampler 8 to calculate the basic mode of the neutron flux in the present state of the reactor core in step S5. When starting upon the requirement made by the operator is performed, the process control computer 9 first sets the state of the reactor core by using the input/output device 11 in step S6, and reads the result of the latest monitoring in step S7. In next step S8, the process control computer 9 calculates the fundamental mode of the neutron flux distribution in the set state of the reactor core. The subcriticality evaluation device 17 first reads of the fundamental mode of the neutron flux calculated by the process control computer 9 in step S9, calculates the RL value from Equation (16) in step S10 and estimates the subcriticality of the reactor core from the relationship between the RL value and the subcriticality in step S11. In step S12, the subcriticality evaluation device 17 displays and notifies the result to the operator by way of the input/output device 11. In the next step S13, a discrimination is made whether or not the other state is present. If it is present, the flow returns to step S6. If the same is not present, the process is completed in step S14. Thus, the operator makes use of the prediction function of the process control computer 9 to easily predict an arbitrary state of the reactor core, for example, where the re-circulation pump trips and the core flow reduces to a natural circulation or a case when the selected rods have been inserted (SRI) to prevent the core-wide oscillation. Further, the subcriticality in the foregoing predicted state can quickly be estimated. Although many control rod patterns are usually provided for use to perform the selected rod insertion (SRI), the optimum control rod pattern capable of preventing the regional oscillations can be selected by evaluating the state of the core with respect to all of the provided control rod patterns. FIG. 14 illustrates a third embodiment of the system for monitoring the power of a nuclear reactor according to the present invention. The system for monitoring the power of a nuclear reactor according to this embodiment comprises both a filter computing device serving as the filter computing means and the subcriticality evaluation device serving as the subcriticality evaluation means. Specifically, the structure is arranged in such a manner that the subcriticality evaluation device is included by the apparatus for monitoring the power of a nuclear reactor shown in FIG. 1. The same structures are given by the same reference numerals and their descriptions are omitted here. The system for monitoring the power of a nuclear reactor according to this embodiment estimates the easiness of the occurrence of the power oscillation phenomenon, such as the regional oscillations, that cannot easily be detected by the conventional APRM signal, from the viewpoint of the spatial higher mode subcriticality by means of the subcriticality evaluation device. Further, the filter computing device is used to obtain the filter for extracting the characteristics of the changes of the respective LPRM signals, the filter thus-obtained is used to filter and average the respective LPRM signals so that the operational state of the reactor core can be monitored. Therefore, the system for monitoring the power of a nuclear reactor is able to estimate the easiness of the occurrence of the regional oscillations, to simultaneously control the reactor core while preventing the regional oscillations and to monitor the oscillation state of the core. FIG. 15 illustrates a fourth embodiment of a system for monitoring the power of a nuclear reactor. In this embodiment, a higher mode calculating device 18 is used in place of the subcriticality evaluation device 17 according to the second embodiment and the neutron flux detectors 5 are omitted. The system for monitoring the power of a nuclear reactor according to this embodiment comprises the data sampler 8 which receives core present state data supplied from a core present data measuring device 7 as shown in FIG. 15, the data sampler 8 being arranged to supply the data, as core state data, to the process control computer 9 periodically or at a requirement made by the operator. The process control computer 9 calculates the neutron flux distribution (fundamental mode) in the reactor core 2 at the time of the execution of the SRI in accordance with core state data supplied from the data sampler 7 and the previously-registered control rod pattern at the time of the execution of the SRI as shown in FIG. 15. The results of the calculations are supplied to the higher mode calculating device 18. The higher mode calculating device 18 calculates the higher mode of the neutron flux calculated by the process control computer 9 by solving Equation (2). The higher mode calculating device 18 notifies the results of the calculations to the operator by way of the input/output device 11. FIG. 16 shows a flow of the process to be performed by the system for monitoring the power of a nuclear reactor according to this embodiment. When the system for monitoring the power of a nuclear reactor is started in step S21, the process control computer 9 reads the core state data supplied from the reactor core present state data measuring device 7 by way of the data sampler 8 in step 22. Further, the process control computer 9 sets the state of the core by way of the input/output device 11 in step S23. This setting is performed by setting, in step S24, the state of the core evaluated by the operator by making use of the input/output device 11. Then, the basic mode of the neutron flux in the set state of the core is calculated in step S25. On the other hand, the higher mode calculating device 18 reads the fundamental mode of the neutron flux calculated by the process control computer 9 in step S26. In next step S27, Equation (2) is solved in terms of the first mode of the neutron flux, and in next step S28, the results are displayed to the operator by way of the input/output device 11. As a result, the subcriticality calculated by the higher mode calculating device 14 is displayed on the input/output device 11 to be notified to the operator. By evaluating the subcriticality of the higher mode of the neutron flux at the time of the initiation or operation of the SRI as described above, the possibility of the regional oscillations in the core condition can be notified to the operator. Therefore, the nuclear reactor can be operated at a reduced cost economically and efficiently. Although the foregoing description about the embodiment comprises the process control computer that has a function as the neutron flux distribution calculating means, it may have the higher mode calculating means and the subcriticality evaluation means. FIG. 19 shows a fifth embodiment of an apparatus for monitoring power of a nuclear reactor. Referring to FIG. 19, in the core 2 of the reactor 1, usually more than 100 LPRMs 3 are arranged. Further, arranged inside the reactor 1 is a core present state data measuring device 7 for measuring data of the core states such as the total flow rate of the coolant, the core-inlet/outlet temperatures of the coolant, and the control rod positions. The enumerated data on the LPRMs 3 and the measured data obtained by the core present state data measuring device 7 are sampled periodically by the data sampler 8, or upon request of the operator, and input to the process control computer 9 and a higher mode calculating device 14. The calculation results obtained by these calculators are outputted through an input/output device 11 and reported to the operator. The process control computer 9 is initiated in synchronism with the data sampling by the data sampler 8 shown in FIG. 19, calculating the neutron flux distribution inside the core 2 at the time or state. This corresponds to the monitoring function, which is one of the functions of the process control computer 9, in which the neutron flux distribution inside the core 2 is calculated. Apart from this monitoring function, the process control computer 9 has a predicting function. With this predicting function, the core condition as designated by the operator is calculated on the basis of the latest results obtained by the monitoring function, calculating the neutron flux distribution in this core condition. In this case, the process control computer 9 is initiated upon request of the operator. The calculation results of the process control computer 9 are input to the higher mode calculating device 14, which is initiated in synchronism with the process control computer 9. By solving Equation (2), the the higher mode of the neutron flux calculated by the process control computer 9 is calculated. This calculation method is described, for example, in the publication as mentioned hereinbefore. Further, the higher mode calculating device 14 is supplied with LPRM enumerated data from the data sampler 8 until there is a request from the operator, performing the following calculation: [Formula 18] ##EQU9## where SM: LPRM enumerated data The calculation result of Equation (18) is, unlike that of equation (5'), to be regarded as a mode substitute value in that the LPRM measured data and the LPRM calculated data are used instead of the neutron flux itself. As shown in FIG. 19, the calculation result of the higher mode calculating device 14 is inputted to the input/output device 8 along with the output from the process control computer 9. The input/output device 11 displays the result obtained by the monitoring function of the process control computer 9 and the calculation result of the higher mode calculating device 14 and, at the same time, is used to designate the core state in executing the predicting function of the process control computer 9. FIGS. 20A and 20B show the present invention as applied to a power output oscillation in the reactor of a 1,100,000 kwe class. FIG. 20A shows the case of a core-wide power oscillation, and FIG. 20B shows the case of a regional power oscillation. As is apparent from FIGS. 20A and 20B, in the case of a core-wide oscillation, the magnitude of the fundamental mode oscillates greatly, but the magnitude of the first harmonics mode is almost constant. In contrast, when a regional power oscillation occurs, the magnitude of the first harmonics mode oscillates greatly, whereas the magnitude of the fundamental mode scarcely changes. Thus, in accordance with this embodiment, a regional oscillation is coped with from the viewpoint of neutron higher modes, and the magnitude of each higher mode is indicated with respect to time, so that it is possible to quickly inform the operator of any regional oscillation, thereby enabling the reactor to be operated safely and efficiently. As described above, the system for monitoring power of a nuclear reactor according to the present invention monitors the reactor power and the power distribution by using the respective neutron flux detection signal (LPRM signal) in such a manner that the filter calculating means obtains the filters (the filter coefficients W1 (t), W2 (2) and W3 (k, m) for extracting the characteristics of the signal change in response to the neutron flux detection signal. The filters thus-obtained are used to filter the respective neutron flux detection signals so that the decay ratio and the amplitude of the oscillations showing the operational state of the core and the amplitude showing the degree of the power change (oscillation) can be obtained. Therefore, the stability of the core can be monitored. The apparatus for monitoring power of a nuclear reactor according to the present invention comprises the filter calculating means in addition to the conventional APRM signal obtained by averaging the analog signals to monitor the reactor power and the reactor power distribution by using each neutron flux detection signal. The filter calculating means obtains the filter corresponding to the state of the core or obtains the same corresponding to the change characteristics of the signal in response to each neutron flux detection signal, the filter for extracting the characteristics of the signal change being used to filter each neutron flux detection signal so that the decay ratio, the period of the oscillations and the amplitude showing the stability of the state of the core are obtained at the time of monitoring the stability of the core. The calculation of the filter performed by a filter calculating means by a calculating step for periodically calculating the filter in accordance with the change of the spatial distribution characteristics of the reactor power whenever the operation condition is changed and by a sequential calculating step for calculating it in accordance with the amplitude difference or the phase difference between the signals. The former is calculated in accordance with information from the neutron flux distribution calculating means, which is a process control computer and that from a higher mode calculating means, while the latter is calculated in response to the neutron flux detection signal, which is an actually measured signal that is sequentially detected. The power signal filtered by the filter calculated by the filter calculating means is received by the stability monitoring means to obtain sequentially the decay ratio and the oscillation period showing the stability of the reactor core and the amplitude showing the power change. The obtained values are used to monitor the stability of the reactor core to be evaluated in an on-line manner. The system for monitoring power of a nuclear reactor is able to accurately detect the power change phenomenon, and, in particular, the power oscillation phenomenon due to the regional oscillations, which has been difficult to be detected by using the conventional APRM signal. Therefore, the apparatus is able to contribute to improve the stability of the reactor core and the availability of the nuclear reactor. The system for monitoring power of a nuclear reactor according to the present invention is able to discriminate the possibility of the generation of the regional oscillations from the subcriticality of the state of the core obtained by the subcriticality evaluation means, to estimate the easiness of occurring the regional oscillations, to monitor the stability of the state of the core, to control the reactor core while preventing the generation of the regional oscillations and to operate the nuclear reactor safely and efficiently. The system for monitoring power of a nuclear reactor according to the present invention calculates the higher mode of the neutron flux in a state of the core when the selected rod insertion (SRI) is initiated and discriminates whether or not its subcriticality is smaller than a predetermined limit value. Therefore, the possibility of the excitation of the regional oscillations at the time of the operation of the SRI can quickly be discriminated. Therefore, the nuclear reactor can be operated safely and efficiently. |
054694809 | abstract | The currently used atomic reactors has to be refueled periodically. During this refueling, the checking and repair of the major sections of the atomic reactor are carried out, and therefore, a low water level operation, i.e., mid-loop operation, is carried out for removing the residual heat. According to the present invention, a round-about pipe conduit is additionally installed between a suction pipe conduit and a discharge pipe conduit of the residual heating removing pump, and a flow rate adjusting valve is installed on the round-about pipe conduit. Thus the flow passing through the pump is maintained at the normal operation level during the mid-loop operation, while, as the residual heat is decreased, the round-about flow rate is gradually increased until the suction rate from the hot leg can be maintained at a proper level, thereby preventing the introduction of air into the residual heat removing pump. |
047568747 | abstract | In water-cooled nuclear reactors where zinc is added to the water to remove or lessen the accumulation of radioactive cobalt, radioactivity arising from the zinc itself as a result of neutron capture is lessened or eliminated entirely by modifying the isotopic composition of the zinc prior to its injection into the system. The modification of the isotopic composition consists of lowering the proportion of .sup.64 Zn or removing this isotope entirely. |
summary | ||
051456370 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, a boiling water reactor system 1 includes reactor pressure vessel 2 with bottom head 3, as shown in FIG. 1. Below reactor core 4 sits core support plate 5 with circular openings on which sit which fuel assemblies, dry-tubes, and other internal parts of the core. Dispersed below core 4 are incore guide tubes 6. These are welded to the top of incore housing tubes 7 that penetrate bottom head 3 of the pressure vessel wall. These penetrations are sealed with incore housing welds 8, which are crucial since the inside of pressure vessel 2 is under pressure and is radioactive. Access to this region, as well as core 4, is facilitated by top guide 9, which is a metal grid with a matrix of square openings. Equipment and parts in this region are handled from refueling bridge 10, which is a trolley that rides across the refueling platform on rails. A hoist on refueling bridge 10 uses hoist cable 11 to raise and lower equipment and parts into this region. Adjacent to pressure vessel 2 is a refueling pool 12, which contains spare reactor fuel. In order to check the region around weld 8 for flaws a combination of ultrasonic testing of the weld region, and eddy current testing of the inner surface of housing tube 7 is employed. A submersible device for performing such an examination is shown in FIG. 1; hoist cable 11 is used to lower a unit including scanning tool 21, probe 22, and probe tube 23 into position at the weld to be tested. Probe 22 is lowered through incore guide tube 6 and incore housing tube 7 until it is level with weld 8, and scanning tool 21 is clamped to top guide 9 with a mechanical clamping device. Probe tube 23 is clamped to scanning tool 21 at a previously determined location so that when scanning tool 21 and top guide 9 are at the same level, probe 22 and weld 8 are at the same level. Scanning tool 21 moves probe 22 automatically to perform the inspection, and data is sent to electronic processing and control equipment outside pressure vessel 2 via cable bundle 24 for analysis. Wiring to probe 22 runs through probe tube 23. The nature of any defects found during inspection is determined with reference to a previously manufactured set of defects found in calibration standard 26, which is a duplication of the housing weld configuration. Support bracket 25 is used for storage as well as calibration of the inspection equipment. Positioning of the incore housing inspection equipment is most easily seen from above the reactor, as shown in FIG. 2. The inspection equipment is moved using refueling bridge 10 until scanning tool 21 is located above an incore housing. These are below the intersections in the metal matrix of top guide 9. Scanning tool 21 is mounted at such an intersection for weld inspection. The hoist on refueling bridge 10 moves equipment in the vertical direction. Bridge 10 moves along the refueling platform on rails, which in turn moves between pressure vessel 2 and refueling pool 12, also along two parallel rails. Cable bundle 24 sends commands to scanning tool 21 and the probe (beneath the scanning tool), as well as carries data back to work station 27, which is outside the pressure vessel. FIG. 3 shows a side view of the inspection equipment, and also shows a box diagram of the electronic gear used to control and receive data from the inspection equipment. Relative electrical impedance data (both vertical and horizontal components) is digitally recorded for the four eddy current coils with the eddy current instrument, eddy current computer, and storage tape. The eddy current instrument records raw data, and the eddy current computer prepares it for storage. The eddy current instrument also drives the eddy current coils, and can drive each one independently at different frequencies. Reflection data for the six ultrasonic transducers is recorded with a pulser/receiver, data aquisition unit (which includes a central processing unit), and an optical disk recording module. Both systems are connected to the motion controller, which is connected to the motors and position encoders in scanning tool 21 to move probe 22 automatically. Both systems also have printers for hard copy read-outs. The ultrasonic system also has a monitor for an electronic read-out. The method of determining the direction of the high side of the housing welds, is shown in FIG. 4. Pressure vessel 2 is assigned a permanent coordinate system with a central origin. Scanning tool 21 is mounted on top guide 9 with clamp 28 secured to top guide 9. When the inspection equipment is first lowered into pressure vessel 2 and clamped into place the probe (the straight-on transducer on the probe) faces the 0.degree. reference direction. The angle .beta. which the probe must be rotated to face the high side of the weld is determined by the location of scanning tool 21 relative to the origin in the pressure vessel's coordinate system, since the bottom head of pressure vessel 2 is rotationally symmetric. Thus the probe can be oriented to face the high side of the weld by remote-control, given the scanning tool's coordinates, which are the same coordinates as those of the incore housing. If the initial rotational orientation of the probe is known, then its rotational orientation is known throughout the inspection. Knowing the rotational orientation of the probe gives clues as to the type of indications which might be found, what their size is, and whether they are classified as acceptable or non-acceptable. The basic mechanical components of scanning tool 21 are shown in FIG. 5. Scanning tool 21 comprises a fixture with two DC motors with positioning encoders attached. The DC motors drive the probe in the circumferential and verical directions with encoders providing the positioning data. The mechanical portion of the tool is housed in a cylindrical can which is locked in position on the pressure vessel top guide by a mechanical clamping device. Probe tube 23 fits through shaft 31, and is clamped thereto with clamp 32 after the length and angular orientation of probe tube 23 is set so probe 22 will initially face the high side of the weld after a rotation through an angle .beta., as discussed in connection with FIG. 4. The length of the lower extension of probe tube 23 is set by sliding it vertically through shaft 31 until probe 22 will be at weld level. The rotational orientation is set by aligning scribe marks on probe tube 23 and shaft 31, so the probe will point in the same direction as the mechanical clamping device that fastens scanning tool 21 to the pressure vessel top guide. Brackets 33 also hold scanning tool 21 in place on the top guide. Once in place the circumferential drive rotates shaft 31, probe tube 23, and probe 22 clockwise through the angle .beta. to put probe 22 in its initial position before weld inspection. Once probe 22 is in its initial position the weld and housing tube inspection is performed automatically. Probe 22 is driven with vertical and circumferential drive motors in such a way as to inspect the housing weld and housing tube from at least 40 mm above the weld to at least 40 mm below the weld. In practice, this distance is about 2 inches. The eddy current and ultrasonic inspections are done independently. Probe 22 moves vertically from above the weld to below the weld, then rotates 5.degree., and moves upwards to above the weld, then rotates 5.degree.. This repeats until it has rotated 360.degree.. The two drive motors each have encoders to control them, based on the position of the probe. Vertical movement of probe 22 coincides with the movement of travel plate 34, since they are connected via probe tube 23 and shaft 31. Stops 35 and 36 are the upper and lower limits of motion for the travel plate. The START SCAN position of travel plate 34 before the respective eddy current (EC) and ultrasonic (UT) inspections is different; on probe 22 the eddy current coils are located about 2.7 inches below the ultrasonic transducers. To inspect the same region above the weld, travel plate 34, and hence probe 22, must be raised 2.7 inches higher for the eddy current inspection than for the ultrasonic inspection. The vertical drive moves travel plate 34 down until the eddy current coils are about two inches below the weld for the eddy current inspection, and unitl the uppermost transducer (the straight-on transducer) is about two inches below the weld for the ultrasonic inspection. Before the automatic scan the initial position of the straight-on transducer is such that it faces the high side of the weld, as mentioned above. More specifically, it faces the top of the high side of the weld. In this way the probe is raised the same amount to inspect the required region above each weld. The amount the probe is lowered is then varied to inspect the required region below the weld. Welds higher up on the bottom head of the pressure vessel are at a greater angle, so the amount the probe is lowered is correspondingly greater. Probe 22 has six piezo-electric transducers (T1-T6), arranged as shown in FIG. 6. All are turned on during the ultrasonic scan. Transducers T2-T6 are all simultaneously focused so as to interrogate both of the weld fusion zones. They are focused at the same point at the interface between the incore housing and the weld. This permits examination of the entire weld region including the interface between the weld and the bottom head of the reactor. Transducer T1 is focused at the interface between the incore housing and the weld, but above the others. An arbitrary indication (flaw) shows up if it reflects a portion of the beam back to the transducer that sent it, with the greatest reflection coming back if the indication is perpendicular to the direction of the beam. The transducers are pulsed sequentially, with each pulse followed by a time interval for reception. The elapsed time until reception reveals the location of an indication since the speed of sound in the various materials the beam travels through is known. The magnitude of a reception reveals the size of an indication, due to prior instrument calibration. All examination data is stored by computer techniques, and can be presented graphically with a hard copy printer. Space considerations cause straight-on transducer T1 to be located about 2 inches above transducers T2-T6. Transducer T1 is aligned with the top of the high side of the weld in question after the scanning tool is clamped to the top guide, as discussed above. Thus, to position transducers T2-T6 about two inches above the top of the high side of a weld, the vertical drive raises the travel plate 4 inches to the UT START SCAN position. The vertical drive then lowers the travel plate until T1 is about 2 inches below the bottom of the weld. (At this point the other five transducers T2-T6 are 4 inches below the weld, which results in additional data in the interval from 2-4 inches below the weld. When T2-T6 are 2 inches above the weld T1 is 4 inches above the weld, which also results in additional data for the region 2-4 inches above the weld.) The probe rotates 5.degree., then the travel plate returns to the UT START SCAN position, the probe rotates another 5.degree., and repeats the vertical sweep. This continues until probe 22 has rotated 360.degree. to complete the ultrasonic inspection. Transducer T1 is a longitudinal tranducer with a frequency of 2.25 MHz. T1 looks straight-on, i.e. perpendicular to probe 22 in a horizontal direction, and is aligned with the top of the high side of the weld before the scan. Its purpose is to provide indication, thickness, and depth information, and to provide information as to the condition of the weld, e.g. cracking, lack of fusion, inclusions, porosity, etc. There are four 45.degree. shear wave transducers with a frequency of 5.0 MHz. Transducers T2 and T3 look right and left, while transducers T4 and T5 look up and down. Transducers T2 and T3 examine the incore housing and weld circumferentially to detect indications oriented in the axial direction. T4 and T5 examine the volume of material in the axial direction to detect circumferentially oriented indications in the housing and weld. The downward-looking transducer is also used to examine pressure vessel material below the normal plane of coverage. Transducer T6 is a 60 degree refracted longitudinal wave transducer with a frequency of 2.25 MHz. T6 looks down, and is used to ascertain the condition of the weld build-up area which is present in some incore housing weld designs. In these designs a build-up of weld material is applied to the pressure vessel in such a manner that all the incore housing weld attachments are horizontal. The eddy current assembly on probe 22 has four coils 40, as shown in FIG. 6. The coils are positioned 90.degree. apart around the lower end of the probe. Two of the four coils are of the absolute type with one coil, and the other two are of the differential type that use two coils for reference and stabilization purposes. The absolute coils are used to provide the required depth of penetration, which is near surface. The differential coils are used to minimize the effect of conductivity and magnetic permeability variations in the heat-affected zone surrounding the weld. The eddy current assembly is used to examine the inner surface and near surface of the housing for defects. Eddy current coils 40 induce a current in the surface of a conductor, i.e. metal. Variations in the surface of the conductor cause changes in the surface impedance. The changes in impedence have characteristic patterns corresponding to dents, corrosion, or any other flaw with an associated impedence pattern. All examination data is retained digitally on magnetic tape, and can be presented graphically on computer screen and/or be presented in hard copy form with a printer. The EC START SCAN position of the scanning tool's travel plate is higher for eddy current coils 40 than for the transducers because of their lower position on probe 22, but since coils 40 are at the same level the vertical drive moves them from 2 inches above to 2 inches below the weld without taking into account a coil that is not on the same level. (The vertical sweep is longer for the ultrasonic inspection because transducer T1 is above the others, as previously described.) The eddy current inspection is otherwise identical to the ultrasonic inspection, i.e. vertical sweeps are made in 5.degree. increments until probe 22 has rotated 360.degree.. Examination of the inner surface and near surface of a housing tube may be done with only one eddy current coil since both the absolute and differential coils provide adequate sensitivity. All four coils are placed into service, however, in case a mechanical problem diminishes the performance of a primary coil. The absolute coils are 0.25 inches in diameter, and the differential coils are 0.125 inches in diameter. Both types operate at nominal frequencies of 100 KHz, but they may be individually driven at other frequencies to provide additional information for analysis. Each coil is spring loaded to maintain contact with the inner surface of the housing tube in order to minimize the effect of lift-off. Spring-loaded balls 41 roll along the inner surface of the incore housing, and help protect eddy current coils 40 from physical damage. FIGS. 7-12 show the paths of the six transducer beams as they traverse an incore housing weld. In general, indications that present cross-section to the ultrasonic beams will send a reflection back to the probe and be detected. FIG. 7 shows the path the beam from transducer T1 follows as the probe passes weld 8 going either up or down. Above weld 8, the beam reflects at the interface between the wall of housing tube 7 and the water inside the pressure vessel. Below weld 8, the beam reflects at the interface between the wall of housing tube 7 and air gap 50, which is present in the region below weld 8 between the wall of housing tube 7 and bottom head 3 of the pressure vessel. When T1 is level with weld 8, the ultrasonic beam diverges at the interface of the wall of housing tube 7 and weld 8, and it passes into bottom head 3 of the pressure vessel, or is reflected at the interface between weld 8 and the water inside the pressure vessel. Arbitrary indications that cause a sufficient reflection back to the probe as it traverses weld 8 will be detected. FIG. 8 shows the paths the beams from transducers T2 and T3 follow as the probe passes weld 8 going either up or down. Above weld 8, the beams reflect at the interface between the wall of housing tube 7 and the water inside the pressure vessel. Below weld 8, the beam reflects at the interface between the wall of housing tube 7 and air gap 50 between housing tube 7 and bottom head 3 of pressure vessel 2. When T2 and T3 are level with weld 8, the ultrasonic beams pass through the interface of the wall of housing tube 7 and weld 8, and go into bottom head 3 of pressure vessel 2, or are reflected at the interface between weld 8 and the water inside the pressure vessel. T2 and T3 are specifically intended to find indications that are axially oriented (lie in the direction of housing tube 7). FIG. 9 shows a plan view of the ultrasonic beam paths from transducers T2 and T3 at a single location when they are at weld 8 level. Each beam is oriented 45.degree. in the circumferential direction from T1's beam. Probe 22 essentially fills housing tube 7, and the beams pass through housing tube 7, into weld 8 and bottom head 3 of the pressure vessel. Axial indications are "double checked" from both the clockwise and counter-clockwise directions. FIG. 10 shows the path the beam from transducer T4 follows as the probe passes weld 8 going either up or down. Above weld 8, the beam reflects at the interface between the wall of housing tube 7 and the water inside the pressure vessel. Below weld 8, the beam reflects at the interface between the wall of housing tube 7 and air gap 50, between housing tube 7 and bottom head 3 of the pressure vessel. When T4 is level with weld 8, the ultrasonic beam passes into weld 8 until it is reflected at the interface between weld 8 and the water inside the pressure vessel. T4 is specifically intended to find indications that are circumferentially oriented (tend to lie in a horizontal plane in a direction perpendicular to housing tube 7). FIG. 11 shows the path the beam from transducer T5 follows as the probe passes weld 8 going either up or down. Above weld 8, the beam reflects at the interface between the wall of housing tube 7 and the water inside the pressure vessel. Below weld 8, the beam reflects at the interface between the wall of housing tube 7 and air gap 50, between housing tube 7 and bottom head 3 of the pressure vessel. When T5 is level with weld 8, the ultrasonic beam passes into weld 8 and down into bottom head 3 of the pressure vessel below the normal plane of coverage. T5 is also specifically intended to find indications that are circumferentially oriented. Also, circumferential indications that might tend to be slightly oriented upwards in the direction of the T4 beam will form a greater angle with the T5 beam, and circumferential indications that might be oriented downwards in the T5 direction will form more of an angle with the T4 beam, so circumferential indications are also "double checked" as the probe traverses the weld. FIG. 12 shows the path the beam from transducer T6 follows as the probe passes weld 8 going either up or down. Above weld 8, the beam reflects at the interface between the wall of housing tube 7 and the water inside the pressure vessel. Below weld 8, the beam reflects at the interface between the wall of housing tube 7 and air gap 50, between housing tube 7 and bottom head 3 of the pressure vessel. When T6 is level with weld 8, the ultrasonic beam passes into weld 8 and down into bottom head 3 of the pressure vessel below the normal plane of coverage, and closer to housing tube 7 than the T5 beam. Indications that are circumferentially oriented in weld build-up regions, which are employed in some reactor housing attachment welds to make them level, will cause reflections back to the probe as the T6 beam traverses the weld. Since all the transducers are on during the inspection, an indication will generally show up on more than one transducer read-out. The status of the attachment weld is then known. With the additional information available from the eddy current examination, the status of the entire weld region is determined. It is then possible to decide whether or not repairs are needed. Because the examination is normally done when the incore instrumentation is tested (and replaced), there is a considerable savings of time and money inspecting the welds from the inside of the incore housing tubes with access from above. This savings is in addition to the greatly increased margin of safety over the prior method of examining the welds from below, in which workers were exposed to high radiation levels. Also, since the entire scanning process is automated, there is a higher standard of precision than the prior method, which was manual. The invention provides for other embodiments than those described above. For instance, the invention provides for inspection of any circumferential weld about the outside of a tube with access from above, and an overlay suitable for supporting a scanning tool. The weld need not be inside a nuclear reactor pressure vessel. This invention provides for different numbers and types of transducers, depending on the individual circumstances. The transducers need not be focused at the interface of the tube and the weld, but may be focused at other regions of interest. These and other modifications to and variations upon the described embodiments are provided for by the present invention, the scope of which is limited only by the following claims. |
claims | 1. A structure for improving resistance of an inner wall of a fusion reactor to plasma irradiation, comprising:a fusion reactor comprising an inner wall; anda structure for improving resistance of the inner wall of the fusion reactor to plasma irradiation, the structure comprising:a copper substrate; anda plurality of metal sheets combined with the copper substrate, wherein individual metal sheets of the plurality of metal sheets are laminated to one another, each metal sheet having a thickness between 1 μm and 20 μm, and gaps between adjacent metal sheets of the plurality of metal sheets being between 0.01 μm and 1 μm, wherein a plane of the plurality of metal sheets extends in a direction perpendicular to a plane of the inner wall of the fusion reactor. 2. The structure of claim 1, wherein each metal sheet of the plurality of metal sheets comprises a plasma-facing material. 3. The structure of claim 2, wherein the plasma-facing material comprises at least one of tungsten, tungsten alloy, molybdenum or molybdenum alloy. 4. The structure of claim 3, wherein each metal sheet of the plurality of metal sheets comprises the same plasma-facing material. 5. The structure of claim 3, wherein the plurality of metal sheets is manufactured by hot or cold rolling. 6. The structure of claim 3, wherein at least some of the metal sheets of the plurality of metal sheets comprises a different plasma-facing material than an adjacent metal sheet. 7. The structure of claim 1, further comprising channels located in the gaps between the adjacent metal sheets, wherein the channels are configured such that components of a plasma that enter the inner wall of the fusion reactor are diffused from each of the adjacent metal sheets and returned to the plasma through the channels. 8. A method for improving resistance of an inner wall of a fusion reactor to plasma irradiation, the method comprising:laminating a plurality of metal sheets together with gaps between adjacent metal sheets of the plurality of metal sheets being between 0.01 μm and 1 μm, each metal sheet of the plurality of metal sheets having a thickness between 1 μm and 20 μm and comprising a plasma-facing material;positioning the plurality of metal sheets proximate a surface of an inner wall of a fusion reactor with a plane of the plurality of metal sheets extending in a direction perpendicular to a plane of the inner wall of the fusion reactor; andcombining the laminated plurality of metal sheets together with a copper substrate. 9. The method of claim 8, wherein the plurality of metal sheets and the copper substrate are combined together via casting or brazing. 10. The method of claim 8, further comprising forming channels in the gaps between the adjacent metal sheets such that components of a plasma that enter the inner wall of the fusion reactor are laterally diffused from opposing side surfaces of the adjacent metal sheets and returned to the plasma through openings of the channels located adjacent the plasma. |
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description | 1. Field of the Invention The present invention is directed to a method of providing a mid-wall repair, as well as a method of evaluating the mid-wall repair. 2. Discussion of the Related Art In pressurized water (PWR) and boiling water (BWR) nuclear reactors, multiple penetrations are provided in a pressure vessel or piping. The penetrations consist of sleeves and/or nozzles that extend from the exterior of the pressure vessel through openings in a low alloy or carbon steel vessel wall and a nickel-chromium-iron (Ni—Cr—Fe) or stainless steel clad disposed on the interior surface of the pressure vessel. During initial fabrication (i.e., before access to the interior of the pressure vessel is limited, and before the pressure vessel is subjected to radiation and pressurized high temperature water as a result of operation of the nuclear reactor), a J-shaped groove is formed in the vessel interior clad and in some cases the low alloy steel or carbon steel vessel interior wall as well, and a weld material is deposited in the groove to weld the nozzle to the clad and vessel wall, where applicable. Thus, the nozzle is welded from the interior of the pressure vessel to connect the nozzle to the pressure vessel. As a result of operating and residual stresses in the J-groove weld and the primary water environment during operation, the welds, the sleeves or nozzles, and the Ni—Cr—Fe or stainless steel cladding are subject to stress corrosion cracking. Thus, it becomes necessary to repair the connection between the nozzle and the pressure vessel. In a known repair technique, the technician does not have access to the highly radioactive interior of the closed pressure vessel. Thus, repair of the connection between the pressure vessel and the nozzle is conducted from the exterior of the pressure vessel. In the known repair technique, the nozzle is severed at the mid-wall of the pressure vessel and a sacrificial plug installed to create a flush surface at the exterior of the pressure vessel. A welding pad of a material that is not susceptible to stress corrosion cracking, such as Alloy 52, is formed on the exterior of the pressure vessel. A hole is drilled in the welding pad, and a replacement nozzle formed of a material that is not susceptible to stress corrosion cracking, such as Alloy 690, is disposed in the hole. The replacement nozzle is then welded to the welding pad. Because it is not practical to provide postweld heat treatment stress relief of the weld and the adjacent areas, a temper bead welding technique is used to weld the welding pad to the pressure vessel or piping. The known repair technique suffers from a number of disadvantages, however. These disadvantages include that it is often difficult to precisely align the replacement nozzle with the openings in the pressure vessel wall and the new welding pad on the pressure vessel. Further, a relatively large amount of material is used to provide the welding pad of sufficient size (e.g., 6 inch by 6 inch by 0.5 inch) to permit testing and evaluation of the weld pad to the pressure vessel. Further, because formation of the temper bead must be precisely controlled, the weld pad requires a relatively large amount of time to produce, which may increase down time of the nuclear reactor and the amount of radiation to which the technician is exposed during the repair process. The severity of these problems is compounded by the fact that a typical pressure vessel includes multiple nozzles. The present invention provides a method of repairing a connection between a first nozzle and a closed vessel. An entire thickness of the first nozzle is cut through at a location adjacent to the mid-wall of the vessel. A portion of the first nozzle is removed. A replacement nozzle is disposed in a void formed by removal of the portion of the first nozzle. A weld is formed between the replacement nozzle and a surface at the mid-wall of the vessel. The present invention further provides a method of repairing and inspecting a first nozzle penetrating a closed vessel, including removing a portion of the first nozzle, forming a weld between a replacement nozzle and a surface of the mid-wall of the vessel, and evaluating the integrity of the weld at the mid-wall of the vessel. The present invention still further provides a closed vessel. A mid-wall is disposed between an interior wall and an exterior wall of the vessel. A first nozzle extends from a first portion of the mid-wall to the interior of the vessel. A second nozzle extends from a second portion of the mid-wall to the exterior of the vessel. A weld is disposed between the second portion of the mid-wall and the second nozzle. Examples of one or more embodiments of the present invention are described with reference to the drawings, wherein like reference numbers throughout the several views identify like or similar elements. The method of providing and evaluating a mid-wall repair, as shown in the drawings and as described herein, can be provided between a pressure vessel or piping 100 (referred to as pressure vessel in the following discussion) of a PWR or BWR nuclear reactor and at least one nozzle 10. It is to be understood, however, that the method can be applied to various structures, including various nuclear reactor structures as well as structures that are not disposed in a nuclear reactor. As shown in FIG. 1, the pressure vessel 100 can include an interior surface 101 opposite an exterior surface 103, and a mid-wall 105 extending between the interior and exterior surfaces 101 and 103. The interior and exterior surfaces 101 and 103 can be curved or contoured, and the mid-wall 105 can be of a constant thickness, at least in the position through which the nozzle 10 is disposed. A clad material 107 can be disposed on the interior surface 101. In a preferred embodiment, materials of the mid-wall 105 and the clad 107 can include steel, and more preferably can include a low alloy or carbon steel and an Ni—Cr—Fe or stainless steel material, respectively. As discussed above, the pressure vessel 100 can include at least one nozzle 10. In a preferred embodiment, the pressure vessel 100 can include a plurality of nozzles 10. It is to be understood, however, that the pressure vessel 100 can include any number of nozzles 10. As shown in FIG. 2 and FIG. 1, the nozzle 10 can be in the form of a sleeve or nozzle having an exterior surface 13 opposite an interior surface 15, and a heater or other component 20 disposed within an interior defined by the interior surface 15 of the nozzle 10. In a preferred embodiment, a material of the nozzle 10 can include an Alloy 600 or stainless steel material. A weld 109 can be used to connect the pressure vessel 100 and the nozzle 10. In a preferred embodiment, a groove can be formed in the clad 107 or a combination of the clad and vessel wall with weld butter. More preferably, the clad 107 or combination of clad and vessel wall can include a J-shaped groove. The weld 109 can be formed in the groove to weld the pressure vessel 100 to the nozzle 10. It is to be understood, however, that various welds can be used to weld the pressure vessel 100 to the nozzle 10. As shown in FIG. 2, during an initial stage of the mid-wall repair process, a length of the nozzle 10 on an exterior side of the pressure vessel 100 can be removed. In a preferred embodiment, the nozzle 10 can be cut by an abrasive cutting operation commencing on the exterior surface 13 of the nozzle 10. It is to be understood that the various material and component removal processes, including abrasive grinding and cutting, can be performed manually (i.e., by hand or with hand tools) or remotely (i.e., by automatic tools or processes, including those in use or those that are later developed). As shown in FIG. 2, the heater or other component 20 can then be removed from the interior of the nozzle 10, decontaminated, and otherwise repaired or replaced, depending on its condition. As shown in FIG. 3, the length of the nozzle 10 extending from the exterior surface 103 of the pressure vessel 100 can be further reduced. Returning to FIG. 2, a spacer barrier can be disposed within a portion of the nozzle 10 extending above the clad 107 in the interior of the pressure vessel 100 prior to the further reduction of the length. This spacer barrier is a foreign materials exclusion (FME) device to prevent intrusion of foreign materials from the subsequent repair operations into the interior of the vessel. In a preferred embodiment, an abrasive cutting operation commencing on the exterior surface 13 of the nozzle 10 can be used to further reduce the length of the nozzle 10. Preferably, the length of the nozzle is reduced to a predetermined length as close as practical to the curved exterior surface 103 of the pressure vessel 100. As shown in FIG. 4, the nozzle 10 can be severed at a position adjacent the mid-wall 105 of the pressure vessel 100 (i.e., between the interior and exterior surfaces 101 and 103) to provide an upper nozzle portion 17, which is welded to the pressure vessel 100 by the weld 109, and a lower nozzle portion 19, which is no longer connected to the pressure vessel 100. In a preferred embodiment, the nozzle 10 can be severed by an abrasive cutting operation commencing on the interior surface 15 of the nozzle 10. In the preferred embodiment, the nozzle 10 can be severed at a predetermined distance from the bottom of the nozzle 10 that maximizes the lower nozzle portion 19 that will subsequently be removed. As shown in FIG. 5, the lower nozzle portion 19 can be removed from the pressure vessel 100. In a preferred embodiment, the lower nozzle portion 19 can be removed manually. The lower nozzle portion 19 can be removed from the pressure vessel 100 with a slide hammer or other means if it cannot be removed manually. As shown in FIG. 6, the upper nozzle portion 17 can remain welded to the pressure vessel 100, and the FME device can be removed from the upper nozzle portion 17. The upper nozzle portion 17, as well as a portion of the mid-wall 105 exposed by removal of the lower nozzle portion 19 and defining a mid-wall void 113, can be treated, cleaned, or otherwise prepared for subsequent attachment of a replacement nozzle and insertion of a heater or other implement after cleaning the upper nozzle portion 17. In a preferred embodiment, scale or other sediment can be removed from the upper nozzle portion 17, and a surface of the mid-wall void 113 can be cleaned by an abrasive operation. More preferably, an abrasive grinding wheel can be used to clean the upper nozzle portion 17 and the surface of the mid-wall void 113. When access can be permitted to the upper nozzle portion 17 from the interior of the pressure vessel 100, a cap (not shown) can be disposed to cover the upper nozzle portion 17, such that scale or other sediment removed from the upper nozzle portion 17 or the mid-wall void 113 is prevented from contaminating the pressure vessel 100. After cleaning the upper nozzle portion 17 and the mid-wall void 113, the surface of the mid-wall void 113 can be evaluated after dye penetrant testing, to confirm that the surface of the mid-wall void 113, such as a portion of the surface adjacent the upper nozzle portion 17, is acceptable for subsequent installation of the replacement nozzle, as described below. As shown in FIG. 7, an alignment tool 40 can be disposed in the upper nozzle 17 to facilitate alignment and attachment of a replacement nozzle 30 with the pressure vessel 100. The installation tool 43 can include a head portion 41 having an outer diameter corresponding to a diameter of the mid-wall void 113, and having a flat surface configured to contact an end surface of the upper nozzle portion 17. By this arrangement, the installation tool 43 can axially locate the alignment tool in the upper nozzle 17 and the self-centering feature of the alignment tool locates it radially relative the upper nozzle 17 with a high degree of precision. In an embodiment of the invention, the alignment tool 40 can include a sealing portion that seals against an interior surface of the upper nozzle portion 17. Such an alignment tool 40 can permit reactor fuel off-load or refueling while the mid-wall repair is occurring, by permitting the pressure vessel 100 to be filled with water during the repair process of up to the removal of the alignment tool 40 and reinsertion of the heater or instrument. As shown in FIG. 8, the replacement nozzle 30 can be disposed on an alignment shaft 42 piloted in the alignment tool 40, and can be precisely axially and radially located as described above. In a preferred embodiment, the material of the replacement nozzle 30 can be determined so as to resist stress corrosion cracking when the replacement nozzle 30 is welded to the mid-wall 105, and more preferably a material of the replacement nozzle 30 can include Alloy 690 or stainless steel. As shown in FIG. 9, at least one clamping device 50 can be used to maintain the precise axial and radial position of the replacement nozzle 30 in the mid-wall void 113. The clamping device 50 can include an end portion configured to retain the replacement nozzle 30, and can include an opposite end portion configured to retain another one of the nozzles 10 or other available attachment point(s). By this arrangement, it is understood that the replacement nozzle 30 can be maintained at a desired position relative to other nozzles welded to the pressure vessel 100 or some other desired alignment. In a preferred embodiment, a plurality of clamping devices 50 are used to maintain the position of the replacement nozzle 30, and more preferably at least three clamping devices 50 are used. The alignment tool 40 and alignment shaft 42 can be removed from the upper nozzle 17 and the replacement nozzle 30, such that the clamping device maintains the position of the replacement nozzle 30 relative to the pressure vessel 100. As shown in FIG. 10, the replacement nozzle 30 can be welded to the mid-wall 105 of the pressure vessel 100, and more specifically a weld 115 having at least three weld layers can be formed between the surface of the mid-wall void 113 and the replacement nozzle 30. In a preferred embodiment, the weld 115 can include a plurality of weld layers each having a predetermined deposit height, and more preferably can include at least three weld layers with a total predetermined deposit height of at least 0.125 inches, and the overall buildup of the weld 115 can be determined such that the weld 115 extends only minimally beyond an inner diameter of the replacement nozzle 30. A welding tool 60 can be used to provide the weld 115 between the replacement nozzle 30 and the mid-wall 105. The welding tool 60 can include a video camera such that a technician can monitor formation of the weld 115, a wire feed through which the technician can deliver a material for the weld 115, an inert gas delivery system to aid in formation of the weld 115, and a water cooling system for cooling the welding tool 60. A surface of the weld 115 can be prepared for subsequent testing and evaluation. After formation of the weld 115, the weld surface can be prepared for subsequent testing and evaluation. An abrasive grinding operation can be used to remove an excess portion of the weld 115 (e.g., a portion of the weld extending beyond the inner diameter of the replacement nozzle 30). The weld 115 can be inspected to determine the sufficiency of the weld 115. In a preferred embodiment, the weld 115 can be liquid penetrant inspected. In a preferred embodiment, the weld 115 can be ultrasonically inspected. More preferably, an ultrasonic map indicating properties of the weld 115 can be provided, the map including characteristics of portions of the weld 115 such as echodynamic signature including response amplitude and time of flight of the ultrasonic signal. By comparing the ultrasonic map of the weld 115 with a plurality of ultrasonic maps of known defect-free and defective welds, a technician can determine whether the weld 115 is substantially free of defects. The ultrasonic maps of known defect-free and defective welds can be determined by producing ultrasonic maps of various weld samples, and then by destructively evaluating the weld samples to determine the absence or existence of defects. It is understood that the term “defect-free” can include welds that meet or exceed the UT examination standards set forth in ASME Code, Section III, and specifically Paragraph NB-5330, which is hereby incorporated by reference. This is in contrast to the more forgiving UT examination requirements of ASME Code, Section XI, which is invoked for this repair by ASME Code Case N-638, which are also both hereby incorporated by reference. It is also to be understood that the above-described process can be performed to provide a weld that exceeds ASME Code, Section XI requirements. Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. |
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claims | 1. A scintillator material emitting fluorescence in response to an incident radiation,wherein the scintillator material comprises a zinc-oxide single crystal grown on a +C surface or a −C surface of a plate-shaped seed crystal of zinc oxide comprising a C surface as a main surface,wherein the zinc-oxide single crystal comprises In and Li,wherein the fluorescence has a fluorescence lifetime of less than 20 ps, andwherein, in the zinc-oxide single crystal, Li concentration is in a range of 0.15 to 11 times In concentration. 2. The scintillator material according to claim 1, wherein the fluorescence consists of a single component having a fluorescence lifetime of less than 20 ps. 3. The scintillator material according to claim 1, wherein, in the zinc-oxide single crystal, Li concentration is in a range of 0.15 to 6.74 times In concentration. 4. A scintillation detector comprising a scintillator including the scintillator material according to claim 1. |
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description | In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a part of a reactor pressure vessel 1 with upper connecting branches 2 for a primary circulation and a dome 3. Above the upper connecting branches 2, a cross section of the reactor pressure vessel 1 is covered by an upper support plate 4. The support plate 4 has openings 5 for control rods 6. In the reactor pressure vessel 1 with a xe2x80x9chot domexe2x80x9d, an opening 5 is larger than a cross section of a control rod 6. The support plate 4 then takes a form of a lattice plate, for example. In the reactor pressure vessel 1 of the xe2x80x9ccold domexe2x80x9d type the opening 5 is largely identical in size to the cross section of the control rod 6. In order that the medium (coolant) present in the reactor pressure vessel 1 can be exchanged between a lower chamber 1a below the support plate 4 and an upper dome chamber 1b above the support plate 4, an equalization opening (dome bypass) 7 is provided in the support plate 4 in both variants. The equalization opening 7 is smaller in the xe2x80x9chot domexe2x80x9d than in the xe2x80x9ccold domexe2x80x9d. In the xe2x80x9ccold domexe2x80x9d a bypass of coolant through the equalization opening 7 is necessary only in order that the boron concentration may be equalized on both sides of the support plate 4. Otherwise it is desirable in power output operation that as little coolant as possible should pass into the dome chamber 1b, so that the power output of the power station can be maximized. When running the nuclear power station down, however, the rate of cooling in the dome chamber 1b should not be slower than in the lower chamber 1a. A larger temperature difference between the upper and the lower side of the support plate 4 would namely retard the cooling process unnecessarily and lead to problems when opening dome bolts 16, represented in diagrammatic form. Consequently a great exchange of coolant between the lower chamber 1a and the dome chamber 1b is advisable when shutting down. In order that the equalization opening 7 is relatively large when running the nuclear power station down and relatively small in power output operation, a device 8 shown in FIG. 2 is to be fitted into the equalization opening 7 (dome bypass). The device 8 varies the opening cross section and hence the medium flow in the bypass as a function of the temperature. In the event of a temperature drop in the lower chamber 1a to a temperature lower than that in the upper dome chamber 1b, which occurs when running a nuclear power station down, the opening cross section of the equalization opening 7 is enlarged, so that temperature equalization with the still hotter dome chamber 1b is ensured. While the temperature in the lower chamber 1a in power output operation is higher than the temperature in the upper dome chamber 1b, however, the cross section of the equalization opening 7 remains relatively small, sufficient only to ensure the exchange of boronized water between the two chambers 1a and 1b. A power loss as the result of an unnecessarily large dome bypass or an unnecessarily large equalization opening 7 is avoided. The device 8 is shown in detail in FIG. 2. It has a cylinder 9, which is open at both ends. In an upper area, openings 10 are disposed in a side wall of the cylinder 9. In the lower area of the cylinder 9 there is an expansion sleeve 11 known in the art, for example described in Published, Non-Prosecuted German Patent Application DE 196 07 693 A1, which in the event of a temperature rise expands in an axial direction of the cylinder 9. The expansion sleeve 11 is connected to a hollow piston 12. Inside the expansion sleeve 11 there is a duct 18 connected to a lower opening 17 of the device 8, which duct at a lower end opening 19 of the piston 12 opens into the interior of the piston 12. The piston 12, at its upper end, has an upper opening 13, which represents a minimum opening cross section of the device 8. The piston 12 also has additional lateral openings 14, which align with or overlap the openings 10 in the cylinder wall only when the expansion sleeve 11 is contracted. A temperature drop in the lower chamber 1a, which occurs when running the nuclear power station down, leads to a contraction of the expansion sleeve 11, which brings the lateral openings 14 of the piston 12 into contact with the openings 10 in the cylinder wall of the cylinder 9, thereby significantly enlarging the opening cross section of the device 8. The device 8 shown therefore ensures a process for temperature equalization between the chambers 1a and 1b, which varies the flow of medium or coolant through the equalization opening 7 (dome bypass) as a function of the temperature. This affords the advantage that when running the nuclear power station down a large flow of medium is ensured from the lower chamber 1a into the dome chamber 1b for the rapid cooling of the dome 3, while in power output operation only a then sufficiently small flow occurs, so that power losses are avoided. |
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claims | 1. A fuel assembly configured to be positioned in a nuclear water reactor, comprising:an upstream minor portion defining an upstream end,a downstream minor portion defining a downstream end,a main portion connecting the upstream minor portion and the downstream minor portion,a plurality of elongated fuel rods arranged in parallel with a longitudinal axis extending through the upstream end and the downstream end,a flow interspace between the upstream end and the downstream end, the flow interspace being configured to permit a flow of coolant through the fuel assembly along a flow direction from the upstream end to the downstream end in contact with the fuel rods, andat least one elongated tube forming an internal passage extending through the main portion in parallel with the fuel rods and permitting a stream of the coolant through the internal passage,wherein the elongated tube comprises a bottom, an inlet to the internal passage at the upstream minor portion and an outlet from the internal passage at the downstream minor portion,wherein:the elongated tube comprises an inlet pipe positioned partially in the elongated tube, the inlet pipe forming the inlet to the elongated tube,the inlet pipe having an inlet end and an outlet end,the outlet end of the inlet pipe is located inside the internal passage at a distance of at least 0.2 m downstream from the bottom and at most 1 m downstream from the bottom, wherein the inlet pipe extends no more than 33% up into the elongated tube thereby forming a space in the internal passage between the outlet end of the inlet pipe and the bottom, a length of the inlet pipe configured to capture debris from the stream of coolant in the space in the internal passage between the outlet end of the inlet pipe and the bottom. 2. A fuel assembly according to claim 1, wherein the elongated tube has an inner diameter and wherein the inlet pipe at the outlet end has an outer diameter being smaller than the inner diameter of the elongated tube. 3. A fuel assembly according to claim 1, wherein the inlet end of the inlet pipe forms an opening which extends along a plane being non-parallel to the longitudinal axis. 4. A fuel assembly according to claim 1, wherein the inlet pipe extends through the bottom. 5. A fuel assembly according to claim 4, wherein the space is an annular space around the inlet pipe. 6. A fuel assembly according to claim 4, wherein the elongated tube comprises a bottom end plug forming said bottom and wherein the inlet pipe extends through the bottom end plug. 7. A fuel assembly according to claim 1, wherein the elongated tube is cylindrical. 8. A fuel assembly according to claim 1, wherein the elongated tube comprises at least one magnet provided to attract magnetic material towards the bottom. 9. A fuel assembly according to claim 1, wherein the fuel assembly comprises a debris filter at the upstream minor portion upstream the fuel rods. 10. A fuel assembly according to claim 9, wherein the inlet end of the inlet pipe is located upstream the debris filter. 11. A fuel assembly according to claim 9, wherein the inlet end of the inlet pipe is located downstream from the debris filter. 12. A fuel assembly according to claim 1, wherein the fuel assembly is configured to be positioned in a boiling water reactor, and wherein the elongated tube forms a water rod for conveying non-boiling water through the internal passage. 13. A fuel assembly according to claim 12, wherein the fuel assembly comprises at least two elongated tubes each forming a water rod for conveying non-boiling water through the respective internal passage. 14. A fuel assembly according to claim 1, wherein the fuel assembly is configured to be positioned in a pressure water reactor, and wherein the elongated tube forms a guide tube for receiving a control rod. |
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062597590 | claims | 1. An incore piping section maintenance system for performing a preventive-maintenance operation to a maintenance target portion in a reactor pressure vessel, comprising: a maintenance system main body fixed to the reactor pressure vessel in the vicinity of the maintenance target portion; a moving means mounted to the maintenance system main body and movable with respect to the maintenance system main body; a support means connected to the moving means and movable toward the maintenance target portion as the moving means moves with respect to the maintenance system main body, the support means including a laser de-sensitization treatment means to irradiate the maintenance target portion with a laser beam and seal means to keep an area around the maintenance target portion free of water; a laser generation means for generating the laser beam; and an optical transmission means guiding the laser beam to the laser desensitization treatment means. 2. The incore piping section maintenance system according to claim 1, wherein the laser de-sensitization treatment means includes an inspection monitoring means for monitoring the maintenance target portion. 3. The incore piping section maintenance system according to claim 1, wherein the laser de-sensitization treatment means includes a polishing means for polishing the maintenance target portion. 4. The incore piping section maintenance system according to claim 1, further comprising a cylinder member fixed to the maintenance system main body and an actuating rod extending from the cylinder member for pressing an inner wall of the reactor pressure vessel to fix the maintenance system main body to the reactor pressure vessel. 5. The incore piping section maintenance system according to claim 1, wherein the seal means include expandable seal members disposed around the laser desensitization treatment means and the area around the maintenance target portion between the expandable seal members is filled with a gas. 6. The incore piping section maintenance system according to claim 5, wherein the maintenance target portion is a pipe located in the reactor pressure vessel. 7. The incore piping section maintenance system according to claim 1, wherein the laser de-sensitization treatment means includes a maintenance target portion detector for detecting and confirming the maintenance target portion. 8. The incore piping section maintenance system according to claim 7, wherein the maintenance target portion detector is an ultrasonic flaw detector. 9. The incore piping section maintenance system according to claim 7, wherein the maintenance target portion detector is an ferrite indicator for distinguishing a difference in ferrite quantity between the maintenance target portion and a base material around the maintenance target portion. 10. The incore piping section maintenance system according to claim 9, wherein the maintenance target portion is a weld zone of a pipe located in the reactor pressure vessel. |
abstract | A nuclear reactor scram control system for a nuclear reactor includes a solenoid pilot valve (SSPV). The SSPV includes a solenoid indicator light electrically coupled to an SSPV solenoid of the SSPV. The solenoid indicator light may be selectively activated based on an energization state of the SSPV solenoid, thereby providing an immediate and visually observable indication of the SSPV energization state. The immediate and visually observable indication of the SSPV energization state may enable quicker and more reliable verification of SSPV solenoid energization state. As a result, operator radiation exposure associated with verification may be reduced, and a risk of inadvertent nuclear reactor scram based on a de-energized SSPV solenoid may be reduced, thus streamlined nuclear reactor operations. |
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044951450 | summary | BACKGROUND OF THE INVENTION The present invention relates to the loading of fuel rods with spherical nuclear fuel. In recent years it has been discovered that conventional nuclear reaction fuel composed of fuel pellets encased in cladding tubes may lead to the splitting of the cladding tubes thereby releasing radioactive material to the adjacent cooling water. This splitting is due to an interaction between the pellet and cladding. One way of avoiding this problem is to limit the surface interaction between the fuel and cladding. This may be achieved by loading the fuel cladding tubes with nuclear fuel in the shape of spheres. If three different sizes of spheres are used, than appropriate packing of the spheres into the rods will result in a sufficient density of nuclear fuel to be properly used in a nuclear reactor. One method for loading a fuel rod is to simply drop the spheres into a vertical cladding tube while vibrating the rod to assist in packing. However, this method is not satisfactory for several reasons. The distribution of the particles sizes freely falling from a height of 6 to 12 feet into a cladding tube does not lead to uniform distribution. This method also leads to the trapping of air which requires a longer time to evacuate at the sealing of the tube. In addition, the vibrating packing is extended because of the random loading of the spheres. SUMMARY OF THE INVENTION The invention is a loading probe for the loading of spherical nuclear fuel into a fuel rod. The probe includes a funnel means for receiving the spherical nuclear fuel, the funnel means maintaining a separation of the spherical fuel of different diameters; tubing means corresponding to each of the spherical nuclear fuel diameters, the tubing means of sufficient length so that one end of the tubing means extends about the length of the fuel rod in the load portion; valve means for releasably containing the fuel spheres within said funnel means, said valve means able to release the fuel spheres to the tubing means; gate means between the valve means and the tubing means for regulating the rate of flow of each the spherical fuel as it passes from the funnel means through the valve means into the end of the tubing means away from the fuel rod; and deflector means attached to the end of the tubing means within the fuel rod for mixing the fuel as it emerges from the tubing means; |
description | This is a continuation, under 35 U.S.C. §120, of copending international application PCT/EP2007/006317, filed Jul. 17, 2007, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent applications DE 10 2006 034 001.9, filed Jul. 22, 2006 and DE 10 2006 038 748.1, filed Aug. 17, 2006; the prior applications are herewith incorporated by reference in their entirety. The invention relates to a device for removing solid particles from the cooling medium which circulates in the primary circuit of a nuclear reactor, especially in the primary circuit of a boiling-water nuclear reactor. The invention additionally relates to a reactor core of a nuclear reactor having such a device. It may be the case, due to servicing works in the primary circuit of a nuclear reactor, that foreign bodies in the form of small solid particles may get into the primary circuit and are constantly circulated with the cooling medium. These solid particles deposit in dead zones of the flow and in gaps and can, in the case of disassembly processes within the framework of maintenance works, result in jamming or heaviness in moving the components to be disassembled. Furthermore, these solid particles can lead to increased erosion in narrow gaps through which the cooling medium flows. It is known from European patent EP 0 432 738 B1 and U.S. Pat. No. 5,219,517 for avoiding erosion or abrasion damage caused by foreign bodies, in fuel rods of a fuel assembly for a pressurized-water reactor to arrange a dirt trap in the form of a strainer screen or of a funnel-shaped strainer below the base plate of the fuel assembly. The dirt trap prevents foreign particles from penetrating the fuel assembly. In the embodiment with the funnel-shaped strainer having a free passage in the center, guide vanes are connected upstream of it, which guide vanes produce a circular flow and prevent foreign particles from flowing into the central free passage. Although such a strainer screen or such a funnel-shaped strainer makes it possible to prevent foreign particles from penetrating into the interstices between the fuel rods, it is a problem that a dirt trap of this kind can partially clog and adversely affect the flow conditions in the fuel assembly. In order to avoid problems relating to foreign particles from the outset, the aim is in principle to clean the cooling medium in filter installations in order to reduce in this way the amount of such foreign substance particles, which are entrained in the cooling medium, from the outset. It has been found here that the filter installations which are usually present in nuclear power stations for cleaning the cooling medium do not suffice for removing these solid particles from the cooling medium circuit, since it could be observed that solid particles would collect again at the previously mentioned locations even after such a cleaning process has been carried out. It is accordingly an object of the invention to provide a device for removing solid particles which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which specifies a device which can be used to reliably remove solid particles from the cooling medium which is circulated in the primary circuit of a nuclear reactor, especially of a boiling-water nuclear reactor, in a simple manner. With the foregoing and other objects in view there is provided, in accordance with the invention, a device for removing solid particles from a cooling medium circulating in a primary circuit of a nuclear reactor, wherein the nuclear reactor has a reactor core with defined fuel assembly positions for the placement of fuel assemblies, the device according to the invention having geometric dimensions and shapes configured for insertion thereof into an empty fuel assembly position in the reactor core of the nuclear reactor, like a fuel assembly that is configured for said nuclear reactor and instead of such a fuel assembly. In other words, the geometric dimensions and shapes of the device are such that the latter can be inserted into an empty fuel assembly position in the reactor core of the nuclear reactor like a fuel assembly which is configured for said nuclear reactor and instead of such a fuel assembly. This measure provides a filter or cleaning device which is active during the entire duration of normal operation of the nuclear reactor and eliminates the solid particles from the circulated cooling medium successively and effectively on account of the long period of use, i.e. separates them from the cooling medium flow, due to said solid particles depositing inside the device during operation of the nuclear power station. The device can then be removed from the reactor core and cleaned like a fuel assembly within the framework of usual servicing and maintenance works, for example at the end of an operating cycle. Once the solid particles deposited therein have been removed, the device can once again be inserted at the same or another empty fuel assembly position in order to begin operation again after the start-up of the nuclear reactor. Alternatively, it is also possible to dispose of the entire device like a burnt out fuel assembly, for example after use for a number of operating cycles. In a device which is especially suited for use in a boiling-water nuclear reactor, the device comprises a carrying structure which extends in a longitudinal direction and in which at least one separator is arranged, but preferably a plurality of separators which are arranged one after another in the longitudinal direction. In particular flow separators are here provided as the separator, in which cooling medium and solid particles are separated due to the action of gravity or a centrifugal force. The use of a flow separator enables structural designs which have a low flow resistance with sufficient separation action. The carrying structure is in particular a hollow case. Such a device is suitable especially for use in a boiling-water reactor. In a particularly preferred embodiment of the invention, an insert which can be inserted into the carrying structure and is provided with an inlet opening for the cooling medium is provided as the separator and has, opposite and at a spacing from said inlet opening, a deflection device for deflecting the cooling medium, and is provided with an accumulation zone for collecting the solid particles which are separated during deflection due to the centrifugal force. Such a separator has a simple design and can be produced with little technical complexity and can be matched flexibly to the respective requirements which are specific to the power station. If a cyclone, especially in the form of a fixed guide vane, is provided as the deflection device, which cyclone imparts on the cooling medium, which flows in the longitudinal direction inside the carrying structure, a circular motion about said longitudinal direction, a high degree of separation is achieved with low flow resistance and low tendency to flow-induced vibrations. In another preferred embodiment, a plurality of separators are arranged in the longitudinal direction one after the other and releasably connected to one another. A stack which is formed in this manner can be installed in, or removed from, the carrying structure particularly simply in its entirety. If a plurality of separators are arranged one after the other in the longitudinal direction and have different designs from one another in order to achieve a different separation effect, solid particles which differ physically and in terms of their geometry from one another can be deposited from the cooling medium with a high degree of efficiency in a single device. If the flow resistance of the device corresponds at least approximately to the flow resistance of a fuel assembly, the hydraulic conditions in the area surrounding the device are at most influenced to an acceptable degree, compared to operation with an inserted fuel assembly. In a reactor core of a nuclear reactor, in which a device according to the invention is inserted in an empty fuel assembly position, the device is preferably located at the edge, especially in a corner position, since the fuel assemblies which are located in these positions have the lowest output to the core and thus the overall output of the core is reduced as little as possible if such a fuel assembly is replaced by the device according to the invention. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in device for removing solid particles from the cooling medium which circulates in the primary circuit of a nuclear reactor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a device to be inserted in the reactor core of a boiling-water reactor. The device includes, according to the invention, a base part 2 and a top part 4, which is provided with a handle 3 and the dimension and shape of which are such that the device can be inserted like a fuel assembly, which is configured for this nuclear reactor, between a top core grid and a bottom core grid instead of such a fuel assembly in an empty fuel assembly position in the reactor core. Base part 2 and top support 4 are connected to one another by a carrying structure 8 which extends in a longitudinal direction 6, in the example a case, which has the external dimensions of the case of a fuel assembly which is configured for said boiling-water reactor. A large number of separators 10 are arranged inside the case (carrying structure 8), one after the other in the longitudinal direction 6, such that the cooling medium, which flows through the inside of the carrying structure 8, in the example through the case, flows through them successively. FIG. 2 shows the upper end of the device, which faces the top part 4 with the handle 3, in an enlarged representation. The separators 10 are in the form of an insert which is inserted in the case (carrying structure 8) and comprise in the exemplary embodiment a carrying plate 12 having an inlet opening 14 in its center, which inlet opening 14 conducts the cooling medium K flowing in the case into a flow passage 16, the cross section of which tapers in the direction of flow in the form of a nozzle. At the outlet of the flow passage 16, there is a deflection device 18 which is used to deflect the cooling medium K. In this exemplary embodiment, the deflection device 18 is formed by a spherical cap 19 which deflects the incident cooling medium flow by nearly 180°. An outlet opening 20 in the form of a circular ring is formed between the spherical cap 19 and the wall of the case, from which outlet opening 20 the cooling medium K exits, such that it flows outside the flow passage 16 along its outer wall in the direction of the carrying plate 12 which, together with the inner wall of the case, effects another deflection of the cooling medium K by likewise nearly 180°, such that the latter can flow upward (axially in the direction twoards the top part 4) through an outlet passage 21, which is formed between the wall of the case and deflection device 18, to the next separator 10. The edge region of the accumulation plate 12 forms a dead space 22 and thus an accumulation zone for solid particles P which deposit there on account of the centrifugal force which is effected by the lower deflection of the cooling medium K. In the exemplary embodiment according to FIG. 3, cyclones 23 are provided as the deflection devices 18 in the separators 10. In this exemplary embodiment, the separators 10 are also in the form of individual modules or inserts which can be inserted in the case (the carrying structure 8). Each separator 10 has a rectangular hollow section 24 which is provided at one of its end faces with the inlet opening 14 and is open at the opposite end face 25. A short flow passage 16 is also connected to the inlet opening 14. The cyclone 23, which comprises a fixed accumulation body 26 having a plurality of vanes or guide vanes 28, is arranged at the outlet, which merges into the hollow section 24, of the centrally arranged flow passage 16, i.e. the flow passage 16 which after installation into the carrying structure is aligned with the longitudinal direction 6. The guide vanes 28 are likewise positionally fixed to the accumulation body 26 and impart on the cooling medium K, which flows in the longitudinal direction 6, a circular motion about said longitudinal direction 6 (angular momentum parallel to said longitudinal direction 6) and thus produce a motion of the cooling medium K along a helical path about said longitudinal direction 6. This circular movement causes a force which is directed outwardly (centrifugal force) to be exerted onto the solid particles 22 which flow out of the flow passage 16, which force transports the particles outwardly in the direction of the inner wall of the hollow section 24 into zones which are calm in terms of flow, where they sink, due to the action of gravity, into a dead space 22 which surrounds the flow passage 16 and at the same time serves as the collection space. FIGS. 4A and 4B show that the hollow section 24, which is open at the top (in the installed state during operation), has at its (upper) edge 30 which is located at the end face opposite the inlet opening 14 a plurality of resilient tongues 32 which extend in the longitudinal direction 6 and have arranged at their free ends nubs 34 which project radially outward. In FIG. 5, the nubs 34 engage in openings 36 of the adjacent separator 10, which is located above it and rests on the upper edge 30, and form a snap-action or latching connection such that the separators 10, which are arranged in the form of a stack, are interconnected with a positive fit and can be lifted out of the carrying structure 8 together as the stack. The snap-action connection can also be unlocked using a tool in order to be able to remove the inserts individually as well. In the region of the inlet opening 14, the hollow section 24 is shaped similarly to a truncated pyramid, such that it projects into the separator 10 with its inlet opening 14 if it rests with a circumferential collar 38 (see also FIGS. 4A and 4B), which is located on the base of the truncated pyramid, on the upper edge of the hollow section 24 of said separator 10 which is located underneath it (in the installed state). In the exemplary embodiments shown in FIGS. 1-5, the separators are in the form of flow separators having a deflection device which effect a change in the flow direction of the cooling medium—a deflection—and in which the solid particles are driven into zones which are calm in terms of flow due to the centrifugal forces which act on them, where they are no longer entrained by the cooling medium and collect in the dead zones which are provided as accumulation space. FIG. 6 shows a detail from the edge region of a reactor core 40, whose cells 42 are in each case occupied by a fuel assembly. In the figure, “x” and “o” now identify fuel assembly positions 44, 46 at the edge of the reactor core which are particularly suitable for insertion of a device according to the invention. These are preferably corner positions 46 where only two side edges of the device adjoin an adjacent fuel assembly. A reactor core 40 which is fitted in this manner with one or more such devices ensures a reliable and continuous removal of solid particles from the primary circuit. |
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summary | ||
description | This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/658,178 filed Apr. 16, 2018, which is incorporated by reference in its' entirety. This invention relates to tank cleaning, and in particular to devices, apparatus, systems, vehicles and methods for cleaning contaminated tanks without free water tanks having high temperature, low temperature conditions, high doses of radiation, and flammable liquids or vapors. Radioactive material is stored in hundreds of underground storage tanks at the United States Department of Energy's sites such as Savannah River, The Hanford Site in Eastern Washington State, USA and elsewhere around the world. A problem occurs when it is time to clean up the inside of these known leaking tanks. Since 2001 equipment developed and manufactured by AGI Engineering of Stockton, Calif., has been used to break up and retrieve the material located in these tanks. Existing technology used to clean most tanks containing chemical, radioactive and/or hazardous materials or other waste relies primarily on the use of water or water based liquefiers to break up waste so it can be pumped out of the tanks. In many cases the use of water or fluids as liquefier poses significant challenges. For instance, if a tank is known or suspected of having structural flaws any system requiring large volumes of free fluid in the tank provides potential for leakage into the environment that may carry contaminated material with it which then contaminate neighboring properties as well as subterranean and potentially underground water. Additionally, the use of fresh water or water based liquefier costs money and resources and also produces large quantities of contaminated liquefier that will then have to be treated and disposed of. Thus, the need exists for solutions to the above problems with the prior art. A primary objective of the present invention is to provide devices, apparatus, systems, vehicles and methods for cleaning liquids, sludges, and solid nuclear waste from contaminated tanks, and further, breaking down and classifying the waste in to small particles without introducing free liquid, water or liquefier into the tanks. The Tank Excavator primarily is a self propelled mechanical device that break up and collects material from inside chemical, radioactive and/or hazardous tanks. The use of interchangeable tooling allows broken, fouled, or jammed assemblies to be replaced, and allows tool selection to be tailored to the specific waste being encountered. In order to fit though a minimal round opening, as small as approximately 34″ in diameter, the Tank Excavator can be folded into a stowed position and unfolded into an operating position after deployment in the tank. The invention can be remotely operated for use in radioactive and/or flammable environments. A preferred embodiment of a tank excavator device for cleaning contaminated tanks, can include a mobile vehicle having a front end and a rear end, a gathering arm assembly having a first end and a second end attached to the front end of mobile vehicle, the first end for breaking up waste from a contaminated waste tank, a bucket assembly on the front end of the mobile vehicle, having a receptacle for collecting the waste from the first end of the gathering arm assembly, and a pump and tank assembly adjacent a rear end of the mobile vehicle, for collecting waste material in the bottom of the contaminated waste tank with a pump. The mobile vehicle can include a first pair of wheels with a first track of parallel tank threads on a left side of the mobile vehicle, and a second pair of wheels with a second track of parallel tank threads on a right side of the mobile vehicle. The gathering arm assembly can include a scraper on the first end of the gathering arm assembly, and a plurality of hardened tines attached to the scraper. The plurality of hardened tines can be reciprocated linearly up and down through pneumatic actuation. The plurality of hardened tines can be reciprocated linearly up and down through hydraulic actuation. The gathering arm assembly can include a scraper with squeegee on the first end of the gathering arm assembly. The gathering arm assembly can include a scraper with squeegee and grinding drum assembly on the first end of the gathering arm assembly. The gathering arm assembly can include a pivotable mast with a lover end pivotally attached to the front end of the mobile vehicle, and an upper end, and a boom having a first end pivotally attached the upper end of the mast, and a second end pivotally attached to a base of a scraper. The gathering arm assembly can include a mast elevation cylinder having a lower end pivotally attached to the vehicle and an upper end pivotally attached to an upper portion of the pivotable mast for controlling pivoting positions of the pivotable mast relative to the mobile vehicle, and a boom elevation cylinder for having a first end pivotally attached to another upper portion of the pivotal mast and a second end pivotally attached to another portion of the base of the scraper. The bucket assembly can include pivoting arms for allowing the bucket assembly to pivot up or pivot down relative to the front end of the mobile vehicle. The bucket assembly can include a ramp having a front end which is lowerable to rest on a surface, and a rear end that rises up to the receptacle. The bucket assembly can include a trough in the receptacle that gravity feeds a screw which feeds the collected waste material into an educator. The bucket assembly can include a crusher in the receptacle for further breaking down the collected waste material. The bucket assembly can include a macerator in the receptacle for further breaking down the collected waste material. The bucket assembly can include a jet educator for pushing broken down material from the collected waste to the pump and tank assembly. The tank excavator can include an electrical and controls assembly having onboard controls and hydraulic valves housed in explosion proof enclosures, and communications for the electrical and controls assembly over fiber optics. The electrical and controls assembly can include electrical power is provided by an on-board fluid powered generator. The electrical and controls assembly can include electrical power provided by an on-board pneumatic powered generator. The tank excavator can include an electrical and controls assembly that includes explosion proof hydraulic valves located. outside the contaminated waste tank. Another embodiment of the tank excavator device for cleaning contaminated tanks, can include a mobile vehicle having a front end and a rear end, a gathering arm assembly having a first end and a second end attached to the front end of mobile vehicle, the first end for breaking up waste from a contaminated waste tank, a bucket assembly on the front end of the mobile vehicle, having a receptacle for collecting the waste from the first end of the gathering arm assembly, pivoting arms for allowing the bucket assembly to pivot up or pivot down relative to the front end of the mobile vehicle, a pump and tank assembly adjacent a rear end of the mobile vehicle, for collecting waste material from the discharge of an eductor in the bottom of the bucket assembly in order to pump the waste material out of the waste tank, a scraper on the first end of the gathering arm assembly, a pivotable mast with a lower end pivotally attached to the front end of the mobile vehicle, and an upper end, and a boom having a first end pivotally attached the upper end of the mast, and a second end pivotally attached to a base of the scraper. Further objects and advantages of this invention will be apparent from the following detailed description of the presently preferred embodiments which are illustrated schematically in the accompanying drawings. Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its applications to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. In the Summary above and in the Detailed Description of Preferred Embodiments and in the accompanying drawings, reference is made to particular features (including method steps) of the invention. It is to be understood that the disclosure of the invention in this specification does not include all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects and embodiments of the invention, and in the invention generally. In this section, some embodiments of the invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale. A listing of the components will now be described. 1 gathering arm 2 bucket assembly 4 pump and tank assembly 5 Tank excavator 6 track assembly 8 electrical and control assembly 10 pivotal mast 12 mast elevation cylinder 14 boom 16 boom elevation cylinder 18 scraper assembly 19 upper end of mast 20 scraper elevation cylinder 21 first end of boom 22 tines 23 first end of boom elevation cylinder 24 squeegee assembly 25 second end of boom elevation cylinder 26 grinding drum/assembly 27 second end of boom 28 hydraulically driven grinding drum 29 first end of scrapper elevation cylinder 30 outboard support plates 31 second end of scrapper elevation cylinder 32 intermediate support plate 40 ramp 41 first end of bucket 42 screw conveyor 43 front end of mobile vehicle 44 eductor 45 second end of mobile vehicle 46 bucket elevation cylinder 50 drums 52 bucket rotation cylinder 54 wedge wire screen 56 jets 60 tank 62 pump 64 pump discharge outlet 66 hydraulic motor 68 trap door drain valve 70 trap door cylinder 72 tank elevation cylinder 80 articulation nozzle 82 low flow nozzle 84 high flow nozzle 86 hydraulic motor 100 Pump/tank assembly 102 hose 104 104 tank excavator FIG. 1 is an isometric view of the tank excavator 5. FIG. 2 is a top view of the tank excavator 5 of FIG. 1 along arrow 2Y. FIG. 3 is a front end view of the tank excavator 5 of FIG. 1 along arrow 3X. FIG. 4 is a rear end view of the tank excavator 5 of FIG. 1 along arrow 4X. FIG. 5 is a right side view of the tank excavator 5 of FIG. 4 along arrow 5X. FIG. 6 is a bottom view of the tank excavator 5 of FIG. 5 along arrow 6Y. Referring to FIGS. 1-6, the tank excavator 5 can include a mobile vehicle comprised of a gathering arm 1, bucket assembly 2, pump and tank assembly 4, track assembly 6, and electrical and control assembly 8. A. Gathering Arm Assembly 1 FIG. 7 is an enlarged view of the gathering arm detail portion of FIG. 7. Referring to FIG. 7, the gathering arm assembly 1 can be used to break up waste and pull it into the bucket assembly 2. The gathering arm assembly can include a pivotable mast 10 with a lower end 11 pivotally attached to the front end 13 of the mobile vehicle and an upper end 15 pivotably attached to a mast elevation cylinder 12 in turn having a lower end 17 pivotally attached to the mobile vehicle for controlling pivoting positions of the pivotable mast 10 relative to the mobile vehicle. The upper end 19 of the mast 10 can also pivotably attached to a first end 21 of a boom 14 and a first end 23 of a boom elevation cylinder 16. The boom elevation cylinder 16 can have a second end 25 pivotably attached to the second end 27 of the boom 14 for controlling pivoting positions of the pivotable boom 14 relative to the mast 10. The boom 14 can have a second end 27 pivotally attached to a base of the scraper assembly 18 and a first end 29 of a scraper elevation cylinder 20. The scraper elevation cylinder 10 can have a second end 31 pivotably attached to the base of the scraper assembly 18 for controlling pivoting positions of the scraper assembly 18 relative to the boom 14. The second end of the scraper assembly 18 can be comprised of a plurality of tines 22 used to break waste into smaller particles and pull them into the bucket assembly 2. These tines 22 can be round, square or rectangular in cross section and constructed from any carbon, alloy, tool, or stainless steel in the annealed, tempered or hardened state. In certain embodiments, the tines are spring loaded and incorporate a vibrating or reciprocating motion through hydraulic or pneumatic actuation to provide a jackhammer functionality. The travel of the tines can be limited so as not to engage and damage the tank floor. In an alternate embodiment, the tines can be replaced with a flat plate. FIG. 8 is a front view of the grinding assembly used in the tank excavator 5 shown in FIG. 1. In a further embodiment, a flip down rubber squeegee assembly 24 improves the excavator's ability to pull liquid or light slurries into the bucket assembly 2. In an even further embodiment, FIG. 8 illustrates a grinding drum assembly 26 that can include hydraulically driven grinding drum 28 with teeth, spaced in an offset pattern about the circumference, can provide a surface grinding action. The teeth can be fabricated from any carbon, alloy, tool, or stainless steel in the annealed, tempered or hardened state. In a further embodiment, the teeth can be carbide or carbide tipped. The drum is supported by bearings mounted in two outboard support plates 30 and an intermediate plate 32. These plates 30, 32 can extend past the perimeter of the teeth of the grinding drum 26 to prevent damage though contact between the drum and the floor of a tank. On the leading edge of the plates, a sharpened edge provides means to cut through waste as the gathering arm is dragged through the waste. The drum can be rotated about its longitudinal axis through a hydraulic motor. The grinding drum assembly 26 can be fixed or, in another embodiment, coupled to a rotary actuator for independent movement. The scraper assembly 18 can be equipped with just the tines, just the squeegee assembly, just the grinding drum assembly 26, or any combination therein. B. Bucket Assembly 2 FIG. 9 is an enlarged view of the top view of the tank excavator 5 of FIG. 2. FIG. 10A is a partial cross-sectional view of the bucket section of the tank excavator 5 of FIG. 9 along arrows 10A. Referring to FIGS. 9 and 10A, the bucket assembly 2 can provide a receptacle for the waste gathered by the Gathering Arm assembly 1. Waste is pulled up the ramp 40 of the bucket and collected in a trough area. The trough gravity feeds a centering screw conveyor 42, which pushes the waste into the throat of an eductor 44. The bucket assembly 2 can be pivotally attached to the front end of the mobile vehicle. A first end 41 of a bucket elevation cylinder 46 can also be pivotally affixed to the front end 43 of the mobile vehicle with the second end 45 pivotally attached to a point near the first end of the bucket assembly 2 for up and down adjustment in order to accommodate vehicle movement through varying waste depths as well as to provide increased ground clearance for maneuverability across rough terrain. A macerator or crusher assembly can be included above the centering screw conveyor 42 in order to classify and further break down the material to prevent eductor fouling, allow passage through pumps and meet downstream waste processing requirements. The macerator can be comprised of two opposing drums 50 with teeth, spaced in an offset pattern about the circumference. The teeth can he fabricated from any carbon, alloy, tool, or stainless steel in the annealed, tempered or hardened state. In a further embodiment, the teeth can be carbide or carbide tipped. The drums are axially spaced such that the teeth come in close proximity in order to classify into pieces safe for pumps and other process equipment. The drums are driven through a hydraulic motor. The drums 50 can rotate in opposing directions and draws the waste through towards the screw conveyor 42. The drums 50 can also be reversed to eject any nuts, bolts, or material that can foul the drums. FIG. 10B is another partial, cross-sectional view of the bucket open section of the tank excavator 5 of FIG. 9 along arrows 10A. Referring to FIGS. 9 and 10A-10B, a bucket rotation cylinder 52 can pivot the bucket assembly relative to the mobile vehicle as illustrated in FIG. 10B. in order to allow the bucket to be cleared of debris and the eductor 44 to be back flushed. A parallel bar wedge-wire screen 54 in front of the macerator and/or crusher allows material that is already small enough to pass through the eductor, pump, and other process equipment to bypass the macerator and/or crusher. This prolongs the life of these components and increases the available system throughput. Perimeter jets 56 on the eductor 44 can use pressurized liquefier to provide vacuum on the educator inlet to draw the material in from the centering screw conveyor, while providing positive pressure on the educator outlet to push this material into the Pump/Tank Assembly. The perimeter jet configuration provides an unobstructed throat, helping to prevent fouling and allow for back flushing. C. Pump/Tank Assembly 4 FIG. 11 is another top view of the tank excavator 5 of FIG. 1. FIG. 12 is a partial, side view of the pump/tank assembly detail 4 of FIG. 11 along arrows 12X. Referring to FIGS. 11-12, the Pump/Tank Assembly 4 can collect the material in the bottom of the tank 60. Because of the limited pumping capability of any eductor, a pump 62 within the tank 60 can provide the proper discharge pressure and flow required to pump the retrieved material out of the waste tank 60, out of the pump discharge outlet 64, and to the new double shell storage tank where the waste can be stored safely prior to processing. The pump 62 can be driven through a hydraulic motor 66 for operation in environments with hazardous vapors. The Pump/Tank assembly 4 can be furnished with a trap door drain valve 68 at the bottom. A trap door cylinder 70 can have a first end pivotally attached to the base of the tank 60 and a second end pivotally attached to the base of the trap door 68 such that the drain can be opened to backflush the pump 62 and tank 60 and eliminate any solids that may cause fouling. A. tank elevation cylinder 72 with a first end pivotally can be attached to the back end of the mobile vehicle and a second end pivotally attached to a lower end of the tank 60 in order to control the pivoting position of the tank assembly 4 relative to the mobile vehicle. FIG. 12A references a further embodiment where the pump/tank assembly 4 can also fold down to realize the minimal cross section in the stowed position. This allows the tank excavator 5 to be deployed through the smallest possible opening down to approximately 34″ in diameter. D. Track Assembly 6 Referring to FIGS. 1-6, the track assembly 6 can include parallel tank treads a first pair of wheels with a first track of parallel tank threads on a left side of the mobile vehicle, and a second pair of wheels with a second track of parallel tank threads on a right side of the mobile vehicle. The tank treads can be constructed of metal, rubber, composite, or a combination of materials. The tracks can provide mobility for the Tank Excavator with directional control via skid steering. E. Electrical & Control In order to be operated in hazardous environments the electrical and control systems can be designed to be hazardous/explosion proof rated. Electrical power to operate the control can be provided by fluid power (hydraulic or compressed air) operating an on-board enclosed explosion proof generator and communication for its control can be done over a fiber optic connection. Explosion proof hydraulic valves can be placed near the opening of the tank at grade level or inside an explosion proof enclosure(s) 8 around the valve assembly on the device in the tank 5 in order to ensure the safe operation in flammable hazardous environments. Fiber optic encoders can be located at each or some of the axis for automated or semiautomated control utilizing a signal thru fiber optic cable which does not present an ignition source for flammable gases or materials. F. 2 Axis Articulating Nozzle 80 FIG. 14 is an alternate perspective view of another embodiment of the gathering arm assembly 1 for the tank excavator of FIG. 1 with a 2 axis articulating nozzle assembly 80 and scraper assembly 18. Referring to FIGS. 1 and 14, an optional 2 axis articulating nozzle 80 can be mounted to the boom 14 or the gathering Arm 1. This nozzle 80 can provide a liquefier as needed in a controlled manner in order to help break up waste in tanks that can tolerate liquids or to clean/de-foul the trough of the bucket, macerator, or crusher assemblies if required. The 2 axis articulating nozzle 80 can be comprised of high pressure, low flow nozzles 82, low pressure, high flow nozzles 84, or a combination therein. Low pressure, high flow nozzles can operate at pressures up to, but not limited to, approximately 5000 psig and at flow rates ranging from approximately 10 to approximately 500 GPM. High pressure, low flow nozzles can operate at, but not limited to, a pressure range from approximately 5,000 psig to approximately 50,000 psig and a flow rate range from 0 to approximately 50 GPM. Each axis rotation is controlled through a hydraulic motor 86. Depending on the configuration utilized for specific applications the Articulating Nozzle 80 can be installed by itself at the end of the boom as illustrated in FIG. 15, or back from the end and coupled with another end effector, such as a scraper assembly 18, squeegee 24, crusher, or grinder assembly 26. G. Straight or Curved Blade/Backstop In order to improve waste collection in tanks utilizing other technologies a Straight or Curved Blade/Backstop may also be deployed. This tool allows the Tank Excavator to move material within the tank directly, as well as to direct the flow of liquid material towards existing pumps. H. Interchangeable Tooling The Pump/Tank, Bucket and Gathering Arm Assemblies can be attached in such a way that they can be easily removed, via remote mechanism if necessary, and changed out with a new assembly if a portion becomes inoperable or if a different tool (i.e. macerator, crusher, high pressure nozzles, backstop blade, etc.) would be more effective for the particular application. I. Remote Pump/Tank Assembly FIG. 13 is an upper perspective view of the tank excavator of FIG. 1 with a remote pump/tank assembly. Referring to. FIG. 13, a remote Pump/Tank Assembly 100 can also be optionally mounted at a fixed location within the tank, with a length of hose 102 connecting it to the Tank Excavator 104. This configuration allows for different size pumps and tanks as well as providing different mobility characteristics for the excavator. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. It should he understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale. While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended. |
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abstract | A substrate inspection method includes: generating primary charged particle beams; applying the generated primary charged particle beams to an inspection target of a substrate; condensing first secondary charged particle beams including at least one of secondary charged particles, reflected charged particles, and back scattering charged particles which have been generated from the substrate, or first transmitted charged particle beams which have transmitted the inspection target, a phase difference being generated between the secondary charged particle beams or between the transmitted charged particle beams in accordance with a structure of the inspection target; imaging the secondary charged particle beams or the transmitted charged particle beams; detecting the imaged secondary charged particle beams or transmitted charged particle beams and outputting a signal of a secondary charged particle beam image or a transmitted charged particle beam image including information on the phase difference; and detecting a defect in the inspection target by use of the information on the phase difference included in the secondary charged particle beam image or the transmitted charged particle beam image. |
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description | This application is a continuation of U.S. application Ser. No. 12/568,619 filed Sep. 28, 2009, now U.S. Pat. No. 8,077,830, the disclosure of which is incorporated herein by reference. This invention relates generally to X-ray apparatuses and in particular to beam filter positioning devices and linear accelerators incorporating the same. Linear accelerators are used in a variety of industries including in medical radiation therapy and imaging. A linear accelerator includes a treatment head that houses various components configured to produce, shape or monitor a treatment beam. For example, a target produces X-rays when it is impinged by energetic electrons. A photon flattening filter shapes X-rays to provide a uniform dose distribution across the X-ray field. An ion chamber monitors the energy, dose distribution, dose rate, or other parameters of a radiation beam. In an electron mode operation, an electron scattering foil scatters incident electrons to provide a broadened, uniform profile of a treatment beam. A field light system simulates a treatment field by illuminating e.g. an area on the surface of a patient's skin. In conventional accelerators, exchangers are used to position electron scattering foils and photon flattening filters. Foil-filter exchangers allow switching back and forth between scattering foils and flattening filters for electron or photon mode operations. Fine precision adjustments of the foils and filters in exchangers are accomplished in the factory by manually adjusting and testing the foils and filters, which is a very time consuming process. Conventional foil-filter exchangers do not include a target assembly or field light assembly. In conventional accelerators the targets are located in other areas of the treatment head e.g. inside the accelerator vacuum envelope. The design of target assemblies residing inside the vacuum envelop is complex due to added vacuum walls and interface considerations. Actuation of targets in vacuum is complicated. Any water leaks in target cooling systems would contaminate the vacuum envelope causing extended downtime. A field light system includes a lamp and a mirror, and is used to facilitate patient placement for treatment by providing an intense light field that coincides with the radiation treatment field shaped by collimator jaws or other beam limiting devices. Because of space limitations and other considerations, it is unfeasible to place a lamp in the same location as the radiation source. In conventional accelerators the mirror is fixedly disposed along the beam centerline and is made of a thin film that is generally transparent to radiation or electron beams. Once being installed, the mirror and the lamp projector are manually adjusted in order to achieve the required coincidence with the X-ray field. The mirror located in the beam centerline causes scattering losses and beam contamination. The thin film materials are susceptible to degradation due to exposure to radiation, damage and optical distortion. The present invention provides a beam filter positioning device that allows for significant improvement in automation of production test procedures and operation of medical linear accelerators. It provides significant savings in both test time and occupancy of final test. The beam filter positioning device performs multiple functions in producing, shaping, or monitoring a treatment beam. For instance, the device may position a target button under an electron beam to produce X-rays in a photon mode, or retract a target out of the path of an electron beam for an electron or other modes. The device may accurately position an electron scattering foil or a photon flattening filter to shape the intensity profile of a treatment beam and provide uniform treatment fields. The device may precisely position a field light assembly in simulating a treatment beam for patient alignment. It may also retract an ion chamber from the beam centerline to provide an unimpeded path for the field light. The beam filter positioning device may be modular. It can be mounted to the treatment head of an accelerator and easily removed for repair with proper lifting fixtures. Driving mechanisms such as servo motor control may be used to perform precise movement or adjustments of various device components. In one embodiment, a carousel assembly includes a base plate, a stage supported by the base plate and movable in a linear direction, a filter-foil assembly attached to the stage, a target assembly supported by the base plate, and an ion chamber assembly supported by the base plate. The filter-foil assembly is rotatable about an axis, movable in a linear direction with the stage, and includes a plate member adapted to support one or more photon flattening filters and one or more electron scattering foils. The target assembly includes one or more targets and is movable in a linear direction. The ion chamber assembly is movable in a linear direction. In some embodiments, the carousel assembly may include a field light assembly having a mirror member and a light source. The mirror member is preferably supported by the filter-foil assembly, and the light source is supported by the ion chamber assembly. In a preferred embodiment, the light source includes two or more lamps each being operable to project light to the mirror member for the purposes of providing redundancy. In some embodiments, the carousel assembly may additionally include a backscatter filter assembly attached to the filter-foil assembly. In a preferred embodiment, a plurality of photon flattening filters are positioned in a circular or partial circular configuration having a first radius, and a plurality of electron scattering foils are positioned in a circular or partial circular configuration having a second radius different from the first radius. The second radius is preferably greater than the first radius. In one embodiment, a carousel assembly includes a plate adapted to support one or more photon flattening filters and one or more electron scattering foils, a first linear axis operable to move the plate in a linear direction, and a rotation axis operable to rotate the plate about an axis. In a preferred embodiment, the first linear axis is operable to move the rotation axis in a linear direction. Preferably, the first linear axis and/or the rotation axis comprise a servo motor controllable by a computer. In some embodiments, a plurality of photon flattening filters are positioned in a circular or partial circular configuration having a first radius, and plurality of electron scattering foils are positioned in a circular or partial circular configuration having a second radius different from the first radius. The second radius is preferably greater than the first radius. In one aspect, a system comprises a beam filter positioning device and a control mechanism. The beam filter positioning device comprises a plate configured to support one or more beam filters, and one or more axes operable to move the plate relative to a beam line. The control mechanism is coupled to the one or more axes for controlling the movement of the axes and configured to automatically adjust a position of at least one of the beam filters relative to the beam line. In another aspect, a beam filter positioning device comprises a plate configured to support one or more beam filters, and two or more axes operable to move the plate. The two or more axes may comprise a linear axis operable to translate the plate and a rotation axis operable to rotate the plate. In a preferred embodiment, the linear axis is operable to translate the rotation axis. In a further aspect, a method of automatically adjusting a beam filter position in a radiation system comprises the steps of providing a plate and one or more beam filters supported by the plate, and moving the plate using one or more motion axes to position a beam filter relative to a beam line. A control mechanism operable by computer software is used to automatically adjust the position of a beam filter in the radiation system. In a further aspect, a method of automatically adjusting field light in a radiation system comprises the steps of providing a field light assembly including a mirror and a light source, moving the mirror using a first motion axis and/or moving the light source using a second motion axis to provide a light field that would illuminate from a virtual light source. The moving of the mirror and/or the light source is controlled by a control mechanism operable by computer software, whereby the virtual light source position is automatically adjustable in three degrees of freedom. Various embodiments of beam filter positioning devices and linear accelerators incorporating the devices are described. It is to be understood that the invention is not limited to the particular embodiments described as such may, of course, vary. An aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments. For instance, while various embodiments are described in connection with X-ray linear accelerators, it will be appreciated that the invention can also be practiced in other particle accelerators. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting since the scope of the invention will be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled. The term “carousel” is sometimes used to describe an embodiment that uses a rotational axis; but the invention is not limited to such an embodiment. In addition, various embodiments are described with reference to the figures. It should be noted that the figures are not drawn to scale, and are only intended to facilitate the description of specific embodiments. They are not intended as an exhaustive description or as a limitation on the scope of the invention. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless defined otherwise. Various relative terms used in the description or appended claims such as “above,” “under,” “upper,” “over,” “on,” top,” “bottom,” “higher,” and “lower” etc. are defined with respect to the conventional plane or surface being on the top surface of the structure, regardless of the orientation of the structure, and do not necessarily represent an orientation used during manufacture or use. The following detailed description is, therefore, not to be taken in a limiting sense. As used in the description and appended claims, the singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. As used herein the term “beam filter” refers to a member that modulates one or more parameters of a particle beam such as the energy, intensity, shape, direction, dose distribution, or other beam parameters. A particle beam includes but is not limited to a beam of electrons, photons, protons, heavy ions, or other particles. By way of example, a beam filter includes but is not limited to a photon flattening filter, an electron scattering foil, and a proton scattering foil. As used herein, the term “axis” refers to a mechanism that is operable to move an object in a direction. For example, a “linear axis” refers to a mechanism that is operable to move an object in a linear direction. A “rotation axis” refers to a mechanism that is operable to rotate an object around an axis. An axis may preferably include a servo motor and one or more feedback devices that are electrically coupled to a control mechanism operable with user interface software. A close loop control can be used to control the axis and automatically adjust the position of an object in a system. FIGS. 1A-1D illustrate an exemplary carousel assembly or beam filter positioning device 100 in accordance with some embodiments of the invention. The device 100 may include a movable stage 200, a beam filter assembly or photon flattening filter-electron scattering foil assembly 300 (hereafter “filter-foil assembly” for simplicity of description), an ion chamber assembly 400, a field light assembly 450, and a target assembly 500. The device 100 may also include a backscatter filter 460. The movable stage 200, filter-foil assembly 300, ion chamber assembly 400, field light assembly 450, target assembly 500, and various driving mechanisms or axes are preferably coupled to or supported by a supporting structure 202 such as a frame, a base plate, or the like. FIG. 2 is a bottom perspective view, with the filter-foil assembly and ion chamber not shown for clarity, showing a stage 200 and a base plate 202. The base plate 202 is configured to be mounted to a treatment head and provides support for the device 100. A frame 204 is attached to the base plate 202 along its periphery providing additional support and stiffness for the device 100. The base plate 202 has a cutout 206 e.g. in a generally rectangular shape defining an open area under which the stage 200 is located. The stage 200 supports a primary collimator 208, shielding 210, shielding 224, and filter-foil assembly 300 etc. (see also FIG. 1A), and is operable to move its payload in a direction. For example, the stage 200 can be driven by a linear axis 212 and moved along a direction such as a direction parallel to a linear accelerator plane of symmetry (Y-direction) or other directions. Alternatively, the stage 200 can be driven by a rotation axis and rotate in a direction. The linear axis 212 may include a motor 212a, a ball screw 212b, and a coupler 212c coupling the motor and the ball screw. The motor 212a and ball screw 212b can be supported by mounts 214, 216 respectively. The motor 212a serves to rotate the ball screw 212b, which is adapted to engage the stage 200 and move the stage 200 in a linear direction. Guide rails 218a, 218b fixedly attached to the base plate 202 define the linear movement of the stage 200. Slide guides or other mechanisms (not shown) can be used to engage the stage 200 with the guide rails 218a, 218b. A resolver or sensor 212d may be coupled to the motor 212a to provide primary feedback on the position of the ball screw. A housed resolver 212e may be used to provide redundant or secondary feedback. Preferably, the motor 212a is a servo motor electrically connected to a controller and operable with user interface software. While a specific motor, ball screw, guide, and feedbacks are described in detail for illustrative purposes, it should be appreciated that other types of drive mechanisms or feedbacks can also be used and anticipated by the inventors. The stage 200 may have an opening adapted to receive the primary collimator 208 (see also FIG. 1C). The primary collimator 208 may be provided with a step on the bottom side so that it can fit in the opening and held in place. Pins, screws, and other suitable means can be used to secure the primary collimator 208 to the stage 200. The primary collimator 208 can be made of tungsten or other suitable high density metals. The primary collimator 208 is provided with a passageway 222 (see also FIG. 1C) e.g. in a cone shape to define or shape the field of X-rays produced. Shielding 224 is located under the stage 200 and can be attached to the stage 200 via pins, screws etc. Shielding 224 is provided with a passageway 226 e.g. in a cone shape that extends from and aligns with the passageway 222 in the primary collimator 208. A circular channel 228 is provided on the bottom side of the shielding 224 to provide a travel path or clearance for photon flattening filters 302 to rotate about an axis as will be described in more detail below. A central opening 230 in the shielding 224 allows a structural member 306 passing through to fixedly attach the filter-foil assembly 300 to the stage 200 (see also FIG. 1C). The stage 200 may be configured to support an axis such as a rotation axis 312, which is adapted to rotate or move the filter-foil assembly 300 as will be described in more detail below. For example, the stage 200 may have a U-shaped cutout at a side to provide space for the rotation axis 312. The rotation axis 312 may be supported by a bracket, which may be attached to the stage 200 by e.g. screws. FIG. 3 is a perspective view of a filter-foil assembly or beam filter assembly 300 in accordance with some embodiments of the invention. For clarity photon flattening filters are not installed or shown in FIG. 3. The filter-foil assembly 300 supports one or more beam filters. For example, the filter-foil assembly 300 may support photon flattening filters 302 and electron scattering foils 304, and positions the two in photon modes and in electron modes respectively (see also FIG. 1C). The filter-foil assembly 300 is operable to move in a linear direction and rotate around an axis. Alternatively, the filter-foil assembly is operable to translate in both X- and Y-directions. The linear movement of the filter-foil assembly 300 can be accomplished by moving the stage 200 which is driven by the axis 212. The filter-foil assembly 300 can be fixedly attached to the stage 200 via a structural member 306 using e.g. pins, screws or other suitable means 308. The structural member 306 is coupled to the filter-foil assembly 300 via a bearing assembly 310 including bearing rings, bearing retainer, bearings etc. The bearing assembly 310 allows the filter-foil assembly 300 to rotate with respect to the structural member 306. The rotation of the filter-foil assembly 300 can be actuated and controlled by the rotation axis 312, which is supported by the stage 200. The rotation axis 312 includes a motor 312a, a pulley 312b, roller guides 312c, and a timing belt 312d (see also FIGS. 2, 1C, and 1D). The timing belt 312d (FIG. 1D) is wound around the pulley 312b and the filter-foil assembly plate 316b. Therefore, when actuated, the motor 312a drives the pulley 312b to turn, which transmits the rotation force to the timing belt 312d. The timing belt 312d engages filter-foil assembly plate 316b and rotates it around the structural 306. The roller guides 312c can be adjusted to control the driving force transmitted to the filter-foil assembly 300. A resolver or sensor 314 can be coupled to the motor 312a to provide primary control feedback. A second housed resolver may be used to provide redundant or secondary feedback. Preferably, the motor 312a is a servo motor electrically connected to a controller and is operable with user interface software. It should be appreciated that while a specific motor, roller guides, and feedbacks are described in detail for illustrative purposes, other types of drive mechanisms or feedback devices can also be used and anticipated by the inventors. The beam filter assembly can be driven by either a linear axis or a rotation axis, or both, or by two linear axes in X-Y directions to position a beam filter or adjust the position of a beam filter. As illustrated in FIG. 3, the filter-foil assembly 300 includes a supporting structure 316 such as a plate or the like configured to support or position one or more beam filters such as a plurality of photon flattening filters 302 and electron scattering foils 304. For clarity photon flattening filters 302 are not shown in FIG. 3. In some preferred embodiments, the photon flattening filters 302 are positioned in a circular or partial circular configuration having a first radius. The scattering foils 304 are positioned in a circular or partial circular configuration having a second radius. The second radius is preferably different from the first radius. For example, the electron scattering foils 304 may be positioned in a partial circular configuration at locations proximate to the periphery of the plate 316, and the photon flattening filters 302 may be positioned in a circular or partial circular configuration at locations proximate to the midpoint of the radius of the plate 316. In some preferred embodiments, the plate 316 may include a first portion 316a supporting electron scattering foils 304 or other elements, and a second portion 316b supporting photon flattening filters 302. The first and/or second portions 316a, 316b may be in a circular shape or other regular or irregular shapes. The second portion 316b may be attached to the first portion 316a by e.g. screws or other suitable means. The second portion 316b may have a plurality of ports 318 configured to receive a plurality of beam filters such as photon flattening filters 302. In FIG. 3, six ports are shown in the second portion 316b. It should be noted that a different number of ports can be provided. The photon flattening filters 302 can be in various forms including e.g. conical form, and can be held in the ports 318 by pins, screws or other suitable means. The conical filters 302 may point upwards or downwards from the plate 316. The materials, forms and/or configuration of the photon flattening filters 302 can be chosen to match the energy of the X-rays produced based on specific applications. The electron scattering foils 304 may include primary scattering foils 304a and secondary scattering foils 304b. The combination of primary and secondary scattering foils 304a, 304b may provide a broadened, uniform profile of a treatment beam. Nine pairs of electron scattering foils are shown in FIG. 3, six grouped together on one side and three grouped together on the opposite side. It will be appreciated that a different number of electron scattering foils can be provided. The primary foils 304a may be supported by a bridge structure 320 mounted to the first plate portion 316a. The bridge structure 320 may raise the primary foils 304a above the secondary foils 304b and vertically aligns a primary foil with a secondary foil. The increased distance between the primary and secondary scattering foils allows the primary scattering foils to be higher in the treatment head and closer to the same elevation or location where the photon source (the target) is located. Having the source of electrons and the source of photons at an about same location is desirable since treatment planning and other design aspects of the treatment head are generally optimized around the location of the photon source. The increased separation between the primary and secondary electron foils also makes electron beam performance less sensitive to small machining variations in the thickness of the secondary foils and in the separation distance. An electron foil assembly with small separation between the upper and lower foils requires tighter tolerances on spacing and thickness of the lower foils to achieve uniform electron beam performance. The linear axis 212 and rotation axis 312 or two linear axes allow for automated adjustments of the position of the electron scattering foils 304 and photon flattening filters 302. The motorized axes 212, 312 may be controlled by a computer and adjustments can be made using a software interface rather than manual adjustment as in the prior art. With a suitable 2D radiation sensor (such as a grid ion chamber array) and an automated tuning software application, these adjustments can be made without human intervention. The use of both rotation and linear axes 212, 312 to adjust the position of electron scattering foils and photon flattening filters makes it practical to place the foils 304 and filters 302 on a different radius of a carousel assembly 300. To position the filters and foils at two different radii allows for a greater number of filters or foils available at two radii, as compared to confining both the filters and foils at a same radius. A greater selection of filters and foils may allow for a greater selection of X-ray and electron energies. The two-radius design of filter-foil assembly 300 makes it possible that the primary collimator 208, a large piece of radiation shielding located around the photon flattening filters 302, to be absent when using electron scattering foils 304 in electron modes. The absence of the primary collimator 208 improves the performance in electron modes by reducing scatter. The two-radius design also allows for a smaller inner radius for the flattening filters 302. A smaller inner radius of the filter travel path 228 would introduce a greater curvature in the shielding 224 gaps, hence substantially reducing the direct radiation leakage paths which would otherwise require heavy and expensive shielding plugs. The use of a separate inner radius for filter motion allows for a large, simple and effective primary collimator 208. Prior art designs have significant compromises to the primary collimator below the target. In most prior designs, the primary collimator is fixed and chopped up in complex and inefficient ways to allow motorized filters and foils to penetrate it. Earlier designs place primary collimator shielding further from the radiation target requiring significantly greater mass, complexity and cost of shielding components. Returning to FIG. 3, in some preferred embodiments, a mirror 420 can be installed on the filter-foil assembly 300. The mirror 420 constitutes a member of a field light assembly 450 and serves to reflect light from a light source. Because the mirror 420 is located on the filter-foil assembly 300, it can be moved out of the way of the radiation or electron beam by motorized axes 212 and 312 when it is not used in field light simulation. As a result, the mirror 420 is not required to be transparent to electron or radiation beams and can be made from any suitable materials, including a thin film or preferably a more robust material such as metal, glass etc. This is advantageous over prior art mirrors which are typically made of a thin film transparent to radiation or electron beams since it is fixedly located in the beam centerline. Thin film materials such as Mylar are more susceptible to degradation due to exposure to radiation, damage and optical distortion. They may also cause scattering losses and beam contamination. Another benefit of disposing the field light mirror on the carousel assembly or beam filter positioning device is that the radiation shielding in the collimator assembly can be greatly simplified. In prior art accelerators, the field light mirror is typically located in the collimator assembly above the jaws, necessitating complex shielding design to allow for mounting and service of the mirror. The access allowances require shielding voids that are duplicated for symmetry, resulting in inefficient shielding requiring complicated, expensive milled pieces of shielding such as tungsten to meet shielding requirements. Without a mirror in the collimator assembly, symmetrical shape of less expensive shielding such as molded lead can be used. This would result in an improvement in electron scatter due to the more efficient shielding. FIG. 4 is a perspective view of an exemplary ion chamber assembly 400 in accordance with some embodiments of the invention. The ion chamber assembly 400 is located under the filter-foil assembly 300 for detecting the parameters of a treatment beam such as beam energy, dose distribution, and dose rate etc. The ion chamber 402 can be supported by a structural member 404 such as a bracket, which is attached to a movable member such as a plate 406. The plate 406 is driven by an axis such as a linear axis 408 which is supported by a support member such as a plate 410. The support plate 410 is attached to the base plate 202 and the frame 204. The linear axis 408 includes a motor 408a, a ball screw 408b, a coupler 408c coupling the motor and the ball screw, and a ball nut 408d engaging the ball screw. The motor 408a can be supported by a mount 412, which is attached to the support plate 410. The ball nut 408d is fixed to or otherwise engaged with the plate 406. The motor 408a serves to rotate the ball screw 408b through the coupler 408c. The ball nut 408d is engaged with the ball screw 408b and moves linearly as the ball screw 408b rotates. The plate 406 to which the ball nut 408d is fixed moves linearly as the ball nut 408d moves. Linear guide rails 412a, 412b fixedly attached to the support plate 410 define the linear movement of the plate 406. Slide guides (not shown) or other suitable mechanisms can be used to engage the plate 406 with the guide rails 412a, 412b. Therefore, when actuated, the motor 408a rotates the ball screw 408b, and moves the ball nut 408d and the plate 406 in a linear direction. The ion chamber 402, which is supported by the bracket 404 attached to the plate 406, moves with the plate 406 along the guide rails 412a, 412b in a linear direction. A cable duct 414 (see also FIG. 1B) is attached to the bracket 404 to house various cables connected to the ion chamber 402. A resolver or sensor 408e can be coupled to the motor 408a to provide primary feedback on the position of the ball screw 408b. A second housed resolver 408f may be used to provide redundant or secondary feedback. A rack and pinion gear assembly 413 may be used to provide additional feedback. Preferably, the motor 408a is a servo motor electrically connected to a controller and is operable with user interface software. It should be appreciated that while a specific motor, ball screw, and feedbacks are described in detail for illustrative purposes, other types of drive mechanisms or feedbacks can also be used and anticipated by the inventors. It should be noted that the ion chamber can be driven, positioned, or adjusted by either a linear axis or a rotation axis. The bracket 404 may include an extension member 416. Two light sources such as filament lamps 418a, 418b can be mounted proximate to the end of the extension member 416. The light sources 418a, 418b, together with the mirror member 420 installed on the filter-foil assembly 300, forms a field light assembly 450. The extension member 416 distances the ion chamber 402 from the light sources 418a, 418b. In a photon mode operation, the ion chamber 402 is located under a photon flattening filter 302 for detection of the parameters of a treatment beam. In an electron mode operation, the ion chamber 402 is located under an electron scattering foil in the beam centerline for detection of the parameters of a treatment beam. In field light simulation, the linear axis 408, rotation axis 312, and linear axis 212 work collectively to adjust the position of the light source 418a or 418b and mirror 420 to optically project the light source to a virtual position coincident with the same location of the radiation source. The three degree of freedom (X, Y, and Z) adjustment of the virtual light source can be accomplished by mounting the mirrors and light sources on motion axes already needed for other purposes. No additional motion axes need to be provided to achieve the three degree of freedom adjustment. The use of motorized axes to move the lamp and mirror assemblies allows for automated adjustment of the field light system. The motorized axes can be controlled by a computer and the adjustment of the field light system can be performed using a software interface rather than the existing manual process. This would save factory adjustment time. Because the lamp assembly 418 is mounted to a motorized axis 408, additional spare lamps can be added to the motorized axis 408 and moved into place in the event that a lamp fails. Both lamps may be factory adjusted into position relative to the assembly interface. Automatically switching to a spare lamp in the event that a light bulb fails allows a medical linear accelerator to continue to be used for treating patients until the failed lamp is replaced at a convenient time. Referring to FIG. 1B, the beam filter positioning device 100 may further include a backscatter filter 460 located under the ion chamber assembly 400. A backscatter filter 460 such as a thin tantalum filter passes high energy photons in the beam direction, but stops low energy photons primarily caused by upward scatter off the upper collimator jaws located downstream. The backscatter filter 460 can greatly reduces unwanted backscattered radiation into the ion chamber 400. This scattered radiation has an unwanted effect on the calibration of the ion chamber 402. The backscatter filter 460 can be supported by a structure 462, which can be fixedly attached to the bottom portion of the structural member 306 e.g. with screws. The backscatter filter 460 can therefore be moved together with the filter-foil assembly 300 in a direction. Preferably the backscatter filter 460 is positioned to have a radius from the structural member 306 about the same as for the photon flattening filters 302, so that when in an electron mode, the backscatter filter 460, like the photon flattening filters 302, can be moved out of the path of an electron beam. Preferably, the structure 462 is a box-like structure having an upper plate and a lower plate with the backscatter filter 460 being attached to the lower plate. The box-like structure 462 is preferably side open to allow the ion chamber 402 passing though the structure 462 between the upper and lower plates. In some embodiments, the backscatter filter 460 can be moved by a rotation axis. FIG. 5 is a perspective view of an exemplary target assembly 500 in accordance with some embodiments of the invention. The target assembly 500 positions a target in the beam path for generation of X-rays in a photon mode, or moves a target out of the beam path in an electron mode. The target assembly 500 can be fixedly attached to the base plate 202 via a channel mount 502. The target assembly 500 includes a substrate 504 supporting one or more target buttons 506 and a cooling tube 508 coupled to the substrate 504 for supplying a cooling fluid. Channels can be provided in the substrate 504 adjacent or surrounding the target buttons 506 for circulating a cooling fluid to dissipate heat generated during target operation. The substrate 504 and the cooling tube 508 can be supported by a mount assembly 510, which is movable relative to the channel mount 502. A shielding block 512 is placed atop and attached to the mount assembly 510 by e.g. screws or pins. The target assembly 500 can be moved by a linear axis 514. The linear axis 514 includes a motor 514a, a ball screw (not shown), a coupler 514b coupling the motor and the ball screw, and a ball nut 514c engaging the ball screw. The motor 514a can be supported by mount 516, which is attached to the channel mount 502. The ball nut 514c is fixed to or otherwise engaged with shielding block 512. The motor 514a serves to rotate the ball screw through the coupler 514b. The ball nut 514c is engaged with the ball screw and moves linearly as the ball screw rotates. As a result, the shielding block 512, to which the ball nut 514c is fixed, moves linearly as the ball nut moves. The mount assembly 510, which supports the substrate 504 and cooling tube 508 and is attached to the shielding block 512, moves linearly as the ball nut 514c moves. Linear guide rail (not shown) fixedly attached to the channel mount 502 defines the linear movement of the mount assembly 510. Slide guides (not shown) can be used to engage the mount assembly 510 with the guide rail. A resolver or sensor can be coupled to the motor 514a to provide primary feedback on the position of the ball screw. A second housed resolver may be used to provide redundant or secondary feedback. Preferably, the motor 514a is servo motor electrically connected to a controller and is operable with user interface software. It should be appreciated that while a specific motor, ball screw, and feedbacks are described in detail for illustrative purposes, other types of drive mechanisms or feedbacks can also be used and anticipated by the inventors. It should also be noted that the target assembly can be driven, positioned, or adjusted by either linear axis or a rotation axis. The target assembly 500 may include one or more targets each being optimized to match the energy of an incident electron beam. For example, the target assembly 500 may include a first target 506a adapted for a first photon mode, a second target 506b for a second photon mode, and a third target 506c for a third photon mode. The material of a target can be chosen and/or the thickness of a target be optimized for an incident electron beam with a particular energy level. By way of example, a first target 506a may be optimized for an incident electron beam having an energy level ranging from 4 to 6 MV. A second target 506b may be optimized for an incident electron beam having an energy level ranging from 8 to 10 MV. A third target 506c may be optimized for an incident electron beam having an energy level ranging from 15 to 20 MV. It should be noted that a different number of targets may be included in the target assembly 500. In operation, the linear axis 514 moves or positions one of the targets 506 in the beam path for a photon mode. In an electron mode, the linear axis 514 removes the targets 506 out of the beam path to allow an electron beam passes unimpeded. FIG. 6 illustrates an exemplary beam filter positioning device or carousel assembly 100 in a photon mode operation in accordance with some embodiments of the invention. The primary collimator 208 and shielding 224 have been positioned and aligned in the beam centerline. The ion chamber 402 and the backscatter filter 460 have also been positioned in the beam centerline. Rotation axis 312 is actuated to rotate the filter-foil assembly 300 clockwise or counter-clockwise to align one of the photon flattening filters 302 in the beam centerline. Sequentially or simultaneously, the linear axis 514 is actuated to position a target button 506 in the beam centerline. An electron beam 602 impinges the target button 506 and X-rays 604 are produced. The field of X-rays 604 is shaped as the X-rays produced pass through the passageways in the primary collimator 208 and shielding 224. A radiation beam with a uniform dose distribution is obtained as the X-rays pass through a flattening filter 302. The parameters of the treatment beam are detected as the beam passes through the ion chamber 402. Backscatter filter 460 located under the ion chamber 402 blocks backscatter radiation from entering the ion chamber 402 to ensure accurate measurement of the radiation beam parameters. Because the mirror 420 is installed on the filter-foil assembly 300 and is off the beam centerline in the photon mode, the treatment beam generated pass downstream unimpeded by the mirror. Depending on the energy of an incident electron beam 602 for a particular application, the linear axis 514 may move the target assembly 500 to position a target button 506 this is optimized for such beam energy in the beam path for optimized performance of the target. Similarly, depending on the energy of an incident electron beam, the rotation axis 312 may rotate to position a flattening filter 302 that is optimized for such beam energy in the beam centerline for optimized performance of the filter. FIG. 7 illustrates an exemplary beam filter positioning device or carousel assembly 100 in an electron mode in accordance with some embodiments of the invention. In an electron mode, linear axis 514 is actuated and drives the target assembly 500 to move the target 506 away from the beam centerline. Linear axis 214 is actuated and drives the stage 200 to move the primary collimator 208, shielding 224, and backscatter filter 460 away from the beam centerline. Because the electron scattering foils 304 have a different or greater radius than the photon flattening filters 302 on the filter-foil assembly 300, driving the filter-foil assembly 300 to move the flattening filters 302 away from the beam centerline would bring the scattering foils 304 to the beam centerline. Rotation axis 312 is actuated and the filter-foil assembly 300 rotates clockwise or counterclockwise to align one of the electron scattering foils 304 with beam centerline. The primary and secondary scattering foils 304 scatter the electron beam to produce a broadened, uniform profile of a treatment beam 606. Depending on the energy of an incident electron beam for a particular application, the rotation axis 312 may rotate the filter-foil assembly 300 to align a scattering foil that is optimized for such beam energy in the beam path for optimized performance of the foil. The parameters of the treatment beam are detected as the beam passes through the ion chamber 402. FIG. 8 illustrates an exemplary beam filter positioning device or carousel assembly in a field light simulation mode in accordance with some embodiments of the invention. Linear axis 408 is actuated and drives the ion chamber assembly 400 to move the ion chamber 402 away from the beam centerline. Linear axis 214 is actuated and drives the stage 200 to move the primary collimator 208, shielding 224, and backscatter filter 460 away from the beam centerline. Because the mirror member 420 has a greater radius than the photon flattening filters 302 on the filter-foil assembly 300, driving the filter-foil assembly 300 to move the flattening filters 302 away from the beam centerline would bring the mirror member 420 to the beam centerline. Rotation axis 312 is actuated and rotates the filter-foil assembly 300 clockwise or counterclockwise to position the mirror member 420 in the beam centerline. The linear axis 408 moves and adjusts the position of a lamp 418 to project the lamp filament to a virtual radiation source position 802. Mirror 420 reflects light projected from the lamp 418 to illuminate an area e.g. on the surface of a patient's skin for simulation. One of the advantages of the beam filter positioning device of the invention is that it can be configured to automatically adjust the position of beam filters, field light assembly, or other device components. The automatic adjustment can be accomplished by a control system operable by a computer software interface such as a Graphical User Interface (GUI). The control system may include a processor such as for example, a digital signal processor (DSL), a central processing unit (CPU), or a microprocessor (μP), and a memory coupled to the processor. The memory serves to store programs for the operation of the beam filter positioning device and other programs. The processor executes the program and generates signals for operation of the motion axes or other components of the beam filter positioning device. Responsive to the signals from the control system, the beam filter positioning device operates in which one or more motion axes move the beam filters, field light source, mirror, or other device components in a controlled and automatic manner based on a plan or routine, or based on a demand input from a user. The control system also receives feedback signals from sensors or resolvers in the motion axes, or from other device components such as the ion chamber, and generates signals for adjustment when necessary. For example, based on the beam parameter signals provided by the ion chamber to the control system, the control system may recalculate and generate signals for adjustment to the motion axes. The motion axes respond and automatically adjust the position of the beam filters. Similarly, based on the field light image or information, the control system may recalculate and generate signals for adjustment to the motion axes. The motion axes respond and automatically adjust the position of the light source and/or mirror to adjust the virtual light source position in three degrees of freedom. Exemplary embodiments of beam filter positioning devices or carousel assemblies have been described. Those skilled in the art will appreciate that various modifications may be made within the spirit and scope of the invention. All these or other variations and modifications are contemplated by the inventors and within the scope of the invention. |
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claims | 1. A rotatable and replaceable plunger type multi-source radiator comprising a radiation source shield, plural shield cavities, a rotatable radiation source selection device, a radiation aperture, one or plural plunger pipes, one or plural radiation source rod, one or plural radiation source box, one or plural radiation sources, a mechanical arm, a positioning lever device, a control device, a radiation aperture, and a reserve radiation location, wherein the radiation source rod consists of a handle, a packing gland, a top shield, a radiation source box and a bottom shield, wherein the control device consists of a timer, a displacement controller and a CPU. 2. The rotatable and replaceable plunger type multi-source radiator according to claim 1, wherein the radiation source shield and the rotatable radiation source selection device form a main block of radiation sources, wherein the shield cavity is formed on the radiation source shield for accommodating the rotatable radiation source selection device, a radiation aperture formed on left side of the main block for radiation, and bottom side of the main block kept hollowed for routing transmission lines. 3. The rotatable and replaceable plunger type multi-source radiator according to claim 1, wherein the rotatable radiation source selection device containing one or plural plunger pipes in an annular and symmetrical configuration with its center is inserted from top into the cavity of the radiation source shield for ease of loading and unloading radiation source rods. 4. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the radiation source rod comprising a handle, a packing gland, top shield, a radiation source box, bottom shield may be inserted in the plunger pipe directly. 5. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the radiation aperture with staircases may use the shield beneath the radiation source rod to prevent leakage and interference from the other radiation sources within the radiation source rod. 6. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the mechanical arm is used for moving the radiation source rod up and down for positioning the radiation source in alignment with the radiation aperture. 7. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the radiation source shield, the rotatable radiation source selection device and the radiation source rod use heavy metal material covered with iron plate. 8. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the radiation source selection device may be adjusted in precision with the positioning lever device. 9. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the mechanical arm is capable of returning to the reserve radiation location by gravitation while a power failure occurred. 10. The plunger type rotatable and replaceable multi-source radiator according to claim 1, wherein the control device is used to command the exposure time of the radiation source and to start the operation of the radiation source selection device and the mechanical arm. |
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062953346 | abstract | In a synchrotron radiation light transmission system, a mirror is disposed in a mirror box for reflecting synchrotron radiation light, the mirror box being formed with an incoming opening and an outgoing opening through which the synchrotron radiation light having a horizontally elongated cross section passes. A swinging mechanism supports the mirror so as to allow the synchrotron radiation light entered the mirror box via the incoming opening to be reflected by the mirror and to change a travelling direction in a vertical plane and for swinging the mirror to change a change angle of the travelling direction. The swing axis is on a cross line, or on its extension, between an incidence plane of the synchrotron radiation light and a tangential plane of the mirror at a reflection point and also on an incidence side of the synchrotron radiation light from the reflection point. The swinging mechanism swings the mirror so that the reflection point of the synchrotron radiation light moves on a reflection plane of the mirror as the mirror swings, and that an incidence angle becomes larger as a distance between a light source of the synchrotron radiation light and the reflection point becomes longer. |
abstract | A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprising fissile material is disposed the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core and are mounted on a suspended support assembly including a plurality of hanger plates connected by tie rods. The upper internals include at least guide frames and internal control rod drive mechanisms (CRDMs) with CRDM motors. The plurality of hanger plates includes a mid-hanger plate that is not the uppermost plate of the plurality of hanger plates and is not the lowermost plate of the plurality of hanger plates. The internal CRDMs are disposed above the mid-hanger plate, the guide frames are disposed below the mid-hanger plate, and the mid-hanger plate engages both the internal CRDMs and the guide frames. |
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claims | 1. A nuclear reactor control rod comprising:a plurality of wing sections arranged radially around an axis extending in vertical direction in such a way as to be disposed with spaces therebetween in a circumferential direction, each of the wing sections being a flat plate spreading in a direction of the axis and in a radial direction, each of the wing sections including a plurality of storage tubes made of SiC material or SiC-fiber-reinforced SiC composite material, the storage tubes being arranged in parallel with one another in a flat plane, and the storage tubes containing a neutron absorbing member containing a neutron absorbing material, each of the wing sections including a wing surface structural member formed by molding of SiC-fiber-reinforced SiC composite material in such a way as to cover surfaces of the plurality of the storage tubes and formed to have an outward shape of a flat plate; anda central joint section made of SiC material or SiC-fiber-reinforced SiC composite material, the central joint section bundling the plurality of wing sections together at center, whereinthe plurality of storage tubes are bundled together with fibers made of SiC or a textile made of SiC. 2. The nuclear reactor control rod according to claim 1, whereinorientation directions of SiC fibers in the SiC-fiber-reinforced SiC composite material is such that arithmetic mean of cos2 θ for all fibers is ½ or greater, where θ is the angle formed with the longitudinal direction of each fiber of the wing section. 3. The nuclear reactor control rod according to claim 2, whereinSiC fibers in the SiC-fiber-reinforced SiC composite material are oriented in two directions, one group is oriented in axial direction and the other group is oriented in a direction perpendicular to the axial direction. 4. The nuclear reactor control rod according to claim 2, whereinthe SiC-fiber-reinforced SiC composite material includes a reinforced sheet where arithmetic mean of cos2 θ for all SiC fibers of the reinforced sheet is adjusted to be greater than or equal to ½. 5. The nuclear reactor control rod according to claim 1, wherein:the neutron absorbing member includes a plurality of rod-shaped absorbers each comprising a cladding tube made of SiC-fiber-reinforced SiC composite material, the rod shaped absorbers being arranged inside the wing surface structural member, and the cladding tubes containing the neutron absorbing material; andorientation directions of the SiC fibers in the SiC-fiber-reinforced SiC composite material used for each cladding tube is such that the arithmetic mean of cos2 φ for all fibers is ½ or greater, where φ is an angle that each fiber of the cladding tube form with the circumferential direction of the cladding tube. 6. The nuclear reactor control rod according to claim 1, whereinthe neutron absorbing member includes a plurality of inner tubes, each of the inner tubes being stored in each of the storage tubes, each of the inner tubes containing the neutron absorbing material, each of the inner tubes being sealed at upper end and lower end. 7. The nuclear reactor control rod according to claim 1, whereinthe neutron absorbing material includes B4C. 8. The nuclear reactor control rod according to claim 1, whereinthe neutron absorbing material includes Hf or Hf alloy. 9. The nuclear reactor control rod according to claim 1, wherein each of the wing sections and central joint section are connected to each other with a bolt made of the SiC/SiC composite material and a nut made of the SiC/SiC composite material. 10. The nuclear reactor control rod according to claim 1, wherein each of the wing sections and the central joint section are joined together by diffusion bonding. |
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claims | 1. A method of refueling a fuel assembly from a reactor core of a nuclear reactor, the method comprising:connecting a lifting tool of a crane with a plurality of lifting pins of the fuel assembly, each lifting pin being non-rotatably affixed to an upper nozzle plate of the fuel assembly and extending upwardly therefrom, the lifting tool comprising a plurality of downwardly extending bars, wherein each of the downwardly extending bars has an upper portion and a lower portion capable of circumferential rotation independent of both the upper portions and the other downwardly extending bars, the connecting including forming a bayonet connection by lowering the downwardly extending bars over the lifting pins so that the lifting pins are disposed within the lower portions of the downwardly extending bars and circumferentially rotating only the lower portion of each of the downwardly extending bars to create a mating connection between each of the downwardly extending bars and the lifting pin over which each of the downwardly extending bars was lowered, whereinthe mating connection is made between a grooved portion and a narrowed portion of the lifting pin and a recess portion and a narrowed region of the lower end of the downwardly extending bars. 2. The method of claim 1, including moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane. 3. The method of claim 1, including releasing the lifting tool from the top of the fuel assembly, the releasing including circumferentially rotating the lower portion of each of the downwardly extending bars to release the bayonet connection. 4. The method of claim 1, wherein the removal method includes simultaneously removing both the fuel assembly and a control rod assembly that is inserted in the fuel assembly, and wherein the control rod assembly vertically overlaps the lifting tool when the fuel assembly is connected with the lifting tool. 5. The method of claim 4, wherein the overlap between the control rod assembly and the lifting tool is at least one-half of the vertical height of the lifting tool. 6. The method of claim 4, wherein the overlap between the control rod assembly and the lifting tool is at least one-half of the vertical height of the downwardly extending bars of the lifting tool. 7. The method of claim 6, wherein each of the downwardly extending bars comprises a motor and the motor provides operative force to circumferentially rotate the lower portion of each of the downwardly extending bars. 8. The method of claim 1, wherein the removal method does not include removing the control rod assembly from the fuel assembly and wherein the lower portions of the downwardly extending bars of the lifting tool surround an upper end of the inserted control rod assembly when the fuel assembly is connected with the lifting tool. 9. A method of removing a fuel assembly from a reactor core of a nuclear reactor, the method comprising:lowering a lifting tool of a crane onto a plurality of lifting pins of the fuel assembly, each lifting pin being non-rotatably affixed to an upper nozzle plate of the fuel assembly and extending upwardly therefrom, the lowered lifting tool including a plurality of downwardly extending bars each including an upper portion and a circumferentially rotatable lower portion having a recess and a narrowed portion, each lifting pin being disposed in a recess of a corresponding downwardly extending bar after the lifting tool is lowered onto the lifting pins;locking the downwardly extending bars of the lowered lifting tool with corresponding mating features of the lifting pins by circumferentially rotating the lower portion of each downwardly extending bar to create a bayonet connection, whereinthe mating connection is made between a grooved portion and a narrowed portion of the lifting pin and the recess and the narrowed portion of the lower end of the downwardly extending bars. 10. The method of claim 9, including moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane. 11. The method of claim 9, including disconnecting the lifting tool from the lifting pins of the fuel assembly by circumferentially rotating the lower portion of the downwardly extending bars and unlocking the downwardly extending bars from the corresponding mating features of the lifting pins. 12. The method of claim 11, wherein the lifting tool is disconnected from the fuel assembly in the spent fuel pool. |
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050376071 | summary | BACKGROUND OF THE INVENTION The present invention relates to fast breeder reactors, and more particularly, it relates to structural components for constituting a reactor core, a core of reactor constituted by such components, and a method for operating such reactor. In general, a core of a fast breeder reactor is formed by bundling a plurality of fuel assemblies each comprising a bundle of cladding tubes in which fuel pellets are filled respectively and each enclosed by a hexagonal duct, to provide a coolant flow channel. Further, in such reactor core, the breeding of the fuel is improved by enclosing the core by axial and radial blankets of fertile material. The fuel such as enriched uranium or plutonium added uranium is mounted in the core, and the fertile material such as natural uranium or depleted uranium is mounted in the blankets. When the fertile material captures fast neutrons having high energy escaped from the core, useful fissile materials are produced. At the same time, the fast neutrons are absorbed in the members constituting the reactor core such as the cladding tubes and ducts, thus expelling atoms from such members and/or nuclear-reacting with impurity to create bubbles of helium gas, thereby swelling the material of such members. The life of the fuel in the fast breeder reactor is often limited by bundle-duct interaction (BDI) between the fuel bundle and the corresponding duct and/or duct-duct interaction (DDI) between the adjacent ducts, due to the swelling of material of the core constituting members. Similarly, in some cases, the life of a control rod which forms a part of the structural component constituting the reactor core is limited by the interaction between the absorber rod bundle and the corresponding duct. The degree of the swelling of the core constituting members depends upon fast neutron fluence and/or irradiation temperature with respect to the fuel assemblies. FIG. 4 shows the axial distribution of these features (i.e., the fast neutron fluence and irradiation temperature) with respect to the fuel assembly in which the fast neutron fluence of the core in a homogeneous core of electrical rating of 1,000 MW is maximum. As apparent from FIG. 4, in the vicinity of the axial center of the reactor core where the fast neutron fluence is maximum, a cladding temperature differs from a duct temperature by about 100.degree. C. In the conventional design of the fast breeder reactors, in many cases, the cladding tubes were made of the same material as the ducts. With such construction, the BDI or DDI will occur owing to the difference in the swelling rates between the cladding tubes and ducts due to the difference in the irradiation temperatures between the cladding tubes and the ducts. That is to say, when the temperature at which the swelling rate of the material becomes peak or maximum (i.e., the peak swelling temperature) is in the vicinity of the range of the irradiation temperature of the cladding tube (cladding temperature), the BDI will occur since the swelling of the cladding is larger than that of the duct whose temperature is lower than the cladding. On the other hand, when the peak swelling temperature of the material is in the vicinity of the range of the irradiation temperature of the duct (duct temperature), the BDI will not occur since the swelling of the duct is larger than that of the cladding. But in this latter case, the DDI will occur. In order to reduce the BDI, an improved fuel assembly comprising cladding tubes made of material having relatively small swelling rate and ducts made of material having relatively large swelling rate has been proposed, as disclosed in the Japanese Patent Laid-open No. 57-166591. With such conventional fuel assembly, the BDI can be reduced or prevented since the swelling of the cladding is smaller than that of the duct. However, in such conventional fuel assembly, since the reduction regarding the swelling of the duct is not devised, when the fuel life is limited by the occurrence of the DDI, it is not expected that the fuel life is extended or increased. SUMMARY OF THE INVENTION A first object of the present invention is to provide structural components for constituting a reactor core, which can reduce both bundle-duct interaction (BDI) and duct-duct interaction (DDI) simultaneously. A second object of the present invention is to provide a core of reactor constituted by such components, which can reduce both the bundle-duct interaction and the duct-duct interaction simultaneously. A third object of the present invention is to provide a method for operating such reactor, which can reduce both the bundle-duct interaction and the duct-duct interaction simultaneously. According to the present invention, in order to achieve the above-mentioned first object, there are provided structural components for constituting a reactor core, comprising one and the other metallic members arranged adjacent to each other in a reactor, and means for relatively reducing the swelling of both of the metallic members due to neutron irradiation thereto. According to the present invention, in order to achieve the above:-mentioned second object, there is provided a core of reactor constituted by such structural components, in which a plurality of structural components each comprising one and the other metallic members arranged adjacent to each other in the reactor and means for relatively reducing the swelling of both of the metallic members due to neutron irradiation thereto are mounted. According to the present invention, in order to achieve the above-mentioned third object, there is provided a method for operating a reactor having a plurality of metallic tubular members arranged in a core of the reactor and each enclosing a plurality of metallic cladding tubes in each of which substance capable of being heated by neutron irradiation and being cooled by passing coolant through the reactor core is filled, wherein the reactor is operated under the condition that an average used temperature of the cladding tubes is higher than an irradiation temperature that the swelling rate of the cladding material due to neutron irradiation thereto becomes maximum and an average used temperature of the tubular members is lower than an irradiation temperature that the swelling rate of the tubular material due to neutron irradiation thereto becomes maximum. |
abstract | A system for generating tunable pulsed monochromatic X-rays includes a tabletop laser emitting a light beam that is counter-propagated against an electron beam produced by a linear accelerator. X-ray photon pulses are generated by inverse Compton scattering that occurs as a consequence of the xe2x80x9ccollisionxe2x80x9d that occurs between the electron beam and IR photons generated by the laser. The system uses a novel pulse structure comprising, for example, a single micropulse. In this way, pulses of very short X-rays are generated that are controllable on an individual basis with respect to their frequency, energy level, xe2x80x9cdirection,xe2x80x9d and duration. |
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abstract | An electron beam irradiation device having an electron beam generating unit R, an irradiation chamber E for irradiating an electron beam to a irradiated object F, and an oxygen cutoff section S for blowing inert gas N on an upstream side of the irradiated chamber. The oxygen cutoff section is designed so that a gap Ws between partitions across the irradiated object is smaller than a gap We between the partitions across the irradiated object in the irradiation chamber (Ws<We). The gap Ws is made uniform, or almost uniform, throughout the entire area of the oxygen cutoff section, and a blowing slit 55 for blowing the inert gas to the processing surface of the irradiated object is provided on a partition with no projection nor recess involved. |
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abstract | An injection molded anti-scatter grid is fabricated from an engineered thermoplastic to form a focused x-ray absorbent framework defining a plurality of inter-spaces. The engineered thermoplastic has higher yield strength than conventional anti-scatter grid fabrication materials, which produces a structurally rigid grid that renders conventional fiber-like inter-space material unnecessary, and further allows the grid to be flexed in one or more directions to change an effective focal length of the grid. The engineered thermoplastic is loaded with high density particles in order to be x-ray absorbent, while still maintaining desired structural properties. |
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description | This application claims the priority to Chinese Patent Application No. 201310715096.5 titled “COMPUTED TOMOGRAPHY SYSTEM AND X-RAY COLLIMATOR THEREOF”, filed with the Chinese State Intellectual Property Office on Dec. 19, 2013, the entire disclosure of which is incorporated herein by reference. The present application relates to the technical field of medical machinery, and particularly to an X-ray collimator of a computed tomography system. The present application also relates to a computed tomography system having the X-ray collimator. In the computed tomography (CT) system, X-rays, which are radiated from the focal spot of an X-ray resource like a point, pass through a subject to be checked. After penetrating the subject, the X-rays are attenuated in two-dimensional distribution and measured by a detector, and then its distributed data are processed by a computer to generate a corresponding tomography image. In the current medical computed tomography system, a solid detector is mainly used for X-ray measurement. Such a solid detector is often an array of an X-ray photoelectric receivers, for example, 16×16 or 16×32 pixel matrix, formed by arranging a plurality of photoelectric semiconductor units in a grid matrix. In the ideal condition, an X-ray travels in a straight line. The data that shall be collected on each pixel of an X-ray detector correspond to the attenuation of the X-rays which penetrate the subject to be checked in the straight path from the focal spot to this pixel. The X-ray that is radiated from the focal spot to the X-ray detector in a straight line is referred to as a primary ray. In the practical use, when an X-ray emanated from the focal spot passes through the subject to be checked to a surface of the detector, it is inevitable that the X-ray interacts with the subject so that the primary ray is scattered to form a scattered ray referred to as a secondary ray. The secondary ray formed by scattering travels in a path deviated from its original straight path and radiates on a surface of a pixel in the vicinity of the original pixel. Finally, besides the primary rays, the X-rays detected by each pixel of the detector further include the scattered secondary rays. It can be known from the principle of formation of the secondary ray that a noise source may certainly be formed as a result of the secondary rays blending with the primary rays traveling in straight lines, causing reduction of the recognition capability of the detector on small difference of the contrast and decrease of the density resolution of the image system. Thus, it is a technical problem to be solved presently for those skilled in the art to reduce the scattered rays reaching the detector. To solve the above technical problem, an X-ray collimator is often placed between the subject to be checked and the detector for reducing the influence of the scattered rays on the image density resolution. Reference is made to FIG. 1, which is a schematic view of a conventional CT scanner having an X-ray collimator in the prior art. A conventional X-ray collimator consists of a structure array which can absorb X-rays and is similar to the array of detector. A Chinese patent application No. 03826552.4 discloses an anti-scattered X-ray collimator of a CT scanning device. As shown in FIG. 1, the CT scanning device includes an X-ray source 2′, which may generate a conical X-ray beam 1′ indicated by dash lines in a controllable way, and an array 4′ of the X-ray detector 3′. The conical X-ray beam 1′ radiates from the focal spot 21′ of the X-ray source 2′. The array 4′ includes rows 31′ and columns 32′ of the X-ray detector 3′, wherein the rows 31′ are orthogonal or approximately orthogonal to the scanning center axis of the scanning device, and the columns 32′ are parallel or approximately parallel to the scanning center axis. The X-ray detector 3′ in the array 4′ is shielded by a two-dimensional X-ray collimator 5′. The X-ray collimator 5′ in FIG. 1 is partially cut away to illustrate the X-ray detector 3′. The X-ray collimator 5′ includes “row” slices 51′ positioned between the rows 31′ of the X-ray collimator 3′, and “column” slices 52′ positioned between the columns 32′ of the detector 3′. The “row” slices 51′ and “column” slices 52′ can be positioned such that their respective planes substantially intersect at the focal spot 21′. With the above X-ray collimator 5′, the “raw” slices 51′ and “column” slices 52′ define and form a plurality of through holes or through gaps whose side walls are oriented in line with the straight paths from the focal spot 21′ to the surface of the X-ray detector 3′. That is to say, the extensions of the side walls of the plurality of through holes or through gaps intersect at the focal spot 21′. In this way, the area of the X-ray detector 3′ shielded by the side walls of the through holes or through gaps is smallest, i.e., the primary ray is shielded minimally, so that the primary rays may pass through the through holes or through gaps to the X-ray detector 3′ with least attenuation, thereby ensuring a high efficiency of the X-ray detector 3′. As can be known from the above operating principle of the X-ray collimator 5′, there is a need for the X-ray collimator 5′ to absorb the scattered rays as many as possible on the one hand and to make most of the primary rays reach the surface of the X-ray detector 3′ with least attenuation on the other hand. The above requirement can be met by adjusting the height of the X-ray collimator 5′, the thickness of the walls of each through hole, and the shape of each through hole. And, it also has a high requirement for the size precision of each through hole in the X-ray collimator 5′. If the through holes cannot align with the pixel units of the X-ray detector 3′, on the one hand, the effective primary rays may be shielded, causing decrease of the detecting efficiency, and on the other hand, the non-uniform of the units may cause the image distortion. Therefore, the X-ray collimator 5′ plays an important role on a high-quality image scanned through a computed tomography system. The current X-ray collimator as shown in FIG. 1 may be made by a first method in which sheet metal is stamped to form bended grid members and the grid members are adhered to each other, referring to the Chinese patent application No. 03826552.4 titled “Anti-scattered X-ray collimator of a CT scanning device” for further details. However, the collimator formed by the first method has a low precision due to springback during stamping. The X-ray collimator as shown in FIG. 1 can be made by a second method in which the slices with an array of grids are stacked, referring to the Chinese patent application No. 200810009502.5 titled “stacked CT collimator and the manufacturing method thereof” for further details. However, the stacked structure of multiple slices formed by the second method is complicate, and it is difficult to ensure uniformity of anti-scattering since the regions of slices where the primary rays pass through are required to have uniform sizes. The X-ray collimator can be made by a third method similar to 3D printing, referring to the Chinese patent applicant No. 02144468.4 titled “method of manufacturing scatting grid or collimator” for further details. However, the wall thickness of the through holes formed by printing in the third method may be thicker so as to greatly shield the primary rays, and may be non-uniform so as to cause non-uniformity of anti-scatting effect. The X-ray collimator may be formed by a fourth method of tenon connection, referring to the U.S. patent application with publication No. 20070258566A1 titled “ANTI-SCATTER-GRID” for further details. However, the X-ray collimator formed by the fourth method has a large number of components, causing the complicate assembling process. Therefore, it is a technical problem to be solved presently for those skilled in the art to design an X-ray collimator of computed tomography system having an improved collimation effect and a simple structure. An object of the present application is to provide an X-ray collimator of a computed tomography system having a simple structure and a good collimation effect. Another object of the present application is to provide a computed tomography system having the X-ray collimator, which has a high detecting precision. To solve the above problems, there is provided in the present application an X-ray collimator of a computed tomography system, including a plurality of first plates extending in the circumferential direction of the computed tomography system and a plurality of second plates extending in the axial direction of the computed tomography system. The first plates and the second plates are inserted and engaged with each other, and two adjacent first plates and two adjacent second plates define a through hole. The extensions of the side walls of each through hole intersect at the focal spot of the X-ray source, making the X-ray pass through the through hole in a straight line. The X-ray collimator of the present application is formed by a plurality of first plates and second plates inserted and engaged with each other, and adjacent first plates and adjacent second plates define a plurality of through holes. The extensions of the side walls of each through hole intersect at the focal spot of the X-ray source, which ensures the through hole to extend in the radiation direction of the corresponding X-rays. Thus, an X-ray radiating from the focal spot of the X-ray source can pass through the through hole in a straight line, and finally reach a detecting unit of the X-ray detector without any shielding while having a good collimation effect. Furthermore, the side walls of the through hole may absorb and block the scattered rays, which would otherwise interfere with the X-rays in the through hole, thereby improving the anti-scattering effect and increasing the detecting precision. The assembling process of the X-ray collimator of the present application can be completed simply by inserting and engaging the first plates and the second plates with each other. Thus, the structure of the X-ray collimator is simple and the manufacturing and assembling process thereof is simple. Preferably, each of the first plates has a plurality of first slits spaced apart in the circumferential direction, and each of the second plates is positioned and inserted in the corresponding first slit. The first slits may be provided only in the first plate. Then, the second plate is inserted in the first slit, so that the structure is simplified and the assembling efficiency is improved. Preferably, the first slit extends from top towards bottom and does not run through the lower end face of the first plates, and the second plate is provided at its lower end with a plurality of second slits extending from bottom towards top. The first slits are engaged with the middle-upper portions of the second plates, and the second slits are engaged with the lower ends of the first plates. The first slits may also be partial-through slits, and a solid portion is left at the lower end of the first plate. The second plate is provided with a plurality of second slits for engaged with the solid portion. Thus, the middle-upper portion of the second plate is engaged with the first slit, and the second slit is engaged with the lower end of the first plate, so that the first plates and the second plates can be positioned reliably so as to define the structures of the through holes. Preferably, the first slit is provided in the middle of the first plate, and its height is not smaller than the height of the second plate, so that the entire second plate is inserted into the first slit in the axial direction. The first slits may also be provided in the middle of the first plate, and the entire second plate may be inserted into the first slits, so that the structure of the first plates and second plates is further simplified and the assembling convenience is improved. Preferably, the upper end face and the lower end face of the second plate are fixed with the upper end face and the lower end face of the first slit by adhesive bonding or welding. Preferably, the upper end of the second plate is provided with second upper slits extending from top to bottom, so that the second upper slits receive and are engaged with the upper ends of the first plates. Additionally or alternatively, the lower end of the second plate is provided with second lower slits extending from bottom to top, so that the second lower slits receive and are engaged with the lower ends of the first plates. When the second plate is inserted into the first slit in its entirety, because the first slits are arranged in the middle of the first plate, the upper end and the lower end of the first plate are solid portions. The upper end and/or lower end of the second plate may further be provided with slits, thereby achieving an engagement of the first plates and the second plates at their upper and lower ends and improving the reliability of positioning. Preferably, the second plate may include two or more sub-plates stacked in a vertical direction. The second upper slits are provided in the top sub-plate and the second lower slits are provided in the bottom sub-plate. The second plate may further include an infill plate which could press and position the sub-plates in the first slit. The second plate may include a plurality of sub-plates stacked in a vertical direction. Then, each of the sub-plates could be pressed and positioned in the first slit by the infill plate, thereby improving the reliability of positioning. Preferably, the first slit may include a first upper slit at upper end and a second lower slit at lower end. The second plate may include an upper plate engaged and positioned in the first upper slit and a lower plate engaged and positioned in the first lower slit. When the first slit includes the first upper slit and the first lower slit, the second plate may include an upper plate and a lower plate. Then, the upper plate may be engaged with the first upper slit, and the lower plate may be engaged with the first lower slit, which not only improves the positioning reliability of the first plate and the second plate, but also avoids a deformation since the second plate is too high. Therefore, it ensures the orientation of through hole to be identical with the radiation direction of the corresponding X-ray, and the collimation effect is improved. Preferably, the lower end of the upper plate has a plurality of upper plate slits extending in from bottom to top, and the upper plate slits are engaged with the lower end of the first upper slit. Additionally or alternatively, the lower end of the lower plate has lower plate slits extending from bottom to top, and the lower plate slits are engaged with the lower end of the first lower slit. Accordingly, the lower ends of the upper plate and the lower plate may be provided with slits, thereby achieving a crossing connection with the upper slit and the lower slit of the first plate, and improving the positioning reliability. Preferably, it further includes a positioning plate, which has a plurality of positioning grooves extending in the circumferential direction, and each of the positioning grooves is engaged with and positioned relative to the upper end of the corresponding first plate. The positioning plate functions to a positioning tool for the first plate, and is provided with a corresponding positioning groove for mounting each of the first plates. Then, the upper end of each first plate is inserted and positioned in the positioning groove, thereby mounting the first plate precisely and quickly. Also, the positioning plate may serves as a cover plate, which covers the top of the first plates and closes the entire the X-ray collimator, preventing foreign matters such as dust from falling into the collimator. Preferably, the positioning groove is a run-through groove. Preferably, the positioning groove includes two or more sub-grooves spaced apart in the circumferential direction. The solid portion between the adjacent sub-grooves is set to have a predetermined width. The upper end of each of the first plates is provided with cutout notch for accommodating the solid portion. The positioning groove may include a plurality of sub-grooves. Then, the entire positioning plate can have a good rigidity. Compared with a long groove in the circumferential direction, the plurality of sub-grooves may avoid the positioning plate from bending to cause reduction of precision. Although it needs to provide cutout notch for accommodating the corresponding solid portion at the upper end of the first plate, the size of the notch is much smaller than the height of the first plate, which hardly influences the structure of the through hole. Preferably, a first guard plate is provided at each of two ends of the first plate, and a second guard plate is provided at each of two ends of the second plate. The first guard plates 5 and the second guard plates 6 enclose the ends of the first plates and the second plates. Preferably, the thickness of the first guard plate is substantially half of the thickness of the second plate, and the thickness of the second guard plate is substantially half of the thickness of the first plate. The thickness of the first guard plate and the second guard plate may be set. When the adjacent X-ray collimators are joined, the two first guard plates are joined and serve as a second plate engaged with the first plate. The two second guard plates are joined and serve as a first plate engaged with the second plate. Two adjacent X-ray collimators may be joined to form a large X-ray collimator, which can be joined with more X-ray collimators. There is further provided in the present application a computed tomography system, including an X-ray detector and an X-ray collimator for collimating the X-rays radiating to the X-ray detector. The X-ray collimator is one of the above X-ray collimators. Preferably, the X-ray collimator is mounted on the X-ray detector, and each through hole corresponds to a detecting unit of the X-ray detector. A plurality of partition grooves are provided in partition regions between pixels of the X-ray detector, and the lower ends of the first plates are embedded into the partition grooves. Because the computed tomography system of the present application includes one of the above mentioned X-ray collimators, the computed tomography system may produce the same technical effects generated by the X-ray collimator computed tomography system, which is not described here any more. In FIG. 1: 1′conical X-ray beam;2′X-ray source;21′focal spot;3′X-ray detector;31′row;32′ column; 4′array;5′X-ray collimator;51′“row” slice;52 “column” slice; In FIGS. 2-17: 1first plate;11first slit;12first upper slit;13first lower slit;14notch;2second plate;21second slit;22second upper slit;23second lower slit;24sub-plate;25infill plate;26upper plate;261slit of upper plate;27lower plate;271slit of lower plate;3through hole;4positioning plate;41positioning groove;411sub-groove;5first guard plate;6second guard plate;7X-ray detector;8X-ray collimator. An X-ray collimator of a computed tomography system is provided according to an aspect of the present application. The X-ray collimator has a simple structure and a good collimation effect. A computed tomography system having the X-ray collimator is provided according to another aspect of the present application. The computed tomography system has a high detecting precision. For those skilled in the art to better understand technical solutions of the present application, the present application will be described in detail in conjunction with drawings and embodiments hereinafter. Referring to FIGS. 2 and 16, FIG. 2 is a schematic structural perspective view of the X-ray collimator according to one embodiment of the present application; and FIG. 16 is a schematic structural perspective view of the X-ray collimator in FIG. 2 mounted on an X-ray detector. The X-ray collimator 8 in the present application includes a plurality of first plates 1 and a plurality of second plates 2. The first plates 1 each extend in the circumferential direction of the computed tomography system, and the second plates 2 each extend in the axial direction of the computed tomography system. The first plates 1 and the second plates 2 are crossed and engaged. Two adjacent first plates 1 and two adjacent second plates 2 define and form a plurality of through holes 3. The extensions of side walls of the through holes 3 intersect at the focal spot of the X-ray source, i.e., the extension planes of the first plates 1 and the second plates 2 intersect at the focal spot of the X-ray source. Then, the X-rays radiating from the focal spot of the X-ray source may pass through the corresponding through hole 3 in a straight line without shielding, and further be effectively received by the X-ray detector 7. The side walls of the through holes 3 also can shield the scattered rays when the X-rays penetrate the subject to be checked, which would otherwise adversely affect the detecting result. Though the X-ray collimator in the present application includes a plurality of the first plates 1 and a plurality of the second plates 2, it will be appreciated that the number of the first plates 1 may be not equal to that of the second plates 2. That is to say, the term “plurality of” as mentioned herein refers to an uncertain number. The circumferential direction and the axial direction herein are defined with reference to the entire computed tomography system, wherein the axial direction refers to a direction parallel to the scanning central axis of the computed tomography system, and the circumferential direction refers to a rotation direction of the computed tomography system during scanning. The first plate 1 extending in the circumferential direction of the computed tomography system means that the first plate 1 may substantially extend in the circumferential direction of the computed tomography system with a deviation from the circumferential direction of the computed tomography system by an angle, generally a small deviation. The second plate 2 extending in the axial direction of the computed tomography system means that the second plate 2 may substantially extend in the axial direction of the computed tomography system with a deviation from the axial direction by an angle, generally a small deviation. The first plates 1 and the second plates 2 both may be configured as curved plates, flat plates or other regularly-shaped plates, depending on the requirements of mounting of the X-ray detector 7 and the structure of the through hole 3 to be formed. For collimating the X-ray, the through holes 3 each shall be oriented in accordance with the radiation direction of the X-ray, i.e. the extensions of all of the side walls (faces of the first plates 1 and the second plates 2) of the through hole 3 intersect at the focal spot of the X-ray source. The X-ray detector 8 of the present application may be in a sector region of a sphere having a center at the focal spot of the X-ray source and a radius from the focal spot to the detecting unit of the X-ray detector 7. Generally, the X-ray collimator 8 is in a frustum shape. Since the through hole 3 functions as the passage of the X-rays, and the X-rays each are emanated from the focal spot of the X-ray source to the X-ray detector 7, the space of the through hole close to the X-ray source is relatively small. Thus, the size of through hole 3 may gradually increase in the incidence direction of the X-ray, such that the through hole 3 has a sufficient space at a side approximate to the X-ray source in order to facilitate a precise incidence of the X-ray and can, at a side approximate to the X-ray detector 7, be matched with the detecting unit of the X-ray detector 7 perfectly. Compared with the conventional X-ray collimator, the X-ray collimator 8 of the present application uses the first plates 1 and the second plates 2 crossed and engaged with each other to form a plurality of through holes 3. The X-ray collimator 8 may be easily assembled, only by determining orientations of the first plates 1 and the second plates 2 to define the structure of each through hole 3 such that the orientation of the through hole 3 is aligned with the incidence direction of the X-rays, thereby allowing the X-rays to pass through the through hole 3 in a straight line to the detecting unit of the X-ray detector 7 without blocking the X-rays while effectively absorbing or blocking the scattered rays. Accordingly, the X-ray collimator 8 has a good collimation effect. To effectively absorb the scattered rays, the first plates 1 and the second plates 2 may be made of material with high X-ray attenuation, for example, W (tungsten), Mo (molybdenum), Pb (lead), Ta (tantalum), or any alloy thereof. Generally, the thickness of the first plate 1 and the second plate 2 is set between 0.01 mm˜0.3 mm for blocking the X-rays minimally while effectively shielding the scattered rays. In theory, it would be better to have the overall height of the X-ray collimator 8 higher. However, considering the mounting space and manufacturing process and so on, the height may be set to be 5˜50 times of the side length of each pixel, usually 5 mm˜50 mm. It is noted that the height herein means the size of the first plate 1 and the second plate 2 in the incidence direction of the X-ray. The X-ray herein means a primary ray radiating from the focal spot to the X-ray detector 7 in a straight line, and the scattered ray herein means a secondary ray formed by scattering during the process of X-rays penetrating the subject to be checked, unless otherwise stated. A further modification may be made to the X-ray detector of the present application. Referring to FIGS. 3 to 5, FIG. 3 is a schematic structural perspective view of a first plate and a second plate engaged in a first crossing connection according to the present application; FIG. 4 is a front structural schematic view of the first plate shown in FIG. 3; and FIG. 5 is a front structural schematic view of the second plate shown in FIG. 3. In a first embodiment, the first plate 1 may be provided with a plurality of first slits 11, which are spaced apart in the extension direction of the first plate 1, such that the second plates 2 can be inserted and positioned in the respective first slits 11. The first plates 1 each may be provided with the first slits 11, and then the second plate 2 is sequentially engaged with the first plates 1. The second plates 2 may be inserted in the first plates 1, with the second plates 2 being spaced apart in the extension direction of the first plates 1, thereby dividing the space defined by the first plates 1 and the second plates 2 into a plurality of grids to form a plurality of through holes 3. By providing the first slits 11 in the first plate 1, it is not only simple in structure but also may receive the second plates 2 with ease, thereby improving the reliability of the positioning and assembly convenience. Similarly, those skilled in the art should appreciate that the second plate 2 may be provided with the silts, so as to insert the first plates 1 into the second plate 2; or that the first plates 1 and the second plates 2 both may be provided with the silts, so as to interlace them with each other. As shown in FIGS. 3 and 4, the first silt 11 may extend from top to bottom, but does not run through the lower end face of the first plate 1, i.e., the lower end of the first slit 11 is at a distance from the lower end face of the first plate 1, and the portion of the first plate 1 within this distance is solid. The lower end of second plate 2 may be provided with the second slits 21, which may extend from bottom to top. The second plate 2 may be engaged into the first slit 11 from top to bottom, and positioned in the first plate 1 after the middle-upper portion of the second plate 2 is inserted in the first slit 11. When the second slit 21 of the second plate 2 is moved to the lower end of the first slit 11, the second plate 2 continues to go downwards, and as a result, the second slit 21 of the second plate 2 receives and is engaged with the solid portion of the lower end of the first plate 1, as shown in FIG. 3. Thus, the first plate 1 and the second plate 2 are positioned and engaged with each other reliably. The middle-upper portion of the second plate 2 refers to a portion except for the second slit 21 in a vertical direction, i.e., the solid portion of the second plate 2. The term “inserted and engaged” or the like as used herein means that both of the two parts to be engaged are provided with slits, and the two parts are engaged with each other through their slits oppositely, i.e., the two parts are inserted and engaged with each other through the slits aligned with each other. The term “positioned and engaged” means that at least one of the parts to be connected is provided with slits, so as to receive and is fitted with another part to be connected, thereby positioning and engaging the two parts with each other. Apparently, the case of “positioned and engaged” includes the case of “inserted and engaged”. In addition, the solid portion mentioned herein means a solid portion where a structure such as a slit does not run through. The first slit 11 may be in transition or clearance fit with the second plate 2, and the second slit 21 may be in transition or clearance fit with the first plate 1, which is applicable to any inserted or engaged part as mentioned herein and will not be described below. To further improve the reliability of positioning of the first plates 1 and the second plates 2, an adhesive (e.g., 502 glue or the like) with low X-ray attenuation may be used to bond and position the cross joints of the first slits 11 and the second slits 21. Alternatively, the first plates 1 and the second plates 2 may be welded at the cross joints of the first slits 11 and the second slits 21. In any structure using adhesive for positioning as will be described below, the adhesive may be replaced by welding. And, the adhesive used in the bonding refers to an adhesive with a low X-ray attenuation. The transmission direction of the X-ray is defined as a vertical direction. Thus, the “upper or top” part refers to be proximate to the focal spot, and the “lower or bottom” part refers to be proximate towards the X-ray detector 7. Because the X-rays are radiated from the focal spot, each X-ray may define its own vertical direction which is not a uniquely determined direction. That is to say, the extension directions of the first slits 11 and the second slits 21 depend on the orientations of the through holes 3. The first slits 11 extend in different directions, and the second slits 21 extend in different directions. For facilitating the crossing connection, the first slits 11 may extend from the upper end face of the first plate 1 towards the bottom, i.e., the upper end of the first plate 1 is open. The second slits 21 may extend from the lower end face of the second plate 2 towards the top, i.e., the lower end of the second plate 2 is open. Considering the stability of insertion, the height of the first slit 11 should be larger than half of the entire height of the first plate 1, as shown in FIG. 4. In order to avoid the interference between the first slits 11 and the second slits 21 in the insertion process, which may otherwise cause a distortion of the first plates 1 and the second plates 2 and even an impracticable insertion, the height of the second slit 21 should not be too high, usually lower than 5 mm, as show in FIG. 5. That is to say, the first slit 11 is set to be a long slit, and the second slit 21 is set to be a short slit. Similarly, when the first plate 1 is inserted in the second plate 2, the first slit 11 may be set to be a short slit, and the second slit 21 may be set to be a long slit. Unless otherwise particularly stated, the slit that does not run through the plate herein is the long slit, and the slit that is arranged at one end (upper end or lower end) of the first plate 1 or the second plate 2 is often the short slit. In addition, because the height of the second slit 21 is short, and only the lower end of the first plate 1 is inserted in the second slit 21, the second slit 21 may be oriented not to point towards the focal spot, but to be parallel to each other, which can simplify the manufacturing process without influencing the positioning precision of the first plate 1. Considering that only the lower end of the first plate 1 is positioned in the second slits 21, an assembling tool having a plurality of parallel positioning grooves can be used for achieving the assistant positioning and assembling of the upper end of the first plate 1 during assembly. Referring to FIGS. 6 and 7, FIG. 6 is a schematic structural perspective view of the first plate and the second plate engaged in a second crossing connection according to the present application; and FIG. 7 is a schematic structural perspective view of the first plate and the second plate engaged in a third crossing connection according to the present application. The first slit 11 may also be provided in the middle of the first plate 1, i.e., the first slit 11 is set to be an enclosed elongated groove, and the height of the first slit 11 may be not smaller than the height of the second plate 2, so that the second plate 2 may be inserted into the first slit 11 in its entirety in the axial direction, as shown in FIGS. 6 and 7. The middle portion of the first plate 1 means a region that extends from the center of the first plate 1 towards the top end and the bottom end by a certain distance in the vertical direction. That is to say, the middle portion is defined relative to the two ends, not exactly refers to the center portion. In addition, the definition is applicable to any middle portion mentioned herein. In the second embodiment, the upper end of the second plate 2 may be provided with the second upper slits 22 extending from top towards bottom, so that the second upper slits 22 can receive and be engaged with the upper end of the first plate 1. Then, the upper end of the first slit 11 is positioned and engaged with the second upper slit 22, thereby achieving the positioning of the entire second plate 2. Also, the lower end of the second plate 2 may be provided with the second lower slits 23. In this way, the second plate 2 is inserted into the first slit 11 in the axial direction, and is pressed downwards such that the second lower slit 23 receives the lower end of the first plate 1. Thus, the lower end of the first slit 11 is positioned and engaged with the second lower slit 23, as shown in FIG. 6. The cross joints of the first slits 11 and the second upper slits 22 or lower slits 23 may be fixed by adhesive. Compared with the first slit being open, the enclosed first slit 11 has a higher structural stability, which is not easily deformed, thereby positioning the second plate 2 at a higher precision. In the third embodiment, the second plate 2 may not be provided with slits. In this case, the second plate 2 may be inserted into the first slit 11 in its entirety in the axial direction, as shown in FIG. 7. Then, the upper end face of the second plate 2 and the upper end face of the first slit 11 are positioned and bonded by adhesive or welding, and the lower end face of the second plate 2 and the lower end face of the first slit 11 are positioned and bonded by adhesive or welding. Further referring to FIGS. 8 and 9, FIG. 8 is a schematic structural perspective view of the first plate and the second plate engaged in a fourth crossing connection according to the present application; and FIG. 9 is a schematic structural sectional view of FIG. 8 with the second plate positioned in the first slit. In the fourth embodiment, the second plate 2 may include two or more sub-plates 24 which are stacked in the vertical direction, as shown in FIG. 8. Here, two sub-plates 24 are illustrated by way of example. The top sub-plate 24 may be provided at its upper end with the second upper slits 23, and the bottom sub-plate 24 may be provided at its lower end with the second lower slits 23. Then, the top sub-plate 24 may be positioned by the second upper slits 22 receiving and being engaged with the upper end of the first plate 1, and the bottom sub-plate 24 may be positioned by the second lower slits 23 receiving and being engaged with the lower end of the first plate 1, as shown in FIG. 8. Besides, the second plate 2 further includes an infill plate 25, which can be adhesively bonded or welded at the back of each sub-plate 24 so that the sub-plates 24 in the vertical direction are connected to form one piece, as shown in FIG. 9. Because the infill plate 25 together with the sub-plates 24 is inserted into the first slit 11, the first slit 11 can be filled, so that the sub-plates 24 are pressed and positioned in the first slit 11, thereby achieving a stable positioning of the first plate 1 and the second plate 2. Referring to FIG. 10, FIG. 10 is a schematic structural perspective view of the first plate and the second plate engaged in a fifth crossing connection according to the present application. In the fifth embodiment, the first slit 11 includes a first upper slit 12 and a first lower slit 13. The first upper slit 12 and the first lower slit 13 are spaced apart in the vertical direction. The second plate 2 includes an upper plate 26 and a lower plate 27. The upper plate 26 is inserted and positioned in the first upper slit 12, and the lower plate 27 is inserted and positioned in the first lower slit 13. To further improve the connecting reliability and reduce the deformation of the first plates 1 and the second plates 2, the first slit may include an upper sub-slit and a lower sub-slit, and correspondingly, the second plate 2 may include an upper plate 26 and a lower plate 27, which may be inserted into the upper sub-slit and the lower sub-slit respectively. Compared with integral first slits 11 and integral second plates 2, the structure in the fifth embodiment is positioned more precisely, forming through holes 3 at a higher precision. Compared with the fourth embodiment, the fifth embodiment omits the infill plate 25, making the assembling process easier. In the embodiment shown in FIG. 10, the lower end of the upper plate 26 may be provided with the upper plate slits 261, which extend from bottom towards top. Then, the upper plate slit 261 may be inserted and engaged with the lower end of the first upper slit 12. Further, the lower end of the lower plate 27 may be provided with lower plate slits 271 extending from bottom towards top, so that the lower plate slits 271 and the lower end of the first lower slits 13 are engaged with each other and positioned. To positioning reliably, the cross joints of the upper plate slits 261 and the first upper slits 12, as well as the cross joints of the lower plate slits 271 and the first lower slits 13, may be bonded or welded to achieve assistant positioning. Referring to FIGS. 11 to 15, FIG. 11 is a schematic structural perspective view of a X-ray collimator having a positioning plate mounted thereon according to the present application; FIG. 12 is a schematic structural view of the positioning plate shown in FIG. 11 in one arrangement; FIG. 13 is a structural schematic view of the positioning plate in another arrangement according to the present application; FIG. 14 is a schematic structural view of the first plate in one arrangement according to the present application; and FIG. 15 is a partially enlarged schematic view of part A in FIG. 14. Besides, a positioning plate 4 may be further provided in the present application, which may be provided with a plurality of positioning grooves 41 extending in the circumferential direction. The positioning grooves 41 are arranged to be correspond to the first plates 1 respectively. The positioning grooves 41 and the first plates 1 are arranged in the same orientation, such that each of the positioning grooves 41 is engaged with and positioned at the upper end of the corresponding first plate 1. The positioning plate 4 may achieve the auxiliary positioning of the upper ends of the first plates 1, which improves the assembly convenience of the first plates 1. The function of the positioning plate is similar to the assembling tool having a plurality of positioning grooves as mentioned above. Besides, the positioning plate 4 may serve as a cover plate covering on the top of the first plates 1, which may prevent foreign matters such as dust from falling into the through holes 3 of the X-ray collimator 8, further ensuring a reliable collimating effect. The positioning plate 4 may be made of material with low X-ray attenuation, for example, organic glass, polycarbonate (PC), PEC, etc. The thickness of the positioning plate 4 may be set between 0.2 mm˜1 mm. After the positioning plate 4 is engaged with the upper end of the first plate 1, they may be bonded for assistant positioning. Because the top sides of the first plates 1 are straight and substantially parallel to each other, the positioning grooves 41 may be straight and parallel to each other, as shown in FIG. 12. It can be conceived that the positioning grooves 41 may be configured as run-through grooves or blind grooves on the underside of the positioning plate 4. The positioning plate 4 may be processed by mechanical engraving or laser cutting to form the positioning grooves 41. As shown in FIGS. 13 to 15, the positioning groove 41 may include two or more sub-grooves 411 spaced-apart in the circumferential direction. The solid portion between two adjacent sub-grooves 411 is set to have a predetermined width. The predetermined width is much smaller than the smallest value of the lengths of the positioning grooves 41. The predetermined width refers to a size in the circumferential direction. For this, the upper end of the first plate 1 may be provided with a notch 14, as shown in FIGS. 14 and 15. The notch 14 is provided at a place corresponding to the solid portion between the two adjacent sub-grooves 411, so as to accommodate the solid portion, making the positioning plate 4 in a good contact with the first plate 1 and ensuring a reliable connection therebetween. Since the notch 14 has a height much lower than that of the first plate 1 and has a small length in the circumferential direction, the notch 14 has little effect on the uniformity of the pixels. Thus, the collimating unit for each pixel may be regarded as being uniform. It will be appreciated that, although the positioning grooves 41 may include a plurality of sub-grooves 411 to improve the structural stability of the positioning plate 4 and effectively position the first plate 1, the uniformity of collimation effect may be affected if there are too many notches 14. Thus, the number of the sub-grooves 411 should be limited, and generally, two or three sub-grooves are preferable. As shown in FIGS. 2 and 11, first guard plates 5 and second guard plates 6 may be further provided in the present application. The first guard plates 5 are provided at opposite ends of the first plate 1, and the second guard plates 6 are provided at opposite ends of the second plate 2. Thus, the first guard plates 5 enclose the both ends of each of the first plates 1, and the second guard plates 6 enclose the both ends of each of the second plates 2. The both ends of the first plate 1 and the both ends of the second plate 2 refer to the two ends in the respective extending direction of them. The thickness of the first guard plate 5 and the second guard plate 6 can be set. For example, the thickness of the first guard plate 5 may be substantially half of the thickness of the second plate 2, and the thickness of the second guard plate 6 may be substantially half of the thickness of the first plate 1. The wording “substantially” herein includes the meaning of “equal to” and a small deviation. The deviation means that the thickness of the plate formed by joining the two first guard plates 5 or the two second guard plates 6 can meet the requirement of thickness of walls of the through hole 3, i.e., it will not block the X-ray. When joining the two collimators 8 together, the first guard 5 may be joined with another first guard plate 5 of the adjacent X-ray collimator 8 to form a plate with the thickness substantially equal to a second plate, which is engaged with the first plate 1 to define through holes 3 meeting the requirement of collimation. Similarly, the second guard plate 6 may also be joined another adjacent second guard plate 6 so as to join the two or more X-ray collimators 8 one by one to form a large X-ray collimator, i.e., a larger shielding layer. With reference to FIGS. 16 and 17, FIG. 16 is a schematic structural perspective view of the X-ray collimator in FIG. 2 mounted on the X-ray detector; and FIG. 17 is a partially enlarged schematic view of part B in FIG. 16. There is further provided a computed tomography system in the present application. The computed tomography system includes an X-ray detector 7 and an X-ray collimator 8 for collimating the X-rays radiating to the X-ray detector 7. The X-ray collimator 8 may be any one of the above mentioned X-ray collimators 8. For other structures of the computed tomography system, please refer to the conventional computed tomography system in the prior art, which are not described here. Specifically, as shown in FIGS. 16 and 17, the X-ray collimator 8 is mounted on the X-ray detector 7, such that each through hole 3 of the X-ray collimator 8 corresponds to a detecting unit of the X-ray detector 7. A plurality of partition grooves 71 are provided in partition regions between the pixels of the X-ray detector 7, and the lower ends of the first plates 1 of the X-ray collimator 8 are embedded into the partition grooves 71, thereby assembling and positioning the X-ray collimator 8 and the X-ray detector 7. A detailed description has been made to the computed tomography system and the X-ray collimator thereof according to the present application. The principle and the embodiments of the invention have been illustrated by way of examples, and the above description of the embodiments is provided only for better understanding the concept of the invention. It should be noted that those skilled in the art may make many improvements or modifications to these embodiments without departing from the spirit or scope of the present application. These improvements or modifications will fall into the scope of protection as defined in Claims. |
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abstract | A system for an electro magnetic oscillator tube with enhanced isotopes is disclosed herein having at least one magnetron layer. Each layer has a first magnet, a conduction block, and a second magnet of opposite polarity. The conduction block is disposed in a plane about an emitter of isotopic particles, where an opposite electrical polarity relative to the emitter forms between the emitter and the conduction block. The conduction block has an RF port, an interaction space in its inner periphery, and a polar array of resonant cavities forming along its outer periphery, and a diamond or similar material coating the conduction block surfaces. The system also has a connection between selected groups of resonant cavities at locations of like electrical polarity, wherein the connections have conductive strapping elements within the conduction block. |
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abstract | A core spray sparger T-box attachment assembly for a nuclear reactor pressure vessel, wherein the pressure vessel includes a shroud, a sparger T-box penetrating the shroud, a plurality of sparger distribution header pipes coupled to the sparger T-box, and a downcomer pipe. The sparger header pipes may include at least one sparger nozzle, and the sparger T-box attachment assembly may include a downcomer pipe coupling and a sparger T-box clamp. The sparger T-box clamp may include an anchor plate having a draw bolt opening to receive a draw bolt, a first clamp block substantially aligned at one end of the anchor plate, and a second clamp block substantially aligned at the other end of the anchor plate. |
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046506349 | abstract | A refueling machine within a nuclear reactor facility includes an inner mast or gripper tube (12) to the bottom of which is secured a gripper assembly (16). An actuator tube (20) controls the gripper mechanisms of the gripper assembly (16), and in order to insure proper and accurate alignment of the gripper mechanisms with the fuel assembly nozzles, a television camera (26) is mounted within the actuator tube (20). A television monitor (34) is operatively connected to the television camera (26), the monitor (34) being disposed upon the refueling machine personnel trolley. The television camera (26) is removably mounted within the actuator tube (20) by a bayonet-type system which includes camera housing lugs (78) which are adapted to pass through slots (76), subsequent to which the camera housing (28) and the lugs (78) are rotated 90.degree. whereby the lugs (78) are seated within recesses (80). The mounting system further includes shock absorbing spring systems (52, 62) for isolating the camera (26 ) for vertically upwardly and vertically downwardly directed shock loads. |
051046121 | description | DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, FIG. 1 in particular, a typical power generating, water cooled and moderated nuclear reactor plant 10, comprises a reactor pressure vessel 12, having a removable top (not shown) which closes and seals the pressure vessel during operating of the reactor. The removable top of the pressure vessel is disconnected and deposited elsewhere during shutdowns for refueling and/or maintenance service. Reactor pressure vessel 12 is substantially filled with water 14 for moderating the fission produced neutrons, cooling the heat produced by the fissions reaction of the fuel and transferring the generated heat energy in the form of steam or pressurized hot water to means for conversion into mechanical work, such as a turbine. A fuel core 16 is located within the reactor vessel 12 submerged within the coolant/moderator water 14. The fuel core 16 is composed of a multiplicity of fuel bundles 18, each comprising a group of spaced apart sealed tube containers enclosing fissionable fuel and assembled and secured together in a composite unit. The upper end of the fuel bundle is provided with an end piece having a bail-like handle 20 for grasping by mechanical means to enable secure handling and transporting of the fuel bundles 18 when needed for refueling or rearranging partially spent fuel of the fuel core 16. To facilitate handling and transferring of fuel bundles 18 for refueling and/or fuel rearrangement of the core 16, reactor plants 10 commonly employ a fuel bundle handling platform 22. The fuel handling platform 22 usually comprises a platform which bridges across the top of the reactor vessel cavity and the reactor vessel 12 and is movable back and forth over the top of the reactor vessel cavity and the reactor vessel 12 on suitable means such as wheels and track. The movable platform 22 enables operating personnel working thereon to be positioned at any location above any fuel bundle 18 within the fuel core 16 for servicing. A fuel bundle handling mast 24 is supported by and movable about on the fuel bundle handling platform 22, and is extendable downward therefrom into the reactor vessel 12 and the water 14 contained therein to just above the fuel core 16. The mast 24 can be arranged with the full length thereof sliding up and down to reach the core and retract therefrom, or telescoping in structure whereby it expands downward to reach the core and contracts upward therefrom. A grapple head 26 is mounted fixed on the lower end of the fuel handling mast 24 for reaching down into the reactor vessel 12 and its water 14 contents for grasping the fuel bundle handles 20 to lift and transport the fuel bundles 18. The grapple head 26 comprises a housing 28 including complementary hooks 30 for attaching to handles 20 and securely grasping the fuel bundles 18 for transfer. Both the mast 24 and grapple hooks 30 of head 26 are operated remotely by personnel located above the reactor vessel 12, such as on the fuel bundle handling platform 22. In accordance with this invention, a television camera or the like remote viewing means 32 is enclosed within the housing 28 of the grapple head 26. Camera or other viewing means 32 is provided with a transmitting and control cable 34 extending from the camera up the mast 24 to the movable platform 22 for personnel performing on the platform to observe underwater through the camera or viewing means 32 and operate the camera and underwater lighting to enhance the view. The camera cable 34 is connected to a television monitor, such as monitor 36, for viewing by operating personnel, and/or a small screen viewing monitor can be affixed to the upper end of the handling mast 24 for the convenience of the personnel operating the grapple 26 through the mast. The camera or viewing mean 32 is located within the upper portion of the grapple head housing above the grapple hooks 30 whereby it does not interfere with the mechanism or operation of the grapple hooks, which can be of conventional design. Referring to FIGS. 2, 3 and 4 of the drawings, a generally horizontal support shaft 38, comprising a hollow cylinder is secured within the grapple housing 28 for supporting the hook 30 mechanism. Hollow cylindrical sleeves 40 are rotatably mounted on and around support shaft 38, with a sleeve attached to one of at least two complementary hooks 30. Rotatably mounted sleeves 40 are fixed in longitudinal axial positions on the support shaft 38, preferably each hook carrying sleeve being located adjacent to an end of the support shaft, and spaced a distance apart. A spacing sleeve 42 ca be positioned between sleeves 40 on shaft 38 to provide for apt spacing of the sleeve units. Thus arranged, with the rotation of sleeves 40 mounted on shaft 38 over a short arc, the pair of grapple hooks 30 pivot inward toward each other for the purpose of securely grasping a bail handle 20 of a fuel bundle and safely transporting same, then pivot backward away from each other to release a bail handle 20 of a fuel bundle to deposit the bundle at a suitable location. One version of this invention comprises a centrally positioned sleeve 40 with an integrated hook 30 directed in one direction and a pair of end positioned sleeves 40, one on each side of the central sleeve, with each of said end sleeve having a hook 30 directed in the opposite direction of the center hook 30. Thus the outer pair of hooks 30 face the center hook 30 which faces the pair of hooks whereby they complement each other to securely close upon each other and grasp a bail handle. Further in accordance with this invention, the hollow cylindrical support shaft 38 is provided with a pair of complementary orifices 44, positioned generally in a central area in the support shaft 38 between the sleeves 40, one orifice being located in the upper portion of the cylindrical shaft 38 and the other orifice opposite thereto in the lower portion of the cylindrical shaft. The paired upper and lower orifices 44 are vertically aligned one over the other to provide a direct in-line optical viewing path or line of sight downward through the center of generally horizontal support shaft 38 from above. Thus, a remote operator positioned above the grapple means can observe from overhead the area immediately below the grapple hooks 30 by a variety of means including a television camera 32 located above the grapple hooks 30. When a spacing sleeve 42 is employed mounted on the support shaft 38 between the sleeves 40, a pair of orifices 46 are provided in spacing sleeve 42 which aligned with and are generally conterminous to the perimeters of orifices 44 on the upper and lower opposite sides of the support shaft 38. Thus the two pairs of orifices 44 and 46 are each in-line vertically providing a direct optical viewing path or line of sight from above the grapple means to the area immediate below. To illuminate the area immediately beneath the grapple means for facilitating its operation under water by an overhead remote operation above the water's surface, lighting means are preferably associated with the fuel handling system or mechanism. In accordance with invention at least one light source is located within the generally horizontal support shaft 38 contained within grapple housing 28. A light source 48 is positioned inside either or both end areas of support shaft 38 which are surrounded by rotatably mounted sleeves 40 carrying grapple hooks 30. To enable the light source 48 to illuminate the area beneath the grapple hooks 30 for effective viewing by an overhead operator, orifices 50 and 54 are respectively provided in the lower portion of the support shaft 38 and also in a lower portion of the immediate surrounding sleeve 40 rotatably mounted on the shaft and carrying a grapple hook 30. The orifices 50 and 54 respectively in the lower portion of the shaft 38 and sleeve 40 are in alignment and generally conterminous in perimeters when sleeves 40 are rotated in a limited arc with the grapple hooks 30 pivoted back away from each other in a retracted position for release of an object form the grasp of the hooks. When the sleeve 40 is so positioned, light from the source 48 beams downward illuminating the area below the grapple head 26. One or more partitions 54 is provided within support shaft 38 between the light source 48 and the central portion of the shaft 38 containing the viewing orifices 44, and 46. This arrangement blocks light from the light source 48 from entering into the line of vision passing between the orifices 44 and 46 and thereby obscuring the field of view beneath the grapple head 26 and hooks 30 while fully illuminating the area beneath the grapple head 26 and 30 for enhanced operator vision. The measures of this invention provide for direct viewing and/or illuminating of an underwater object such as a fuel bundle through the grapple head and hooks depending therefrom without any need for fiber optics, light pipes or mirrors, and the like. |
description | This application is related to the patent application entitled “Method and Apparatus for Representing, Managing and Problem Reporting in VoIP Networks,” filed in the US Patent and Trademark Office on Jul. 3, 2006, and assigned Ser. No. 11/325,109, and to patent application entitled “Method and Apparatus for Management and Analysis of Services in VoIP Networks,” filed in the US Patent and Trademark Office on Jun. 29, 2007, and assigned Ser. No. 11/824,238, the contents of both of which are incorporated by reference herein. A portion of the disclosure of this patent document contains illustrations of EMC Smarts network model, which is subject to copyright protection. The copyright owner, EMC Corporation, has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The present invention relates generally to Voice over Internet Protocol (VoIP) networks and more particularly, to methods and apparatus for analyzing VoIP network performance. Voice over IP (VoIP) is an emerging technology to package analog audio signal, such as those transmitted over a Public Switched Telephone Network (PSTN), as information packets and transmit the packets over one or more networks. FIG. 1 illustrates a VoIP configuration or network 100 wherein conventional packet-switched network 110, e.g., the Internet, provides service link between telephone 140.1 and 140.2. In this illustrated example, a user, at telephone 140.1 enters the telephone number of telephone 140.2 and the information is provided through router 135.1 to gateway 120.1. Gateway 120.1 provides signals, through router 130 to gateway 120.2 to establish the connection, i.e., pathways within network 110. After the connection is established, telephone 140.1 communicates with telephone 140.2 through the established transport connection 138. With the increasing development of, and dependency upon, networks to provide services, such as VoIP, to businesses and their customers, the need for proper management and operation of the network is increasing more important. Not only does the VoIP service provide a less costly means of providing voice services, it is inherently more reliable in that the voice packets may be dynamically routed in case of fails occurring in the network. The above referred-to patent application Ser. No. 11/325,109 discloses a method for managing aspects of a VoIP network by modeling components within the VoIP network and determining a physical status of the network by analyzing detected or observed events and correlating these events with most-likely causes of the detected or observed events. Such an analysis is referred-to as a root-cause analysis and, more specifically, an availability root cause analysis. VoIP availability root-cause analysis and other similar analysis are presented in detail in the referred-to patent application and need not be discussed in detail herein. However, while an availability analysis will determine whether a component, device or element within the VoIP network is not performing correctly, and, thus, impacting overall performance, conditions within the VoIP network may arise wherein the network elements are performing within their desired operational ranges but some degradation in the performance may be experienced because of other conditions occurring within the network. Hence, there is a need in the industry for a method and system for representing, analyzing and determining root cause of errors in the performance of the VoIP network and the impact of such errors. A method, apparatus and computer product for modeling and analyzing performance of a Voice-over-IP (VoIP) configuration, composed of a plurality of components, is disclosed. The method comprises the step of representing selected ones of the plurality of components and relationships among the selected components, wherein said component representations are selected from the group of configuration non-specific representations consisting of: VoIP-DHCP Service, VoIP-CallOperation Service, VoIP_Signaling Service, VoIP_MediaGateway Service and VoIP_SIP Service, and wherein the representations of relationships are selected from the group of configuration non-specification representations consisting of: Hostedby/HostsServices and Integrates/IntegratedIn, providing a mapping between a plurality of first events and a plurality of second events occurring in the selected components, the mapping representing the relationships along which the first events propagate among the selected components, and determining at least one first event based on at least one of the plurality of second events by determining a measure between each of a plurality of relationship values associated with the plurality of first events and the plurality of second events. Other embodiments of the invention include a computerized device, configured to process all of the method operations disclosed herein as embodiments of the invention. In such embodiments, the computerized device includes a memory system, a processor, a communications interface and an interconnection mechanism connecting these components. The memory system is encoded with a load manager (or store process) application that when performed on the processor, produces a load manager (or store) process that operates as explained herein within the computerized device to perform all of the method embodiments and operations explained herein as embodiments of the invention. Other arrangements of embodiments of the invention that are disclosed herein include software programs to perform the method embodiment steps and operations summarized above and disclosed in detail below. More particularly, a computer program product is disclosed that has a computer-readable medium including computer program logic encoded thereon that when performed in a computerized device provides associated operations explained herein. The computer program logic, when executed on at least one processor with a computing system, causes the processor to perform the operations (e.g., the methods) indicated herein as embodiments of the invention. Such arrangements of the invention are typically provided as software, code and/or other data structures arranged or encoded on a computer readable medium such as an optical medium (e.g., CD-ROM), floppy or hard disk or other a medium such as firmware or microcode in one or more ROM or RAM or PROM chips or as an Application Specific Integrated Circuit (ASIC) or as downloadable software images in one or more modules, shared libraries, etc. The software or firmware or other such configurations can be installed onto a computerized device to cause one or more processors in the computerized device to perform the techniques explained herein as embodiments of the invention. Software processes that operate in a collection of computerized devices, such as in a group of storage area network management servers, hosts or other entities can also provide the system of the invention. The system of the invention can be distributed between many software processes on several computers, or all processes could run on a small set of dedicated computers or on one computer alone. It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not intended as a definition of the limits of the invention. The embodiments shown in the figures herein and described in the accompanying detailed description are to be used as illustrative embodiments and should not be construed as the only manner of practicing the invention. Also, the same reference numerals, possibly supplemented with reference characters where appropriate, have been used to identify similar elements. FIG. 2A illustrates an exemplary embodiment of a VoIP software-based model and FIG. 2B illustrates an extension of the model shown in FIG. 2A in accordance with the principles of the present invention. Referring to FIG. 2A, the model 200 shown is an extension of known network models, such as the EMC Smarts Common Information Model (ICIM), or similarly defined or pre-existing CIM-based model and adapted, herein, for the VoIP network. EMC and SMARTS are trademarks of EMC Corporation, Inc., having a principle place of business in Hopkinton, Ma, USA. The EMC model is an extension of the well-known DMTF/SMI model. A discussion of the EMC model's application to VoIP networks is presented at least in the commonly-owned U.S. patent application Ser. No. 11/263,689, now U.S. Pat. No. 7,107,185, issued on Nov. 1, 2005 to Yemini, Y., et al., and its application to VoIP networks is discussed in the aforementioned related U.S. patent application Ser. No. 11/325,109, the contents of both of which are incorporated by reference herein. Referring to FIG. 2A, an exemplary abstract model 200 of the VoIP infrastructure section of network 100 (FIG. 1) is shown. The existing ICIM model 210 includes at least the elements SoftwareServices 212, SoftwareReducdnacyGroup 214, N-TierApplicationService 216, which represent elements of a network system. For example, the object SoftwareServices represents the attributes and properties associated with a collection of services that represent operations such as call processing, music-on-hold, etc. In addition to the known objects, model 210 includes at least the objects VoIPSoftwareService 230, VoIPSoftwareServiceRedundancyGroup 236, and VoIPApplicationService 240. The element VoIPSoftwareService 230 represents attributes and properties associated with a collection of services that comprise a VoIP application subsystem. VoIPSoftwareServiceRedundancyGroup 236 represents a collection of services that provide resilient VoIP services to some set of IP telephones or other VoIP signaling entities. VoIPSoftwareService 230, VoIPServiceRedundancyGroup 236, and VoIPApplicationService 240, objects represent configuration, i.e., network, non-specific representations of the attributes and parameters of the associated hardware and further inherits the attributes and parameters of associated class and subclass. Similarly, the exemplary model shown is not related to any specific configuration and the illustrated relationships between the objects are not associated with any specification VoIP configuration. Objects associated with VoIPNetworkServices 232 and VoipVoiceService 234, include the attributes or properties associated with the network aspects of the VoIP service and the voice aspects of the VoIP service, respectively. For example, managing the physical gateway is associated with a network service, as shown in block 270, and voice mail service is associated with the voice service, as shown in block 280. Devices providing either voice services or acting as client endpoints in the VoIP system are considered VoIPVoiceServices, whereas elements involved in the transmission and/or routing of voice data traffic are considered VoIPNetworkServices. For example, object H323Devices H.323 Devices represents codecs and tools for conducting multimedia conference calls and object CTIDevices represents Computer Telephony Integration services, such as conducting phone calls in coordination with another application (e.g.: integrated whiteboard and audio conversations). Model 210 also includes object VoIPSystem or UnitarycomputerSyattributes and properties associated with a system or host running on one or more applications that support VoIP. The ICIM model 210 includes element or object VoIPSystem or Unitary Computer System 218, which presents attributes and properties of the physical elements, i.e., processors, and processing systems, of the network. For example, host object 218.1 represents a processing system that upon which aspects of the VoIP service or application reside. Such processing systems may be based on, for example, Pentium processors. Pentium is a registered Trademark of Intel Corporation. To accommodate VoIP service performance attributes, the VoIP_NetworkServices object 232 is extended to include the new object VoIP_PerformanceService 290 object (see FIG. 5B). The VoIP_PerformanceService object 290 represents attributes and properties associated with a collection of performance parameters or characteristics of a VoIP application subsystem. In this illustrated example, specific network performance services may be represented by the VoIP-DHCP Service object 292, VoIP-CallOperation Service object 294, VoIP_Signaling Service object 296 and the VoIP_MediaGateway Service object 298. The VoIP_Signaling Service object 260 may further include a VoIP_SIP Service object 298.1. The VoIP_Signaling Service object describes properties and attributes associated with the VoIP signaling function. The VoIP-CallOperation Service object 294 describes properties and attributes associated with the VoIP call. The VoIP_MediaGateway Service object 298 describes the properties and attributes of the gateway servicing the VoIP connections. Gateways typically provide a path between VoIP networks and older POTS (Poor Old Telephone System) or TDM telephone networks. The VoIP_SIP Service object 298.1 defines the properties and attributes of SIP device handling SIP protocol requests. FIG. 3 illustrates an exemplary causality graph or map associated with the VoIP service model shown in FIG. 2. In this illustrative example, when a host is determined to be in a Down condition (e.g., non-operational), then the VoIP_Network Service is effected by is effectively also operationally down or not-available. Similarly, when a VoIP_Network Service is determined to be operating in a sub- or non-optimal manner, the non-optimal performance may be caused by the detection or determination of a large time jitter among a plurality of data packets carrying the VoIP data, or by the loss of an excessive number of packets, or an excessive MOS score or a determined excessive packet delay (transmission or received). Determination of an excessive time jitter, number of lost packets, Mean Opinion Score (MOS) score or delay, may be determined by a processor maintaining a count of the appropriate condition per unit time and comparing the determined values with corresponding threshold values. For example, a processor may determine a difference in time of arrival of packets and maintain a count of those differences greater than a first known threshold. At the conclusion of a unit time period the count of the differences greater than a first known threshold are compared to a threshold associated with, in this case, time jitter, and determine whether excessive time jitter exists. An indication of non-optimal performance may then be indicated. FIG. 4 illustrates an exemplary causality matrix associated with the model shown in FIG. 2 and causality graph or map shown in FIG. 3 for determining a root-cause of an observed event or symptom. In this form, the mapping illustrates the relationship along which observed events propagate from causing events, wherein the relationship value (i.e, “1”), indicates that a symptom is caused or generated by the associated event. Although the relationship value is shown as deterministic (i.e., 100 percent probability of occurring), it should be recognized that the value may also represent a probability of an event causing a symptom to occur. Hence, the value may also be probabilistic. In this exemplary matrix when a indication of “down” is observed, the cause of such a indication may be associated with the host being non-operational or one of the performance criteria is so excessive that the service is not performing at all. Similarly, if an indication of non-optimal performance is observed, the root-cause may be that at least one of the performance parameters has exceeded its associated threshold value. Information regarding different performance parameters may be determined and provided by well-known methods as previously described. In some aspects of the network processing, although a failure may occur, symptom(s) may, or may not, be generated to indicate that a component is experiencing failures. The root-cause correlation described herein is powerful enough to be able to deal with scenarios in which symptoms are generated to indicate the cause of the failure. An analysis, e.g., a root cause analysis, of the VoIP network, similar to that described in the aforementioned related US patent application may be used to determine from the exemplary causality or behavior model(s) shown, herein. Root Cause analysis by the determination of a measure of the elements of the causality matrix shown in FIG. 4 may be used to determine the most likely root cause of the one or more of the observed symptoms. Such root cause analysis is described in detail in commonly-owned U.S. Pat. No. 7,107,185, issued on Nov. 1, 2005 to Yemini, Y., et al., the contents of which are incorporated by reference herein. In one aspect, a most likely causing event may be determined by determining a minimum Hamming distance between a plurality of observed events and the causing events. As presented herein, the VoIP system resides on or “hosted by” existing network components that may generate alarm indications, associated with errors, independent of corresponding alarm indications that may be generated by the VoIP system. For example, when a port fails on a host, the host may generate a failure report, i.e., an event, trigger, alarms, etc., while the VoIP system may generate a port failure report and the VoIP performance may be degraded. The network failure reporting may further be performed by a second failure system. Thus, performance behavior of a network composed of IP and over-layed VoIP components may be analyzed by formulating behavior models for selected ones of the components,—i.e., managed components—in each of the IP, and VoIP system networks and the VoIP performance domain. An analysis of the each of the networks (referred to as domains) may be separately performed and the results of each analysis may then be correlated through a behavior model which combines the characteristics of each of the domains. Such cross-correlation of the information from the individual networks or domains further refines the analysis provided to a user by removing one or more redundant alarms and providing only the most-likely cause of the alarm indications (i.e., observed events). FIG. 5 represents a block diagram 500 illustrating the integration of the processing of the instant application with similar processing to determine the source or root cause of observed events or symptoms. In this illustrated example, each of a managers associated with the elements of an IP network 510, a VoIP availability manager, 520, and a VoIP performance manager reference an associated causality matrix which determine most-likely causing events (problems) from a plurality of observed events. The selected most-likely causing events from each of the mangers 510, 520, and 530 are provided to a correlator 540 which analyzes the received causing event to determine at least one most-likely causing event. The correlator may include information regarding the relationship of components within each of the domains. For example, a host or application may be considered a managed component in each of two domains and the knowledge of this component being an intersection point between two domains may be used to resolve ambiguity in the causing event associated with observed events in each of two domains. Although not shown it would be recognized that the behavior model described herein may further provide sufficient information to perform an impact analysis, i.e., the affect of a degradation, on the VoIP performance domain. In this case, it may be determined what symptoms may be expected when a problem is introduced or simulated. Impact analysis using the behavior models described herein is more fully described in the aforementioned US patents and patent application and need not be discussed in detail herein. In another aspect, the impact of failures may be projected to determine the impact of a degradation on a higher level function. The examples provided herein are described with regard to root-cause analysis and impact analysis, it would be recognized that the method described herein may be used to perform a system analysis may include: fault detection, fault monitoring, performance, congestion, connectivity, interface failure, node failure, link failure, routing protocol error, and/or routing control errors. FIG. 6 illustrates an exemplary embodiment of a system 600 that may be used for implementing the principles of the present invention. System 600 may contain one or more input/output devices 602, processors 603 and memories 604. I/O devices 602 may access or receive information from one or more devices 601, which represent sources of information. Sources or devices 601 may be devices such as routers, servers, computers, notebook computer, PDAs, cells phones or other devices suitable for transmitting and receiving information responsive to the processes shown herein. Devices 601 may have access over one or more network connections 650 via, for example, a wireless wide area network, a wireless metropolitan area network, a wireless local area network, a terrestrial broadcast system (Radio, TV), a satellite network, a cell phone or a wireless telephone network, or similar wired networks, such as POTS, INTERNET, LAN, WAN and/or private networks, e.g., INTRANET, as well as portions or combinations of these and other types of networks. Input/output devices 602, processors 603, e.g. Pentium processors, and memories 604 may communicate over a communication medium 625. Communication medium 625 may represent, for example, a bus, a communication network, one or more internal connections of a circuit, circuit card or other apparatus, as well as portions and combinations of these and other communication media. Input data from the sources or client devices 601 is processed in accordance with one or more programs that may be stored in memories 604 and executed by processors 603. Memories 604 may be any magnetic, optical or semiconductor medium that is loadable and retains information either permanently, e.g. PROM, or non-permanently, e.g., RAM. Processors 603 may be any means, such as general purpose (e.g., Intel Corporation Pentium processor) or special purpose computing system, such as a laptop computer, desktop computer, a server, handheld computer, or may be a hardware configuration, such as dedicated logic circuit, or integrated circuit. Processors 603 may also be Programmable Array Logic (PAL), or Application Specific Integrated Circuit (ASIC), etc., which may be “programmed” to include software instructions or code that provides a known output in response to known inputs. In one aspect, hardware circuitry may be used in place of, or in combination with, software instructions to implement the invention. The elements illustrated herein may also be implemented as discrete hardware elements that are operable to perform the operations shown using coded logical operations or by executing hardware executable code. In one aspect, the processes shown herein may be represented by computer readable code stored on a computer readable medium. The code may also be stored in the memory 604. The code may be read or downloaded from a memory medium 683, an I/O device 685 or magnetic or optical media, such as a floppy disk, a CD-ROM or a DVD, 687 and then stored in memory 604. Similarly the code may be downloaded over one or more networks, e.g., 650, 680, or not shown via I/O device 685, for example, for execution by processor 603 or stored in memory 604 and then accessed by processor 603. As would be appreciated, the code may be processor-dependent or processor-independent. JAVA is an example of processor-independent code. JAVA is a trademark of the Sun Microsystems, Inc., Santa Clara, Calif. USA. Information from device 01 received by I/O device 602, after processing in accordance with one or more software programs operable to perform the functions illustrated herein, may also be transmitted over network 80 to one or more output devices represented as display 692, reporting device 690 or second processing system 695. As one skilled in the art would recognize, the term computer or computer system may represent one or more processing units in communication with one or more memory units and other devices, e.g., peripherals, connected electronically to and communicating with the at least one processing unit. Furthermore, the devices may be electronically connected to the one or more processing units via internal busses, e.g., ISA bus, microchannel bus, PCI bus, PCMCIA bus, etc., or one or more internal connections of a circuit, circuit card or other device, as well as portions and combinations of these and other communication media or an external network, e.g., the Internet and Intranet. While there has been shown, described, and pointed out fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the apparatus described, in the form and details of the devices disclosed, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. |
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055352502 | abstract | A device for manipulating a synchrotron beam bundle is intended to produce properties of the beam bundle, under vacuum conditions, which are adapted to the respective application of deep X-ray lithography, in particular, which are adapted to the scanning regimen. Pairs of diaphragms which are displaceable relative to one another are provided between the object table and an inlet window within a vacuum chamber containing an object table for receiving an object to be irradiated, which object table is adjustable by a scanning movement relative to the synchrotron beam bundle. The pair of diaphragms for which the direction of relative displacement of the diaphragms coincides with the scanning movement is coupled with the scanning movement. Further, a filter chamber is arranged upstream of the vacuum chamber and contains filters which can be inserted into the synchrotron beam bundle. The device is for use in irradiating equipment for deep X-ray lithography which are used to fabricate microsystems components by means of a technique known as the LIGA process (lithography with synchrotron radiation, electroforming and plastics molding). |
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